Stability Factors

>>  Stability factor indicates degree of change in operating due to variation in temperature. There are three variables which are temperature dependent. We can define three stability factors :


>>  Ideally, Stability factors should be zero to keep operating point stable and fixed.

>>  Practically, Stability factors should have the value as minimum as possible.

>>  Effect of change in ICO, is more dominant over change in β and VBE. Hence S is calculated here.

S = ∂IC / ∂ICO : Rate of change of collector current w.r.t reverse saturation current 

IC = β IB + (1+β) ICO

1 = β (∂IB / ∂IC) + (1+β) ∂ICO / ∂IC

 ⇒  ∂ICO / ∂IC = ( 1 – β ∂I/ ∂IC ) / (1+β)

S = ∂IC / ∂ICO = (1+β) / (1 – β ∂IB / ∂IC)



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