CHAPTER 4 The Components of the System 7.ppt

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1、CHAPTER4TheComponentsoftheSystemUnitPowerSupplyPowerSupplyAllelectroniccircuitsneedapowersourcetowork.Forelectroniccircuitsmadeupoftransistorsand/orICs,thispowersourcemustbeaDCvoltageofaspecificvalue.AbatteryisacommonDCvoltagesourceforsometypesofelectronicequipmentespeciall

2、yportableslikecellphonesandiPods.Mostnon-portableequipmentusespowersuppliesthatoperatefromtheACpowerlinebutproduceoneormoreDCoutputs.ApresentationofeSyst.orgPowerSupplyCharacteristicsTheinputisthe120volt60HzACpowerline.Alternately,theinputmaybe240voltAC.Thepowersupplyconver

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

4、plyMaincircuitsinmostpowersupplies.PowerSupplyTheAClineisfirstpassedthroughalowpassfilteroftheformshowninfigure.ThiseliminatesnoiseontheAClinefrombotheringthepowersupplycircuitsandpreventsunwantedsignalsfromthepowersupplyfrombeingtransferredbackintotheAClinewheretheymightin

5、terferewithotherequipment.TransformerAtransformeriscommonlyusedtosteptheinputACvoltageleveldownorup.MostelectroniccircuitsoperatefromvoltageslowerthantheAClinevoltagesothetransformernormallystepsthevoltagedownbyitsturnsratiotoadesiredlowerlevel.Forexample,atransformerwithat

6、urnsratioof10to1wouldconvertthe120volt60Hzinputsinewaveintoa12voltsinewave.RectifierTherectifierconvertstheACsinewaveintoapulsatingDCwave.Thereareseveralformsofrectifiersusedbutallaremadeupofdiodes.Rectifiertypesandoperationwillbecoveredlater.FilterTherectifierproducesaDCou

7、tputbutitispulsatingratherthanaconstantsteadyvalueovertimelikethatfromabattery.Afilterisusedtoremovethepulsationsandcreateaconstantoutput.Themostcommonfilterisalargecapacitor.RegulatorTheregulatorisacircuitthathelpsmaintainafixedorconstantoutputvoltage.Changesintheloadorthe

8、AClinevoltagewillcausetheoutputvoltagetovary.Mostelectroniccircuitscannotwithstand