In a P-N-P transistor application, the solid state device is turned on when the ________.

In a P-N-P transistor application, the solid state device is turned on when the ________.

• A. Base is positive with respect to the emitter
• B. Base is negative with respect to the emitter
• C. Emitter is negative with respect to base
• D. Collector is positive with respect to base

Answer: (B)

Forward biasing the base-emitter junction is what turns on a PNP transistor. In a PNP device, the emitter is P-type and the base is N-type, so to forward bias this junction you need the base to be at a lower potential than the emitter—i.e., the base is negative with respect to the emitter by about 0.6–0.7 V. This allows holes to be injected from the emitter into the base, enabling current to flow from the emitter to the collector. If the base were positive relative to the emitter, the base-emitter junction would be reverse biased and the transistor would be off.

Forward biasing the base-emitter junction is what turns on a PNP transistor. In a PNP device, the emitter is P-type and the base is N-type, so to forward bias this junction you need the base to be at a lower potential than the emitter—i.e., the base is negative with respect to the emitter by about 0.6–0.7 V. This allows holes to be injected from the emitter into the base, enabling current to flow from the emitter to the collector. If the base were positive relative to the emitter, the base-emitter junction would be reverse biased and the transistor would be off.