# Transistor Power Dissipation

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

1. ### gbm46 Thread Starter Active Member

May 6, 2007
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0
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. ### cumesoftware Senior Member

Apr 27, 2007
1,330
11
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
46
0
Sweet, thanks a lot.