Onsemi TIP31CG NPN Power Transistor: Datasheet, Pinout, and Application Circuit Guide
The Onsemi TIP31CG is a widely used NPN power transistor belonging to the TIP31 series, designed for medium-power linear and switching applications. It serves as a fundamental building block in countless electronic projects, from simple switches to robust power amplifiers. This guide provides a detailed overview of its datasheet specifications, pinout configuration, and a practical application circuit.
Datasheet Overview and Key Specifications
The TIP31CG is packaged in the robust TO-220 package, which is essential for effective power dissipation. Its key electrical characteristics make it suitable for a variety of medium-current and medium-voltage tasks.
Polarity: NPN Bipolar Junction Transistor (BJT)
Collector-Emitter Voltage (VCEO): 100 V – This defines the maximum voltage it can block between collector and emitter when the base is open.
Collector Current (IC): 3 A (continuous) – The maximum continuous current that can flow through the collector.
Collector Dissipation (PD): 40 W – The maximum power the device can dissipate at a case temperature of 25°C. This value is drastically reduced without a suitable heat sink.
DC Current Gain (hFE): Typically 10 to 50 at 3 A – This indicates the transistor's ability to amplify current. A gain of 25, for example, means 1 A of base current can control up to 25 A of collector current.
Transition Frequency (fT): 3 MHz – Suitable for audio frequencies and low-speed switching.
Pinout Configuration
Correctly identifying the pins is crucial for circuit operation and preventing damage. The standard pinout for the TO-220 package of the TIP31CG, when viewed from the front (the side with the metal tab with a hole), is:
1. Pin 1 (Left): Base (B) – The control terminal. A small current into this pin controls a larger current between the collector and emitter.
2. Pin 2 (Center): Collector (C) – The positive power terminal. This pin connects to the load and is typically attached to a heat sink.
3. Pin 3 (Right): Emitter (E) – The negative or ground terminal. The controlled current exits through this pin.
Warning: The metal tab is electrically connected to the Collector (C). If mounting to a heat sink, an insulating kit (mica washer and plastic shoulder washer) must be used to prevent short circuits.
Application Circuit Guide: A Simple Switch
One of the most common uses for the TIP31CG is as a low-side switch. This circuit allows a small signal from a microcontroller (like an Arduino) or a sensor to control a high-power device like a motor, lamp, or relay.
Components Required:
Onsemi TIP31CG Transistor
DC Motor (or 12V Lamp)
12V Power Supply
Arduino or Switch
Resistor (1kΩ)
Flyback Diode (1N4001 or similar) [essential for inductive loads like motors]
Circuit Operation:
1. The Emitter (E) is connected to ground (GND).
2. The load (e.g., a motor) is connected between the 12V supply and the Collector (C).
3. The Base (B) is connected to the control signal (e.g., an Arduino digital pin) through a 1kΩ current-limiting resistor. This resistor is critical to protect the Arduino pin and the transistor's base-emitter junction.
4. A flyback diode is placed in reverse bias across the motor terminals (anode to collector, cathode to 12V). This diode protects the transistor from voltage spikes generated when the inductive load (motor) is switched off.
How it Works:
When the Arduino output pin is set to HIGH (5V), a small current flows into the base via the resistor. This current, amplified by the transistor's hFE, allows a much larger current to flow from the collector to the emitter, thus powering the motor. When the Arduino pin is set to LOW (0V), the base current stops, and the transistor turns off, acting as an open switch and cutting power to the motor.
ICGOOODFIND: The Onsemi TIP31CG remains a versatile and reliable workhorse for designers needing a robust medium-power switch or amplifier. Its high voltage and current ratings, combined with the easy-to-manage TO-220 package, make it an excellent choice for power management tasks in power supplies, motor control, and audio amplifier output stages. Always remember to consult the official datasheet for absolute maximum ratings and implement a sufficient heat sink for high-current applications.
Keywords: NPN Transistor, Power Switching, TO-220 Package, Darlington Pair, Current Amplifier
