Q. Write short notes on the Stability Factor of Biasing circuits.

The degree of success achieved in stabilizing Ic in the face of variations in Ico is expressed in terms of stability factor S and it is defined  as the rate  of change of collector current w.r.t  Ico  keeping  â and VBE constant.

S=dIc/dIco at constant â  and VBE

From  the above equation it is obvious that smaller is the value of S ,higher is the stability.The ideal value of S is unity (because Ic includes Ico) but it is  never possible to achieve it in practice.Actually there are two stability factors Sv and S â  are defined as below:

                                     Sv = ÄIc/ÄIBE at constant Ico and  â

                                     SB ÄIc/ÄI â at constant Ico and  VBE

General expression for Stability Factor

                               S = 1+â/(1- âdIB/dIc)