iwatt原边方案设计说明

1、NewTimesareComing-DigitallyOperatedPrimaryControlTechnologyforAC/DCSMPSAbstractThispaperdescribesawholenewcontroltechniqueandhadbeensuccessfullybeingemployedinoff-linetypeadapter/chargerapplications,whichresultsinsignificantreductiontoexternalcomponentsandvariousperformanceimprovements.IntroductionA

2、newdigitalcontrolmethodologyhasresultedingreatersimplicityanddesignflexibilityinlowpowerSMPStopologieswhichconventionalanalogmethodswouldfinddifficultifnotimpossibletoachieve.Bycombiningthisnewcontrolschemeintoanoff-linetypeofadapterorchargerapplication,itcouldgreatlyreducethenumberofexternalcompone

3、ntsaswellasenhancesupplyperformanceinmanyrespects.Thecontrollerhasbuilt-indigitalcontrolalgorithmstoquicklyandsmoothlytransitionbetweendifferentoperatingmodesforreducedswitchinglossesduringno-loadoperation.Thefull-loadefficiencyisenhancedbytheuseofso-called“emulatedprimarycurrentmodecontrol”toelimin

4、atetheneedforaprimarysensingresistor.Thefull-loadefficiencyisalsoenhancedincellularchargerapplicationsbytheeliminationofsecondary-sideconstantcurrentsensecircuitry.Itsuniquedigitalcontrolalgorithmallowsfastpulse-by-pulseanalysisoftheswitchingwaveformandprovidesaccuratevoltage&constant-currentregulat

5、ionfromtheprimary-sidewithouttheneedforanopto-coupler,secondaryfeedbackandreferencecircuitsrequiredbytraditionalanalogsolutions.Thisinnovativetechnologyisidealforbalancingnewregulatoryrequirementsforgreen-modeoperationwithmorepracticaldesignconsiderationssuchaslowestpossiblecost,smallestsizeandhighe

6、stefficiency.AdvantagesofDigitalPWMBestSolutionforLowestCost,HighestEffiAllowscyclebycyclesignalanalysisarEnablesbestinclassprimaryfeedbackAdaptsinrealtimeAutomaticallyincreasescontrollergaAutomaticallydecreasescontrollerg*IdentifiesfaultsandreactsappropriatedEnableslowcostsolutionsReducesBOMbyelimi

7、natingseconc DigitalPWMOperationThreemodesofoperationareusedtogeneratetheCV/CCcurveasshowninFigure1.Thedigitalcontrolalgorithmwasoptimizedtoprovidealloftherequiredoperatingmodeswithstabletransitionsbetweenmodes.ThecontrolleroperatesinPWMmodeduringhigheroutputpowerlevelsandswitchestoPFMmodeatlightloa

8、dtominimizepowerdissipation.Thedetailsofthemethodofoperationofeachofthemodesaregivenbelow.Allmodes一FilteringextractsdataatcriticaltimingpointsOn-chiiploopcompensation一SignalanalysiscyclebycycleConstantvoltageoperationVoutFigure-2,DigitalPWMControllerFunctionalBlockDiagramConstantVoltageOperationOutp

9、utvoltageregulationisaccomplishedbyaprimary-sidecontroltechniqueandeliminatestheneedfortheOpto-couplerfeedbackandsecondaryvoltagereferencefoundintraditionaldesigns.Thestateoftheoutputisderivedbythedigitalalgorithmsanalysisofeachandeveryprimaryauxiliarywindingwaveformin“real-time”andisthenfedintotheD

10、igitalErrorAmplifier(DEA)togenerateaPWMoutputforswitching.Thistechniqueyieldsaccuratevoltageregulationofbetterthan1.5%underallpossiblelineandloadconditions.ThesuperiorityoftheperformanceascomparedtotraditionalprimaryfeedbacksolutionsisfurtherdetailedinFigure3.LimitationsValleyvoltageTurn-onInstantfo

