PSPICE计算机仿真(三)

PSPICE计算机仿真

SimulationProgramwithIntegratedCircuitEmphasis

CH7

THESTEPRESPONSEAND

SWITCHES

阶跃响应

7.1Simplestepresponse

Example11

■a)Theswitchinthecircuitshownin

Fig.69isclosedatt=0.Attheinstant

theswitchisclosed,theinitialcurrent

inthe10mHinductoris90mA,andthe

voltageacrossthecapacitoris10V.

■Fig.69alsoshowsthereferencesfor

theseinitialconditions.Makea

preliminaryanalysisofthestep

response,andcalculatethemaximum

valueofVcandthetimeatwhichit

occurs.

■b)CreateaPSpiceschematic,perform

transientanalysis,andplotVcversust

from0to3000ps.

■c)ComparethePSpicesolutionwiththe

preliminaryanalysis.

4Solutiona)

■FromthesolutionofExample10,wealready

knowthattheresponseisunderdamped.

■Furthermore,weknowthatthedamped

periodis897.60ps,andthat

、

s1=-1OOO+j，7000

s

2-1000-j7000

■Thestep-responsesolutionforVctakesthe

form

/'.\-1000

乙=L+⑸cos7000%+B2sm7000t)e

■TheinitialvaluesofVcanddVc/dtarethe

sameasinExample10,andthefinalvalueis

21V.HenceB'l=-31VandB'2=2V,so

/.\—1000t

v=21-(31cos7000/-2sm7000t)e,t>0

■ThemaximumvalueofVcis41.22Vat

419.32|JS.

4Solutionb)

■InFig.71,weusedtwocursorsthis

time,andmovedthesecondcursorby

holdingdowntheShiftkeywhileusing

theleftandrightarrowkeys.The

cursorsallowyoutoreadthevaluesof

Vc(max)andTddirectlyfromthe

Probeplot.

4Solutionc)

■TheoutputofthePSpiceanalysisyields

v_(max)=41.361V

TJ=899.503us

V21V

7.2PiecewiseLinearSources

（分段线性电源）

■Example12illustratestheuseofthe

piecewiselinearsourceformodelingthe

switchingthattakesplaceinatransient

analysisproblem.

Example12

■ThecircuitshowninFig.72hasbeenin

operationforalongtime.Att=0,the

80Vsourcedropsinstantaneouslyto20

V.ConstructaPSpiceschematic,using

aPWLsource,tomodelthiscircuit.The

resultsoftheanalysisshouldbeaplot

ofVo(t)versust.

Solution

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Results

■TheProbeplotinFig.76,whichuses

thecursorstodeterminetheoutput

voltageatt=40msandt=80ms,yields

thefollowingresults:

tVo（t）

064

4033.698（书上:33.654）

8022.489（书上:22.498）

■Furthermore,youcanseefromthe

ProbeplotthatVo(t)叩proaches16V

astapproachesoo.

7.3RealisticSwitches

（实际开关）

■Weillustratetheuseofthenormally-

openedswitchinExample13to

examinetheeffectofnonzeroswitch

resistanceonthestepresponseofthe

RLCcircuit.

Example13

■UsePSpicetomodelthecircuitshown

inFig.69,withsomemodifications.

■Assumethatthevoltagesourceisthe

sameasthatusedinExample10,anduse

thesamevaluesinspecifyingtransients

analysis,

■Butassumethattheresistanceofthe

switchintheONpositionis10Q

■ThengenerateaplotofVcversust.

Comparetheresultsherewiththosein

Example10.

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