Hi all,
I have four IGBTs in parallel and I have a suspision that only three are switching. The only access I have is at the collector emitter terminals P+ and N- and to the gate terminal G but i can open/close them all at the same time.

My question is how can I find if one of them is not switching?

Thank you

 

Are you reading a gate voltage on all of them?

Do you have a suspect? Do you think you know which one isn't switching?

 

Temperature differential?

 

I think I am almost 100% sure because it is heating more than the normal and the output is not as high as it should be. But I am asking to find a way to verify it. I know that I can switch the individually and measure the differencial across P+ and N- but I can only swotich them all at the same time.

I know that a voltage drop across a diode should be 0.6V but if all of them switch on except one what should I measure? Is going to be different resistance?

 

Electrically they are a single entity, like a black box, and you cannot learn anything about ONE of them, only the overall performance. If you can't separate them mechanically, or use non-electrical techniques like temperature, that's as far as you can go. Why not disconnect your suspect, and see what happens?

 

I agree. If you disconnect the gate to the suspect and the TOTAL output from the whole doesn't change, you know it is not conducting.

If you are getting a hotter IGBT, then it isn't dead, but something is going wrong.

They should all be running around the same temp.. if one is much cooler or much hotter, time to replace it.