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IDescriptionDoyouknowtheDCregulatedpowersupply?DCregulatedpowersupplyiswidelyusedinindustrialproductionanddailylife,anditsdesignoccupiesaveryimportantpositioninpowersupplytechnology.Therefore,basedontheanalysisoftheproblemsofthetraditionalDCstabilizedpowersupply,themethodandcalculationofeachpartofthe5V,1ADCstabilizedpowersupplybasedonL7805CTaredescribed.Besides,itcanalsoprovidea5VDCpowersupplyforcounters,decoders,anddigitaltubestorealizeadditionandsubtractioncounting.ThesystemcircuitbasedonL7805CTintroducedinthisblogissimple,stable,easytocontrol,cost-effective,andisofhighuse-value.CatalogIDescriptionIIIntroductionIIIDesignrequirementsforDCstabilizedpowersupplyIVHardwareunitcircuitdesign4.1Overallstructureofthepowersupply4.2ComponentselectionVApplicationVIConclusionFAQOrdering&QuantityIIIntroductionWiththecontinuousdevelopmentofelectronictechnology,thedesignrequirementsofelectronicequipmentforpowersupplyaregettinghigherandhigher,fromtraditionalrequirementstohigh-quality,high-efficiency,andhigh-stabilitytomeettheneedsofobjects.ThenormaloperationofelectronicdevicesrequiresDCpower.DCpowersourcesincludesolarbatteries,accumulators,anddrybatteries.Butdoyouknowwhichoneisthemostcost-effective?Ofcourse,themostcost-effectivemethodistoconverttheACpowerprovidedbythegridintotherequiredDCpower.Mostelectronicequipmentusesthismode,andthethree-terminalregulatoristhemostwidelyused.AlthoughpeopleusemanytypesofDCstabilizedpowersupplieswithdifferentfunctions,theprinciplesaresimilar.ThevoltageregulatorchipusedinthesystemintroducedinthisblogisL7805CT.L7805CThastheadvantagesofsmallsize,simpleexternalwiring,stableoperationandstrongapplicability.Itcanmeetpeoplesrequirementsinlife,study,andwork.IIIDesignrequirementsforDCstabilizedpowersupplyThedesignrequirementsoftheDCregulatedsingle-channelpowersupplybasedonL7805CTareasfollows:InputACvoltage220V;OutputDCvoltage+5V;OutputDCcurrent1A;Theoutputrippleofthecircuitislessthan50mV;Theequivalentinternalresistanceislessthan0.15;Ripplecoefficientislessthan0.002%;Voltageadjustmentrate0.001%;Voltagestabilizationcoefficient0.005%.IVHardwareunitcircuitdesign4.1OverallstructureofthepowersupplyThisdesignfocusesontheknowledgeandskillsinvolvedinthemainlinksoftheDCpowersupply,andcompletesthecircuitdesignandproductionof220VACinputand5V,1ADCoutput.TheDCpowersupplyisusuallycomposedoffourlinks:PowerTransformers;Rectifiercircuit;Filtercircuit;Regulatorcircuit.AsshowninFigure1.Figure1.BlockdiagramofDCpowersupply4.1.1PowertransformerThepowertransformerconvertsthehigh-voltageACmainspowerintotheappropriatevoltageACandsendsittothesingle-phasebridgerectifiercircuit.Whenchoosingapowertransformermodel,theparametersweneedtoconsiderarecapacityandoutputvoltage.4.1.2RectifiercircuitTherectifiercircuitusestheunidirectionalconductivityofthediodetocompletetherectification.Commonlyusedrectifiercircuitsareasfollows:single-phasehalf-waverectifiercircuit,single-phasefull-waverectifiercircuitandsingle-phasebridgerectifiercircuit.Throughcomparativeresearch,inordertoovercometheshortcomingsofhalf-waverectification,theL7805CT-basedsystemusesasingle-phasebridgerectifiercircuit.Itconsistsof4diodesVD1~VD4connectedintheformofabridge.Whetheritisapositivehalf-cycleoranegativehalf-cycle,thedirectionofthecurrentflowingtotheloadRListhesame.BothtransformtheACvoltageoutputbythesecondarywindingofthepowertransformerintoapulsatingDCvoltage.Thereversevoltagethateachdevicebearsisthepeakvalueofthepowersupplyvoltage,andsymmetricalcurrentflowsthroughthepositiveandnegativehalfcyclesofthetransformer,theutilizationrateishigherthanthatofthefull-waverectifiercircuit,andthecurrentrippleisreduced.Therefore,thereisnounidirectionalmagnetization.4.1.3FiltercircuitTherectifieddirectcurrentcontainsarelativelylargealternatingcurrentcomponent,andthepulsationcoefficientisrelativelylarge,soitcannotbedirectlyusedasthepowersupplyforelectroniccircuits.FiltercircuitsarecommonlyusedtoremoveorreducetheACcomponentintheoutputvoltage,sothatpureACpowerisusedonthedevice.Thisdesignusestheenergystoragecharacteristicsofcapacitorsandinductorstosetappropriateparameters.Whenthecircuitvoltagerises,theenergystorageelementstoresenergy.Whenthevoltagedrops,theenergystorageelementreleasesenergy,soastoachievethepurposeofreducingpulsation.Thecapacityofthecapacitorisrelatedtothedischargetime.Tomakethefilteringeffectbetter,acapacitorwithalargercapacitycanbeusedasthefiltercapacitor.ThefiltercapacitorisgenerallyselectedasRLC(3~5)T/2.4.1.4VoltagestabilizingcircuitTheDCvoltageobtainedaftertheACpowerisrectifiedandfilteredoftenfluctuateswiththefluctuationofthegridvoltage,temperaturechanges,andloadresistancechanges.Then,thequalityofpowersupplywillbereduced,affectingtheoperationoftheequipment.Therefore,avoltagestabilizingcircuitneedstobeaddedbetweenthefiltercircuitandtheloadlinktoachievethepurposeofstabilizingpowersupply.ThechipL7805CThasthecharacteristicsofgoodvoltageregulationperformance,highreliability,easyinstallationandlowcost.Therefore,thelinearstabilizedpowersupplyreplacesthediscretestabilizedcircuitandiswidelyused.Inordertoreducetheinterferenceandmakethevoltagestabilizingcircuitworknormally,theinputvoltageshouldbeatleast2.5~3Vhigherthantheoutputvoltage.4.2Componentselection4.2.1SelectionofpowertransformerConsideringthediodeforwardvoltagedrop,wireresistance,andpowergridfluctuations,theoutputvoltageUIofthethree-terminalintegratedregulatorshouldmeet:Where:Uomaxisthemaximumoutputofregulatedpowersupply;(UI-UO)ministheminimumvoltagedifferencebetweentheinputandoutputoftheintegratedregulator;UIisthechangeoftheinputvoltagecausedbythefluctuationofthepowergrid(generallytakenas10%ofthesumofUO,(UI-UO)min,andUIP).Fortheintegratedthree-terminalregulator,when(UI-UO)min=2~10V,ithasbettervoltageregulationcharacteristics.WhenU1=10VWhenU2=9VInasingle-phasebridgerectifiercircuit,therelationshipbetweenthetransformersecondarywindingcurrentI2andthecapacitorfilteroutputcurrentIIis:Insummary,chooseatransformerwithacapacityof15VAand9V.4.2.2SelectionofrectifierdiodeBecause,thecurrentflowingthrougheachrectifierdiodeinthebridgecircuitis:Themaximumreversepeakvoltageofeachrectifierdiodeis:Insummary,selectthetransistorIN4001,itsparametersare:ID=1A,URM=50V.4.2.3SelectionoffiltercapacitorAlthoughthecurrentpassingthroughthediodeisapulsatingcurrent,becausethecapacitorChasanenergystorageanddischargefunction,thisreducesthedegreeofvoltagepulsationacrosstheloadRLandincreasestheaveragevalue.TheaveragevalueandsmoothnessoftheDCvoltageontheloadarerelatedtothedischargetimeconstant=RLC.ThelargerthevalueofCorRL,theslowerthedischargeofC.ThelargertheoutputDCvoltagevalue,thebetterthefilteringeffect;otherwise,theworse.Generallytake:TheACpowersupplyinsomeAsiancountriesisa50Hzsinewave,with50identicalwaveformspersecond.Afterfull-waverectification,boththepositiveandnegativehalfwavesbecomepulsatingdirectcurrentinthesamedirection.Atthistime,thereare100identicalwaveformspersecond,thatis,f=100Hz.Sothefiltercapacitorcapacityis:amongthem,TheoutputDCvoltageofthecapacitorfiltercircuitisestimatedas:Insummary,twoelectrolyticcapacitorsof2200Fand50Vcanbeused,andtheyareconnectedinparallel.Inordertofilterouttheinterferenceofhigh-frequencysignalsandimprovethedynamiccharacteristicsofthepowersupply,a105pF,50Vhigh-frequencyceramiccapacitorisconnectedinparallelatbothendsofthefiltercapacitor.4.2.4Howtochooseathree-terminalintegratedvoltageregulatorTheconditionthatthepowerconsumptionofthethree-terminalintegratedvoltageregulatormustmeetisgreaterthan5Wandtheoutputvoltageis5V.ThisdesignchoosesL7805CT,theoutputvoltageis4.8~5.2V,thequiescentcurrentis4.2~8mA,andthemaximumoutputcurrentcanbe1.5A,whichmeetsthedesignrequirements.Consideringthelargeoutputcurrent,aheatsinkneedstobeadded.VApplicationAdoptthedesignbasedonL7805CTtoprovide5VDCpowersupplyforcounter,decoderanddigitaltube.Usethebuttontogenerateasingleclock,realizethecountofmodulo10throughthestandardcountercircuit,andgeneratethecorrespondingcode.Thevalueisoutputtotheintegrateddecodingcircuitthroughthedecodertodisplaythenumbers0-9.UsetheDPsectionoftheintegrateddecodingcircuitasapower-onindication.Thecounterhasaresetbutton,andtheintegrateddecodingcircuitadoptsacommoncathodestructuretorealizeadditionandsubtractioncounting.asshowninfigure2.Figure2.L7805CircuitVIConclusionThe5V,1ADCpowersupplydesignbasedontheL7805CTdescribedinthisblogcanprovide5VDCpowersupplyforcounters,decoders,anddigitaltubestoachieveadditionandsubtractioncounting.ThedesigncircuitoftheL7805CTissimple,withfewcomponents,lowpowerconsumptionandstable.Therefore,itcanbeextendedtootherobjectapplicationsasaDCstabilizedpowersupplytoprovideelectricalenergy.FAQWhatisl7805?AvoltageregulatorICmaintainstheoutputvoltageataconstantvalue.7805IC,amemberof78xxseriesoffixedlinearvoltageregulatorsusedtomaintainsuchfluctuations,isapopularvoltageregulatorintegratedcircuit(IC)....7805ICprovides+5voltsregulatedpowersupplywithprovisionstoaddaheatsink.WhatistheworkingprincipleofIC7805?AvoltageregulatorICmaintainstheoutputvoltageataconstantvalue.7805IC,amemberof78xxseriesoffixedlinearvoltageregulatorsusedtomaintainsuchfluctuations,isapopularvoltageregulatorintegratedcircuit(IC).Thexxin78xxindicatestheoutputvoltageitprovides.HowdoItesta7805withamultimeter?TurnontheDCpowersupplyandadjusttheoutputvoltageofabout8Vorslightlylarger.Oralternativelyyoucanuseabattery9V-12Vasvoltagesource.Lookatthevoltmeterpanelwhenyousetthevoltage.PrepareaDCvoltmeterreadingsonvoltagerange50VtomeasuretheoutputvoltageoftheIC7805.Howdoes7805regulatevoltage?For7805IC,itis+5VDCregulatedpowersupply.ThisregulatorICalsoaddsaprovisionforaheatsink.Theinputvoltagetothisvoltageregulatorcanbeupto35V,andthisICcangiveaconstant5Vforanyvalueofinputlessthanorequalto35Vwhichisthethresholdlimit.

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