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-I-4UC3842PWMMOSFET0.99Multisim20V4.2A20V4.5A90W-II-AbstractSwitchingpowersupplywillnotonlybeabletosaveresourcestoprotecttheenvironment,butalsobringhugeeconomicbenefitsforpeople,whichmakesthedevelopmentoftheswitchingpowersupplyhasbecomeaninevitabletrend.Thenumberofflybackswitchingpowersupplyusingfewercomponentstothecircuitissimple,lowcost,highreliability,alongwiththedemandforminiaturizationofconsumerelectronicsproductsoftheincreasingdemandforsmallswitchingpowersupplyalsowillincreased,sotheflybacktypeswitchingpowersupplyhasbeenwidelyused.Flybackswitchingpowersupplyismainlycomposedoffourparts,namelythemaincircuit,controlcircuit,detectionandprotectioncircuitsandothercircuits.Themaincircuitisaflybackcircuit,PWMcontrolcircuitusingUC3842thisintegratedcontrolchips.Indeterminingtheoveralltopologyflybackswitchingpowersupplyaftercontacttechnicalindicatorsneedtoreach,youcangetthemaincomponentsbuscapacitor,transformer,MOSFETrelatedparametersbycalculation.Forsomeparametersofthedevicecanbeassistedinthesimulationsoftwaredebugobtained.Powerfactorcorrectionusingactivepowerfactorcorrection,canreachmorethan0.99.InMultisimsoftwaretodesignacircuittopologyfordebuggingandsimulation,theoverallfigurecanbeseeninthesimulationoutputvoltageofabout20V,outputvoltagestabilityafterwaitingvoltagewaveformisastraightline,theoutputloadcurrentis4.2Aabouttheneedtomeetthetechnicalspecificationsoftheoutputvoltageis20V,outputcurrentis4.5A,andtheactualresultsoftheindicatorsneededtoachieveacertainerror,theerroriswithintheallowablerange,sothe90Wflybackswitchingpowersupplydesignsimulationcompleted.KeyWords:Switchingpowersupply,Flyback,Simulation,Debugging-III-..................................................................IAbstract.................................................................II................................................................III...............................................................41.1................................................41.2..........................................41.3..............................................41.4................................................4.............................................52.1................................................52.2..................................52.3.3..................................................101MOSFET............................................102..............................................113RCD...............................................114...................................................115...............................................122.3.4.........................................................................13.........................................................143.1.1SaberSketch...................................143.1.2................................................173.1.3..................................................193.1.4............................................203.1.5..................................................213.1.6....................................................233.1.7................................................243.1.8mosfed3844................................253.1.9....................................253.1.10RC..........................................27..........................................................................28Severalnotesofswitchingpowersupplydesign....................29..............................................33...................................................................36.................................................................37-4-1.11.20.950.991.375W100W1.4PWMPulse-5-WidthModulation12PWM342.12.12.12.22.2-6-VDui+N1W1SN2W2++-+-2.2SVDN1SN1N2VDSToniuN1N11iN1N2VDi111ddutiLeS(2.1)2.11e1N1L1N2.1)0(11i1iLuiSS1i0SoffTo222ddutiLeS)0(22o2iLuiS-7-2.32.3.1PC817LED3-4--PC817PC8173-3-13-3-1PC817-8-If(mA)3-3-2PC817VfI2.3.2TL431TL431TL431PC817UC3844TL4312.536V2.5~36V0.1100mA0.22TL4313-3-3-9-3-3-3TL431AKrefUoUrefoURRU)/1(211R2R2.5~36V1mATL431TL4313-3-4-10-3-3-4TL4312.3.3ICMOSFETMOSFET3-3-53-3-52.3.41MOSFETMOSFET(min)max(max)27/300.7378543.785DSoDpsinVVVNNVVVVVVDSS800V1000V-11-Ipk=2.77AIRG4PH30K.1200V/10AMOSFEDR51020152R141%1kIs=2.5V/1k=2.50mA13302.52.511RVVmAk11R=470TL431kaI=20mAPC817fI=3mA11RVARIVfR41.1470003.088PC817fV1.2V12R12111.411.22.61RRfVVVVVV12R1220317RkafIIImAmAmA12R121212/2.61/17154RRRVIVmA3RCDVclamp:VinVDLpLIkVORVBR(DSS)VinmaxVclamp=0.9VBR(DSS)-Vinmax=0.91200-378=702VLIk=1.223%=36.6uHVOR=Vout+VD/(NS/NP)=(300.7)5/27=165.78VIDS-PEAK=2.77AR2=CR=222()2(702165.7)702114.67.652.7752clampORclampLKDSPEAKSVVVKLIfuHkhz670227957025%114.861000521000clampCclampCSVCCpFVRf4outinhpsrVVNNV-12-DC30V303030rVsVpinhoVVNNVV5/27378+30=300V)(minout)1(CpkpkoutfVDIoutIAminD0.1)(pkpkVmVDC+30V152A10.1C34652100FkHzmV346DC-30V171A10.1C17352100FkHzmV180FLC0.3HC16C18100uF144V378V38441mA20V=144201.24100mAk1R7C7CUC3844+16VUC38446UC38441R716VNs18VNs18VUC3844R1R1=100KC7=100uf5C1C20.01~0.47F0.1F/400VLI/A1361012158~122~40.4~0.80.2~0.30.1~0.150.07~0.08-13-/mHL/mH82.50.780.2250.110.073L