毕设翻译英文.docx

毕设翻译英文.docx

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毕设翻译英文

轨道交通学院

毕业设计（论文）外文翻译

题目：

列车车载的直流恒流源的设计

专业电子信息工程

班级10115111

学号1011511137

姓名赵士伟

指导教师陈文

2014年3月3日

本文摘自：

IEEETRANSACTIONSONINDUSTRYANDGENERALAPPLICATIONSVOL.IGA-2,NO.5SEPT/OCT1966

HighlyRegulatedDCPowerSupplies

Abstract-Thedesignandapplicationofhighlyregulateddcpowersuppliespresentmanysubtle,diverse,andinterestingproblems.Thispaperdiscussessomeoftheseproblems（especiallyinconnectionwithmediumpowerunits）butemphasishasbeenplacedmoreoncircuiteconomicsratherthanonultimateperformance.Sophisticatedmethodsandproblemsencounteredinconnectionwithprecisionreferencesuppliesarethereforeexcluded.Theproblemsdiscussedincludethesubjectsoftemperaturecoefficient,short-termdrift,thermaldrift,transientresponsedegenerationcausedbyremotesensing,andswitchingpreregualtor-typeunitsandsomeoftheirperformancecharacteristics.

INTRODUCTION

ANYSURVEYofthecommercialdepowersupplyfieldwilluncoverthefactthat0.01percentregulatedpowersuppliesarestandardtypesandcanbeobtainedatrelativelylowcosts.Whilemostusersofthesepowersuppliesdonotrequiresuchhighregulation,theynever-thelessgetthisatlittleextracostforthesimplereasonthatitcoststhemanufacturerverylittletogivehim0.01percentinsteadof0.1percent.Theperformanceofapowersupply,however,includesotherfactorsbesideslineandloadregulation.Thispaperwilldiscussafewofthese-namely,temperaturecoefficient,short-termdrift,thermaldrift,andtransientresponse.Presentmediumpowerdcsuppliescommonlyemploypreregulationasameansofimprovingpower/volumeratiosandcosts,butsomecharacteristicsofthepowersupplysufferbythisapproach.Someoftheshort-comingsaswellasadvantagesofthistechnologywillbeexamined.

TEMPERATURECOEFFICIENT

Adecadeago,mostcommercialpowersuppliesweremadetoregulationspecificationsof0.25to1percent.Thereferenceelementsweregasdiodeshavingtemperaturecoefficientsoftheorderof0.01percent[1].Consequently,theTC（temperaturecoefficient）ofthesupplywassmallcomparedtotheregulationspecificationsandoftenignored.Today,thereferenceelementoftencarriesaTCspecificationgreaterthantheregulationspecification.Whilethelattermaybeimprovedconsiderablyatlittlecostincrease,thisisnotnecessarilytrueofTC.Therefore,theuseofverylowTCzenerdiodes,matcheddifferentialamplifierstages,andlowTCwirewoundresistorsmustbeanalyzedcarefully,ifcostsaretobekeptlow.AtypicalfirstamplifierstageisshowninFig.1.CRIisthereferencezenerdiodeandR,istheoutputadjustmentpotentiometer.

Fig.1.Inputstageofpowersupply.

Fig.2.Equivalentcircuitofzenerreference.

Letitbeassumedthate3,theoutputofthestage,feedsadditionaldifferentialamplifiers,andundersteady-stateconditionse3=0.Avariationofanyoftheparameterscouldcausetheoutputtodrift;whilethisisalsotrueoftheotherstages,theeffectsarereducedbythegainofallpreviousstages.Consequently,theeffectsofotherstageswillbeneglected.ThefollowingdisculssioncoverstheeffectsofallelementshavingprimaryandsecondaryinfluencesontheoverallTC.

EffectofR3

TheequivalentcircuitofCRI-R3branchisshowninFig.2.Thezenerha'sbeenreplacedwithitsequivalentvoltagesourceE/'andinternalimpedanceR,.Forhighgainregulators,theinputofthedifferentialamplifierwillhavenegligiblechangewithvariationsofR3sothat

beforeandafteravariationofR3ismade.

IfitisfurtherassumedthatIB<

（1）

Also,

EliminatingI,from（2b）,

and

Now,assumingthat

then,

Equation（2b）canalsobewritten

TheZenerDiode

ThezenerdiodeitselfhasatemperaturecoefficientandusuallyisthecomponentthatdominatestheoverallTCoftheunit.ForthecircuitofFig.1,theTCofthecircuitdescribes,inessence,theportionoftheregulatorTCcontributedbythezener.IfthebridgecircuitshowninFig.1wereusedinconjunctionwithadroppingresistorsothatonlyaportionoftheoutputvoltageappearedacrossthebridgecircuitshown,theTCoftheunitandthezenerwouldbedifferent.Sincethecharacteristicofzenersissowellknownandsowelldescribedintheliterature,adiscussionwillnotbegivenhere[2].

VariationofBase-EmitterVoltages

NotonlydothevaluesofV,,ofthedifferentialam-plifierfailtomatch,buttheirdifferentialswithtemperaturealsofailtomatch.Thisshouldnot,however,suggestthatmatchedpairsarerequired.ThetruereferencevoltageofFig.1isnotthevalueE,,butE,+（Vie,-Vbe2）-Since,formostpracticalapplicatioins

theTCofthereferencewillbetheTCofthezenerplus

Consideringthatitisdifficulttoobtainmatchedpairsthathavedifferentialsaspooras50V/°C,itbecomesratherapparentthat,inmostcases,amatchedpairboughtspecificallyforTCmaybeoverdesigning.

