NPN Darlington transistor · TO-220
TIP120 Pinout
Printed face toward you, metal tab at the back, legs pointing down, left to right: 1 base, 2 collector, 3 emitter (B-C-E). The metal tab is joined to the collector.
Two transistors in one TO-220 case: a few mA from an Arduino pin switches up to 5 A.
- Pin 1: Base (B)The control pin. It turns on at about 1.4 V above the emitter at low current (a typical value: the datasheet allows up to 2.5 V at 3 A) and needs only a few mA, always through a resistor.
- Pin 2: Collector (C)Goes to the load (motor, lamp, LED strip). Also joined to the metal tab.
- Pin 3: Emitter (E)Goes to 0 V (ground) when the transistor is used as a switch.
Metal tab: joined to pin 2, the collector, inside the part.
Check your part before wiring. Read the maker and the full part number printed on it, open that maker's datasheet, or test the legs with a multimeter's diode setting.
PNG 1440 × 1280 pixels, SVG to any size. Both keep the wirecora.com mark along the bottom.
Pinout table
Which leg of the TIP120 is which?
| Pin | Name | What it does |
|---|---|---|
| 1 | Base B | The control pin. It turns on at about 1.4 V above the emitter at low current (a typical value: the datasheet allows up to 2.5 V at 3 A) and needs only a few mA, always through a resistor. |
| 2 | Collector C | Goes to the load (motor, lamp, LED strip). Also joined to the metal tab. |
| 3 | Emitter E | Goes to 0 V (ground) when the transistor is used as a switch. |
| Tab | Metal tab C | Joined to pin 2, the collector, so it carries the same voltage. Keep it away from other metal unless you mean it to touch. |
Key ratings
How much can the TIP120 take?
From the onsemi datasheet: TIP120, TIP121, TIP122 (NPN); TIP125, TIP126, TIP127 (PNP) Plastic Medium-Power Complementary Silicon Transistors (TIP120/D, Rev. 10). Stay well inside these limits: they are the most the part takes, not what it should run at.
Open the onsemi datasheet (PDF)Pin order by maker
Is every TIP120 wired B-C-E?
The onsemi datasheet numbers the legs 1 base, 2 collector, 3 emitter (B-C-E) with the printed face toward you, and pin 4, the metal tab, is the collector too.
The PNP TIP125 to TIP127 have the same leg order. Parts from other makers usually do as well, but check their datasheet before wiring.
A first circuit
Run a 12 V motor or LED strip from an Arduino
- Load from +12 V to the collector. Emitter to 0 V, shared with the Arduino's 0 V.
- For a motor, a diode (1N4007) across it, striped end to +12 V.
- A 470 Ω resistor from the Arduino pin to the base: about 7.5 mA. With a gain of at least 1000, that drives a load of 2 A or more.
- Pin high: the load runs. Use analogWrite() on a PWM pin to dim the strip or slow the motor.
At 3 A the TIP120 drops up to 2 V, which is 6 W of heat: that needs a heatsink. Above about 1 A, an IRFZ44N driven properly wastes far less.
The wiring board has the TIP120 in its Transistors group, with its built-in base resistors and diode simulated.
Open the wiring boardTIP120 questions
What is the TIP120 pinout?
With the printed face toward you and the legs down, from left to right: base, collector, emitter (B-C-E). The metal tab is the collector too.
Can an Arduino drive a TIP120 directly?
Yes, through a resistor of 470 Ω to 1 kΩ on the base. Its gain of 1000 or more turns a few mA from the pin into amps at the collector.
Why does my TIP120 get hot?
A Darlington never switches fully on: up to 2 V stays across it at 3 A (4 V at 5 A). Volts times amps is heat, so above about 1 A give it a heatsink.
Does the TIP120 need a diode for a motor?
Yes, across the motor. The TIP120 has a diode inside, but it sits across collector and emitter and does not catch the motor's kick the way a diode across the motor does.
Can I use this pinout picture?
Yes. Download it as PNG or SVG and use it in notes, lessons or posts. The wirecora.com mark along the bottom stays in the picture.
Pin order and ratings from the onsemi datasheet named above. Last reviewed .