IGBTs are normally engaged in hard-switching
applications as the device will switch high currents and
voltages under different inductive loading conditions [1].
Therefore, the IGBTs have to be exposed to different
standard tests to examine the IGBTs safe operating area
(SOA). Typically, there are two standard test circuits for
switching under high inductive loads. The first is the
unclamped inductive load switching test. In this test, the
semiconductor device has to absorb the entire energy
stored in the inductive load as it turns off. The second is
the clamped inductive load switching that employs a
freewheeling diode (FWD) in anti-parallel with the
inductive load. This diode provides a path for the load
inductor current after turning off the device under test
(DUT) [2]. However, the DUT could fail during such
tests resulting in all of the stored energy being transferred
into the failed DUT. This energy will significantly
damage the DUT and obscure any useful insights that
may indicate the origin and cause of failure at the chip
level. As the IGBT ratings increase the testing process
will become more and more problematic due to the very
high energy stored within the reactive elements of the test
circuit. Non-destructive testers (NDT) are implemented
in order to prevent or reduce the severity of such events
and may even protect the device from permanent failure.
NDT circuits can be classified into two categories
according to their principle of operation;