IGBT Modules - Technologies, Driver and Application (Second Edition) - page 168

Fig. 3.39
Determination by measurement of the total stray inductance L
for a diode
turn-off test set-up.
A diode turn-off test according to
s carried out to determine the total module
stray inductance of a single switch or a half-bridge. The module to be tested (DUT) is
considered as a diodewhichmakes up the freewheeling path for the inductance L.With
this test the stray inductance of one complete leg of amodule canbe ascertained. If a 6-
in-1module is to be examined, then always only one half-bridge of it at a timemust be
used. Possibly the other two half-bridges of the module have both to be separated
internally (this constituted adestructivemodification of themodule).
If the measurement is done according to
the result would be a graph as
exemplified in
The measurement is done in such a way that a sufficient U
voltage plateau develops. To do this the DC-bus voltage U
may possibly have to be
adjusted. The zero crossing of the diode current I
is subsequently used as a reference
for the evaluation. This serves to read off the di and dt. It is necessary for this that the
current slope is as linear and free of curls as possible. It may be necessary to adjust the
driver stage (i.e. the gate resistor) of T
. The voltage
then results for the plateau
value to the time dt, viewed at fromwhen I
= 0. Once all parameters have been found
the stray inductance of the total leg of theDUT is calculatedby:
1...,158,159,160,161,162,163,164,165,166,167 169,170,171,172,173,174,175,176,177,178,...548
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