Transistor NPN 2N3904

🛠️ NPN Transistor – 2N3904 (TO‑92)

Overview

The 2N3904 is a widely-used general-purpose NPN transistor suited for both switching and amplification in low-power electronics. It’s perfect for tasks like driving LEDs, relays, or audio signals, commonly paired with microcontrollers.

Key Features

• Collector current: up to 200 mA

• Collector–Emitter voltage: up to 40 V

• Collector power dissipation: 625 mW

• High current gain (h_FE): typically 100–300

• Fast switching: transition frequency (~fₜ) around 300 MHz

• Package: TO‑92 (compact), flat front with leads downward

Pinout (flat face forward, leads pointing down)

1. Emitter (left)

2. Base (middle)

3. Collector (right) media.digikey.com+15en.wikipedia.org+15youtube.com+15

Typical Arduino Switch Wiring

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Arduino GPIO → 1 kΩ resistor → Base  
Emitter → Arduino GND  
Collector → Load → +V supply  

• Use a flyback diode for inductive loads

Applications

• Driving LEDs, small motors, relays

• Audio pre‑amp circuits

• Digital and analog switching

• Oscillators and signal generation

✅ Resources

1. 📄 Datasheet (ON Semiconductor) – provides full specs including ratings, gain, and frequency watelectronics.comkdi-ppi.com

2. 🎥 YouTube Tutorial: "How to use the 2N3904 NPN transistor as a switch" – practical example with Arduino and LEDs onsemi.com+15youtube.com+15mouser.com+15