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

 

β is the current gain of the transistor which equals Ic/Ib

 

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

 

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.

 

Everybody knows where β comes from: The datasheet!