# ULN2003A driver: seven 500 mA channels for relays and small steppers

> Seven Darlington outputs, 500 mA each and 50 V tolerant, with clamp diodes. What the datasheet gives and how to wire a load.

Canonical: https://roboticsengineering.in/components/uln2003a-darlington-driver/ | Published: 2026-11-03 | Updated: 2026-11-03

**The ULN2003A is an array of seven NPN Darlington transistors, each rated 500 mA with outputs that tolerate 50 V, plus clamp diodes for inductive loads.** It is the chip on the small blue board that drives a 28BYJ-48 stepper, and it is a cheap way to switch relays, solenoids and small lamps from logic pins. It sinks current only: the load connects between the supply and the output. Figures are from the Texas Instruments ULx200x datasheet SLRS027T.

## Key specifications

| Channels | 7 NPN Darlington |
| --- | --- |
| Collector current | 500 mA per output |
| Output voltage | up to 50 V |
| Clamp diodes | built in |
| Inputs | TTL / 5 V CMOS (ULx2003A) |
| Packages | SOIC, PDIP, SOP, TSSOP, SOT (16 pin) |

## What the datasheet promises

| Item | Datasheet value |
| --- | --- |
| Channels | Seven NPN Darlington pairs |
| Collector current, single output | 500 mA rated |
| Output voltage | Up to 50 V |
| Clamp diodes | Built in, common cathode, for switching inductive loads |
| Parallel outputs | The datasheet says pairs can be paralleled for more current |
| Inputs | ULx2003A: for TTL or 5 V CMOS. ULx2004A: 10.5 kΩ base resistor for 6 V to 15 V CMOS |
| Packages | SOIC, PDIP, SOP, TSSOP and SOT, all 16 pin |

The 500 mA rating is per output. The datasheet’s total-package limits depend on how many outputs are on at once, so do not assume seven loads of 500 mA each are safe together; check the power dissipation section for your package.

## How to wire a load

- Connect the load between its positive supply and the output pin (1C to 7C).
- Drive the matching input pin (1B to 7B) from a logic pin; high turns the output on.
- Connect COM to the positive supply of an inductive load so the clamp diodes can absorb the spike when it switches off.
- Join the ground of the load supply to the chip ground and the controller ground.

Because it is a Darlington pair, the output does not pull all the way to ground; it leaves a saturation voltage across the chip, so a motor on a low supply sees noticeably less than the supply voltage. For efficient motor drive use a MOSFET driver such as the [TB6612FNG](https://roboticsengineering.in/components/tb6612fng-motor-driver/). The [relay module guide](https://roboticsengineering.in/fix/relay-module-always-on-active-low/) and [flyback diode guide](https://roboticsengineering.in/fix/flyback-diode-relay-motor-spikes-reset-board/) cover the common mistakes.

## Sources and further reading

- [Texas Instruments ULN200x and ULQ200x datasheet (SLRS027T)](https://www.ti.com/lit/ds/symlink/uln2003a.pdf) — every figure in the table above.

Last reviewed: November 2026. Limits are from the Texas Instruments datasheet; modules sold with this chip vary. No price is quoted because it has not been checked.