ULN2803A Darlington Transistor Array

The ULN2803A is a high voltage, high current Darlington transistor array designed to interface low level logic circuits with high power loads. It contains eight NPN Darlington pairs that feature high voltage outputs with common cathode clamp diodes for switching inductive loads. Each individual channel can handle up to 500 Milliamperes, making it ideal for driving solenoids, relays, stepper motors, and LED displays. This IC is particularly popular because it simplifies circuit design by eliminating the need for separate transistors and resistors for each output. Each input has a 2.7 Kilohm series base resistor, allowing it to be connected directly to a microcontroller or logic gate. When driving inductive loads like motors or relays, the common pin (pin 10) must be connected to the load supply voltage to allow the internal diodes to safely clamp back EMF spikes.

Key Features:

Output Current: 500 Milliamperes per channel (continuous).

Output Voltage: Up to 50 Volts.

Input Compatibility: TTL and 5 Volt CMOS logic levels.

Clamping Diodes: Integrated diodes for inductive load suppression.

Parallelable: Outputs can be connected in parallel for higher current capability.