Darlington Transistor Pairs

A Darlington pair, as shown in the schematic Fig.1, is a pair of BJTs in which the emitter of the first transistor is connected to the base of the second transistor. This configuration provides far higher current gain than a single transistor through direct coupling. The pair can be made on a single die and it is packaged in a three-terminal transistor case. The pairs are often used in linear ICs, such as operational amplifiers, and in power amplifier output stages. Its most common application is that of an emitter follower. The output is taken across a resistor from the emitter of the second transistor to ground. The input resistance at the base of the first transistor is raised to a higher value than that of a singletransistor emitter-follower circuit.



Figure 1 Darlington transistor pair symbol.