ULN2803A 8-Channel Darlington Transistor Array IC DIP-18 — 500mA / 50V, Arduino Relay Driver

ULN2803A — 8-Channel Darlington Transistor Array, DIP-18

The ULN2803A is an 8-channel NPN Darlington transistor array IC — the most widely used driver IC for interfacing microcontrollers to high-current loads. Each of its 8 channels can sink up to 500mA at 50V, with built-in flyback diodes on every output for inductive load protection. Connect any 8 Arduino or microcontroller GPIO pins to the inputs, and the ULN2803A drives 8 relays, solenoids, stepper motor coils, or high-power LEDs simultaneously — no external transistors, no external diodes, no additional components required.

The ULN2803A is the 8-channel version of the popular ULN2003A (7-channel). Its DIP-18 package is breadboard-compatible, and its 5V-compatible inputs work directly with Arduino, ESP32, STM32, and Raspberry Pi GPIO pins.

Key Features

• 8 independent Darlington channels — each rated 500mA @ 50V
• Built-in flyback diodes on all outputs — relay and solenoid protection included
• 5V logic compatible inputs — direct connection to Arduino, ESP32, Raspberry Pi GPIO
• Active-low outputs — output sinks current when input is HIGH
• No external components required for basic relay/solenoid driving
• DIP-18 package — breadboard and through-hole PCB compatible
• RoHS compliant

Technical Specifications

Channels	8
Output Voltage (max)	50V
Output Current (per channel)	500mA continuous
Input Voltage (logic HIGH)	2.4V – 5V (TTL/CMOS compatible)
Input Current (per channel)	~1mA @ 5V input
Flyback Diodes	Built-in on all 8 outputs
Output Type	Open-collector (active-low sink)
Package	DIP-18 (through-hole)
Manufacturer	Texas Instruments / STMicroelectronics / Toshiba

ULN2803A vs ULN2003A

• ULN2003A: 7 channels, DIP-16 — standard choice for 7-segment displays and 7-coil stepper motors
• ULN2803A (this): 8 channels, DIP-18 — preferred for 8-relay boards, 8-channel output expanders, and full-byte I/O driving

Typical Applications

• Relay board driver — drive 8 relays from a single IC with built-in flyback protection
• Stepper motor driver — drive bipolar or unipolar stepper motor coils (4-coil motors)
• Solenoid valve array — control 8 solenoids from Arduino or PLC output
• High-power LED driver — drive 8 high-current LEDs or LED segments
• 7-segment display driver — common-anode display digit driver
• Output expander — extend microcontroller I/O to drive 8 high-current loads

Arduino Wiring (Basic Relay Driver)

• ULN2803A inputs (pins 1–8) → Arduino digital pins
• ULN2803A COM pin (pin 10) → relay coil positive supply (5V or 12V)
• ULN2803A outputs (pins 11–18) → relay coil negative terminals
• Arduino GND → ULN2803A GND (pin 9)
• No external diodes needed — flyback diodes are built in

Package Contents

• 1 × ULN2803A 8-Channel Darlington Array IC (DIP-18)

ULN2803A Datasheet (Texas Instruments PDF)

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