From: John Popelish
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Subject: Re: Question about linear derating factor for MOSFETs
Date: Mon, 11 Nov 2002 06:40:35 GMT
NNTP-Posting-Date: Mon, 11 Nov 2002 01:40:35 EST
John Larkin wrote:
> On Mon, 11 Nov 2002 04:36:43 -0000, email@example.com
> (Bob Wilson) wrote:
> >So let's take the 0.5C/W as an example. Pumping 350W across the
> >case-to-heatsink junction will result in a 175 C (!!!!) temperature drop
> >across this interface. In other words, your case temperature will be
> >175C above the heatsink temperature! This clearly tells you that there isn't
> >a hope of approaching the power level you are mentioning, using only one
> The IRFPS37N50A is rated at 446 watts dissipation, and some of the
> TO-247s are even higher. I suppose you could get that if you mount it
> to an isotopic diamond block, but numbers like that don't seem to be
> practical using real-life heat sinking.
> At these power levels, insulators between the transistor and the
> heatsink are pretty much impossible.
Perhaps you could submerge the device in alcohol or freon in a large
chamber with all the air evacuated, so that all the space was filled
with saturated vapor. This can act as a heat sink over the whole
surface of the device with a thermal conductivity a few hundred times
higher than solid copper.