Power Semiconductor Devices_ALL electronics.pdf

Discuss about Power Semiconductor Devices

1. Power Semi –Conductor
Devices

2. MetalOxideSiliconFieldEffect
Transistor(MOSFET)
Threeterminal(Gate,Drain,Source),fourlayerunipolardevice.
Majoritycarrierdevice.
Withnorecombinationdelayinmajoritycarriers,extremelyhighbandwidthsand
switchingtimes.
GateiselectricallyisolatedfromsourcegivingMOSFETgoodinputimpedanceand
goodcapacitance.
Nosecondarybreakdownarea.
Draintosourceresistancehaspositivetemperaturecoefficienthenceselfprotective.
VerylowOnresistanceandnojunctionvoltagedropwhenforwardboased.
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3. MOSFET–Types 28

4. MOSFET–Structure
VerticallyorientedfourlayerstructureofalternatePandNtypelayers.(n+pn-n+)
PtypemiddlelayeristhebodywherechannelisformedbetweenSourceandDrain.
N–layeristhedriftregionwhichdeterminesthebreakdownvoltage.
GateterminalisisolatedbySiliconDioxidelayer.
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5. MOSFET–Ratings
Ratings:
VoltageVDS<500V,
CurrentIDS<300A.
Devices(fewhundredwatts)maygouptoMHzrange.
Frequencyf>100KHzforsomelowpower.
Turningonandoffisverysimple.
–Toturnon:VGS=+15V
–Toturnoff:VGS=0Vand0Vtoturnoff.
Gatedrivecircuitissimple.
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6. MOSFET Features
Basicallylowvoltagedevice.
Highvoltagedeviceareavailableupto600Vbutwithlimitedcurrent.
Canbeparalleledquiteeasilyforhighercurrentcapability.
Internal(dynamic)resistancebetweendrainandsourceduringonstate,RDS(ON),,
LimitsthepowerhandlingcapabilityofMOSFET.
HighlossesespeciallyforhighvoltagedeviceduetoRDS(ON).
Dominantinhighfrequencyapplication(>100kHz).
Biggestapplicationisinswitched-modepowersupplies.
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7. MOSFET Characteristics 32
ThecurrentequationforMOSFETisgivenas
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un=Mobilityoftheelectrons;Cox=Capacitanceoftheoxidelayer;W=Widthofthegatearea;
L=Lengthofthechannel;VGS=GatetoSourcevoltage;VTH=Thresholdvoltage;VDS=DraintoSource
voltage.

8. MOSFET Selection Factors 33
ToselectaMOSFETforaparticularapplication,followingparametershavetobe
consideredfromthedevicedatasheet
1.MaximumDraintoSourcevoltage(V
DSS)
2.On-statedraintosourceresistanceR
DS(ON)
3.DrainCurrentI
D
4.GatetosourceVoltageV
GS
5.ReverserecoverytimeT
rr
6.GatechargeQ
G
7.PowerDissipationP
D

9. Comparison –BJT vs MOSFET
BJT MOSFET
It is a Bipolar Device It is majority carrier device
Current control Device Voltage control Device.
Output is controlled by controlling base currentOutput is controlled by controlling gate voltage
Negative temperature coefficient Positive temperature coefficient
So paralleling of BJT is difficult. So paralleling of this device is easy.
Dive circuit is complex. It should provide
constant current(Base current)
Dive circuit is simple. It should provide constant
voltage(gate voltage)
Losses are low. Losses are higher than BJTs.
So used in high power applications. Used in low power applications.
BJTs have high voltage and current ratings.They have less voltage and current ratings.
Switching frequency is lower than MOSFET.Switching frequency is high.
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10. InsulatedGateBipolarTransistor–IGBT
IGBTsarepreferreddevicesforvoltagesabove300Vandbelow5kV.
Threeterminaldevice:Gate,Source,Drain.
Theyareturnedonandoffbyapplyinglowvoltagepulsestotheirgate.
CombinationofBJTandMOSFETcharacteristics.
Other names: Gain Enhanced MOSFET (GEMFET); COMFET (Conductivity
Modulated FET); Insulated Gate Transistor (IGT).
Superior on –state characteristics, good switching speed and excellent safe operating
area (SOA).
Advantage: High current capability of BJTs and easy control of MOSFET.
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11. InsulatedGateBipolarTransistor
IGBTsarepreferreddevicesforvoltagesabove300Vandbelow5kV.
Theyareturnedonandoffbyapplyinglowvoltagepulsestotheirgate.
CombinationofBJTandMOSFETcharacteristics.
GatebehavioursimilartoMOSFET-easytoturnonandoff.
LowlosseslikeBJTduetolowon-stateCollector-Emittervoltage(2-3V).
Ratings:Voltage:VCE<3.3kV,Current,:IC<1.2kAcurrentlyavailable.
Latest:HVIGBT4.5kV/1.2kA.
Switching frequency up to 100 KHz.
Typicalapplications: 20-50 KHz.
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12. IGBT Equivalent Circuit
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13. IGBT Characteristics Curve
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IGBTareclassifiedas
(i)NonPunchThroughIGBT(NPTIGBT)orsymmetricalIGBT.
(ii)PunchThroughIGBT(PTIGBT)orasymmetricalIGBT.
IGBTshavingn+bufferlayeraretermedasPunchThrough(PTIGBT)s.
IGBTsnothavingn+bufferlayerinknownasNonPunchThrough(NPTIGBT)s.
AsymmetricalIGBTisonehavingequalforwardandreversebreakdownvoltageswhich
arenormallyusedinACapplications.
IntheasymmetricalIGBT,thereversebreakdownvoltageislessthantheforward
breakdownvoltagewhicharenormallyusedinDCcircuitswherethedevicedoesnot
needtoprovidesupportinthereversedirection.

