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The TIP120 is a widely used NPN Darlington power transistor known for its high current gain and ability to switch medium- to high-current loads with very little base drive. This article will talk about the TIP120 transistor’s specifications, features, alternatives, and more.
The TIP120 is a popular NPN Darlington power transistor originally offered by Fairchild Semiconductor and now associated with onsemi. It contains two internally connected NPN transistors, providing a very high current gain, which makes it ideal for driving high-current loads with only a small base current. With a typical collector-emitter voltage rating of 60V and collector current up to 5A, this transistor is commonly used in motor drivers, relay control, solenoids, and various power-switching applications. Its TO-220 package allows for easy mounting and heat sinking when higher power dissipation is required.
Using the TIP120 is straightforward in low-to-medium voltage control designs, especially with microcontrollers like Arduino and Raspberry Pi. Because it is a Darlington device, it has a higher VBE and saturation voltage, so heat management and proper base resistance selection are important. Despite newer options such as MOSFETs, the TIP120 remains a reliable, well-supported choice for many hobby and industrial projects.
If you are interested in purchasing the TIP120, feel free to contact us for pricing and availability.
| Part Number | Type (NPN/PNP) | Darlington | Vce Max (Approx.) | Ic Max (Approx.) |
| TIP127 | PNP | Yes | 100V | 5A |
| 2N5306 | NPN | Yes | 60V | 5A |
| 2N6532 | NPN | Yes | 100V | 7A |
| 2SD1415 | NPN | Yes | 60–80V | 6–8A |
| 2SD2495 | NPN | No | 100V | 8A |
| BDT63 | NPN | Yes | 60–80V | 6–8A |
| BDW2 | NPN | Yes | 60–80V | 10A |
| KSB601 | NPN | No | 60V | 4A |
| KSD560 | NPN | No | 60V | 4A |
| MJF6388 | NPN | Yes | 80–100V | 8A |
The equivalent circuit of the TIP120 transistor shows that it is a Darlington pair, which consists of two NPN transistors connected so their current gains multiply. The base terminal (B) drives the base of the first transistor, whose emitter is directly connected to the base of the second transistor. This configuration allows the device to achieve a very high overall current gain, meaning only a small base current is needed to control a much larger collector-emitter current.
Two resistors, R1 (≈ 8 kΩ) and R2 (≈ 0.12 kΩ), are included inside the transistor package. R1 is connected between the base and emitter of the first transistor to help discharge stored charge and improve switching speed, preventing unwanted turn-on. R2, connected between the emitter of the first transistor and the emitter of the second, further stabilizes operation and ensures proper biasing during conduction.
A diode is placed between the collector (C) and emitter (E) terminals. This diode provides reverse-voltage protection and is especially useful in inductive load applications, such as relays or motors, because it helps suppress voltage spikes generated when the load is switched off.
| Symbol | Parameter | TIP120 Value | Unit |
| VCBO | Collector-Base Voltage | 60 | V |
| VCEO | Collector-Emitter Voltage | 60 | V |
| VEBO | Emitter-Base Voltage | 5 | V |
| Ic | Collector Current (DC) | 5 | A |
| ICP | Collector Current (Pulse) | 8 | A |
| IB | Base Current (DC) | 120 | mA |
| Tj | Junction Temperature | 150 | °C |
| TSTG | Storage Temperature Range | –65 to 150 | °C |
| Symbol | Parameter | Conditions (TIP120) | Min. | Max. | Unit |
| VCEO(sus) | Collector-Emitter Sustaining Voltage | IC = 100 mA, IB = 0 | 60 | — | V |
| ICEO | Collector Cut-off Current | VCE = 30 V, IB = 0 | — | 0.5 | mA |
| ICBO | Collector Cut-off Current | VCB = 60 V, IE = 0 | — | 0.2 | mA |
| IEBO | Emitter Cut-off Current | VEB = 5 V, IC = 0 | — | 2 | mA |
| hFE | DC Current Gain | VCE = 3 V, IC = 0.5 A | 1000 | — | — |
| hFE | DC Current Gain | VCE = 3 V, IC = 3 A | 1000 | — | — |
| VCE(sat) | Collector-Emitter Saturation Voltage | IC = 3 A, IB = 12 mA | — | 2.0 | V |
| VCE(sat) | Collector-Emitter Saturation Voltage | IC = 5 A, IB = 20 mA | — | 4.0 | V |
| VBE(on) | Base-Emitter On Voltage | VCE = 3 V, IC = 3 A | — | 2.5 | V |
| Cob | Output Capacitance | VCB = 10 V, IE = 0, f = 0.1 MHz | — | 200 | pF |
• NPN Darlington Pair Configuration - Provides very high current gain, allowing a small base current to control a large load current.
• High DC Current Gain (hFE ≈ 1000) - Excellent amplification capability, ideal for low-drive switching applications.
• Collector-Emitter Voltage: 60V - Suitable for medium-voltage loads such as motors, relays, and solenoids.
• Collector Current: 5A (DC), 8A (Pulse) - Supports high-current switching, useful in power control circuits.
• Low Base Drive Requirement - Can be driven directly by microcontrollers, sensors, and logic circuits.
• Internal Protection Diode - Built-in flyback diode makes it safe for inductive loads and reduces voltage spikes.
• Internal Base-Emitter Resistors - Helps with faster turn-off, improving switching stability and preventing false triggering.
• TO-220 Package - Easy to mount on heatsinks and suitable for efficient power dissipation.
• Wide Operating Temperature Range - Junction temperature up to 150°C ensures reliable operation in demanding environments.
This circuit clearly shows how the transistor can switch a DC motor using a small control signal from an Arduino. A 2.2kΩ resistor limits the base current to about 1.7mA, which is enough to let about 1A flow through the motor thanks to the Darlington’s high current gain. When the Arduino output is HIGH, the TIP120 turns on and powers the motor; when it is LOW, the motor stops. To make the circuit safer and more complete, a flyback diode should be added across the motor to protect the transistor from voltage spikes. This diagram provides an easy and practical way to demonstrate how the TIP120 can control higher-current loads from a low-power microcontroller.
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