STMicroelectronics ULN2068B

Overview

ULN2068B from STMicroelectronics is a quad NPN Darlington transistor array with integrated clamp diodes, designed for high-current logic-to-load interfacing. It delivers 1.5 A per channel, features 50 V output breakdown voltage, 35 V sustaining voltage at 100 mA, 2.5 kΩ input resistor, and 900 Ω series resistor - enabling direct drive of solenoids, relays, and lamps in industrial control systems.

For engineers reviewing the ULN2068B datasheet, ULN2068B pinout, ULN2068B application, or ULN2068B equivalent, key selection criteria include its pre-driver stage (reducing logic loading), common-emitter configuration with integral flyback diodes, thermal derating behavior at 70 °C ambient, and compatibility with 5 V TTL/CMOS logic families.

Technical Context

The ULN2068B integrates four independent Darlington pairs with on-chip input resistors (R_IN = 2.5 kΩ) and series base resistors (R_S = 900 Ω), forming a current-gain-optimized driver stage. Each channel provides 1.5 A continuous output current with V_CE(SAT) ≤ 1.4 V at I_C = 1.25 A and I_B = 2 mA.

Its internal clamp diodes are connected anode-to-emitter, enabling safe commutation of inductive loads without external components. The device operates over –20 °C to +85 °C ambient, with power dissipation limited to 4.3 W at T_PINS = 90 °C and 1 W at T_AMB = 70 °C due to thermal resistance constraints.

Key Specifications

Pinout & Package

ULN2068B is housed in a PowerDIP-16 package with 0.3-inch body width, 2.54 mm lead pitch, and GND-connected heat slug pins (pins 8 and 16) for enhanced thermal performance. Pin layout follows standard isolated-Darlington-compatible footprint but shares common emitter (pin 9) across all four channels.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2003A and TIP122, ULN2068B offers higher per-channel current (1.5 A vs. 0.5 A or discrete 5 A), integrated pre-driver and clamp diodes, and optimized thermal design for dense PCB layouts - making it preferred for industrial relay banks and stepper drivers requiring compact, robust, and production-ready integration.

Availability

ULN2068B is available at Aetrix Electronics and suitable for industrial automation, factory test equipment, and LED signage systems requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for ULN2068B 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 ICs with broad manufacturing and quality certifications.

The ULN2068B belongs to ST's high-voltage Darlington driver product line, engineered specifically for logic-level interfacing to inductive and resistive loads in harsh industrial environments - emphasizing reliability, thermal robustness, and ease of integration.

FAQ

What is the maximum continuous output current per channel?

The ULN2068B supports 1.5 A continuous output current per channel at T_AMB ≤ 70 °C with adequate PCB copper area. At 85 °C ambient, derating reduces usable current to approximately 1.1 A due to thermal limits - confirmed by Figure 17 in the datasheet showing 1 W max dissipation at 70 °C.

Can ULN2068B drive 24 V solenoids directly?

Yes - its 50 V output breakdown voltage and 35 V sustaining voltage exceed typical 24 V solenoid flyback transients. With internal clamp diodes and 1.5 A rating, it drives standard 24 V/1.2 A solenoids without external protection, provided common emitter (pin 9) is solidly grounded and thermal copper area meets ≥10 cm² per channel.

How does the pre-driver stage reduce logic loading?

The ULN2068B's 2.5 kΩ input resistor and 900 Ω series base resistor form a current-limiting network that draws only ~0.55 mA at 2.75 V input - reducing GPIO current demand by >75% versus driving a bare Darlington base. This prevents voltage droop on weak microcontroller outputs and eliminates need for buffer stages.

Is ULN2068B compatible with 3.3 V microcontrollers?

Yes - its VI(ON) threshold is specified at 2.75 V (min) for guaranteed turn-on, making it fully compatible with 3.3 V logic. Input current remains below 1 mA at 3.3 V, ensuring safe operation without level-shifting. However, output saturation voltage rises slightly above 1.3 V at full 1.5 A load, requiring thermal verification in sustained-duty applications.