Sunday, 18 May 2014

Apparent inconsistency of MOSFET power rating in datasheet: SOA v. max power



I am trying to use an IPP114N03L G (datasheet).


I calculated the maximum power it could handle as follows:


From the first two pages of the datasheet: Rthjc = 3.9K/W Tj(max) = 175C


Assuming I can keep the case under 50C, max. power dissipation should be: (175 - 50) / 3.9 = 32W


So 1A at 30V should be about the maximum.


Now looking at the Safe Operating Area graph on page 4, at 30V it says ~150mA max. and that is with Tc at only 25C.


Why do these figures disagree?


In practice, I have killed two of these devices now, the last one was at around 20V 200mA, so it seems the first calculation is wrong. The case was cool.




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