模拟电路实验Word文件下载.docx
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Introduction:
Mostofthedirectcurrent(DC)powerusedinelectronicdevicesisderivedbyconverting
60Hz,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-voltageregulatorsis
numbered78xx,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"
currentIZK.
5.AfterverifyingyourdesignedvaluesforRandRLwiththeinstructor,constructtheZenerdioderegulatorcircuitofFigure1-2.MeasuretheDCvoltagelevelwiththedigitalvoltmeterfortheminimumvalueofRLalongwithseveralvaluesaboveandbelowtheminimumvalue.BecarefulnottooverloadtheZenerdiode.Commentonthecircuit'
soperationforthesedifferentloadresistances.
6.Constructthe7805regulatorcircuitofFigure1-3beingcarefultoobservethecorrectpinconfigurationoftheregulator.MeasuretheloadvoltageforRLequalto300Ω,200Ω,
and100Ω.Calculatethecurrentforeachofthesecases.Doesthevalueoftheloadresistoraffecttheoutputvoltage?
7.UsingRLequalto200Ω,recordthe7805regulatorinputvoltage(pin1)andoutput
voltage(pin3).DecreasetheregulatorinputvoltagebydecreasingthesettingoftheVariac.Foreachdecreaseinamplitude,recordtheregulatorinputandoutputvoltages.Continuedecreasingtheamplitudeuntiltheoutputoftheregulatordropsameasurableamountbelow5V.Whatistheminimuminputvoltageneededforthe7805regulatortoproducea5Voutput?
Questions:
1.Whycan'
ttheinputsourceandloadhaveacommongroundinthebridgerectifiercircuit?
2.CantheZenerdiodebeusedasaconventionaldiode?
Explainyouranswerandverifywithacurvefromthecurvetracer.
3.Wouldthevalueoftheoutputfiltercapacitorhavetoincrease,decrease,orremainthesametomaintainthesameripplevoltageifthebridgerectifierwerechangedtoahalf-waverectifier?
Explainyouranswer.
4.Howwouldincreasingthefrequencyoftheinputsourceaffecttheripplevoltageassumingallcomponentsremainedthesame?
Project2
AnalogApplicationsoftheOperationalAmplifier
Thisprojectwilldemonstratesomeoftheanalogapplicationsofanoperationalamplifierthroughasummingcircuitandabandpassfiltercircuit.
741op-amp
Figure2-1showsaweightedsummercircuitintheinvertingconfiguration.Thiscircuitcanbeusedtosumindividualinputsignalswithavariablegainforeachsignal.Thevirtualgroundattheinvertinginputterminaloftheop-ampkeepstheinputsignalsisolatedfromeachother.Thisisolationmakesitpossibleforeachinputtobesummedwithadifferentgain.
ThebandpassfiltershowninFigure2-2usesanop-ampincombinationwithresistorsandcapacitors.Sincetheop-ampcanincreasethegainofthefilter,thefilterisclassifiedasanactivefilter.Thisbandpassfiltercircuitisextremelyusefulbecausethecenterfrequencycanbechangedbyvaryingaresistorinsteadofchangingthevaluesofthecapacitors.Thecenterfrequencyisgivenby:
ThecenterfrequencycanbechangedbyvaryingthevariableresistorR3.IncreasingR3decreasesthecenterfrequencywhiledecreasingR3increasesthecenterfrequency.Thebandwidthisgivenby:
NoticethatthebandwidthisindependentofthevariableresistorR3sothecenterfrequencymaybevariedwithoutchangingthevalueofthebandwidth.Thegainatthecenterfrequencyofthebandpassfilterisgivenby:
1.FindtherelationshipbetweentheoutputandinputsfortheweightedsummercircuitofFigure2-1.
2.Designabandpassfilterwithacenterfrequencyof2.0kHzandabandwidthof200Hz.Letthevoltagegainatthecenterfrequencybe20.CheckyourdesignwithPSPICE®
.Use±
15Vsuppliesfortheop-amp.UseRL=2.4kΩ.
Figure2-1:
WeightedSummer
Figure2-2:
BandpassFilter
1.ConstructthesummingamplifierofFigure2-1.Designforthetransferfunctionto
beVO=-2VIN1-VIN2.Use±
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.
1.Couldthesummercircuitbeusedwiththeinputsconnectedtothenoninvertingterminalandproducethesameaffectwithouttheinversion?
Explain.
2.Whatis/arethebenefit(s)ofusinganop-ampcircuittoproduceabandpassfilteroverusinganRLCcircuitwithanoninvertingop-ampattheoutputoftheRLCcircuit?
Project3
AnalogComputerApplicationsusingtheOperationalAmplifier
Thisprojectwillfocusontheuseoftheoperationalamplifierinperformingthemathematicaloperationsofintegrationanddifferentiation.Thedesignofasimplecircuit(analogcomputer)tosolveadifferentialequationwillalsobeincluded.
Figures3-1and3-2illustratetwoop-ampbasedcircuitsdesignedtoperformdifferentiationandintegrationrespectively.Theoperationsareperformed"
real-time"
andcanbehelpfulinobservingbothinitialtransientsandsteadystateresponse.Theanalysisofthecircuitsisbasedonthe"
ideal"
op-ampassumptionsandperformedinthetimedomain.TheresistorRIshowninthetwocircuitsisincludedtohelpwithstabilityandforgeneralcircuitprotection.ThevalueforRIisnominallysete