《模拟电路》综合训练题.docx
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《模拟电路》综合训练题.docx
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《模拟电路》综合训练题
2015年《模拟电子技术基础》综合训练题
注意:
2015年《模拟电路基础》综合训练组队共同讨论完成综合训练题目3-4题。
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)”。
提交报告时间:
期末考试前。
Project1
PowerSupplies
Objective:
Thisprojectwillshowsomeofthebasicprinciplesofpowersuppliesusingfullwaverectifier,Zenerdiode,andfixed-voltageregulatorcircuits.
Components:
BridgeRectifier(50PIV,1A),Zenerdiode(10Vat500mW),7805regulator
Introduction:
Mostofthedirectcurrent(DC)powerusedinelectronicdevicesisderivedbyconverting60Hz,115Valternatingcurrent(AC)powertodirectcurrentpower.ThisACtoDCconversionusuallyinvolvesastep-downtransformer,rectifier,filter,andaregulator.Thestep-downtransformerisusedtodecreasetheAClinevoltagefrom115VRMStoanRMSvalueneartheDCvoltageneeded.Theoutputofthestep-downtransformeristhenfedintoadioderectifiercircuitthatonlyoutputspositivehalvesoftheinputsinusoid.AfilteristhenusedtosmooththerectifieroutputtoachieveanearlyconstantDCvoltagelevel.Aregulatorcanbeaddedafterthefiltertoensureaconstantoutputvoltageinspiteofchangesinloadcurrentandinputvoltages.
Twodifferenttypesofvoltageregulatorswillbeusedinthisproject.ThefirstinvolvesaZenerdiodecircuitandthesecondinvolvesavoltageregulatorcircuit.AZenerdiodecanbeusedasavoltageregulatorwhenthediodeisreversebiasedandoperatedinthebreakdownregion.Tomaintainvoltageregulation,theZenerdiodemustbeoperatedinthebreakdownregionatacurrentgreaterthanthe"knee"current(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.WiththeoscilloscopeonDCcoupling
observeVL.MeasuretheDCvoltagelevelusingthedigitalvoltmeter.WiththeoscilloscopeonACcouplingobservetheripplevoltageVR.Comparethesemeasuredvalueswiththecalculatedvalues.
3.Observetheeffectofloadingonthecircuitbychangingtheloadresistorfrom1kΩ
to500Ω.MeasuretheDCvoltagelevelwiththedigitalvoltmeter.ObservetheripplevoltagewiththeoscilloscopesetonACcoupling.Comparethesevalueswiththepreviouslyrecordedvalues.
4.RecordtheZenerdiodecharacteristiccurvefromthedigitalcurvetracer.Notethevalueofthebreakdownvoltageinthebreakdownregion.Alsonotethevalueofthe"knee"currentIZK.
5.AfterverifyingyourdesignedvaluesforRandRLwiththeinstructor,constructtheZenerdioderegulatorcircuitofFigure1-2.MeasuretheDCvoltagelevelwiththedigitalvoltmeterfortheminimumvalueofRLalongwithseveralvaluesaboveandbelowtheminimumvalue.BecarefulnottooverloadtheZenerdiode.Commentonthecircuit'soperationforthesedifferentloadresistances.
6.Constructthe7805regulatorcircuitofFigure1-3beingcarefultoobservethecorrectpinconfigurationoftheregulator.MeasuretheloadvoltageforRLequalto300Ω,200Ω,and100Ω.Calculatethecurrentforeachofthesecases.Doesthevalueoftheloadresistoraffecttheoutputvoltage?
7.UsingRLequalto200Ω,recordthe7805regulatorinputvoltage(pin1)andoutputvoltage(pin3).DecreasetheregulatorinputvoltagebydecreasingthesettingoftheVariac.Foreachdecreaseinamplitude,recordtheregulatorinputandoutputvoltages.Continuedecreasingtheamplitudeuntiltheoutputoftheregulatordropsameasurableamountbelow5V.Whatistheminimuminputvoltageneededforthe7805regulatortoproducea5Voutput?
Questions:
1.Whycan'ttheinputsourceandloadhaveacommongroundinthebridgerectifiercircuit?
2.CantheZenerdiodebeusedasaconventionaldiode?
Explainyouranswerandverifywithacurvefromthecurvetracer.
3.Wouldthevalueoftheoutputfiltercapacitorhavetoincrease,decrease,orremainthesametomaintainthesameripplevoltageifthebridgerectifierwerechangedtoahalf-waverectifier?
Explainyouranswer.
