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NPN Transistor BC 549 (BJT)
🔋 BC549 – NPN Bipolar Junction Transistor (BJT)
The BC549 is a low-noise NPN transistor designed for general-purpose switching and signal amplification. It is commonly used in audio circuits, low-power amplifiers, and digital logic switching. With low collector current and low saturation voltage, it’s ideal for precise, noise-sensitive applications.
⚙️ Technical Specifications
| Parameter | Specification |
|---|---|
| Transistor Type | NPN BJT |
| Part Number | BC549 |
| Collector-Emitter Voltage | 30V |
| Collector Current | 100 mA |
| Collector Dissipation | 500 mW |
| DC Current Gain (hFE) | 110 – 800 (depending on variant) |
| Noise Figure | ≤ 2 dB |
| Transition Frequency (f<sub>T</sub>) | ~150 MHz |
| Package Type | TO-92 (Plastic, Through-hole) |
| Complementary PNP | BC559 |
📎 Pin Configuration (TO-92 Package)
FRONT VIEW _______ | | | | |_______| | | | C B E
C – Collector
B – Base
E – Emitter
✅ Features
🔇 Low-noise transistor – excellent for audio preamps
⚙️ Suitable for small-signal switching
📶 Works well in amplifier circuits and signal boosters
🧰 Compatible with Arduino, ESP32, and sensor circuits
🛠️ Breadboard-friendly TO-92 package
🧠 Example Application: Audio Signal Amplifier
Used in:
🎙️ Microphone preamplifiers
🔊 Small audio amplifiers
📟 Logic-level signal switching
🧪 Lab signal test circuits
🧪 Example Basic Amplifier Circuit
Base: Connect through resistor (e.g., 10kΩ) to input signal
Collector: Connect to Vcc through a load resistor (e.g., 4.7kΩ)
Emitter: Connect to GND (optionally via small resistor for gain control)