practical power...

PRACTICALPOWERELECTRONICSAPPLICATIONS,EXPERIMENTSANDANIMATIONS

MUSTAFAHUSAIN

Copyright©2015byMustafaHusain.

ISBN: Hardcover 978-1-4828-5464-0

Softcover 978-1-4828-5463-3

eBook 978-1-4828-5465-7

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CONTENTSPreface

PARTITHEORY

1Introduction

1.0Objectives

1.1HistoryofPowerElectronics

1.2ClassificationofPowerElectronics

1.3Converters

1.4Applications

2Devices

2.0Introduction

2.1PN-JunctionDiode

2.2Thyristors

2.2.0SiliconControlledRectifier(SCR)

2.2.1GateTurnOff(GTO)

2.2.2TriodeAC(TRIAC)

2.2.3Light-ActivatedDevices

2.2.4ThyristorFiringandProtectionCircuits

2.2.5UnijunctionTransistor(UJT)

2.2.6DiodeAC(DIAC)

2.2.7ProtectionAgainstdi/dtanddv/dt

2.3BipolarJunctionTransistors(BJT)

2.3.0NPNTransistor

2.3.1DarlingtonTransistor

2.4MOSFET

2.5InsulatedGateBipolarTransistor(IGBT)

3DiodeRectifiers

3.0Introduction

3.1Half-WaveRectifier

3.2Full-WaveRectifier

4ThyristorRectifiers

4.0Introduction



5Inverters

5.0Introduction

5.1ApplicationsOfInverters

5.2Half-BridgeInverter

5.3BridgeInverter

5.4UninterruptiblePowerSupply(UPS)

6Choppers

6.0Introduction

6.1Step-DownChopper

6.2Step-UpChopper

6.3StepUp/DownChopper

7Single-PhaseVoltageRegulators

7.0Introduction

7.1Phase-AngleControl

7.2On-OffControl

7.3CommercialApplication

8UnderstandingDataSheets

8.0Introduction

8.1TheDiode

8.2TheThyristor

8.3TheBJT

8.4TheMOSFET

8.5TheIGBT

PartIIExperiments

Experiment1TestingofPowerElectronicDevices

1.0Objectives

1.1Equipment

1.2Discussion

1.3TestingofSemiconductorSwitches

1.3.1Diode

1.3.2SCR

Experiment2CharacteristicsofPN-JunctionDiode

2.0Objectives

2.1Equipment

2.2Discussion

2.3Experiment

2.3.0ForwardBias

2.3.1ReverseBias

Experiment3UncontrolledAC-DCConverter

3.0Objectives

3.1Equipment

3.2Discussion

3.3Experiment

3.3.0Half-WaveRectifier

3.3.1Full-WaveRectifierUsingDiscreteDiodes

3.3.2Full-WaveRectifierUsingBridgeRectifierChip

Experiment4ControlledAC-DCConverter

4.0Objectives

4.1Equipment

4.2Discussion

4.3Experiment

Experiment5DC-DCConverter

5.0Objectives

5.1Equipment

5.2Discussion

5.3Experiment

5.3.0Step-DownChopper

Experiment6AC-ACConverter

6.0Objectives

6.1Equipment

6.2Discussion

6.3Experiment

6.3.0Phase-AngleControlMethod

6.3.1On-OffControlMethod

DATASHEETS

InmemoryoflateElbazAyad

Work.Finish.Publish.

MichaelFaraday(1791-1867)

PREFACEWhyanotherbookonpowerelectronics?Itisnotjustanotherbook.Mostofthepublishedbooks in this area focus on the design aspects and they are full of mathematics thatdistracts the learners from understanding the operating principles which practicingengineers and technicians need in their daily jobs. Moreover, when it comes toexperiments,theavailablebooksarescarce.

We know of many electrical engineering graduates who passed a power electronicscoursebut,when they joined the industry, theysawabiggapbetweenwhatwas taughtandwhat knowledge and skills the industry needs. For instance in a power electronicscourse,allgraduatesshouldknowthesymbol,operationandapplicationsofthethyristor.Butmany of themmight not touch or see the physical appearance of the thyristor normighttheyseeindustrialapplicationsofthethyristor.Thiswouldbequiteashockifthesegraduatescaughtjobsthathappentoinvolvetheoperationandmaintenanceofthyristorsinbigsystems.Howcanwepreparelearnersforsuchjobs?

Thisbookaimstobethefirststepinnarrowingthegapbetweenacademiaandindustry.It isanorganizedcollectionofusefulnotes thatwehaveused for15years to teach thebasicsofpowerelectronicstheoreticallyandpractically.Weletourstudentstouchandfeelpower electronics. We do practical demonstrations and we dismantle appliances andpanels to show them the physical appearances of devices and controllers that worktogether to form a power electronics converter.We have different shapes and sizes ofdevices and converters manufactured by a variety of global designers. In addition, weorganize industrial visits to see the applications and operation of power electronics.Instructors are strongly advised to carrywith them power electronic devices and showthemtotheirclassesandalsotogivetheirstudentstheopportunitytotouchandfeelthedevices.

Itiswisetokeepthesenotesinabookanditisapleasuretosharethemwithinterestedinstructors and professionals worldwide. Being concise, it aims to explain the basicoperatingprinciplesbrieflyandtopresentsomeapplicationsofpowerelectronicswithoutdeepexplanation.

Thebookisdividedintotwoparts;theoreticalandexperimental.Thefirstpartconsistsofeightchapterscoveringtheoperationofdevicesandcircuits.Thebasicconvertersareac-dc,ac-ac,dc-acanddc-dcconverters.Someapplicationsoftheseconvertersarelistedand some are briefly explained. The second part has six experiments thatwill help thelearnerhave the feelingofpowerelectronicsand tounderstand theconceptspractically.Included also is the employment of microcontrollers to provide simple control ofconverters.

To assist the learner further, photos of power electronic devices and circuits of somegadgets andappliances thatweusedailyare included.The text is enrichedwith simplediagrams. For easier and quicker understanding, some concepts were animated. Theanimations are available on EduMation.Org, a website dedicated for educationalanimations.Theanimationsmayalsobe foundon theEduMationchannelonYouTube.Datasheetsofpowerelectronicdevicesareattachedattheendofthebook.

This book is valuable for teaching a first hands-on course on power electronics fortechnicalinstitutes,polytechnicsandin-housetrainingforindustries.Instructorswillfinditeasyandstraightforwardwhilepreparingfortheirclasses.

I shall express my gratitude to the kindness and support offered by the followingpersons.My colleagues at Bahrain Training Institute: The lateMr. Elbaz Ayad alwayscorrectedmistakesandprovided invaluablecomments;hisdeparturewasagreat loss toour team. I am indebted toMr. Abdulhusain Buhusain for his team spirit and restlessencouragement.IfeelverygratefulforMr.HassanAlkhayerwhopreparedthetemplateofthemanuscript.SpecialappreciationgoestoMr.FayezAbbaswhoconstructedandtestedamicrocontroller-basedon-offac-acconverter.ManythankstoourexperiencedcolleagueMr.YosriIdreeswhodismantledpowerthyristorsfromanoldUPSsystem,andhekindlyallowedustousethemduringpowerelectronicscourses.

IamindebtedtoPowerexIncwhogavemepermissiontousephotosanddatasheetsofsomeof theirproducts.Myappreciation isalsoextended toONSemiconductor IncandDiodesIncfortheirdatasheets.

ThemanuscriptwasproofreadbyEthra forTranslationandResearch; they thankfullyprovidedvaluablecommentsaswell.Thebookwouldnothavebeenstartedwithout thesupportofmywifeandchildrenAli,KawtharandMahmood.

Sharing comments and ideas with you will help me improve the book. If you havecommentsorsuggestions,pleasedonothesitate tosend themviaemailorWhatsApp. Iwillbegladtohearfromyou.

Dr.MustafaHusain

Founder-EduMation.org

Mobile/WhatsApp:+97335579902

Email:[email protected]

http://www.edumation.org

mailto:[email protected]

PARTI

THEORY

1

INTRODUCTION1.0Objectives

Power electronics are devices made of semiconductor materials the most common ofwhich are silicon and germanium. Their main function is switching, and thus they areutilized for electrical energyconversion and control.Manyconverters canbebuiltwithpower electronics such as rectifiers, inverters, choppers and so on. They are of greatimportancetotheelectricpowerindustryworldwide.

Powerelectronicdevicesdiffer fromelectronicdevices in theirpower ratings.Hence,any electronic device can be classified as either a signal or power device. A signalelectronicdeviceisusedforlow-powerapplicationsrequiringlowvoltageandcurrent.Apowerelectronicdevicewithstandshighvoltageandcurrent.

We are concerned with power electronic devices and systems but the knowledge ofsome signal devices may be essential.We will study the basic principles, circuits andapplications.

1.1HistoryofPowerElectronics

AfterWWII,aresearchwasstartedatBellLabsintheUSAtoreplacethermionicvalvesthat were bulky, inefficient and of a short life. Semiconductors such as silicon andgermaniumwereproposed.Aftersmartthinkingandhardwork,semiconductorelectronicssaw light in December 1947. John Bardeen, Walter Brattain and William Shockleyinvented the contact-point transistor as an amplifier. In 1956, they received the NobelPrize in Physics for this breakthrough.A replica of the first transistormanufactured byBellLabsappearsinFig.1.1.Ithastwogoldcontactspressedonahigh-puritygermaniumslab.

The transistor revolutionized the electronics industry, and it gave birth to theinformationtechnologythatweusenowadays.Anothermilestoneis theinventionofthethyristorin1958whichurgedGeneralElectrictoproducecommercialproductsknownasSCRs.TheTRIACandGTOwereintroducedinthe1960’swhereasthepowerMOSFETSandBJTscameoutinthe1970’s.Manyotherdeviceswereinventedandtheprocessisstillgoingon.

