Arduino control 12v LED with tip120 transistor switching.


                                     Tutorial  @Mr.ElectroUino

Hello Friends,

In this blog, we will learn about how to control 12v LED with arduino and a transistor (tip120) as switching.

Why can’t we connect the 12v LED to Arduino? Why are we using transistors? 

Since Arduino digital pin is only capable of supplying 5v and 40mA, but we need a 12 volt to turn on the 12v LED, so it’s not possible to regulate High power led by Arduino that is why we are using a transistor to switch high power load. With the help of a transistor, we can connect the external power supply to switch-on the LED.

We are using the Darlington transistor (tip120) it is a medium power NPN transistor.Now we can control high power LEDs and motor by switch loads up to 60v and 5A. There are some other Darlington pair NPN transistors like tip122 for higher voltage and ampere for controlling high power electronics.

How tip120 Arduino together work?

Transistor has three leads; Base (B), Collector (C), and Emitter (E).
    1. Base: Used for switching on or off the transistor. It's like a door open and close.
    2. Collector: The current goes through the collector, usually connected to a load.
    3. Emitter: Current Drains out through emitter, usually connected to ground.


The base of the transistor is connected to Arduino digital pins. When Arduino sends a high signal on the base pin, the transistor switches on, and the current flows through the collector to the emitter.When Arduino sends a low signal on the base pin, the transistor switches off and zero current flow.

That why we connect a light or motor GND pin to the collector pin, the light or motor positive pin is connected to the external power supply, and the power supply GND pin to the emitter pin. When the Arduino signal is high, the Transistor switches and completes the circuit.

Now we can control a high electronics device by switch a load by applying a small current on the base of the transistor, we can control larger currents.

Features of tip120 transistor:

1. NPN moderate-power Darlington Transistor

2. Continuous Collector current (IC) is 5A

3. Collector-Emitter voltage (VCE) is 60V

4. Collector-Base voltage (VCB) is 60V

5. Emitter Base Voltage (VBE) is 5V

6. Base Current(IB) is 120mA

7. Peak load current is 8A


  • Can be used to switch high current (up to 5A) loads
  • Used where high amplification is needed
  • Speed control of Motors
  • Inverter and other rectifier circuits


Component requirements:

    1. Arduino.

    2. TIP120.

    3. Resistor 2.2k.

    4. 12v LED.

    5. 12v power supply.

    6. Breadboard.

    7. Jumper wire.


Pin connection:

1. Connect arduino digital 13 pin to 2.2k resistor and connect the resistor to transistor base pin.
2. Connect arduino ground pin to transistor emitter pin.
3. Connect power supply (12v) positives pin is connected to led positive terminal and negative pin is connected to transistor emitter pin.
4. Connect led negative terminal to transistor collector pin. Now Circuit is complete lets go to coding part.

void setup()
  pinMode(13, OUTPUT);

void loop()
  digitalWrite(13, HIGH);
  delay(1000); // Wait for 1000 millisecond(s)
  digitalWrite(13, LOW);
  delay(1000); // Wait for 1000 millisecond(s)

TAGS: 12v led bulb control arduino, 12v transistor switch circuit, tip120, arduino transistor led, tip120 arduino, arduino control 12v, darlington transistor, tip120 darlington transistor, transistor switching circuits, tip122, npn transistor switching circuit.

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