Home > Circuit Bricks > Darlington Driver IC
UPDATED:.21:04 21 October 2013

FUNCTION BLOCK
DESCRIPTION
  • A Darlington driver that comes in an IC 18 pin DIL package.
  • There are 8 drivers in the IC, each driving up to 500mA
CIRCUIT DETAILS

This is a Darlington driver (a combination of 2 transistors)

Each driver can produce up to 500mA but if every driver is producing 500mA the IC will get hot - possibly very hot.

Two or more drivers can be connected directly in parallel to produce more current.

They can connect to voltages of up to 50v (30v input).

Every output has a diode coonected to it - in reverse bias, shown dotted - with the cathodes all connected together. This is used for inductive loads, such as motors to protect the dirvers from high EMF voltages created by the coils in the motor. This can be left unconnected if not required.

Remember that the output sinks current, and thus it should be connected to the negative connection of any device, with the positive connected to the supply.

The internal circuit of each driver is shown right - it contains protection and bias resistors.

Circuit symbol

Internal Circuit

COMPONENT TYPES

There are 2 types with 8 drivers in:

  • ULN2803 = for conneciotn from TTL logic
  • ULN2804 = for conneciton from CMOS logic

Note pin 9 is the 0v connection and should have a thick PCB track to carry the current load of all drivers.

ULN2803/4 pin connections
Written by Phil Townshend - 2008
www.edutek.ltd.uk - Working Electronics For Students & Teachers