TIP120 NPN Darlington Power Transistor 60V/5A

TIP120 NPN Darlington Power Transistor — 60V / 5A / hFE≥1000, TO-220

The TIP120 is a classic NPN Darlington power transistor in TO-220 package, combining two transistors in a Darlington pair configuration to achieve a very high current gain (hFE ≥ 1000). This means a tiny base current of just 1–5mA from an Arduino GPIO pin can switch up to 5A of collector current — making it one of the simplest ways to control medium-power loads (motors, fans, solenoids, high-power LEDs) directly from a microcontroller without any additional driver IC.

While MOSFETs have largely replaced Darlington transistors in new designs due to lower saturation voltage and faster switching, the TIP120 remains popular for its simplicity, robustness, and the fact that it can be driven directly from any MCU GPIO with just a single base resistor.

Key Specifications

• Manufacturer: Fairchild / ON Semiconductor / ST Microelectronics
• Part Number: TIP120
• Type: NPN Darlington power transistor
• Package: TO-220 (through-hole)
• Collector-Emitter Voltage (Vceo): 60V
• Collector-Base Voltage (Vcbo): 60V
• Continuous Collector Current (Ic): 5A
• Peak Collector Current (Ic peak): 8A
• DC Current Gain (hFE): ≥1000 (Darlington pair)
• Saturation Voltage (Vce(sat)): ~2V @ 3A (higher than MOSFET Rds(on) × I)
• Operating Temperature: −65°C to +150°C

TO-220 Pinout

• Pin 1 (left): Base (B)
• Pin 2 (center): Collector (C) — connects to load
• Pin 3 (right): Emitter (E) — connects to GND
• Tab (metal): Collector (C)

Arduino Motor/Fan Control Wiring

• Base (B) → Arduino PWM pin via 1kΩ resistor
• Collector (C) → Motor/fan negative terminal (or load negative)
• Emitter (E) → GND
• Motor/fan positive → 12V supply (up to 60V)
• Add 1N4001 flyback diode across motor (cathode to 12V, anode to Collector)
• Control speed: analogWrite(pin, 0–255);
• No pull-down needed — transistor is OFF when base is at 0V

Base Resistor Calculation

To saturate the TIP120 at 5A collector current with hFE=1000, minimum base current = 5A / 1000 = 5mA. For 5V GPIO: Rb = (5V − 1.4V) / 5mA = 720Ω. A 1kΩ resistor provides ~3.6mA base current — sufficient for loads up to ~3.6A. For full 5A, use 680Ω.

TIP120 vs. Power MOSFET (IRFZ44N)

• TIP120 advantage: Simpler drive circuit (single base resistor), no gate driver needed, more forgiving of gate/base voltage spikes
• TIP120 disadvantage: Vce(sat) ≈ 2V at 3A — significant power dissipation (P = Vce × Ic = 2V × 3A = 6W). MOSFET Rds(on) × I² is typically much lower.
• IRFZ44N advantage: Rds(on) = 17.5mΩ — at 5A, P = 0.0175 × 25 = 0.44W vs. TIP120’s ~10W. Far more efficient at high current.
• Use TIP120 when: Simplicity matters more than efficiency; load current ≤2A; switching frequency is low (<1kHz)
• Use MOSFET when: Efficiency matters; current >2A; high-frequency PWM (>1kHz)

Typical Applications

• Arduino PWM DC motor speed control (12V, up to 5A)
• 12V fan speed control with potentiometer or MCU PWM
• Solenoid valve driver (12V/24V)
• High-power LED driver (12V, up to 5A)
• Relay coil driver
• General-purpose NPN power switch for loads up to 60V/5A

Package Contents

• 1 × TIP120 NPN Darlington power transistor, TO-220

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