STMicroelectronics ULN2074B

Overview

ULN2074B from STMicroelectronics is a quad NPN Darlington transistor array in PowerDIP-16 package, designed for high-voltage, high-current switching with isolated emitter outputs. It delivers 1.5 A per channel, features 50 V output breakdown voltage, 35 V sustaining voltage at 100 mA, and 350 Ω input resistor per channel-enabling direct interface with 5 V TTL/CMOS logic in industrial relay drivers and stepper motor phase control.

For engineers reviewing the ULN2074B datasheet, ULN2074B pinout, ULN2074B application, or ULN2074B equivalent, key selection criteria include isolated Darlington configuration (no common emitter), absence of integrated clamp diodes, compatibility with 5 V logic families, and suitability for emitter-follower load configurations requiring independent emitter access.

Technical Context

The ULN2074B implements four independent NPN Darlington pairs with dedicated emitter terminals-unlike ULN2064B/2068B which share emitters and integrate suppression diodes. Each channel includes a 350 Ω series input resistor to limit base current and ensure logic-level compatibility without external components.

It operates with V_CEX = 50 V (breakdown), V_CE(SUS) = 35 V (sustaining at I_C = 100 mA), and V_CE(SAT) ≤ 1.4 V at I_C = 1.25 A / I_B = 2 mA. Input voltage range is 0–30 V, with I_I(ON) = 3.3–4.3 mA at V_I = 2.4–3.75 V.

Key Specifications

Pinout & Package

ULN2074B uses a 16-pin PowerDIP (dual in-line package) with 0.3-inch body width, 2.54 mm pin pitch, and exposed substrate for thermal dissipation. Pin 8 is GND (substrate), pins 1–4 and 13–16 are inputs, and pins 5–7 and 9–12 are collector/emitter terminals arranged for isolated Darlington operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2064B, ULN2074B trades integrated clamping for emitter flexibility-critical for precision current control and noise-sensitive layouts. Versus TIP122, it offers quad integration and logic compatibility but lower per-device current and voltage ratings.

Availability

ULN2074B is available at Aetrix Electronics and suitable for industrial relay drivers, stepper motor phase control, LED array backlighting, and solenoid actuation requiring stable component supply across extended production lifecycles.

Supply support for ULN2074B 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 automotive ICs.

The ULN2074B belongs to ST's legacy high-voltage Darlington driver family, engineered for robust industrial interfacing where logic-to-load isolation, thermal resilience, and configurable emitter topology are essential.

FAQ

What is the purpose of the isolated emitter configuration in ULN2074B?

The isolated emitter terminals allow each Darlington channel to reference its own ground or sense node-enabling independent current monitoring, floating load connections, and elimination of shared-emitter crosstalk. This is essential for precision solenoid control and multi-rail systems where ground separation prevents noise coupling between channels.

Can ULN2074B drive inductive loads without external diodes?

No-ULN2074B lacks integrated clamp diodes, so external flyback diodes (or RC snubbers) must be added across each inductive load. This design choice provides flexibility for optimizing transient suppression in high-reliability or EMI-sensitive applications, unlike ULN2064B which includes built-in diodes.

How does ULN2074B differ from ULN2064B in pin compatibility?

ULN2074B and ULN2064B share identical PowerDIP-16 footprints and input pin assignments (pins 1–4), but differ in output pin mapping: ULN2074B uses pins 5–7 and 9–12 as isolated collectors/emitters, while ULN2064B uses pins 5–8 and 10–13 with common emitters. Direct replacement requires PCB layout modification.

What thermal considerations apply when operating ULN2074B at 1.5 A continuously?

At 1.5 A per channel and V_CE(SAT) ≈ 1.4 V, power dissipation exceeds 2 W per active channel. The substrate (pin 8) must be soldered to ≥4 cm² of 35 µm copper to maintain junction temperature below 125 °C at 70 °C ambient. Derating to 1.0 A is recommended without enhanced heatsinking.