模拟电路实验.docx

模拟电路实验.docx

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模拟电路实验

Project1

PowerSupplies

Objective:

Thisprojectwillshowsomeofthebasicprinciplesofpowersuppliesusingfullwaverectifier,Zenerdiode,andfixed-voltageregulatorcircuits.

Components:

BridgeRectifier（50PIV,1A）,Zenerdiode（10Vat500mW）,7805regulator

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"knee"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

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.Designforthetransferfunctionto

beVO=-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.TheresistorRIshowninthetwocircuitsisincludedtohelpwithstabilityandforgeneralcircuitprotection.ThevalueforRIisnominallysete