Stability factor indicates the 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 , is more dominant over the change in and . Hence is calculated here.
Rate of change of collector current w.r.t reverse saturation current