From a 3.3 V or 5 V pin
| Pin | Verdict | Why | In free air |
|---|---|---|---|
| ESP32 · 3.3 V | Works | 120 Ω on the base: up to 1.7 A of load at a gain of 250 | 800 mA (heat) |
| Arduino Uno · 5 V | Works | 220 Ω on the base: up to 2.8 A of load at a gain of 250 | 800 mA (heat) |
In free air at 25 °C, with the junction 25 °C below its 150 °C maximum and θJA 62.5 °C/W, from a 20 mA pin at the datasheet’s forced gain, and no further than the highest current with a guaranteed saturation voltage.
Specifications
| Type | NPN Darlington |
|---|---|
| Package | TO-220 |
| Maximum voltage | 60 V |
| Maximum current | 5 A |
| Minimum gain hFE | 1,000 at 500 mA · 1,000 at 3 A |
| VCE(sat), maximum | 2 V at 3 A (IC = 250 × IB) · 4 V at 5 A (IC = 250 × IB) |
| VBE(on), maximum | 2.5 V at 3 A (VCE 3 V) |
| Thermal resistance | θJA 62.5 °C/W · θJC 1.9 °C/W |
| Maximum junction temperature | 150 °C |
| Datasheet used | onsemi |
Pinout
| Pin | Function |
|---|---|
| 1 | Base |
| 2 | Collector |
| 3 | Emitter |
Printed face toward you, leads down: pin 1 is on the left. The metal tab is connected to pin 2.
Similar parts
| Part | Package | VCE(sat), guaranteed | Max voltage | Max current |
|---|---|---|---|---|
| TIP120 | TO-220 | 4 V at 5 A (IC = 250 × IB) | 60 V | 5 A |
| 2N2222A | TO-92 | 1 V at 500 mA (IC = 10 × IB) | 40 V | 600 mA |
| 2N3904 | TO-92 | 0.3 V at 50 mA (IC = 10 × IB) | 40 V | 200 mA |
| BC547 | TO-92 | 0.6 V at 100 mA (IC = 20 × IB) | 45 V | 100 mA |
| S8050 | SOT-23 | 0.6 V at 500 mA (IC = 10 × IB) | 25 V | 500 mA |
Tips
The base resistor is sized for IC = 250 × IB, the condition of the datasheet’s saturation voltage. A higher gain from the hFE column would leave the transistor half on and hot.
Every coil needs a flyback diode across it, cathode to the positive supply. Without it the voltage spike at turn-off can destroy the transistor at the first switching.
The TIP120’s internal diode (emitter to collector) only conducts when the collector goes below the emitter: it doesn’t catch the coil’s turn-off spike, so fit the flyback diode across the load.
A TO-220 in free air sheds little heat: fit a heatsink, insulated if the tab must not touch it (the tab is the drain or collector).
Open the calculator →Check the TIP120 with your own load, supply, PWM frequency and temperature.
Other transistors
2N2222A 2N3904 BC547 S8050 2N7000 BS170 AO3400A Si2302 IRLML6344 IRLZ44N IRLB8721 IRF520 IRF540N AO3401A IRF9540N
Frequently asked questions
Does the TIP120 work with a 3.3 V ESP32?
Yes, with a base resistor: at the gain of 250 the datasheet uses for saturation, a 20 mA pin drives the TIP120 up to 1.7 A of load. For more current use a logic-level MOSFET.
How much current can the TIP120 switch without a heatsink?
About 800 mA from a 3.3 V ESP32 pin, in free air at 25 °C, keeping the junction 25 °C below its 150 °C maximum (limit: heat).
What is the TIP120 pinout?
TO-220: 1 base, 2 collector, 3 emitter. Printed face toward you, leads down: pin 1 is on the left. The metal tab is connected to pin 2.
Source of the figures: onsemi datasheet (PDF)