Tip120: Basics on TIP120 Transistor

Introduction to TIP120 Transistor

The TIP120 is a popular NPN Darlington transistor widely used in electronic projects for switching and amplification purposes. It is known for its high current gain, making it suitable for controlling high-current loads such as motors, relays, and high-power LEDs. In this article, we will explore the basics of the TIP120 transistor, its characteristics, applications, and how to use it effectively in your projects.

What is a TIP120 Transistor?

The TIP120 is an NPN Darlington transistor, which means it consists of two bipolar junction transistors (BJTs) connected in a cascade configuration. This configuration allows for a high current gain, typically in the range of 1000 to 10,000. The TIP120 is housed in a TO-220 package, which provides good heat dissipation capabilities.

Key Specifications of TIP120

How TIP120 Transistor Works

The TIP120 operates on the principle of current amplification. When a small current is applied to the base pin, it allows a much larger current to flow from the collector to the emitter. The current gain (hFE) of the TIP120 is typically around 1000, which means that for every 1mA of base current, the transistor can allow up to 1A of collector current to flow.

TIP120 Pinout

The TIP120 has three pins:

1. Base (B)
2. Collector (C)
3. Emitter (E)

The base pin is used to control the transistor’s operation. When a sufficient current is applied to the base, the transistor turns on, allowing current to flow from the collector to the emitter. The collector pin is connected to the load, while the emitter pin is usually connected to ground.

Applications of TIP120 Transistor

The TIP120 is widely used in various electronic applications due to its high current handling capability and high current gain. Some common applications include:

1. Motor control: The TIP120 can be used to control DC motors, Stepper Motors, and servo motors. It can handle the high current required by these motors and provides efficient switching.

2. Relay driving: TIP120 is often used to drive relays, which are used for switching high-current loads. The transistor can handle the inductive load of the relay coil and provide reliable switching.

3. LED driving: The TIP120 can be used to control high-power LEDs or LED arrays. It can provide the necessary current to drive the LEDs while also offering protection against over-current conditions.

4. PWM control: TIP120 is suitable for pulse-width modulation (PWM) applications, such as dimming LEDs or controlling motor speed. It can handle the high-frequency switching required for PWM.

5. Audio amplification: In some audio amplifier circuits, TIP120 transistors are used as power amplifiers to drive speakers or headphones.

Using TIP120 in a Circuit

When using the TIP120 in a circuit, there are a few important considerations to keep in mind:

1. Base resistor: A resistor is required between the controlling signal and the base pin of the TIP120. This resistor limits the base current and prevents damage to the transistor. The value of the resistor depends on the desired base current and the controlling signal voltage.

2. Collector-emitter voltage: The voltage applied between the collector and emitter pins should not exceed the maximum rating specified in the datasheet (60V for TIP120). Exceeding this voltage can damage the transistor.

3. Heat dissipation: When the TIP120 is handling high currents, it can generate significant heat. Proper heat dissipation measures, such as using a heatsink, should be employed to prevent overheating and ensure reliable operation.

4. Flyback diode: When using the TIP120 to control inductive loads like motors or relays, it is important to include a flyback diode across the load. This diode protects the transistor from voltage spikes generated by the collapsing magnetic field of the inductive load when the transistor turns off.

Example Circuit: DC Motor Control

Here’s an example circuit that demonstrates how to use the TIP120 to control a DC motor:

       +12V
        |
        |
       / \
      /   \
     /     \
    /       \
   /         \
  /           \
 |             |
 |             |
 |     DC      |
 |    Motor    |
 |             |
 |             |
  \           /
   \         /
    \       /
     \     /
      \   /
       \ /
        |
        |
        |
       /-\
      |   |
      |   |
      |   |
      |   |
      |   |
      | B |
 |----| C |----
 |    | E |
 |     \_/
 |      |
 |      |
 |     ___
 |     \ /
 |      |
 |     ___
 |     ___
 |
GND

In this circuit, the TIP120 is used to control the DC motor. The base of the transistor is connected to a controlling signal through a resistor. When the controlling signal is high, the transistor turns on, allowing current to flow through the motor. The flyback diode is connected across the motor to protect the transistor from voltage spikes.

TIP120 vs. Other Transistors

The TIP120 is often compared to other popular transistors, such as the 2N2222 and the BD139. Here’s a comparison of their key specifications:

As evident from the table, the TIP120 has a higher current handling capability and higher current gain compared to the 2N2222 and BD139. It is suitable for applications that require controlling high-current loads. However, if your project doesn’t require such high currents, transistors like the 2N2222 or BD139 may be more appropriate.

Frequently Asked Questions (FAQ)

1. Q: What is the maximum current that a TIP120 can handle?
   A: The TIP120 can handle a continuous collector current of up to 5A and a peak current of up to 8A.

2. Q: Do I need a heatsink when using a TIP120?
   A: If the TIP120 is handling high currents and dissipating significant power, it is recommended to use a heatsink to prevent overheating and ensure reliable operation.

3. Q: Can I use a TIP120 to control an AC load?
   A: No, the TIP120 is designed for controlling DC loads only. For controlling AC loads, you would need to use a different type of transistor or a solid-state relay.

4. Q: What is the purpose of the base resistor in a TIP120 circuit?
   A: The base resistor is used to limit the base current and protect the transistor from excessive current. It also ensures proper biasing of the transistor based on the controlling signal.

5. Q: Can I parallel multiple TIP120 transistors to increase the current handling capacity?
   A: Yes, it is possible to parallel multiple TIP120 transistors to increase the current handling capacity. However, it is important to ensure proper load balancing and heat dissipation when doing so.

Conclusion

The TIP120 transistor is a versatile and widely used component in electronic projects. Its high current gain and high current handling capability make it suitable for controlling a wide range of loads, including motors, relays, and high-power LEDs. By understanding the basics of the TIP120, its characteristics, and how to use it properly in a circuit, you can effectively incorporate it into your projects and achieve reliable switching and amplification.

When working with the TIP120, remember to consider factors such as base resistor selection, voltage ratings, heat dissipation, and flyback diode protection for inductive loads. By following best practices and understanding the transistor’s limitations, you can ensure optimal performance and longevity of your circuits.

As you explore further applications and projects involving the TIP120, don’t hesitate to consult the datasheet and application notes provided by the manufacturer for more detailed information and guidance.

Happy building and experimenting with the TIP120 transistor!