Darlington pairs, also known as Darlington Transistors are discrete semiconductor devices consisting of a package of two standard BJT transistors (bipolar junction transistor). One of the transistors is high-gain while the other is high current. RS offer a wide range of high-quality Darlington Transistors from leading brands including ON Semiconductor, STMicroelectronics, Texas Instruments and Nexperia.

How do they work?

The emitter of one transistor is connected to the base of the other transistor which effectively creates one transistor. They are used to amplify weak signals from one circuit to another circuit or microprocessor. This means that the tiny current from a sensor or microcontroller I/O pin can be amplified to drive a large load. Darlington pairs can also be operated as an ON/OFF switch. Darlington pairs work together as a single transistor but feature a much higher current gain. They also offer high input impedance in comparison to single transistors.

Why should you use a Darlington pair?

Darlington pairs provide a very high current gain. Working as two transistors within one package, Darlington pairs have a very compact footprint which takes up minimal space on a (PCB) printed circuit board.

What applications would you use them in?

With high current gain, Darlington transistors are well suited to power applications such as driving motors and relays. Darlington pairs are ideal for application in display drivers, audio outputs, power regulators, light sensors, touch sensors and power supply outputs. It is not recommended to use them in applications that require high frequency as it is not possible to shut the base current off immediately.

What are the different types?

Darlington pairs can consist of either NPN (negative-positive-negative) transistors, PNP (positive-negative-positive) transistors or both.
Darlington pairs are typically supplied in one of two ways. You can purchase them as an array (called a Darlington array) within a single integrated circuit (IC) package, or as a simple single discrete component.

Standard package type examples include SOT-23, SOIC, TO-220 and TO-252 (DPAK)