Tkool Electronics

IntroductonLM386isalowvoltageaudiopoweramplifier.LM386adopts8-pindoublein-lineplasticpackagewithworkingvoltageof4V-15V.Whenthepowersupplyvoltageis12V,300mWoutputpowercanbeobtainedonan8load.VariousoscillatorscanbeeasilyproducedwithLM386.CatalogIntroductonCatalogISimplestOscillatorIIBlockingOscillatorIIIElectronicPianoIVSquare-waveOscillatorVSinusoidalOscillatorFAQOrdering&QuantityISimplestOscillatorFigure1.CircuitofSimplestOscillatorInFigure1,theoutputendandin-phaseinputendofLM386areconnectedbypiezoelectricceramicchipHTD.Theamplifierformspositivefeedbackandgeneratesoscillation.HereHTDisbothafeedbackcapacitorandasound-generatingdevice.Componentparametersinthefigure:D1~D4are1N4001,C1=220pF,HTDispiezoelectricceramicsheetwithauxiliaryacousticcavity.IIBlockingOscillatorFigure2.CircuitofBlockingOscillatorAsshowninFigure2,asimpleoscillatorconsisitofLM386,C3,C4andloudspeakers.RPandC2makethisoscillatorproduceblocking-oscillation.Afterconnectingthepowersupply,LM386doesnotworkbecausetheinitialterminalvoltageofC2iszero,andthepowersupplychargesC2throughRP.WhenC2chargingvoltageishigherthanacertainvalue,LM386oscillatorstartstovibrate.Astheamplitudecontinuestoincrease,thecurrentconsumptionoftheoscillatoralsoincreases.ThiscurrentflowsthroughRP,anditsvoltagedroponRPalsoincreases,causingtheLM386powersupplyterminal6pinvoltagetocontinuetodrop.EventuallytheLM386cannotworkandtheoscillatorstops.ThepowersupplyrechargesC2viaRPagain,causingthevoltageatC2torise.WhenthevoltageatC2risestoacertainvalue,theLM386oscillatorstartsagain.Inthisway,theoscillatorwillproduceblocking-oscillation,andthespeakeremitsbeep,beep,beepsound.Componentparametersinthefigure:D1~D4are1N4001,C1=C3=220F,C2=47F.C4=0.01F,RP=4.7K.IIIElectronicPianoFigure3.CircuitofElectronicPianoFigure3isasimpleelectronicpianocircuit.Onthepin3ofLM386,theintegratedcircuithasa10Kresistortoground.Thisbuilt-inresistorandtenscaleresistorsRP1~RP10constitutethetimingresistoroftheoscillator.C2isthetimingcapacitor.ByadjustingthevaluesofRP1~RP10,thespeakerscansequentiallyemitmusicalsoundsfromlowoctavedo,re,mitohighoctavedo,re,mi.KI~K10arekeyswitches.Componentparametersinthefigure:Cl=C3=220F.C2=2200FIVSquare-waveOscillatorFigure4.CircuitofSquare-waveOscillatorFigure4showsasquare-waveoscillatorcomposedofLM386.R1isthetimingresistor.C2isthetimingcapacitor.R2andR3providevoltagebiasforLM386in-phaseinput.BecausethevoltageattheC2terminalcannotchangeabruptly,theinvertinginputterminalpin2oftheLM386islowlevel,andpin5isthemidpointoftheinternalOTLoutputstageoftheamplifier.Itis1/2Vocinstaticstate,anditissuppliedtothethird-phaseinputpin3afterdividingpressureviaR2andR3.Obviouslythepotentialofthispinishigherthanthesecondpin.Therefore,pin5outputshighlevel.ThishighlevelchargesC2viaR1.WhenthevoltageofC2terminalishigherthanthepotentialofpin3,pin5outputslowlevel.C2dischargestopin5viaR1.WhenC2isdischarged,thepotentialofpin2dropsandislowerthanthepotentialofpin3.Pin5outputshighlevelagain.Inthisway,thecircuitformsoscillation,andtheoscillationsignaldrivestheloudspeakertosoundthroughC3.Componentparametersinthefigure:C1=C3=220F,C2=0.33F.R1=22K,R2=1K.R3=9.4KVSinusoidalOscillatorFigure5.CircuitofSinusoidalOscillatorFigure5isasinusoidaloscillatormadeofLM386.ThecircuitadoptsWienbridgeoscillationmode,andtheoutputsignaldistortioncoefficientofthecircuitisverylow.TheflashlampHandtheresistorR3formanegativefeedbackcircuit,whichkeepstheamplitudeoftheoscillatoroutputsignalstableandhaslowdistortion.WhenthevaluesofcapacitorsC1andC2arethesame,theoscillationfrequencyofthecircuitcanbeobtainedbytheformulaf=1/2C1R1R2.Inactualproduction,Hcanuse3V,15mAflashlamp.FAQHowdoesanLM386work?TheLm386integratedchipisalowpoweraudiofrequencyamplifier,whichuseslowlevelpowersupplylikebatteriesinelectroniccircuits.Itisdesignedas8pinminiDIPpackage.Thisprovidesvoltageamplificationof20.Byusingexternalpartsvoltagegaincanberaisedupto200.Islm386anopamp?TheLM386isatypeofoperationalamplifier(Op-Amp)....Inanamplifiercircuit,theLM386takesanaudioinputsignalandincreasesitspotentialanywherefrom20to200times.Thatamplificationiswhatsknownasthevoltagegain.Whatislm386IC?TheLM386isanintegratedcircuitcontainingalowvoltageaudiopoweramplifier.Itissuitableforbattery-powereddevicessuchasradios,guitaramplifiers,andhobbyelectronicsprojects.Howdoyoucalculatelm386gain?VoltageGainAnalysis:Withoutanyexternalcomponents,ithasagainofGv=2x15K/(150+1350)=20(26dB).Withacapacitor(orshortcutting)betweenpins1and8,ithasagainofGv=2x15K/150=200(46dB).WhichICisusedinaudioamplifier?TheICLM386isalow-poweraudioamplifier,anditutilizeslowpowersupplylikebatteriesinelectricalandelectroniccircuits.ThisICisavailableinthepackageofmini8-pinDIP.WhataresomeprojectsthatusetheLM386audioamplifiercircuit?LM386isanintegratedclassABampandisgoodforbeginnerssmallaudioamplifierapplicationsforexampleinaRFreceiver,smallStereosystem,cheaplowvoltageamplifieretcdrawbacksisthatitcannothandlemuchpowerandhencecreatesdistortionwhenyoucrankupthevolumetoomuch..SootherICsareusedinpractical.HowtomakeanLM386audioamplifiercircuit?

IRFD320PBF-VISHAY

IntroductonLM386isalowvoltageaudiopoweramplifier.LM386adopts8-pindoublein-lineplasticpackagewithworkingvoltageof4V-15V.Whenthepowersupplyvoltageis12V,300mWoutputpowercanbeobtainedonan8load.VariousoscillatorscanbeeasilyproducedwithLM386.CatalogIntroductonCatalogISimplestOscillatorIIBlockingOscillatorIIIElectronicPianoIVSquare-waveOscillatorVSinusoidalOscillatorFAQOrdering&QuantityISimplestOscillatorFigure1.CircuitofSimplestOscillatorInFigure1,theoutputendandin-phaseinputendofLM386areconnectedbypiezoelectricceramicchipHTD.Theamplifierformspositivefeedbackandgeneratesoscillation.HereHTDisbothafeedbackcapacitorandasound-generatingdevice.Componentparametersinthefigure:D1~D4are1N4001,C1=220pF,HTDispiezoelectricceramicsheetwithauxiliaryacousticcavity.IIBlockingOscillatorFigure2.CircuitofBlockingOscillatorAsshowninFigure2,asimpleoscillatorconsisitofLM386,C3,C4andloudspeakers.RPandC2makethisoscillatorproduceblocking-oscillation.Afterconnectingthepowersupply,LM386doesnotworkbecausetheinitialterminalvoltageofC2iszero,andthepowersupplychargesC2throughRP.WhenC2chargingvoltageishigherthanacertainvalue,LM386oscillatorstartstovibrate.Astheamplitudecontinuestoincrease,thecurrentconsumptionoftheoscillatoralsoincreases.ThiscurrentflowsthroughRP,anditsvoltagedroponRPalsoincreases,causingtheLM386powersupplyterminal6pinvoltagetocontinuetodrop.EventuallytheLM386cannotworkandtheoscillatorstops.ThepowersupplyrechargesC2viaRPagain,causingthevoltageatC2torise.WhenthevoltageatC2risestoacertainvalue,theLM386oscillatorstartsagain.Inthisway,theoscillatorwillproduceblocking-oscillation,andthespeakeremitsbeep,beep,beepsound.Componentparametersinthefigure:D1~D4are1N4001,C1=C3=220F,C2=47F.C4=0.01F,smd resistor codeRP=4.7K.IIIElectronicPianoFigure3.CircuitofElectronicPianoFigure3isasimpleelectronicpianocircuit.Onthepin3ofLM386,theintegratedcircuithasa10Kresistortoground.Thisbuilt-inresistorandtenscaleresistorsRP1~RP10constitutethetimingresistoroftheoscillator.C2isthetimingcapacitor.ByadjustingthevaluesofRP1~RP10,thespeakerscansequentiallyemitmusicalsoundsfromlowoctavedo,re,mitohighoctavedo,re,mi.KI~K10arekeyswitches.Componentparametersinthefigure:Cl=C3=220F.C2=2200FIVSquare-waveOscillatorFigure4.CircuitofSquare-waveOscillatorFigure4showsasquare-waveoscillatorcomposedofLM386.R1isthetimingresistor.C2isthetimingcapacitor.R2andR3providevoltagebiasforLM386in-phaseinput.BecausethevoltageattheC2terminalcannotchangeabruptly,theinvertinginputterminalpin2oftheLM386islowlevel,andpin5isthemidpointoftheinternalOTLoutputstageoftheamplifier.Itis1/2Vocinstaticstate,anditissuppliedtothethird-phaseinputpin3afterdividingpressureviaR2andR3.Obviouslythepotentialofthispinishigherthanthesecondpin.Therefore,pin5outputshighlevel.ThishighlevelchargesC2viaR1.WhenthevoltageofC2terminalishigherthanthepotentialofpin3,pin5outputslowlevel.C2dischargestopin5viaR1.WhenC2isdischarged,thepotentialofpin2dropsandislowerthanthepotentialofpin3.Pin5outputshighlevelagain.Inthisway,thecircuitformsoscillation,andtheoscillationsignaldrivestheloudspeakertosoundthroughC3.Componentparametersinthefigure:C1=C3=220F,different types of capacitorsC2=0.33F.R1=22K ,how to test diodesR2=1K.R3=9.4KVSinusoidalOscillatorFigure5.CircuitofSinusoidalOscillatorFigure5isasinusoidaloscillatormadeofLM386.ThecircuitadoptsWienbridgeoscillationmode,andtheoutputsignaldistortioncoefficientofthecircuitisverylow.TheflashlampHandtheresistorR3formanegativefeedbackcircuit,whichkeepstheamplitudeoftheoscillatoroutputsignalstableandhaslowdistortion.WhenthevaluesofcapacitorsC1andC2arethesame,theoscillationfrequencyofthecircuitcanbeobtainedbytheformulaf=1/2C1R1R2.Inactualproduction,Hcanuse3V,15mAflashlamp.FAQHowdoesanLM386work?TheLm386integratedchipisalowpoweraudiofrequencyamplifier,whichuseslowlevelpowersupplylikebatteriesinelectroniccircuits.Itisdesignedas8pinminiDIPpackage.Thisprovidesvoltageamplificationof20.Byusingexternalpartsvoltagegaincanberaisedupto200.Islm386anopamp?TheLM386isatypeofoperationalamplifier(Op-Amp)....Inanamplifiercircuit,theLM386takesanaudioinputsignalandincreasesitspotentialanywherefrom20to200times.Thatamplificationiswhatsknownasthevoltagegain.Whatislm386IC?TheLM386isanintegratedcircuitcontainingalowvoltageaudiopoweramplifier.Itissuitableforbattery-powereddevicessuchasradios,guitaramplifiers,andhobbyelectronicsprojects.Howdoyoucalculatelm386gain?VoltageGainAnalysis:Withoutanyexternalcomponents,ithasagainofGv=2x15K/(150+1350)=20(26dB).Withacapacitor(orshortcutting)betweenpins1and8,ithasagainofGv=2x15K/150=200(46dB).WhichICisusedinaudioamplifier?TheICLM386isalow-poweraudioamplifier,anditutilizeslowpowersupplylikebatteriesinelectricalandelectroniccircuits.ThisICisavailableinthepackageofmini8-pinDIP.WhataresomeprojectsthatusetheLM386audioamplifiercircuit?LM386isanintegratedclassABampandisgoodforbeginnerssmallaudioamplifierapplicationsforexampleinaRFreceiver,smallStereosystem,cheaplowvoltageamplifieretcdrawbacksisthatitcannothandlemuchpowerandhencecreatesdistortionwhenyoucrankupthevolumetoomuch..SootherICsareusedinpractical.HowtomakeanLM386audioamplifiercircuit?

