NPN BIASING

The normal method of biasing an npn transistor is to have the emitter more negative than the collector. In most cases, the emitter is at or near zero potential while the collector is connected to a source of positive dc voltage. This is shown by the connection of the battery in Fig. 1. Typical voltages range from 3 V to approximately 50 V.
The base is labeled “control” because the flow of current through the transistor depends on the base bias voltage, denoted E_B or V_B, relative to the emitter-collector bias voltage, denoted E_C or V_C.

Fig. 1. Typical biasing of an npn transistor.