What is a Darlington pair?

 Darlington pair is a pair of bipolar junction transistors connected in such a way that the emitter of one transistor is connected to the base of the other. The current amplified by the first transistor is amplified further by the second transistor. Collectors of both transistors are connected together. The Darlington pair has a higher current gain than each transistor taken separately. Combination of two transistors connected together in a single package is also available. Alternatively two transistors can be connected in the Darlington configuration to get a Darlington pair. The first transistor can be of low power type, but the second one needs to have higher power rating. The configuration was invented by Sidney Darlington in 1953.


The maximum rated collector current of the Darlington pair is that of the second transistor. One such integrated device is 2N6282, which has current gain (hFE) of 2400 at a collector current of 10 A. A disadvantage of the Darlington pair is doubling of the base-emitter voltage as there are two junctions involved. In case of a silicon pair, with 0.65 V for a single junction, the combination will have a base-emitter voltage of 1.3 V. On the other hand, for high gain transistor combination, the total gain is almost the product the gains of the individual transistors. A shunt resistor is often needed between the base and emitter of the second transistor to increase switching speed. 2N6282 has a built-in shunt resistor in the package.

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