Transistor circuit configurations of BJT

Transistor circuit configurations

There are three types of circuit connections for operating a transistor based on the terminal that is used in common to both input and output circuits.

Common-Base(CB) configuration

The base is common to both the input and output circuits. The schematic and circuit symbol are shown in Figure 9.26(a) and 9.26(b). The input current is the emitter current IE and the output current is the collector current IC. The input signal is applied between emitter and base, the output is measured between collector and base.

Common-Emitter(CE) configuration

In this configuration, the emitter is common to both the input and output loops as shown in Figure 9.27. Base current, IB is the input current and the collector current, IC is the output current. The input signal is applied between the emitter and base and the output is measured between the collector and the emitter.

Common-Collector(CC) configuration

Here, the collector is common to both the input and output circuits as shown in Figure 9.28. The base current IB is the input current, the emitter current IE is the output current. The input signal is applied between the base and the collector, the output is measured between the emitter and collector.

As the output is taken from the emitter in common collector configuration, it is called an emitter follower.