Transistors, Triodes and Amplifiers
Noel M. Morris · 1977
A bipolar junction transistor (see figure 10.1) is formed in a single crystal of semiconductor material, and there are two types: n-p-n and p-n-p . Each contains three regions known as the emitter , the base and the collector . When the transistor is used in amplifier circuits the base — emitter junction is forward-biased and the collector — base junction is reverse-biased. The arrow on the circuit symbols points in the direction of conventional current flow (that is, of hole flow). The most widely used type is the n-p-n silicon transistor.