1.2ClassificationofPowerElectronics

Thepowerelectronicdevicesmaybeclassifiedintermsoftheirturnon/offcharacteristicsas:

• Uncontrolledturnon/off:anexampleisthediodebecauseitsturnon/offcannotbecontrolled.

• Controlledturnon/off:theBJT,GTO,MOSFETandIGBTcanbeturnedonandoffsimply.

• Controlledturnonanduncontrolledturnoff:theSCRcanbeturnedonviaitsgate

butitcannotbeturnedoffinthesamemanner;someschemesmaybeimplementedfortheturn-offprocess.

Thegaterequirementsofthesedevicesmaybeclassifiedas:

• Continuousgatesignal:BJT,MOSFETandIGBT• Pulsegatesignal:SCRandGTO

Somedeviceswithstandreversevoltageorcurrentpolarityandtheycanbeclassifiedas:

• Unipolarvoltagecapability:BJT,MOSFET,GTO,andIGBT• Bipolarvoltagecapability:SCRandGTO• Unidirectionalcurrentcapability:Diode,SCR,GTO,BJT,MOSFETandIGBT• Bidirectionalcurrentcapability:TRIAC

Fig.1.1Replicaoffirsttransistor.©MarkRichards

1.3Converters

Wewill study different types of circuits which are called converters. A converter is acircuitthatconvertselectricpowerfromoneform(ACorDC)intoanother(ACorDC).Anycourseinpowerelectronicscoversthefollowingconverters:

• UncontrolledRectifiers:usingdiodes,powercanbeconvertedfromfixedACintofixedDC.

• Controlled Rectifiers: using SCRs, power can be converted from fixed AC intovariableDC.

• Inverters:thisisaDC-ACconverterusingSCRs,BJTsorMOSFETS.• Choppers:thisisaDC-DCconverterwhereDCvoltagecanbesteppedupordown.• ACVoltageController: this isanAC-ACconverter.UsingSCRs, thepower flow

canbecontrolledbycontrollingthephaseangleofthevoltagesignal.

1.4Applications

Power electronics have changed the world and there are countless applications. Amicrowaveovenwouldcontainahigh-voltagediode,aTRIACandvoltageregulators;the

automaticwashingmachine, refrigerator andvacuumcleaner alloperatewith theaidofpowerelectronics.

AC motors are controlled by power electronic devices. Electric trains (Fig.1.2) aredriven by such motors with the aid of power electronics and microprocessors. Fig.1.3presents an optimistic application foreseen and invested by PayPal’s cofounder ElonMusk.Thiselectriccaremploysa3-phasesquirrel-cagemotordriveinsteadofaninternalcombustionengine.Themotordriveusesasetofinsulated-gatebipolartransistors(IGBT)whichoperateasarectifierinchargingmodeandasinverterindrivingmode.

Inpowergenerationplants,thefieldsystemofasynchronousgeneratorisregulatedbycontrolled rectifiers using SCRs. Modern power supplies employ many devices.Telephonecompanies require theirpower supplyavailable for itscomputer systemsandtelephone exchanges. Power electronics are utilized to make systems that maintain theflow of electric power to these systems with the aid of Uninterruptible Power Supply(UPS).Nowadays,UPSsystemsareusedinhospitals,moneyexchanges,airports,etc.

Fig.1.2Powerelectronicsareemployedtodrivethistrain.©DubaiMetro

Fig.1.3 TeslaMotors’Model S being charged, amodern electric car. The liquid-cooledpower train consists of a 60kWhLi-ionbattery, squirrel-cagemotorwith copper rotor,drive inverter and a gearbox. The car can be controlled from a touch screen. © TeslaMotorsInc

2

DEVICES2.0Introduction

Thebasicpower electronicdevices are covered in this chapter.Allof thesedevices arestaticswitchesbuttheydifferinhowtheyareturnedonoroff.Theyarealsodifferentintheir maximum power ratings and their speed of operation. These devices aremanufacturedindiscreteormoduleforms.Therearedifferenttypesofpackagesforeachdevice.

2.1PN-JunctionDiode

Thediodeisthebasicsemiconductordeviceusuallymadeofsilicon,andthereareseveraltypes of diodes.The pn-junction diode is themostly used device in power applicationsespeciallyinrectifiers.Itisalsousedinhomeappliances,inautomotives,inmotordrives,inweldingmachines,etc.

Construction:Several power diodes are shown inFig.2.1.They aremanufactured indifferent packages some ofwhich are:DO-41, capsule and stud-mount type.The diodeconsistsoftwoterminals:anode(A)andcathode(K).ThesymbolofthediodeisshowninFig.2.2.Theanodeis thepositiveterminalandthecathodeis thenegativeterminal.Thepolarityheredoesnotnecessarily imply that the anodemust be connected to apositivepolaritypointor the cathode to anegativepoint.Thepolarity is used for indicating theturn-on/offprocess.

Operatingprinciple:Whentheanodeismorepositivethanthecathode,thediodeturnsonandactslikeaclosedswitch(Fig.2.3a).Thediodeturnsoffwhenthecathodeismorepositivethantheanode(Fig.2.3b).Thediodebreaksdownwhenthecathodeisataveryhigherpositivepotentialthantheanode.

Fig.2.1Avarietyofdiodepackages.©MustafaHusain

Fig.2.2Symbolofpn-junctiondiode.

a)Diodeturnsonwhenanodeismorepositivethancathode.

b)Diodeturnsoffwhencathodeismorepositivethananode.

Fig.2.3Diodeswitchingconditions.

TestingwithDigitalMultimeter (DMM):Testingapowerdiodewith aDMMisverysimple. Ithelpsus identify its terminalsandguideus inknowing itsworkingcondition.TestingwiththeDMMisnotalwaysconclusive.Moreaccuratejudgmentcanbemadebybuildingacircuitofadcsourceandalampconnectedinserieswiththediodeinforwardandreverseconnections.

Letusassumewewanttotestadiodeofthe1N54xxseriesthephysicalappearanceofwhichisdrawninFig.2.4.TotestthediodewithaDMM,theDMMmustbeswitchedonandsettothedioderange.Thenthepositiveterminalofthemetermustbeconnectedtotheanode,andthecommonterminaltothecathodeasillustratedinFig.2.5.

TheDMMshouldreadbetween0.5-0.7V.SomeDMMsreadtheresistanceofthediodeinΩ.Ifthepositiveterminalofthemeterwasconnectedtothecathodeandthecommonterminaltotheanode,themeterwouldread1orOL(overload)whichindicatesanopencircuit.

Fig.2.4Physicalappearanceof1N5401diode.

Fig.2.5TestingthediodewithaDMM.

Example1:Basicunderstanding

Arethefollowingsilicondiodesonoroff?Justifyyouranswers.

a)

b)

c)

Solution

a) On because the anode potential ismore positive than the cathode potential by atleast0.7V.

b) Offbecausetheanodepotentialisnotmorepositivethanthecathodepotentialbyatleast0.7V.

c) Offbecausetheanodepotentialisnegative.

Example2:Advancedunderstanding

Describetheturn-onprocessofthediodesD1andD2shownbelowatallintervals0-t2.TheanodepotentialofD1isv1andthatofD2isv2.ThecathodesareconnectedtoaresistorRL.

Solution

Fromtimet=0tot=t1, theanodepotentialofD1 isnegativeand thecathodepotential iszero.Hence,D1isoff.Atthesametime,theanodepotentialofD2ispositiveandsoitison.

From time t= t1 to t= t2,D1 switches on because the potential of its anode rises topositivevalues.Duringthisinterval,D2switchesoffasitsanodegoesthroughanegativepotential.

2.2Thyristors

Onedrawbackof thediodeis itsuncontrolledoperation.Itautomatically turnsonoroffdependingonthepotentialvaluesoftheanodeandcathode.Itisadvantageoustomakeadevicewhichcanbeoperatedatwill;thethyristorwasinventedforthispurpose.

There are different types of thyristors depending on the method of switching: SCR,GTO,IGCTandTRIAC.Likethediode,thethyristorsarewidelyusedespeciallyinmotordrives, electric trains,HVDC,electricheatingcontrol, electricwelding,UPSandsoon.Therearetwomaintypesofapplicationsdependingonthespeedofswitching:

• Phase-controlthyristorsUsedinlow-speedswitchingapplications.Theyoperateatthelinefrequency.

• InverterthyristorsTheyarefast-switchingdeviceswhichareusedinchoppersandinverters.

2.2.0SiliconControlledRectifier(SCR)

TheSCRisthefirstthyristortypetobeinvented.Untiltoday,itistheonlydevicethatcanhandlethehighestpower.

Construction:TwoindustrialSCRsareshowninFig.2.6.Thedatasheetsareattachedin the appendix.TheSCR consists of three terminals: anode (A), cathode (K) and gate(G).TheSCRsymbolisshowninFig.2.7.

Capsulepackage

Stud-mountpackage

Fig.2.6IndustrialSCRs.©PowerexInc

Fig.2.7SymbolofSCR.

Operating principle: The SCR can be turned on when the anode potential is morepositivethanthecathodepotential,andwhenapositivecurrentpulseofshortdurationisinjected into the gate as illustrated in Fig.2.8. Once turned on, it cannot be turned offthrough itsgate. It turnsoffwhen thecathodepotentialbecomesmorepositive than theanodepotential(Fig.2.8b).

a)SCRturnson.

b)SCRisoff

c)SCRisoff

Fig.2.8SCRswitchingconditions

Italsoturnsoffwhenthecurrent(fromanodetocathode)dropsbelowtheholdingcurrent,orwhen thedirectionof thecurrentbecomesnegative (cathode toanode).The thyristordoesnotturnonbyapplyinganegativepulsetothegateeveniftheanodeismorepositivethanthecathode(Fig.2.8c).

