PNP BIASING

For a pnp transistor, the bias situation is a mirror image of the case for an npn device, as shown in Fig. 1. The power-supply polarity is reversed. To overcome forward breakover at the E-B junction, an applied signal must have sufficient negative polarity.
Either the pnp or the npn device can serve as a “current valve.” Small changes in the base current IB induce large fluctuations in the collector current IC when the device is operated in that region of the characteristic

Fig. 1. Typical biasing of a pnp transistor.

curve where the slope is steep. While the internal atomic activity is different in the pnp device as compared with the npn device, the performance of the external circuitry is, in most situations, identical for practical purposes.