commoncollectorkonfiguraatiossa

Common-collector configuration, also known as the emitter follower, is a transistor amplifier arrangement in which the collector terminal is common to both the input and the output circuits. The input is applied to the base and the output is taken from the emitter. The collector is typically connected to a supply through a resistor or a load, while the emitter follows the base voltage minus the base-emitter voltage drop.

In this configuration the voltage gain is approximately unity, meaning the output voltage closely tracks the input voltage. The current gain is high and roughly equal to the transistor’s beta, making the stage an effective current amplifier. The input impedance is relatively high, and the output impedance is low, which makes the emitter follower a good buffer between a high-impedance source and a low-impedance load. The emitter voltage is about 0.6–0.7 V below the base for silicon transistors, providing a predictable level shift.

Biasing is used to set the operating point, typically with a base bias network and an emitter resistor that provides negative feedback to stabilize the quiescent current against component variations and temperature changes. The collector is connected to the supply, and the emitter drives the load.

Common-collector stages are widely used for impedance matching, buffering, and driving low-impedance loads, such as headphone drivers or subsequent amplifier stages. They are also valued for their temperature stability and wide bandwidth compared to configurations with larger voltage gain. In Finnish-language sources, this configuration is sometimes referred to as commoncollectorkonfiguraatiossa.