iwatt 原边方案设计说明.pdf

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1、NewTimesareComing–DigitallyOperatedPrimaryControlTechnologyforAC/DCSMPSAbstractThispaperdescribesawholenewcontroltechniqueandhadbeensuccessfullybeingemployedinoff-linetypeadapter/chargerapplications,whichresultsinsignificantreductiontoexternalcomponentsandvariousperformanceimprov

2、ements.IntroductionAnewdigitalcontrolmethodologyhasresultedingreatersimplicityanddesignflexibilityinlowpowerSMPStopologieswhichconventionalanalogmethodswouldfinddifficultifnotimpossibletoachieve.Bycombiningthisnewcontrolschemeintoanoff-linetypeofadapterorchargerapplication,itcoul

3、dgreatlyreducethenumberofexternalcomponentsaswellasenhancesupplyperformanceinmanyrespects.Thecontrollerhasbuilt-indigitalcontrolalgorithmstoquicklyandsmoothlytransitionbetweendifferentoperatingmodesforreducedswitchinglossesduringno-loadoperation.Thefull-loadefficiencyisenhancedby

4、theuseofso-called“emulatedprimarycurrentmodecontrol”toeliminatetheneedforaprimarysensingresistor.Thefull-loadefficiencyisalsoenhancedincellularchargerapplicationsbytheeliminationofsecondary-sideconstantcurrentsensecircuitry.Itsuniquedigitalcontrolalgorithmallowsfastpulse-by-pulse

5、analysisoftheswitchingwaveformandprovidesaccuratevoltage&constant-currentregulationfromtheprimary-sidewithouttheneedforanopto-coupler,secondaryfeedbackandreferencecircuitsrequiredbytraditionalanalogsolutions.Thisinnovativetechnologyisidealforbalancingnewregulatoryrequirementsforg

6、reen-modeoperationwithmorepracticaldesignconsiderationssuchaslowestpossiblecost,smallestsizeandhighestefficiency.1DigitalPWMOperationThreemodesofoperationareusedtogeneratetheCV/CCcurveasshowninFigure1.Thedigitalcontrolalgorithmwasoptimizedtoprovidealloftherequiredoperatingmodeswi

7、thstabletransitionsbetweenmodes.ThecontrolleroperatesinPWMmodeduringhigheroutputpowerlevelsandswitchestoPFMmodeatlightloadtominimizepowerdissipation.Thedetailsofthemethodofoperationofeachofthemodesaregivenbelow.Figure-1,ModesofOperationFigure-2,DigitalPWMControllerFunctionalBlock

8、Diagram21.ConstantVoltageOperationOutput