# doubt

#### whale

Joined Dec 21, 2008
111
in common emitter configuration,the collector current is product of gain(β) and base current,
from whare the factor β comes?

#### mik3

Joined Feb 4, 2008
4,846
β is the current gain of the transistor which equals Ic/Ib

#### Dave

Joined Nov 17, 2003
6,960
in common emitter configuration,the collector current is product of gain(β) and base current,
from whare the factor β comes?
It is a function of the physical attributes of the transistor; namely doping concentrations in the n- and p-type semiconductor parts, physical dimensions (width, length), electron/hole diffusivity, and the minority-carrier lifetime.

Dave

#### studiot

Joined Nov 9, 2007
5,003
Try to think of it this simple way.

A transistor has three legs (terminals).

Therefore it has three terminal currents Ie , Ic, and Ib

By Kirchoffs current law, since they all meet at a point within the transistor

Ie+Ic+Ib = 0

We can also define three ratios with these currents, however only two are independant, we can always get the third by cross cancelling.

Originally the two that were chosen were called alpha and beta, after the first two letters of the Greek alphabet

So

alpha = Ic/Ie

Beta = Ic/Ib

Whatever these values turn out to be.

The fact that these values have desireable properties makes the transistor such a valuable device.

#### DickCappels

Joined Aug 21, 2008
5,755
Everybody knows where β comes from: The datasheet!