14. IGBT Characteristics Curve
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15. IGBT –Merits & Demerits
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Merits
1.Voltagecontrolleddevice
2.LessOnstateloss
3.Highswitchingfrequency
4.Nocommutationcircuit.
5.Gatehasfullcontroloveroperation
6.Flattemperaturecoefficient.
Demerits:
1.Staticchargeproblem.
2.CostlierthanBJTandMOSFET.

16. IGBT –Comparison
41
Device
Characteristic
Power
Bipolar
Power
MOSFET
IGBT
Voltage Rating High <1kV High <1kV Very High >1kV
Current Rating High <500A Low <200A High >500A
Input Drive
Current, h
FE
20-200
Voltage, V
GS
3-10V
Voltage, V
GE
4-8V
Input Impedance Low High High
Output Impedance Low Medium Low
Switching Speed Slow (uS) Fast (nS) Medium
Cost Low Medium High

17. Gateturn-offThyristor(GTO)
Behavelikenormalthyristor,butcanbeturnedoffusinggatesignal
Howeverturningoffisdifficult.
Needverylargereversegatecurrent(normally1/5ofanodecurrent).
Gatedrivedesignisverydifficultduetoverylargereversegatecurrentatturnoff.
Ratings:Highestpowerratingsswitch:
Voltage:VAK<5kV;Current:IA<5kA.Frequency<5KHz.
Verystiffcompetition:
Lowend-fromIGBT.HighendfromIGCT
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18. Classification-GTO
1.AsymmetricalGTO:
TheAsymmetricaltypeGTOsarethemostcommontypeonthemarket.
ThistypeofGTOsarenormallyusedwithaanti-paralleldiode.
Theydonothavehighreverseblockingcapability.
TheyareusedinVoltageFedConverters.
2.SymmetricalGTO:
ThesymmetricaltypeGTOshaveanequalforwardandreverseblockingcapability.
TheyareusedinCurrentFedConverters.
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19. Construction-GTO
AlmostsimilartoSCR.
Inthis,n+layeratthecathodeendishighlydopedtoobtainhighemitterefficiency.
Durtothis,breakdownvoltageoftheJ3junctionislow(20to40V).
Thedopinglevelofptypegateishighlygradedastradeoffbetweenhighemitter
efficiency(lowdopingrequired)goodturnoffproperties(highdopingrequired).
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20. Construction-GTO
Junctionbetweenp+anodeandNbaseiscalledanodejunction.
Heavilydopedp+anoderegionisrequiredtoobtainhighefficiencyonturnonproperty.
ButturnOffpropertyisaffected.
Thisproblemissolvedbyintroducingheavilydopedn+layersatregularintervalsinp+
anodelayer.
ThisiscalledanodeshortedGTOstructure.
ThiscausestheelectronstotravelfrombaseNtoanodemetalcontactdirectlywithout
causingholeinjectionfromp+anode.
ButreverseblockingcapacityofGTOisreducedandspeedsupturnOffmechanism.
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21. Working-GTO
TheGateturnoffthyristor(GTO)isafourlayerPNPNpowersemiconductor
switchingdevicethatcanbeturnedonbyashortpulseofgatecurrentandcanbe
turnedoffbyareversegatepulse.
Thisreversegatecurrentamplitudeisdependentontheanodecurrenttobeturnedoff.
Thereisnoneedforanexternalcommutationcircuittoturnitoff.
Soinvertercircuitsbuiltbythisdevicearecompactandlow-cost.
Thedeviceisturnedonbyapositivegatecurrentanditisturnedoffbyanegativegate
cathodevoltage.
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22. GTOCharacteristicsCurve 47

