Conditioning a Switch-Mode Power Supply

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1、ApplicationReportSLOA044-March2000ConditioningaSwitch-ModePowerSupplyCurrentSignalUsingTIOPAmpsLarrySpazianiAAPPrecisionAnalogABSTRACTTheswitch-modepowersupplyprimarycurrentisoftensensedusingapowerresistor.Usinganopamptoamplifythecurrent-sensesignalcanre

2、ducecostandimprovenoiseperformanceandefficiency.Thisreportreviewstheadvantagesofusinganopampcircuitandanalyzesthedesigncriterianeededtochoosetheproperopamp.ContentsIntroduction.............................................................................2

3、CircuitDesign...........................................................................3Advantages..............................................................................4ChoosingtheOpAmp............................................................

4、........5Conclusion..............................................................................7ListofFigures1TypicalRsenseMethodandProposedOp-AmpMethodforSensingPrimarySideSwitchCurrent..................................................................

5、.22CurrentSenseWaveforms...............................................................6ListofTables1SuggestedTexasInstrumentsOpAmpsforCurrentSensing..................................71SLOA044IntroductionSwitch-modepowersuppliesalmostalwaysrequireknowled

6、geoftheswitchingcurrent,oftensensedontheprimarysideofthepowertransformer.CurrentSensingSolutionsforPowerSupplyDesigners1reviewsmanymethodsforsensingtheswitchedcurrent.Inlower-powerswitch-modepowersupplies,themethodmostoftenusedemployesasenseresistor.Thet

7、ypeofsenseresistorusedisoftenahighpower,lowinductanceresistorthatcanaddsignificantcostandpowerdissipationtothepowersupplydesign.ThiscircuitisshowninFigure1(a).PWMICREFRLEBISenseCLEB++VSVSenseRSense––GNDAPA(a)TypicalRsense-ConfiguredPWMICVREFR3AR2TIOPAMP+

8、ISense++–VSenseVSA––ARiGNDRfRSenseCfPA(b)AmplifyingaSmallSignalUsingaTIDifferentialAmplifierFigure1.TypicalRsenseMethodandProposedOp-AmpMethodforSensingPrimarySideSwitchCurrent1CurrentSensingSolutionsforPowerSupplyDesigner