ST-LLC Analysis

I&PCDiv.-Off-lineSMPSAppl.LabMLDGROUPINDUSTRIAL&POWERCONVERSIONDIVISIONOff-lineSMPSBUApplicationLabSimplifiedAnalysisandDesignofSeries-resonantLLCHalf-bridgeConvertersI&PCDiv.-Off-lineSMPSAppl.LabPresentationOutline•LLCseries-resonantHalf-bridge:operationandsignificantwaveforms•Simplifiedmodel(FHAapproach)•300WdesignexampleI&PCDiv.-Off-lineSMPSAppl.LabSeries-resonantLLCHalf-BridgeTopologyandfeaturesHalf-bridgeDriverVinCrVout
Multi-resonantLLCtankcircuit
Variablefrequencycontrol
Fixed50%dutycycleforQ1&Q2
Dead-timebetweenLGandHGtoallowMOSFET’sZVS@turn-on
fsw≈fr,sinusoidalwaveforms:lowturn-offlosses,lowEMI
Equalvoltage¤tstressforsecondaryrectifiers;ZCS,thennorecoverylosses
Nooutputchoke;costsaving
Integratedmagnetics:bothL’scanberealizedwiththetransformer.
Highefficiency:96%achievableLLCtankcircuitLsLpPreferablyintegratedintoasinglemagneticstructureVoutCenter-tappedoutputwithfull-waverectification(lowvoltageandhighcurrent)Single-endedoutputwithbridgerectifiication(highvoltageandlowcurrent)fr112π⋅LsCr⋅⋅fr212π⋅LsLp+()Cr⋅⋅3reactiveelements,2resonantfrequenciesfr1fr2Q1Q2I&PCDiv.-Off-lineSMPSAppl.LabLLCResonantHalf-bridgeWaveformsatresonance(fsw=fr1)Gate-drivesignalsTransformercurrentsDead-timeDiodevoltagesDiodecurrentsMagnetizingcurrentistriangularOutputcurrentTankcircuitcurrentissinusoidalCCMoperationHBmid-pointVoltageResonantcapvoltageI&PCDiv.-Off-lineSMPSAppl.LabLLCResonantHalf-bridgeSwitchingdetailsatresonance(fsw=fr1)Gate-drivesignalsTransformercurrentsDiodevoltagesDiodecurrentsDead-timeZVS!ZCS!MagnetizingcurrentTankcircuitcurrent0I(D1)=0V(D1)0HBmid-pointVoltageResonantcapvoltageI&PCDiv.-Off-lineSMPSAppl.LabLLCResonantHalf-bridgeOperatingSequenceatresonance(Phase1/6)Q1ONQ2OFFQ1OFFQ2ONQ1OFFQ2ON1/6VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1isOFF,Q2isON
D1isOFF,D2isON;V(D1)=-2·Vout
Lpisdynamicallyshorted:V(Lp)=-n·Vout.
CrresonateswithLs,fr1appears
OutputenergycomesfromCrandLs
PhaseendswhenQ2isswitchedoffCoutI&PCDiv.-Off-lineSMPSAppl.LabQ1ONQ2OFFQ1OFFQ2ONQ1OFFQ2ONLLCResonantHalf-bridgeOperatingSequenceatresonance(Phase2/6)VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1andQ2areOFF(dead-time)
D1andD2areOFF;V(D1)=V(D2)=0;transformer’ssecondaryisopen
I(Ls+Lp)chargesCOSS2anddischargesCOSS1,untilV(COSS2)=Vin;Q1’sbodydiodestartsconducting,energygoesbacktoVin
I(D2)isexactlyzeroatQ2switchoff
PhaseendswhenQ1isswitchedonCout2/6I&PCDiv.-Off-lineSMPSAppl.LabQ1ONQ2OFFQ1OFFQ2ONQ1OFFQ2ONLLCResonantHalf-bridgeOperatingSequenceatresonance(Phase3/6)VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1isON,Q2isOFF
D1isON,D2isOFF;V(D2)=-2·Vout
Lpisdynamicallyshorted:V(Lp)=n·Vout.
