When a transistor is used as an amplifier, the forward biased junction is the emitter-base junction, while the base-collector junction is reverse biased. This is the proper biasing configuration for the transistor to operate in its active region, which allows it to amplify signals.
Explanation:
- The emitter-base junction is forward biased to allow current carriers (electrons or holes depending on transistor type) to flow from the emitter into the base.
- The base-collector junction is reverse biased to prevent current flow in that junction but allows the injected carriers from the emitter to be collected at the collector, resulting in amplification.
- This biasing ensures that small variations in the base current cause large variations in the collector current, enabling the transistor to function as an amplifier.
This setup is characteristic of the commonly used "forward-active" mode of a bipolar junction transistor (BJT) used as an amplifier.
