designdocumentfinal.docx

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designdocumentfinal

SwitchingPowerSupply

Submittedto:

ProfessorJosephPicone

ECE4522:

SeniorDesignII

DepartmentofElectricalandComputerEngineering

MississippiStateUniversity

MississippiState,Mississippi39762

April28,2003

Submittedby:

TeamLeader:

F.Runnels

TeamMembers:

T.Carpenter,C.Jones,D.Lenoir,andJ.Stevens

FacultyAdvisor:

Dr.NoelSchulz

DepartmentofElectricalandComputerEngineering

MississippiStateUniversity

Email:

{flr1,tjc1,djl4,jws1}@ece.msstate.edu

TABLEOFCONTENTS

1.PROBLEM1

2.OBJECTIVES2

2.1.DeliveringConstantVoltagewithVaryingInputVoltage3

2.2.PerformanceInVaryingWeatherConditions3

2.3.EfficiencyAndCircuitProtection3

2.4.FCCandIECRegulations3

2.5.SizeandCost4

3.APPROACH4

3.1.SurgeProtection5

3.2.InputRectification5

3.3.Switching8

3.4.FlybackTransformer13

3.5.OutputRectification14

3.6.FeedbackNetwork25

3.7.ControllerCircuitry17

4.TESTSPECIFICATIONS18

4.1.Pspice19

4.2.Cadence20

4.3.Oscilloscope20

4.4.HighVoltageLab21

4.5.HeatChamber21

4.6.ESDSimulator21

4.7.EPOCH-10Multi-Amp22

4.8.SpectrumAnalyzer22

5.TESTCERTIFICATION22

5.1.Pspice22

5.2.Cadence25

5.3.Oscilloscope28

5.4.HighVoltageLab31

5.5.HeatChamber32

5.6.ESDSimulator33

5.7.EPOCH-10Multi-Amp34

5.8.SpecturmAnalyzer35

6.SUMMARYANDFUTUREWORK36

7.ACKNOWLEDGEMENTS37

8.REFERENCES38

9.APPENDIX40

EXECUTIVESUMMARY

Powersuppliesarebeingusedmoreandmoreinindustriesthroughouttheworld.Companieswantmoreefficientandbetter-designedpowersuppliestomeettheirspecifications.Traditionalswitchingpowersuppliescanonlyhandleinputvoltagesrangingfrom90to265VDC.Thecompaniesthatneedtouseawiderrangeofinputvoltageshavetospendmoremoneyforadditionalpowersuppliestocompensateforthiswiderrangeofvoltages.Thereneedstobeaswitchingpowersupplythatiscapableofhandlingawiderrangeofinputvoltagesandmoreefficientthanthecommercialpowersuppliesavailable.

MississippiPowerCompany（MPC）hascarefullydesignedaswitchingpowersupplyofthiscaliber;however,theyhavesomeproblemswiththeirdesign.ThemainproblemswiththeirdesignwerethePCBlayout,theMOSFEToverheating,thevoltagespikesontheoutput,andextremelyhighnoiseemissionlevels.Thefirstapproachconsideredtocorrecttheseproblemswastodesignafilterthatwouldfilteroutanyunwantedharmonicsinthecircuit,butthisapproachprovedtobeineffective.Softswitchingwasalsoconsidered,butitisdifficulttoimplementbecausethecircuithastobetunedpreciselybeforeimplementationcanbedone.DesigningasnubbercircuitandanewPCBlayoutprovedtobethebestapproachtomeetthedesignconstraints.Thesnubbercircuitconsistsofaresistor,capacitor,andadiode.TheringingfrequencywasmeasuredfromtheMOSFET.Thisvaluewasusedtocalculatethevalueofthecapacitor（720pF）.Thevalueof1kΩwaschosenfortheresistor,andthediodeisaMUR1100E.ThiscausedtheMOSFETtostopoverheatingaswellasproducedlessvoltagespikesontheoutput.ThenewPCBlayouthasshorter,fattertracesthathelpedtoreducethenoiseemissionlevel.

ThepowersupplythatMPCdesignedhadvoltagespikesthatrangedfrom6to8V.Theredesignedpowersupplyonlyhasvoltagespikesthatrangefrom0.7to1.2V.MPC’sdesignonlyhadaconstant13.5VDContheoutput.Afterdesigningthesnubbercircuitandthenewlayout,theredesignedpowersupplymetthedesignconstraintof13.5VDContheoutput.Inhigherpowerlevelpowersupplies,thesnubbercircuitusuallycausesthepowersupplytobelessefficient;however,theefficiencyofthisdesignstayedthesame.ThepowersupplythatMPCdesignedwas85%efficient,andtheredesignedpowersupplywas84.9%efficient.Oneoftheotherconstraintswastohave40Wattsofoutputpower.Thepowersupplyproduces41Wattsofoutputpoweratfullload.Atfullload,theresistanceisabout4.44Ωandtheoutputcurrentis3.04A.

Theredesignedpowersupply,willallowMississippiPowertobeabletodoawaywiththeirconventionalpowersupplies.SinceMississippiPowercurrentlyhastousethreepowersupplies,thenewlydesignedpowersupplywillbemorecostefficient.Similarswitchingpowersuppliesexist,butthererangeofinputvoltagesdoesnotmeetMississippiPower’srequirements.Thereareonlyafewswitchingpowersuppliesthatcanhandleaninputvoltageof310VAC.Thosepowersuppliesareratedforasmallerrangeofinputvoltages,anddonothavesomethecapabilitiesofthepowersupplythatwasredesigned.

