Parameters of Bipolar Transistor

There are two important parameters of a transistor: the (α) and the (β). The relation between emitter current I_e and the collector current I_c is given by the parameter, known as alpha (α) of the transistor. Similarly, the relation between collector current I_c and the base current I_b is given by the parameter, known as beta (β) of the transistor.

Alpha (α): It is defined as the ratio of change in collector current I_c to the corresponding change in the emitter current I_e – 

α = ΔI_c / ΔI_e < 1

The value of alpha (α) is always less than unity, because emitter current is always greater than the collector current.

Beta (β): It is defined as the ratio of change in collector current I_c to the corresponding change in base current I_b –

β = ΔI_c / ΔI_b > 1

The value of beta (β) is always greater than unity, because collector current is always greater than the base current.