Power-Supplies.ppt

1,Unit5PowerSupplies,电源,2,Pre-reading,Readthefollowingpassage,payingattentiontothequestion.1)Whatisthefunctionofanelectronicpowersupply?2)Whatdoesanelectronicpowersupplyinclude?,3,5.1.1InformationonPowerSupplies,Therearemanytypesofelectricalandelectronicpowersupplies,providingvariousalternatingcurrent(AC)anddirectcurrent(DC)voltagesforequipmentoperation.,电气的,电子的,设备,电压,4,5,DCvoltagesareneededformostelectroniccircuits,andgenerallyanelectronicpowersupplyisconsideredasadevicethatconvertsACintoDC.,电路,beconsideredas1.被看作2.被认为是,装置、设备,转换,6,TheACvoltagefromthepowerlinescanberectifieddirectlyorpassedthroughanisolationtransformer(aturnsratioof1:1).,Rectifyrektifai改正，校正;电整流,隔离变压器,7,8,DependingonthevalueofDCvoltageneeded,thetransformermaybeofeitherastep-uporstep-downtype.,根据,升压,降压,9,Afterthetransformer,theACisrectifiedintopulsatingDCbydiodesintheformofahalf-waverectifier,afull-waverectifier,orabridge(full-wave)rectifier.,plseitvi.搏动;悸动;有规律地跳动,二极管,10,half-waverectifier,full-waverectifier,bridge(full-wave)rectifier,11,ThepulsatingDCisthenfilteredorsmoothedoutbycapacitors,inductors,andresistorssoastoproduceaconstantDCoutput.,滤波,smoothout弄平;缓和，调解,12,5.1.2Bridge(Full-wave)Rectifier,Thebridgerectifierproducesafull-waveDCoutputwiththeuseoffourdiodes(Fig5.1).,13,Whenthepositivehalf-cycleappears,theanodeofdiode1ispositiveanditconducts,andthecathodeofdiode2isnegativeanditconducts.,anode，阳极，正极cathode，阴极，负极,14,CurrentflowsfromtheACsourcethroughdiode1,throughRL,throughdiode2,andbacktothesource.Diodes3and4arereversedbiasedandnocurrentflowsthroughthem.Theyappearasopencircuits.,反向偏置,15,Onthenegativehalf-cycletheanodeofdiode4ispositiveanditconducts,andthecathodeofdiode3isnegativeanditconducts.,16,CurrentflowsfromtheACsourcethroughdiode4,throughRL,throughdiode3,andbacktothesource.Diodes1and2arereverse.,17,VoltageoutputUoisthepeakvoltagelesstwotimestheUFacrossthediodes(twodiodesareconductingatatime):,最高的;最大值的,18,输出电压平均值：UL=0.9u2,输出电流平均值:IL=UL/RL=0.9u2/RL,流过二极管的平均电流：ID=IL/2,主要参数：,19,Full-wavebridgerectifiermodulescontainingfourdiodesinasingleunitarecommerciallyavailable.,商业上的,模块;组件,20,5.1.3Filter,CapacitorsareusedinpowersuppliestosmoothoutpulsatingDCandtoproducesteadyDCvoltage.Asimplecapacitorfilterisconnectedacrosstheoutput.,21,电容滤波电路,工作原理,滤波电容,无滤波电容时的波形,加入滤波电容时的波形,22,u2上升，u2大于电容上的电压uc，u2对电容充电，uo=ucu2,u2下降，u2小于电容上的电压。二极管承受反向电压而截止。