Guru
Joined: 08/02/2015
Location: New ZealandPosts: 1255
| Posted: 08:05am 08 Aug 2026 |
Those points marked in red on the SOA curve are the steady state DC level, your mosfets are not permanently at that point on the SOA curve, they are or should be turned on in a few tens of nano-seconds, thusly the current capability increases as shown higher up the curves with decreasing on times.
Most likely it is a voltage spike thats killing them, 72v battery voltage, you need really 150v mosfets, perhaps the circuit requires the correct snubber RC network across the Drain\Source pins to control any voltage spike or ringing; look at it on a scope; generally the more current drawn the larger any ringing spikes.
Moving to compound die mosfets doubles the charge currents needed to switch them on in the shortest time, having 4 paralleled places a lot of extra stress on the mosfet driver and its bias supply, if the bias supply sags and cannot supply the required driver current then that will also blow them up, if you go for dual die versions, then a 2watt psu for the bias would be needed.
Cheers
Mike