Luis Moreira wrote:
> So the question is how do I calculate the power dissipated on the
> Transistor?

Start by calculating the power during the pulse on time.  The current is

  I = 8A * (T/Ton)

And the power dissipation is

  P = I**2 * Rdson = 64 A**2 * Rdson * (T**2 / Ton**2)

Now integrate P for T = 0 to Ton.  That yields the total energy dissipated
during the pulse.  Now divide that by the repitition period (10uS in your
example) to get the average power dissipation due to conduction during the
pulse.

However, as others have pointed out also, the FET could be dissipating
significant power during the on to off transition unless the gate is being
driven very fast.

Also note that this FET has a fairly high on resistance.  At 8A the
voltage accross it will be 6.4V.  You might be a lot better off with a
bipolar transistor.


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