1.PROBLEM

ThetraditionalACtolowvoltageDCpowersupplyusedintheelectricutilityindustrytypicallyhasafixedinputvoltageratedat120VACor130VDC.Pastapplicationstendedtobetelemetryandotherelectronicequipmentlocatedwithinsubstationenvironmentswhere120VACstationserviceor130VDCstationbatteryservicewasavailable.Atalmostallresidential/commercial/smallindustrialcustomerservicepoints,theonlyactivecomponenthasbeentheenergymeter.However,overthepast10yearstheneedfortelemetrydatafromindustrialandcommercialcustomerservicepointshasincreased.WiththisincreaseddemandfordatahascamethedemandforlowvoltageDCtopowercommunicationsaswellasothermicroprocessorbasedmonitoringequipment[1].

Withintheelectricutilityenvironment,voltageatthemeterpoint–dependinguponservicetype–mayrangefrom66VACto310VACphasetoground,whichisawiderangeforthelinearpowersuppliesusedinthepast.Vendorshaveattemptedtocompensatebyaddingmultipleinputvoltage“taps”.Thelinemenhadtothenselectwhatinputvoltagewouldbeusedbythepowersupplyeitherbywiringtheinputvoltagetoaparticularterminalappropriatefortheappliedvoltageortheselectionoftheinputvoltageviaa“slideswitch”.Inpractice,MississippiPowerCompanyMeteringServiceshasexperiencedanapproximate5%failurebytrainedemployeeswhofailedtoselectthecorrecttapwheninstallingthesetypepowersupplies.Assumingacommerciallypowersupplycostof$100,0.5hourstoreplacethefailedunit,anda$65perhourlaborrate,thecostofeachfailureis$132.50.Withawiderangeswitchingpowersupply,theselossescouldbeeliminated[2].

Atpresentswitchingpowersuppliesareavailablewithinputvoltagesrangingfrom90to265VAC[3].Sincetheutilitycompaniesalsoroutinelyuse277VACservices,thisrangeisnotadequate.Therefore,theutilitycompaniesareforcedthestockseveraldifferentpowersuppliesorinstrumenttransformersthatcanbeusedtomatchtheservicevoltagetothatofthepowersupply.In1995BryanSeal,aseniorengineeratMississippiPower,ledateamofengineerstobuildpowersupplythatwouldaddresstheproblemstheyhadwiththeconventionalpowersupplies.Theteamdesignedaswitchingpowersupplyandtheninstalleditinaboutahundredvariousunits.However,thepowersupplieshavesomeproblems.Themainproblemisthatthepowersuppliesareelectronicallytoonoisy.Theoutputsignalhadseveraltransientsonit.Thesetransientswouldspikeupto3voltshigherthantheintendedoutputvoltageof13.5volts.MississippiPoweraskedforanalysisoftheircurrentpowersupplyandforamoreefficientpowersupplydesign[3].

ThepowersupplythatMississippiPowerneedsshouldbeabletoacceptaninputvoltageanywherefrom90to310VAC.TheyneedacontinuousDCoutputvoltageof13.5volts,withatoleranceof+/-5%.Thepowersupplyalsoneedstosupply40wattsofpower.MississippiPoweralsorequiresthatnoiselevelbebelow200mVpeak-to-peak.Thepowersupplyshouldbeconstructedforlessthan$100,sincetobecompetitivewithconventionalpowersupplies[2].

Sincetheinputvoltagewillsowide,theutilitycompanieswillnothavetostockotherpowersupplytypesandinstrumenttransformers.Thereforetheequipmentinventoryfortheutilitycompanieswillbereduced.Alsotherewillbethebenefitofincreasinginventory“turnover”andloweringhandlingcost.Anadditionalbenefitisthereductionintrainingtimenecessaryforsingletypepowersupplyinstallationovervariousotherlinearandswitchingpowersupplydesigns[2].

2.OBJECTIVES

ThemainproblemwiththeoriginalpowersupplythatMississippiPowerCompany（MPC）designedwasthatithadseveralvoltagespikesontheoutputsignalrangingfrom6.5to8.5VAC（pk-pk）.Thesespikescausedthedevicethatwasbeingpoweredtoreset.AnotherproblemwithMPC’sdesignwasthattheelectromagneticinterference（EMI）createdbythepowersupplywasinterferingwiththecellulartransmissionsoftheirequipment.Theobjectivesoftheredesignedpowersupplyconsistoffivetechnicalrequirementsandfiverealworldconstraints.Themajorconcernsofthenewdesignareoutputnoisereduction,EMIreduction,andoperatingefficiencyimprovement.Thenewdesignwillachieve13.5VDC+/-1.5%outputwithenoughpowertosupplyasmall40-wattradiotransmitter.TheEMIofthenewpowersupplywillbereducedtoconformtoFCCclass15emissions.

1.Performance:

Thedesignwillachieve13.5VDCoutputwitharipplevoltageoflessthan0.2VACrms.

2.Performance:

Thedesignwillbeabletooperatebetweenthetemperaturerangesof-20°to60°C（-4°to120°F）.

3.Performance:

Thepowersupplywillwithstandstrayvoltagesfromlig