Transistor Power Dissipation

Thread Starter


Joined 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.


Joined 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).