Hitachi IGBT Module Application Manual
Equation 43:
Q
res
= i
gsc
!
t
scv
Definitions:
v
ge
(i)
V
GP
i
gsc
t
scv
Gate voltage of IGBT
Terminal voltage of driver output (approx. 16V)
Gate current from gate to driver
Collector voltage increase term (approximately 3 to 5
µ
s).
The IGBT gate voltage ( v
ge
(i) ) can be calculated using Equation 44.
Equation 44:
v
ge
(i) = Q
res
!
R
G
/ t
scv
+ V
GP’
For example,
V
GP’
Q
res
R
G
t
scv
v
ge
(i)
= 16 V
= 700 nC (for an MBM300GS12A device)
= 4.3 ohms
= 3
µ
s
= 17 V (approx.)
5.8.5 Prevention of Gate Voltage Increase
Saturation value of short circuit current increases with gate voltage increase, especially in the hard cut-
off method for short-circuit protection. Also, overshoot voltage increases with cut-off current increase.
To prevent gate voltage increase, use the following approach.
(1)
Connect a diode from emitter toward the collector of transistor (Q1) to bypass
the current. Especially for the case involving the hard cut-off method, the
emitter follower output circuit is not necessary, as the CMOS output circuit
is already an effective means. (Note that there is an inner diode in the
MOSFET.)
(2)
Connect in series the zener diode and diode between gate (G) and emitter (E)
terminals.
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