Hfe

hFE, also written hfe, is the DC current gain of a bipolar junction transistor (BJT) in the forward-active region. It is defined as the ratio of the collector current Ic to the base current Ib: hFE = Ic / Ib. It is often referred to as the forward current gain or beta (β). In datasheets, hFE is given as a range at specified test conditions, not as a fixed value, and varies with device, temperature, and bias.

Measurement and conditions: hFE is measured with a fixed collector-emitter voltage Vce at a specified value (commonly a few volts) and a known base current, yielding Ic, from which hFE is calculated. Different manufacturers may specify hFE at different Ic or Ib points; common test conditions are Ic of a few milliamps and Vce around 5V, but ranges exist.

Variation: Device-to-device and batch-to-batch variation is large. A single part number can have hFE ranging widely (for example from tens to several hundreds). Temperature also affects hFE; as temperature changes, Ic for a given Ib changes, and so does the ratio. Power devices and small-signal devices have characteristic ranges that reflect their design.

Usage and modeling: In circuit design and SPICE models, hFE is used as the forward DC gain parameter (often labeled hfe or beta). Because hFE is not constant, designs that depend on fixed gain rely on negative feedback or bias stabilization to maintain performance across variations.