Darlington Arrays & Relay Driver ICs — ULN2003, ULN2004, ULN2001

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2026/05/06

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Darlington Array & Relay Driver ICs — ULN2003, ULN2004, ULN2001 Darlington transistor array ICs are the simplest and most reliable way to drive high-current loads (relays, solenoids, stepper motors, LEDs) directly from microcontroller GPIO pins. A single GPIO pin (limited to 20–40mA) cannot drive a relay coil directly — a Darlington array IC provides the current amplification needed, with built-in flyback diodes to protect against inductive voltage spikes. The ULN2003 and ULN2004 are the most widely used relay driver ICs in the world, found in countless Arduino relay boards, stepper motor drivers, and industrial control systems. Available Darlington Array ICs ULN2003A (DIP-16 / SOP-16): 7 channels, TTL/CMOS input (5V), 50V/500mA per channel — the standard relay driver for 5V Arduino and microcontroller systems ULN2004A (DIP-16 / SOP-16): 7 channels, PMOS/CMOS input (5V–15V), 50V/500mA per channel — for higher-voltage logic inputs and CMOS systems ULN2001 (SOP-8): 3 channels, compact SMD package — for space-constrained PCBs needing 3 or fewer drive outputs ULN2003 vs ULN2004 — Input Voltage Selection ULN2003: Input threshold optimized for 5V TTL/CMOS — use with Arduino (5V), Raspberry Pi (3.3V with pull-up), and standard 5V microcontrollers ULN2004: Input threshold optimized for 5V–15V PMOS/CMOS — use with higher-voltage logic or when driving from 12V logic signals Both have identical output specifications: 50V, 500mA per channel, built-in flyback diodes Typical Applications Arduino relay control: Drive 5V or 12V relay coils from Arduino GPIO pins Stepper motor driver: Drive unipolar stepper motor coils (28BYJ-48 uses ULN2003) Solenoid valve control: Drive solenoid valves and actuators from microcontroller outputs LED array driver: Drive high-current LED strings beyond GPIO current limits Industrial output module: Drive industrial loads from PLC digital outputs All Darlington array ICs are new, original parts with built-in flyback diodes. Available in DIP-16, SOP