Jim Tellier wrote:

> But to my original question, did I calc power dissipation correctly?  I
> guess if I did, I'm just a little surprised that it's so low (haven';t
> really used these devices before, so not intimately familiar with them).

Hi Jim,

Yes, you calculated your power dissipation correctly. Great devices aren't
they?

Now that I know what MOSFET and package you are using, I would not worry
about things -- you are not even making it sweat at 1/10 W power
dissipation. :) Its power dissipation is rated at 43 watts (obviously not
without adequate heat-sinking), but you need to read between the lines on
that -- that's where the data sheet is crucial.

I've been *really* liking the way Vishay/Siliconix lists some of the data
parameters versus International Rectifier. On some of Vishay's data sheets,
they list the absolute maximum specs over two columns: 10 secs duration and
steady state. Gives me a better feel for things very quickly.

If your MOSFET is passing only 0.25 amps, I would forgo the heat sink. It
sounds like you will mount it upright. If you need the MOSFET to supply more
current, you might consider switching to one that has a lower RDSon. I would
imagine it would not be too difficult to find something in the same price
range with a lower RDSon -- your power losses will be lower (I^2 * R). But
if the current levels won't significantly increase from what you posted than
it would make no sense unless you can find something cheaper. But there are
a lot of details that I'm not aware of on your side.

Best regards,

Ken Pergola

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