Transistor Current Gain (β)

Formula

Description

Beta (also called hFE) is the DC current gain of a bipolar junction transistor, defined as the ratio of collector current to base current. It quantifies the transistor's amplification ability: a small base current controls a much larger collector current. Typical beta values range from 50 to 500, but beta varies significantly with collector current, temperature, and manufacturing tolerances. Good circuit design should never depend on a precise beta value; instead, use feedback or design for the minimum guaranteed beta from the datasheet.

Variables

• β — DC current gain (dimensionless)
• IC — Collector current (A)
• IB — Base current (A)

Practical Notes

Beta decreases at very low and very high collector currents. Temperature increases beta by roughly 0.5-1% per °C. For switching applications, drive enough base current to ensure saturation at minimum beta. For amplifier design, use negative feedback to make gain independent of beta. Darlington pairs multiply beta values, achieving gains of 1000-10000.