Hitachi IGBT Module Application Manual
At turn-OFF, it moves to an OFF state due to the discharge of C
ies
. However, C
res
is discharged due to
the gate current I
Gres
(off) (see Equation 31) until it becomes constant at the voltage V
th
(off) where v
ge
depends only on I
C
and the collector voltage v
ce
becomes source voltage V
CE
. Collector current I
C
declines only when v
ce
= V
CE
.
Equation 31:
I
Gres
(off) = (V
GP
+ V
th
(off))/( R
G
+ Z
off
)
where Z
off
is the OFF-gate voltage output impedance of the driver.
The turn-ON delay time is a time t
d
(off) until C
res
is charged to V
CE
whose value can be determined
using Equation 32:
Equation 32:
t
d
(off)= -( R
G
+ Z
off
)
!
(C
ies
+ C
res
(0))
!
ln{(V
GN
+ V
th
(off))/
(V
GP
+ V
GN
)} + Q
GQ
/ I
Gres
(off)
= -(R
G
+ Z
off
)(3 C
ies
)
!
ln{(V
GN
+ V
th
(off))/(V
GP
+ V
GN
)} + Q
GQ
/ I
Gres
(off)
Definitions:
C
res
(0)
Q
GQ
Reverse transfer capacitance (set equal to 2 C
ies
here)
when V
CE
is approximately 0V
Total recharging charge (gate charge) of C
res
(see Figure 44).
Figure 44. Parasitic Capacitance
40
Pages: Home Index