STMicroelectronics ULN2003A

Overview

ULN2003A from STMicroelectronics is a 7-channel high-voltage, high-current Darlington array IC with open-collector outputs, integrated flyback diodes, 500 mA continuous per channel, 50 V output voltage rating, and TTL/CMOS-compatible inputs-designed for driving relays, solenoids, and LED displays in industrial control and automation systems.

For engineers reviewing the ULN2003A datasheet, ULN2003A pinout, ULN2003A application, or ULN2003A equivalent, this device is selected for robust inductive load switching where logic-level interfacing, thermal reliability in DIP-16 packaging, and paralleled-output current scaling are required.

Technical Context

The ULN2003A integrates seven independent Darlington transistor pairs with common-emitter configuration and on-chip clamping diodes connected anode-to-ground and cathode-to-collector-enabling safe commutation of inductive loads without external snubbers. Each channel operates with saturated V_CE(SAT) ≤1.3 V at 200 mA and supports input logic thresholds compatible with 5 V TTL and CMOS.

It features pinout symmetry (inputs on one side, outputs on the opposite) to minimize PCB trace crosstalk and routing complexity. Thermal resistance R_thJA is 70 °C/W in DIP-16, enabling sustained 500 mA operation at ambient temperatures up to +85 °C with appropriate board layout.

Key Specifications

Pinout & Package

ULN2003A is supplied in a 16-pin plastic dual in-line package (DIP-16L) with copper leadframe for enhanced thermal performance. Pin 9 is the common cathode connection for all internal clamp diodes and must be tied to the positive rail of the inductive load supply.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Darlington array applications.

Compared with TI ULN2003ADR and ON ULQ2003A, the ST ULN2003A offers optimal thermal performance in through-hole form factor, tighter V_CE(SAT) tolerance, and proven long-term availability in industrial DIP-16 sockets-making it the default choice for retrofit, repair, and legacy control board designs.

Availability

ULN2003A is available at Aetrix Electronics and suitable for industrial relay control, stepper motor interface, LED display multiplexing, and thermal print head driving requiring stable component supply across extended product lifecycles.

Supply support for ULN2003A includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, power, MCU, and sensor solutions for automotive, industrial, and consumer markets.

The ULN2003A belongs to ST's high-voltage interface IC portfolio, engineered specifically for robust, cost-effective replacement of discrete transistor/diode combinations in electromechanical control systems.

FAQ

Can ULN2003A drive 12 V relays directly?

Yes. With its 50 V output voltage rating and 500 mA per channel capability, ULN2003A can directly switch 12 V DC relays having coil resistances ≥24 Ω (e.g., 12 V / 500 mA = 24 Ω). The internal clamp diode protects against back-EMF, eliminating external diodes. Ensure Pin 9 (COM) connects to the 12 V supply rail.

What is the maximum safe duty cycle for 500 mA continuous operation?

At 25 °C ambient and with standard PCB copper pour, ULN2003A sustains 500 mA continuously per channel. Derating is required above 25 °C: at 70 °C ambient, maximum continuous current drops to ~350 mA (per Figure 17, DIP-16). For pulsed operation, peak current reaches 600 mA at ≤50% duty cycle with adequate heatsinking.

Why must Pin 9 (COM) be connected to the load supply?

Pin 9 is the common cathode node for all seven internal clamp diodes. Connecting it to the positive side of the inductive load (e.g., relay coil's +12 V) provides a low-impedance recirculation path for stored magnetic energy when the Darlington turns off-preventing voltage spikes that could damage the IC or upstream logic. Leaving it floating disables protection.

Is ULN2003A RoHS-compliant and halogen-free?

Yes. ULN2003A is manufactured in ST's ECOPACK2-compliant DIP-16L package, meeting RoHS Directive 2011/65/EU and halogen-free requirements per IEC 61249-2-21. Full compliance documentation, including material declarations and test reports, is available via ST's quality portal.