Week 7 (S1"11)

The Darlington Transistor Array
 

For more compact version of the Darlington pair transistor you could use the Texas Instrument ULN2803A which is contain 8 Darlington pair transistors with has build in 2K7 base resistor and clamp diode for each Darlington pair transistors. This makes this Darlington transistor array suitable for driving the relay or motor up to 500mA (this is a maximum datasheet value) directly from the microcontroller output.

To increase the output current up to 1 A (2 x 500mA, remember this is a maximum datasheet value, for practical application use just half or 2 x 250 mA) you could simply use two Darlington transistor array connected in parallel, the following is the sample circuit for driving two DC motors using the ULN2803A Darlington transistor array:

 Thanks to the build in internal 2K7 base resistor and the two clamp diode, you don’t need any external component when using ULN2803A to drive the DC motor from your microcontroller port. The Darlington transistor array ULN2803A could be used to drive up to 50 volt voltage load.