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《CHAPTER 4 The Components of the System 7. Power Supply》由會員上傳分享，免費在線閱讀，更多相關(guān)內(nèi)容在教育資源-天天文庫。
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
