How to Use TIP120 Hi-Current Darlington Transistor: Examples, Pinouts, and Specs

The TIP120 is a widely used NPN Darlington transistor capable of handling high current loads. It is designed for general-purpose amplifier and low-speed switching applications. The TIP120 is particularly useful for interfacing with microcontrollers, such as the Arduino UNO, to control devices like motors, solenoids, and relays that require more current than a microcontroller can provide directly.

• DC motor control
• Relay drivers
• Solenoid control
• LED light dimming
• Power regulators

• Collector-Emitter Voltage (Vce): 60V
• Collector-Base Voltage (Vcb): 60V
• Emitter-Base Voltage (Veb): 5V
• Collector Current (Ic): 5A (Continuous)
• Total Power Dissipation (Pd): 65W (at 25°C)
• DC Current Gain (hFE): 1000 (Minimum)
• Operating Junction Temperature (Tj): -65°C to +150°C

1. Connect the base of the TIP120 to a digital output pin of a microcontroller through a current-limiting resistor (typically 1kΩ to 2.2kΩ).
2. Connect the collector to the positive side of the load you wish to control.
3. Connect the emitter to the ground of the power supply.
4. Ensure the power supply voltage and current do not exceed the TIP120's maximum ratings.

• Always use a base resistor to limit the current into the base of the transistor.
• Use a flyback diode across inductive loads (like motors and solenoids) to prevent back EMF damage.
• Consider heat sinking if operating near the maximum power dissipation limits.
• Ensure proper insulation and spacing on high-voltage or high-current circuits.

// Define the pin connected to the base of the TIP120
const int controlPin = 3;

void setup() {
  // Set the control pin as an output
  pinMode(controlPin, OUTPUT);
}

void loop() {
  // Turn on the load connected to the TIP120
  digitalWrite(controlPin, HIGH);
  delay(1000); // Wait for 1 second
  
  // Turn off the load
  digitalWrite(controlPin, LOW);
  delay(1000); // Wait for 1 second
}

• Load does not activate: Check the base resistor and connections. Ensure the control signal is being sent from the microcontroller.
• Transistor overheating: Verify that the current and power dissipation are within limits. Consider adding a heat sink.
• Unexpected behavior in the load: Ensure a flyback diode is used with inductive loads.

• Base Resistor Value: If the base resistor is too high, the transistor may not fully saturate. If it's too low, it could damage the microcontroller's output pin or the transistor's base.
• Heat Sinking: Attach a heat sink to the TIP120 if it gets too hot to touch, or if operating near its maximum ratings.
• Flyback Diode: Always use a flyback diode when controlling inductive loads to prevent voltage spikes that can damage the transistor.

Q: Can I use the TIP120 to control an AC load? A: No, the TIP120 is designed for DC applications only.

Q: What is the function of the Darlington pair inside the TIP120? A: The Darlington pair configuration within the TIP120 allows for high current gain, enabling control of high-current loads with a very small base current.

Q: How do I choose the correct base resistor value? A: The base resistor value depends on the voltage of the control signal and the desired base current. Use Ohm's law (R = V/I) to calculate the appropriate resistor value, ensuring the base current does not exceed the microcontroller's maximum current rating for a pin.