电路分析与电子线路综合训练题（DOC43页）

2018年《电路分析与电子线路》综合训练题注意：2018年《电路分析与电子线路》综合训练组队共同讨论完成综合训练题目3-4题，以书面形式撰写报告，需要详细的讨论过程和仿真的结果。请同学们自学“数值分析软件（如MATLAB等）及电路仿真软件（如Multisim或Pspice等）”。提交书面报告时间：6月20日前。Project1PowerSuppliesObjective:Thisprojectwillshowsomeofthebasicprinciplesofpowersuppliesusingfullwaverectifier,Zenerdiode,andfixed-voltageregulatorcircuits.Components:BridgeRectifier(50PIV,1A),Zenerdiode(10Vat500mW),7805regulatorIntroduction:Mostofthedirectcurrent(DC)powerusedinelectronicdevicesisderivedbyconverting60Hz,115Valternatingcurrent(AC)powertodirectcurrentpower.ThisACtoDCconversionusuallyinvolvesastep-downtransformer,rectifier,filter,andaregulator.Thestep-downtransformerisusedtodecreasetheAClinevoltagefrom115VRMStoanRMSvalueneartheDCvoltageneeded.Theoutputofthestep-downtransformeristhenfedintoadioderectifiercircuitthatonlyoutputspositivehalvesoftheinputsinusoid.AfilteristhenusedtosmooththerectifieroutputtoachieveanearlyconstantDCvoltagelevel.Aregulatorcanbeaddedafterthefiltertoensureaconstantoutputvoltageinspiteofchangesinloadcurrentandinputvoltages.Twodifferenttypesofvoltageregulatorswillbeusedinthisproject.ThefirstinvolvesaZenerdiodecircuitandthesecondinvolvesavoltageregulatorcircuit.AZenerdiodecanbeusedasavoltageregulatorwhenthediodeisreversebiasedandoperatedinthebreakdownregion.Tomaintainvoltageregulation,theZenerdiodemustbeoperatedinthebreakdownregionatacurrentgreaterthanthekneecurrent(IZK).ForcurrentsgreaterthanIZK,theZenerdiodecharacteristiccurveisnearlyverticalandthevoltageacrossthediodechangesverylittle.Ofcoursethereisamaximumcurrentthediodecantolerate,sogoodregulationisprovidedwhenthediodeisreversebiasedwithcurrentsbetweenIZKandIZMAX.Zenerdiodesareavailablewithawidevarietyofbreakdownvoltages.Anothertypeofvoltageregulatorisavailablewiththe7800seriesregulators.Thisseriesoffixed-voltageregulatorsisnumbered78xx,wherexxcorrespondstothevalueoftheoutputvoltage.Outputvoltagesfrom5to24voltsareavailable.Theseregulatorsareeasytouseandworkverywell.Design:1.FindapproximationsfortheDCvoltagelevelandACpeaktopeakripplevoltageforthebridgerectifierandfiltercircuitofFigure1-1.2.FortheZenerdioderegulatorcircuitofFigure1-2assumethattheZenerdiodewillregulateat10Voveracurrentrangeof5mAto25mA.AssumingthatthecurrentflowingthroughRisalwaysbetween5mAand25mAandtheZenerdiodeisregulatingat10V,findtheminimumvaluesofRandRLrequired.Youmayassumetheforwarddiodedropforthetwodiodesis1V.LabProcedure:1.ConstructthebridgerectifiercircuitofFigure1-1withoutthecapacitor.UsetheVariacwiththestep-downtransformerfortheinputvoltagetothebridgerectifier.WiththetransformerpluggedintotheVariac,adjusttheVariacuntilthesecondaryvoltagefromthetransformerequals12VRMS.BECAREFULnottoshortthesecondaryterminals!Observethesecondarywaveformontheoscilloscope.PuttheoscilloscopeonDCcouplingandobservetheloadvoltagewaveformVL.Rememberthatboththeinputsourceandtheloadcannotshareacommongroundterminal.2.Removepowerfromthecircuit.InsertthecapacitorasshowninFigure1-1beingsuretoobservethecorrectpolarity.Energizethecircuit.WiththeoscilloscopeonDCcouplingobserveVL.MeasuretheDCvoltagelevelusingthedigitalvoltmeter.WiththeoscilloscopeonACcouplingobservetheripplevoltageVR.Comparethesemeasuredvalueswiththecalculatedvalues.3.Observetheeffectofloadingonthecircuitbychangingtheloadresistorfrom1kto500.MeasuretheDCvoltagelevelwiththedigitalvoltmeter.ObservetheripplevoltagewiththeoscilloscopesetonACcoupling.Comparethesevalueswiththepreviouslyrecordedvalues.4.RecordtheZenerdiodecharacteristiccurvefromthedigitalcurvetracer.Notethevalueofthebreakdownvoltageinthebreakdownregion.AlsonotethevalueofthekneecurrentIZK.5.AfterverifyingyourdesignedvaluesforRandRLwiththeinstructor,constructtheZenerdioderegulatorcircuitofFigure1-2.MeasuretheDCvoltagelevelwiththedigitalvoltmeterfortheminimumvalueofRLalongwithseveralvaluesaboveandbelowtheminimumvalue.BecarefulnottooverloadtheZenerdiode.Commentonthecircuit'soperationforthesedifferentloadresistances.6.Constructthe7805regulatorcircuitofFigure1-3beingcarefultoobservethecorrectpinconfigurationoftheregulator.MeasuretheloadvoltageforRLequalto300,200,and100.Calculatethecurrentforeachofthesecases.Doesthevalueoftheloadresistoraffecttheoutputvoltage?7.UsingRLequalto200,recordthe7805regulatorinputvoltage(pin1)andoutputvoltage(pin3).DecreasetheregulatorinputvoltagebydecreasingthesettingoftheVariac.Foreachdecreaseinamplitude,recordtheregulatorinputandoutputvoltages.Continuedecreasingtheamplitudeuntiltheoutputoftheregulatordropsameasurableamountbelow5V.Whatistheminimuminputvoltageneededforthe7805regulatortoproducea5Voutput?Questions:1.Whycan'ttheinputsourceandloadhaveacommongroundinthebridgerectifiercircuit?2.CantheZenerdiodebeusedasaconventionaldiode?Explainyouranswerandverifywithacurvefromthecurvetracer.3.Wouldthevalueoftheoutputfiltercapacitorhavetoincrease,decrease,orremainthesametomaintainthesameripplevoltageifthebridgerectifierwerechangedtoahalf-waverectifier?Explainyouranswer.4.Howwouldincreasingthefrequencyoftheinputsourceaffecttheripplevoltageassumingallcomponentsremainedthesame?Proje