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ULN2003 Relay Driver IC

Today, I will introduce you to ULN2003. It is basically a relay driver IC and a Darlington array with high voltage and high current. It consists of seven open collector Darlington pairs with common emitters, indicating that ULN2003 has the ability to process seven different relays at a time.

What is ULN2003

The ULN2003 is a relay driver IC consisting of a Darlington array. It consists of seven open collector Darlington pairs with a common emitter. In addition, the ULN2003A has the ability to process seven different relays simultaneously. A pair of Darlington consists of two bipolar transistors and operates from 500mA to 600mA.

A pair of Darlington transistors consists of two bipolar transistors and operates from 500mA to 600mA. The ULN200X is a well-known IC series. ULN2003 is also part of the series. The ULN2003 operates on 5V and TTL (transistor logic) and CMOS (complementary metal oxide semiconductor). Its pin configuration is designed such that the input pin is on the left side of the IC and its output pin is on the right side in front of the corresponding input pin. The IC has a very wide range of applications. They are commonly used as relay drivers to drive a variety of loads. The ULN2003A can also be used to drive different motors (such as DC motors or stepper motors), PIC microcontrollers or 8051 microcontrollers, etc. via a microcontroller (such as the Arduino). Other applications of the ULN 2003 include logic buffers, lamp drivers, line drivers, LED displays, motor driver circuits, and the like.

ULN2003 Datasheet

ULN2003 Pinouts and Pin Configuration

ULN2003 has 16 pins in total :

  • 7 Input pins (Pin # 1 to Pin # 7)
  • 7 Output pins (Pin # 10 to Pin # 16)
  • 1 Ground pin (Pin # 8)
  • 1 COM pin (Pin # 9)

And the pin configuration is as following:

Pin NumberPin NameDescription
1 to 7Input 1 to Input 7Seven Input pins of Darlington pair, each pin is connected to the base of the transistor and can be triggered by using +5V
8GroundGround Reference Voltage 0V
9COMUsed as test pin or Voltage suppresser pin (optional to use)
10 to 16Output 1 to Output 7Respective outputs of seven input pins. Each output pin will be connected to ground only when its respective input pin is high(+5V)

ULN2003 Key Features

  • 500mA rated collector.
  • High output voltage of around 50V.
  • Relay driver application.
  • Output clamp diode.
  • Input compatible with popular logic types.

ULN2003 Circuit Diagram

The figure below shows the internal circuit diagram of the ULN 2003 with different resistors and diodes.

url2003 circuit
url2003 circuit

ULN2003 Application

  • Logical buffer.
  • Line driver.
  • Relay driver (used to drive different loads).
  • Light driver.
  • LED display driver (display device).
  • Motor (step and DC brushed motor) drive.

How does ULN2003 Work

As mentioned above, the ULN2003 is a 16-pin IC. It has seven Darlington pairs inside, each capable of driving loads up to 50V and 500mA. For these seven Darlington pairs, we have seven input and output pins. In addition to this, we can also ground and general purpose pins. The ground pin is grounded as usual, and the use of a common pin is optional. Surprisingly, the IC does not have any Vcc (power) pins. This is because the power required to operate the transistor will be taken from the input pin itself. The circuit below is a simple circuit that can be used to test the operation of the ULN2003 IC.

ULN2003 testing circuit
ULN2003 testing circuit

In the circuit, the LED is considered a load and the logic pin (blue) is used as a pin for a microcontroller connected to a digital circuit or an Arduino. Note that the positive pin of the LED is connected to the positive load voltage and the negative pin is connected to the output pin of the IC. This is because when the input pin of the IC goes high, the corresponding output pin will be grounded. Therefore, when the negative terminal of the LED is grounded, it completes the circuit and thus illuminates. The maximum load connected to the output pins is 50C and 500mA, respectively. However, you can run a higher current load and combine two or more output pins. For example, if you combine three pins together, you can drive up to (3 * 500mA) ~ 1.5A.

The COM pin is grounded through the switch and the connection is optional. It can be used as a test switch, which means that when this pin is grounded, all output pins will be tied to ground.

ULN2003 Function

  • Contains 7 high voltage and high current Darlington pairs
  • Each pair is rated at 50V and 500mA
  • Input pins can be triggered by + 5V
  • All seven output pins can be connected to aggregate to drive loads up to (7 x 500 mA) ~ 3.5A.
  • Can be directly controlled by digital gates, Arduino, PIC and other logic devices
  • Available in 16-pin DIP, TSSOP, SOIC packages

Where to use ULN2003

The ULN2003 is a 16-pin IC. It has seven Darlington pairs inside, each capable of driving loads up to 50V and 500mA. For these seven Darlington pairs, we have seven input and output pins. In addition to this, we can also ground and general purpose pins. The ground pin is grounded as usual, and the use of a common pin is optional. Surprisingly, the IC does not have any Vcc (power) pins. This is because the power required to operate the transistor will be taken from the input pin itself. The circuit below is a simple circuit that can be used to test the operation of the ULN2003 IC.

The above is all in the ULN2003 Getting Started Guide. I hope you really like this tutorial. If you encounter any problems with any issues, you can always ask me in the comments without even hesitation. If possible, I will try my level to entertain you and solve your problem in a better way.

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