 Hitachi IGBT Module Application Manual
5.7.3 Parametric Effects on Switching Delay Time
5.7.3.1
Examining Influential Parameters
Equation 33 allows us to examine the effects of collector current and junction temperature on IGBT
module operating conditions:
Equation 33:
T
D’
= T
D
- ( t
3
+ t
4
) + ( t
1
+ t
2
)
Equation 33 provides a means for calculating the real dead time (
T
D’
) relative to a dead time (
T
D
)
setting, and this equation allows for finite driver output delays (
t
1
and
t
3
). Often, these particular delay
times are judged to be negligible and are set to zero. Realistically, however, all driver delay times must be
checked.
T
D’
) of IGBT output terminals (C and E) are expressed by Equation 34:
Equation 34:
T
D’
= T
D
+ t
2
- t
4
Here,
T
D
represents a theoretical setting and times
t
2
and
t
4
are turn-ON and turn-OFF delay times,
respectively, which can be determined using Equation 35 and Equation 36.
Equation 35:
Equation 36:
t
d
(on)=-(R
G
+ Z
on
)
!
C
ies
!
ln{(V
GP
- V
th
(on))/(V
GP
+ V
GN
)
t
d
(off)= -(R
G
+ Z
off
)
!
3 C
ies
!
ln{(V
GN
+ V
th
(on))/(V
GP
+ V
GN
)} + Q
GC
/ I
Gres
(off)
Substituting these for Equation 34, you will get
Equation 37:
T
D’
=T
D
[-{(R
G
+ Z
on
)
!
C
ies
!
ln((V
GP
- V
th
(on))/
(V
GP
+ V
GN
)}]
-[-{(R
G
+ Z
off
)
!
3 C
ies
!
ln{(V
GN
+ V
th
(off))/(V
GP
+ V
GN
)}}
+ Q
GC
/ (I
G
res
(off)]
where OFF-gate current I
G
res
(off) can be determined with Equation 38:
Equation 38:
I
G res
(off)=( V
GP
+ V
th
(off)) / (R
G
+ Z
off
)
Substituting this expression into Equation 37 results in Equation 39:
Equation 39:
T
D’
= T
D
+[-{( R
G
+ Z
on
)
!
C
ies
!
ln((V
GP
- V
th
(on))/(V
GP
+ V
GN
)}]
-[-{(R
G
+ Z
off
)
!
3 C
ies
!
ln{(V
GN
+ V
th
(off))/(V
GP
+ V
GN
)}}
+ Q
GC
(R
G
+ Z
off
) / (V
GN
+ V
th
(off)]
5.7.3.2
Effect on Gate Voltages
In Equation 39, collector current I
C
and junction temperature T
j
affect two gate voltages: V
th
(on) and
V
th
(off) which have a relationship as shown in Figure 45 with collector current.
Figure 45. Gate Voltage - Collector Current Characteristics
41
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