DescriptionDS1302isalow-powerreal-timeclockchipwithtricklecurrentchargingcapability.Itcantimetheyear,month,day,week,hour,minute,andsecond.ThisVideoIntroducesDS1302ArduinoRealtimeClockCatalogDescriptionDS1302PinoutDS1302DocumentsandMediaDS1302CADModelsDS1302ParametersDS1302FeaturesDS1302AdvantageDS1302ApplicationsDS1302TypicalOperatingCircuitDS1302EnvironmentalandExportClassificationsDS1302BlockDiagramHowtoUseDS1302DS1302RTCModuleDS1302CommandByteFAQOrdering&QuantityDS1302PinoutThefigurebelowshowsthepinarrangementofDS1302.Amongthem,Vcc2isthemainpowersupply,andVCC1isthebackuppowersupply.Thecontinuousoperationoftheclockcanbemaintainedevenwhenthemainpowerisoff.DS1302ispoweredbythelargerofVcc1orVcc2.WhenVcc2isgreaterthanVcc1+0.2V,Vcc2suppliespowertoDS1302.WhenVcc2islessthanVcc1,DS1302ispoweredbyVcc1.X1andX2aretheoscillationsourcesandanexternal32.768kHzcrystaloscillator.RSTisthereset/chipselectline.AlldatatransfersarestartedbydrivingtheRSTinputtohigh.RSTinputhastwofunctions:First,RSTturnsonthecontrollogic,allowingtheaddress/commandsequencetobesenttotheshiftregister;second,RSTprovidesamethodtoterminatesingle-byteormulti-bytedatatransmission.WhenRSTishigh,alldatatransfersareinitialized,allowingoperationsonDS1302.IfRSTissettoalowlevelduringthetransfer,thedatatransferwillbeterminatedandtheI/Opinwillbecomehighimpedance.Duringpower-onoperation,RSTmustremainlowbeforeVcc2.0V.OnlywhenSCLKislow,canRSTbesethigh.I/Oisaserialdatainputandoutputterminal(two-way),whichwillbedescribedindetaillater.SCLKistheclockinputterminal.PinNumberPinNameDescription1VCC2PrimaryPower-SupplyPininDualSupplyConfiguration.VCC1isconnectedtoabackupsourcetomaintainthetimeanddateintheabsenceofprimarypower.TheDS1302operatesfromthelargerofVCC1orVCC2.WhenVCC2isgreaterthanVCC1+0.2V,VCC2powerstheDS1302.WhenVCC2islessthanVCC1,VCC1powerstheDS1302.2X1ConnectionsforStandard32.768kHzQuartzCrystal.Theinternaloscillatorisdesignedforoperationwithacrystalhavingaspecifiedloadcapacitanceof6pF.Formoreinformationoncrystalselectionandcrystallayoutconsiderations,refertoApplicationNote58:CrystalConsiderationsforDallasReal-TimeClocks.TheDS1302canalsobedrivenbyanexternal32.768kHzoscillator.Inthisconfiguration,theX1pinisconnectedtotheexternaloscillatorsignalandtheX2pinisfloated.3X24GNDGround5CEInput.CEsignalmustbeassertedhighduringareadorawrite.Thispinhasaninternal40kΩ(typ)pulldownresistortoground.Note:PreviousdatasheetrevisionsreferredtoCEasRST.Thefunctionalityofthepinhasnotchanged.6I/OInput/Push-PullOutput.TheI/Opinisthebidirectionaldatapinforthe3-wireinterface.Thispinhasaninternal40kΩ(typ)pulldownresistortoground.7SCLKInput.SCLKisusedtosynchronizedatamovementontheserialinterface.Thispinhasaninternal40kΩ(typ)pulldownresistortoground.8VCC1Low-PowerOperationinSingleSupplyandBattery-OperatedSystemsandLowPowerBatteryBackup.Insystemsusingthetricklecharger,therechargeableenergysourceisconnectedtothispin.ULrecognizedtoensureagainstreversechargingcurrentwhenusedwithalithiumbattery.DS1302DocumentsandMediaDatasheetsDS1302OtherRelatedDocumentsTipsforWritingBulletproofReal-TimeClockControlCodeMfgApplicationNotesEstimatingSuperCapacitorBackupTimeonTrickle-ChargerReal-TimeClocksSelectingaBackupSourceforReal-TimeClocksOscillatorDesignConsiderationsforLow-CurrentApplicationsStateMachineLogicinBinary-CodedDecimal(BCD)-FormattedReal-TimeClocksEnvironmentalInformationHalogenCertificateRedPhosphorousCertificateMaterialDeclarationDS1302PCNObsolescence/EOLMultDevOBS15/Jul/2015HTMLDatasheetDS1302EDA/CADModelsDS1302bySnapEDADS1302byUltraLibrarianDS1302CADModelsDS1302SymbolDS1302FootprintDS1302ParametersBaseProductNumberDS1302BatteryBackupSwitchingBackupSwitchingCategoryIntegratedCircuits(ICs)Clock/Timing-RealTimeClocksCurrent-Timekeeping(Max)0.3A~1A@2V~5VDateFormatYY-MM-DD-ddFeaturesLeapYear,NVSRAM,Trickle-ChargerFunctionCalendar,Clock,NVTimekeepingRAM,TrickleChargerInterface3-WireSerialManufacturerMaximIntegratedMaximumOperatingTemperature+70CMinimumOperatingTemperature0CMountingStyleThroughHoleOperatingTemperature0C~70CPackageTubePackage/Case8-DIP(0.300,7.62mm)PackagingTubePartStatusObsoleteProductCategoryRealTimeClockRoHSNRTCBusInterfaceSerialRTCMemorySize31BSubcategoryClockTimerICsSupplierDevicePackage8-PDIPSupplyVoltage-Max5.5VSupplyVoltage-Min2VTimeFormatHH:MM:SS(12/24hr)TypeClock/CalendarVoltage-Supply,Battery2V~5.5VDS1302FeaturesCompletelyManagesAllTimekeepingFunctionsoReal-TimeClockCountsSeconds,Minutes,Hours,DateoftheMonth,Month,DayoftheWeek,andYearwithLeap-YearCompensationValidUpto2100o31x8Battery-BackedGeneral-PurposeRAMSimpleSerialPortInterfacestoMostMicrocontrollersoSimple3-WireInterfaceoTTL-Compatible(VCC=5V)oSingle-ByteorMultiple-Byte(BurstMode)DataTransferforReadorWriteofClockorRAMDataLowPowerOperationExtendsBatteryBackupRunTimeo2.0Vto5.5VFullOperationoUsesLessThan300nAat2.0V8-PinDIPand8-PinSOMinimizesRequiredSpaceOptionalIndustrialTemperatureRange:-40Cto+85CSupportsOperationinaWideRangeofApplicationsUnderwritersLaboratories(UL)RecognizedDS1302AdvantageTheDS1302trickle-chargetimekeepingchipcontainsareal-timeclock/calendarand31bytesofstaticRAM.Itcommunicateswithamicroprocessorviaasimpleserialinterface.Thereal-timeclock/calendarprovidesseconds,minutes,hours,day,date,month,andyearinformation.Theendofthemonthdateisautomaticallyadjustedformonthswithfewerthan31days,includingcorrectionsforleapyear.Theclockoperatesineitherthe24-houror12-hourformatwithanAM/PMindicator.InterfacingtheDS1302withamicroprocessorissimplifiedbyusingsynchronousserialcommunication.Onlythreewiresarerequiredtocommunicatewiththeclock/RAM:CE,I/O(dataline),andSCLK(serialclock).Datacanbetransferredtoandfromtheclock/RAM1byteatatimeorinaburstofupto31bytes.TheDS1302isdesignedtooperateonverylowpowerandretaindataandclockinformationonlessthan1W.TheDS1302isthesuccessortotheDS1202.InadditiontothebasictimekeepingfunctionsoftheDS1202,theDS1302hastheadditionalfeaturesofdualpowerpinsforprimaryandbackuppowersupplies,programmabletricklechargerforVCC1,andsevenadditionalbytesofscratchpadmemory.DS1302ApplicationsTheapplicationsofDS1302includeincorporateddigitalclocks/timersofvariousmodulesinourreallives.OtherequivalentsICsofRTCare:DS1307,DS3231,DS3232DS1302TypicalOperatingCircuitDS1302EnvironmentalandExportClassificationsAttributeDescriptionRoHSStatusRoHSnon-compliantMoistureSensitivityLevel(MSL)1(Unlimited)HowtoUseDS1302AtypicaloperatingcircuitforDS1302isgivenbelow.DS1302havetwopowerinput,oneisfromcellandotherisfromcontroller.Acrystaloscillatorof32.768kHzisusedtogeneraterequiredfrequency.ForinterfacingDataline,ResetPinandSerial-clockpinsofDS1302areconnectedwiththemicro-controller.DS1302BlockDiagramDS1302RTCModuleDS1302isatickle-chargetimekeepingchipwhichcontainsareal-timeclock/calendarand31bytesofstaticRAM.DS1302usesserialcommunicationtointeractwithmicrocontrollers.Also,itautomaticallyadjustthedateforthemonthwithfewerdays.Clockoperatesin24hror12hrformatwithanAM/PMindicator.DS1302chipisalsocommonlyusedasDS1302RTCmodulewhichcomeswitha32kHzcrystalandon-boardbatterybackupallinasmallSIPmodulethatiscompatiblewithabreadboard.DS1302moduleareusedbymakerswithArduino,RaspberryPiandotherMicro-controllers.ADS1302RTCmodulepinoutisshowninbelowimage.DS1302CommandByteAcommandbyteinitiateseachdatatransfer.TheMSB(bit7)mustbealogic1.Ifitis0,writestotheDS1302willbedisabled.Bit6specifiesclock/calendardataiflogic0orRAMdataiflogic1.Bits1to5specifythedesignatedregisterstobeinputoroutput,andtheLSB(bit0)specifiesawriteoperation(input)iflogic0orreadoperation(output)iflogic1.ThecommandbyteisalwaysinputstartingwiththeLSB(bit0).DS1302RegisterDS1302has12registers,ofwhich7registersarerelatedtocalendarandclock.ThestoreddatabitsareintheformofBCDcodes.Thecalendar,timeregistersandtheircontrolwordsareshowninTable1.Inaddition,DS1302alsohasyearregister,controlregister,chargingregister,clockburstregister,andRAM-relatedregisters.Theclockburstregistercanreadandwritethecontentsofallregistersexceptthechargingregisterinsequenceatonetime.TheDS1302andRAM-relatedregistersaredividedintotwocategories:OneisasingleRAMunit,with31intotal.Eachunitisconfiguredasan8-bitbyte,anditscommandcontrolwordisC0H~FDH.Amongthem,oddnumbersarereadoperations,andevennumbersarewriteoperations;theothertypeisRAMregistersinburstmode.Inthismode,all31bytesofRAMcanbereadandwrittenatonce,andthecommandcontrolwordsareFEH(write)andFFH(read).FAQWhatisDS1302?DS1302isatickle-chargetimekeepingchipwhichcontainsareal-timeclock/calendarand31bytesofstaticRAM.DS1302usesserialcommunicationtointeractwithmicrocontrollers.Also,itautomaticallyadjustthedateforthemonthwithfewerdays.WhatdoesanRTCdo?Areal-timeclock(RTC)isacomputerclock(mostoftenintheformofanintegratedcircuit)thatkeepstrackofthecurrenttime.Althoughthetermoftenreferstothedevicesinpersonalcomputers,serversandembeddedsystems,RTCsarepresentinalmostanyelectronicdevicewhichneedstokeepaccuratetime.HowdoyouuseRTC?WiringItUp.5VisusedtopowertotheRTCchipwhenyouwanttoqueryitforthetime.Ifthereisno5Vsignal,thechipgoestosleepusingthecoincellforbackup.ConnectGNDtocommonpower/dataground.ConnecttheSCLpintotheI2CclockSCLpinonyourArduino....ConnecttheSDApintotheI2CdataSDApinonyourArduino.DescriptionTheTDA2822isadual-channel,single-chippoweramplifierintegratedcircuitdevelopedbyStMICROelectronics.Itiscommonlyusedasanaudioamplifierinportablecassetteplayers,cassetterecorders,andmultimediaactivespeakers.Ithasthecharacteristicsofsimplecircuit,goodsoundquality,widevoltagerangeandsoon.Itcanworkinthecircuitformofstereosoundandbridgeamplification(BTL).HowtoMakeaStereoAmplifierUsingICTDA2822?CatalogDescriptionTDA2822PinoutTDA2822CADModelTDA2822ParameterTDA2822ApplicationsTDA2822FeaturesTDA2822AdvantagesWheretouseTDA2822AmplifierICHowtouseTDA2822AmplifierTDA2822SchematicDiagramTDA2822DocumentsandMediaTDA2822EnvironmentalandExportClassificationsTDA2822CircuitOrdering&QuantityTDA2822PinoutPinNumberPinNameDescription1,3OutputProvidestheamplifiedAudiooutput5,8InvertingInput(IN-)TheInvertingPinofanamplifierisnormallygrounded6,7Non-InvertingInput(IN+)TheNon-Invertingpinisprovidedwiththeaudiosignal4Vcc-Connectedtothenegativesupplyrail2Vcc+ConnectedtoPositiveSupplyRailTDA2822CADModelTDA2822SymbolTDA2822FootprintTDA2822ParameterAudio-LoadImpedance8OhmsBaseProductNumberTDA2822BrandSTMicroelectronicsCategoryIntegratedCircuits(ICs)Linear-Amplifiers-AudioClassClass-ABDescription/FunctionHeadphone/SpeakerFactoryPackQuantity25Features-Gain39dBHeight4.59mmIb-InputBiasCurrent0.1uAInputTypeSingleLength20mmManufacturer:STMicroelectronicsMaxOutputPowerxChannels@Load3.2Wx1@8Ohm;1.7Wx2@4OhmMaximumOperatingTemperature:+150CMfrSTMicroelectronicsMinimumOperatingTemperature-40CMountingStyleThroughHoleNumberofChannels2ChannelOperatingSupplyCurrent12mAOperatingSupplyVoltage5V,9V,12VOperatingTemperature-40C~150C(TJ)OutputCurrent1500mAOutputPower3.2WOutputSignalTypeDifferential,SingleOutputType1-Channel(Mono)or2-Channel(Stereo)PackageTubePackage/Case16-DIP(0.300,7.62mm)Package/CasePDIP-16PackagingTubePartStatusObsoletePd-PowerDissipation4000mWProductAudioAmplifiersPSRR-PowerSupplyRejectionRatio40dBSeriesTDA2822SubcategoryAudioICsSupplierDevicePackage16-PowerDIPSupplyTypeSingleSupplyVoltageMax15VSupplyVoltageMin3VTHDplusNoise0.2%TypeClassABType1-ChannelMonoor2-ChannelStereoUnitWeight0.057419ozVoltageSupply3V~15VWidth7.1mmTDA2822ApplicationsAMandFMRadioamplifiersPortablemusicplayersLowPowerAudioamplifiersWienbridgeoscillatorPowerAmplifiersAudioboostersTDA2822FeaturesDualAmplifiersinoneDIP-8similarforLM368.Givepowerwattsat1W+1Wat4ohmsspeakers.Itisenough.WearehappyListeninginourcorner.Startvoltagesupplyof1.8Vto15V.Thewidealot.Saveenergywithonly6mA,Min.Thebandwidthexpansionratesat40dB120kHz.CheapandeasytouseTDA2822AdvantagesTDA2822isalowpowerstereoOpAmplifierusedinWalkmanplayersandHearingaids.Itcangive250mWoutput.TDA2822isanidealOpampforlowoutputapplications.Itisagoodchoiceasapreamplifierinstereohighpoweramplifiercircuits.Ithastwoinputsandtwooutputswhichcandeliver250milliwattsoutputpower.TheamplifiercircuitwithintheICiswellsetfornoisefreeoperation.Outputscanbedirectlycoupledtothespeakersthroughthedecouplingcapacitors.WheretouseTDA2822AmplifierICTheTDA2822isaDualAudioAmplifierIC,meaningithastwoOp-Ampsinsideitspackage,andtheyarecommonlyusedforaudioamplificationbecauseoftheirwidebandwidthgain.Thetwooutputscandeliver250milliwattsoutputpower.ThisICcanbeusedinportableaudiosystems,preamplifiers,hearingaidminiradio,headphoneamplifier,etc.SoifyouarelookingforadualpackageOperationalamplifierICwithhigh-gain,andwidebandwidthforaudioamplification,thenthisICmightbetherightchoiceforyou.HowtouseTDA2822AmplifierAnapplicationcircuitfromTDA2822datasheetisgivenbelowTheleftloadisconnectedtooutputpin1oftheICthroughelectrolyticcapacitorC4,andtherightloadisconnectedtooutputpin3throughelectrolyticcapacitorC5.TheInvertingInputPins(5and8)areconnectedtothegroundviaelectrolyticcapacitors.Non-InvertingInputPins(7and6)areconnectedtoinput1andinput2.Pin2isconnectedtoDCsupplyandpin4isconnectedtoground.ElectrolyticcapacitorC3connectedacrossVCCandground,workasafiltercapacitor.TDA2822SchematicDiagramTDA2822DocumentsandMediaDatasheetsTDA2822DesignResourcesDevelopmentToolSelectorHTMLDatasheetTDA2822TDA2822EnvironmentalandExportClassificationsAttributeDescriptionRoHSStatusROHS3CompliantMoistureSensitivityLevel(MSL)1(Unlimited)TDA2822CircuitTDA2822TestCircuit(Stereo)TDA2822TestCircuit(Bridge)TDA2822TypicalApplicationinPortablePlayersTDA2822LowCostApplicationinPortablePlayersTDA28223VStereoCassettePlayerwithMototSpeedControl

IRFD320PBF-VISHAY

