power semiconductor switches

2/5/2010

1

Power Semiconductor Switches

Pekik Argo Dahono

Power Semiconductor Switches

• Diodes (Uncontrolled switches)

• Thyristors (Controllable at turn-on but

uncontrolled at turn-off or commonly called

as latched devices). Triac is under the same

category.

• BJT, MOSFET, IGBT, GTO, MCT etc. are

fully controllable switches.

Pekik A. Dahono -- Elektronika Daya 2

2/5/2010

2

Power Diodes

A

K

P

N

A

K

P

N

−N

A

K

AKv

AKi

AKv

AKi


Reverse Recovery Problems

dE FD

S

oI

rrt

SI

oI

FDI

FDV


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Power diodes

Diodes are classified as:

- general purpose or line-frequency diodes

- Fast recovery diodes

- Schottky diodes


Schottky Diode

• The schottky diode has a smaller voltage

drop compared to conventional diodes

(about 0.3 V).

• The schottky diode has a smaller voltage

breakdown than conventional diodes (less

than 200 V).


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Sample of diodes


Thyristor

P

P

N

N

K

G

A

Ai

AKv

Ai


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Thyristor Model

GI

1Q

2Q

1BI1EA II =

2CI 1CI

2BI

2EI

( )21

02012

02222

01111

1 αα

α

α

α

+−

++=

+−=

+−=

CCGA

CEC

CEC

IIII

III

III


Thyristor in Simple Circuit


• For successful turn-off, reverse voltage required for an

interval greater than the turn-off interval

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Thyristor Classification

• Phase control thyristors

• Inverter-grade or fast-type thyristors

• Light activated thyristors

• Reverse conducting thyristors


Thyristor Features

• Latching devices

• Double carrier devices

• Having forward and reverse blocking

capabilities

• Very high gain (IA/Ig)

• Low on-state voltage

• Can be protected by fuse


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Sample of thyristors


Thyristor Modules


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Snubbers for Diodes and Thyristors

• Maximum dv/dt across diodes or thyristors

must be limited and can be done by using an

RC snubber that is connected in parallel to

the devices.

• Maximum di/dt through diodes or thyristors

must be limited and can be done by using an

inductor that is connected in series to the

devices.


Switching Characteristics

dont

ritfvt dofft

rvtfit

signal

Gate

current

& voltage

Transistor

power

Transistor

TvTi

dEoI

sonodson tIEW2

1=

soffodsoff tIEW2

1=

cdP

fvrison ttt += firvsoff ttt +=

dETi

Tv

oI


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Desired Switch Characteristics

• Small leakage current in the off state

• Small on-state voltage

• Short turn-on and turn-off times

• Large forward and reverse blocking voltage capabilities

• High on-state current rating

• Positive temperature coefficient of on-state resistance

• Small control power

• Wide Safe Operating Area

• Large dv/dt and di/dt ratings


Safe Operating Area

v

i

off-turn

on-turn


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Losses

Switching losses :

Conduction losses :

( )soffsonsods ttfIEP +=21

s

ONooncd

T

TIVP =

fs is switching frequency.

Ts is switching period.


Bipolar Junction Transistor

N

PN

C

E

BB

C

E

Ci

Bi

CEv

Ci

01 =Bi2Bi3Bi4Bi5Bi

12345 BBBBB iiiii >>>>

CEv

Ci


• Used commonly in the past

• Now used in specific applications

• Replaced by MOSFETs and IGBTs

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VI characteristics of BJT

CEv

CI

00 =BI

1BI

2BI3BI4BI

5BI

0<BI

SUSBV 0CBBV

breakdown Second

breakdown

Primary

saturation-Quasisaturation-Hard


Operating region

• Hard-saturation provides low voltage-drop but a

large storage time (turn-off time)

• Quasi-saturation provides high voltage-drop but a

small storage time.

• Second breakdown must be avoided by using a

snubber and proper base current control.

• Negative base current results in higher voltage

breakdown.


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Antisaturation circuit

C

E

B'B

1D

2D

3D


BJT Features

• Current controlled devices

• Double carrier devices

• No reverse blocking capability

• Low gain (Ic/Ib)


• Can not be protected by fuse

• Second breakdown problem


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Darlington Configuration


MOSFET

Di

01 =GSv2GSv3GSv4GSv5GSv

12345 GSGSGSGSGS vvvvv >>>>

DSv

Di

G

D

S

Di

DSv


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MOSFET Features

• Voltage controlled devices

• Single carrier devices

• High on-state voltage

• Very high gain


• No second breakdown problem

• Can not be protected by fuse


Integrated Power MOSFET


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Gate-Turn-Off (GTO) Thyristor

AKv

Ai

condition

Blocking


GTO switching characteristic

IGR

(b)

Vd

Anodecurrent

Anodevoltage

Tail

current

Spikevoltage

IA

0Time


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Turn-Off Snubber for GTO


GTO Features

• Controllable at turn-on and turn-off

• High-voltage capability

• Can be designed with reverse blocking

capabilty

• Low gain at turn-off


• High turn-off losses


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GTO vs IGCT


GTO vs IGCT


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Insulated Gate Bipolar Transistors (IGBTs)

C

E

Ci

GCEv

Ci

12345 GEGEGEGEGE vvvvv >>>>

01 =GEv2GEv3GEv4GEv5GEv


IGBT Features

• Combining the advantages of BJT and

MOSFET


• No second breakdown

• High gain at turn on and turn off


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IGBT vs IGCT


Other Switching Devices

• Static Induction Transistor and Static Induction

Thyristor. The main problems are normally-on and

high conduction loss. The advantage is that the

speed is very high.