电容C通过RL放电，uc按指数规律下降，时间常数=RLC,工作原理,23,Whenthispeakvoltagebeginstodecrease,thestoredelectronsinthenegativesideofthecapacitorwilldischargeandflowthroughtheloadinanattempttokeepthevoltageconstantacrossthecapacitor.,24,AnotherpulsatingDCcomessoonafterthedischargeandchargesthecapacitortopeakvoltageagain.Theslightcharginganddischargingofthecapacitorproducesaripplevoltage(ACcomponent)thatissuperimposedonthetopofthesteadyDC(Fig5.2).,25,5.1.4ZenerDiode,Azenerdiodeisaspeciallydopeddiodethatoperatesthesameasaregulardiodeintheforward-biasedcondition(itallowslargecurrenttoflow).,26,However,inthereverse-biasedcondition(Fig5.3),itwillnotconductuntilitreachesthezenervoltage(Uz)atwhichitisdesigned.,27,Atthispointthezenerdiodeconductscurrentinthereversedirection,whilemaintainingthezenervoltageacrossitsterminals(Fig5.4).,28,Theamountofcurrentthatflowsthroughitisdeterminedbytwofactors,aseries(current-limiting)resistor(RS)andtheparallelloadresistance(RL).,29,Fig5.3ZenerCircuit,30,Fig5.4Theoutputcharacteristicofazener,31,ResistorRSisfoundbytheformulawhere.Withnoload,aspecificamountofcurrent(Iz=IRs)flowsthroughthezenerdiodeandRS.,32,VoltagedropURsplusUzwillequalUsource(Usourceshouldbeatleast1VgreaterthanUz).,33,Whenaloadisconnectedacrossthezenerdiode,thediodecurrentdecreasesbytheamountdrawnbytheloadsothatthecurrentthroughRSremainsconstant(Iz=IRs-IRL).,34,Thezenerdiodemaintainsthevoltageacrossitsterminalsbyvaryingthecurrentthatflowsthroughit.,35,5.1.5LinearVoltageRegulator,The78xx(alsosometimesknownasLM78xx)seriesofdevicesisafamilyofself-containedfixedlinearvoltageregulatorintegratedcircuits（Fig5.5）.,36,The78xxfamilyisaverypopularchoiceformanyelectroniccircuitswhichrequirearegulatedpowersupply,duetotheireaseofuseandrelativecheapness.,37,Fig5.578xxICs,38,WhenspecifyingindividualICswithinthisfamily,thexxisreplacedwithatwo-digitnumber,whichindicatestheoutputvoltagetheparticulardeviceisdesignedtoprovide(forexample,the7805hasa5voltoutput,whilethe7812produces12volts).,39,The78xxarepositivevoltageregulators,meaningthattheyaredesignedtoproduceavoltagethatispositiverelativetoacommonground.,40,Thereisarelatedlineof79xxdeviceswhicharecomplementarynegativevoltageregulators.78xxand79xxICscanbeusedincombinationtoprovidebothpositiveandnegativesupplyvoltagesinthesamecircuit,ifnecessary.,41,5.4Exercises,1.PutthePhrasesintoEnglish2.PutthePhrasesintoChinese,42,1.PutthePhrasesintoChinese,1）稳压电源2）桥式整流器3）脉冲直流电4）二极管的正极5）峰值电压,1)electronicpowersupply或steadyDCVoltagesource2)bridgerectifier3)pulsatingDC4)anodeofdiode5)peakvoltage,单击鼠标显示答案,43,6）电容滤波器7）充电和放电8）稳压管9）电气电子工程师学会10）专业技术组织,6)capacitorfilter7)chargeanddischarge8)zenerdiode9)IEEE(InstituteofElectricalandElectronicsEngineers)10)technicalprofessionalassociation,单击鼠标显示答案,44,2.PutthePhrasesintoEnglish,1)equipmentoperation2)devicethatconvertsACintoDC3)thepowerlines4)dependingonthevalueofDCvoltageneeded5)ahalf-waverectifier,1)设备的运行2)把交流电转换成直流电的器件（设备）3)电源线4)根据（取决于）所需要的直流电压值5)半波整流器,单击鼠标显示答案,45,6)soastoproduceaconstantDCoutput7)inthenegativesideofthecapacitor8)flowthroughtheload9)intheforward-biasedcondition10)aseries(current-limiting)resistor,6)从而产生一个稳定的直流输出7)在电容的负极8)流过负载9)在加