I.Description74LS138isa3-lineto8-linedecoder/demultiplexer.Thechipisdesignedtobeusedinhigh-performancememory-decodingordata-routingapplications,requiringveryshortpropagationdelaytimes.Inhighperformancememorysystemsthesedecoderscanbeusedtominimizetheeffectsofsystemdecoding.Thethreeenablepinsofchip(inwhichTwoactive-lowandoneactive-high)reducetheneedforexternalgatesorinverterswhenexpanding.CatalogI.DescriptionII.DigitalVoltmeterCircuitFAQOrdering&QuantityII.DigitalVoltmeterCircuitWeuseAD574andAT89C2051toformahighprecisiondigitalvoltmeter.TheschematicdiagramisshowninFigure1.AD574isa12-bitsuccessivecomparisonA/Dconverterwith12datalinesintotal.P1ofAT89C2051isdirectlyconnectedtothehigh8-bitdatalineofAD574.Thelow4-bitdatalineofAD574isdirectlyconnectedwiththeupperhalf4-bitp1.4-p1.7ofsingle-chipmicrocomputer.Datareadingisbasedonthecontrollineofsinglechipmicrocomputer.P3.5isconnectedtoAD574byteshortperiodcontrolline(A0).P3.4isconnectedtoreadconversiondatacontrolpin.AndP3.7isdirectlyconnectedwiththeterminalofindicatingworkingstatus(STS).Suchstructuredeterminesthatitcanonlybe8-bitoutput,sothedatamodeselectionendcanbedirectlygrounded.AT89C2051hasonly15I/Oportwires,11ofwhichareusedabove,andonly4ofthemareleft.Theoutputdataisoutputthroughtheserialportofthesingle-chipmicrocomputer,andanexternal74LS164(serialinandparallelout)decoderisconnectedforexpansion.Atthesametime,thedatadisplayedis4bits,andtheremaining2portlinesstillcannotmeettherequirements.A74LS138decoderisneededtogatetheaddressofthedisplayLED.Hereweusetheinputmodeof10Vrange.Pin13ofAD574istheinputterminalofthemeasuredvoltage.BecauseonlyoneAD574conversionchipisused,theCSterminalcanbedirectlygrounded.Theconverteruses12Vpowersupplyvoltageandtheworkingvoltageis+5V.74LS164isaserialinputandparalleloutputdecoder.TheBCDserialcodeoutputbyAT89C2051throughtheserialportisdecodedby74LS164andoutputasaseven-segmentBCDcode,whichisdirectlyconnectedtoa-goftheLED,andthedatalinesofthefourLEDsareconnectedonebyone.LEDdigitaltubeusescommonanodetype.Theaddresscodeoutputby74LS138isconnectedtothecommonterminalofLEDviaatransistor2SA1015(PNP).Thedisplayofthefour-digitLEDistime-sharingstrobethroughtheaddressline,whichisourcommonlyuseddynamicscanningdisplaymethod.Itisworthmentioningthatinthedynamicscanningdisplaymode,thefrequencyofdynamicscanninghascertainrequirements.Ifthefrequencyistoolow,theLEDwillflicker.Ifthefrequencyistoohigh,thelightingtimeofeachLEDistooshort,andthebrightnessoftheLEDistoolow.Itcantbeseenclearlywithnakedeye.Soitisgenerallyappropriatetotakeabout10ms.Thisrequiresthatwhenwritingaprogram,acertainLEDshouldbeonandkeptforacertainperiodoftime.Theprogramoftenusesthecalldelaysubroutine.FAQWhatisthedifferencebetween74hc138and74LS138?Bothhavethesamefunction.74HC138ismadeofhigh-speedCMOSprocess,withlowpowerconsumption,highoutput,lowlevelandwiderange.74LS138adoptstheearlybipolarprocess,anditsdrivingcapabilityisrelativelylarger.Whatisthefunctionaldifferencebetween74ls138decoderand74ls148?74ls138isa3-8wiredecoder/multiplexer,74ls148isan8-3wireoctalpriorityencoder.Oneisdecodingandtheotherisencoding.OppositeeffectWhatsthedifferencebetween74LS138Dand74LS138N?Thosetwoarethesamechip,DisSOPpackage,NisDIPpackage.Whataretheoutputcharacteristicsof74LS138decoder?UnderthepremisethattheenableterminalsS1(activehigh),S2(activelow),andS3(activelow)arevalidatthesametime,onlyoneoutputterminalislowatatime(therestarehigh);Iftheenableterminalisinvalid,theoutputisallhighlevel.Whatdothelettersandnumbersin74ls138standfor?74ls138isa3-8-linedecoder.Thenumber74representsthe74seriesofthe54/74series,andthe74serieshasanoperatingtemperatureof0degreesto70degrees.LSisaseries,representingthelow-powerSchottkyseries.138isthevarietycode.Whatstheworkingprincipleof74ls138?74LS138workingprinciple①Whenonestrobeterminal(E1)ishighlevel,andtheothertwostrobeterminals(E2)and(E3)arelowlevel,attheoutputterminalscorrespondingtoY0toY7,thebinarycodeofaddressterminals(A0,A1,A2)canbedecodedatlowlevel.Forexample:whenA2A1A0=110,theY6outputterminaloutputsalow-levelsignal.②UsingE1,E2andE3,itcanbecascadedtoexpandintoa24-linedecoder;ifanexternalinverterisconnected,itcanalsobecascadedtoexpandintoa32-linedecoder.③Ifoneofthestrobeterminalsisusedasadatainputterminal,74LS138canalsobeusedasadatadistributor.④Itcanbeusedin8086decodingcircuittoexpandmemory.Introduction74LS138isa3-lineto8-linedecoder/demultiplexer.Thechipisdesignedtobeusedinhigh-performancememory-decodingordata-routingapplications,requiringveryshortpropagationdelaytimes.Inhighperformancememorysystemsthesedecoderscanbeusedtominimizetheeffectsofsystemdecoding.Thethreeenablepinsofchip(inwhichTwoactive-lowandoneactive-high)reducetheneedforexternalgatesorinverterswhenexpanding.CatalogIntroductionIFullAdderCircuitIIResponderCircuitIIILogicFunctionIVFullSubtractorCircuitVThree-inputMajorityVotingFAQOrdering&QuantityIFullAdderCircuitThefulladderhas3inputterminals:An,Bn,Cn-1;2outputterminals:Sn,Cn.The74LS1383-lineto8-linedecoderhas3datainputterminals:A,B,C;3enableterminalsand8outputterminals.Here,the3datainputterminalsofthe3-lineto8-linedecodercanberegardedasthe3inputterminalsofthefulladder.Thatis,theinputsA,B,andCofthe3-lineto8-linedecodercorrespondtotheinputsAn,Bn,andCn-1ofthefulladderrespectively.Setthe3enableterminalsofthe3-lineto8-linedecodertotheeffectiveleveltomaintainnormaloperation.Thekeypointhereistodealwiththerelationshipbetweenthe8outputterminalsofthe3-lineto8-linedecoderandthe2outputsofthefulladder.UsetheoutputOUT(1,2,4,7)ofthe3-lineto8-linedecoderasa4-inputorgateinput,andthegateoutputasthesumoftheadder.UsetheoutputOUT(3,5,6,7)ofthe3-lineto8-linedecoderasa4-inputorgateinput,thegateoutputisusedasthecarryoutputoftheadder.Whentheinputoftheadderis:a=1,b=0,ci=1,theinputofthecorresponding3-lineto8-linedecoderisA=1,B=0,C=1.Theoutputofthedecoderisout(5)=1andtherestis0.Accordingtotheconnectionrelationshipdesignedabove,S=0,CO=1,whichsatisfiesthefunctionoffulladder.Figure1.FullAdderCircuitIIResponderCircuitFigure2.ResponderCircuitIIILogicFunctionF=ABC+ABC+ABC=111+110+101=Y7+Y6+Y5Accordingtotheruleof74LS138,Aisthelowbit(LSB)andDisthehighbit(MSB).The74LS138decodingoutputislowleveleffective.With74LS10NANDgate,theactuallogicisinputlowleveleffectiveorgate.Figure3.CircuitofLogicFunctionIVFullSubtractorCircuitFigure4.FullSubtractorCircuitVThree-inputMajorityVotingThedeviceconsistsofa3-lineto8-linedecoder(74LS138)andtwo4-inputNANDgates(74LS20).Therearethreebuttonsforuser.Pressthebuttontoagree,nottopressmeanstoreject.Whennoonepressesthebutton,orwhenonlyonepersonpressesthebutton,forexample,S1ispressed,butS2andS0arenotpressed.Theredlightison,thegreenlightisoff,andthebuzzerissilent,indicatingveto.Whentwoormorepeoplepressthebutton,forexample,ifS1andS2arepressed,theredlightwillbeoff,thegreenlightwillbeon,andthebuzzerwillsoundtoindicateapass.Use74LS138decoderandfour-inputNANDgate74LS20torealizethislogicfunction.Figure5.CircuitofThree-inputMajorityVotingFAQWhatisthedifferencebetween74hc138and74LS138?Bothhavethesamefunction.74HC138ismadeofhigh-speedCMOSprocess,withlowpowerconsumption,highoutput,lowlevelandwiderange.74LS138adoptstheearlybipolarprocess,anditsdrivingcapabilityisrelativelylarger.Whatisthefunctionaldifferencebetween74ls138decoderand74ls148?74ls138isa3-8wiredecoder/multiplexer,74ls148isan8-3wireoctalpriorityencoder.Oneisdecodingandtheotherisencoding.OppositeeffectWhatsthedifferencebetween74LS138Dand74LS138N?Thosetwoarethesamechip,DisSOPpackage,NisDIPpackage.Whataretheoutputcharacteristicsof74LS138decoder?UnderthepremisethattheenableterminalsS1(activehigh),S2(activelow),andS3(activelow)arevalidatthesametime,onlyoneoutputterminalislowatatime(therestarehigh);Iftheenableterminalisinvalid,theoutputisallhighlevel.Whatdothelettersandnumbersin74ls138standfor?74ls138isa3-8-linedecoder.Thenumber74representsthe74seriesofthe54/74series,andthe74serieshasanoperatingtemperatureof0degreesto70degrees.LSisaseries,representingthelow-powerSchottkyseries.138isthevarietycode.Whatstheworkingprincipleof74ls138?74LS138workingprinciple①Whenonestrobeterminal(E1)ishighlevel,andtheothertwostrobeterminals(E2)and(E3)arelowlevel,attheoutputterminalscorrespondingtoY0toY7,thebinarycodeofaddressterminals(A0,A1,A2)canbedecodedatlowlevel.Forexample:whenA2A1A0=110,theY6outputterminaloutputsalow-levelsignal.②UsingE1,E2andE3,itcanbecascadedtoexpandintoa24-linedecoder;ifanexternalinverterisconnected,itcanalsobecascadedtoexpandintoa32-linedecoder.③Ifoneofthestrobeterminalsisusedasadatainputterminal,74LS138canalsobeusedasadatadistributor.④Itcanbeusedin8086decodingcircuittoexpandmemory.Description74LS138isa3-lineto8-linedecoder/demultiplexer.Thechipisdesignedtobeusedinhigh-performancememory-decodingordata-routingapplications,requiringveryshortpropagationdelaytimes.Inhighperformancememorysystemsthesedecoderscanbeusedtominimizetheeffectsofsystemdecoding.Thethreeenablepinsofchip(inwhichTwoactive-lowandoneactive-high)reducetheneedforexternalgatesorinverterswhenexpanding.A24-linedecodercanbeimplementedwithnoexternalinverters,anda32-linedecoderrequiresonlyoneinverter.74LS138isusedinde-multiplexingapplicationsbyusingenablepinasdatainputpin.Alsothechipinputsareclampedwithhigh-performanceSchottkydiodestosuppressline-ringingandsimplifysystemdesign.CatalogDescriptionCatalogCADModelsFeaturesApplicationPinoutLogicDiagramPackageParametersProductComplianceComponentDatasheetProductManufacturerFAQOrdering&QuantityCADModels74LS138Symbol74LS138FootprintFeaturesDesignedSpecificallyforHigh-Speed:MemoryDecodersDataTransmissionSystems3EnableInputstoSimplifyCascadingand/orDataReceptionSchottky-ClampedforHighPerformanceApplicationLinedecodersServersDigitalsystemsLineDe-multiplexingTelecomcircuitsMemorycircuitsPinoutPinFunctionPinNameDescription1A0Addressinputpin2A1Addressinputpin3A2Addressinputpin4E1Enableinput(activeLOW)5E2Enableinput(activeLOW)6E3Enableinput(activeHIGH)7O7Outputpin78GNDGround9O6Outputpin610O5Outputpin511O4Outputpin412O3Outputpin313O2Outputpin214O1Outputpin115O0Outputpin016VCCPowersupplypinLogicDiagramPackageParametersFunctionDecoder,DemultiplexerTechnologyFamilyLSVCC(Min)(V)4.75VCC(Max)(V)5.25Channels(#)1Voltage(Nom)(V)5F@nomvoltage(Max)(MHz)35ICC@nomvoltage(Max)(mA)10tpd@nomVoltage(Max)(ns)41Configuration3:8ProducttypeStandardIOL(Max)(mA)8IOH(Max)(mA)-0.4RatingCatalogOperatingtemperaturerange(C)0to70Bits(#)8Digitalinputleakage(Max)(uA)5ESDCDM(kV)0.75ESDHBM(kV)2ProductComplianceECCNEAR99USHTS8542390001ComponentDatasheetDatasheet74LS138DatasheetProductManufacturerTexasInstrumentsInc.(TI)isanAmericantechnologycompanythatdesignsandmanufacturessemiconductorsandvariousintegratedcircuits,whichitsellstoelectronicsdesignersandmanufacturersglobally.ItsheadquartersareinDallas,Texas,UnitedStates.TIisoneofthetoptensemiconductorcompaniesworldwide,basedonsalesvolume.TexasInstrumentssfocusisondevelopinganalogchipsandembeddedprocessors,whichaccountsformorethan80%oftheirrevenue.TIalsoproducesTIdigitallightprocessing(DLP)technologyandeducationtechnologyproductsincludingcalculators,microcontrollersandmulti-coreprocessors.Todate,TIhasmorethan43,000patentsworldwide.FAQWhatisthedifferencebetween74hc138and74LS138?Bothhavethesamefunction.74HC138ismadeofhigh-speedCMOSprocess,withlowpowerconsumption,highoutput,lowlevelandwiderange.74LS138adoptstheearlybipolarprocess,anditsdrivingcapabilityisrelativelylarger.Whatisthefunctionaldifferencebetween74ls138decoderand74ls148?74ls138isa3-8wiredecoder/multiplexer,74ls148isan8-3wireoctalpriorityencoder.Oneisdecodingandtheotherisencoding.OppositeeffectWhatsthedifferencebetween74LS138Dand74LS138N?Thosetwoarethesamechip,DisSOPpackage,NisDIPpackage.Whataretheoutputcharacteristicsof74LS138decoder?UnderthepremisethattheenableterminalsS1(activehigh),S2(activelow),andS3(activelow)arevalidatthesametime,onlyoneoutputterminalislowatatime(therestarehigh);Iftheenableterminalisinvalid,theoutputisallhighlevel.Whatdothelettersandnumbersin74ls138standfor?74ls138isa3-8-linedecoder.Thenumber74representsthe74seriesofthe54/74series,andthe74serieshasanoperatingtemperatureof0degreesto70degrees.LSisaseries,representingthelow-powerSchottkyseries.138isthevarietycode.Whatstheworkingprincipleof74ls138?74LS138workingprinciple①Whenonestrobeterminal(E1)ishighlevel,andtheothertwostrobeterminals(E2)and(E3)arelowlevel,attheoutputterminalscorrespondingtoY0toY7,thebinarycodeofaddressterminals(A0,A1,A2)canbedecodedatlowlevel.Forexample:whenA2A1A0=110,theY6outputterminaloutputsalow-levelsignal.②UsingE1,E2andE3,itcanbecascadedtoexpandintoa24-linedecoder;ifanexternalinverterisconnected,itcanalsobecascadedtoexpandintoa32-linedecoder.③Ifoneofthestrobeterminalsisusedasadatainputterminal,74LS138canalsobeusedasadatadistributor.④Itcanbeusedin8086decodingcircuittoexpandmemory.

IRFD320PBF-VISHAY

I.IntroductionTheheartrateisakeyindicatorvaluereflectingthehealthofthebody.Simplyput,theheartratereferstothefrequencyofcardiovascularbeatswithin1minute.Thetestofheartratecanshowscientificevidenceinworksuchasdiseasediagnosis,patientcare,andathletetraining.Inrecentyears,manymedicalequipmentandfitnessequipmentdevelopedandmanufacturedbycountriesaroundtheworldhaveadoptedheartratetestpowercircuits.Thelowcostofproductdevelopmentandhighperformanceheartratetestpowercircuitshaveimportantapplicationvalues.ThearticleintroducesthiskindofheartbeatratedetectionsystembasedonAD620integratedICindetail.Usingtheexcellentlow-noisecharacteristicsofAD620integratedIC,pluseffectivefilteringandamplifyingcircuits,combinedwithmicroprocessorsolutions,ahigh-precisionheartratemonitoringsystemisobtained.Figure1AD620CatalogI.IntroductionII.AD620ChipIII.CircuitDesign3.1BlockDiagram3.2SignalExtractionCircuitBasedonAD6203.3FilterAmplifierCircuit3.4MicroprocessorCircuit3.5ExperimentalResultsandDiscussionIV.ConclusionFAQOrdering&QuantityII.AD620chipAD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyneedsanexternalresistortosetthegain,andthegainrangeis1to10000.Inaddition,AD620adopts8-pinSOICandDIPpackage,thesizeissmallerthanthediscretecircuitdesign,andthepowerconsumptionislower,soitisverysuitableforbattery-poweredandportableapplications.Itscharacteristicsareasfollows:EASYTOUSEGainSetwithOneExternalResistor(GainRange1to10,000)WidePowerSupplyRange(2.3Vto18V)HigherPerformancethanThreeOpAmpIADesignsAvailablein8-LeadDIPandSOICPackagingLowPower,1.3mAmaxSupplyLOWNOISE9nV/Hz,@1kHz,InputVoltageNoise0.28Vp-pNoise(0.1Hzto10Hz)EXCELLENTDCPERFORMANCE(BGRADE)50Vmax,InputOffsetVoltage0.6V/Cmax,InputOffsetDrift1.0nAmax,InputBiasCurrent100dBminCommon-ModeRejectionRatio(G=10)EXCELLENTACSPECIFICATIONS120kHzBandwidth(G=100)15sSettlingTimeto0.01%III.CircuitDesign3.1BlockDiagramThesurfaceofthehumanskincontainshumanECG,EMG,andpowerfrequencysignals.Generally,thenoiseoftheECGsignalcontainingheartrateinformationismuchsmallerthanthatofthepowerfrequencysignal.InordertoextracttheweakECGsignal,alow-noiseoperationalamplifiermustbeusedandareasonablefilteramplifiercircuitmustbedesigned.Figure2isablockdiagramoftheheartratedetectionsystem.Thewholeheartratedetectionsystemconsistsoffourparts:thesensorheadincontactwiththehumanskinsurface,thesignalextractioncircuit,thefilteramplifiercircuitandthemicroprocessorcircuit.Thesensorheadisgenerallyametalthatiseasytoconductelectricity.Aftercontactingthesurfaceofthehumanskin,ithascomplexelectricalsignalssuchashumanECGsignals,electromyographicsignals,andpowerfrequencysignals.Weusethelow-noiseAD620operationalamplifierasthecorechipoftheheartbeatrateextractioncircuit.Inthefilteringandamplifyingcircuitpart,asimplelow-passfilteringcircuitisused.Theexperimentalresultsshowthatthisfilteringcircuitissufficienttoextracttheheartratesignal.Afterfilteringtheamplifiedsignal,anadjustablecomparatorcombinedwithatransistorcircuitisusedtoforma5voltTTLlevelsignal,andfinallyconnectedtothemicroprocessor,theheartbeatsignalisprocessedbythemicrocomputer,andtheheartbeatrateiscalculatedanddisplayed.Figure2Blockdiagramofheartratedetectionprinciple3.2SignalExtractionCircuitBasedonAD620AD620operationalamplifier,usuallyusedinhigh-precisiontestinstruments,themaximumnonlinearerrorof40ppm,themaximumvoltageoffsetof50uV,themaximumtemperaturedriftof0.6uV/℃,becauseofitslownoise,lowbiascurrent,lowpowerconsumptioncharacteristics,itItiswidelyusedinmedicalfieldssuchaselectrocardiogram(ECG)andbloodpressuremonitoring.Figure3isasignalextractioncircuitbasedonAD620,inwhichtheLEFT_ARM,RIGHT_ARM,LEGthreeleadsareconnectedtothealuminumsheet(iethesensorhead),whicharerespectivelyconnectedtotheleftandrighthandsandrightfeetofthehumanbody.OurexperimentalresearchresultsshowthattheR4gainofLEFT_ARMis1K,thecorrespondingAD620operationalamplifiergainis50.Toomuchgainwillweakenthefinalsignal-to-noiseratio,sotheR4resistancevalueshouldbesetreasonablyintheexperiment.The0.1uFcapacitancebetweentheLEFT_ARMandRIGHT_ARMleadsistoeffectivelyweakenthepowerfrequencynoise.TheLEGleadisconnectedtoAD620throughTL082A,whichprovidesthereferencepotentialofthehumanbodyforthedifferentialsignalofLEFT_ARMandRIGHT_ARM.Figure3SignalextractioncircuitbasedonAD6203.3FilterAmplifierCircuitFigure4isafilteramplifiercircuit.Threeoperationalamplifiersconstituteathree-stageamplification,eachamplifying100times.Duetocircuitloss,especiallythelossoftheisolationcapacitor,theactualsignalamplificationislessthan1milliontimes.TheratiooftheresistancevaluesofR6andR5,R9andR8,R11andR10inthecircuitdeterminesthemagnificationfactor,andtheseresistancevaluesshouldbeadjustedreasonablyinpracticalapplications.Alow-passfiltercircuitshouldbeusedwhileamplifyingthesignaltoachievetheeffectoffilteringpowerfrequencynoise.Sincethefrequencyofthepowerfrequencynoiseis50Hz,thedesignedfiltercircuithasapassbandbandwidthoflessthan50Hz,thatis,theRCtimeconstantofthecapacitorresistormustbeofthesameorderofmagnitudeasthepowerfrequencysignalperiod.R7andC10inthecircuitformalow-passfilter.Weuse1uFcapacitorisolationbetweenlevelsofamplification.Thesecapacitorswillattenuatethesignalatthesametime,andthethreeoperationalamplifiersareselectedforsignalamplification,sothesignal-to-noiseratioisimproved.Itshouldbepointedoutthatiftheisolationcapacitoristoolarge,itiseasytocausetheoutputelectricalsignaltodrift.Figure4FilteramplifiercircuitFigure5istheshapingcircuit.Theheartbeatratesignalandsignal-to-noiseratioofthe2ND_OUTleadarelargeenough(thepulserateoftheheartbeatrateis1~5V),afterthehalf-waveshapingofD1,thentheadjustablecomparator,andfinallythetransistorQ1isconvertedtothemicrocontrollerlevel.Figure5Shapingcircuit3.4MicroprocessorCircuitThefinalsignalisprocessedbyAT89C51,andtheheartrateisdisplayedbyLEDdigitaltube.ThemicroprocessorcircuitwithAT89C51asthecoreisverymature,soitsnoneedtorepeathere.3.5ExperimentalResultsandDiscussionFigure6showstheactualmeasurementresultsofthehumanheartrateusingtheabovesystem.Figure6(a)isthevoltagesignalafterthesignal2ND_OUTisshapedbyD1.ItcanbeseenfromthefigurethatthisisactuallyacompleteECGsignal.Inacycleofsignals,therearetwomoreobviouspulsesignals.Thispulsecharacteristicvariesfrompersontoperson.ItisfoundthatthereisatleastonepulsesignalthroughactualmeasurementoftheECGsignalsofdifferentpeople.Figure6(b)showstheelectricalsignalofHEART_PULSE,whichisobtainedafterthesignalofFigure6(a)passesthroughthecomparatorandthetransistorswitch.Thesignalcanbedirectlyinputtotheportofthemicroprocessor,andthemicroprocessorcalculatesandoutputstheheartrate.Figure6HeartratesignaldiagramWhendevelopingtheabove-mentionedheartratedetectionsystem,thereareseveralkeypointstopayspecialattentionto:(1)ConnectingcapacitorstoLEFT_ARMandRIGHT_ARMcangreatlyimprovethesignal-to-noiseratio;themainenergyoftheheartratesignalonLEFT_ARMandRIGHT_ARMisatafrequencyofabout1Hz,andthecapacitorisalow-passfilterthatcanfilterandsuppressnoise;Choosealargecapacitortoeliminatehigh-frequencynoise.Intheexperiment,a10uFnon-polarcapacitorisused,andtheeffectisverygood;(2)Thelow-passfiltercircuiteffectivelyweakensthepowerfrequencysignalandimprovesthesignal-to-noiseratio;itadoptsacombinationofactivefilteringandpassivefilteringtofilterwhileamplifying,whichhasabettereffectthanfilteringafteramplification;(3)Capacitorisolationattenuationandmulti-stageamplificationarebeneficialtoimprovethesignal-to-noiseratio;themainnoiseis50Hzpowerfrequencysignals.Althoughthemulti-stageamplificationandfilteringincreasethermalnoise,ithasgreatsuppressionofpowerfrequencynoise.Ofcourse,thenumberofamplificationstagescannotbeinfinite,andthebestnumberofstagesistheminimumsumofpowerfrequencynoiseandthermalnoise;(4)SmallcapacitorisolationshouldbeusedtosuppressDCsignaldrift.Thisisshownbytheexperimentalresults,andthereasonneedstobefurtherstudied.IV.ConclusionThisarticlediscussesaschemebasedonAD620chipheartratedetection,andintroducesthecircuitdesignofthesensorhead,signalextraction,filteramplificationandmicroprocessorthatmakeupthesystem.Givesthemethodtoimprovethesystemperformance.ExperimentsshowthatthesystemcanobtainbetterECGsignalsandaccurateheartrate.Theheartbeatratedetectionsysteminthisarticlehasstronganti-interferenceability,simplestructureandlowcost.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstrumentsI.IntroductionTheamplificationofweaksignalshashighrequirementsandhighdifficulty.Thesignalamplificationisrelatedtotherequirementsofstabilityandaccuracyofsignalamplification.Differentialamplificationtechnologyhasthecharacteristicsofsuppressingcommonmodesignalsandonlyamplifyingdifferentialmodesignalswithhighgain,soitisappliedtosmallsignalamplificationtechnology.ThesystemdesignadoptstheAD620chipwithdifferentialamplificationfunctiontoamplifytheweakvoltagesignalofthestrainsensortoachievethehighprecisionrequirementsofthesystem.Thisarticleusesvirtualinstrumenttechnologytocollectandanalyzetheamplifiedsignal,andwritethecorrespondingdisplayinterface.Themeasurementdataisanalyzedbythesecond-orderinterpolationmethodtoverifytheaccuracyofthecircuit.AD620CatalogI.IntroductionII.SystemDesignIII.SystemHardwareCircuitDesign3.1PressureMeasurementCircuit3.2VoltageSignalAmplifierCircuit3.3ReferenceVoltageSourceCircuitandVoltageZeroingCircuit3.4Voltage-currentConversionCircuitIV.TheOverallSoftwareDesignoftheSystemV.QuantitativeTestingandResultAnalysis5.1DataProcessingMethod5.2DataProcessingResults5.3ErrorAnalysisVI.ConclusionFAQOrdering&QuantityII.SystemDesignThesystemisprovidedwithtwovoltagesof12Vand5VfromaDCstabilizedsource.Whensetting12Vpowersupply,thesystemvoltageoutputfullrangeis5V,andthesensorwithstandsstaticpressurefullrangeis19.6N.Whenmeasuringwithinthefull-scalerange,themaximumabsoluteerrorofthestaticpressuresignalis9.810-3N,andtherelativeerroris0.02%.Theoutputsignaloftheloadcellprovidestwooutputmodes:voltageoutputandcurrentoutputaftertheamplifiercircuit.III.SystemHardwareCircuitDesignTheoveralldesignprocessofthesystemisshowninFigure1.ThesystemhardwarecircuitismainlycomposedofLC7012loadcell,AD620instrumentationamplifier,referencevoltagesource,voltagezeroingcircuit,signalfilteringandshapingcircuitandvoltage-currentconversioncircuit.Figure1Systemhardwarecircuitoveralldesignprocess3.1PressureMeasurementCircuitPressuremeasurementadoptsLC7012loadcell,withfullbridgemeasurementcircuit.LC7012loadcellhasthefollowingtwocharacteristicswhensubjectedtopressure:(1)Underthesamepressure,thestrainofthesensorstraingaugeandtheoutputvoltageofthebridgeareconstantandhavenothingtodowiththeprecisepositionofthepressureactingontheloadendofthesensor.(2)Theoutputvoltageandpressureofthefullbridgecircuitcomposedofstraingaugesarebasicallylinear.The4piecesofresistancestraingaugesintheLC7012loadcellareattachedtothestrainzoneofthedouble-holebeam.Whenthereisstaticpressure,thedouble-holebeamproducesquadrilateraldeformationundertheactionofthepressureandthesupportingforceofthesystemchassisonthedouble-holebeam.Thefourstraingaugesareconnectedtoafullbridgecircuitinafullbridgemode.Undertheexcitationofthebridgevoltage,differentweakvoltagesignalsareoutputwithdifferentpressures,andtheamplifiercircuitamplifiestheweakvoltagesignalssentbythebridge.Thefull-bridgeequal-armbridgehassimplestructure,strongsymmetry,highsensitivity,andgoodconsistencyoftheparametersofeacharm.Theeffectsofvariousinterferencescancanceleachother,forexample,itcansuppresstheeffectsoftemperaturechangesandsuppresstheinterferenceoflateralforces.Itiseasiertosolvetheproblemofcompensationoftheloadcell.Thefull-bridgemeasurementcircuitenablestheoutputoftheweakvoltagesignaltoeliminateerrorscausedbythecircuititselfasmuchaspossible,andprovidestheinitialguaranteefortheoverallaccuracyofthesystem.3.2VoltageSignalAmplifierCircuitInordertoimprovetheamplificationaccuracyoftheweakvoltagesignaloutputbythebridge,thesignalamplifyingcircuitselectstheAD620chipproducedbyADIasthecoreelement,anddesignsaspecialadjustablereferencevoltagesourceforittomeetthereferencevoltagerequirementsofdifferentvoltagesources.Andtheneedtoaccuratelyamplifyweaksignals.Figure2AD620PinoutAD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyneedsanexternalresistortosetthegain.Thegainrangeis1to10000dB.AndAD620powerconsumptionislow,themaximumoperatingcurrentis1.3mA.AD620hasthecharacteristicsofhighprecision(maximumlinearity4010-6),lowoffsetvoltage(maximum50V)andlowoffsetdrift(maximum0.6V/℃),makingitanidealchoiceforprecisiondataacquisitionsystemssuchassensorinterfaces.Figure2showsitspinarrangement.AD620monolithicstructureandlasercrystaladjustmentallowcircuitcomponentstobecloselymatchedandtracked,thusensuringtheinherenthighperformanceofthecircuit.AD620isathree-op-ampintegratedinstrumentationamplifierstructure,inordertoprotectthehighprecisionofgaincontrol,theinputtransistorprovidesdifferentialbipolarinput,andusesprocesstoobtainlowerinputbiascurrent,throughthefeedbackoftheinputstageinternalop-amp,Keepthecollectorcurrentoftheinputtransistorconstant,andaddtheinputvoltagetotheexternalgaincontrolresistorRG.AD620internalgainresistanceisadjustedtoanabsolutevalueof24.7k,soanexternalresistancecanbeusedtoachievepreciseprogrammingofthegain.ThegainformulaisThevoltagesignalamplifiedbytheAD620canpassthroughafilteringandshapingcircuitandbedisplayedindigitalformwithadigitaltubethroughtheanalog-to-digitalconvertermodule.Inordertofullyutilizeanddemonstratethefunctionsofvirtualinstruments,thesystemusesLabVIEWtodesignthecorrespondingsignalacquisitionandprocessingprogramanddisplayinterface.3.3ReferenceVoltageSourceCircuitandVoltageZeroingCircuitThereferencevoltagesourcecircuitismainlycomposedofaZenerdiodeLM285,alow-powerdualoperationalamplifierchipLM258,avariableresistorandanumberoffixedresistanceresistors,asshowninthelowerleftpartofFigure3.ThisreferencevoltagesourcecircuitcanprovideAD620with1.25Vor2.5Vaccuratereferencevoltage.Figure3VoltagesignalamplifiercircuitThevoltagestabilizingdiodeLM285providestheprimarystablevoltage,butthetemperaturedriftofthediodeislarge,andthevoltagestabilizationvalueofdifferentdiodesinthesamebatchisnotthesame,sothecorrespondingauxiliaryvoltagestabilizingcircuitmustbedesignedforit.TheoperationalamplifierLM258U1AamplifiesthevoltagefromtheZenerdiodeandfeedsbacktheoutputvoltagethroughthefeedbackresistorR2,makingtheoutputvoltagemorestable.ResistorR5andpotentiometerW1dividetheoutputvoltageoftheZenerdiode.PotentiometerW1hastwofunctions:(1)AdjustingW1canmakethevoltagefollowercomposedofoperationalamplifierLM258U1Bhavedifferentoutputvoltages,andthenprovidedifferentstablereferencevoltagestoAD620.(2)ThepotentiometerW1alsoplaysaroleofzeroadjustmentontheamplifyingcircuitcomposedofAD620.Thevoltagefollowerisusedbecausethevoltagefollowercanincreasetheinputimpedanceandreducetheoutputimpedance,andtherequirementofthepowersupplyisthatthecircuithasasmalleroutputresistance.AD620itselfhasaninternalzeroadjustmentfunction,butaccordingtoactualmeasurement,itisfoundthatwhenthedifferentialinputiszero,theoutputisnotzero,butaboutafewtenthsofmV.Therefore,inordertoimprovetheaccuracyoftheoutput,itisnecessarytoperformtheAD620Externalzeroadjustment,byprovidingdifferentreferencevoltagestotheAD620referencevoltagepins,theoutputvoltageoftheinstrumentationamplifierAD620canbezerowhenthedifferentialinputiszero.ThecircuitjustadjustsW1tomaketheoutputterminalofthevoltagefollowerhavedifferentvoltageoutput,adjuststhereferencevoltageofAD620,thusplaystheroleofzeroadjustmenttoAD620.TheinstabilityofthereferencevoltagewilldirectlyaffectthestabilityoftheamplifiercircuitcomposedofAD620,andleadtoinaccuracyofthefinaloutputresult.Therefore,thesystemdoesnotdirectlyusetherelativelystable-12Vor-5VprovidedbytheDCstabilizedsourceasthereferencevoltage.3.4Voltage-currentConversionCircuitThevoltage-currentconversioncircuitenablesthesystemtooutputintheformofcurrent.TheAD620iscombinedwithanAD705operationalamplifierandtworesistors(asshowninFigure4)toformaquietcurrentsource.AD705providesabufferforthereferencepin.Ensuregoodcommonmoderejection(CMR)performance.TheoutputvoltageofAD620appearsontheresistanceRL,thelatterconvertsitintoelectriccurrentoutput.Figure4Schematicdiagramofvoltage-currentconversioncircuitAD705isalow-power,bipolaroperationalamplifierwithabipolarfieldeffecttransistorinputstage.Therefore,ithasthecharacteristicsofhighinputimpedance,lowinputoffsetvoltage,smallinputbiascurrent,andsmallinputoffsetvoltagedrift.TheinputbiascurrenthasreachedthepAlevel.Itnotonlyhasmanyadvantagesofbipolarfieldeffecttransistorsandbipolaroperationalamplifiers,butalsoovercomesthedefectoflargebiascurrentdriftinthefulltemperaturerange.Inthefulltemperaturerange,thetypicalvalueofthebiascurrentofAD705onlyincreasesby5times,andthebiascurrentofthegeneralbipolarfieldeffecttransistoroperationalamplifierincreasesby1,000times.ComparedwithOP07,thetemperaturedriftvalueis1/2ofOP07,themaximuminputbiascurrentisonly1/5ofOP07,andtheinputoffsetvoltageisonly1/20ofOP07.Becauseitisabipolarfieldeffecttransistorinputpole,thesignalsourceimpedanceismuchhigherthanOP07,whileitsDCaccuracyremainsunchanged.IV.TheOverallSoftwareDesignoftheSystemThesystemsoftwareiswritteninLabVIEW.LabVIEWisagraphicalprogramminglanguage,whichiswidelyusedinvariousfieldsasastandardfordataacquisitionandinstrumentcontrolsoftware.LabVIEWisapowerfulandflexiblesoftware.Useittoeasilybuildyourownvirtualinstrument.Inthecaseofonepieceofhardware,differentfunctionsofdifferentinstrumentscanberealizedbychangingthesoftwareprogramming,whichisconvenientandfast.Combinedwiththenewdevelopmentdirectionofthecurrenttestingfieldinstruments,thefinaloutputanalogvoltagesignaliscollectedbyAdvantechsUSB4716universaldataacquisitionmoduleandtransmittedtothecomputer.UseNIvirtualinstrument(LabVIEW)todesignvoltagesignalacquisitioncontrolprogramandvoltagedatareal-timedisplayinterface.UseLabVIEWsoftwareplatformtoanalyzeandprocessthedigitalvoltagesignalfromUSB4716.ThepartprogramofLabVIEWvoltagesignalacquisitioncontrolanddisplayisshowninFigure5.Figure5VoltagesignalacquisitionprogramV.QuantitativeTestingandResultAnalysis