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Transistor Power Dissipation

Discussion in 'Homework Help' started by gbm46, Oct 11, 2007.

  1. gbm46

    Thread Starter Active Member

    May 6, 2007
    I am stuck on a homework question which asks to find the maximum power dissipation in a transistor. It is a BJT, the data sheet is supplied. I think that the power dissipation is Vce * Ie but I would really appreciate confirmation on this. I can find Ie max and Vce is 5V.
  2. bloguetronica

    AAC Fanatic!

    Apr 27, 2007
    In general terms, you can consider that. It the base current is relevant, you can consider:
    P = Vbe * Ib + Vce * Ic.

    Since Ic is aprox. equal to Ie, then:
    P = Vbe * Ib + Vce * Ie (used moslty when the transistor it is within it's saturation region)

    Notice that the term Vbe * Ib will not be important if the transistor is in it's active region. The you can simplify:
    P = Vce * Ie

    P.S.: Vbe can be 0.7V while Vbe can be only 0.15V. That is why the Vbe * Ib term is so important when a transistor is being used in it's saturation region (as a key).
  3. gbm46

    Thread Starter Active Member

    May 6, 2007
    Sweet, thanks a lot. :) :) :)