Symbols, Signs, Fundamental Circuit

Abstract

The technical symbol for the p-n-p transistor has already been shown in the fundamental circuit, the common emitter circuit, in Fig. 2.7. In this circuit the emitter is the common connecting point for all applied transistor voltages. All the current and voltage directions are based on the technical current direction from positive to negative. The voltage indication — V _BE signifies that the voltage does not operate according to the given index BE, from the base to the emitter, but in the opposite direction and is therefore negative. All direct currents which flow to the interior of the transistor are indicated with the positive sign. A current — I _C thus means that the current flows away from the transistor. These direction signs are customary in published characteristic fields. In the n-p-n transistor the emitter current and the collector current are reversed in direction compared with the p-n-p transistor. The transistor symbol therefore shows a reversed arrow for the emitter.