TestingwithDMM:TheequivalentcircuitoftheSCRisshowninFig.2.9.Thegate-cathode junction can be tested with the DMM just like testing the diode. When thepositive terminalof theDMMisconnected to thegateand thecommon terminal to thecathode,themeterwillreadaround0.7ViftheSCRisOK.ItwillreadopeniftheSCRisdamaged i.e the gate-cathode junction is damaged.Themeterwill also read open if itsterminalsareconnectedbetweentheanodeandcathode(Fig.2.11).

Fig.2.9DiodeequivalentcircuitofSCR

Fig.2.10Physicalappearanceof2N6397SCR

Fig.2.11IdentificationandtestingtheSCRwiththeDMM

2.2.1GateTurnOff(GTO)

TheGTO thyristor is amodification to the SCR. It is favored over the SCR formanyapplications.

Construction: Italsoconsistsofanode,cathodeandgate.Thesymbolof theGTOis

slightlydifferent(Fig.2.12).Thetwoarrowsshowthebidirectionaloperationofthegate.

Operating principle: Like the SCR, the GTO can be switched on by applying apositive current to the gate.Unlike the SCR, this gate current should be continuous toensurereliableoperationoftheGTO.TheGTOcanbeturnedoffbyapplyinganegativecurrent pulse to the gate. The drawback is that the negative gate current is quite bigcomparedtothetriggeringcurrent.

Fig.2.12SymbolofGTO.

a)GTOturnsonbyapositivepulse.

b)GTOturnsoffbyanegativepulse.

Fig.2.13OperationofGTO.

2.2.2TriodeAC(TRIAC)

TheSCRandGTOareunidirectionalswitchesandsotheywouldpassonlyahalfcycleofasinewave; in thiscase,halfof thepowerwouldbeutilized.Bidirectionalswitchingisnecessary to control the full acwaveform. The TRIAC is a bidirectional switch that isusedinheatingandlightingapplications.LightandfancontrollersemploytheTRIACtocontroltheintensityoflightandthespeedofthefan.

Construction:The TRIAC is a three-terminal device consisting of two anti-parallelSCRs but with a single gate. It is packaged in a single chip. Its terminals are: mainterminal1(MT1),main terminal2(MT2)andgate(G).Thesymbol is twoanti-paralleldiodeswithagate.

Fig.2.142N6073TRIAC.

Fig.2.15SymbolofTRIAC.

Operatingprinciple:Theturn-onprocessisillustratedschematicallyinFig.2.16.IfMT2ismorepositivethanMT1,theTRIACcanbeturnedonbyapplyingapositivegatepulsewithrespecttoMT1.IfMT1ismorepositivethanMT2,theTRIACcanbeturnedonbyapplyinganegativegatepulsewithrespecttoMT1.

a)Positivegatepulse

b)Negativegatepulse

Fig.2.16TRIACswitchingconditions.

2.2.3Light-ActivatedDevices

AphotoSCRistriggeredbyapplyinglightontoitsgate.Hence,ithasonlytwoterminals.The light is often provided by an LED, and the SCR and LED are packaged into onedeviceknownassolidstaterelay(SSR).It isusedinhighpowerapplicationswherethefiringcircuitisoflowpowerandisolatedfromthepowercircuit.Thepowercircuitisofhigh power and the rating of the SCR could be in kW but the rating of the triggeringcircuitcouldbeinmW.

Fig.2.17SymbolofphotoSCR

Fig.2.18AnassortmentofSSR.©MustafaHusain

2.2.4ThyristorFiringandProtectionCircuits

In thyristor circuits, the gate circuit is the control circuit whereas the power circuit isbetween the anode and cathode.The power circuit is at higher voltage than the controlcircuit.Typicalvaluesforpowercircuitsarehigherthan100V,and12to30Vforcontrolcircuits.

Thecontrolcircuitmustbeisolatedfromthepowercircuit.Thiscanbeachievedbythefollowingmethods:

• Opto-coupler:Anopto-coupleroropto-isolatoremploysaninfra-redlightemittingdiode(ILED)whichformstheinputandaphotosemiconductordevicewhichformstheoutput.Apulseappliedtotheinputofthecouplerturnsonthediodewhoselightactivatesthegateofthephotodevice.ThephotodevicecouldbeaBJT,Darlington,SCRorTRIAC.

• Pulsetransformer:Thisisa1:1transformerwithoneprimarywindingandoneormultiplesecondarywindingstobefedtoanumberofdevices.

a)Optocoupler.

b)Pulsetransformer.

Fig.2.19Methodsofpulseisolation.

2.2.5UnijunctionTransistor(UJT)

TheUJTiscommonlyusedtogenerate triggeringpulsesfor theSCRandTRIACbut itmaybeused to triggerotherdevices. It has three terminals: emitterE, baseoneB1 andbasetwoB2.

TheUJTswitchesonwhenanadequatevoltageVEappearsbetweenEandB1.Apulsegenerator or relaxation oscillator employing aUJT is shown in Fig.2.20. The capacitorchargesthroughRuntilitsvoltagereachesapeakvaluethatisenoughtoturnontheUJT.ThisissobecausethecapacitorvoltageisthesameastheE-B1voltage.

WhentheUJTison,thecapacitordischargesthroughRB1untilitsvoltageisnolongerenough to bias the transistor and so theUJT switches off.This process repeats and thevoltageacrossRB1 represents thecharginganddischargingprocessof thecapacitor.ThetriggeringpulsesacrossRB1canbefedintothegateofathyristor.

Fig.2.20PulsegenerationwithUJTcircuit.

2.2.6DiodeAC(DIAC)

TheDIACistwoanti-parallelconnecteddiodesbutassembledinonechip.ItisoftenusedtoprovidetriggeringpulsesfortheTRIACespeciallyinlightdimmercircuits.Unlikethediode, It canconduct inbothdirections and itsbreak-overvoltage,VBO, ismuch higherthantheforwardvoltageofthediode.AtypicalvalueofVBOis30V.Forhighervalueslike250V,theDIACisnameddifferently:SIDAC.

Fig.2.21SymbolofDIAC.

2.2.7ProtectionAgainstdi/dtanddv/dt

TheSCRmaybedamagedifitscurrentrisestooquickly(di/dt)orifthevoltageacrossitbuildsup tohighvalues in a shortperiodof time (dv/dt).TheSCRhas tobeprotectedagainsthighdi/dtratesbyincorporatinganinductorinserieswiththedevice,andanRCcircuitisconnectedacrossthedevicefordv/dtprotection(Fig.2.22).TheRCcircuithereiscalledasnubber.

Fig.2.22Snubbercircuitforprotectionagainstdi/dtanddv/dt.

2.3BipolarJunctionTransistors(BJT)

TheBJTtransistorswitchesonandofffasterthantheSCRandthustheyareusedinhighfrequencyapplicationsashighas50kHzbuttheirpowercapabilityislowerthantheSCR.TheBJTisacurrent-controlleddevicethatcomesintwotypes:NPNandPNP.TheNPNtransistorismostlyusedinpowerelectronicapplicationsandsoitwillbestudiedhere.

2.3.0NPNTransistor

Ithasthreeterminals:base(B),collector(C)andemitter(E).

Fig.2.23SymbolofNPNtransistor.

Operatingprinciple:ThetransistorcanbeturnedoffwhenthebasecurrentIBiszeroorwhenitisnotsufficient.ItturnsonwhenIBissufficientlylargedependingonthevalueofthecollectorcurrentIC.

Thebaseshouldbeatahigherpositivepotentialthantheemitter.Whenthetransistorison,thereisavoltagedropacrossitdefinedasVCE.Thisvoltagedropispractically1-2Vforpowertransistors.Theflowofthecollectorcurrentandtheoccurrenceofthevoltagedropresultsinlossesintheformofheat.

• VCEO:Themaximumallowablecollector-to-emittervoltagewhenthebaseterminalisleftopencircuit.

• hFE(min)@IC:Itisthedccurrentgainanditisdefinedastheratioofdccollectorcurrenttodcbasecurrentatthestatedcollectorcurrentor:

ThevalueofhFE increasesas temperature increases,and it increasesascollectorcurrentincreases.Thetransistorturnsonwhen

2.3.1DarlingtonTransistor

ItiscommonlyappliedtodriverelaysandsolenoidswhereitreceivespulsesfromaPLC,a microprocessor or logic circuits. In such applications, it is favored over the discretetransistorbecauseitneedslowerbasecurrenttoturnonanditcanhandlehigherpower.

Construction:ADarlingtontransistorismadeupoftwoBJTtransistorsconnectedasdepicted inFig.2.24.Thepaircomes fabricated inonepackagebutaDarlingtoncanbeformedbytwodiscretetransistors.ThepurposeoftheDarlingtonconfigurationistohavehighergainandhigherpower.

Fig.2.24SymbolofDarlingtontransistor.

2.4MOSFET

TheMetalOxideSemiconductorFieldEffectTransistor(MOSFET)isavoltage-controlledtransistor.ItisasolutiontothebreakdownphenomenonthatisoftenexperiencedwiththeBJT. It isveryfastandhence it is incorporated inapplicationsrequiringhighfrequency(upto1MHz)andlowpower(uptoafewkW’s)suchasinvertersandchoppers.

Construction:There are two types according to the direction of currents:N-channelandP-channel.Itconsistsofagate(G),drain(D)andsource(S)andthesymbolofanN-channelMOSFETisshowninFig.2.25.

