The effect is compounded when the second device is considered. The gains of the individual devices are always stated as within a range, often quite broad. It is quite possible to construct your own Darlington pairs, or even arrays, but there is a challenge when more than one Darlington pair is used. WHAT IS A DARLINGTON?Ī Darlington pair is the name for two transistors connected as a current amplifier in such a way that the Darlington gain is the product of the individual gain of each transistor of the pair. It does have the ability to control seven separate single-channel loads, or for outputs to be paralleled to increase current capacity. The integrated circuit (IC) is an array of seven Darlington transistors, with flyback diodes common-cathode connected inside, specifically for driving inductive loads. The reason for this is that it has uses far beyond driving stepper motors with microcontrollers.

The ULN2003 has been around longer than Arduino or Raspberry Pi, and even predates the now almost unheard of Picaxe.

This specialised IC provides a neat and effective interface between a stepper motor and an Arduino or Raspberry Pi.