ULN2803A is a monolithic integrated high withstand voltage, high current Darlington tube array column, the circuit contains eight independent Darlington tubes driving a single circuit. There is a freewheeling diode inside the circuit, which can be used to drive relays, Inductive loads such as stepper motors. A single Darlington collector can Output 500mA current. Paralleling Darlington tubes can achieve higher output current capability. This circuit can be widely used in relay drive, Lighting drivers, display drivers (LEDs), stepper motor drivers and logic editing buffer.
Each Darlington tube of ULN2803A is connected in series with a 2.7K base electrode resistors, can directly interface with TTL/CMOS at 5V operating voltage circuit connections that directly address standard logic buffers previously required to process the data.