Fig.2.25SymbolofMOSFET.

Operatingprinciple:Thetransistorcanbebiasedbyapositivevoltagebetweenthegateand source (VGS).Current flows from thedrain to the source and so a voltagedropVDSdevelopsacrossthedevice.Thetransistorisnowswitchedon,anditcanbeswitchedoffbyremovingthegatesignal.

2.5InsulatedGateBipolarTransistor(IGBT)

TheBJTcaneasilybreakdownduetotheconnectedjunctionsinitsstructure.TheIGBTconsists of a gate similar to that of the MOSFET. The insulated gate makes it less

vulnerable to the secondary breakdownphenomenon common to theBJT.The IGBT isvoltage-controlled.ItisfasterthantheBJTbutslowerthantheMOSFETbutithashighercurrentdensitiesthanpowerMOSFETs.Therefore,theyaremorecost-effectiveinmanyhighpower,moderatefrequencyapplications.

Fig.2.26SymbolofIGBT.

3

DIODERECTIFIERS3.0Introduction

ArectifierconvertsfixedACvoltageintofixedDCvoltage.Thisisknownasuncontrolledrectification because the output DC voltage cannot be varied. There are severalconfigurationsof diode rectifiers.Most rectifier circuits are used asDCpower suppliesandthustheyemploystep-downtransformers.TheyarealsoappliedfortheoperationofDCmotors.


Thisrectifierconsistsofasinglediodeanditisthesimplesttypeofrectifiers.Acommonapplicationis thehighvoltagecircuitforamicrowaveovenwhichappearsinFig.3.1.Itconsists of a single diode, a capacitor, a transformer and amagnetron.The transformersteps up the mains voltage to around 3 kV and the diode converts it into DC. Themagnetronemitsmicrowaveenergythatheatsupfood.

Fig.3.1HVcircuitofmicrowaveoven.Caution:Around3kVisproducedbytheHVtransformer.Onlyqualifiedtechnicianscancheckthecircuit.©MustafaHusain.

Asingle-phase,half-wavedioderectifiercircuitisshowninFig.3.2a.Theacsignalisfirststepped down fromVP toVin, rectified by the diode and then applied across a purelyresistiveload.Duringthepositivecycleofvin(Fig.3.2b),thediodeconductsandbecomesan ideal switchbecause its anode ismorepositive than thecathode. Ideally, thevoltagedrop across the diode is zero but practically there is a voltage dropof around0.7V forsilicondiodes.Theloadvoltageandcurrentareinphase.Duringthenegativecycleofvin(Fig.3.2c),theanodebecomeslesspositivethanthecathodeandthusthediodeturnsoff

andactslikeanopenswitch.Therefore,thevoltageacrossthediodeisequaltothatofvin.Theloadvoltageandcurrentarezero.TheoutputvoltagewaveformisshowninFig.3.2dwhere it ismadeupof thepositivewaveof the inputvoltage.Theaveragevalueof theoutputvoltageis


Acombinationof four diodes is formed tomake a single-phase, full-waveuncontrolledrectifier.ThecircuitisshowninFig.3.3a.Thisconfigurationiscommonlyappliedintheindustry.

a)Circuit

b)D1on

c)D1off

d)Inputandoutputwaveforms

Fig.3.2Half-waveuncontrolledrectifier.

a)Circuit

b)D1andD2on

c)D3andD4on

d)Inputandoutputwaveforms

Fig.3.3Full-waveuncontrolledrectifier

During the positive cycle of vin, the anode ofD1 is positive and the cathode ofD2 isnegative,andthesourcecurrentflowsfromthesupplytotheloadthroughD1andbacktothesupplythroughD2.

During thenegative cycleofvin, the anodeofD3 is positive and the cathode ofD4 isnegative,andthesourcecurrentflowsfromthesupplytotheloadthroughD3andbacktothesupplythroughD4.Thedirectionofthesourcecurrent(ac)reverseseveryhalfacycle,buttheloadcurrentisunidirectional.

Theloadcurrent(dc)isinphasewiththeloadvoltagebecausetheloadisresistive.ThecorrespondingwaveformsareshowninFig.3d.Theaveragevalueoftheoutputvoltageis:

Filtering

The rectifier arrangements discussed above lack a vital stage which is filtering. TherectifiedwaveformsshowninFig.3.2dandFig.3.3darenotpureDC.For instance, theywouldcauseamotortovibrateandthusnoiseisproduced.Itisfavoredtohaveastraightline.

Usually,acapacitorisconnectedacrosstheoutputoftherectifierinordertoobtainassmoothDCvoltageaspossible.TheeffectofthecapacitorisillustratedinFig.3.4whereabridgerectifierisused.

The potential signal at point 1 is a pure sinewave. The potential at point 2 is a fullwave.Duringtherisingsegmentofthiswave,thecapacitorcharges.Asthewavetendstodecrease,thecapacitordischargesuntilanothercycleappearswhereitchargesagain.Thecharging time is slower than the discharging time and so a smooth output voltage isproduced.

With filtering, the output voltage increases beyond the values defined by Eq.3.1 andEq.3.2anduptothepeakoftheinputvoltage.

Fig.3.4Filteringofrectifiedwaveform

4

THYRISTORRECTIFIERS4.0Introduction

Like the diode, the SCR can be used to rectify an AC signal. Unlike the diode, theconduction of an SCR can be controlled through its gate by external circuitry. This isknownascontrolledrectificationbecausetheoutputDCvoltagecanbevariedbyvaryingthetriggeringtime(orangle)oftheSCR.


Asingle-phase,half-wavecontrolledrectifiercircuitisdrawninFig.4.1a.TheacsignalisfirststeppeddownfromVPtoVin, rectifiedbytheSCRandthenappliedacrossapurelyresistiveload.

Duringthepositivecycleofvin(Fig.4.1b),theanodeismorepositivethanthecathode.The thyristor conducts and acts as a closed switchwhen a positive voltage pulse vG isappliedtoitsgateatanangleα.

During the negative cycle of vin (Fig.4.1c), the anode becomes less positive than thecathodeandthustheSCRturnsoffandactslikeanopenswitch.Theturn-offprocessofthethyristorhereiscallednaturallinecommutation.ApplyingapositivepulsecannotturnontheSCRnow.

ThevoltageandcurrentwaveformsareshowninFig.4.1dwheretheoutputvoltageismadeupofthepositivewaveoftheinputvoltage.ThefiringoftheSCRisrepeatedafteronecyclewhichisanangleof360o.Theaveragevalueoftheloadvoltageis

Atableshowingthevaluesoftheoutputvoltagebasedondifferentfiringanglesishelpfultounderstand this rectifier.Theoutputvoltage ishighatvery low firingangles.As thefiringangleisincreased,theoutputvoltagedecreases.

Table4.1

α Vout Remarks

0 0.225(1+1)Vin=0.45Vin Justlikeanuncontrolledrectifier.

60o 0.225(1+0.5)Vin=0.3375Vin Theoutputvoltageis33.75%oftheinputvoltage

90o 0.225(1+0)Vin=0.225Vin Theoutputvoltageis22.5%oftheinputvoltage

120o 0.225(1-0.5)Vin=0.1125Vin Theoutputvoltageis11.25%oftheinputvoltage

180o 0.225(1-1)Vin=0 Theoutputvoltagevanishes

a)Circuit

b)Operatingmodes.

c)Inputandoutputwaveforms.

Fig.4.1Single-phase,half-wavecontrolledrectifier.

PracticalCircuit:Asimplepracticalcircuittodemonstratetheoperationofahalf-wavecontrolled rectifier canbe constructed frombasic components (Fig.4.2).TheRCcircuitproducesthefiringangleαwhichcanbevariedbyvaryingtheresistanceR,anditcanbedeterminedfrom:

where f is the frequency of the input voltage. The diode allows only positive pulsesthroughthegateoftheSCR.ADCfilterisnotincludedinthecircuitbutitcanbeadded.

Fig.4.2Practicalcircuitforrealizinghalf-wavecontrolledrectifier.


Acombinationof four thyristors is formed tomakea single-phase, full-wavecontrolledrectifier.ThecircuitisshowninFig.4.3aandthecorrespondingwaveformsareshowninFig.4.3d.

During the positive cycle of vin, the anode ofT1 is positive and the cathode ofT2 isnegative.TriggeringbothSCRsatanangleαallowsthesourcecurrenttoflowfromthesupplytotheloadthroughT1andbacktothesupplythroughT2.

During the negative cycle of vin,T1 andT2 turn off naturally and thewhole negativewaveformappearsacrossthem.NowT3andT4canbefiredatanangleα+πbecausetheanodeofT3ispositiveandthecathodeofT4isnegative.Consequently,thesourcecurrentflowsfromthesupplytotheloadthroughT3andbacktothesupplythroughT4.T3andT4turn off naturally during the positive cycle and the whole positive waveform appearsacrossthem.

Thedirectionofthesourcecurrent(AC)reverseseveryhalfacycle,buttheloadcurrentisunidirectional.Theloadcurrent(DC)isinphasewiththeloadvoltagebecausetheloadis resistive. The firing of two SCRs together is repeated after an angle of 180o. Theaveragevalueoftheloadvoltageis

a)Circuit

b)T1andT2on

c)T3andT4on

d)Inputandoutputwaveforms.

Fig.4.3Single-phase,full-wavecontrolledrectifier.

5

INVERTERS5.0Introduction

An inverter is a DC-to-AC converter that converts a fixed DC voltage into fixed orvariable AC voltage. The frequency of the output voltage can also be varied. Thewaveform of the output voltage should be ideally sinusoidal. Practically, low- andmedium-power invertersproduce squareorquasi-squareoutputwaveforms.High-powerinvertersaredesignedtoproducesinusoidalvoltageorcurrentwaveforms.

