Bipolar Junction Transistor (BJT)
A three-terminal active semiconductor device (NPN or PNP) in which a small base current controls a much larger collector-emitter current.
Governing formula
I_E = I_B + I_C, I_C = β I_B
SI unit
A (Current)
In depth
Current gain β (typically 50 to 300) amplifies input current. BJTs function as electronic switches in digital logic or as linear signal amplifiers in audio circuits.
Examples in the real world
Transistor amplifier stages boosting weak microphone audio signals into high-power loudspeaker signals.