5.1DataProcessingMethodSecond-orderinterpolation(parabolicinterpolation):select(x0,y0),(x1,y1),(x2,y2)correspondinginterpolationequationsfromasetofdata.5.2DataProcessingResultsInordertoobtainanaccuratecorrespondencebetweenpressureandvoltageandfacilitatesubsequentanalysisofabsoluteandrelativeerrors,theexperimentusesstaticmeasurementmethodstomeasureaseriesofstaticpressurevalues,andquantitativelyanalyzetheexperimentalresultstodeterminetheaccuracyofthecircuit.Commonlyusedwaveformtimedomainandfrequencydomainanalysismethods.Table1Brightness/ContrastComparisonPressure/N0...2.94...8.829.8...13.72...19.6219.6Voltage/V0...0.75...2.2472.498...3.498...4.755.001Measure20staticpressurevaluesfromsmalltolargewithinthefullscalerange,andmakethepressureincrement△thesame.Let△=0.98N,andusethesecond-orderinterpolationmethodtoanalyzetherelationshipbetweenvoltageandpressure.SelectthreerepresentativepointsfromTable1:(x0,y0)=(0,0);(x1,y1)=(2.498V,9.8N);(x2,y2):(5.001V,19.6N).Bringinsecond-orderinterpolationTherelationshipcurvebetweenthepressureonthesensorandthesystemoutputvoltageisY=(-1.56810-3)x2+3.927x(3)5.3ErrorAnalysisTheabsoluteerrorreflectsthedeviationofthemeasuredvaluefromthetruevalue,thatis,theabsolutevalueofthedifferencebetweenthemeasuredvalueandthetruevalue.Theabsoluteerrorcanbedefinedas:=|X-L|(4)Intheformula,istheabsoluteerror;Xisthemeasuredvalue;Listhetruevalue.Relativeerroristheratioofabsoluteerrortothemeasuredvalueortheaveragevalueofmultiplemeasurements,andtheresultisusuallyexpressedasapercentage,soitisalsocalledpercentageerror.Absoluteerrorcanindicatethereliabilityofameasurementresult,whilerelativeerrorcancomparethereliabilityofdifferentmeasurementresults.Whenmeasuringwiththesametool,thelargerthemeasuredvalue,thesmallertherelativeerrorofthemeasurementresult.TheabsoluteerrorandrelativeerrorofthestraingaugepressuresensortestsystemareshowninFigure6andFigure7.Thetwofiguresrespectivelyshowtheabsoluteerrorandrelativeerrorcurvesoftwootherdataprocessingmethods:linearinterpolationandaverageselectionmethod.ItcanbeseenfromFigure6andFigure7thatthecalculationaccuracyofthesecond-orderinterpolationmethodishigherthantheothertwomethods,whichalsoprovesthatthechoiceofthedataprocessingmethodiscorrect.Figure6AbsoluteerrorcurveFigure7RelativeerrorcurveVI.ConclusionKnownfromtherelativeerrorandabsoluteerrorgraphthat,themeasurementresulterrorofthecircuitintherangeof0~4.9Nisrelativelylarge,butitstillmeetsthesystemdesignrequirements.Afteranalyzingthesensorandtheexperimentalmeasurementcircuit,itisbelievedthatthereasonforthelargererrorcomesfromtherigidityofthecantileverbeammaterialofthesensorandtheflexibleinfluenceoftheviscousmaterialthatfixesthestraingauge.Becausetheaccuracyoftheweakvoltagesignaloutputbythebridgeisaffected,theerrorisalsoamplifiedafterpassingthroughtheamplifyingcircuit,resultinginalargererrorintheexperimentalresultwhenthemeasuredvalueissmall.Insummary,thepressuresignalamplificationsystemsatisfiesthedesignrequirementsofabsolutefull-scaleerror9.810-3Nandrelativeerror.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstruments

IRFD320PBF-VISHAY

IDescriptionAD620isalow-power,high-precisioninstrumentationamplifier.BasedontheinformationprovidedbytheADcompany,thisblogintroducesthecharacteristicsandtypicalusageofAD620.Besides,thisblogalsointroducestheapplicationofAD620.Theapplicationsaremainlyaboutphotoelectricdetection,ultrasonictesting,etc.Figure1.AD620IDescriptionIIIntroductionIIIAD620PinoutandWorkingPrincipleIVAD620TypicalUsageVAD620Application5.1ApplicationinPhotoelectricDetection5.2ApplicationinUltrasonicTestingVIConclusionFAQOrdering&QuantityIIIntroductionAD620isalow-power,high-precisioninstrumentationamplifier.Anditcansettheamplificationfactorfrom1to1000withonlyanexternalresistor.Itissmallinsize,inan8-pinSOICorDIPpackage;thepowersupplyrangeis2.3V~18V;themaximumpowersupplycurrentisonly1.3mA.AD620hasgoodDCandACcharacteristics.Itsmaximuminputoffsetvoltageis50V,themaximuminputoffsetvoltagedriftis1V/℃,andthemaximuminputbiascurrentis2.0nA.WhenG=10,itscommon-moderejectionratioisgreaterthan93dB.Theinputvoltagenoiseisat1kHz,thepeak-to-peakvalueoftheinputvoltagenoiseis0.28Vintherangeof0.1Hz~10Hz,andtheinputcurrentnoiseisWhenG=1,itsgainbandwidthis120kHz,andthesettlingtimeis15s.Ingeneral,thecharacteristicsofAD620canbesummarizedasfollows:AD620canensuretheperformanceindicatorsrequiredforhigh-gainprecisionamplification.Forexample,lowoffsetvoltage,lowoffsetvoltagedrift,andlownoise,etc.;Withonlyoneexternalresistor,themagnificationcanbesetfrom1to1000;Smallsize,with8pins;Lowpowerconsumptionanditsmaximumsupplycurrentare1.3mA.IIIAD620PinoutandWorkingPrincipleThepinofAD620isshownasinFig.2,itsstructurediagramisshownasinFig.3.Figure2.AD620PinoutFigure3.AD620StructureDiagramAD620isamonolithicinstrumentamplifier.Itisdevelopedonthebasisoftheimprovementofthetraditionalthree-opamplifiercombination.TheinputtransistorsQ1andQ2providetheonlybipolardifferentialinput.Duetotheinternalsuperprocessing,itsinputoffsetcurrentis10timeslowerthannormal.ThroughthefeedbackoftheQ1-A1-R1loopandtheQ2-A2-R2loop,thecollectorcurrentsofQ1andQ2arekeptconstant.Thus,theinputvoltageisequivalenttothetwoendsoftheexternalresistorRg.AndthedifferentialamplificationfactorfromtheinputtotheA1/A2outputisG=(R1+R2)/Rg+1.TheunitygainsubtractorcomposedofA3eliminatesanycommon-modecomponents.Andthenitproducesasingle-channeloutputrelatedtothepotentialoftheREFpin.ThevalueofRgalsodeterminesthetransconductanceofthepreviousstageopamp.WhenRgdecreases,theamplificationfactorincreases.Andthetransconductancetotheinputtransistorgraduallyincreases.Thishasobviousadvantages:theincreaseintheamplificationfactorincreasestheopen-loopgain.Thus,theerrorrelatedtogainisreduced.Thegain-bandwidthproductdeterminedbyC1,C2andthepre-opamptransconductanceincreases.Thus,thefrequencyresponseisimproved.Theinputvoltagenoiseismainlydeterminedbythecollectorcurrentoftheinputtransistorandthebaseresistance.Andtheinputvoltagenoiseisreducedto.TheinternalgainresistorsR1andR2areaccuratelydeterminedas24.7k.Inthiscase,theoperationalamplifiergainisaccuratelydeterminedbyRg.G=49.4k/Rg+1orRg=49.4k/(G-1)IVAD620TypicalUsage(1)Theinputbiascurrentisthecurrentrequiredtobiastheinputtransistoroftheopamp,anditmusthaveareturnloop.Therefore,whenamplifyinganAC-coupledsignalsourcelikeatransformer,eachinputpointmusthaveaDCpathtoground.AsshowninFigure4-6.Figure4.BiasCurrentLoopwithTransformerCoupledInputFigure5.BiasCurrentLoopforThermocoupleInputFigure6.BiasCurrentLoopWhenACCoupledInput(2)Allinstrumentamplifiersrectifythesignaloutsidethechannel.Ifasmallsignalisamplified,thisrectifiedvoltagebecomesaDCoffsetvoltage.ThestructureofAD620allowsafirst-levelfiltertobeinsertedbetweenthebaseandemitteroftheinputtransistortofilteroutunwantedrectifiedsignals,asshowninFigure5.RC=1/2f,fisgreaterthanorequaltothebandwidthofAD620,C150pF.Figure7.PrimaryFilterPrincipleDiagram(3)TheoutputvoltageofAD620isrelatedtothereferenceterminal.ConnectingtheREFterminaltoanappropriategroundingpointcansolvemanygroundingproblems.Manydataacquisitionsystemsseparatetheanaloggroundfromthedigitalground.Howcome?Justaimingtoisolatethelow-levelanalogsignalfromthenoisydigitalenvironment.Thegroundingprincipleisasfollows:eachindependentgroundloopminimizesthecurrentflowingfromthesensitivepointtotheground.Thesegroundloopsmustbeconnectedtogetheratsomepoint,usuallyontheADC.LetstakealookatFigure7.Thereferenceterminal5oftheAD620,thegroundterminalofthesample-and-holdAD585.Andthegroundterminaloftheanalogpowersupplyarerespectivelyconnectedtotheanaloggroundterminaloftheanalog-to-digitalconverterAD574A.Thegroundterminalofthedigitalpowersupplyisconnectedwiththedigitalgroundoftheanalog-to-digitalconverterAD574A.Finally,theanaloggroundanddigitalgroundareconnectedtotheAD574A.Inmanyapplications,shieldedcablesareoftenusedtoreducenoiseinterferenceattheinput.Properdrivetotheshieldcanreducethedifferentialphaseshiftcausedbycablecapacitanceandstraycapacitance.AndensurethattheACcommon-moderejectionratiodoesnotdrop.Figure8showsthedifferentialshielddriveconnection.Figure9showsthecommon-modeshielddriveconnection.Figure8.DifferentialShieldDriveFigure9.CommonModeShieldDriveVAD620Application5.1ApplicationinPhotoelectricDetectionPhotoelectricdetectioniswidelyusedintheindustry.Theprincipleofdesigningaphotoelectricdetectionsystemistoreducethetotalsystemnoisetoaminimum.Thenoiseofthesystemmainlyincludesdetectornoise,resistancenoise,andoperationalamplifiernoise.Becausetheyareindependentofeachother,thetotalnoisecanbeexpressedasUn(T)=[Un2(D)+Un2(L,F)+Un2(A)]1/2Intheformula:Un2(D)Detectornoisevarieswithdifferentphotodetectors.Theappropriatedetectorshouldbeselectedaccordingtothesystemrequirements;Un2(L,F)Loadresistancenoise;Un2(A)Opampnoise.ThenoiseofAD620isverysmall.Therefore,itisoftenusedasthepre-opamplifierofthephotoelectricdetectioncircuit.Takethephotodiodeasthedetectorasanexampletoillustrate.Here,supposethecurrentofthephotodiodeisID,thenID=ISC+IdarkIntheformula:ISCPhotocurrent.Itisproportionaltothelightintensity,whichistheeffectiveinformationdetected;IdarkDarkcurrent.ItconsistsofthecurrentonthesurfaceofthediodeandtheusualPNjunctioncurrent.Itbelongstoinvalidinformationinthesystem.Weneedtoeliminatetheinfluenceofdarkcurrent.TwodiodesD1andD2withthesameperformanceandtworesistorsR1andR2withtheresistancevalueofRareselectedtoformabridge.AsshowninFigure10.Figure10.PhotoelectricDetectionPreamplifierCircuitWhenD1haslightandD2hasnolight,theinputvoltageatbothendsoftheop-ampis(ISC+Idark)-R1-Idark-R=ISC-R1.Itisonlyrelatedtothephotocurrent,thuseliminatingtheinfluenceofthedarkcurrent.5.2ApplicationinUltrasonicTestingInthefieldofultrasonictesting,especiallywhenultrasonicwavespropagateinanon-uniformandattenuatedmedium,theechoafterencounteringtheinterfaceisveryweak.Ifageneralop-ampisusedforpre-processing,thenoiseisoftenlargeandeffectivesignalscannotbeobtained.ChoosingAD620asthepre-amplifiercircuithasasimpleconnectionandlownoise.AsshowninFigure11.Figure11.UltrasonicDetectionReceivingFrontCircuitVIConclusionAD620isahighprecisioninstrumentationamplifier.Intheapplication,wealsoneedtopayattentiontopreventtheblockageoftheamplifier.IfastrongDCsignalissuperimposedontheweaksignal,wemustsetupaseparationcircuit.Inthisway,theDCsignalcanbeseparated.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstruments

IIntroductionHere,youcanlearnabouttheAD620instrumentamplifiercircuit.Besides,youcanalsobrowseAD620mainfeatures,workingprinciples,andapplications.Thisbloggenerallydiscussesthefollowing3basicquestions:1.Whatisaninstrumentationamplifier;2.Howdoesitwork;3.Howandwheretouse.Figure1.AD620CatalogIIntroductionIIDescriptionIIIAD620TechnicalIndicatorsIVAD620WorkingPrincipleVAD620ApplicationVIConclusionFAQOrdering&QuantityIIDescriptionOperationalamplifiershaveevolvedoverthedecadesandasaresult,thereisawidevarietyofthem.Theycanbeeasilycategorizedaccordingtotheirapplicationrequirements.Themaincategoriesincludegeneral-purpose,low-voltage,low-power,high-speed,andhigh-precisiontypes.Inrecentyears,applicationssuchasconsumerelectronics,communication,andnetworkinghavebeendevelopingcontinuously.Andtheseconstantlydevelopingindustriesalsoputforwardnewtechnicalrequirementsforop-ampproducts.AD620instrumentamplifieristheproductofADcompany.Duetoitssupertechnology,AD620hasthefollowingcharacteristics:1.3mAMaximumWorkingCurrent5VInputOffsetVoltage1V/℃InputOffsetDriftMaximum93dBCommonModeRejectionRatioAdjustableGainRangeEasytoAdjustandLowNoise.AndwhycanAD620becomeanindustry-standardhigh-performance,low-costinstrumentationamplifier?ThatsbecausethecoreofAD620isathree-stageop-ampcircuit,whichhasahighcommon-moderejectionratio,goodtemperaturestability,wideamplificationband,andlownoise.Andithasthecharacteristicsofhighaccuracy,easyuse,andlownoise.sothisisalsothereasonwhyAD620canbesopopular.IIIAD620TechnicalIndicatorsThemaintechnicalindicatorsofAD620areasfollows:Bandwidth800MHzOutputpower2.4mWPowergain120dBWorkingvoltage15VStaticpowerconsumption0.48mWInoltage60VConversionrate1.2V/SPackageformDIP8Operatingtemperaturerange-55℃~+125℃IVAD620WorkingPrincipleThefunctionalstructureoftheAD620amplifierisshowninFig.2.Figure2.AD620FunctionalBlockDiagramDoyouknowwhatthecharacteristicsofthisamplifierare?Theansweris:differentialinput,asingle-endedoutput.ThevoltagegaincanbedeterminedbyaresistorRG.Thegainsareadjustable,whichsolvestheproblemofconnectingthesubsequentloadtotheground.Besides,A1andA2formadifferentialinputandadifferentialoutputwithin-phasehighinputimpedanceandundertakeallgainamplificationtasks.Becausethecircuitstructureissymmetrical,whichmeanswhenthegainchanges,theinputimpedancedoesnotchange.ThefeedbackresistanceRl=R2=24.7k.Thecommon-modegain,offset,drift,andothererrorsoftheamplifiersA1andA2aremutuallycompensated.ThegainofthelatterstageA3is1,whichhasahighercommon-moderejectionratioandanti-interferenceability.AD620isamonolithicintegratedamplifier.Anditisdevelopedonthebasisoftheimprovementofthetraditionalthree-opamplifiercombination.AsshowninFigure2,theinputtransistorsQ1andQ2providetheonlybipolardifferentialinput.Duetotheinternalultra-processing,itsinputoffsetcurrentis10timeslowerthanthegeneralcase.ThroughthefeedbackoftheQ1-A1-R1loopandtheQ2-A2-R2loop,theintegratedpolecurrentofQ1andQ2iskeptconstant.SotheinputvoltageisequivalenttothetwoendsoftheexternalresistorRG.ThedifferentialamplificationfactorfrominputtoA1/A2outputisG=(R1+R2)/RG+1.TheunitygainsubtractorcomposedofA3eliminatesanycommon-modecomponents.Thereby,itproducesasingle-channeloutputrelatedtothepotentialoftheREFpin.Figure3.AD620SowhataboutRG?ThevalueofRGalsodeterminesthetransconductanceofthepreviousstageop-amp.WhenRGdecreases,themagnificationincreases.WhenRGdecreases,thetransconductancetotheinputtransistorgraduallyincreases.Thishasthefollowingtwoobviousadvantages:First,theincreaseintheamplificationfactorincreasestheopen-loopgain.Therebyreducingthegain-bandwidthproductandincreasingthefrequencyresponse;Second,itismainlydeterminedbytheinputtransistorcollectorcurrentandbaseresistance.ByaccuratelycorrectingthevalueoftheinternalgainresistorsR1andR2to24.7k,wecanmaketheoperationalamplifiergain(derivedbycalculation)accuratelydeterminedbyRG:G=49.4k/RG+1orRG=49.4k/(G-1)Figure4.AD620CircuitStructureDiagramRGistheexternalgainadjustment.Tomeettherequiredamplificationfactor,wecanconnectthishigh-precisionresistancebetweenpin1and8.ByusingtheamplifierAD620,thegainerrorcanbelessthan0.01%,andthenon-linearityislessthan0.002%.Fromtheapplicationpointofview,AD620isparticularlysuitableforapplications.Suchassensorinterface,ECGmonitor,precisionvoltagecurrentconversionandotherapplications.Ifweanalyzethecircuittechnologyperformance,wewilladeeperunderstandingofAD620.Thatis,AD620isactuallyalow-power,high-precisioninstrument,broadbandintegratedoperationalamplifier.VAD620ApplicationInstrumentationamplifiersaresometimesmisunderstoodbypeople.Here,weneedtopointout2ideas:First,notallamplifiersusedforinstrumentationareinstrumentationamplifiers;Second,allinstrumentationamplifiersarebynomeansonlyusedforinstrumentation.Instrumentationamplifiersareusedinmanyfields.Frommotorcontroltodataacquisitionandautomotivesystems.Instrumentationamplifierisaclosed-loopgainunit.Andwithdifferentialinputandsingle-endedoutputrelativetothereferenceend.Inmostcases,theimpedanceofthetwoinputendsoftheinstrumentationamplifierisbalanced.Theresistanceisveryhigh,anditstypicalvalueis109.Theinputbiascurrentisalsoverylow,typically1nAto50nA.Liketheoperationalamplifier,itsoutputimpedanceisverylow,usuallyonlyafewmilliohmsinthelowfrequencyrange.Theclosed-loopgainofanoperationalamplifierisdeterminedbytheexternalresistance.Theexternalresistanceisconnectedbetweenitsinvertinginputandoutput.Therearedifferencesbetweentheinstrumentamplifierandtheamplifier.Theinstrumentamplifierusesaninternalfeedbackresistornetwork,whichisisolatedfromitssignalinput.Toapplyinputsignalstothetwodifferentialinputterminalsoftheinstrumentationamplifier.Thegaincaneitherbepresetinternallyorsetbytheuser.Throughapinconnectedtoaninternalorexternalgainresistor,whichisalsoisolatedfromthesignalinputterminal.Figure5showsablockdiagramofadifferentialamplifier.Figure5.DifferentialAmplifierICThistypeofICisaspecial-purposeinstrumentationamplifier.Anditwhichusuallyconsistsofasubtractoramplifierfollowedbyanoutputbuffer(perhapsone-stagegain).ThefourresistorsusedforthesubtractorareusuallyinsidetheIC,sotheycanbepreciselymatchedtoachieveahigherCMR.Manydifferentialamplifiersaresuitableforapplications.Wherethecommon-modevoltageandsignalvoltagemayeasilyexceedthesupplyvoltage.Thesedifferentialamplifiersusuallyusehigh-valueinputresistorstoattenuatethesignal.Generallyspeaking,instrumentationamplifiersanddifferentialamplifiersareusedinthefollowingranges:DataAcquisitionThemainpurposeoftheinstrumentationamplifieristoamplifytheweaksignaloutputbythesensorinanoisyenvironment.Amplificationofsignalsfrompressuresensorsortemperaturesensorsiscommon.Commonbridgeapplicationsincludestrainforceandweightmeasurement.MedicalInstrumentsInstrumentationamplifiersarewidelyusedinmedicalequipment.Suchaselectrocardiographsandelectroencephalographs,bloodpressuremonitors,anddefibrillators.Thedifferentialamplifierofmonitoringandcontrolelectronicscanbeusedtomonitorthevoltageandcurrentinthesystemandtriggerthealarmsystemwhenthenormalvalueisexceeded.Becausedifferentialamplifiershavetheabilitytosuppresshighcommon-modevoltages,theyareoftenusedinsuchapplications.Figure6.ElectrocardiographSoftwareProgrammableApplicationsToallowsoftwaretocontrolthehardwaresystem,wecanturntoinstrumentationamplifiers.Instrumentationamplifierscanbeusedonchipswithsoftwareprogrammableresistors.AudioApplicationsBecauseinstrumentationamplifiershavehighCMR,theyareusedforaudio(e.g.microphonepreamplifiers)toextractweaksignalsinnoisyenvironments.Also,itcanbeusedtominimizetheoffsetcausedbygroundloopsVoltageandnoise.High-speedSignalConditioningDuetotheincreasedspeedandaccuracyrequirementsoftodaysvideodataacquisitionsystems,thedemandforbroadbandinstrumentationamplifiersisincreasing.EspeciallyinthefieldofCCDimagingequipmentthatrequiresoffsetcorrectionandinputbuffering.Inthisfield,doublecorrectionsamplingtechnologyisusuallyusedtocorrecttheCCDimage.Generallyusetwosample-and-holdamplifierstomonitortheimageandreferencelevel,andsendthesignalvoltagetoaninstrumentationamplifiertoprovideaDCcorrectionoutput.Figure7.CCDCameraVideoApplicationsHigh-speedinstrumentationamplifiersareusedinmanyvideoandcableradiofrequency(RF)systemstoamplifyorprocesshigh-frequencysignals.PowerControlApplicationsInstrumentationamplifierscanalsomonitorthemotor(monitoringandcontrollingthemotorsspeed,torque,etc.)bymeasuringthemotorsvoltage,currentandthephaserelationshipofthethree-phaseACmotor.Thedifferentialamplifierisusedwhentheinputsignalvoltageexceedsthepowersupplyvoltage.VIConcusionGenerallyspeaking,high-speedoperationalamplifiersaremainlyusedincommunicationequipment,videosystems,andtestandmeasurementinstruments.Advancedapplicationsintestandmeasurement,communications,medical,imagingandotherfieldsarethemaindrivingforcestoimproveamplifierperformance;DSLandconsumervideoapplicationsareitslargestmarkets.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstrumentsIDescriptionWhatisLM2596?LM2596isaswitchingvoltageregulatorforstep-downpowermanagementmonolithicintegratedcircuits,capableofoutputting3Adrivecurrent,whilehavinggoodlinearityandloadregulationcharacteristics.ThefixedoutputversionsofLM2596are3.3V,5Vand12V,andtheadjustableversioncanoutputvariousvoltageslessthan37V.Withonlyafewexternalcomponents,wecanusethisvoltageregulator!Moreover,theLM2596switchingfrequencyis150KHz,whichmeansthatcomparedwithlow-frequencyswitchingregulators,wecanusesmallerspecificationsoffiltercomponents.Inaddition,LM2596integratesfrequencycompensationandfixedfrequencygenerator.Thisblogwillintroduce4typicalapplicationcircuitsofLM2596.Figure1.LM2596CatalogIDescriptionIICircuitofLM2596Output3.3V,5VIIICircuitofStep-DownVoltageRegulatorsIVLM2596ApplicationCircuitVLM2596AdjustableCurrentLimitingRegulatorFAQOrdering&QuantityIICircuitofLM2596Output3.3V,5VHaveyounoticedthatinthedesignbelow,allLM2596chipschooseasupplyvoltageof5V,3.3Vor1.8V?Thisisbecause,inthedesignofthewholecontrolsystem,ifthepowersupplysystemistoocomplexandredundant,itwillnotonlycauseelectromagneticinterferencetootherpartsofthecircuit,butalsotheeconomicbenefitisnotgood.Therefore,theselectionof5V,3.3Vor1.8Vsupplyvoltageisbeneficialtotheexperimentaldesign.Whataretheotherbenefits?Inthisway,the24Vvoltagecanbedirectlyconvertedintothedesiredvoltagebyusing3LM2596andsomecapacitors,inductors,diodesandsoon.Thiskindofdesigncircuitisnotonlysimpleandconvenient,butalsoveryeconomical.ThepowersupplycircuitisshowninFigure2.Whenweuseit,wecanchoosethechipsofLM2596+5V,LM2596+3.3VandLM2596+1.8Vaccordingtoourneeds:Toobtaintheconnectionofgraph(a)when+1.8Vand+5V,Toobtaintheconnectionofgraph(b)when+3.3V.Figure2.LM2596CircuitDiagramIIICircuitofStep-DownVoltageRegulatorsWhenyouthinkaooutthevoltageregulatorandstep-downmoduleinthesingle-chipmicrocomputersystem,willyouthinkofcommonchipssuchasLM7805andAMS117?SinceLM7805andAMS117arelowincostandcanbeuseddirectlywithoutexternalexpansionofothercomponents,theyhavebeenwidelyused.ButdontforgetthatLM7805hasafataldisadvantage:highheatgenerationandlowoutputcurrent.Inthemicrocontrollersystem,iftheexternaldevicecurrentisverysmall,thenitsOKtochooseLM7805.However,onceweneedtodrivemoduleswithlargercurrentssuchasrelays,LM7805appearstobepowerless,becausehighheatgenerationmeanspowerloss.Inaddition,iftheinputvoltageofLM7805isabout15V,evenifthecurrentrequiredfortheoutputloadissmall,itsheatgenerationisabout85℃(Ithinkthisshouldbeabletofryanegg),soaheatsinkoracoolingfanmustbeaddedtoit.ThismeansthatcostandPCBlayoutwillbeaffected.TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.Thesedevicesareavailableinfixedoutputvoltagesof3.3V,5V,12V,andanadjustableoutputversion.However,itshouldbenotedthatbecauseLM2596isaswitchingvoltageregulator,itsowncalorificvalueisverysmall.ThismeansthatthewideinputvoltagerangecomparedwiththeLM7805,LM2596needstoaddseveralexternalcomponents.Figure3.LM2596Step-DownVoltageRegulatorsFromtheabovefigure,wecanseethatcomparedwithLM7805,LM2596has4moreexternalcomponents,anditsoutputcurrentcanreach3Aatmost,whichisenoughtodealwithcommonsingle-chipmicrocomputersystems,atthesametime,theinputvoltagerangeiswideandthemaximuminputvoltageis40V.LM2596alsohasanadjustableversion.Iftheadjustableversionisusedtomakea0-30vhigh-currentadjustablepowersupply,itiscompletelyfeasible.Figure4.AdjustableLM2596TheabovefigureisacircuitdiagramofanadjustableversionofLM2596,whichcanoutputaDCvoltageof0-37v,whichismuchbetterthanLM317.IVLM2596ApplicationCircuitLM2596supportsadjustableoutput.Whentheinputis40V,theoutputcanbecontinuouslyadjustedto0~37V.Thetypicalapplicationcircuitisasfollows:Figure5.LM2596ApplicationCircuitNote:Thefeedbackwireshouldbefarawayfromtheinductance,andthethickwireinthecircuitmustbeshort.Herewedbettershielditwithagroundwire.TheresistorsR1andR2thatregulatetheoutputvoltageshouldbeclosetothe4pinsoftheLM2596.VLM2596AdjustableCurrentLimitingRegulatorLM2596doesnothavethefunctionofcurrentlimiting,butinsomeelectronicdesignsandauxiliaryequipment,thereisacertaindemandforthefunctionofcurrentlimiting.Althoughthestandardapplicationcircuitgivenbythemanufacturercannotaccomplishthisfunction,wecanaddafunctioncircuittomakeitrealizethecurrentlimitingfunction.AsshowninFigure6:Figure6.LM2596AdjustableCurrentLimitingRegulatorFAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.

IDescriptionThisbloghasdesignedastep-downDCswitchingpowersupply(itsvoltagecanbeadjustedfrom0V)forneutrontubestorage.ThepowersupplyadoptstheBUCKtopology,andtherail-to-railLMV358operationalamplifiervoltagefeedbackcircuitisdesignedtocooperatewiththeLM2596internalerroramplifiertoovercometheshortcomingsthattheminimumoutputvoltageoftheLM2596step-downchipcannotbelowerthan1.2V,therebytheoutputvoltagecanbeadjustedfrom0V.ThisvideoreviewsanLM2596DCtoDC,adjustable,stepdownregualtorCatalogIDescriptionIIIntroductionIIILM2596BasicCircuitIVDesignofZero-startingPeripheralCircuit4.1VoltageReferenceCircuit4.2VoltageFeedbackCircuitVPowerInductorParameterVIAnalysisofExperimentalResultsVIIConclusionFAQOrdering&QuantityIIIntroductionBeforewestartreadingthisblog,pleasetakeafewsecondstolookatthefollowingtwoquestions:①Whatistheneutrontubestorage?②WhatistherelationshipbetweentheneutrontubestorageandtheDCpowersupplythatrequiresthevoltagecanbeadjustedfrom0V?Figure1.LM2596Whatistheneutrontubestorage?Neutrontubestorageisgenerallycomposedofpowderwithstronghydrogenabsorptioncapacityandheatingwire,usedtostoredeuteriumandtritiumgasfornuclearfusionreaction.Bycontrollingthecurrentoftheheatingwire,theoutgassingvolumeofthereservoirandtheairpressureinthetubeareindirectlycontrolled,therebycontrollingtheneutronyield.Itscoldresistanceofthereservoirisabout3.Whenthepassingcurrentreaches0.35A,thereservoirstartstoreleasedeuteriumandtritiumgas.Theadditionoftheionsourcevoltagewillionizethegasintheionsource,andtheaccelerationhighvoltagewillcausetheionizeddeuterium-tritiumionsintheionsourcetobeextractedandaccelerated,andadeuterium-tritiumfusionreactionoccursonthetargettoproduceneutrons.WhatistherelationshipbetweentheneutrontubestorageandtheDCpowersupplythatrequiresthevoltagecanbeadjustedfrom0V?Inordertoaccuratelycontroltheheatingcurrentofthestorage,thepowersupplyoftheneutrontubestoragerequiresthatthevoltagecanbeadjustedfrom0V.Afterwetookaquicklookatoneofthecircuitprotagonists,neutrontubestorage,discussedinthisblog,letstakealookatanotherequallyimportantrole:theLM2596chip.ThevoltagereferenceoftheLM2596integratedvoltageerroramplifieris1.2V,sothatitslowestoutputvoltageisnotlessthan1.2V.ItseemsthattheLM2596chipitselfcannotbeadjustedfrom0V?Howcanthisdefectberesolved?Wecanusetherail-to-railopampLMV358poweredbyasinglepowersupplytodesignthevoltagefeedbackcircuit.Byisolatingthesamplingterminalandthefeedbackterminal,thelinearadjustmentintervaloftheopampcanbeusedtocompensateforthevariationofthefeedbackvoltage,whichcansolvetheproblemofthelowestoutputofLM2596thatcannotbelowerthantheproblemcausedby1.2V.Afterexperimentaltests,thedesignofthepowersupplyfeedbackcircuitissimpleandefficient.Notonlythepoweroutputvoltagecanbeadjustedfromzero,butalsotheoutputvoltageadjustmentaccuracyishigh,sotheactualapplicationneedscanalsosolved.IIILM2596BasicCircuitLM2596isavailableinfixedandadjustableversions.Amongthem,theoutputvoltageoftheadjustableversionrangesfrom1.2vto37V,withthemaximuminputvoltagedoesnotexceed45V.Underloadconditions,thecircuitshowsthefollowingcharacteristics:Voltageregulation4%.Donotneedtoomanycomponentsforperipheralcircuits.Lowpowerbypassmode.Thetypicalstaticcurrentis80A.LM2596minimumoutputvoltage1.2VapplicationcircuitisshowninFigure2.AscanbeseenfromFigure1,thefeedbackresistorsR1andR2determinethevoltagedividerratioofthepowersupplyoutputvoltage,whichcanbeadjustedthroughadjustingR1.WhenR1isadjustedto0,theoutputvoltageistheminimum,whichistheinternalvoltagereferenceoftheLM2596chip.Figure2.LM2596BasicCircuitTheinternalvoltagereferenceatthefeedbackendoftheLM2596chipis1.2V,whichlimitstheoutputvoltageofthepowersupplytobeadjustedfromzero.IVDesignofZero-startingPeripheralCircuitFirst,trytoconnecttheFBterminalandtheVsterminalinFigure1,andadjusttheR1resistanceto0.Atthistime,theVoutisatleast1.2V.Whatshouldwedotoachievethepurposeofadjustingfromzero?WecandisconnectVs,designanindependentvoltagefeedbackcircuittoadjusttheFBterminalvoltage,andchangetheerrorvariationoftheLM2596internalvoltageerroramplifierthroughtheexternalinputvoltagetoincreaseordecreasethePWMoutputdutycycle,whichinturnenablestheoutputvoltagetobeadjustedfromzero.4.1VoltageReferenceCircuitSo,howtoensurethattheFBterminalvoltageofU1isaround1.2V?Sincethesamplingvoltagefeedbackterminalneedsavoltageregulatorforcompensation,wecanuseasimplifiedcircuitdesignmethod,thatis,usingTL431toachievethisgoal.WhatisTL431?TL431hasthefollowingcharacteristics:TL431isatypicalthree-terminalprecisionvoltageregulatorTheoutputvoltagefrom2.5to36Vcanbearbitrarilysetwith2resistorsItsdynamicimpedanceis0.2Theaccuracyofthevoltagereferenceis0.6%ThevoltagereferencecircuitbasedonTL431isshowninFigure3.Figure3.TL431VoltageReferenceCircuitInthiscircuit,thevoltagereferencehavetwofunctions:itcanbothbeusedastheexternalinputvoltagereferenceandthecompensationvoltageofopampinphase.Theexternalinputvoltageisusedtochangetheoutputvoltage,whilethecompensationvoltageisusedtocompensateforthechangeinvoltageatthefeedbackterminal.4.2VoltageFeedbackCircuitThenon-invertingendofU1sinternalvoltageerroramplifierisintegratedwitha1.2VvoltagereferenceandtheoutputvoltagefeedbackresistorR2isconnectedtotheinvertingendoftheerroramplifier:Whenthevoltageatthefeedbackterminalisgreaterthan1.2V,theerroramplifiergeneratesanegativeerrorsignal,thePWMoutputdutycycledecreases,andtheoutputvoltagedecreases;Whenthevoltageatthefeedbackterminalislessthan1.2V,theerroramplifiergeneratesapositiveerrorsignal,thePWMoutputdutycycleincreases,andtheoutputvoltageincreases.Regardlessofwhethertheoutputvoltageofthepowersupplybecomeslargerorsmaller,thechipcankeeptheoutputvoltagestablebycontrollingtheontimeoftheswitchtube,buttheminimumoutputvoltageis1.2V.ThevoltagefeedbackcircuitdesignedbyLMV358isshowninFigure4.Figure4.LMV358VoltageFeedbackCircuitHereisaquestion:Whatisthekeytorealizetheoutputvoltageadjustmentfromzero?Infact,itisverysimple.ThekeyiswhetherthelowestvoltageofFBintheoperationalamplifierfeedbackcircuitcanbe0V.Inthecaseofasinglepowersupply,theopamphasintegratedtransistors,anditsminimumoutputvoltageisabout0.6V(whichobviouslydoesnotmeettheaboverequirements).Ifwewanttosolvethisproblem,wecanchooseLMV358opamppoweredbyrail-to-railsinglepowersupply,withaminimumoutputvoltageof65mV,soastomeettherequirementofpoweradjustmentfromzero.make:M=R14/R13N=R16/(R16+R18)Q=R19/R20Thenthevoltagefeedbackcircuitparametersarecalculatedasfollows:(1)Vo1=Vs(2)Vo2=(1+M)Vref-VadM(3)Vo3=N(Vo1+Vo2)(1+Q)(4)Vo4=kVo3=VfbIntheaboveformula:kisavariablecoefficient.LetFB=1.2V.Whenthepowerisinitiallypoweredon,Vad=0V,Vref=2.5V,buttheoutputvoltageoftheoperationalamplifierdoesnotnecessarilymeetFB=1.2V,causingLM2596tomalfunction.Inordertoavoidthissituation,wecanuseR21tocorrectthevoltagevalueofVfbattheinitialpower-on,sothatFB=1.2V.IncreasetheVadterminalvoltage,theVo2terminalvoltagedecreasesandtheoutputvoltageincreases,sothatVo1increases.Conversely,Vo2compensatesthevariationofVo1toensurethatthevoltageatthefeedbackterminalofthechipisequalto1.2V,sothatthesamplingvoltageVsfollowsthechangeoftheVadvoltage,andthepowersupplycanbeadjustedfromzero.ThetestdataofthevoltagefeedbackcircuitisshowninTable1.Table1.TestDataFromtheabovetestdata,wecanseethatwecanmakeuseofthelinearoutputcharacteristicsoftheoperationalamplifiertoachievethepurposeoflinearadjustmentoftheoutputvoltage.TheVschangeswiththeVad,thechipreferenceterminalvoltageVfbremainsunchanged,andtheoutputvoltagerangeisdeterminedbytheresistancepartialvoltageratio.Undertheconditionoffullload,whentheVadinputvoltagechangesfrom0to5V,thesamplingresistorVsterminalvoltageoutputrangecanbe0to5V,andthepowersupplyoutputvoltageisadjustablefrom0to35Vthroughtheresistordividerratio.VPowerInductorParameterThereare3operatingmodesfortheinductorcurrentintheBUCKcircuit.ThisblogdesignstheinductoraccordingtotheCCMworkingstate,andfine-tunestheinductorparametersaccordingtotheactualtestresults.Whenthepowertubeisturnedon,theinductorcurrentriseslinearly,andthecurrentincrementexpressionis:(5)ION=(VONTON)/LVON,TON,andLaretheinductorconductionvoltage,turn-ontimeandinductance,respectively.Thecurrentdecrementintheturn-offphaseofthepowertubecanbeexpressedas:(6)IOFF=(VOFFTOFF)/LVOFFandTOFFaretheinductorvoltageandturn-offtimewhenturn-off.Inaswitchingcycle,theincrementanddecrementoftheinductorcurrentareequal,andthevolt-secondlawcanbeusedtoobtain:(7)VONTON=VOFFTOFFInthebucktopology,VON=VIN-VO,VOFF=VO,theaboveformulaistransformedtoderivethedutycycleequationofBUCKtopologywork:(8)D=VO/VINHowtodeterminethedutycycle?Thepowersupplyinputvoltageisafixedvalueof40V,andtheoutputvoltagerangeis0-35V.Fromthis,thedutycycleD=0-0.875canbecalculated.Here,wedesigntheinductorparametersaccordingtotheprincipleofmaximumdutycycleandmaximumoutputpower.SohowisILdetermined?ThemaximumloadcapacityofLM2596is3A.FortheBUCKtopology,theaverageinductorcurrentILisequaltotheloadcurrentIO.Wecansetthecurrentrippleratertobe0.3,andthechoiceofraffectsdeviceselectionandcircuitcost.Theexpressionofrisdefinedasfollows:(9)r=I/ILIntheaboveformula:Iisthechangeoftheinductorcurrentinaperiod,andtheparametersaresubstitutedintotheaboveformulatoobtainI=0.9A.Accordingtothelawofelectromagneticinduction,theinductanceiscalculatedasthefollowingformula:(10)L=(VOND)/(rILf)ItisknownthattheswitchingfrequencyoftheLM2596chipis150kHz,andthecalculatedparametersaresubstitutedintotheaboveformulatocalculateL=259H.Intheactualdebugging,thetheoreticallycalculatedinductanceparameterscannotmeetthepracticalapplicationrequirements.Accordingtotheactualdebuggingresults,thehighfrequencypowerinductorwithratedinputcurrent4Aandinductancevalue330Hisselected.VIAnalysisofExperimentalResultsMakeaprototypeaccordingtothedesignparameters.Undertheconditionoffullload,given40Vinputvoltage,theoutputvoltageofthepowersupplyunderdifferentinputvoltageismeasuredbyadjustingtheexternalVadvoltage.Table2showstheoutputvoltagetestdataatload10.1.Inpracticalapplication,theefficiencyofpowersupplyisthefirstconcern.Table3showsthedataformeasuringvoltageandcurrentattheinputandoutputofthepowersupply,respectively.Ascanbeseenfromtables2and3,theinputandoutputvoltagesareproportionaltoeachother,andtheregulationaccuracyoftheoutputvoltageisabout0.05V.Theoutputvoltageofthepowersupplycanbeadjustedfromzero,whichsolvesthedeficiencyof1.2VofthelowestoutputvoltageoftheLM2596chip.Usingtheabovecalculationmethod,theaverageefficiencyofthepowersupplyis93.44%.Usingthetestdataunderno-loadandfull-loadconditions,itiscalculatedthattheloadadjustmentrateofthepowersupplyat35Voutputis1.3%.Inaddition,thepowersupplycannotonlyworkforalongtime,thetemperatureriseisnormal,butalsotheperformanceisstable.Table2.TestData:LM2596DCRegulatedPowerSupply(10.1)Table3.TestData:LM2596DCRegulatedPowerSupplyEfficiencyVIIConclusionInordertosolvetheshortcomingthattheoutputvoltageofLM2596cannotbeadjustedfromzero,thisblogadoptsthemethodofisolatingthesamplingvoltageandthefeedbackendofthechiperroramplifier,thatis:avoltagefeedbackcircuitbydesigningarail-to-railopamptomaketheoutputvoltagecapableofadjustingfromzero.Inaddition,weanalyzedthedesignoftheinductanceparametersoftheadjustableBUCKpowersupplyinprinciple,andmakeaprototypeaccordingtotheparameterstoverifythecorrectnessandreliabilityofthedesign.Theexperimentalresultsshowthattheloadadjustmentrateofthepowersupplyis0.88%,themaximumworkingefficiencyunderratedloadis95.08%,andthefullloadpoweris105W,whichcanmeettheneedsofpracticalapplications.FAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.IDescriptionTheswitchingpowersupplychipLM2596iscompact,low-cost,low-power,high-efficiencyandeasytousecomparedwithspecializedinstruments.ThepowersupplydescribedinthisblogisasteplessadjustableDCregulatedvoltagesupplybasedontheswitchingpowersupplychipLM2596.Figure1.LM2596CatalogIDescriptionIILM2596CircuitandDesignProcess2.1CircuitofSteplessAdjustableDCPowerSupply2.2DesignProcessofAdjustableDCVoltageSourceIIIHowtoApplyandUseLM2596SteplessAdjustableDCPowerSupply3.1HowtoApply?3.2HowtoUse?FAQOrdering&QuantityIILM2596CircuitandDesignProcess2.1CircuitofSteplessAdjustableDCPowerSupplyThispowersupplycircuitmainlyusesLM2596-ADJ.LM2596-ADJisastep-downswitchingpowersupplychip.Itsoutputvoltagerangeis1.2V-37V,anditsmaximumloadcurrentis3A,withexcellentlinearityandloadregulationcharacteristics.Only4externalcomponentsareneededinthemaincircuittoadjusttheoutputvoltage.TheLM2596-ADJchipintegratesfrequencycompensationandafixedfrequencygenerator,andtheswitchingfrequencyis150KHz,whichfacilitatestheuseofsmallerfiltercomponents,therebyreducingvolume,weight,lossandcost.Undercertaininputvoltageandoutputloadconditions,theoutputvoltageerroriswithin4%,theoscillationfrequencyerrorrangeiswithin15%,andthestandbycurrentcanbeonly80uA.Itcanrealizeexternalpower-offandhasaself-protectioncircuit(atwo-stagefrequencyreductioncurrent-limitingprotectioncircuitandanover-temperaturecompleteprotectioncircuitthatiscutoffinabnormalcases).TheLM2596-ADJpackageinthisarticleisTO220(T),whichrequiresanexternalheatsink.VOUT=1.23V*(1+R2/R1)WhendesigningthePCBboard,theexternalcomponentsshouldbeascloseaspossibletotheLM2596-ADJ,andusegroundwireshieldingorsingle-pointgrounding,andusemagneticshieldinginductors.Iftheinductorcoreusedisopen,andtheinductancefluxcrossesthesensitivefeedbackline,thegroundlineoftheintegratedchipandtheconnectionoftheoutputcapacitorCOUTmayhaveproblems.ThefeedbackresistorshouldbeclosetotheLM2596-ADJIC,andtherelatedwiringshouldbefarawayfromtheinductor.Figure2.AdjustableDCVoltageSourceCircuit2.2DesignProcessofAdjustableDCVoltageSourceVOUTistheadjustableoutputvoltageVIN(max)isthemaximumDCinputvoltage,ILOAD(max)isthemaximumloadcurrent,F=switchingfrequency(150KHz)1)OutputVoltageCalculationVOUT=VREF*(1+R2/R1)Amongthem,VREF=1.23V.Inthisblog,R1isa1Kmetalfilmresistorwithalowertemperaturecoefficientof1%accuracy;R2usesa30Kpotentiometer.2)InductorSelectionCalculatetheproductE*Toftheinductorvoltageandmicrosecondsbythefollowingformula:E*T=(VIN-VOUT-VSAT)*(VOUT+VD)/(VIN-VSAT+VD)*1000/150KHz(VuS)VSATistheinternalsaturationvoltageoftheswitch,VSAT=1.16VVDistheforwardvoltagedropofthediodeVD=0.5VUsetheE*TvalueintheformulatofindthematchinginductornumberfromtheordinateinFigure3,andselectthemaximumloadcurrentofthecircuitontheabscissa;determineaninductanceareabytheintersectionoftheE*Tvalue,andthemaximumloadcurrent,andeachareaiscorrespondingtoaninductancevalueandaninductanceserialnumber(LXX).SelecttheappropriateinductorfromthecomponentnumberofthemanufacturerlistedinTable1forLM2596-ADJcircuit,preferablyamagneticshieldinductor.Thisblogchooses68uHinductance.Figure3.LM2596-ADJApplicationInformation3)OutputCapacitorCOUTNumber/Inductance(H)/Current(A)SchottRencoPulseEngineeringCoilcraftIn-LineSurfaceMountIn-LineSurfaceMountIn-LineSurfaceMountSurfaceMountL15/22/0.996714835067148460RL-1284-22-43RL1500-22PE-53815PE-53815-SDO3308-223L21/68/0.996714407067144450RL-5417-5RL1500-68PE-53821PE-53821-SDO3316-683L22/47/1.176714408067144460RL-5417-6-PE-53822PE-53822-SDO3316-473L23/33/1.406714409067144470RL-5417-6-PE-53823PE-53823-SDO3316-333L24/22/1.706714837067148480RL-1283-22-43-PE-53824PE-53825-SDO3316-223L25/15/2.106714838067148490RL-1283-15-43-PE-53825PE-53824-SDO3316-153L26/330/0.806714410067144480RL-5471-1-PE-53826PE-53826-SDO5022P334L27/220/1.006714411067144490RL-5471-2-PE-53827PE-53827-SDO5022P224L28/150/1.206714412067144500RL-5471-3-PE-53828PE-53828-SDO5022P154L29/100/1.476714413067144510RL-5471-4-PE-53829PE-53829-SDO5022P104L30/68/1.786714414067144520RL-5471-5-PE-53830PE-53830-SDO5022P683L31/47/2.206714415067144530RL-5471-6-PE-53831PE-53831-SDO5022P473L32/33/2.506714416067144540RL-5471-7-PE-53932PE-53832-SDO5022P333L33/22/3.106714439067144500RL-1283-22-43-PE-53933PE-53833-SDO5022P223L34/15/3.406714440067144790RL-1283-15-43-PE-53934PE-53834-SDO5022P153L35/220/1.7067144170-RL-5473-1-PE-53935PE-53835-S-L36/150/2.1067144180-RL-5473-4-PE-54036PE-53836-S-L37/100/2.5067144190-RL-5472-1-PE-54037PE-53837-S-L38/68/3.1067144200-RL-5472-2-PE-54038PE-53838-S-L39/47/3.5067144210-RL-5472-3-PE-54039PE-53839-S-L40/33/3.506714422067148290RL-5472-4-PE-54040PE-53840-S-L41/22/3.506714423067148300RL-5472-5-PE-54041PE-53841-S-L42/150/2.7067144410-RL-5473-4-PE-54042PE-53842-S-L43/100/3.4067144240-RL-5473-2-PE-54043-L44/68/3.4067144250-RL-5473-3-PE-54044-Table1.ProductmodelofaninductormanufacturerInmostcases,wecanuselowequivalentresistanceelectrolyticcapacitorsorsolidtantalumcapacitorsbetween82uF~820uF.Wheninuse,thecapacitorshouldbeclosetotheforLM2596-ADJIC,andthepinsandconnectingcopperwiresshouldbeasshortaspossible.SeeTable2below.Inordertosimplifytheselectionofcapacitors,Table1containsthedifferentoutputvoltagesandoutputcapacitorsrequiredforthebestdesign.Thewithstandvoltageofthecapacitorisatleast5timestheoutputvoltage.Sometimes,inordertoobtainalowerrippleoutputvoltage,ahighercapacitorwithstandvoltagevalueisrequired.Thisblogchooses220uF/50Velectrolyticcapacitors.VOUTIn-LineCapacitorSurfaceMountCapacitorPANASONICHFQ(F/V)NICHICONPL(F/V)FeedforwardCapacitorAVXTPS(F/V)VISHAY595D(F/V)FeedforwardCapacitor2820/35820/3533nF330/6.3470/433nF4560/35470/3510nF330/6.3390/6.310nF6470/25470/253.3nF220/10330/1033nF9330/25330/251.5nF100/16180/161.5nF12330/25330/251nF100/16180/161nF15220/35220/35680pF68/20120/20680pF24220/35150/35560pF33/2533/25220pF28100/50100/50390pF10/3515/50220pFTable2.OutputCapacitorandFeedforwardCapacitorSelection4)FeedforwardCapacitorCFFWhentheoutputvoltageislarge,acompensationcapacitorwithatypicalvaluebetween100pFand33nFisrequired,whichisconnectedinparallelwiththeoutputvoltageadjustmentresistorR2.Itsfunctionistocompensatethefeedbackloopandincreasethephasemargintoimprovethestabilityoftheloop.Forhighoutputvoltage,lowinput-outputvoltageand/orlowequivalentresistanceoutputcapacitors,thiscapacitormakesthecircuitmorestable,suchassolidtantalumcapacitors.TheselectionstillreferstothecorrespondingfeedforwardcapacitorvalueinTable1.Thisblogchooses33nFceramiccapacitors.CFF=1/(31*1000*R2)Thiscapacitorcanbeaceramiccapacitor,plasticormicacapacitor.5)ZenerDiode(D1)SelectionThemaximumcurrentcapacityoftheZenerdiodeisatleast1.3timesthemaximumloadcurrent.Ifthedesignedpowersupplyistowithstandcontinuousshort-circuitoutput,themaximumcurrentcapacityoftheZenerdiodeisequaltothelimitoutputofLM2596Current.Itsfunctionistoprovideapathfortheinductorcurrentwhentheswitchisclosed.ThereversevoltageoftheZenerdiodeisatleast1.25timesthemaximumoutputvoltage;theZenerdiodemustbeafastrecoverydiodeandmustbeclosetotheLM2596-ADJIC.Atthesametime,thepinsandtheconnectedcopperwiresshouldbeshort.Therefore,weshouldfirstchooseSchottkydiodes.Thisblogchooses1N5825Schottkydiodehere.6)InputCapacitanceCINTheinputcapacitorisanelectrolyticcapacitorortantalumcapacitorwithalowequivalentresistance,whichisalsoclosetotheIC,andtheDCloadcurrentmustexceedtwicetherootmeansquareoftheinputcapacitorcurrent.Foraluminumelectrolyticcapacitors,themaximuminputvoltageis2/3ofthewithstandvoltage;fortantalumcapacitors,selectcapacitorsthatthemanufacturerhastestedforsurgecurrent.Wecanselecttheappropriateinputcapacitanceaccordingtothegraphshown.Thiscapacitorpreventsexcessivetransientvoltagefromappearingattheinput,andatthesametimeprovidestransientcurrentforLM2596-ADJeverytimeitswitches.Thisbloguses680uF/50Velectrolyticcapacitors.VROutputCurrent:3AOutputCurrent:4A~6ALnlineSurfaceMountLnlineSurfaceMountSchottkySuperFastRecoverySchottkySuperFastRecoverySchottkySuperFastRecoverySchottkySuperFastRecovery20VTheminimumwithstandvoltageofallsuchdiodesis50VMURS32030WF10IN5820Theminimumwithstandvoltageofallsuchdiodesis50VMURS320Theminimumwithstandvoltageofallsuchdiodesis50VMURS62050WF10SR502Theminimumwithstandvoltageofallsuchdiodesis50VMURS620HER601SK32SR302IN5823MBR320SB52030V30WQ03IN5821SK33MBR33050WQ03SR50331DQ03IN582440VIN5822SB530SK34SR30450WQ04SR504MBRS340MBR340IN582530WQ0431DQ04SB54050VorHigherSK35SR305MBRS360MBR35050WQ05SB55030WQ0531DQ0550SQ080Table3.ChoiceofDiodeFigure4.LM2596-ADJapplicationinformationIIIHowtoApplyandUseLM2596SteplessAdjustableDCPowerSupply3.1HowtoApply?ThedevicecanbeusedasapowersupplythatrequiresaDCvoltagesourcekit:radiopowersupplydoorbellpowersupplyalarmpowersupplypoweramplifierpowersupply51single-chippowersupply,etc.3.2HowtoUse?Theanodeoftheoutputend(redalligatorclip)isconnectedtotheanodeofthecircuit,andthecathodeoftheoutputend(blackalligatorclip)isconnectedtothecathodeofthecircuit.Plugthe220Vpowercordintothemainssocket.Turnonthepowerswitch,theDCvoltagesourceindicator(red)willlightup,adjusttheknobtooutputthevoltagechange,anditsvaluewillbedisplayedonthevoltmeterhead.FAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.Afterreadingtheblog,haveyoubetterunderstandLM2596?Finally,ifyouhaveanyquestionsaboutLM2596,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!