• MOS Controlled Thyristor. Combining the

advantages of MOSFET and Thyristor. Still under

development.

• IGCT (Integrated Gate Controlled Thyristor). This

is further development of GTOs.


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Switching Device Development

THYRISTOR

GTO

BPT

10-1

10-1 100 101 102 104

101

102

103

104

P (k

VA

)

f (kHz)

1 9 8 0

HIG

H P

OW

ER

EASY D

RIV

EHIG

H FREQUENCY

1 9 9 0

THYRISTOR

103

104

10-1

10-1 100 101 102 104

102

P (k

VA

)

f (kHz)

105

101

GTO

BPT

MOS

IGBT

2 0 0 0

10-1

10-1 100 101 102 104

OPERATION FREQUENCY f (kHz)

105

MOS

106

103

104

102

CO

NT

RO

LL

AB

LE

PO

WE

R

P (k

VA

)

101

105

BPT

IGBT

MCT SI Thy

GTO

THYRISTOR

GTO : GATE TURN-OFF THYRISTOR

MCT : MOS CONTROLLED THYRISTOR

SI Thy : STATIC INDUCTION THYRISTOR

BPT : BIPOLAR POWER TRANSISTOR

IGBT : INSULATED GATE BIPOLAR TRANSISTOR


Reverse Conducting and

Reverse Blocking Switching Devices

conducting Reverse blocking Reverse


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Bidirectional Switches


Switching devicesSwitch Ideal

switch eduncontroll onalUnidirecti

switch lledsemicontro onalUnidirecti

switch controlled fully conducting Reverse

switch lledsemicontro nalBidirectio

switch controlled fully blocking Reverse

switch controlled fully nalBidirectio

switch controlled fully conducting Reverse


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Properties and Rating of

Semiconductor Power Switches

Switch Control signal

Control characteristic

Switching frequency

Voltage drop

Maximum voltage

rating

Maximum current

rating

Diode medium 6.5 kV 5 kA

SCR current trigger low medium 6 kV 4 kA

TRIAC current trigger medium 1 kV 50 A

GTO current trigger low medium 6.5 kV 4.5 kA

BJT current linear medium low 1.5 kV 1 kA

MOSFET voltage linear Very high high 1 kV 200 A

IGBT voltage linear high medium 3.5 kV 2 kA


Properties of New MaterialsProperty Si GaAs 3C-SiC 6H-SiC Diamond

Bandgap at 300 K (eV)

1.12 1.43 2.2 2.9 5.5

Relative dielectric constant

11.8 12.8 9.7 10 5.5

Saturated drift velocity (cm/s)

1x107

2x107

2.5x107

2.5x107

2.7x107

Thermal

conductivity (W/cm/oC

1.5 0.5 5.0 5.0 20

Maximum

operating temperature (K)

400 460 873 1240 1100

Melting

temperature (C)

1415 1238 Sublime>1800 Sublime>1800 Phase change

Electron mobility at 300 K (cm2/Vs)

1400 8500 1000 600 2200

Breakdown

electric field

(V/cm)

3x105

4x105

4x106

4x106

1x107


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Applications

• Thyristor is only used for very large power applications.

• Forced commutated thyristors are no longer used.

• Bipolar junction transistors are no longer used.

• MOSFET is commonly used in low-power applications.

• IGBT is used from low-power up to medium power applications.

• GTO is used for large power applications.


Loss Considerations

• Conduction losses

• Switching losses

• The loss will determine the junction temperature and the heatsink and cooler required.

• In many cases, the switching frequency is limited by the temperature instead of device speed.


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Snubbers

• Turn-off losses can be reduced by using a turn-off snubber. This snubber is also useful to limit high dv/dt across the device.

• Turn-on losses can be reduced by using a turn-on snubber. This snubber is also useful to limit high di/dt through the device.

• Snubbers are useful to reduce the switching losses on the switching devices. The total switching losses, however, may still the same or even increase.


Turn-ON and turn-OFF Snubbers


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Reducing Switching Losses

• Switching losses can be reduced by using lossless snubbers. These snubbers, however, may make the converter circuit became complicated.

• IGBTs may operate without snubbers.

• GTOs and IGCTs usually need a turn-off snubber because of high tail current.

• Switching losses can be reduced or even eliminated by using soft-switching techniques. These methods, however, may increase the required voltage and/or current ratings.


The End

power semiconductor switches

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