In active-mode, the collector-base junction is reverse-biased.

In active-mode, the collector-base junction is reverse-biased.

• A. True
• B. False
• C. Not biased
• D. Undetermined

Answer: (A)

In active-mode a bipolar junction transistor is biased with the emitter-base junction forward and the collector-base junction reverse-biased. Forward bias at the emitter-base junction injects carriers (electrons in an NPN) from the emitter into the base. The base is thin and lightly doped, so most of these carriers diffuse across the base and reach the collector. The reverse bias on the collector-base junction creates a strong electric field that sweeps those carriers into the collector and broadens the depletion region, which minimizes carrier recombination in the base. This setup makes the collector current primarily determined by the emitter injection (and thus the base current, giving high gain), while remaining largely independent of the exact collector-emitter voltage within the active range. If the collector-base junction wasn’t reverse biased, the device wouldn’t operate in its active, amplifying region; it could move toward saturation or cutoff, where amplification is lost.

In active-mode a bipolar junction transistor is biased with the emitter-base junction forward and the collector-base junction reverse-biased. Forward bias at the emitter-base junction injects carriers (electrons in an NPN) from the emitter into the base. The base is thin and lightly doped, so most of these carriers diffuse across the base and reach the collector. The reverse bias on the collector-base junction creates a strong electric field that sweeps those carriers into the collector and broadens the depletion region, which minimizes carrier recombination in the base. This setup makes the collector current primarily determined by the emitter injection (and thus the base current, giving high gain), while remaining largely independent of the exact collector-emitter voltage within the active range. If the collector-base junction wasn’t reverse biased, the device wouldn’t operate in its active, amplifying region; it could move toward saturation or cutoff, where amplification is lost.