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vo (1 v/div)
1
vo (1 v/div)
2
io (5一个/div)
2
horiz 规模: 10 ms/div
vin (5 v/div)
vo (1 v/div)
horiz 规模 5 ms/div
Start−Up
时期
PTV12010L
PTV12010W
SLTS234–DECEMBER2004
prebiascancauseproblemswithpowermodulesthatincorporatesynchronousrectifiers.thisisbecauseunder
mostoperatingconditions,suchmodulescansinkaswellassourceoutputcurrent.the12-vinputmodules
incorporatesynchronousrectifiers,butdonotsinkcurrentduringstartup,orwheneverthe
Inhibit
pinisheldlow.
startupincludesaninitialdelay(approximately8–15ms),followedbytheriseoftheoutputvoltageunderthe
controlofthemoduleinternalsoft-startmechanism;seefigure19.
ConditionsforPrebiasHoldoff
inorderforthemoduletoallowanoutputprebiasvoltagetoexist(andnotsinkcurrent),certainconditionsmust
bemaintained.themoduleholdsoffaprebiasvoltagewhenthe
Inhibit
pinisheldlow,andwhenevertheoutput
isallowedtoriseundersoft-startcontrol.powerupundersoft-startcontroloccursontheremovaloftheground
signaltotheinhibitpin(withinputvoltageapplied),orwheninputpowerisappliedwithauto-trackdisabled
2
.至
furtherensurethattheregulatordoesnotsinkoutputcurrent(evenwithagroundsignalappliedtoits
Inhibit
),这
inputvoltagemustalwaysbegreaterthantheappliedprebiassource.thisconditionmustexistthroughoutthe
电源-upsequence
3
.
thesoft-startperiodiscompletewhentheoutputbeginsrisingabovetheprebiasvoltage.onceitiscomplete,
themodulefunctionsasnormalandsinkscurrentifavoltagehigherthanthenominalregulationvalueisapplied
toitsoutput.
便条:
ifaprebiasconditionisnotpresent,thesoft-startperiodiscompletewhentheoutputvoltagehasrisento
eithertheset-pointvoltage,orthevoltageappliedatthemoduletrackcontrolpin,whicheverislowest,toits
输出.
DemonstrationCircuit
figure20showsthestart-upwaveformsforthedemonstrationcircuitshowninfigure21.theinitialriseinv
O
2is
theprebiasvoltage,whichispassedfromthevcciotothevcorevoltagerailthroughtheasic.notethatthe
outputcurrentfromthemodule(i
O
2)isnegligibleuntilitsoutputvoltagerisesabovetheappliedprebias.
figure19.ptv12010wstartupfigure20.prebiasstart-upwaveforms
注释:
1.theprebiasstart-upfeatureisnotcompatiblewithauto-追踪.iftheriseintheoutputislimitedbythe
voltageappliedtothe
追踪
controlpin,theoutputsinkscurrentduringtheperiodthatthetrackcontrol
voltageisbelowthatoftheback-feedingsource.forthisreason,自动-trackshouldbedisabledwhennot
beingused.thisisaccomplishedbyconnectingthe
追踪
pintotheinputvoltage,v
I
.thisraisesthe
追踪
pinwellabovetheset-pointvoltagepriortostartup,therebydefeatingtheauto-trackfeature.
2.tofurtherensurethattheregulatoroutputdoesnotsinkcurrentwhenpowerisfirstapplied(evenwitha
groundsignalappliedtothe
Inhibit
controlpin),theinputvoltage
必须
alwaysbegreaterthantheapplied
prebiassource.thisconditionmustexist
全部地
thepower-upsequenceofthepowersystem.
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