 Hitachi IGBT Module Application Manual
5.7.2 Calculating Delay Times of IGBTs
5.7.2.1
Turn-ON and Turn-OFF Switching Waveforms
Figure 43 illustrates the turn-ON and turn-OFF switching waveforms for an inductive load.
Figure 43. Inductive Load Turn-ON and Turn-OFF Switching Waveforms
5.7.2.2
Calculating Switching Delay Times
Note:
V
GP
and V
GN
in the equations are positive values.
At turn-ON, driver output voltage v
g
( out ) changes from -V
GN
to V
GP
, the gate input capacitance
C
ies
is charged, the gate voltage ( V
GE
) exceeds the gate threshold voltage ( V
th
), and a collector current
( i
c
) starts flowing. Immediately after the collector current starts flowing, the gate voltage remains constant
at voltage V
th
( on ) determined by collector current I
C
for some time (several microseconds) due to effects
of reverse transfer capacitance ( C
res
), and discharges return capacitance due to the gate current I
G res
(on)
(see Equation 29).
Equation 29:
I
G res
(on) = (V
GP
- V
th
(on))/(R
c
+ Z
on
))
where Z
on
is the ON-gate voltage output impedance of the driver.
The time until a collector current starts flowing, that is, the turn-ON delay time t
d
(on) is given by
Equation 30:
Equation 30:
t
d
(on) = -( R
G
+ Z
on
)
!
C
ies
[ln{( V
GP
- V
th
(on))/( V
GP
+ V
GN
) }]
Note:
Here, t
d
(on) is a delay time from the time when the gate voltage is
( -V
GN
). If the gate voltage becomes an intermediate voltage due
to a narrow control signal input, V
GN
should be replaced with the
intermediate voltage.
39
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