The ULN2003 is a high-voltage, high-current Darlington transistor array. Each IC contains seven open-collector Darlington pairs with common emitters. It is designed to act as a bridge between low-power logic (like microcontrollers or CMOS gates) and high-power loads. Each channel can handle up to 500mA and features integrated suppression diodes for inductive load switching. Unlike the L293D, the ULN2003 is not an H-bridge; it is a “low-side” switch, meaning it connects the load to ground. It is most famous for driving 5-wire unipolar stepper motors and large relay banks.
ULN2003 Pinout (DIP-16)
The ULN2003 is a 16-pin IC. Inputs are on the left side, and the corresponding outputs are directly opposite on the right side.
| Pin | Terminal | Function |
| 1 – 7 | Inputs 1-7 | Logic input signals from microcontroller |
| 8 | Ground (GND) | Common emitter ground connection |
| 9 | COM | Common cathode for flyback diodes (connect to V+) |
| 10 – 16 | Outputs 7-1 | Open collector outputs for the loads |
Technical Specifications
- Output Voltage: 50V (Maximum)
- Output Current: 500mA per channel
- Input Voltage: 5V (Compatible with TTL and 5V CMOS)
- Power Dissipation (PD): 1W per package
- Clamp Diode Voltage: 50V
- Collector-Emitter Saturation Voltage: 1.1V to 1.3V
Key Features & Benefits
- Seven Channels: Control up to seven separate devices with a single chip.
- High-Gain Darlington: Can be driven by very low current logic signals.
- Inductive Protection: Built-in diodes make it safe for relays and motors.
- Parallelable Outputs: Outputs can be connected in parallel to handle higher currents.
Common Applications
- Unipolar Stepper Motors: Driving 28BYJ-48 style stepper motors.
- Relay Drivers: Controlling multi-channel relay boards from a single MCU.
- LED Matrix Drivers: Switching high-power LED segments or strings.
- Thermal Printhead Drivers: Managing the heating elements in small printers.
ULN2003 Equivalent & Substitutes
- ULN2001 / ULN2002 / ULN2004 (Different input voltage versions)
- ULN2803 (8-channel version in an 18-pin package)
- TBD62003A (Modern DMOS-based higher efficiency replacement)
- MC1413 (Direct equivalent from other manufacturers)
Related Tutorials on ElxHub
- Basics: Learn more in Integrated Circuits – Basics, Types and Working
- Selection Guide: Compare power options in our Ultimate IC Selection Guide
Conclusion
The ULN2003 is an essential interface IC for anyone needing to control multiple medium-power loads. Its simple “input-to-output” layout and integrated protection make it a compact and efficient alternative to using seven individual transistors and seven separate diodes. For relay control and unipolar stepper projects, the ULN2003 is the industry-standard choice.
Download the IC’s Datasheet pdf
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