# doubt

Discussion in 'Physics' started by whale, Jan 14, 2009.

1. ### whale Thread Starter Active Member

Dec 21, 2008
111
0
in common emitter configuration,the collector current is product of gain(β) and base current,
from whare the factor β comes?

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
β is the current gain of the transistor which equals Ic/Ib

3. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
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

4. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
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.

5. ### DickCappels Moderator

Aug 21, 2008
2,774
671
Everybody knows where β comes from: The datasheet!