STATIC CURRENT AMPLIFICATION

The maximum obtainable current amplification factor of a bipolar transistor is known as the beta of the transistor. Depending on the way in which a transistor is manufactured, the beta can range from a factor of a few times up to hundreds of times. One method of expressing the beta of a transistor is as the static forward current transfer ratio, symbolized HFE. This is the ratio of the collector current to the base current:
H_FE = I_C/IB
For example, if a base current IB of 1 mA produces a collector current I_C of 35 mA, then H_FE = 35/1 = 35. If I_B = 0.5 mA and I_C = 35 mA, then H_FE = 35/0.5 = 70.