ILN2003 – 7-Channel Darlington Transistor Array

Introduction

The ILN2003 (commonly known as ULN2003) is a 7-channel Darlington transistor array designed to drive high-current loads using low-power logic signals. It contains seven Darlington transistor pairs, each capable of switching up to 500mA at 50V. With its built-in freewheeling diodes, the ILN2003 efficiently drives inductive loads such as relays, stepper motors, solenoids, and LED displays. It is widely used in microcontroller-based circuits, automation, and motor control applications.

Working Principle of ILN2003

The ILN2003 consists of seven Darlington pairs, which are two bipolar junction transistors (BJTs) connected together to amplify the input signal. Each channel acts as a switch, where a low-current input from a microcontroller (such as Arduino, PIC, or Raspberry Pi) can control a high-power device.

Pin Configuration

The ILN2003 comes in a 16-pin DIP or SOIC package, with the following pin functions:

Operation

• When a high signal (logic 1) is applied to an input pin, the corresponding output pin goes low, completing the circuit and activating the load.
• When a low signal (logic 0) is applied, the output remains high, and the load is turned off.
• The built-in freewheeling diodes protect the circuit from voltage spikes caused by inductive loads like motors and relays.

Key Features of ILN2003

✔ Seven Darlington pairs with high current gain
✔ Maximum output current of 500mA per channel
✔ Maximum output voltage of 50V
✔ Built-in freewheeling diodes for inductive load protection
✔ TTL & CMOS logic compatible (3.3V & 5V logic support)
✔ Compact 16-pin DIP or SOIC package

Common Applications of ILN2003

1. Stepper Motor Control

ILN2003 is commonly used to drive stepper motors, such as the 28BYJ-48 motor. It receives signals from a microcontroller and energizes the motor coils sequentially, allowing precise control of motor movement.

2. Relay and Solenoid Drivers

Since microcontrollers cannot directly drive relays and solenoids, the ILN2003 acts as an interface, allowing small logic-level signals to control high-power devices.

3. LED Matrix and Display Driving

Large LED arrays, 7-segment displays, and dot matrix displays require high current, which ILN2003 can provide. It helps control multiple LEDs using low-power logic signals.

4. Industrial Automation

ILN2003 is widely used in industrial automation systems for controlling solenoid valves, motors, and actuators in machines and robots.

Advantages of ILN2003

✔ Allows microcontrollers to control high-power devices
✔ Simplifies circuit design with built-in protection diodes
✔ Supports multiple output channels for flexible control
✔ Compatible with both 3.3V and 5V logic

Conclusion

The ILN2003 is a powerful 7-channel Darlington transistor array that enables microcontrollers to drive motors, relays, LEDs, and other high-power components efficiently. With its built-in diodes for inductive protection and high current capacity, it is widely used in stepper motor control, automation, and power switching applications. Its simplicity, reliability, and affordability make it an essential component in embedded systems and industrial electronics.