STMicroelectronics ULN2066B

Overview

ULN2066B from STMicroelectronics is a quad NPN Darlington transistor array with integrated clamp diodes, designed for high-voltage, high-current switching of inductive loads such as relays, solenoids, and lamps. It delivers up to 1.5 A per channel, supports 50 V output breakdown voltage, sustains 35 V at 100 mA, and accepts 6–15 V CMOS/PMOS logic inputs - used in industrial control panels and programmable logic output stages.

For engineers reviewing the ULN2066B datasheet, ULN2066B pinout, ULN2066B application, or ULN2066B equivalent, key selection criteria include input voltage compatibility (6–15 V), per-channel saturation voltage (1.3 V @ 1 A), integral flyback diode integration, thermal derating above 70 °C ambient, and PowerDIP-16 package mounting constraints.

Technical Context

The ULN2066B implements four independent NPN Darlington pairs with common-emitter outputs and shared emitter pins, each featuring an integrated cathode-connected clamp diode to suppress inductive kickback. Input resistors are internally trimmed to 3 kΩ, enabling direct interface with 6–15 V CMOS/PMOS logic without external biasing.

It operates over –20 °C to +85 °C ambient, with absolute maximum output voltage rated at 50 V and sustaining voltage guaranteed at ≥35 V at 100 mA. Power dissipation is limited to 4.3 W at 90 °C pin temperature, requiring PCB copper area or heatsink attachment for sustained 1.5 A operation.

Key Specifications

Pinout & Package

ULN2066B is housed in a PowerDIP-16 package with 16 leads, featuring gull-wing lead form and internal thermal pad connection via pins 8 and 16 (GND). The package supports through-hole mounting and requires heatsinking via GND pins soldered to ≥200 mm² copper area.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2064B and ULN2068B, the ULN2066B uniquely supports 6–15 V logic directly, avoids external level-shifting, and offers balanced input impedance for mixed-voltage industrial control buses - making it optimal for PMOS-driven PLC outputs and legacy panel interfaces.

Availability

ULN2066B is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor control circuits, LED display modules, and solenoid actuation systems requiring stable component supply across extended product lifecycles.

Supply support for ULN2066B 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, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The ULN2066B belongs to ST's high-voltage Darlington array product line, engineered specifically for robust, cost-effective switching of inductive and resistive loads in harsh industrial environments.

FAQ

What logic families are compatible with ULN2066B inputs?

The ULN2066B is explicitly designed for 6–15 V CMOS and PMOS logic families. Its 3 kΩ internal input resistor allows direct connection without external biasing. It is not compatible with standard 5 V TTL or LVTTL due to insufficient input current at 5 V - use ULN2064B instead for 5 V systems.

Can ULN2066B drive a 24 V relay coil drawing 1.3 A?

Yes - the ULN2066B supports 1.5 A per channel continuously. At 1.3 A, V_CE(SAT) is ≤1.35 V, resulting in <1.76 W dissipation per channel. With adequate PCB copper heatsinking (≥300 mm² 35 µm Cu), it remains within safe thermal limits at 70 °C ambient.

Are the clamp diodes connected to V_CC or GND?

The internal clamp diodes are cathode-connected to the output pins (OUT1–OUT4) and anode-connected to GND (pin 9). This configuration protects against positive-going inductive kickback when switching inductive loads referenced to V_CC, making it ideal for low-side switching topologies.

Does ULN2066B require external pull-down resistors on its inputs?

No - the ULN2066B has no internal pull-downs, but its 3 kΩ input resistors provide defined logic thresholds. When driven by open-drain or floating sources, a 10–100 kΩ external pull-down to GND is recommended to ensure OFF-state stability and prevent false triggering from noise.