11、rPowerPulseMEASURED-怙 ConstantCurrentOperation:Theconstantcurrent(CC)featureusesthesamefeedbacktechniqueasinconstant-voltagemode,butmonitorsboththelinevoltageandtheoutputvoltagefeedbacksignal.ThesesignalsareprocessedandpassedontotheDEAandtON/tOFFcalculatorblocks.Theaccuracyofthiscontroltechniqueyiel

12、dssuperiorCCtolerance(typically2%)excludingthetoleranceofthetransformersprimaryinductance.Thiscombinationofcontroltechniquesallowsthedesignertoeliminateallsecondarycurrentandvoltagesensingcircuitry,resultinginasimple,lowcostsolutionwithimprovedefficiency.,lOUT=0mAVIN=100Vdc;ITon=1.8us;lPK=72mAJfOT=2

13、1KHzVIN=100Vdc;ITon=8us;lPK=325mAs3lOUT=750mProtectionFeatures(PrimaryUV,OV,SecondaryOVP,OCP&SSP):PrimaryOvervoltage&UndervoltageProtectionisprovidedbymonitoringtheVINvoltage(alsothebulk-capvoltage)toshutdowntheswitchingoperationwhenthethresholdisexceededformorethanaspecifiednumberofcycles.Secondary

14、OvervoltageProtectionisaccomplishedbymonitoringtheVSENSEpinthreshold.TheICwillshutdownafteraspecifiednumberofconsecutivefaultconditionswitchingpulses.TheICwillthenattempttorestart.i.esvi.3XVnom/ReadVMS7VNQMTfekHBnSsingleseq2505/sTTekktMWsingleSeq2.5Figure-5,OvervoltageShutdownWaveforms&DecisionTr264

15、Vac,NoLoadVmax_ovp=.2CVCcntiniieGenerateAnalogFeedbackVoltageRMTimeWaveformAnalyzerSecondaryOverCurrentProtection(appliedtoadapterwithsingleoutputdesign)limitstheoutputcurrenttowithinasmallrangeindependentofACinputlinevoltagevariations.PO_MAXgon2xLxTSxtxn)2OCPgon2xLxTxVMSOUTxnNote:(Vxt):ConstantPara

16、meter(二900V-us)gon L:CouplingInductanceBetweenPrimaryandSecondaryMT:OperationalPeriodTimeSn:Efficiency(ExceptPrimary-Loss)卜INonlinevoltagedependenceOverCurrentProtection(OCP)-sjj11-sr-BSE3.ss：=-=:=*-I0.5A/Div:SecondaryOutputShort-circuitProtectionisprovidedthroughanalysisoftheprimaryVSENSEwaveformob

17、tainedfromthebiaswindingandisbasedonaschemetoavoidcoresaturation.1.Ensureseachcycleisfullyresetbeforenextonpulsesisapplied.2.LimitsoperatingV-s(1O50V-s)toguaranteeVMAXwillnotbeexceededinagivenswitchingcycle.Thistechniqueensuresthatnobuildupoffluxenergyinthecorecanoccurfromcycletocycle.Toavoidoperati

18、onincontinuousconduction(CCM)mode,thecontrollerchecksforthefallingedgeoftheVSENSEinputoneverycycle.IfafallingedgeofVSenseisnotdetectedduringthenormal25psperiod,theswitchingperiodwillbeextendeduntilthefallingedgeVSENSEdoesoccur.Iftheswitchingperiodreaches75pswithoutVSENSEbeingdetected,thecontrollerwi

19、llimmediatelyshutoff.ckwhenloadgiI*i1ipuitProtectionA:400mV396mVgItothecontrolloopgainsbasedontheQQpgainIs】ncrea;edbyfourtimeswhenpuceslheLgainbaOtherFeatures:Ch4SOOmVFigur1.Dynamic只esponseisimpjoam5untofdeviationfrotiCseesasigntantload-cnanr,7；丫conditionsstabilize.chjjuoniv12.-0m%i匚4rxMi认2.Soft-StartThedeviceincorporatesaninternalsoft-startfunctionwithnoexternalcomponents.Thesoft-starttimeissetat3.5ms.OncetheVINpinvoltagehasreacheditsturn-onthreshold,thecontrollerstartsswitching,butlimitstheON-timetoapercentageofthemaximumON-timeasshowninFig