IIntroduction1.1WhatisLM2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuits.Thesecircuitscanprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.Thesedevicesarealsoavailableinfixedoutputvoltagesof3.3V,5V,12V,andanadjustableoutputversion.1.2WhatisLM2577?TheLM2577ismonolithicintegratedcircuitthatprovideallofthepowerandcontrolfunctionsforstep-up(boost),flyback,andforwardconverterswitchingregulators.Thedeviceisavailableinthreedifferentoutputvoltageversions:12V,15V,andadjustable.Figure1.LM2596CatalogIIntroduction1.1WhatisLM2596?1.2WhatisLM2577?IICircuitStructure2.1PowerTransformer2.2RectifierCircuit2.3FilterCircuit2.4VoltageRegulatorCircuitIIIPowerSupplyOverview3.1IntroductiontoPowerSupply3.2Comparisonof2TypesofPowerSupplies3.3ThePowerSupplySelectionIVPerformanceIndicators4.1WorkingMode4.2PCBandPrintedCircuitBoardFAQOrdering&QuantityIICircuitStructure2.1PowerTransformerWeneedDCpower.Byadoptingastep-downtransformer,thegridACvoltage220VistransformedintoacompositeACpowersource.AfterthisACvoltageisrectified,theDCvoltagerequiredbytheelectronicdevicecanbeobtained.2.2RectifierCircuitUseasingle-phasebridgerectifiercircuit.Byusingthiscircuit,itispossibletoconvert50Hzalternatingcurrentwithvaryingdirectionandmagnitude.Here,weneedtotransformitintodirectcurrentinthesamedirectionbutstillpulsatinginmagnitude.Sowhatarethebenefitsofdoingthis?Theyareasfollows:Highervoltage;Smallerripplevoltage;MakethemaximumreverseACcurrentthattherectifierdiodebearsflow;Highutilizationrateofthetransformer.2.3FilterCircuitWecanusethepropertiesofthecapacitorC(theenergystorageelement).Thatis,thevoltageacrossthecapacitorcannotchangesuddenly.Inthisway,byusinganRCfiltercircuittofilteroutmostofthepulsatingcomponentsoutputbytherectifiercircuit,wecangetarelativelysmoothdirectcurrent.2.4VoltageRegulatorCircuitTherectifiedandfilteredDCvoltagedoesnotchangewiththedisturbanceoftheACpowergridandload.Here,duetotheadoptionofalargenumberofhigh-performanceintegratedmodules,thecircuitstructureissimplified.Theresultofthisisthat,thekeypartofthepowerconversionproblemishighlighted.Throughharddebuggingandtesting,theoverallcircuitperformanceisgoodandthedesignpurposecanbebetterachieved.Asavariablevoltagestabilizerorcurrentstabilizersource,thispowersupplycannotonlybeusedalone,butalsocanbeplacedinotherelectronicequipment.IIIPowerSupplyOverview3.1IntroductiontoPowerSupplyThepowersupplyistheheartofelectronicequipment.Thequalityofthepowersupplydirectlyaffectsthereliabilityofelectronicequipment.Since60%ofthefailuresofelectronicequipmentcomefromthepowersupply,asthebasiccomponentoftheelectronicequipment,thepowersupplyhasreceivedmoreandmoreattention.Thepowersuppliesusedinmodernelectronicequipmentroughlyfallinto2categories:linearregulatedpowersuppliesandswitchingregulatedpowersupplies.3.2Comparisonof2TypesofPowerSupplies3.2.1LinearRegulatedPowerSupplyTheso-calledlinearregulatedpowersupplyhasthefollowingmeaning.Theregulatortubeintheregulatedpowersupplycircuitworksinthelinearamplificationarea.Afterthe220V,50Hzpowerfrequencyvoltageissteppeddownbyalineartransformer,itisrectified,filtered,andstabilizedtooutputaDCvoltage.Advantages:Highpowersupplystabilityandloadstability;Smalloutputripplevoltage;Fasttransientresponsespeed;Thelinestructureissimpleandeasytomaintain;Noswitchinterference.Disadvantages:Highpowerconsumptionandlowefficiency,theefficiencyisgenerallyonly35~60%;Bigvolume,heavyweight,andcannotbeminiaturized;Musthavealargercapacityfiltercapacitor.Amongthem,thelowswitchingefficiencyisanimportantshortcoming,causingaseriouswasteofresources.Inthiscontext,theswitchingpowersupplycameintobeing.AnyelectronicdeviceneedsaDCpowersupplytosupplythecircuittowork.Especiallyelectronicproductspoweredbythepowergrid.Nowthattherearegridvoltagefluctuationsandchangesintheworkingstateofthecircuit,weneedtofindwaystoadapt.Intermsofpowersupply,itisnecessarytohaveaDCregulatedpowersupplythatadaptstothischange.Withthedevelopmentofelectronictechnology,peoplehaveenteredin-depthresearchonhowtoimprovethepowerconversionefficiency.Thusenhancingtheadaptabilitytothepowergrid,reducethevolume,andreducetheweight.Sotheswitchingpowersupplycameintobeing.3.2.2SwitchingRegulatedPowerSupplyAdvantage:Highexchangeefficiency.Theregulatortubeoftheswitchingregulatedpowersupplyworksintheswitchstate.Itsmainadvantageisthattheexchangeefficiencycanbeashighas70-95%.Lowpowerconsumptionandhighefficiency.Undertheexcitationoftheexcitationsignal,thetransistorsalternatelyworkintheon-offswitchingstate.Atthesametime,theswitchingspeedisveryfast,andthefrequencyisgenerallyabout50kHz.Thepowerconsumptionoftheswitchingtransistorisverysmall,andtheefficiencycanbeimprovedtoover80%.Smallsizeandlightweight.Nobulkypowerfrequencytransformerisusedintheswitchingpowersupply.Afterthepowerdissipationontheadjustmenttubeisgreatlyreduced,alargerheatsinkisomitted.Widevoltageregulationrange.Theoutputvoltageoftheswitchingpowersupplyisadjustedbythedutycycleoftheexcitationsignal.Thechangeoftheinputsignalvoltagecanbecontrolledbyfrequencymodulationorwidthmodulation.Whenthepowerfrequencygridvoltagechangesgreatly,itcanstillensureaneffectiveandstableoutputvoltage.Therearealsomanymethodsforswitchingregulatedpowersuppliestoachievevoltageregulation.Accordingtoactualapplicationrequirements,wecanchoosedifferenttypesofswitchingregulatedpowersupplies.Disadvantages:Thecircuitismorecomplicated.Theoutputripplevoltageishighandthetransientresponseispoor.Thereisalsomoreseriousswitchinginterference.Nowadays,difficultiesinfurtherpromotionandapplicationofswitchingregulatedpowersuppliesareasfollows:First,theproductiontechnologyisdifficult;Second,themaintenanceistroublesome;Last,thecostishigh.Highrequirementsforcircuitcomponents.Theefficiencyoftheswitchingpowersupplyisproportionaltotheswitchingspeedoftheswitchingtube.Aswitchingtransformerisusedintheswitchingpowersupply.Theswitchingtransformercanbeinputbyonegroup,andgetmultipleoutputswithdifferentpolarityandsize.Tofurtherimproveefficiency,theoperatingfrequencyofthepowersupplymustbeincreased.However,whenthefrequencyisincreased,therequirementswouldhavebeenfurtherimproved.Affectthenormaloperationofnearbyelectronicequipment.Thestabilizedpowersupplyhasthedualfunctionsofvoltagestabilizationandfiltering.Therefore,theserieslinearregulatedpowersupplydoesnotproduceswitchinginterference.Andtheripplevoltageoutputcanalsobesmall.However,whentheswitchtubeintheswitchingregulatedpowersupplyisintheon-offstate,thingshavechanged.Itsalternatingvoltageandoutputcurrentwillproducestrongspikeinterferenceandresonanceinterferencethroughthecomponents.Theseinterferenceswillenterthemainsgridandaffectthenormaloperationofnearbyelectronicdevices.3.3ThePowerSupplySelectionAccordingtothecomparison,wechoosealinearpowersupply.MostelectroniccircuitsrequireaDCpowersourcetowork.TheDCpowersupplyistheguaranteeoftheworkingstateofelectroniccircuitsandtheproviderofenergy.Butmostfixedpowersuppliesallowtheoutputvoltagetovarywithin10%,whichstillcannotmeettherequirementsofsomecircuits.Sowedesignedapowersupplywithadjustableoutputorallowingalargerrangeofvariation.Theperformanceofthispowersupply:Ontheonehand,itisdesignedandmadewithallintegratedcircuitsandhasthefunctionofautomaticshort-circuitandoverloadprotection.Ontheotherhand,ithashighaccuracy,stablecurrentperformance,andcontinuousadjustment.Besides,itcanbeusedformultipleexperimentalpower.IVPerformanceIndicators4.1WorkingModeTheoutputvoltagecanbeadjustedandchangedthroughoutthecurrentrange.ThispowersupplycanalsoworkinaDCsourcemodewithinacertainrange.Letsintroducetheworkproducedbyanetizen.First,the18VACoutputfromthetransformerisconvertedinto20VDCthrougharectifierfiltercircuit.Asshownbelow.Figure2.RectifierFilterCircuitAndthentheadjustablestep-downregulatorcircuitcomposedofLM2596-ADJoutputsavoltageof1.25to19V.Thecircuitisshowninthefigurebelow.AdjustingRW1canchangetheoutputvoltage,andincreasingtheinputvoltagecanincreasetheoutput.Themaximumsupplyvoltageis45V.Figure3.LM2596AdjustableStep-downRegulatorCircuitThenthroughthestep-upvoltageregulatorcircuitcomposedofLM2577,theoutputvoltageofLM2596isincreasedby1to11times.Thatistosay,ifRW1isadjustedtomakeLM2596output3V,RW2inLM2577isadjustedtooutputvoltageof3to33V.Thefigureofthecircuitisshownbelow.ChangingtheresistanceofRW2andtheinputvoltageofLM2577canoutputavoltageof3to100V.Figure4.LM1577Step-upVoltageRegulatorCircuitUndertheconditionoftheinputvoltageof220V,50HZandthevoltagerangeof+15%~-20%ofthemodifiedregulatedpowersupply:Theadjustablerangeofoutputvoltageis+1.25V~inputvoltage;Themaximumoutputcurrentis5A;Thevoltageadjustmentrateisnotmorethan0.5%;Theloadadjustmentrateisnotmorethan2%;Thehighestinputvoltageandoutputripplevoltageatfullloadarenotmorethan10mV.DC-DCconverter,undertheconditionofinputvoltage+2.6V~+18V:Theoutputvoltageisadjustablefrom+2.6Vto100V;Themaximumoutputcurrentis3A;Voltageregulationrateisnotmorethan1.5%,theloadregulationrateisnotmorethan3%;Thepowersupplyalsohasover-currentandshort-circuitprotectionfunctions.Aftereliminatingtheshort-circuitfault,itwillautomaticallyreturntothenormalstate.Anti-reverseconnection,diodesformavoltageindicator.4.2PCBandPrintedCircuitBoardThepicturesbelowarethePCBdrawnbyanetizenandtheprintedcircuitboard.Figure5.PCBandPrintedCircuitBoardFAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.Asweallknow,switchingregulatedpowersuppliesarewidelyusedinelectronicequipmentduetotheirsmallsize,lightweight,andhighconversionefficiency.However,thistypeofpowersupplyisonlysuitableforoccasionswheretheoutputvoltageisfixedortherangeofchangeissmall.Therefore,thispaperproposesaseriesswitchingpowersupplycomposedofamonolithicswitchingregulatorLM2576-ADJinsteadofalinearregulator.Inadditiontotheadvantagesofawiderangeoflinearpowersupplies,thepowersupplyefficiencyisgreatlyimproved.Themaximumoutputpowerofthiscircuitisabout75w,thevoltageadjustmentrangeis1.23V~25V,andtheoutputcurrentcanreach3A.CatalogI.CircuitConfigurationII.PrincipleAnalysis2.1VoltageStabilizingCircuit2.2VoltageAdjustmentCircuit2.3VoltageDisplayCircuitIII.OverallCircuitIV.ConclusionFAQOrdering&QuantityI.CircuitConfigurationThewholecircuitiscomposedoffourparts:astep-downrectifiercircuit,avoltagestabilizingcircuit,anumericalcontrolcircuit,andadigitaldisplaycircuit.ItscircuitblockdiagramisshowninFigure1.Figure1.SystemblockdiagramII.PrincipleAnalysis2.1VoltageStabilizingCircuitThevoltagestabilizingpartofthiscircuitusesLM2576.Inordertogeneratedifferentoutputvoltages,thenegativeterminalofthecomparatorisusuallyconnectedtoareferencevoltage(1.23V),andthepositiveterminalisconnectedtoavoltagedividerresistornetwork.Theoutputvoltagethroughthevoltagedividerresistornetworkiscomparedwiththeinternalreferencevoltageof1.23V.Ifthereisadeviationinthevoltage,anamplifiercanbeusedtocontroltheoutputdutycycleoftheinternaloscillatortokeeptheoutputvoltagestable.ItstypicalapplicationcircuitisshowninFigure2.Figure2.TypicalapplicationcircuitwithadjustableoutputvoltageInthefigure,+V1Nisthevoltageinputterminal.The4pinsoftheregulatorcontrolterminalareconnectedtothevoltagedividercircuitcomposedofpotentiometerWandresistorR.ChangingWcanchangethevoltagedivisionratioandadjusttheoutputvoltage.TherelationshipbetweentheoutputvoltageVoutandR1andR2isUo=UREF(1+R2/R1),andthereferencevoltageUREFofthevoltageregulatorsamplingcircuitis1.23V.ThechoiceofinductanceL1shouldbebasedontheLM2576outputvoltage,maximuminputvoltage,maximumloadcurrentandotherparameters.First,calculatethevoltagemicrosecondconstant(ET)accordingtothefollowingformula:Intheaboveformula,VinisthemaximuminputvoltageofLM2576,VoutistheoutputvoltageofLM2576,andfistheoperatingoscillationfrequencyvalueofLM2576(52KHz).AfterETisdetermined,youcanrefertothecorrespondingvoltagemicrosecondconstantandloadcurrentgraphtofindtherequiredinductancevalue,asshowninFigure3.Figure3.CurvesofvoltagemicrosecondconstantandloadcurrentInthiscircuit,Vin=28V,Vout=25V,soaccordingtotheformula:Itcanbeseenfromthefigurethataccordingtothemaximumloadcurrentselection,thevalueoftheinductanceLshouldbe68H.CINistheinputfiltercapacitor,whichshouldgenerallybegreaterthanorequalto100F.ItisrequiredtobeascloseaspossibletotheinputpinofLM2576duringinstallation,anditswithstandvoltagevalueshouldmatchthemaximuminputvoltagevalue.COUTisthefiltercapacitorattheoutputend,andthecapacitorshouldbevaluedaccordingtothefollowingformula:WhereVinisthemaximuminputvoltageofLM2576,VoutistheoutputvoltageofLM2576,andListhevalueofinductanceL1selectedbycalculationandlookuptable.ThewithstandvoltagevalueofcapacitorCshouldbegreaterthan1.5to2timestheratedoutputvoltage.DiodeD1selectstheSchottkydiodeoftheMBR360series.2.2VoltageAdjustmentCircuitThevoltageadjustmentpartofthiscircuitusestheelectronicpotentiometerX9511asthevoltageadjustmentunit.ItstypicalapplicationdiagramisshowninFigure4.X9511contains31seriesresistancearraysand32shaftheads.ThepositionoftheshaftheadiscontrolledbytwobuttonsandcanbestoredintheinternalEEPROMmemoryforrecallingwhenthepoweristurnedonnexttime,andtheshaftheadpositionisautomaticallyrestored.Voltageadjustmentcircuitdiagram,seeFigure5.Figure4.TypicalapplicationdiagramofX9511Figure5.VoltageadjustmentcircuitAccordingtotheapplicationprincipleofLM2576-ADJ,itsoutputvoltageUo=(1+R/R2),whereRcanchooseadigitallycontrolledpotentiometercomposedofIC3(X9511,50K),UREF=1.23V,Uo=UOMAX=25V,andso:Thatis,thevalueofR2isabout2.6K.Fromtheaboveanalysis,wecanseethatthevoltageadjustmentrangeofthiscircuitisapproximateasfollows:WhenRis0:WhenRis50K:2.3VoltageDisplayCircuitInthisunit,weuseavoltagedisplaycircuitcomposedofMAX1496.Itsworkingpowersupplyisasinglepowersupplyfrom2.7Vto5.25V.ThetypicalapplicationcircuitisshowninFigure6,andthevoltagedisplaycircuitisshowninFigure7.Figure6.M-AXI496typicalapplicationcircuitFigure7.UsingtheresistancedividermethodtoextendtherangeTheRANGEpinisarateselectionpin.Sincethedisplayedvoltagerangeis1.23V~25V,anditsrangeisupto2V,ifyouwanttodisplaythevoltagecorrectly,youshouldexpanditsrangeto200V.Toexpandtherange,youcanusetheresistordividermethod.Addavoltagedividercircuitasshowninfigure7betweenAIN+andAIN1oftheMAX1496.Accordingtotheresistancevalueinthefigure,itcanbecalculatedthattherangehasbeenexpandedby100times,variable resistor symbolthatis200V.Atthistime,themaximumvoltageof200Vismeasured,andafterthevoltageisdividedbythevoltagedividercircuit,thefull-scalevoltageof200V0.01=2Vcanbeobtained.DPSET1and2pinssetthedisplaypositionofthedecimalpointfordisplayindifferentranges.ThespecificsettingsandeffectsareshowninTable1.Becausethefull-scaledisplayinthiscircuitis200V,thefirstsettingformatinthetablecanbeselected,anditsdisplayresolutionis0.1.DPSET1DPSET2DISPLAYOUTPUTZEROINPUTREADING00188.80.00118.880.001018880111.8880.000X=Dontcare.Table1.MAX1496decimalpointdisplaysettingsTheHOLDandPEAKpinsarethesettingbitsfordataretentionandpeakdisplay,andtheirspecificsettingsandeffectsareshowninTable2.Thefirstisthelatchedstate,whichisusedtosavethemeasuredvalue;thesecondisthepeakdisplaymode,whichisusedtodisplaythehighestvaluemeasured.Inthisexample,youcanchoosethelastwaytodisplaythelatestresults.HOLDPEAKDISPLAYVALUESFORM1XHoldvalue01Peakvalue00LatestADCresultX=Dontcare.Table2.MAX1496displaymodesettingMAX1496adoptsthedynamicdisplaymodeofbitsegmentscanning,itsdisplayscanningfrequencyreaches640Hz,thedisplayisstableandclear,andthepowerconsumptionisgreatlyreducedcomparedwithastaticdisplay.Inthisdesign,thecommonlyusedfour-digitscanningLEDdisplaycanbeused.III.OverallCircuitTheoverallcircuitisshowninFigure8.AfterthecommercialpowerissteppeddownbythetransformerT,thebridgerectifiercircuitD1andthefiltercircuitformedbythecapacitorC1convertthelow-voltageACintoaDCvoltageofabout30V.OneofthisvoltageissenttothevoltageofIC2(LM2576).Attheinputend,theotherwaysendsa+5VpowercircuitcomposedofVT1,D2,andIC1(LM7805)astheworkingpowersupplyforIC3(X9511)andJC4(MAX1496).Figure8.SystemdiagramIV.ConclusionThisarticlesummarizesthedesignschemeofdigitallycontrolledadjustableswitchingpowersupplybasedonLM2576,whichhastheadvantagesofsimplecircuit,reliable,highconversionefficiency,andlowprice.Onlyafewcomponentsinthecircuitcanformaswitchingregulatorwithasupplycurrentof3A.Whenthecircuitisusedforlighterloads,LM2576doesnotneedtoinstallaradiator,whichnotonlysavesequipmentspacebutalsoreducesheatloss.Afteractualtesting,itsperformanceindicatorscanfullymeetgeneralneeds,itisthebestsubstituteforthepopularthree-terminallinearregulator.FAQWhereisLM2576used?LM2576isusuallyusedasavoltagestabilizingdevicewhentheinputandoutputvoltagedifferenceislargeandtheoutputcurrentisalsolarge.Becauseitisaswitchingregulator,ithasahigherconversionefficiencyandlowheatgenerationthanalinearregulator.WhatsthedifferencebetweenLM2576T-ADJandLM2576S-ADJ?LM2576T-ADJisthepackageofTO-220,LM2576S-ADJisthepackageofTO-263-5,thereisnodifferenceintheirfunctions.WhatisthedifferencebetweenLM2940andLM2576?Whichcircuitaretheyapplicableto?LM2940isalow-dropoutlinearstabilizedintegratedcircuit.Thelinearstabilizedpowersupplyischaracterizedbyarelativelysimplecircuit,highprecision,andsmallripplecoefficient.Itissuitableforprecisionpowersupplieswithhighvoltagerequirements.ThedisadvantageisthattheefficiencyisverylowandtheoutputThecurrentisrelativelysmall(relativetotheswitchingpowersupply)LM2576isaswitchingpowersupplyintegratedcircuit.Switchingpowersupply,thecircuitismorecomplicated,buttheoutputcurrentislarge,theefficiencyishigh,thedisadvantageisthattheaccuracyislowerandtheripplecoefficientislarger.WhydoswitchingpowersupplychipsLM2576andLM2596havediodes,inductorsandcapacitorsbehindtheoutputpins?ThefunctionofthediodeandtheinductanceisthattheoutputcurrentcanbecontinuouswhentheLM25XXisintheoffstate,andthefunctionofthecapacitoristopreventtheoutputvoltagefromsuddenchangeswhentheLM25XXisturnedonandoff.Infact,itisfiltering.WhythehighertheswitchingfrequencyofLM2576andLM2596,thesmallertheoutputinductanceandcapacitancevalue?Quitesimply,thecapacitivereactanceofacapacitordecreasesasthefrequencyincreases,andtheinductanceofaninductorincreasesasthefrequencyincreases.Thatistosay,theeffectofusinganinductanceof33uHinthecaseof150Khzisbasicallythesameastheeffectofusinganinductanceof100uHinthecaseof52khz,andtheprincipleofcapacitanceisthesame.LM2596isanupgradedversionofLM2576.ButLM2576alsohastheadvantageoflessswitchinglossandlessinterference.

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