What is hFE of a Transistor?

hFE of a transistor is the current gain or amplification factor of a transistor.

hFE (which is also referred to as β) is the factor by which the base current is amplified to produce the amplified current of the transistor. The unamplified current is the base current, which then undergoes amplification by a factor of hFE to produce an amplified current which flows through the collector and emitter terminals.

A transistor works by feeding a current into the base of the transistor. The base current is then amplified by hFE to yield its amplified current. The formula is below:

IC= hFEIB=βIB

So if 1mA is fed into the base of a transistor and it has a hFE of 100, the collector current will be 100mA.

Every transistor has its own unique hFE. The hFE is normally seen to be a constant value, normally around 10 to 500, but it may change slightly with temperature and with changes in collector-to-emitter voltage.

Check the transistor's datasheet for the hFE value in its specifications.

Note that hFE may refer to DC or AC current gain. Many datasheets may just specify one value, such as the DC gain. The datasheets will normally specify whether the hFE value is for DC or AC current gain.

Also, note that as the hFE value is highly variable, many datasheets will specify a minimum and maximum hFE for the transistor. It is very hard for transistors to be produced with a precise hFE value during the manufacturing process. Therefore, manufacturers generally specify a range that hFE may be within.

Because hFE is so widely variable and unpredictable in nature, good transistor circuit design is important to give stable, predictable amplification for transistor circuits to account for this unpredictability.