Low-Cost AC Solid-State Relay With MOSFETs (Rev. …

1 Copyright 2016, texas instruments IncorporatedUndervoltage lockoutLP339(A)DC power supply2 ATL431 Control logicSN74 LVC1G74LP339(B,C,D)MOSFET switch2 CSD18541F524 VACLoadONOFF1 TIDUC87A September2016 RevisedMarch2017 SubmitDocumentationFeedbackCopyright 2016 2017,TexasInstrumentsIncorporatedLow-Cos tAC solid -StateRelayWithMOSFETsTI DesignsLow-CostAC solid -StateRelayWithMOSFETsDescriptionTh e low-costAC solid -staterelay(SSR)withMOSFET sreferencedesignis a singlerelayreplacementthat enablesefficientpowermanagementfor a low-poweralternativeto standardelectromechanicalrelaysin SSRreferencedesignis the basemodelof theself-poweredSSRprovidinga E2E ExpertsFeatures No ClickingSound Low-CostBOM MOSFETB asedDesignfor FastON/OFFS witching Self-Powered ZeroPowerFromThermostatBattery InherentSnubberCircuitReducingVoltageSpi keCreatedby InductiveLoads Low Powerand QuiescentCurrentComponents UndervoltageProtectionApplications

2 Thermostats HVACS ystems BuildingAutomationAn IMPORTANTNOTICEat the end of this TI referencedesignaddressesauthorizeduse, intellectualpropertymattersand otherimportantdisclaimersand 2016, texas instruments IncorporatedUndervoltage lockoutDC power supplyControl logicMOSFET switch24 September2016 RevisedMarch2017 SubmitDocumentationFeedbackCopyright 2016 2017,TexasInstrumentsIncorporatedLow-Cos tAC solid -staterelay(SSR)is an electronicswitchingdevicethat switcheson or off whena smallexternalvoltageis appliedacrossits an inputlogicto respondto an appropriateinput(controlsignal)

3 ,a solid -stateelectronicswitchingdeviceto switchpowerto the load circuitry,and acouplingmechanismto enablethe controlsignalto activatethis SSRmay be designedto controleitheran AC or DC voltageor servesthe samefunctionas anelectromechanicalrelay,but has no powersemiconductordevicessuchas thyristorsor transistorsto switchcurrentsup to 100 switchingspeedscomparedto electromechanicalrelaysand haveno physicalcontactstowearout. To applyan SSR,the usermustconsidertheirlowerabilityto withstandmomentaryoverload,comparedto electromechanicalcontacts,and theirinitialhigher"on" ,an SSRprovidesonly limitedswitchingarrangements(single-pole ,single-throwswitching).

4 This SSRis a low-costreferencedesignfor a singlemechanicalrelayreplacementin low-costthermostatapplications,whichonly usesone SSRis self-poweredthroughthe AC line of theHVAC systemand providesundervoltagelockout(UVLO).See Figure1 for the TI Designsportfoliohas threeavailableSSRreferencedesigns:the TIDA-00377,TIDA-00751, termsof powerconsumption,galvanicisolation,volta geand currentprotection,and Table1 for a featurecomparisonbetweenthe Comparisonof SSRR eferenceDesignsPARAMETERTIDA-00377 TIDA-00751 TIDA-01064 Self-powered Isolation Snubbercircuit UVLO OCP Low cost TIDA-00377and TIDA-01064do not consumeany powerfromthe self-poweredand consume< mA fromthe.

5 The TIDA-00751consumespowerfromthe thermostatbatteryduringbothon and mA fromthe batteryduringon-stateand < September2016 RevisedMarch2017 SubmitDocumentationFeedbackCopyright 2016 2017,TexasInstrumentsIncorporatedLow-Cos tAC TIDA-00751includesgalvanicisolation,wher easthe TIDA-00377and TIDA-01064do not. The TIDA-00377and TIDA-01064are designedfor singlerelayreplacementin it is replacinga singlerelay,isolationis not necessary,use a differentTI CurrentProtectionThe TIDA-01064includesUVLO,the TIDA-00377includesbothprotectioncircuits ,and the UVLO protectsthe low AC powersupply,whichalso translatesto the DC powersupplyof the will enablethe overcurrentprotection(OCP)

