STMicroelectronics ULN2802A

Overview

ULN2802A from STMicroelectronics is an 8-channel Darlington array IC designed for high-voltage, high-current switching of inductive loads such as relays, solenoids, and stepper motor windings. It integrates eight NPN Darlington pairs with common emitters, 10.5 kΩ input resistors, and Zener-clamped inputs optimized for 14–25 V PMOS logic interfaces. Each channel delivers 500 mA continuous output current and withstands 50 V off-state voltage, with integrated flyback diodes enabling direct drive of inductive loads without external protection.

For engineers reviewing the ULN2802A datasheet, ULN2802A pinout, ULN2802A application, or ULN2802A equivalent, key selection criteria include input resistor value (10.5 kΩ), compatible logic supply range (14–25 V PMOS), per-channel saturation voltage (≤1.3 V at 200 mA), thermal resistance (55 °C/W), and DIP-18 package layout compatibility with input-opposite-output routing.

Technical Context

The ULN2802A implements eight independent Darlington transistor stages, each with a built-in 10.5 kΩ series input resistor and Zener clamp to support direct interfacing with 14–25 V PMOS logic families. Its input structure eliminates the need for external current-limiting resistors while maintaining safe base drive under overvoltage conditions.

All channels share a common emitter connection and feature integrated suppression diodes connected anode-to-emitter, enabling bidirectional energy clamping during inductive turn-off transients. The device operates across –20 °C to +85 °C ambient and supports paralleling of outputs for higher current capability up to 4 A total (with derating).

Key Specifications

Pinout & Package

ULN2802A is supplied in an 18-lead plastic DIP (Dual In-line Package) with copper lead frame, featuring input pins on one side (1–8) opposite output pins (11–18), and shared emitter (9) and common cathode clamp diode (10). This layout simplifies PCB routing for multi-load driver applications.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803A and TD62003APG, the ULN2802A uniquely provides factory-trimmed 10.5 kΩ input resistors and Zener clamping for direct 14–25 V PMOS compatibility - eliminating both external components and level-shifter circuitry in industrial control designs.

Availability

ULN2802A is available at Aetrix Electronics and suitable for industrial relay control, stepper motor phase driving, solenoid actuation, and automated test equipment load switching requiring stable component supply and long-term production continuity.

Supply support for ULN2802A 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, specializing in power management, analog, microcontrollers, and discrete devices for industrial, automotive, and consumer markets.

The ULN2802A belongs to ST's high-voltage Darlington array product line, engineered specifically for robust, low-component-count interfacing between PMOS logic and industrial inductive loads.

FAQ

What logic families is the ULN2802A designed to interface with?

The ULN2802A is specifically optimized for 14–25 V PMOS logic families. Its internal 10.5 kΩ input resistors and Zener clamping allow direct connection without external biasing components. It is not intended for 3.3 V, 5 V TTL, or CMOS logic - those require ULN2803A or ULN2804A variants instead.

Can multiple ULN2802A outputs be paralleled for higher current?

Yes - the datasheet explicitly permits paralleling outputs to increase current capacity. All eight channels share thermal coupling and matched V_CE(SAT), enabling up to 4 A total (500 mA × 8) with appropriate PCB copper area and derating per the 2.25 W package power limit and 55 °C/W thermal resistance.

What is the function of pin 10 (common cathode) on the ULN2802A?

Pin 10 is the common cathode connection for all eight integrated flyback diodes. During inductive load turn-off, stored energy flows from the load through the diode anode (internal to each channel) to this cathode node, then back to the positive supply rail - providing safe, self-contained transient suppression without external diodes.

Does the ULN2802A require external heat sinking in typical operation?

Not under typical single-channel operation: at 500 mA and 1.1 V V_CE(SAT), power dissipation is ~0.55 W per active channel. With R_thJA = 55 °C/W, junction rise is ~30 °C above ambient - within safe limits. Heat sinking becomes necessary only when >3 channels operate continuously near full load or ambient exceeds 60 °C.