Definition
A transistor amplifier circuit in which the collector terminal is common to both the input and output signals. The input signal is applied between the base and collector, and the output is taken from between the emitter and collector. This configuration produces a voltage gain slightly less than one, but a high current gain and a high input impedance, making it useful as a buffer or impedance-matching stage. It is also commonly called an emitter follower because the emitter voltage closely follows the base voltage.
Plain English
A type of transistor circuit wired so that the collector pin is shared by both the incoming and outgoing signals. It doesn't make the signal voltage bigger, but it lets a weak signal source drive a heavier load without being overwhelmed.
Context Anchor
Seen in aircraft electronics, avionics, and electrical-system troubleshooting when describing transistor amplifier stages.
Derivation
Called 'common-collector' because the collector terminal of the transistor is the one shared (common) between the input side and the output side of the circuit. The other two configurations are named the same way: common-base and common-emitter, depending on which terminal is shared.
Why Pilots Care
Maintains clear, undistorted signals in aircraft communication and navigation radios by matching impedance between stages.
Analogy
It is like a helper between two people: the helper may not make the message louder, but makes sure the next person can receive and use it properly.
Intuition Check
“Common” does not mean ordinary here. It means the collector connection is the shared reference point for the input and output of the circuit.
Example Sentence 1
The technician identified the stage as a common-collector amplifier because the output was taken from the emitter while the collector tied to the supply rail.
Example Sentence 2
Replacing the common-collector amplifier restored full volume to the cockpit intercom without distortion.