In a P-N-P transistor, which condition turns the device on?

• A. Base is positive with respect to the emitter.
• B. Emitter is negative with respect to the base.
• C. Base is negative with respect to the emitter.
• D. Base is at the same potential as the emitter.

Answer: (C)

Forward biasing the base–emitter junction turns a transistor on. For a PNP transistor, that means the base must sit at a lower voltage than the emitter by about 0.6–0.7 volts. With the base negative relative to the emitter, holes flow from the emitter into the base, allowing current to flow from emitter to collector.

So the condition that turns the device on is the base being negative with respect to the emitter. If the base were more positive than the emitter, the base–emitter junction would not be forward biased for a PNP device; if the emitter were negative relative to the base or if the base and emitter were at the same potential, the junction would not conduct.