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IntroductionLM339(Quaddifferentialcomparator)consistoffourindependentvoltagecomparators.Itisacommonintegratedcircuitandismainlyusedinhigh-voltagedigitallogicgatecircuits.UsingLM339caneasilyformvariousvoltagecomparatorcircuitsandoscillatorcircuits.CatalogIntroductionCatalogICircuitofSingleLimitComparatorIIOverheatDetectionandProtectionCircuitIIIHysteresisComparatorIVOver-voltageDetectionCircuitVDoubleLimitComparatorVIUsingLM339toformanOscillatorFAQOrdering&QuantityICircuitofSingleLimitComparatorFigure(a)showsabasicsinglelimitcomparator.AddtheinputsignalUIN(i.e.voltagetobecompared)tothein-phaseinputterminal,andconnectareferencevoltageUrattheanti-phaseinputterminal.WhentheinputvoltageUinUr,theoutputishighlevelUOH.Figure(b)showsitstransmissioncharacteristics.Figure1.CircuitofSingleLimitComparatorIIOverheatDetectionandProtectionCircuitItispoweredbyasinglepowersupply.Afixedreferencevoltageisaddedtotheanti-phaseinputterminalof1/4LM339,anditsvaluedependsonR1andR2.UR=R2/(R1+R2)*UCC.Thevoltageatthein-phaseterminalisequaltothevoltagedropofthethermistorRT.Whenthetemperatureinsidethemachineisbelowthesetvalue,the+terminalvoltageisgreaterthanthe-terminalvoltage,andUoisahighpotential.Whenthetemperaturerisesabovethesetvalue,the-terminalvoltageisgreaterthanthe+terminal,andtheUooutputisatzeropotential,whichcausestheprotectioncircuittooperate.AdjustingthevalueofR1canchangethethresholdvoltage,whichsetsthetemperaturevalue.Figure2.OverheatDetectionandProtectionCircuitIIIHysteresisComparatorThehysteresiscomparatorcanalsoberegardedasasinglelimitcomparatorwithpositivefeedback.Inthesinglelimitcomparatordescribedabove,iftheinputsignalUinhasslightinterferencenearthethreshold,theoutputvoltagewillproducecorrespondingundulation.Thisshortcomingcanbeovercomebyintroducingpositivefeedbackintothecircuit..Figure(a)showsahysteresiscomparator.ThefamiliarSchmidtcircuitisacomparatorwithhysteresis.Figure(b)showsthetransmissioncharacteristicsofthehysteresiscomparator.Figure3.HysteresisComparatorItisnotdifficulttoseethatoncetheoutputstateischanged,theoutputvoltagewillbestableaslongastheinterferencenearthejumpvoltagevaluedoesnotexceedthevalueofU.Accordingly,itcomestoareductioninresolution.Forthehysteresiscomparator,itcantdistinguishtwoinputvoltageswhosedifferenceislessthanU.Thehysteresiscomparatorwithpositivefeedbackcanacceleratetheresponsespeedofthecomparator,whichisoneofitsadvantages.Inaddition,sincethepositivefeedbackaddedbythehysteresiscomparatorisverystrongandmuchstrongerthantheparasiticcouplinginthecircuit,thehystericcomparatorcanalsoavoidtheself-oscillationcausedbytheparasiticcouplingofthecircuit.IVOver-voltageDetectionCircuitFigure4showsthepartofover-voltagedetectioncircuitinaninductioncookercircuit.Whenthegridvoltageisnormal,1/4lm339u42.8v,thecomparatorturnsover.Theoutputis0VandBG1iscutoff.ThevoltageofU5iscompletelydeterminedbythepartialvoltagevalueofR1andR2,whichis2.7V.ItmakesU4largerthanU5,whichmakesthestateafteroverturningextremelystableandavoidstheinstabilitycausedbythesmallfluctuationofgridvoltageneartheover-voltagepoint.Duetocertainhysteresis,afterovervoltageprotection,theinductioncookerstartstoworkagainwhenthegridvoltagedropsto242-5=237vandU4U3.Figure4.Over-voltageDetectionCircuitVDoubleLimitComparatorThecircuitinFigure5consistsoftwoLM339toformawindowcomparator.WhenthecomparedsignalvoltageUinisbetweenthethresholdvoltages(UR1UinUR2),theoutputishighpotential(UO=UOH).WhenUinisnotbetweenthethresholdpotentialrange,(UinUR2orUinUR1)theoutputislowpotential(UO=UOL),andthewindowvoltageU=UR2-UR1.Itcanbeusedtojudgewhethertheinputsignalpotentialisbetweenthespecifiedthresholdpotential.Figure5.DoubleLimitComparatorVIUsingLM339toformanOscillatorFigure6showsthecircuitofanaudiosquarewaveoscillatorcomposedof1/4LM339.ChangingC1canchangethefrequencyoftheoutputsquarewave.Inthiscircuit,whenC1=0.1uF,f=53Hz;whenC1=0.01uF,f=530Hz;whenC1=0.001uF,f=5300Hz.LM339canalsoformahigh-voltagedigitallogicgatecircuit,andcandirectlyinterfacewithTTLandCMOScircuits.Figure6.LM339OscillatorFAQWhatisLM339?LM339isavoltagecomparatorICfromLMx39xseriesandismanufacturedbymanyindustries.Thedevicesconsistoffourindependentvoltagecomparatorsthataredesignedtooperatefromasinglepowersupply.WhatisthedifferencebetweenLM324andLM339?TheLM324hasacomplementaryoutputwhiletheLM339isopencollector.Inthecomplementaryoutput,currentcanflowineitherdirectionasrequired(eithersourceorsink)whiletheopencollectoroutputcanonlysinkcurrent.HowdoesLM339comparatorwork?TheLM339isaquadopampcomparator.Acomparatorworksbyasimpleconcept.Eachopampofacomparatorhas2inputs,ainvertinginputandanoninvertinginput.Iftheinvertinginputvoltageisgreaterthanthenoninvertinginput,thentheoutputisdrawntoground.Whatiscomparatoric?Acomparatorisanelectroniccircuit,whichcomparesthetwoinputsthatareappliedtoitandproducesanoutput.Theoutputvalueofthecomparatorindicateswhichoftheinputsisgreaterorlesser.Pleasenotethatcomparatorfallsundernon-linearapplicationsofICs.WhatisthereplacementforLM339?LM311,LM324,LM397,LM139,LM239,LM2901Whatisacomparatorcircuit?Acomparatorcircuitcomparestwovoltagesandoutputseithera1(thevoltageattheplusside;VDDintheillustration)ora0(thevoltageatthenegativeside)toindicatewhichislarger.Comparatorsareoftenused,forexample,tocheckwhetheraninputhasreachedsomepredeterminedvalue.WhatistheuseofLM339?LM339isusedinapplicationswhereacomparisonbetweentwovoltagesignalsisrequired.Inadditionwithfourofthosecomparatorsonboardthedevicecancomparefourpairsofvoltagesignalsatatimewhichcomesinhandyinsomeapplications.

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