Power Semiconductor Switches Power Semiconductor Switches

2/5/2010

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

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Power Diodes A

iAK

A

iAK

A P

P

v AK

v AK

N− N

N

K K

K

Pekik A. Dahono -- Elektronika Daya

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Reverse Recovery Problems VFD

S I FD

Ed

FD

t rr

Io IS


Io 4

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Power diodes Diodes are classified as: - general purpose or line-frequency diodes - Fast recovery diodes - Schottky diodes


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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


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Thyristor A

iA iA

P

N

v AK G

P

N

K


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Thyristor Model I A = I E1

I B1 Q1

I C1 = −α1I E1 + I C 01 I C1 IG

IC 2 Q2

I C 2 = −α 2 I E 2 + I C 02 IA =

α 2 I G + I C 01 + I C 02 1 − (α1 + α 2 )

I B2 IE2 Pekik A. Dahono -- Elektronika Daya

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Thyristor in Simple Circuit

•

For successful turn-off, reverse voltage required for an interval greater than the turn-off interval Pekik A. Dahono -- Elektronika Daya

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Thyristor Classification • • • •

Phase control thyristors Inverter-grade or fast-type thyristors Light activated thyristors Reverse conducting thyristors


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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 Pekik A. Dahono -- Elektronika Daya

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Sample of thyristors


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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. Pekik A. Dahono -- Elektronika Daya

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Switching Characteristics Gate signal

Io Ed

iT

vT

Transistor voltage & current

iT

Ed

Io

tdon

vT

t fv tri t = t + t son ri fv

Transistor power

Wson =

tdoff

t fi trv t soff = trv + t fi

1 Ed I ot son 2

Wsoff =

1 Ed I ot soff 2

Pcd


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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


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Safe Operating Area i turn - on

turn - off

v Pekik A. Dahono -- Elektronika Daya

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Losses Switching losses :

(

Ps = 12 E d I o f s t son + t soff

)

fs is switching frequency.

Conduction losses :

Pcd = Von I o

TON Ts

Ts is switching period. Pekik A. Dahono -- Elektronika Daya

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Bipolar Junction Transistor iC C

C

B

N P N E

iC iB B

iB 5 iB 4 iB 3 iB 2 iB1 = 0

vCE E

iC

vCE

iB5 > iB 4 > iB3 > iB 2 > iB1

• Used commonly in the past • Now used in specific applications • Replaced by MOSFETs and IGBTs Pekik A. Dahono -- Elektronika Daya

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VI characteristics of BJT Hard - saturation Quasi - saturation

Second breakdown

IC

I B5 I B4 I B3 I B2 I B1

I B0 = 0

Primary breakdown

IB < 0

BVSUS

vCE

BVCB0


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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. Pekik A. Dahono -- Elektronika Daya

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Antisaturation circuit C

D1 B'

B D2 D3

E


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BJT Features • • • • • • •

Current controlled devices Double carrier devices No reverse blocking capability Low gain (Ic/Ib) Low on-state voltage Can not be protected by fuse Second breakdown problem Pekik A. Dahono -- Elektronika Daya

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Darlington Configuration


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MOSFET

iD

D iD G

vGS 5 vGS 4 vGS 3 vGS 2 vGS1 = 0 vDS

S

iD

v DS

vGS 5 > vGS 4 > vGS 3 > vGS 2 > vGS1 Pekik A. Dahono -- Elektronika Daya

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MOSFET Features • • • • • • •

Voltage controlled devices Single carrier devices High on-state voltage Very high gain No reverse blocking capability No second breakdown problem Can not be protected by fuse Pekik A. Dahono -- Elektronika Daya

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Integrated Power MOSFET


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Gate-Turn-Off (GTO) Thyristor iA

Blocking condition v AK


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GTO switching characteristic Anode voltage Anode current

IA Vd

Spike voltage

Tail current

0

Time

IGR (b)


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Turn-Off Snubber for GTO


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GTO Features • Controllable at turn-on and turn-off • High-voltage capability • Can be designed with reverse blocking capabilty • Low gain at turn-off • Low on-state voltage • High turn-off losses Pekik A. Dahono -- Elektronika Daya

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GTO vs IGCT


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GTO vs IGCT


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Insulated Gate Bipolar Transistors (IGBTs)

iC C

iC G

vGE 5 vGE 4 vGE 3 vGE 2 vGE1 = 0 vCE

E

vGE5 > vGE 4 > vGE3 > vGE 2 > vGE1 Pekik A. Dahono -- Elektronika Daya

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IGBT Features • Combining the advantages of BJT and MOSFET • No reverse blocking capability • No second breakdown • High gain at turn on and turn off


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IGBT vs IGCT


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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. Pekik A. Dahono -- Elektronika Daya

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MCT : MOS CONTROLLED THYRISTOR

QU RE

EN

1990

104 THYRISTOR

103

GTO

1980 P (kVA)

GTO : GATE TURN-OFF THYRISTOR THYRISTOR

CY

CONTROLLABLE POWER

GH HI

F

2000 105

P (kVA)

HIG H PO WER EA SY DR IV E

Switching Device Development 104

SI Thy : STATIC INDUCTION THYRISTOR BPT : BIPOLAR POWER TRANSISTOR

GTO

IGBT : INSULATED GATE BIPOLAR TRANSISTOR

SI Thy

MCT 103

IGBT 102

BPT 101

102

IGBT MOS

104

P (kVA)

THYRISTOR 103 102

GTO

101

BPT

10-1 -1 10

100

BPT

10-1 -1 10

101

100

MOS 10-1 -1 10

101 102 f (kHz)

100

101 102 f (kHz)

104

101 104 102 OPERATION FREQUENCY f (kHz)

105

106

105

104


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Reverse Conducting and Reverse Blocking Switching Devices

Reverse conducting

Reverse blocking


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Bidirectional Switches


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Switching devices Ideal Switch

Unidirectional uncontrolled switch Unidirectional semicontrolled switch

Bidirectional semicontrolled switch

Reverse conducting fully controlled switch

Reverse conducting fully controlled switch

Reverse blocking fully controlled switch

Bidirectional fully controlled switch


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Properties and Rating of Semiconductor Power Switches Switch

Diode SCR TRIAC GTO BJT MOSFET IGBT

Control signal

Control characteristic

Switching frequency

current current current current voltage voltage

trigger trigger trigger linear linear linear

low low medium Very high high

Voltage drop medium medium medium medium low high medium

Maximum voltage rating 6.5 kV 6 kV 1 kV 6.5 kV 1.5 kV 1 kV 3.5 kV

Maximum current rating 5 kA 4 kA 50 A 4.5 kA 1 kA 200 A 2 kA


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Properties of New Materials Property Bandgap at 300 K (eV) Relative dielectric constant Saturated drift velocity (cm/s) Thermal conductivity (W/cm/o C Maximum operating temperature (K) Melting temperature (C) Electron mobility at 300 K (cm2 /Vs) Breakdown electric field (V/cm)

Si 1.12

GaAs 1.43

3C-SiC 2.2

6H-SiC 2.9

Diamond 5.5

11.8

12.8

9.7

10

5.5

1x107 1.5

2x107 0.5

2.5x107 5.0

2.5x107 5.0

2.7x107 20

400

460

873

1240

1100

1415

1238

Sublime>1800

Sublime>1800

Phase change

1400

8500

1000

600

2200

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. Pekik A. Dahono -- Elektronika Daya

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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. Pekik A. Dahono -- Elektronika Daya

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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. Pekik A. Dahono -- Elektronika Daya

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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. Pekik A. Dahono -- Elektronika Daya

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The End

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