Feb 5, 2010 ... 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
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
Pekik A. Dahono -- Elektronika Daya
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).
Pekik A. Dahono -- Elektronika Daya
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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
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