BJT Common-Emitter Amplifier Circuit

BJT Common-Emitter Amplifier

A common-emitter amplifier uses a bipolar NPN transistor to turn a small base signal into a larger voltage change at the collector. The bias divider establishes an operating point, while the collector and emitter resistors set current and stabilise the stage. An emitter bypass capacitor can increase AC gain without changing the DC bias. The output is inverted relative to the input. This schematic is a teaching example rather than a finished audio design: the required bias depends on the transistor, supply, source level, and desired output swing. Measure or simulate the collector voltage and adjust values so the transistor has room to amplify both halves of the waveform.

Type Schéma électriqueNorme IEEE Std 315 / ANSI Y32.2Moteur schematex-circuitMis à jour 24/09/2026

La demande

“Draw a 9 V NPN common-emitter amplifier with a 100 kΩ and 10 kΩ bias divider, 2.2 kΩ collector resistor, 1 kΩ emitter resistor, 100 µF bypass capacitor, and 10 kΩ collector load.”

Essayez ensuiteRemove the emitter bypass capacitor.Change the collector resistor to 4.7 kΩ.

Ce que contient ce dessin

Comprenez les décisions qui le sous-tendent.

01Bias

Use a divider to set the transistor base voltage.

02Gain

Use a collector resistor as the voltage load.

03Stability

Use an emitter resistor and optional bypass capacitor.

Use for a basic NPN common-emitter amplifier stage.

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FAQ

Questions fréquentes

Why is it called common-emitter?

The emitter is the reference node shared by the input and output signal paths.

Why use a bias divider?

It sets a predictable base voltage so the transistor operates in its active region.

Is the output inverted?

Yes. Increasing base current lowers collector voltage in a common-emitter stage.