Hitachi IGBT Module Application Manual
How to Check Vertical Motion
Figure 48 represents waveforms observed at the time of the verification. The turn-OFF of the bottom
arm is regarded as the point (Point B) where the gate voltage starts shifting to a reverse bias, and the phase
relationship between it and the peak point (Point A) of the gate current of the top arm is used to determine
whether overlap or non-overlap is present.
Figure 48. Control Signal and Gate Waveforms
If Point A occurs earlier than does Point B, the top and bottom arms can be considered to be short-
circuited. (See Figure 48.) When the top and bottom arms are short-circuited, collector current becomes
something like what is indicated by broken lines in Figure 48, with a rise in switching loss. In the gate voltage
waveform at this time, a rise in Point B voltage is observed. (If significant short-circuiting arises, the system
shifts from gate source voltage to reverse bias voltage.)
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