What is the formula for Common-Collector Current Gain?

The Common-Collector Current Gain formula is Ai = β + 1, where Ai—Common-collector current gain; β—Common-emitter current gain.

What does Ai mean in the Common-Collector Current Gain formula?

Ai is Common-collector current gain.

Common-Collector Current Gain

Q: How do you calculate Common-Collector Current Gain?

Use the formula Ai = β + 1. A common-collector stage (emitter follower) has a current gain of beta plus one, because the emitter current is the sum of the base and collector currents. Enter the values you know in the calculator above and it solves for the remaining variable.

Ai = β + 1

Calculator

Current Gain

Current Gain β

Result

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Formula

Ai = β + 1

Description

A common-collector stage (emitter follower) has a current gain of beta plus one, because the emitter current is the sum of the base and collector currents. This high current gain, combined with near-unity voltage gain, is what lets the follower deliver large load current from a small base current while buffering the previous stage.

Variables

Ai — Common-collector current gain
β — Common-emitter current gain

Practical Notes

The emitter current Ie = (β+1)·Ib. Together with the input-impedance multiplication (β·RE), this current gain is the basis of the follower’s impedance-transforming action.

Related Concepts

All Discrete Amplifiers formulas →

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