The notion that bipolar junction transistors (BJTs) are current-controlled is a common misconception. In reality, BJTs are voltage-controlled devices. The input voltage at the base-emitter junction controls the flow of current between the collector and emitter terminals. This control mechanism is better understood through the input-output relationship, known as the transconductance.
When a small input voltage is applied across the base-emitter junction, it modulates the conductivity of this junction, influencing the current flow between the collector and emitter. Hence, it’s accurate to say that the base current controls the transistor’s behavior, but it’s crucial to recognize that this control is exerted through voltage modulation.
This understanding is pivotal in circuit analysis and design, as it allows engineers to model and predict the behavior of BJTs accurately. It’s not about the current directly controlling the transistor, but rather the voltage across the base-emitter junction influencing the output current.
