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I would like to know:

1) Why, almost on every IGBT datasheet that \$I_{cm}\$ (maximum peak current) is 2 times \$I_c\$? - for example see datasheet

How, can I measure this \$I_{cm}\$, to verify that it is really 2 times \$I_c\$? Or is there maybe some regulation that on a datasheet that \$I_{cm}=2*I_c\$ ?

2) Energy losses: I see on the oscilloscope, that there is a tail current after switching. To calculate Eoff, for example how much time do I have to consider the tail current? Some company determine toff for 1us. Why? Some rule specified that time of tail current for Eloss evaluation must be 1us? Or everyone could choose the time that they want?

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On Semiconductor published a guide on how to interpret their IGBT datasheets. It says that:

The pulsed collector current describes the peak collector current pulse above the rated collector current specification that can flow while remaining below the maximum junction temperature. The maximum allowable pulsed current in turn depends on the pulse width, duty cycle and thermal conditions of the device. (P. 2)

So this is not some exact figure that is linked to the steady current by a factor of two; it is really a multi-dimensional limit. If a data sheet gives this figure for a specified pulse width, but doesn't give the duty cycle, there has to be some understood duty cycle. Obviously, the 1ms pulse cannot be repeated again and again, with just a microsecond of off time in between!

The assumption may be for a maximum duty cycle of 50%. If twice the current is turned on, but for half the time, and the thermal conditions are otherwise the same, junction temperature should be about the same, provided that the pulses are sufficiently narrow.

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In answer to your question #1:

There is no need for you to measure this, this value in the datasheet is the manufacturer saying, "Do NOT exceed his value" or bad things will start to happen to your device. Typically maximums are not tested for in devices that will then be used in production as these are typically destructive or damaging tests.

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