Power Electronics Interview Questions

5/23/2015 PowerElectronicsInterviewQuestionsandAnswers:Set2

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INTERVIEW QUESTIONS 2

PowerElectronicsTechnicalInterviewQuestions:Set-2 December 25, 2013PowerElectronicsTechnicalInterviewQuestionsandAnswers:

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Powerelectronicstechnicalinterviewquestions withanswers aregiven in this post.These questionswere asked invarious powerelectronicscompanyinterviews tosome of ourfriends. Wecollected thequestions fromour friends andanswer them indetail. We areconfident thatthese PowerElectronicsTechnicalInterviewQuestions will behelpful for you,while preparingfor interviews

[Q-1] Draw the

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Power Electronics Basics (7)

Power Semiconductor Devices (12)

SCR Tutorials (6)

Switch Mode Power Supply [SMPS] (2)

Uninterruptible power supply [UPS] (5)

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buck topology?In most of thepower electronicsinterviewquestions, youare going to facethis basicquestion. Notonly buckconverter, theinterviewer mayask you to drawotherfundamentaltopologies too

So you should befamiliar withother basictopologies likeFlyback, Boost ,Buck-boost.

[Q-2] Which is thegood choiceamong the 2options mentionedbelow to get the12V as an output?why?Option I: Inputvoltage = 48V,



Option II:Inputvoltage = 24V

Answer: We knowthatDuty cycle D =Vout / VInput

For case ID = 12/48 = 0.25

For case IID = 12/24 = 0.5

So for case II, theduty cycle ismore than case I.It means deviceis turned ONmore time in thesecond case.while designingSMPS we have toconsider theprinciplementioned in Q-3.

[Q-3] What iseffect of havingmore duty cycleand less dutycycle? (continuation ofabove question)If the duty cycle



D is greater than0.5, the corewould not becompletelydemagnetized atthe end of theoff-period, and aDCmagnetization ofthe core wouldbuild up, resultingin coresaturation.Relate thisanswer thepreviousquestion.

[Q-4] To designthe buckconverter, whatare basic &essentialinformation(parameters) weneed to get fromthe Customer?We need thefollowing inputsfrom thecustomer,Output VoltageVOUTInput Voltage VIN



Output Current(load current) IOUTMaximum Ripplevoltage allowedat the output sideEfficiency of theconverter

[Q-5] How toselect the inductorfor the buckconverter?Once thetopology isfinalized in theprocess of powersupply design,the next step isselecting theInductor.We know thefollowing basicequationVoltage acrossInductor VL = L

di/dtRewriting theabove equationas followsL = VL.dt/di

VL = Maximum

voltage appearsacross theInductor



dt= The timeduring which themaximumvoltage appearsacross theinductordi = RipplecurrentVL The maximum

voltage appearsacross theinductor whenthe power switchis turned on.During that timethe voltage willbeVL = VOUT VINdt = The timeduring which themaximumvoltage appearsacross theinductor= D/FS= Dutycycle/Switchingfrequencydi = Ripplecurrent= Generally it isassumed inbetween 10% to30% of the load



currentBy knowing allthese values wecan get therequired inductorvalue for thebuck converter.

[Q-6] What arethe variousparameters wehave to consider,while selectingIGBT?In IGBTdatasheet, wehave to focus onfollowingparametersCollector toemitter voltageVCESCollector CurrentICCollectorDissipation PCJunctionTemperature Tj

[Q-6] For SelectingMOSFET, what arethe majorparameters wehave to consider in



the datasheet?In MOSFETdatasheet, wehave to focus onfollowingparameters:Drain to SourceVoltage VDSSOn state Drain toSourceResistance RDS(ON)ReverseRecovery CurrentIRRReverseRecovery ChargeQRRGate Charge QGBody DiodeCharacteristicsID at ambient

temperatureChannel powerdissipationChanneltemperature

We believe thatthesepowerelectronicstechnicalinterviewquestions might



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have stimulatedyour technicalknowledge Ifyou havequestions whydont you sharewith oursubscribers?

Related Posts:PowerElectronics BasicInterviewQuestions: Set-3PowerElectronicsInterviewQuestions: Set-1

Prabhat February 11, 2015 at 5:56amVery good questions.

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ajaz ahmed k April 28, 2015 at 6:32 amthanks for giving goodinformation

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Power Electronics Interview Questions