Chapter 9
Practical Application Issues
of Power Semiconductor Devices
Outline
9.1 Gate drive circuit
Power
9.2 Protection of power semiconductor devices
9.3 Series and parallel connections of power
semiconductor devices
2
9.1 Gate drive circuit
Power
Basic function of gate drive circuit:
Generate gate signals to turn-on or turn-off power
semiconductor device according to the commanding
signals from the control circuit.
Other functions of gate drive circuit:
Reduce switching time (including turn-on time and turnoff time)
Reduce switching loss (including turn-on loss and turnoff loss) and improve efficiency
Improve protection and safety of the converter
Gate drive circuits provided by power semiconductor
manufacturers and Integrated gate drive chips are
more and more widely used.
3
Electrical isolation in the gate drive circuit
Power
Gate drive circuit usually
provides the electrical
isolation between control
circuit and power stage.
Two ways to provide
electrical isolation
ID
R
IC
E
R1
Uin
Photo
transistor
Uout
LED
– Optical
• Optocoupler, fiber optics
• Transformer
Schematic of an optocoupler
– Magnetic
4
Thyristor gate current pulse requirments
Shape of gate current
pulse waveform:
Power
– Enhanced leading part
Magnitude requirement
(for the enhanced leading
part and the other part)
Width requirement (for the
enhanced leading part and
the whole pulse)
Power of the triggering
signal must be within the
SOA of the gate I-V
characteristics
IM
I
t
t1 t2
t3
t4
Ideal gate current pulse
waveform for thyristors
5
Typical thyristor gate triggering circuit
+E1
Power
Input from
control circuit
TM
VD2
R4
VD3
VD1
R1
+E2
R3
V1
R2
V2
6
Typical gate signal and gate drive circuit
for GTO
uG
t
VD2
O
C2 VD3
R1
R2
Power
GTO
VD1
iG
O
t
50kHz
N1
50V
N2
N3
V1
C1
VD4
L
C3 V2
C4
R3
V3
R4
7
A typical gate drive circuit for IGBT based on
an integrated driver chip
4 VCC
Detection
circuit
14
1 Sensing
Power
Timer and
reset circuit
Interface
circuit
8
+5V
14
5 uo
Turn-off
circuit
13
4.7k
8
Error
indicating
6 VEE
1
Fast recovery diode
trr¡Ü0.2s
30V
5
3.1
4
M57962L
ui
1
+15V
13
100F
100F
6
-10V
M57962L integrated driver chip
8
9.2 Protection of power semiconductor
devices
Power
Protection circuits
Overvoltage protection
Overcurrent protection
Snubber circuits—specific protection circuits that
can limit du/dt or di/dt
Turn-on snubber
Turn-off snubber
9
Causes of overvoltage on power
semiconductor devices
Power
External reasons
Overvoltage caused by operation of mechanic
swithes
Overvoltage caused by thunder lightening
Internal reasons
Overvoltage caused by the reverse recovery of
diode or thyristor
Overvoltage caused by the turning-off of fullycontrolled devices
10
Measures to protect power semiconductor
devices from overvoltage
SD C
T
LB
M
S
U
C
Power
F
RV
D
RC1
Lightening arrestor
RC2
RC3
RC4
RCD
图1-34
RC or RCD snubbers (will be discussed later)
Zener diode, Metal Oxide Varistor (MOV), Break Over
Diode (BOD)
11
Measures to protect power semiconductor
devices from overcurrent
Fuse
Circuit breaker
Power
Protection with current feedback control in the control
circuit
Protection with overcurrent detection in the gate drive
circuit—the fastest measure
12
Functions and classifications of snubbers
Functions
Power
Limiting voltages applied to devices during turn-off transients
Limiting device currents during turn-on transients
Limiting device current rising rate (di/dt) at device turn-on
Limiting the rate of rise (du/dt) of voltages across devices
during device turn-off
Shaping the switching trajectory of the device
Classifications
According to different switching transients
– Turn-off snubber (sometimes just called snubber)
– Turn-on snubber
According to the treatment of energy
– Power dissipating snubber
– Lossless snubber
13
Operation principle of typical snubbers
Circuit configuration
uCE
iC
without turn-off snubber
without turn-on snubber
uCE
iC
Ri
with turn-off
snubber
O
t
with turn-on snubber
Turn-off
snubber
iC
V
VDs
Power
VDi
Li
Turn-on
snubber
Rs
B
A
without turn-off snubber
Cs
L
VD
D
with turn-off snubber
O
Switching trajectory
图1-39
C
uCE
14
Other turn-off snubbers
Ed
L
Rs
Turn-off
snubber
Cs
Load
Cs
Ed
Turn-off
snubber
VDs
Power
L
Rs
Load
15
9.3 Series and parallel connections of
power semiconductor devices
Object
To increase the capability to deal with voltage or current
Issues and solutions
Series connection
Power
– Issue: even voltage sharing
– Solutions:
• Selection of devices that are closer to each other in the characteristics
• Voltage sharing circuit
Parallel connection
– Issue: even current sharing
– Solutions:
• Selection of devices that are closer to each other in the characteristics
• Current sharing circuit and symmetrical circuit layout
16
Series Connection of thyristors
I
VT1
VT2
VT1
RP
C
IR
Power
O
R
UT1
UT2
U
VT2
RP
R
C
a)
Voltage sharing circuit
b)
图1-41
– Steady-state voltage sharing circuit
– Dynamic voltage sharing circuit
17
Power
Parallel Connection of Power MOSFETs
Easy to realize because of the positive temperature of their onstate resistance
Need a small damping resistor in series with the individual gate
connections
Still need to select devices that are closer to each other in the
characteristics
Circuit layout should be symmetrical
18