onsemi TIP102G Darlington Transistor: Datasheet, Pinout, and Application Circuits

The onsemi TIP102G is a venerable and robust NPN power Darlington transistor designed for a wide range of high-current switching and amplification tasks. Belonging to the TIP100 series, this device is renowned for its ability to handle significant power levels with minimal drive current, making it a staple in power supply units, motor controllers, audio amplifiers, and various industrial systems.

This article provides a detailed overview of the TIP102G, covering its key specifications, pinout configuration, and practical application circuits.

Datasheet Overview and Key Specifications

The TIP102G is packaged in the industry-standard TO-220 package, which facilitates easy mounting to a heatsink for efficient thermal management. Its Darlington pair configuration internally connects two transistors, resulting in an extremely high DC current gain (`hFE`), typically around 1000. This allows a small base current to control a much larger load current.

Here are some of the critical absolute maximum ratings from its datasheet:

Collector-Emitter Voltage (VCEO): 100 V

Collector Current (IC): 8 A (continuous)

Base Current (IB): 120 mA (continuous)

Total Power Dissipation (PTOT): 2 W at 25°C (Derate 16.7 mW/°C above 25°C). When mounted on an adequate heatsink, this rating can be significantly higher.

DC Current Gain (hFE): 1000 (min) at IC = 3 A, VCE = 4 V

Collector-Emitter Saturation Voltage (VCE(sat)): 2.0 V (max) at IC = 3 A, IB = 12 mA

The relatively high saturation voltage is a characteristic trade-off of Darlington transistors but is justified by the immense current gain.

Pinout Configuration

The TIP102G’s TO-220 package has a standard pinout. When viewing the component from the front (the side with the metal tab and mounting hole), the pins are arranged from left to right as follows:

1. Pin 1 (Base): This is the control input pin. A small current applied to this pin (relative to the emitter) allows a large current to flow from the collector to the emitter.

2. Pin 2 (Collector): This pin connects to the main load (e.g., a motor, solenoid, or lamp). The high-side power supply for the load is connected to this pin.

3. Pin 3 (Emitter): This is the common ground/reference pin for both the base current and the collector current. It is typically connected to the circuit ground.

Always consult the datasheet for your specific supplier to confirm the pinout, as some manufacturers may have variations.

Application Circuits

The TIP102G excels in low-side switching applications. Here are two common circuit examples.

1. Basic DC Motor Driver / High-Current Switch

This is a fundamental circuit for controlling a DC motor or other inductive load.

A digital signal from a microcontroller (e.g., Arduino, 3.3V or 5V) or logic gate is applied to the base of the TIP102G through a current-limiting resistor (`R1`, typically 1kΩ to 470Ω).

The flyback diode (D1), such as a 1N4007, is absolutely critical for protecting the transistor. It provides a path for the inductive kickback current generated when the motor is switched off, preventing damage to the TIP102G.

When the input signal is HIGH, the transistor turns on, allowing current to flow from the positive supply (`Vmotor`), through the motor, and to ground via the transistor's Collector-Emitter path.

When the input signal is LOW, the transistor turns off, stopping the motor.

2. Simple Linear Power Amplifier

While not as efficient as a push-pull configuration for audio, a Darlington transistor can be used in a simple Class A amplifier stage to drive a small speaker. The high current gain allows for a small audio signal from a pre-amplifier to directly drive the base. The biasing resistors (`R1` and `R2`) set the operating point, while the emitter resistor (`RE`) provides thermal stability. A coupling capacitor (`C1`) blocks DC from the input source. This circuit is simple but is generally used for low-to-medium power applications due to the heat dissipation in the linear region.

ICGOODFIND Summary

The onsemi TIP102G remains a highly reliable and effective solution for controlling high-power loads with low-power control signals. Its exceptional current gain simplifies driver circuit design, reducing the need for pre-driver stages. While modern MOSFETs may offer lower saturation voltages in some applications, the TIP102G's robustness, ease of use, and ability to be driven directly from logic-level signals ensure its continued relevance in power electronics projects, from hobbyist creations to industrial equipment. Proper heatsinking and the use of protection diodes for inductive loads are essential for reliable long-term operation.

Keywords:

Darlington Transistor

Power Switching

Current Gain

TO-220

Low-side Switch