onsemi TIP122G NPN Darlington Transistor: Datasheet, Pinout, and Application Circuits
The onsemi TIP122G is a popular and robust NPN Darlington power transistor designed for medium-power linear and switching applications. Housed in the versatile TO-220 package, it is a workhorse component for hobbyists and engineers, capable of handling high currents and voltages, making it ideal for driving motors, solenoids, relays, and high-power LEDs.
Datasheet Overview and Key Specifications
The TIP122G is part of a series (TIP120/121/122) that offers varying voltage ratings. Its Darlington pair configuration provides an exceptionally high DC current gain, allowing a small input current to control a much larger output current.
Key absolute maximum ratings from the datasheet include:
Collector-Emitter Voltage (VCE): 100 V
Collector Current (IC): 5 A (Continuous)
DC Current Gain (hFE): 1000 (minimum) at IC = 3A, VCE = 4V
Power Dissipation (PD): 65 W (at case temperature TC = 25°C)
These specifications highlight its suitability for medium to high-power switching tasks. However, it is crucial to note that the device requires a heatsink for operations near its maximum ratings to manage thermal dissipation effectively.
TIP122G Pinout Configuration
The TIP122G comes in a standard TO-220 package with three pins. When facing the flat side with the leads pointing downward, the pinout is as follows:
Pin 1 (Base): The input control terminal. A small current into this pin controls the larger current flow between the collector and emitter.
Pin 2 (Collector): Connected to the load. This pin handles the high current, typically connected to the positive supply voltage.
Pin 3 (Emitter): Connected to the ground or common return path. The output current flows out of this pin.
Correct pin identification is critical to prevent damage to the transistor and other circuit components.
Application Circuits
The TIP122G excels in two primary types of circuits: as a switch and as a linear driver.
1. High-Current Switch (e.g., for a DC Motor)
This is the most common application. A small signal from a microcontroller (e.g., an Arduino GPIO pin) or a sensor can be used to switch a motor drawing several amperes.
Operation: A small current (a few mA) is supplied to the base pin, typically through a current-limiting resistor (e.g., 1kΩ). This allows a much larger current (up to 5A) to flow from the collector to the emitter, powering the motor. A flyback diode (1N4007) is connected across the motor terminals to protect the transistor from voltage spikes generated when the motor is switched off.
2. Linear Power Driver (e.g., for a Power LED Strip)
While not as efficient as a switch, the TIP122G can be used in its linear region to control the brightness of a high-power LED strip.
Operation: The transistor acts as a variable resistor. By applying a variable voltage (e.g., from a potentiometer) to the base, the current flowing through the collector-emitter path can be precisely controlled, thereby dimming the LEDs. A series resistor is often still needed to set the maximum current and ensure stability.
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ICGOO FIND: The onsemi TIP122G remains a highly reliable and cost-effective solution for controlling high-current loads with low-power control signals. Its built-in Darlington pair offers immense simplification for designers, eliminating the need to build a discrete two-transistor array. While modern MOSFETs may offer lower switching losses in high-frequency applications, the TIP122G's simplicity, high gain, and ability to be driven directly from logic-level outputs secure its enduring place in power electronics projects, from simple motor controllers to robust linear regulators. Always remember to use an appropriate heatsink when operating near its power limits.
Keywords: Darlington Transistor, High-Current Switch, TO-220 Package, DC Motor Driver, Power Dissipation.