The inverter simply consists of semiconductor switches likeMOSFETs,BJTs, IGBTsandGTOs.Thesearefavoredforlow-andmedium-powerapplicationsbecausetheycanbe turnedonandoffwithout theneed for external circuitry for commutation.Forhigh-powerapplications,theSCRisusedbecauseitwithstandshighvoltageandcurrentbutithasthedrawbackthatitneedstheturn-offcircuitry.

Inverters are classified as single-phase and three-phase, and as half-bridge and full-bridge inverters. They are also classified according to themethod bywhich the outputvoltagecanbecontrolled.

5.1ApplicationsOfInverters

TheusageofinvertersistoprovideACpowertoloadswhennoalternatorisavailablebutaDCsourceisavailable.DieselgeneratorsareusedtoobtainACpowerbutinvertersarecheaper,quieterandmaintenancefree.Theinverterfindsmanyapplications.ItcanconverttheDCvoltageofsolarcellsintoACandhenceitispossibletoconvertthesolarenergyintoelectricalenergywhichweneedinourhomesforlighting,airconditioningandsoon.Ifyouarehavingapicnicsomewherebythebeach,youcanuseaninvertertoconverttheDCpowerofasparecarbattery intoACpowerwhichyoumayneedforaTV, lightingandafan.

5.2Half-BridgeInverter

Thisinverterisfedwithabatteryasinput,anditconsistsoftwosemiconductorswitches.AtypicalcircuitisshowninFig.5.1a.Adiodeisconnectedinparallelacrosseachswitch.The diodes protect the switches against voltage spikeswhen they are off.The switchescouldbeBJT,SCR,MOSFET,etc.Inpowerapplications,capacitorswithverylargeandequalfaradsareemployedtoprovidedcblockingthroughtheloadsothattheloadcurrentdoes not have any dc component. The capacitors also overcome the problem oftransformer saturation from the primary side if a transformer is used at the output toprovideisolation.

LetusstudytheoperationofthecircuitinFig.5.1a.Oneswitchisturnedonatatime.LettheperiodoftheoutputsignalbeT,andletusassumeeachswitchconductsforT/2.WhenS1 is on andS2 off, current flows from the positive terminal of the battery toS1,throughtheloadandC2andthenbacktothebatteryviathenegativeterminalasshownin

Fig.5.1b.Halfofthebatteryvoltageappearsacrosstheload(+Vin/2).

WhenS2isonandS1off,currentflowsfromthepositiveterminalofthebatterytoC1,throughtheloadandS2andthenbacktothebatteryviathenegativeterminal(Fig.5.1c).Again,halfofthebatteryvoltageappearsacrosstheload(-Vin/2).ThewaveformisshowninFig.5.1dforaresistiveloadwherethebatteryvoltageisconstantbuttheoutputvoltageisasquarewavethatvariesbetween+Vin/2and-Vin/2.Theloadcurrentissinusoidal.

a)Circuit

b)S1onc)S2on

d)Outputwaveform.

Fig.5.1Circuitandoperationofhalf-bridgeinverter.

Thermsoutputvoltageis

5.3BridgeInverter

A single-phase, full-bridge inverter employs four semiconductor switches. A bridgeinverterwith four IGBT’s forphotovoltaicapplications is shown inFig.5.2 followedbythe power circuit. The control circuit is not included. The control circuit provides thecontrolsignalsandthesecanbeproducedbyelectronicormicrocontrollercircuits.

Theoperationofthecircuitisverysimple.Onlytwoswitchesareturnedonatatime.WhenS1andS2areturnedon,thecurrentflowsfromthepositiveterminalofthebatterytotheloadviaS1andbacktothebatteryviaS2(Fig.5.4a).

Fig.5.2Bridgeinvertermodule.©PowerexInc.

Fig.5.3Bridgeinvertercircuit.

AfteratimeT/2,S1andS2areturnedoffandS3andS4are turnedon.Thecurrent flowsfrom the positive terminal of the battery to S3, through the load and then back to thebatteryviaS4(Fig.5.4b).Thefullbatteryvoltageappearsacrosstheload(-Vin).

Thewaveform is shown inFig.5.4c for a resistive loadwhere theoutputvoltage is asquarewavethatvariesbetween+Vinand-Vin.Thermsoutputvoltageis

a)S1andS2onb)

S3andS4on

c)Outputwaveform.

Fig.5.4Operationofbridgeinverter.

5.4UninterruptiblePowerSupply(UPS)

TheUPSisusedinhospitals,airports,telephonecompaniesandcommercialmallstoactas a stand by supply when the utility power is interrupted. Control centers at powerstations use UPS for their computer systems and basic lighting. Hospitals need it forlighting and the operations ofmedical equipment especially in intensive care units andoperations theatres. Commercial malls need UPS systems for lighting, lifts and otherimportant equipment.The applicationsofUPSareversatile andnumerous.Theyplay abig role in our life. The block diagram of a basic UPS system is shown in Fig.5.5. Itconsistsofthreemainblocks:

• Chargingsystem:arectifierthatchargesabankofbatteryoftenconnectedinseriesandparallelinordertohavebiggercurrentandvoltage.

• Battery:itprovidesthepowerwhenutilitypowerisinterrupted• Inverter: itconverts theDCvoltageof thebattery intoACduringpoweroutages.

Theinverterincorporatesalotoffilteringcircuitssothatsinusoidalacvoltagecanbeobtainedattheoutput.

• TheUPShastwoinputs:acinputwhichisthepowerline,anddcinputwhichisthebattery.Theoutputisacvoltagethatisfedtotheload.TheUPScanbesingle-phaseorthree-phase.

Fig.5.5BlockdiagramofUPSsystem

6

CHOPPERS6.0Introduction

Choppers are DC-DC converters that convert a fixed DC voltage into a variable DCvoltage.TheyarewidelyappliedintheindustrytocontrolthespeedofDCmotors.Theyare called choppers because they chop the input DC signal on and off. They are alsoemployed inDC regulators that convert an unregulatedDC supply into a regulatedDCsupply;theyareknownasswitching-moderegulators.

6.1Step-DownChopper

ItisalsoknownasabuckchopperandanindustrialproductisshowninFig.6.1followedbythepowercircuit.TheswitchmaybeatransistororSCR.

Operatingprinciple:Therearetwomodesofoperationoftheswitch.Whentheswitchturnsonforton,theinductivefilterstoresmagneticenergyanditscurrent,iL,rises.Whentheswitchisturnedoff,thestoredenergyintheinductorisreleasedtothecapacitorandload and the output current continues to flow. It is observed in Fig.6.3c that the inputvoltageischoppedandthat theoutputcurrent isDC.ThebuckchopperstepsdownDCvoltage.

Fig.6.1Step-downchopper.©PowerexInc

Fig.6.2Buckchopper.

Theaverageoutputvoltagecanbedeterminedfrom:

wherekisthedutycycledefinedastheratiooftheturn-ontimetontotheperiodT.

wheref istheswitchingfrequencyofthesemiconductorswitchwhichistypicallyabove20kHz.

a)Switchison.

b)Switchisoff.

c)Outputwaveform.

Fig.6.3Operatingmodesofstep-downchopper.

6.2Step-UpChopper

It is also known as a step-up chopper and its circuit is depicted in Fig.6.4a. The boostchopperstepsupDCvoltage.Theaverageoutputvoltagecanbedeterminedfrom:

a)Circuit

b)Switchison

c)Switchisoff

Fig.6.4Step-upchopper

6.3StepUp/DownChopper

Insomeapplications,itisrequiredtostepupandstepdowndcvoltage.Aconfigurationwas developed which integrates the operation of buck and boost choppers into one

chopper knownas buck-boost or stepup-downchopper.This configuration is shown inFig.6.5a.

This chopper steps up or downdc voltage depending on the duty cycle k.The averageoutputvoltageisdeterminedfrom:

a)Circuit.

b)Switchison.

c)Switchisoff.

Fig.6.5Stepup/downchopper.

7

SINGLE-PHASEVOLTAGEREGULATORS7.0Introduction

ACvoltagecontrollersarewidelyappliedinindustrialheating,speedcontrolofinductionmotors, transformer tap-changing and light control (dimmers). Two SCRs connectedinversely in parallel form a voltage controller. Hence, a TRIAC can also function as avoltagecontroller.However,theTRIACisusedforlower-powerapplicationswhereasthetwoSCRscanhandlehighervoltageandcurrentthantheTRIAC.

The power consumed by the load is controlled by two back-to-back SCRs (Fig.7.1).TherearetwomethodsofcontrollingtheSCRs:phase-anglecontrolandon-offcontrol.

7.1Phase-AngleControl

S1 istriggeredatanangleαduringthepositivecycleofvinwhereasS2 is triggeredatanangleπ+αduringthenegativecycle.ThewaveformsareshowninFig.7.2.Decreasingtheangleαincreasesthepowerdeliveredtothesource,andviceversa.ItispossibletoreplacetheSCRswithoneTRIACifitmeetsthepowerrequirement.Thisloadisoftenalamporafanmotorandthecircuitiscalledadimmercircuit.

Fig.7.1Single-phasevoltagecontroller

Fig.7.2Phase-anglecontrolmethod

7.2On-OffControl

This is also referred to as integral half-cycle controlmethod, and it employs the samecircuitofFig.7.1.Thethyristors(orTRIAC)aretriggeredatthezerocrossingsoftheACinputvoltage.Theinputsignalispassedontotheloadforanumberofintegralhalf-cyclesm,anditisinterruptedforanumberofintegralhalfcyclesn.Thepowersuppliedtotheloadcanbecontrolledbycontrollingtheratiom/n.ThewaveformsareshowninFig.7.3foraratioof2/5.Thermsoutputvoltageisexpressedas:

whereVinistheACinputvoltageandkisthedutycycle.FromthisequationwefindfortheoutputwaveforminFig.7.3that63%oftheinputpowerissuppliedtotheload.Ifitisdesiredtoraisetheoutputvoltage,thenumberofoncyclesmustbeincreased.

