# Stability Factor

# Stability Factor

It is desirable and necessary to keep I_{C}

constant in the face of variations of I_{CBO} (sometimes represented as I_{CO}). The extent to which a biasing circuit is successful in achieving this goal is measured

by stability factor S. It is defined as under :

The rate of change of collector current I_{C}

w.r.t. the collector leakage current *I_{CO} at constant β

and I_{B}

is called stability factor i.e.

Stability factor,

S =

at constant I_{B} and β

The factor indicates the change in collector current I_{C}

due to the change in collector

leakage current I_{CO}. Thus a factor 50 of a circuit means that I_{C}

changes 50 times as much as

any change in I_{CO}. In order to achieve greater thermal stability, it is desirable to have as low stability

factor as possible. The ideal value of S is 1 but it is never possible to achieve it in practice. Experience shows that values of S exceeding 25 result in unsatisfactory performance.

The general expression of factor for a C.E. configuration can be obtain as under:

I_{C}

= β I_{B}(β + 1) I_{CO}

Differentiating above expression w.r.t. I_{C}

, we get,

1 =

S =

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