NPN Transistor bc 549

🛠️ NPN Transistor – BC549 (TO‑92 / SOT‑54)

Overview

The BC549 is a low-noise, general-purpose NPN transistor designed for signal amplification and switching in low-current circuits. It excels in sensitive audio or RF applications due to its low noise performance, making it ideal for use with Arduino, sensor inputs, or audio preamplifier stages 

Key Features

• Collector current: up to 100 mA

• Collector–Emitter voltage: 30 V

• Collector–Base voltage: 30 V

• Power dissipation: ~500–625 mW

• High DC current gain (hₙE): 110–800 depending on variant

• Transition frequency (fₜ): ~100–300 MHz

• Low noise — well-suited for audio/RF amplification

• Available in TO‑92 plastic or SOT‑54 metal packages

Pinout

(Flat face forward, leads pointing down):

1. Emitter

2. Base

3. Collectorg

Typical Arduino Wiring – Low-Side NPN Switch

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

• Use a flyback diode for inductive loads like motors or relays

• Ensure a common ground between Arduino and load

Applications

• Low-current load switching (LEDs, small relays)

• Audio pre-amplifier or RF signal boost

• Sensor signal conditioning

• Pulse circuits, oscillators, waveform generators

• Input stages in delicate electronics where noise matters

✅ Resources

1. 📄 Datasheet: BC549/BC550 NPN low-noise enamel transistor datasheet from Fairchild/NXP (30 V, 100 mA, low noise) youtube.com+5youtube.com+5youtube.com+5youtube.com+1youtube.com+1youtube.com+14alldatasheet.com+14media.digikey.com+14

2. 🎥 YouTube Tutorial: “BC549 Transistor Complete Details | Working Principle and Equivalent Transistors” – includes pinout, features & practical use youtube.com+10youtube.com+10ovaga.com+10