IGBT Modules - Technologies, Driver and Application (Second Edition) - page 165

Fig. 3.35
Static avalanche breakdown for an IGBT
Also a dynamic avalanche breakdownmay occur during the IGBT turn-off due to the co-
existenceof ahigh current and a high voltage.
Fig. 3.36
Dynamic voltage limiting of a 1.2kV NPT IGBT above its nominal static
breakdown voltage
The mechanism here is similar to that of a diode avalanche break-over which will be
described below. As long as the SOA limits of the IGBT are not exceeded during this
process the component will not be destroyed. With a dynamic avalanche the NPT and
FS IGBTs show a limiting of the maximum occurring over-voltage which is above the
specified breakdown voltage U
of the IGBT. Fig. 3.36 shows an example of this,
where a 1.2kVNPT IGBT limits the occurring over-voltage between collector andemitter
to a value of around 1850V. This is an operating condition, which is outside the SOA of
the IGBT and is hence strictly to be avoided. Latest developments aim at the dynamic
limiting of the voltage to below the nominal breakdown voltage in order to save the
IGBTs from destruction. This feature is called "Dynamic Clamping" or "Switching Self
ClampingMode (SSCM)".
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