Power ElectronicsPower Electronics

Chapter 9 Practical Application Issues

of Power Semiconductor Devices

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OutlineOutline9.1 Gate drive circuit 9.1 Gate drive circuit

9.2 Protection of power semiconductor devices9.2 Protection of power semiconductor devices

9.3 Series and parallel connections of power 9.3 Series and parallel connections of power semiconductor devicessemiconductor devices

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9.1 Gate drive circuit9.1 Gate drive circuitBasic function of gate drive circuit:Basic function of gate drive circuit: Generate gate signals to turn-on or turn-off power Generate gate signals to turn-on or turn-off power

semiconductor device according to the commanding semiconductor device according to the commanding signals from the control circuit.signals from the control circuit.

Other functions of gate drive circuit:Other functions of gate drive circuit:

Reduce switching time (including turn-on time and turn-Reduce switching time (including turn-on time and turn-off time)off time)Reduce switching loss (including turn-on loss and turn-Reduce switching loss (including turn-on loss and turn-off loss) and improve efficiencyoff loss) and improve efficiencyImprove protection and safety of the converterImprove protection and safety of the converter

Gate drive circuits provided by power semiconductorGate drive circuits provided by power semiconductormanufacturers and Integrated gate drive chips aremanufacturers and Integrated gate drive chips aremore and more widely used.more and more widely used.

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Electrical isolation in the gate drive circuitElectrical isolation in the gate drive circuit

Gate drive circuit usually pGate drive circuit usually provides the electrical isolatirovides the electrical isolation between control circuit on between control circuit and power stage. and power stage.

Two ways to provide electrTwo ways to provide electrical isolationical isolation– OpticalOptical

• Optocoupler, fiber opticsOptocoupler, fiber optics

• TransformerTransformer

– MagneticMagnetic

E

RUin

Uout

R1

ICID

LED

Phototransistor

Schematic of an optocoupler

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Thyristor gate current pulse requirmentsThyristor gate current pulse requirments

Shape of gate current Shape of gate current pulse waveform:pulse waveform:– Enhanced leading partEnhanced leading part

Magnitude requirement Magnitude requirement (for the enhanced leading (for the enhanced leading part and the other part)part and the other part)

Width requirement (for the Width requirement (for the enhanced leading part and enhanced leading part and the whole pulse)the whole pulse)

Power of the triggering Power of the triggering signal must be within the signal must be within the SOA of the gate I-V SOA of the gate I-V characteristicscharacteristics

I

t

IM

t1 t2 t3 t4

Ideal gate current pulse waveform for thyristors

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Typical thyristor gate triggering circuitTypical thyristor gate triggering circuit

T M

R 1

R 2

R 3

V 1

V 2

VD

1

VD

3

V D 2 R 4+ E 1 + E 2

In p u t fro mc o n tro l c irc u it

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Typical gate signal and gate drive circuit Typical gate signal and gate drive circuit for GTOfor GTO

O t

tO

u G

iG

5 0 k H z5 0 V

G T O

N 1

N 2

N 3

C 1 C 3

C 4

C 2 R 1

R 2

R 3

R 4

V 1

V 3

V 2

LV D 1

VD

2

V D 3

V D 4

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A typical gate drive circuit for IGBT based on A typical gate drive circuit for IGBT based on an integrated driver chipan integrated driver chip

13Error

indicating

Sensing

VCC

Interfacecircuit

Turn-offcircuit

Timer andreset circuit

Detectioncircuit

4

1

5

8

6

14

13

uo

VEE

81

5

4

6-10V

+15V

30V+5V

M57962L

14

ui1

Fast recovery diodetrr¡Ü0.2s

4.7k

3.1

100F

100F

M57962L integrated driver chipM57962L integrated driver chip

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9.2 Protection of power semiconductor 9.2 Protection of power semiconductor 　　 　　 devicesdevices

Protection circuitsProtection circuits

Overvoltage protectionOvervoltage protection

Overcurrent protectionOvercurrent protection

Snubber circuits—specific protection circuits that Snubber circuits—specific protection circuits that can limit du/dt or di/dtcan limit du/dt or di/dt

Turn-on snubberTurn-on snubber

Turn-off snubberTurn-off snubber

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Causes of overvoltage on power Causes of overvoltage on power semiconductor devicessemiconductor devices

