Guru
Joined: 08/10/2011
Location: AustraliaPosts: 2498
| Posted: 01:04pm 25 Mar 2017 |
Gate source resistors need to keep the gate off when it is supposed to be off. Perhaps 20K that we are using is too high, easy enough to try, I can put another 20k in parallel and see if that has any effect on a board I have that works but is producing spikes so I have only run it for a few seconds at a time, that will make it 10K. With 6 FETs this may behave differently than 1 big FET with only 1 gate.
From how I see it the things that will kill FETs is over current which could happen if both sides of the bridge happen to turn on at the same time. Working them hard when the inverter is running properly does not seem to cause any issue if they are kept at a reasonable temperature. Over temperature would kill them also but I have never measured more than 60 degrees with the big heatsinks I am using. Even running at 8KW for over 30 minutes with ambient temperature over 35 degrees. The other big killer is over voltage, this could come from snubbers not doing their job properly.
There are only 10 types of people in the world: those who understand binary, and those who don't.