Fig.7.3On-offcontrolmethod

7.3CommercialApplication

Fanregulatorsandlightdimmersaregoodapplicationsofthephase-anglecontrolmethod.Insteadoftwoanti-parallelSCRs,aTRIACisemployed.

Atypicalcircuit forafanregulator isdrawninFig.7.4andanactualoneisdisplayedthereafter. The ac filter is not included in the circuit diagram. The DIAC provides thepulsesduringbothhalfcyclesandtheRCcircuitdecidesthefiringangleaccordingtothevalueofthevariableresistor.

Fig.7.4Basicfanregulatorcircuit

Fig.7.5Commercialfanregulator

8

UNDERSTANDINGDATASHEETS8.0Introduction

Every electrical or electronic component, appliance, machine or system has voltage,currentandpowerratings.Powerelectronicdevicesarebasicallysolid-stateswitchesmostofwhichhavetworatings.Oneratingisforthecontrolsignal,andanotherforthepowercircuit.For instance, theSCRhasa rating for thegate signalandanother rating for thevoltage across and current through the anode-cathode junction.The diode has only oneratingbecauseitisanuncontrolleddevice.

Wewillstudyhowtoselectthebestdeviceforacertainapplicationbyunderstandingitsdata sheet.Adevicedata sheet ispublishedby thedevicemanufacturer, and it containsdetailedinformationaboutthedevicesuchasitsrating,graphs,applications,etc.Wehavealready studied the operation and characteristics of each device theoretically andpractically, and so interpreting the informationcontained in adata sheet shouldbe easynow.

8.1TheDiode

Thedioderatingislimitedbythefollowingratings:

• Peak Inverse Voltage (PIV) or Peak Repetitive Reverse Voltage (VRRM): Themaximum value of the voltage the diode can withstand without being damagedwhenthediodeisreversebiasedi.e.whenthecathodeispositiveandtheanodeisnegative.

• Forward Voltage (VF): The maximum voltage drop that occurs acorss the diodewhenthediodeisON.

• ForwardCurrent(IF):TheratedaverageorRMSvalueofcurrentthatthediodecanwithstandwhenitison.

8.2TheThyristor

The thyristor heremeans either anSCRor aTRIAC.Both devices share the followingdefinitions.

• PeakRepetitiveoff-StateForwardVoltage(VDRM)andReverseVoltage(VRRM):Itisthemaximumvalueofthevoltageacrossthedevicewhenthedeviceisoffi.e.whenno gate pulse applied. The device will remain off and undamaged unless thesevaluesareexceeded.Forwardmeanswhentheanode(orMT2) ispositiveandthecathode(orMT1)isnegative.Reversemeanswhentheanode(orMT2)isnegativeandthecathode(orMT1)ispositive.

• PeakForwardandReverseBlockingCurrent (IDRM&IRRM):This is themaximumvalueof current thedevice canblockwhenVDRMorVRRM is appliedbetween the

anode and cathode (or MT2 and MT1) with the gate left open. These values ofcurrent are very small leakage currents that flow through the device but do notmeanthedeviceisON.Typicalvaluesareinmicroamperes(µA).

• PeakOn-StateVoltage(VTM):ItisthevoltagedropacrossthedevicewhenitisON.• On-StateCurrent(ITM):ItistheRMScurrentthatflowsthroughthedevicewhenit

ison.Often,theaveragevalueofcurrentisalsogiven.ThevaluesITMandVDRMandVRRMarethecurrentandvoltageratingsofthethyristor.Anytechnicianorengineerlookingforathyristorshouldaskaboutthesevaluesfirst.Infact,thesevaluesareshownexplicitlyatthestartofadatasheet.

• HoldingCurrent(IH):WhenthecurrentflowingthroughtheSCRbetweentheanodeandcathodedropsbelowtheholdingcurrent,theSCRturnsoff.ThiscurrentisalsodefinedfortheTRIACbetweenMT2andMT1.

• GateTriggerCurrent:Itisthegatecurrentthatturnsonthethyristor.Itsmimimumandmaximumvaluesaregiveninthedatasheet,andthemaximumvaluemustnotbeexceeded.

• GateTriggerVoltage: It is thevoltageappliedbetween thegateandcathodewiththe cathode being the reference. The minimum value is often 0.7V, and themaximumvaluemustnotbeexceeded.

8.3TheBJT

Inpowerelectronics,theBJTisusedasaswitch.Supposewewanttoselectatransistortoswitcha12V,2AincandescentlamponandoffasdepictedinFig.8.1.WhentheswitchSis open (no base current), the transistor is OFF and so the full supply voltage of 12Vappearsacrossthetransistor.

Weshouldselectatransistorthatwithstandsthesupplyvoltage.ThevoltageacrossthecollectorandemitterwhenthetransistorisOFFisdesignatedVCEO.Therefore,weneedtolookforatransistorwithVCEO>12V.Whentheswitchisclosed,thetransistorturnsONwhenenoughbasecurrentflows.Then,thelampturnsonanditscurrentisthecollectorcurrentIc.TheresistorRshouldbecalculatedsothatonlyenoughbasecurrentflows.

Moreover,weshouldselectatransistorwithIcratingofmorethan2A.Avoltagedropoccursbetweenthecollectorandemitterdueto theflowof thecollectorcurrent,andsothetransistorheatsup.ThevoltagedropisdesignatedVCE(sat)anditshouldbesmallsothatalmostallofthesupplyvoltageappearsacrossthelampwhichmeansfulllampintensity.Becausetheswitchingspeedhereisnotcritical,wecanignoretheturn-ontimeandturn-offtime.

Fig.8.1NPNtransistorasaswitch.

Weshouldselectatransistorthatisalittleoverratedthan12Vand2A.Agoodchoicemaybeselectinga15V,3Atransistor.

8.4TheMOSFET

The MOSFET is mostly used in high-frequency applications due to its fast switchingcapability.However, letus again supposewewant touse it as a switch for the lamp inFig.8.2.WeshouldselectaMOSFETwiththefollowingratings:

• GatetosourcevoltageVGS>12V• DraincurrentID>2A

8.5TheIGBT

TheIGBTcanbeselectedjustlikeselectingtheBJTexceptthattheIGBThasavoltage-controlledgateinsteadofacurrent-controlledbasefortheBJT.SupposetheIGBTistobeusedinsteadoftheBJTofFig.8.1,thenweshouldselect15V,3AIGBTwithgatevoltagecapabilityVGEof15V.

Fig.8.2MOSFETasaswitch.

PARTII

EXPERIMENTS

EXPERIMENT1

TESTINGOFPOWERELECTRONICDEVICES1.0Objectives

• To learn how to test power electronic devices with a digital multimeter, and byusingalampandadcvoltagesupply

1.1Equipment

Serial Component/apparatus Quantity

1 Breadboard 1

2 Powerresistor470Ω,17W 1

3 DMM 2

4 12Vlamp 1

5 1N5401diode 1

6 2N6397SCR 1

7 2N6073TRIAC 1

8 2N3055NPNtransistor 1

9 IRL3303N-typeMOSFET 1

10 BUP400IGBT 1

11 30VD.C.powersupply 1

1.2Discussion

MostofpowersemiconductordevicescanbetestedoutofcircuitwithaDMM.Thepn-junctionsilicondiodeisthebasisforunderstandingandapplyingDMMtesting.Mostofthese devices have diode equivalent circuits. Therefore, the diode will be used fordemonstrationpurposes.

There are twoways to test the diodewith theDMM.The simplestway is to set theDMM to the diodemode.Here, theDMM supplies a constant current of 20mA if thediodeisconnectedlikethedemonstrationpresentedinFig.1.1.

AnotherwayistosettheDMMtotheohmrangeasdemonstratedinFig.1.2.Whenthediode is forwardbiased, theohmmetermeasures thediodeon-stateresistance. If reversebiased,ahealthydiodemustexhibitanopencircuit.

Fig.1.1Diodetesting

Fig.1.2Ohmtesting

Testingwith theDMM is not always conclusive and itmay lead to incorrect judgmentwhetherthedeviceisdefectiveornot.Asanalternative,alampandadcsourceshouldbeusedtocheckthecorrectoperationalconditionofthedevice.Inthisexercise,youwilltestavarietyofdevices.

1.3TestingofSemiconductorSwitches

1.3.1Diode

1N5401 silicon diodewill be used. Its fundamental ratings are listed inTable 1. Thesevaluesmustnotbeexceeded.Thediodewillbe testedwith theDMM,andforwardandreverse operation will be conducted for more reliable judgment on its operationalcondition.

Table1.1

Maximumrectifiedcurrent 3A

Maximumreversevoltage 100V

Procedure

1. Set the DMM to the diode range. Test the diode with the DMM and record theresultsinTable1.2.

2. Withthepowersupplyoffandthevoltageknobtotheminimumsetting,connectthecircuitofFig.1.3.

3. Turnonthepowersupplyandsetthevoltageto12Vdc.4. Measurethevoltageacrossthesupply,diodeandlamp.Recordyourmeasurements

inTable1.3.5. MeasurethelampcurrentandrecordthereadinginTable1.3.Switchoffthepower

supply.6. ReversetheconnectionofthediodeasillustratedinFig.1.4.7. Turnonthesupply.Repeatsteps4-6.YoumayneedtosettheammeterrangetoµA.

