In a bipolar transistor, what does the base current control?

In a bipolar transistor, the base current is crucial because it controls the amount of current that flows from the collector to the emitter. This principle is fundamental to how bipolar transistors function. The base current, while small, allows the transistor to amplify current; a small change in base current results in a larger change in the collector-emitter current. This relationship allows for effective control of the overall device operation, enabling it to act as an amplifier or a switch, depending on the circuit configuration.

This mechanism is essential in applications like signal amplification in audio equipment or switching in digital circuits where the base current's influence on the collector current is leveraged to control larger currents and voltages, making it a key concept in electronics.