# IGBT Modules - Technologies, Driver and Application (Second Edition) - page 146

134
diode switching losses P
sw,D
are calculated by multiplying E
rec
with the switching
frequency f
SW
.
Alternatively the switching losses P
sw,D
may be calculated according to the datasheet
value of E
rec
(I
nom
U
nom
,T
vj
) while considering the application parameters. Usually the
valueE
rec
(I
nom
, U
nom
,T
vj
) is shown in the datasheet of the diode for a specific current I
nom
and voltage U
nom
. Also a particular
dt
di
F
is specified which the manufacturer defines.
Matching this to the real application is done by linear adaptation. This approach is
sufficiently accurate for adeviation from thenominal values by
±
20%.
nom
DC
nom
vj
nom nom rec
sw
D,sw
U
U
I
)T, U, I( E f1 P
π
=
Eq. 3.16
Bearing in mind that there is no linear dependency of the reverse recovery energy E
rec
then entering
+ ⋅
=
55.0
I
45.0 )T, I( E)iˆ( E
nom
vj
nom rec
rec
Eq. 3.17
into
a better approximation of the diode turn-off losses can be achieved in
practice.
nom
DC
nom
vj
nom rec
sw
D,sw
U
U 55.0
I
45.0 )T, I( E f1 P
⋅
+ ⋅
π
=
Eq. 3.18
Aside from the switching losses, the so-called soft recovery is of interest with the diode.
This defines a soft turn-off behaviour which is not marked by snapping off of the
recovery current and the oscillations resulting from it. Usually this is defined by the soft-
factor Swhich describes the ratioof the times t
s
to t
f
.
s
f
t
t S
=
Eq. 3.19
However, in practice this soft-factor has not established itself very well, as it describes
the soft or hard turn-off process insufficiently. Instead the following definition can be
found in the literature
:
max
r
A0 I
F
dt
di
dt
di
S
F
=
=
Eq. 3.20
With this definition even the centre case in
can be correctly ascertained.
According to the definition in
the switching behaviour would be classified as
soft, despite the snappingof the current at the end of time t
f
.
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