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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.

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