What is the bias stability factor (S) for a fixed bias circuit?

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Question

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RRB JE EE 22 Apr 2025 Shift 1 CBT 2 Official Paper

Answer 1

Concept

Stability factor (S): The stability factor is determined by the rate of change of the collector current I_C with respect to the I_CBO.

\(S= \frac{\partial I_C}{\partial I_{CBO}}\)

Stability factor for a fixed bias circuit:

F1 Madhuri Engineering 23.02.2023 D12

\(I_C = β I_B \space +\space (1+\beta)I_{CBO}\)

\(S= \frac{\partial {(β I_B \space +\space (1+\beta)I_{CBO})}}{\partial I_{CBO}}\)

Since IC is independent of ICBO in a fixed bias (no feedback), its derivative is 0.

\(S= 0+(1+\beta)\times 1\)

S = (1 + β)