STMicroelectronics ULN2803A

Overview

ULN2803A from STMicroelectronics is an 8-channel Darlington transistor array optimized for 5 V TTL/CMOS logic interfacing, featuring integrated flyback diodes, 500 mA continuous output current per channel, 50 V output voltage rating, and DIP-18 package with input-opposite-output pinout. It drives relays, solenoids, and LED displays in industrial control panels.

For engineers reviewing the ULN2803A datasheet, ULN2803A pinout, ULN2803A application, or ULN2803A equivalent, key selection criteria include input resistor value (2.7 kΩ), saturation voltage at 200 mA (≤1.1 V), clamp diode forward voltage (1.7–2.0 V), thermal resistance (55 °C/W), and parallel-output capability for higher current loads.

Technical Context

The ULN2803A integrates eight independent NPN Darlington pairs with common-emitter outputs and monolithically embedded suppression diodes-each configured to handle inductive kickback without external components. Its 2.7 kΩ series input resistor enables direct connection to 5 V logic while limiting base current to ~1.35 mA at VI = 3.85 V.

Each channel delivers up to 600 mA peak current (500 mA continuous) with V_CE(SAT) ≤ 1.3 V at 350 mA, and supports paralleling of outputs to scale load current. The device operates across –20 °C to +85 °C ambient and features a total package power dissipation limit of 2.25 W.

Key Specifications

Pinout & Package

Supplied in an 18-lead plastic dual in-line package (DIP-18) with copper lead frame and standard 0.3-inch body width. Input pins (1–8) are positioned opposite corresponding output pins (18–11), enabling straight-through PCB trace routing and minimizing crosstalk.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2003A, ULN2803A adds one channel and uses DIP-18 for consistent layout scaling; compared with TBD62083AFG, it offers plug-and-play 5 V logic compatibility and through-hole mounting without external biasing.

Availability

ULN2803A is available at Aetrix Electronics and suitable for industrial relay control, LED display driving, stepper motor phase switching, and printer solenoid actuation requiring stable component supply across long-lifecycle production programs.

Supply support for ULN2803A 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, designing and manufacturing analog, MCU, power, and sensor solutions for industrial, automotive, and consumer markets.

The ULN2803A belongs to ST's legacy high-voltage Darlington array product line, engineered specifically for robust, low-cost interfacing between digital logic and medium-power inductive or resistive loads.

FAQ

What is the maximum safe continuous current per channel?

The ULN2803A supports 500 mA continuous collector current per channel at TA ≤ 25 °C with adequate PCB copper area. Derating is required above 25 °C ambient - at 70 °C, max continuous current drops to ~350 mA based on its 55 °C/W thermal resistance and 2.25 W total package power limit.

Can outputs be paralleled, and what is the resulting current capacity?

Yes - outputs can be wired in parallel to increase current capacity. Two outputs yield ~900 mA continuous (derated), and three outputs support ~1.3 A, assuming matched thermal conditions and equal current sharing. Layout symmetry and shared heatsinking are recommended to avoid thermal runaway.

What voltage must be applied to pin 18, and why?

Pin 18 (common cathode) must be connected to the positive supply rail of the inductive load (e.g., +12 V or +24 V). This ties the anodes of all internal clamp diodes to that rail, allowing flyback current from energized coils to recirculate safely through the diode and back to the supply instead of damaging the Darlington junctions.

Is the ULN2803A RoHS-compliant and halogen-free?

Yes - the ULN2803A is manufactured in STMicroelectronics' ECOPACK®-compliant DIP-18 package, meeting RoHS Directive 2011/65/EU and halogen-free requirements per IEC 61249-2-21. Full compliance documentation is available in ST's official product change notifications and material declarations.