What are the applications of bipolar transistors (bipolar junction transistors: BJTs)?

Bipolar transistors (bipolar junction transistors: BJTs) can control the collector current via the current applied to the base. Typically, the collector current is the base current times the DC current gain (hFE)*. It is this gain that allows bipolar transistors to be used as amplifiers. Bipolar transistors are also utilized as switches using their characteristics in the saturation and cut-off regions.

Common-collector amplifier (emitter follower)
Common-collector amplifier (emitter follower)
Common-emitter amplifier
Common-emitter amplifier
Common-base amplifier
Common-base amplifier
Switching circuit
Switching circuit

*hFE varies with the collector-emitter voltage, which depends on external circuitry.
For a description of hFE, also see the FAQ entry, “What is the relationship between the base-emitter and the collector-emitter voltages of a bipolar transistor?”.　

Back to FAQs of MOSFETs / Bipolar Transistors / IGBTs

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