6 Is toprotectthe MOSFET switchfromovercurrentand to residentialas well as commercialbuildingautomationapplication, 24 VACis usedas the SSRis usedin thermostatapplicationsas a replacementfor the mechanicalrelay,the maximumoperatingvoltageof the powerswitchis the peakvoltageof one accountthe inputvoltagevariations(20 to 30 VAC), the peakDC voltagerisesup to 43 V. For thatreason,this designusespowerMOSFET swith a breakdownvoltageof 60 thermostatapplications,powerconsumptioni s one of the ensurea long batterylife,the controllogic,in mostcasesa dedicatedmicrocontroller,providesa controlsignalfor a shortperiodoftime beforeit goesin a low poweror turnoffsignalsare two differentsignalsthatare activefor shortperiodsof the that reason,the inputcontrollogicusesthe TexasInstrumentslow-powerAUPD-typeflip-f lop,SN74 AUP1G74with a circuitwill set the outputsignalhigh on a short.

7 Low-ONpulseand resetthe outputsignallow whena short, fast turnonand turnofftime of the powerMOSFET sare necessaryfor the self-poweringfunctionofthe time is controlledby the currentflow duringthe gate-to-sourcecapacitancechargeanddischa rgeof the opendraincomparatorcannotachievea fast chargeof the gateof theMOSFETso an additionalNPNtransistoris neededto speedup the equivalentturnongateresistanceis the pullupresistor,dividedby the hFEof the transistor,in additionwith the built-ininternalseriesgateresistanceof the pullingthe outputof two comparatorsto a negativeDCvoltagerail, the baseof the NPNtransistorwill be negativelybiasedturningthe transistoroff, whilethecomparatorwill quicklydischargethe gatecapacitanceallowingfast addition.

8 The secondcomparatorwill keepthe gatevoltageof the MOSFET closeto zeroincreasingthe chosenfor this functiondue to the low quiescentcurrentand part servestwo purposeswith two comparatorsusedfor the secondpurposeisfor UVLOas explainedin anothermainconcernin thermostatapplicationsbecausethe circuitry,whichmakesup the thermostatcontrol,consumesits powerfroman avoidadditionalpowerconsumptionand the lifetimeof the battery,this SSRreferencedesignis self-poweredthroughthe 24 VACpowerline. By usingthe bodydiodesof the powerMOSFET sand two additionaldiodes,the 24 VACisrectifiedto 33 VDC, whichis furthersteppeddownto providepowerto the remainingof the voltageregulationis performedby two low-powershuntregulators,ATL431, with a quiescentcurrentof 25 2016, texas instruments IncorporatedUndervoltage lockoutLP339(A)DC power supply2 ATL431 Control logicSN74 LVC1G74LP339(B,C,D)

9 MOSFET switch2 CSD18541F524 September2016 RevisedMarch2017 SubmitDocumentationFeedbackCopyright 2016 2017,TexasInstrumentsIncorporatedLow-Cos tAC properlyregulatethe voltageof the DC powersupply,the inputDC voltagemustmaintaina the AC voltageor rectifiedAC voltageof the load (VDC) dropsbelowthe desiredrailvoltages,the shuntregulatorswill no longerbe able to regulate,disablingthe operabilityof the the natureof the DC powersupplyduringthe ON time of the MOSFETs ,the DC supplycapacitorwillwantto fully preventthis, a referencevoltageis set on the UVLOto shortlyturn off theMOSFET swhenthe minimumvoltageis met and allowsthe DC supplycapacitorto rechargewithoutaffectingthe will keepVDCat a voltagewherethe shuntregulatorscan function.

10 One of the comparatorsfromthe LP339is use the UVLOas a controlsignal,a secondcomparatorfromthe LP339is usedto performa logicANDfunctionbetweenthe UVLOand SystemSpecifications(1)TypicalR JA= 245 C/WTable2. Key VSee voltageinputrange20 to 30 VSee A(1) Turnonand turnofftime< 1 sSee (typ)190 ASee (typ)370 ASee C to 60 C WorkingenvironmentIndoorbuildingautomati on SSRreferencedesignfeaturesthe followingdevices: CSD18541F5:60-VN-ChannelFemtoFETP owerMOSFET SN74 AUP1G74:Low-PowerSinglePositive-Edge-Tri ggeredD-TypeFlip-Flop ATL431 IQAdjustablePrecisionShuntRegulator LP339.