CHAPTER 4 The Components of the System 7. Power Supply

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1、CHAPTER4TheComponentsoftheSystemUnitPowerSupplyApresentationofeSyst.orgPowerSupplyAllelectroniccircuitsneedapowersourcetowork.Forelectroniccircuitsmadeupoftransistorsand/orICs,thispowersourcemustbeaDCvoltageofaspecificvalue.AbatteryisacommonDCvoltagesourceforsometypesofelectronicequipmentespe

2、ciallyportableslikecellphonesandiPods.Mostnon-portableequipmentusespowersuppliesthatoperatefromtheACpowerlinebutproduceoneormoreDCoutputs.PowerSupplyCharacteristicsTheinputisthe120volt60HzACpowerline.Alternately,theinputmaybe240voltAC.ThepowersupplyconvertstheACintoDCandprovidesoneormoreDCout

3、putvoltages.Somemodernelectroniccircuitsneedtwoormoredifferentvoltages.Commonvoltagesare48,24,15,12,9,5,3.3,2.5,1.8,1.5,1.2and1volts.AgoodexampleofamodernpowersupplyistheoneinsideaPCthatfurnishes12,5,3.3and1.2volts.ComponentsofaPowerSupplyMaincircuitsinmostpowersupplies.PowerSupplyTheAClineis

4、firstpassedthroughalowpassfilteroftheformshowninfigure.ThiseliminatesnoiseontheAClinefrombotheringthepowersupplycircuitsandpreventsunwantedsignalsfromthepowersupplyfrombeingtransferredbackintotheAClinewheretheymightinterferewithotherequipment.TransformerAtransformeriscommonlyusedtosteptheinpu

5、tACvoltageleveldownorup.MostelectroniccircuitsoperatefromvoltageslowerthantheAClinevoltagesothetransformernormallystepsthevoltagedownbyitsturnsratiotoadesiredlowerlevel.Forexample,atransformerwithaturnsratioof10to1wouldconvertthe120volt60Hzinputsinewaveintoa12voltsinewave.RectifierTherectifie

6、rconvertstheACsinewaveintoapulsatingDCwave.Thereareseveralformsofrectifiersusedbutallaremadeupofdiodes.Rectifiertypesandoperationwillbecoveredlater.FilterTherectifierproducesaDCoutputbutitispulsatingratherthanaconstantsteadyvalueovertimelikethatfromabattery.Afilterisusedtoremovethepulsationsa

7、ndcreateaconstantoutput.Themostcommonfilterisalargecapacitor.RegulatorTheregulatorisacircuitthathelpsmaintainafixedorconstantoutputvoltage.ChangesintheloadortheAClinevoltagewillcausetheoutputvoltagetovary.Mostelectroniccircuitscannotwithstand