CrresonateswithLs,fr1appears
I(Ls)flowsthroughQ1’sRDS(on)backtoVin(Q1isworkinginthe3rdquadrant)
PhaseendswhenI(Ls)=0Cout3/6I&PCDiv.-Off-lineSMPSAppl.LabQ1ONQ2OFFQ1OFFQ2ONQ1OFFQ2ONLLCResonantHalf-bridgeOperatingSequenceatresonance(Phase4/6)4/6VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1isON,Q2isOFF
D1isON,D2isOFF;V(D2)=-2·Vout
Lpisdynamicallyshorted:V(Lp)=n·Vout.
CrresonateswithLs,fr1appears
I(Ls)flowsthroughQ1’sRDS(on)fromVintoground
EnergyistakenfromVinandgoestoVout
PhaseendswhenQ1isswitchedoffCoutI&PCDiv.-Off-lineSMPSAppl.LabQ1ONQ2OFFQ1OFFQ2ONQ1OFFQ2ONLLCResonantHalf-bridgeOperatingSequenceatresonance(Phase5/6)5/6VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1andQ2areOFF(dead-time)
D1andD2areOFF;V(D1)=VD(2)=0;transformer’ssecondaryisopen
I(Ls+Lp)chargesCOSS1anddischargesCOSS2,untilV(COSS2)=0;Q2’sbodydiodestartsconducting
I(D1)isexactlyzeroatQ1switchoff
PhaseendswhenQ2isswitchedonCoutI&PCDiv.-Off-lineSMPSAppl.LabQ1ONQ2OFFQ1OFFQ2ONQ1OFFQ2ONLLCResonantHalf-bridgeOperatingSequenceatresonance(Phase6/6)6/6VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1isOFF,Q2isON
D1isOFF,D2isON
Lpisdynamicallyshorted:V(Lp)=-n·Vout.
CrresonateswithLs,fr1appears
I(Ls)flowsthroughQ2’sRDS(on)(Q2isworkinginthe3rdquadrant)
OutputenergycomesfromCrandLs
PhaseendswhenI(Ls)=0,Phase1startsCoutI&PCDiv.-Off-lineSMPSAppl.LabLLCResonantHalf-bridgeWaveformsaboveresonance(fswfr1)Gate-drivesignalsTransformercurrentsDead-timeDiodevoltagesDiodecurrentsMagnetizingcurrentistriangularOutputcurrentTankcircuitcurrentCCMoperationHBmid-pointVoltageResonantcapvoltageSinusoid@f=fr1~LinearportionI&PCDiv.-Off-lineSMPSAppl.LabLLCResonantHalf-bridgeSwitchingdetailsaboveresonance(fswfr1)Gate-drivesignalsTransformercurrentsDiodevoltagesDiodecurrentsDead-timeZVS!ZCS!OutputcurrentMagnetizingcurrentTankcircuitcurrent0I(D1)=0V(D1)0Slope~-(Vc-n·Vout)/LsHBmid-pointVoltageResonantcapvoltageI&PCDiv.-Off-lineSMPSAppl.LabLLCResonantHalf-bridgeOperatingSequenceaboveresonance(Phase1/6)Q1ONQ2OFFQ1OFFQ2ONQ1OFFQ2ON1/6VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1isOFF,Q2isON
D1isOFF,D2isON;V(D1)=-2·Vout
Lpisdynamicallyshorted:V(Lp)=-n·Vout.
CrresonateswithLs,fr1appears
OutputenergycomesfromCrandLs
PhaseendswhenQ2isswitchedoffCoutI&PCDiv.-Off-lineSMPSAppl.LabLLCResonantHalf-bridgeOperatingSequenceaboveresonance(Phase2/6)VinVoutQ1Q2LsLpCrn:1:1D1D2Coss1Coss2
Q1andQ2areOFF(dead-time)
D1andD2areOFF;V(D1)=V(D2)=0;transformer’ssecondaryisopen
I(Ls+Lp)chargesCOSS2anddischar