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页数:12页
时间:2018-07-07
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1、CURRENTSOURCEAcurrentsourceisanelectricalorelectronicdevicethatdeliversorabsorbselectriccurrent.Acurrentsourceisthedualofavoltagesource.Thetermconstant-currentsinkissometimesusedforsourcesfedfromanegativevoltagesupply.Figure1showsaschematicforanidealcurrentsourcedrivingaresistorload.Figu
2、re1IdealcurrentsourcesIncircuittheory,anidealcurrentsourceisacircuitelementwherethecurrentthroughitisindependentofthevoltageacrossit.Itisamathematicalmodel,whichrealdevicescanonlyapproachinperformance.Ifthecurrentthroughanidealcurrentsourcecanbespecifiedindependentlyofanyothervariableina
3、circuit,itiscalledanindependentcurrentsource.Conversely,ifthecurrentthroughanidealcurrentsourceisdeterminedbysomeothervoltageorcurrentinacircuit,itiscalledadependentorcontrolledcurrentsource.SymbolsforthesesourcesareshowninFigure2.Figure2Anindependentcurrentsourcewithzerocurrentisidentic
4、altoanidealopencircuit.Forthisreason,theinternalresistanceofanidealcurrentsourceisinfinite.Thevoltageacrossanidealcurrentsourceiscompletelydeterminedbythecircuititisconnectedto.Whenconnectedtoashortcircuit,thereiszerovoltageandthuszeropowerdelivered.Whenconnectedtoaloadresistance,thevolt
5、ageacrossthesourceapproachesinfinityastheloadresistanceapproachesinfinity(anopencircuit).Thus,anidealcurrentsourcecouldsupplyunlimitedpowerforeverandsowouldrepresentanunlimitedsourceofenergy.Connectinganidealopencircuittoanidealnon-zerocurrentsourceisnotvalidincircuitanalysisasthecircuit
6、equationwouldbeparadoxical,e.g.,5=0.Norealcurrentsourceisideal(nounlimitedenergysourcesexist)andallhaveafiniteinternalresistance(nonecansupplyunlimitedvoltage).However,theinternalresistanceofaphysicalcurrentsourceiseffectivelymodeledincircuitanalysisbycombininganon-zeroresistanceinparall
7、elwithanidealcurrentsource(theNortonequivalentcircuit).ResistorcurrentsourceThesimplestcurrentsourceconsistsofavoltagesourceinserieswitharesistor.Thecurrentavailablefromsuchasourceisgivenbytheratioofthevoltageacrossthevoltagesourcetotheresistanceoftheresistor.Foranearlyid
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