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1、后备式UPS切换供电时微机自检原因分析CauseanalysisofmicrocomputerselfcheckinginstandbyUPSswitchingpowersupplyFromyourJiangsu1994-01-07Thus,werefertotherelevantbooks,testingandanalysisofthisphenomenon,wehaveachievedonly20Fenofthesolutiontothisproblem.Firstunderstandthestartprocessofthemicrocomputer:Whenthemicr
2、ocomputerpowerswitchisswitchedon,fourDCoutputvoltages(+5V,+12V,-5V,-12V)oftheinternalpowersourcearestarted・Delay100ms-500ms+5Vaftertheestablishmentofthevoltage,powersupplythroughtheconnectorP8tothehostboardPWRGOODsendsa"power"signal(hereinafterreferredtoasP-Gsignal),thesignalissenttothe11foo
3、tRES8284end,by8284controlbuttonswithCLK88synchronoustimingoutputhighlevelRESETsignal,thesystemisreset,powertheoperationof8088intotheworkoftheRESETsignal,needtokeep50Stime,8088toachieveastableworkingstate,andinitializationofrelatedparts・Furtherdiscussiononmicroprocessor-basedundervoltageprote
4、ctionThemicrocomputerregulatedpowersupplywithpowerundervoltageprotectioncircuit,whenthegridvoltageisbelowaceriainvalue(powersupplyundervoltageprotectionis75V,110Vis150Vto220Vpowergrid),theprotectivecircuitmakePGsignalfrom+5Vdowntozerolevel,overaperiodoftimebacktopowergridthenormalvalueofP,Gs
5、ignalbackto+5V,thehostcircuitisequivalenttorestartthesame・Inordertofindoutthereason,thatistodistinguishbetweenthemicrocomputerproblemortheUPSproblem・Performthefollowingtests.DetectUPSswitchingpowersupplyPowerlossafterUPSswitchingpowersupply,ACvoltageswitchinginstant(MF14multimeter)droppedto1
6、75V,usingtheoscilloscopeobservation,sinewavesignalforswitchingbetween,afterswitchingtherectangularwavewithotherharmonic(seeFigure1).Thetransientvoltagewaveformisdiscontinuous・Thepowersystemof+5Vmicrocomputerinswitchingpowersupplyandthemultimeterisusedtoobservethevoltagevalueonthe+5Vpointeral
7、ways,nofluctuationphenomenon,withnochangeintheamplitudeoftheoscilloscopetoobservetheDCregulatedpowersupplysystem,thestabilizingeffectisgood・DetectingundervoltageprotectionofMicrocomputerAsshowninFigure2,amicrocomputerisconnectedtothegridbyaregulato