RecordyourreadingsinTable1.3.8. Writedownaconclusionexplainingwhatyouhavelearned.

Table1.2

DMMreadingacrossanode-cathode

DMMreadingacrosscathode-anode

Table1.3 Forward(Fig.1.3) Reverse(Fig.1.4)

Voltageacrosssupply,Vin

Voltagedropacrossdiode,VAK

Voltagedropacrosslamp,Vout

Lampcurrent,IAK

Fig.1.3Circuitfortestingdiodeinforwardstate.

Fig.1.4Circuitfortestingdiodeinreversestate

1.3.2SCR

2N6397SCRwillbetestedinforwardandreversestates.ThevoltageandcurrentratingsareincludedinTable1.4.

Table1.4

Maximumrmson-statecurrent 12A

Maximumforward/reverseblockingvoltage 400V

Maximumgatetriggervoltage 1.5V

Maximumgatetriggercurrent 30mA

Typicalholdingcurrent 6mA

Procedure

1. TesttheSCRwiththeDMMandrecordtheresultsinTable1.5.

Table1.5

DMMreadingacrossgate-cathode

DMMreadingacrosscathode-gate

DMMreadingacrossgate-anode

DMMreadingacrosscathode-gate

DMMreadingacrossanode-cathode

DMMreadingacrosscathode-anode

2. Keepingthepowersupplyoffandthevoltageknobtotheminimumsetting,connectthecircuitofFig.1.5.

3. Turnonthepowersupplyandsetthevoltageto12Vdc.

Fig.1.5CircuitfortestingSCRinforwardstate.

4. Measurethevoltageacrossthesupply,SCRandlamp.RecordyourmeasurementsinTable1.6.

5. VerifyKirchoff’svoltagelawbycomparingthesupplyvoltagewiththesumofthevoltageacrossthelampandthevoltageacrosstheSCR.

6. Switch off the power supply. Make proper arrangements to measure the lampcurrentandthegatecurrentsimultaneously.

Table1.6

Operatingmodes Forward(Fig.1.5) Reverse(Fig.1.6)

Voltageacrosssupply,Vin

VoltagedropacrossSCR,VAK

Voltagedropacrosslamp,Vout

Lampcurrentwithgateresistorconnected

Lampcurrentwithgateresistorremoved

SCRgatecurrent

7. Turnon thesupplyandobserve theDMMreadings.Record thereadings inTable1.6.

8. Keeping the supply on and the DMMs connected as ammeters, remove the gateresistor.ObservetheDMMreadings.RecordthereadingsinTable1.6.

9. Switchoffthepowersupply.10. ReversetheconnectionoftheSCR(Fig.1.6).

Fig.1.6CircuitfortestingSCRinreversecondition

11. Turnonthesupply.Repeatsteps4-6.RecordthereadingsinTable1.6.12. Writeaconclusionexplainingbrieflywhatyouhavelearned.

EXPERIMENT2

CHARACTERISTICSOFPN-JUNCTIONDIODE2.0Objectives

• TostudyandplottheV-Icharacteristicsofthediode

2.1Equipment


1 Breadboard 1

2 12Vlamp,20W 1

3 DMM 2

4 1N5401diode 1

5 30VD.C.powersupply 1

2.2Discussion

If the relationship between the voltage across and the current through the pn-junctiondiode is obtained, the behavior and operation of the diode can be explored. Moreinformationaboutelectricalquantitiescanbegatheredsuchastheratedvoltage,current,powerandresistance.

This experiment will allow you to observe and record the behavior of the currentthroughthediodewhenthevoltageacrossitsterminalsisvariedduringtwostates:whenthediodeisforwardbiasedandwhenitisreversebiased.

2.3Experiment

2.3.0ForwardBias

Procedure

1. Turnonthepowersupplyandsettheoutputto0V.Switchoffthesupply.2. ConnectthecircuitofFig.2.1.SettheammetertothemArange.

Fig.2.1Forward-biaseddiode

3. Turn on the supply. Vary the output of the supply so that the voltage across thediodeVAKis0.1V.

4. MeasureandrecordthecurrentinTable2.1.5. Repeatstep4byincreasingVAKinstepsof0.1Vuntil1V.Recordthecorresponding

valuesofIAK.6. Resettheoutputofthesupplyto0V.Switchoffthesupply.7. For each row inTable2.1, calculate the ratioVAK / IAK andput the results in the

table.

Table2.1

VAK(V) IAK(mA) VAK/IAK

0

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

2.3.1ReverseBias

1. UsingthesamecircuitofFig.2.1,reversetheconnectionsofthediodeasillustratedinFig.2.2.

2. Set the ammeter range toµA.Turnon thepower supply.Gradually increaseVAK

according to thevalues listed inTable2.2.Measureandrecord thecorrespondingvaluesofIAK.

3. CalculatetheratioVAK/IAKandputtheresultsintheTable2.2.

Fig.2.2Reverse-biaseddiode

Table2.2

VAK(V) IAK(µA) VAK/IAK

0

-1.00

-2.00

-3.00

-4.00

-5.00

-6.00

-7.00

-8.00

-9.00

-10.00

-11.00

-12.00

-13.00

-14.00

-15.00

-16.00

-17.00

-18.00

-19.00

-20.00

-21.00

-22.00

-23.00

-24.00

-25.00

4. PlottheresultsofTable2.1andTable2.2inFig.2.3.PutthevaluesofIAKinthex-axisandthevaluesofVAKinthey-axis.

5. Summarizeyourconclusion

Fig.2.3V-Icurve

EXPERIMENT3

UNCONTROLLEDAC-DCCONVERTER3.0Objectives

• Tostudytheoperationofthediodeasahalf-waverectifier• Tostudytheoperationofthediodeasafull-waverectifier

3.1Equipment


1 Breadboard 1


3 12Vdcmotor 1

4 DMM 2

5 1N5401diode 4

6 DF06bridgerectifierIC 1

7 15-0-15Vacpowersupply 1

3.2Discussion

Theconversionofacvoltage intodcvoltagewillbecarriedout in thisexperiment.Theexperiment will be conducted in three stages. In the first stage, you will study theoperationofthediodeasahalf-waverectifier.Thesamecircuitwillbeusedinthesecondstage butwith adding threemore diodes so that the four diodes operate as a full-waverectifier.Inthelaststage,thefourdiodeswillbereplacedwithonechipcontainingfourdiodes.

Inall stages, thevalueandwaveformof theoutputvoltagewillbeobtained.Cautionmustbetakenasapolarizedcapacitorwillbeused.Thepositiveterminalofthecapacitormustbealwaysconnectedtoapositiveterminal.

3.3Experiment

3.3.0Half-WaveRectifier

Procedure

1. Withthepowersupplyoff,connectthecircuitofFig.3.1.

Fig.3.1Half-waverectifier

2. Turnonthesupply.3. Measuretheinputvoltage,outputvoltageandloadcurrent.PuttheresultsinTable

3.1.4. Putyourhandonthechassisofthemotor.Writedownyourobservation:

5. DrawthewaveformsoftheinputandoutputvoltagesinFig.3.2.6. Switchoffthesupply.7. CalculatetheratioVout/VinandinserttheresultinTable3.1.8. Connectthecapacitoracrossthemotor.Thepositiveterminalofthecapacitormust

beconnectedtothecathodeofthediodeandthenegativeterminaltotheneutraloftheacsupply.

9. Switchonthesupply.10. Putyourhandonthechassisofthemotor.Writedownyourobservation:

11. Measuretheinputvoltage,outputvoltageandloadcurrent.PuttheresultsinTable3.1.

Table3.1

Quantity Measuredvaluewithoutcapacitor

Vout/Vin

Measuredvaluewithcapacitor

Vout/Vin

Vin(V)

VAK(V)

Vout(V)

IAK(mA)

12. DrawthewaveformsoftheinputandoutputvoltagesinFig.3.2andFig.3.3.13. Switchoffthesupply.14. CalculatetheratioVout/VinandinserttheresultinTable3.1.15. Summarizewhatyouhavelearned:

Fig.3.2Voltageswithoutacapacitor

Fig.3.3Voltageswithacapacitor

3.3.1Full-WaveRectifierUsingDiscreteDiodes

Procedure


Fig.3.4Full-waverectifier

2. Turnonthesupply.3. Measuretheinputvoltage,outputvoltageandloadcurrent.PuttheresultsinTable

3.2.4. Putyourhandonthechassisofthemotor.Writedownyourobservationcompared

withthesituationofusingonediode:

5. DrawthewaveformsoftheinputandoutputvoltagesinFig.3.5.6. Switchoffthesupply.7. CalculatetheratioVout/VinandinserttheresultinTable3.2.8. Connectthecapacitoracrossthemotormindingthepolarity.9. Switchonthesupply.10. Measuretheinputvoltage,outputvoltageandloadcurrent.PuttheresultsinTable

3.2.11. Putyourhandonthechassisofthemotor.Writedownyourobservation:

12. DrawthewaveformsoftheinputandoutputvoltagesinFig.3.6.

Table3.2


Vout/Vin


Vout/Vin

Vin(V)

VAK(V)

Vout(V)

IAK(mA)

13. Switchoffthesupply.14. CalculatetheratioVout/VinandinserttheresultinTable3.2.15. Summarizewhatyouhavelearned:

Fig.3.5Voltageswithoutacapacitor

Fig.3.6Voltageswithacapacitor

3.3.2Full-WaveRectifierUsingBridgeRectifierChip

Procedure


Fig.3.7Full-waverectifier

2. Turnonthesupply.3. FillinTable3.3usingthesameprocedureofsection3.3.1.

Table3.3


Vout/Vin


Vout/Vin

Vin(V)

VAK(V)

Vout(V)

IAK(mA)

4. Summarizewhatyouhavelearned:

EXPERIMENT4

CONTROLLEDAC-DCCONVERTER4.0Objectives

• TostudytheoperationoftheSCRasahalf-waverectifier• TostudytheoperationoftheSCRasafull-waverectifier

4.1Equipment


1 Breadboard 1


3 12Vdcmotor 1

4 DMM 2

5 2N6397SCR 4

6 DF06bridgerectifierIC 1

7 15-0-15Vacpowersupply 1

4.2Discussion

The conversion of ac voltage to fixed dc voltage was conducted in the previousexperimentusingthepn-junctiondiode.Inthisexperiment,youwillbeabletovarythedcvoltageusingtheSCRinsteadofthediode.Ahalf-wavecircuitwillbeused.

