STMicroelectronics ULN2804A

Overview

ULN2804A 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-emitter outputs, 10.5 kΩ input resistors optimized for 6–15 V CMOS/PMOS logic, 50 V output voltage rating, 500 mA continuous output current per channel, and built-in flyback diodes for inductive load protection.

For engineers reviewing the ULN2804A datasheet, ULN2804A pinout, ULN2804A application, or ULN2804A equivalent, key selection considerations include input resistor value (10.5 kΩ), output voltage capability (50 V), continuous current rating (500 mA/channel), integrated clamp diode functionality, and DIP-18 input-opposite-output layout compatibility with legacy industrial control PCBs.

Technical Context

The ULN2804A implements eight independent Darlington transistor stages, each with a monolithic 10.5 kΩ series input resistor and integrated cathode-connected clamp diode to suppress inductive kickback. Its input threshold is tailored for 6–15 V CMOS/PMOS logic families, enabling direct interface without external biasing.

Each channel delivers 500 mA continuous collector current at V_CE(SAT) ≤ 1.3 V (IC = 350 mA, IB = 500 µA), with thermal design supported by R_thJA = 55 °C/W and total package power dissipation up to 2.25 W. The device operates across –20 °C to +85 °C ambient temperature.

Key Specifications

Pinout & Package

ULN2804A is housed in an 18-lead plastic DIP (Dual In-line Package) with copper lead frame and standard 0.3" body width. Pin layout follows input-opposite-output configuration: inputs on one side (pins 1–8), outputs on the opposite side (pins 11–18), with common emitter (pin 9) and ground (pin 10) centrally located.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803A and TD62003APG, ULN2804A uniquely combines 10.5 kΩ input termination, 6–15 V logic compatibility, and integrated clamping in a drop-in DIP-18 footprint-making it optimal for retrofitting legacy 12 V industrial control panels without redesigning input networks.

Availability

ULN2804A is available at Aetrix Electronics and suitable for industrial relay drivers, stepper motor phase control, solenoid actuator interfaces, and LED array signage requiring stable component supply and long-term obsolescence management.

Supply support for ULN2804A 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 automotive, industrial, and power management solutions with broad analog, digital, and mixed-signal product portfolios.

The ULN2804A belongs to ST's legacy high-voltage Darlington driver family, engineered specifically for robust, low-component-count interfacing between modern logic controllers and rugged electromagnetic loads in factory automation and building management systems.

FAQ

What logic families does ULN2804A support?

The ULN2804A features an internal 10.5 kΩ input resistor optimized for 6–15 V CMOS and PMOS logic families. It accepts logic-high signals in that range without external biasing, delivering ~0.47 mA input current at 5 V and ~1.14 mA at 12 V. It is not intended for 3.3 V logic without level translation.

Can multiple ULN2804A outputs be paralleled?

Yes-outputs can be safely paralleled to increase current capacity, as confirmed in the ST datasheet. When paralleling channels, ensure matched PCB trace lengths and thermal paths; two channels yield ~1 A continuous sink capability with appropriate derating for package power dissipation (2.25 W max).

Does ULN2804A require external flyback diodes?

No. Each channel includes an integrated clamp diode connected from output to common emitter (pin 9). This diode conducts inductive kickback energy back into the load return path, eliminating the need for external diodes when switching relays, solenoids, or stepper windings.

What is the maximum operating temperature for ULN2804A?

The ULN2804A is rated for ambient operating temperatures from –20 °C to +85 °C. At +85 °C, its usable power dissipation is reduced to ~1.25 W due to thermal resistance (R_thJA = 55 °C/W); full 2.25 W rating applies only at 25 °C ambient.