Hitachi IGBT Module Application Manual
Table 3. Snubber Capacitor Values
Rated Collector
Current ( I
C
)
50 A class
75 A class
100 A class
150 A class
200 A class
300 A class
400 A class
600 A class
Snubber Capacitor
Values (
µ
F )
0.10 to 0.22
0.15 to 0.33
0.22 to 0.68
0.33 to 1.00
0.47 to 1.50
0.68 to 2.20
1.00 to 3.30
2.20 to 4.70
Depending on the inductance of the main circuit wiring, larger capacitance values than are listed in
frequency characteristics.
5.2.5 Snubber Resistance Selection
The resistor value varies according to capacitor value and the IGBT’s driving frequency. When voltage
∆
V
overcharged to the snubber is used,
ε
S
n
generated when the current I is turned OFF becomes,
according to Equation 8:
Equation 8:
ε
S
n
= 0.5
!
C
S
!
(
∆
V)
2
Most of this energy can be considered to be consumed by snubber resistance. Supposing that the output
current of a voltage inverter or something similar is a sinusoidal current with current I in Equation 7 as a peak
value, the energy of the snubber circuit can be considered to occur as a sine wave with
ε
S
n
as a peak value. The average generated loss
P
SN
in the P-N snubber circuit, taking into account the
switching of the top and bottom arms becomes, according to Equation 9:
Equation 9:
P
SN
= (2/
Ï€
)
!
ε
S
n
!
f
c
where
f
c
is a switching frequency.
Equation 10 indicates what resistance value must be selected to prevent oscillation of the collector
current at IGBT turn-ON.
Equation 10:
R
s
> 2
(
Lsn
)
-------------
-
Cs
where
L
sn
is the inductance of the snubber wiring.
Note:
R
s
represents resistance in discharging
∆
V overcharged to C
s
,
so that the top limit must be noted.
5.2.6 Snubber Diode Selection
Select a snubber diode having the same class as the IGBT’s rated collector emitter voltage value. Use an
IGBT module with a current rating of 1/10 to 1/5 that of the IGBT used.
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