Example2:

Astandardavailablelow-costmatchedpairlaims30AV/°C.Inconjunctionwitha1N752,theontributiontotheoverallTCwouldbe

Tests,performedbytheauthoronthirteenstandardgermaniumsignaltransistorsinthevicinityofroomtemperatureandatacollectorcurrentlevelof3mA,indicatedthatitisreasonabletoexpectthat90to95percentoftheunitswouldhaveabase-emittervoltagevariationof-2.1to-2.4mV/°C.Spreadsofthismagnitudehavealsobeenverifiedbyothers（e.g.,Steiger[3]）.Theworstmatchingoftransistorsledtolessthan400,V/°Cdifferential.Inconjunctionwitha1N752,eventhiswouldgiveaTCofbetterthan0.007%/0C.

VariationofBaseCurrents

Thebasecurrentofthetransistorsisgivenby

Avariationofthiscurrentcausesavariationinsignalvoltageattheinputtothedifferentialamplifierduetofinitesourceimpedances.Matchingsourceimpedancesisnotparticularlydesirable,sinceitreducesthegainofthesystemandrequiresthattransistorsmatchedforI,oandAbeused.Hunter[4]statesthattheTCofaisintherangeof+0.2%/0Cto-0.2%7/'Candthat1,,maybeapproximatedby

whereAoisthevalueatTo.

βisalsotemperaturedependentandSteiger[3]experimentallydeterminedthevariationtobefromabout0.5%/°Cto0.9%/0C.

And，

Fig.3.InputcircuitofQ2.

ThecurrentAIBflowsthroughthesourceimpedanceperFig.3.Thedropsintheresistancestring,however,aresubjecttotheconstraintthatEB（andAEB）aredeterminedbythezenervoltageandthebase-emitterdropsofQ1andQ2.Consequently,ifingoingfromtemperatureT1toT2achangeAEBoccurs,

Thechangeinoutputvoltageis

And

Example3:

ForQ2（at25°C）

（seeExample1）∴

VariationofR,

TheeffectsofavariationoftheTCbetweenRIAandRIBissufficientlyself-evidentsothatadiscussionofthecontributionisnotincluded.

SHORT-TERMDRIFT

Theshort-termdriftofasupplyisdefinedbytheNationalElectricalManufacturersAssociation（NEMA）as"achangeinoutputoveraperiodoftime,whichchangeisunrelatedtoinput,environment,orload[5]."Muchofthematerialdescribedinthesectionontemperaturecoefficientisapplicablehereaswell.Ithasbeendeterminedexperimentally,however,thatthermalairdraftsinandnearthevicinityofthepowersupplycontributesenormouslytotheshort-termcharacteristics.Thecoolingeffectsofmovingairarequitewellknown,butitisnotoftenrecognizedthatevenextremelyslowairmovementsoversuchdevicesaszenersandtransistorscausethejunctiontemperatureofthesedevicestochangerapidly.IftheTCofthesupplyislargecomparedtotheregulation,thenlargevariationsintheoutputwillbeobserved.UnitshavinglowTC'sachievedbycompensation-thatis,bycancelingouttheeffectsofsomeomponentsbyequalandoppositeeffectsofothersmaystillbeplaguedbythesedraftsduetothedifferenceinthermaltimeconstantsoftheelements.

Oftentimes,amatchedtransistordifferentialamplifierinacommonenvelopeisusedforthefirstamplifierjusttoequalizeandeliminatethedifferenceincoolingeffectsbetweenthejunctions.Approximationstothismethodincludecementingorholdingthetransistorstogether,imbeddingthetransistorsinacommonmetalblock,etc.Excellentresultswereachievedbytheauthorbyplacingtheinputstageandzenerreferenceinaseparateenclosure.ThisconstructionisshowninFig.4.TheimprovementindriftobtainedbymeansoftheadditionofthemetalcoverisdemonstrateddramaticallyinFig.5.

Fig.5.Short-termdriftofapowersupplysimilartotheoneshowninFig.4withandwithoutprotectivecovers.Theunitwasoperatedwithoutthecoveruntiltimetl,whenthecoverwasattached.Theinitialvoltagechangefollowingt,isduetoatemperatureriseinsidethebox.

Fig.5.Short-termdriftofapowersupplysimilartotheoneshownnFig.4withandwithoutprotectivecovers.Theunitwasoperatedwithoutthecoveruntiltimetl,whenthecoverwasattached.Theinitialvoltagechangefollowingt,isduetoatemperatureriseinsidethebox.

Ifpotentiometersareusedinthesupplyforoutputadjustment（e.g.,RI）,careshouldbeusedinchoosingthevalueanddesign.Variationsofthecontactresistancecancausedrift.Itisnotalwaysnecessary,however,toresorttotheexpenseofhigh-resolutionmultiturnprecisionunitstoobtainlowdrift.Areductioninrangeofadjustment,useoflow-resistancealloysandlow-resolutionunitswhichpermitthecontactarmtorestfirmlybetweenturns,maybejustassatisfactory.Ofcourse,otherconsiderationsshouldincludetheabilityofboththearmsandthewiretoresistcorrosion.Sil