The TIP122 NPN Darlington Transistor is a high-gain power component designed for applications where a low-power signal needs to control a high-power load. At Electrapac, we recommend the TIP122 for enthusiasts and engineers who need more switching "sensitivity" than a standard BJT can provide, making it the perfect bridge between microcontrollers and heavy-duty hardware.

Product Overview

The TIP122 is not just a single transistor; it is a Darlington Pair. This means it contains two NPN transistors internally connected so that the current amplified by the first is amplified further by the second. This results in an extremely high current gain (h_FE), allowing you to switch up to 5A of current using only a tiny fraction of a milliamp from an Arduino or ESP32 pin.

Key Features for Electrapac Customers

• Ultra-High Gain: With a minimum gain of 1000, it is much easier to drive than the TIP41C. You can control heavy loads with almost zero "stress" on your control circuit.

• 100V Capacity: The TIP122 is the high-voltage version of the series, making it suitable for 24V and 48V industrial systems.

• Integrated Protection Diode: Features a built-in "anti-parallel" commutating diode between the Collector and Emitter, which helps protect the transistor from inductive spikes.

• Monolithic Construction: The internal resistors (Base-Emitter) are built-in to ensure the transistor turns off quickly and reliably.

• Standard TO-220 Form Factor: Easy to mount to common aluminum heatsinks for high-wattage operation.

Technical Implementation Guide

To ensure your Electrapac project is built to last, follow these integration guidelines:

1. Low Input Current: Because the gain is so high, you only need a small base resistor (typically 1k to 2.2k) when connecting to a 5V logic pin.

2. Saturation Voltage (V_CE(sat)): Darlington transistors have a higher voltage drop than standard BJTs—typically around 2V. This means the TIP122 will get hotter than a MOSFET when passing high current.

   Electrapac Heat Warning: If switching more than 1.5A, an aluminum heatsink is mandatory to prevent thermal shutdown.

3. Inductive Loads: While it has an internal diode, we still recommend adding an external 1N4007 diode across motors or solenoids for double protection in high-frequency switching environments.

Primary Applications

• Solenoid & Valve Drivers: Perfect for automated water valves or pneumatic systems.

• High-Power Stepper Motors: Acting as the switching stage for unipolar stepper motors.

• Relay Replacement: Use the TIP122 to switch DC loads silently without the "click" of a mechanical relay.

• LED Strip Dimming: Excellent for PWM control of long 12V or 24V LED strips.

• Audio Power Stages: Used in the output sections of low-to-medium power audio amplifiers.

Why Shop at Electrapac?

We source the TIP122 Darlington Transistor from manufacturers that guarantee the high h_FE needed for logic-level switching. Visit us at for the high-gain components that make complex power control simple.