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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