23. GTOV–ICharacteristics: 48
ItissimilartoSCRduringturnon.
The1
st
quadrantcharacteristicsaresimilartothatofSCR.
LatchingcurrentandholdingcurrentareconsiderablyhigherthanSCR.
Thegatedrivecanberemovedifanodecurrentismorethantheholdingcurrent.
Itisthoughnotrecommendedascathodeissubdividedintosmallfingerelements
causingtheanodecurrenttogobelowtheholdingcurrenthencedestroyingthedevice.
GTOisturnedoffbyapplyingreversegatecurrentineitherramporstepmode.
Thedashedlineinthefigureshowsi-vtrajectoryduringtheturnOFFforaninductive
load.
dV/dttriggeringisavoidedbyplacingaratedresistorbetweengateandcathodeorby
meansofareversebiasvoltage.

24. GTOV–ICharacteristics: 49
AsymmetricGTOhashigherreverseblockingcapabilitythananasymmetrictype.
Afterasmallreversevoltage(20to30V)GTOstartsconductinginthereverse
directionduetoanodeshortstructure.

25. GTOTurnOFFCurrentGain: 50
TheTurnOffCurrentGainofaGTOisdefinedastheratioofanodecurrentpriorto
turnofftothenegativegatecurrentrequiredforturnoff.
Itistypicallyverylow(4or5).
Itmeansa6000AratingGTOrequires1500Agatecurrentpulse.
However,thegatepulsedurationandthepowerlossduetothegatepulseissmall.
ItcanbesuppliedbylowvoltagepowerMOSFETs.
Thisgateturnoffcapabilityisadvantageousbecauseitprovidesincreasedflexibilityin
circuitapplication.
NowitbecomespossibletocontrolpowerinDCcircuitswithoutuseofelaborated
commutationcircuitry.

26. SummaryGTO 51
AdvantagesofGTO:
1.Highblockingvoltagecapabilities.
2.Highovercurrentcapabilitiesduringturnoff..
3.Exhibitslowgatecurrents.
4.Fastandefficientturnoff.
5.Betterstaticanddynamicdv/dtcapabilities.
6.EnhancedSafeOperatingAreaduringturnoff.
Disadvantages:
1.Magnitudeoflatching,holdingcurrentsisseveraltimesmorethanthyristors.
2.Onstatevoltagedropandtheassociatedlossismore.
3.DuetomulticathodestructureofGTO,triggeringgatecurrentishigherthanthatrequired
fornormalSCR.
4.Gatedrivecircuitlossesaremore.
5.Itsreversevoltageblockingcapabilityislessthantheforwardvoltageblockingcapability.

27. SummaryGTO 52
ApplicationsofGTO:
1.Motordrives,
2.staticVARcompensators(SVCs)
3.AC/DCpowersupplieswithhighpowerratings.
4.DCcircuitbreakers
5.Inductionheating
6.Lowpowerapplications.
7.DCchoppers.

28. Insulated Gate-CommutatedThyristor(IGCT)
SpecificationsGTO IGCT IGBT
Full Form Gate Turn-Off Thyristor
Insulated Gate Commutated
Thyristor
Insulated Gate Commutated
Thyristor
Advantages
•Controlled turn-off ability.
•Relatively high overload
capacity.
•Series connection
possibility.
•Working frequency of
hundreds of Hz.
•Controlled turn-off ability.
•Relatively high overload
capacity.
•Low on-state losses.
•Working frequency of kHz.
•Series connection possibility.
•High cyclic resistance.
•Controlled turn-off
ability.
•Minimum working
frequency up to 10 kHz.
•Very low control power.
Disadvantages
•Higher on-state losses.
•High control power.
•Very high on-state losses.
•Relatively low cyclic
resistance.
Applications
•High power drives
•Static compensators
•Continuous supply sources
•Induction heating sources
•High power drives
•Supply inverter sources for DC
transmissions
•Big frequency converters
•Choppers
•Continuous supply
sources
•Staticalcompensators and
active filters
•Switching sources
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