IGBT Modules - Technologies, Driver and Application (Second Edition) - page 164

process of the IGBT module, and this may be higher by several orders of magnitude
than the real cut-off (quiescent) current. Correspondingly, there is little sense in practise
to calculate the off-state power loss by multiplying U
and I
. The proportion of the
off-state power loss in relation to the other losses (on-state and switching losses) is
Aside from the thermal energy, the cut-off current I
may also be caused by cosmic
radiation (chapter
. The influence of the cosmic radiation depends on the level
(height) at which the component is operated, the junction temperature, the applied off-
state voltage aswell as the voltage rating of the component. The higher above sea level
the component is operated at, the greater is its probability of failure. This is expressed
by an increaseof theFIT rat
Fig. 3.34
Dependency of the blocking voltage on the junction temperature using the
example of a 6.5kV IGBT
3.8 Static anddynamic avalanchebreakdown
If an IGBT is operated above its specified collector-emitter off-state voltage U
then it
may come to an avalanche breakdown (chapter
. If the field strength of the pn-
junction between the p-doped base and the n
-dope drift zone is exceeded then this pn-
junction J
loses its blocking capability. An avalanche-like breakdown occurs, during
which large amounts of carriers are torn from the crystal lattice structure. This causes a
large current to flow in forward blocking direction. This type of avalanche breakdown
occurs in the static off-state phase of the IGBT and it leads to the destruction of the
FIT stands for "Failure inTime" (chapte
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