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Common-Emitter Current Gain

 

 

Common-emitter current gain or static current gain is expressed as hfe. It is defined as the ratio of the input dc current and the output dc current of the transistor. This parameter is also known as . The ratio of collector current to base current, ß is the fundamental parameter characterizing the amplifying ability of a bipolar transistor. Common-emitter current gain is usually assumed to be a constant figure in circuit calculations, but unfortunately this is far from true in practice. As such, manufacturers provide a set of ß (or "hfe") figures for a given transistor over a wide range of operating conditions, usually in the form of maximum/minimum/typical ratings. It may surprise you to see just how widely ß can be expected to vary within normal operating limits. One popular small-signal transistor, the 2N3903, is advertised as having a ß ranging from 15 to 150 depending on the amount of collector current. Generally, ß is highest for medium collector currents, decreasing for very low and very high collector currents.

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Transistors are electronic devices made of semiconductor material that amplify a signal or open or close a circuit. Search by Specification | Learn more about Transistors
Small-signal bipolar transistors (BJT) are semiconductors that amplify small AC or DC signals. They consist of a base n-type or p-type layer sandwiched between emitter and collector layers of the opposite type. Search by Specification | Learn more about Small-signal Bipolar Transistors (BJT)
RF bipolar  transistors consist of an N-type or P-type layer sandwiched between two layers of the opposite type. They are designed to handle high-power radio frequency (RF) signals in devices such as stereo amplifiers, radio transmitters, and television monitors. Search by Specification | Learn more about Bipolar RF Transistors
Darlington transistors (Darlington pairs) are semiconductor devices that combine two bipolar transistors in a single device. They provide high current gain (commonly written ß) and require less space than configurations that use two discrete transistors. Search by Specification | Learn more about Darlington Transistors
Power bipolar transistors are semiconductors in which a base n-type or p-type layer is sandwiched between emitter and collector layers of the opposite type. The junctions between the semiconductor sections amplify weak incoming electrical signals. Search by Specification | Learn more about Power Bipolar Transistors
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