External reasonsExternal reasons

Overvoltage caused by operation of mechanic switOvervoltage caused by operation of mechanic switheshes

Overvoltage caused by thunder lighteningOvervoltage caused by thunder lightening

Internal reasonsInternal reasons

Overvoltage caused by the reverse recovery of dioOvervoltage caused by the reverse recovery of diode or thyristorde or thyristor

Overvoltage caused by the turning-off of fully-contrOvervoltage caused by the turning-off of fully-controlled devicesolled devices

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Measures to protect power semiconductor Measures to protect power semiconductor devices from overvoltagedevices from overvoltage

Lightening arrestorLightening arrestor

RC or RCD snubbers (will be discussed later)RC or RCD snubbers (will be discussed later)

Zener diode, Metal Oxide Varistor (MOV), Break Over Zener diode, Metal Oxide Varistor (MOV), Break Over

Diode (BOD)Diode (BOD)

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Measures to protect power semiconductor devicMeasures to protect power semiconductor devices from overcurrentes from overcurrent

Fuse Fuse

Circuit breakerCircuit breaker

Protection with current feedback control in the control cProtection with current feedback control in the control c

ircuitircuit

Protection with overcurrent detection in the gate drive cProtection with overcurrent detection in the gate drive c

ircuit—the fastest measureircuit—the fastest measure

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Functions and classifications of snubbersFunctions and classifications of snubbers

FunctionsFunctionsLimiting voltages applied to devices during turn-off transientsLimiting voltages applied to devices during turn-off transientsLimiting device currents during turn-on transientsLimiting device currents during turn-on transientsLimiting device current rising rate (di/dt) at device turn-onLimiting device current rising rate (di/dt) at device turn-onLimiting the rate of rise (du/dt) of voltages across devices duriLimiting the rate of rise (du/dt) of voltages across devices during device turn-offng device turn-offShaping the switching trajectory of the deviceShaping the switching trajectory of the device

ClassificationsClassificationsAccording to different switching transientsAccording to different switching transients– Turn-off snubber (sometimes just called snubber)Turn-off snubber (sometimes just called snubber)– Turn-on snubber Turn-on snubber

According to the treatment of energy According to the treatment of energy – Power dissipating snubberPower dissipating snubber– Lossless snubberLossless snubber

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Operation principle of typical snubbersOperation principle of typical snubbers

Circuit configurationCircuit configuration

R i

V D

L

V

T u rn -o nsn u b b e r

T u rn -o ffsn u b b e r

L iV D i

R s

C s

VD

st

uCEiC

O

without turn-on snubber

with turn-on snubber

with turn-offsnubber

without turn-off snubber

uCE

iC

Switching trajectory

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Other turn-off snubbersOther turn-off snubbers

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9.3 Series and parallel connections of 9.3 Series and parallel connections of power semiconductor devices power semiconductor devices

ObjectObject

To increase the capability to deal with voltage or currentTo increase the capability to deal with voltage or current

Issues and solutionsIssues and solutions

Series connectionSeries connection– Issue: even voltage sharingIssue: even voltage sharing

– Solutions: Solutions: • Selection of devices that are closer to each other in the characteristicsSelection of devices that are closer to each other in the characteristics• Voltage sharing circuitVoltage sharing circuit

Parallel connectionParallel connection– Issue: even current sharingIssue: even current sharing

– Solutions: Solutions: • Selection of devices that are closer to each other in the characteristicsSelection of devices that are closer to each other in the characteristics• Current sharing circuit and symmetrical circuit layoutCurrent sharing circuit and symmetrical circuit layout

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Series Connection of thyristorsSeries Connection of thyristors

Voltage sharing circuitVoltage sharing circuit– Steady-state voltage sharing circuitSteady-state voltage sharing circuit

– Dynamic voltage sharing circuitDynamic voltage sharing circuit

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Parallel Connection of Power MOSFETsParallel Connection of Power MOSFETs

Easy to realize because of the positive temperature of their on-Easy to realize because of the positive temperature of their on-

state resistancestate resistance

Need a small damping resistor in series with the individual gate Need a small damping resistor in series with the individual gate

connectionsconnections

Still need to select devices that are closer to each other in the Still need to select devices that are closer to each other in the

characteristicscharacteristics

Circuit layout should be symmetricalCircuit layout should be symmetrical