avalanche breakdown at MOSFET on state

[ljy4468]

Hi all

I have a question about avalanche breakdown at MOSFET .

I know that avalanche breakdown occurs when voltage exceed bvdss at OFF state.

Then is it possible that avalanche breakdown occurs when mosfet's ON state???? (if sudden voltage spikes occured at drain or source)

Thanks in advance.

 

[schmitt trigger]

In the forward biased mode, the limiting factor is junction temperature. In other words how much power the fet is dissipating.

Have you seen the pulse duration curves on the datasheet? for instance, figure 11 on the following datasheet:
https://www.onsemi.com/pub_link/Collateral/NVMFS4C05N-D.PDF

As you can see, for a few microseconds, the fet can withstand a very high current and voltage. The curve is derated substantially for continuous operation, i.e DC.