VERY unusual if this FET has a positive TCR of resistance.. the OP should get a real power mosfet instead of a strange device.

There should be a second breakdown spot on the SOA curve in that daatsheet then as well.

 

You can connect Mosfets in parallel because their on-resistance increases when they get hot. The opposite of junction transistors.

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Uncle $crooge

 

Please cite some "real power mosfets" with zero or negative TCR.

I've only seen power mosfets with a positive TCR.

 

I dont believe there are any.. what I mean to point out is.. when a MOSFET on resistance increases *and* causes MORE power dissipation which then further increases the on resistance.. this is thermal runaway and the part will self destruct. Audio guru was pointing this out.. yet, there is no 2nd breakdown area in the SOA...why not??? Usually the positive TCR keeps this from happening.. Audio's original comment made it sound like that is not the case.... This is what I find strange.

 

The power dissipation in the Mosfet is maximum when its resistance equals the load resistance. When its resistance increases above the load's resistance then its power dissipation becomes less.

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Uncle $crooge

 

Optikon you are right if the MOSFET is in an amplifier and biased for class A operation. AudioGuru is right when the MOSFET is used as a switch in say a class D amplifier. Two different applications and two different effects as the junction temperature increases.
As you can see from the diagram, at high drain currents the SOA is limited by the RDSon value which increases with temperature. (IRLZ44)

Attached Images

FetSOA.GIF (20.6 KB, 4 views)

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