4.Howwouldincreasingthefrequencyoftheinputsourceaffecttheripplevoltageassumingallcomponentsremainedthesame?
Project2
AnalogApplicationsoftheOperationalAmplifier
Objective:
Thisprojectwilldemonstratesomeoftheanalogapplicationsofanoperationalamplifierthroughasummingcircuitandabandpassfiltercircuit.
Components:
741op-amp
Introduction:
Figure2-1showsaweightedsummercircuitintheinvertingconfiguration.Thiscircuitcanbeusedtosumindividualinputsignalswithavariablegainforeachsignal.Thevirtualgroundattheinvertinginputterminaloftheop-ampkeepstheinputsignalsisolatedfromeachother.Thisisolationmakesitpossibleforeachinputtobesummedwithadifferentgain.
ThebandpassfiltershowninFigure2-2usesanop-ampincombinationwithresistorsandcapacitors.Sincetheop-ampcanincreasethegainofthefilter,thefilterisclassifiedasanactivefilter.Thisbandpassfiltercircuitisextremelyusefulbecausethecenterfrequencycanbechangedbyvaryingaresistorinsteadofchangingthevaluesofthecapacitors.Thecenterfrequencyisgivenby:
ThecenterfrequencycanbechangedbyvaryingthevariableresistorR3.IncreasingR3decreasesthecenterfrequencywhiledecreasingR3increasesthecenterfrequency.Thebandwidthisgivenby:
NoticethatthebandwidthisindependentofthevariableresistorR3sothecenterfrequencymaybevariedwithoutchangingthevalueofthebandwidth.Thegainatthecenterfrequencyofthebandpassfilterisgivenby:
Design:
1.FindtherelationshipbetweentheoutputandinputsfortheweightedsummercircuitofFigure2-1.
2.Designabandpassfilterwithacenterfrequencyof2.0kHzandabandwidthof200Hz.Letthevoltagegainatthecenterfrequencybe20.CheckyourdesignwithPSPICE®.Use±15Vsuppliesfortheop-amp.UseRL=2.4kΩ.
Figure2-1:
WeightedSummer
Figure2-2:
BandpassFilter
LabProcedure:
1.ConstructthesummingamplifierofFigure2-1.DesignforthetransferfunctiontobeVO=-2VIN1-VIN2.Use±15Vsuppliesfortheop-amp.UseRL=2.4kΩ.
2.LetVIN1bea1Vpeaksinewaveat1kHzandVIN2equalto5VDC.Verifytheamplifier'soperationbymonitoringtheoutputwaveformontheoscilloscope.
3.ConstructthebandpassfilterofFigure2-2.Usethedesignedvaluesfortheresistorsandcapacitors.Use±15Vsuppliesfortheop-amp.UseRL=2.4kΩ.
4.Recordandplotthefrequencyresponse(youmaywanttousecomputercontrolforthesweepanddatacollection).Findthecenterfrequency,cornerfrequencies,bandwidth,andcenterfrequencyvoltagegaintoverifythatthespecificationshavebeenmet.
5.ChangeR3tolowerthecenterfrequencyfrom2.0kHzto1.0kHz.Repeatpart4forthenewfrequencyresponse.Verifythatthenewcenterfrequencyis1.0kHz.Whatisthenewbandwidth?
Whatisthenewcenterfrequencyvoltagegain?
ComparewiththemeasurementsofProcedure4.
Questions:
1.Couldthesummercircuitbeusedwiththeinputsconnectedtothenoninvertingterminalandproducethesameaffectwithouttheinversion?
Explain.
2.Whatis/arethebenefit(s)ofusinganop-ampcircuittoproduceabandpassfilteroverusinganRLCcircuitwithanoninvertingop-ampattheoutputoftheRLCcircuit?
Project3
AnalogComputerApplicationsusingtheOperationalAmplifier
Objective:
Thisprojectwillfocusontheuseoftheoperationalamplifierinperformingthemathematicaloperationsofintegrationanddifferentiation.Thedesignofasimplecircuit(analogcomputer)tosolveadifferentialequationwillalsobeincluded.
Components:
741op-amp
Introduction:
Figures3-1and3-2illustratetwoop-ampbasedcircuitsdesignedtoperformdifferentiationandintegrationrespectively.Theoperationsareperformed"real-time"andcanbehelpfulinobservingbothinitialtransientsandsteadystateresponse.Theanalysisofthecircuitsisbasedonthe"ideal"op-ampassumptionsandperformedinthetimedomain.TheresistorRIshowninthet
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