Active-mode PNP transistors in circuits:

In the figure, the arrows showing current point in the direction of conventional current - the flow of electrons is in the opposite direction of the arrows since electrons carry negative electric charge. Within active mode, the ratio of the collector current to the base current is called the DC current gain. This gain is generally 100 or more, but robust circuit designs do not depend upon the exact value (for instance see op-amp). The value of this gain for DC signals is considered to as h_FE, and the value of this gain for AC signals is considered to ash_fe.

 Though, while there is no particular frequency range of interest, the symbol β is employed. It should as well be noted that the emitter current is related to V_BE exponentially. At room temperature, increment in V_BE by almost 60 mV increases the emitter current by a factor of 10. Since the base current is approximately proportional to the collector and emitter currents, they change in the same way.

Active-mode PNP transistors in circuits