ULN2001

ULN2001 High-Voltage, High-Current Darlington Array

Overview

The ULN2001 is a high-voltage, high-current Darlington transistor array designed for interfacing between low-level logic circuitry and high-power peripheral devices. It is part of the ULN20xx series, which includes multiple configurations for various applications. The device is widely used in industrial, automotive, and consumer electronics due to its ability to drive inductive loads such as relays, solenoids, and stepper motors. The ULN2001 is available in dual in-line (DIP) and small-outline IC (SOIC) packages, making it suitable for both through-hole and surface-mount applications.

Features

• TTL, DTL, PMOS, or CMOS-compatible inputs for versatile interfacing
• High output current capability of up to 500 mA per channel
• Output voltage rating of up to 95 V for driving high-voltage loads
• Transient-protected outputs for enhanced reliability in inductive load applications
• Available in dual in-line plastic package (ULN20xxA series) or small-outline IC package (ULN20xxL series)
• Electrically identical performance across package variants
• Integrated suppression diodes for inductive load switching

Applications

The ULN2001 is designed for a wide range of applications requiring high-current and high-voltage switching. Common uses include:

• Relay Drivers: Controlling electromechanical relays in automation systems
• Solenoid and Lamp Drivers: Driving high-current solenoids and incandescent lamps
• Stepper Motor Controllers: Providing the necessary current for stepper motor windings
• Display Drivers: Multiplexing LED or other display technologies
• Logic Buffers: Amplifying logic signals to drive higher-power devices
• Industrial Control Systems: Interfacing between microcontrollers and high-power actuators

Electrical Characteristics

The following table summarizes the key electrical specifications of the ULN2001:

• Input Compatibility: TTL, DTL, PMOS, CMOS (2.0V to 6.0V logic levels)
• Output Current (per channel): 500 mA (maximum continuous)
• Output Voltage (max): 95 V
• Input Current (max): 1.5 mA
• Output Saturation Voltage: 1.1V typical at 200 mA
• Power Dissipation (per package): 2.25W (DIP), 1.0W (SOIC)
• Operating Temperature Range: -20°C to +85°C

Package Information

The ULN2001 is available in two standard package configurations:

Dual In-Line Package (DIP-16)

• Package Designator: ULN2001A (A suffix)
• Package Dimensions: 19.3mm x 6.35mm x 4.57mm
• Pin Spacing: 2.54mm (standard DIP spacing)
• Mounting: Through-hole
• Thermal Characteristics: θJA = 70°C/W

Small Outline IC Package (SOIC-16)

• Package Designator: ULN2001L (L suffix)
• Package Dimensions: 9.9mm x 3.9mm x 1.75mm
• Pin Spacing: 1.27mm
• Mounting: Surface mount
• Thermal Characteristics: θJA = 85°C/W

Functional Description

The ULN2001 contains seven Darlington transistor pairs with common emitters and integral suppression diodes for switching inductive loads. Each Darlington pair features a high current gain (minimum 1000 at 500 mA) allowing small input currents to switch relatively large loads. The integrated suppression diodes provide a path for the inductive kickback current when switching off inductive loads, protecting both the device and the driving circuitry.

The input side of each Darlington pair is compatible with a wide range of logic families. A series input resistor (typically 2.7kΩ) allows direct interface with 5V logic while limiting input current. The outputs are capable of sinking up to 500 mA continuously, with higher peak currents possible for short durations.

Thermal Considerations

When operating at maximum current ratings, proper thermal management is essential:

• The DIP package can dissipate up to 2.25W at 25°C ambient temperature
• The SOIC package can dissipate up to 1.0W at 25°C ambient temperature
• For continuous operation at high currents, additional heatsinking or forced air cooling may be required
• When driving multiple channels simultaneously, power dissipation is cumulative

Reliability and Protection Features

The ULN2001 incorporates several features to enhance reliability in demanding applications:

• Transient Suppression: Integrated clamp diodes protect against voltage spikes from inductive loads
• Current Limiting: The Darlington configuration inherently limits current gain at high currents
• Thermal Shutdown: While not explicitly specified, the device's thermal characteristics provide inherent protection against thermal runaway
• Input Protection: Series resistors protect the input stages from voltage transients

Design Considerations

When designing with the ULN2001, consider the following:

• For inductive loads, always use the integrated suppression diodes by connecting the COM pin to the positive supply voltage
• When driving multiple high-current loads simultaneously, verify that total power dissipation does not exceed package limits
• For CMOS logic interfaces, ensure the input voltage reaches at least 3.5V for reliable switching
• When driving relays, allow sufficient margin for contact bounce and inrush currents
• For high-frequency switching applications, consider the Darlington pair's relatively slow turn-off time