The SCRwill be triggeredwith an RC circuit, and the firing angle will be changedgraduallyfrom0oto180obyavariableresistor.Thecapacitorofthecontrolcircuitisnon-polarized. The filter capacitor is polarized and so the polarity must be known andconnectedcorrectly.

Theloadisadcmotorsothatyoucanseetheeffectofvariablevoltageonmotorspeed.

4.3Experiment

Procedure


Fig.4.1Half-wavecontrolledrectifier

2. Setthevariableresistor,R1,tothemiddleposition.3. Turnonthesupply.4. Measuretheinputvoltage,outputvoltage,motorcurrentandgatecurrent.Put the

resultsinTable4.1.5. Connect Channel 1 of the CRO across the ac supply and Channel 2 across the

motor.Thepositiveterminalmustbeconnectedtothelineandthenegativeterminaltotheneutral.DrawtheinputwaveforminFig.4.1.

6. ConnectChannel 2 of theCROacross themotor.Draw the outputwaveforms inFig.4.2.

7. WhilegraduallyreducingthevalueofR1,observethemotorspeedandtheoutputwaveform.

8. Set R1 to its minimum value. Measure the input voltage, output voltage, motorcurrentandgatecurrent.PuttheresultsinTable4.1.

9. PlottheoutputwaveforminFig.4.2justbelowthepreviouswaveform.10. SetR1 to its maximum value. Measure the input voltage, output voltage, motor

currentandgatecurrent.PuttheresultsinTable4.1.11. PlottheoutputwaveforminFig.4.2justbelowthepreviouswaveforms.12. Summarizewhatyouhavelearned:

Table4.1

Quantity Measuredvalue

R1=mid R1=min R1=max

Inputvoltage,Vin(V)

Outputvoltage,Vout(V)

Motorcurrent,IAK(mA)

Gatecurrent,IG(mA)

Fig.4.2Inputwaveform

Fig.4.3Outputwaveform

EXPERIMENT5

DC-DCCONVERTER5.0Objectives

• TolearnthebasicconceptofDC-DCconverter• Tostudytheeffectofdutycycleontheoutputvoltage

5.1Equipment


1 Resistor100Ω,17W 1

2 Resistor1kΩ 1

3 Inductor15mH 1

4 PolarizedCapacitor1000µF 1

5 TIP31ANPNtransistor 1

6 1N5401diode 1

7 DCpowersupply 1

8 Functiongenerator 1

9 Oscilloscope 1

5.2Discussion

Inthisexperiment,youwillbuildaDC-DCconvertercircuitthatcanstepdownDCinputvoltage.Thecircuitiscomposedoftwobasicelements:twosemiconductorswitchesandtwo filters.ABJTwill be used as the controlled switch and a pn-junction diode as theuncontrolledswitch.Afastrecoverydiodeishighlyrecommendedforproperoperationoftheconverter.

Withaconstant-frequencycontrolsignalsuppliedfromafunctiongenerator,thecircuitcanvarytheoutputvoltagebyvaryingtheturn-ontimeoftheBJT.

5.3Experiment

5.3.0Step-DownChopper

Procedure

1. ConnectthemainoutputofthefunctiongeneratortoChannel1oftheCRO.TurnonthefunctiongeneratorandtheCRO.

2. Adjust themainoutputof thefunctiongenerator toproduceasquarewavewithapeak-to-peakvoltageof20Vat1kHz.

3. Keepthemark-spaceknobofthefunctiongeneratoroff.4. TurnoffthefunctiongeneratorandCRO.5. Turnonthepowersupplyandadjustittoproduce15Vdc.6. Turnoffthesupply.7. ConnectthecircuitofFig.5.1.

Fig.5.1Step-downchopper

8. ConnectChannel2oftheCROacrosstheload.9. Connect the output of the function generator to the base of the transistor via the

resistorR1.10. TurnonthesupplyandCRO.11. MeasurethevoltagesatpointsA,BandCwithrespecttothenegativeterminalof

thesupply.RecordtheresultsinTable5.1.12. Turnonthefunctiongenerator.Repeatstep11.

Table5.1

Quantity

Measuredvaluewithoutcontrolsignal

Measuredvaluewithcontrolsignal

VA(V)

VB(V)

VC(V)

13. PlotthewaveformoftheloadvoltageinFig.5.2.14. Removethecapacitor.

15. PlotthewaveformoftheloadvoltageinFig.5.3.16. Turnoffthesupply,CROandfunctiongenerator.17. Summarizewhatyouhavelearned:

Fig.5.2Outputwaveformwithcapacitor

Fig.5.3Outputwaveformwithoutcapacitor

EXPERIMENT6

AC-ACCONVERTER6.0Objectives

• Tolearnthebasicconceptofac-acconverter• Tostudythephase-angleandon-offmethod

6.1Equipment


1 15Vacpowersupply 1

2 2N6073TRIAC 1

3 1N5401diode 2

4 Resistor330Ω 1

5 Variableresistor10kΩ 1

6 Non-polarizedcapacitor100µF 1

7 4N35andMOC3011optocouplers 1

8 PIC16F628 1

6.2Discussion

ThelampdimmerisagoodapplicationofAC-ACconverterswhichconvertafixedACvoltageintovariablevalues.Youwillexperimentwithtwomethods.

In the first part of the experiment, you will build a simple lamp dimmer using twodiodes,oneTRIACandsomebasiccomponents;thisisthephase-anglemethod.Youwillvaryaninputvoltageof15V~byvaryingthefiringanglewithavariableresistorandyouwillobservethischangeonthevoltmeterandtheCRO.

Thesecondpartistheon-offcontrolmethod.Youwilluseamicrocontroller,twoSCRsand an optocoupler. The recommended microcontroller is the well-known and cheapPIC16F628.

6.3Experiment

6.3.0Phase-AngleControlMethod

Procedure

1. Withthepowersupplyoff,connectthecircuitofFig.6.1.2. Setthevariableresistortoroughlyitsminimumposition.3. ConnectChannel1oftheCROacrossthelampandChannel2betweentheTRIAC

gateterminalandtheneutralofthesupply.4. Connect a voltmeter across the lamp and connect an ammeter in series with the

TRIACgateterminal.5. TurnonthesupplyandtheCRO.6. ObservethewaveformsofthelampvoltageandthegatevoltageontheCRO.

Fig.6.1Dimmercircuit

Table6.1


R1=mid R1=min R1=max


Gatecurrent,IG(mA)

7. RecordthevoltageandcurrentreadingsinTable6.1.8. PlotthewaveformsinFig.6.2.9. Setthevariableresistortoroughlyitsmiddleposition.10. RecordthevoltageandcurrentreadingsinTable6.1.11. PlotthewaveformsinFig.6.3.12. Setthevariableresistortoroughlyitsmaximumposition.13. RecordthevoltagecurrentreadingsinTable6.1.14. PlotthewaveformsinFig.6.4.15. TurnoffthepowersupplyandCRO.16. Writedownyourconclusion

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6.3.1On-OffControlMethod

Pre-start

Inthispart,theRCcircuitandthediodeswillberemoved.ThetriggeringpulseswillbeprovidedbythemicrocontrollerPIC16F628A.TheinputsignalwillbeisolatedfromthetriggeringcircuitbytheoptocouplerMOC2021.

Prior to starting, the code for generating the triggering pulsesmust be loaded on thePIC16F628A.ThecodeislistedinTable6.2.

Table6.2

Fig.6.5Dimmercircuitusingon-offmethod

Procedure

1. LoadthecodelistedinTable6.2ontothePIC16F628A.2. Withthepowersupplyoff,connectthecircuitofFig.6.5.3. ConnectChannel1oftheCROacrossthelampandChannel2betweentheTRIAC

gateterminalandtheneutralofthesupply.4. Connect a voltmeter across the lamp and connect an ammeter in series with the

TRIACgateterminal.5. TurnonthesupplyandtheCRO.6. PresstheswitchSWonce.Observethewaveformsofthelampvoltageandthegate

voltageontheCRO.7. RecordthevoltageandcurrentreadingsinTable6.3.8. PlotthewaveformsinFig.6.6.9. PresstheswitchSWagain.10. RecordthevoltageandcurrentreadingsinTable6.3.11. PlotthewaveformsinFig.6.7.12. PresstheswitchSWoncemore.13. RecordthevoltageandcurrentreadingsinTable6.3.14. PlotthewaveformsinFig.6.8.15. TurnoffthepowersupplyandCRO.16. Writedownyourconclusion

Table6.3


SW=firsttimepressed

SW=secondtimepressed

SW=thirdtimepressed


Gatecurrent,IG(mA)

Fig.6.6OutputandgatevoltagewaveformswhenSWpressedfirsttime

Fig.6.7OutputandgatevoltagewaveformswhenSWpressedsecondtime

Fig.6.8OutputandgatevoltagewaveformswhenSWpressedthirdtime

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