Table of Contents
Introduction
The BC547 is an NPN bipolar junction transistor (BJT) widely used in low current, low noise, and medium voltage circuits. It is the most popular member of the BC546–BC550 family, commonly used for signal amplification and switching. The BC547 can handle a collector current (Ic) of 100 mA and a collector-emitter voltage (Vce) of 45 V, making it suitable for general-purpose applications in audio amplifiers, oscillators, and digital switching.
Its excellent gain range (110–800) and low noise characteristics make it ideal for audio and sensor circuits, where signal clarity is essential. The BC547 comes in a TO-92 package, which is compact, cost-effective, and easy to mount on breadboards or PCBs. It is often used in educational circuits, microcontroller projects, and general electronic experiments because of its availability and stable performance.
BC547 Pinout
| Pin Number | Pin Name | Description |
|---|---|---|
| 1 | Collector (C) | Current enters through this terminal. |
| 2 | Base (B) | Controls transistor switching and biasing. |
| 3 | Emitter (E) | Current flows out through the emitter, usually to ground. |
When viewed from the flat face of the transistor, the pin order is 1 – Collector, 2 – Base, 3 – Emitter.
Electrical Characteristics
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Collector–Emitter Voltage | VCE | 45 | V |
| Collector–Base Voltage | VCB | 50 | V |
| Emitter–Base Voltage | VEB | 6 | V |
| Collector Current | IC | 100 | mA |
| DC Current Gain | hFE | 110–800 | — |
| Transition Frequency | fT | 150 | MHz |
| Power Dissipation | Ptot | 500 | mW |
| Junction Temperature | Tj | 150 | °C |
Features
- NPN Silicon Transistor
- Designed for low current, low noise, and medium voltage use
- Collector-Emitter voltage: 45V
- Maximum collector current: 100mA
- High DC current gain (hFE): 110–800
- Low leakage current for high accuracy
- Available in TO-92 package
- Reliable for signal amplification and switching
Equivalent / Alternative Transistors
| Equivalent Transistor | Type | Remarks |
|---|---|---|
| BC546 | NPN | Higher voltage (65V) variant |
| BC548 | NPN | Similar characteristics, slightly different noise level |
| 2N2222 | NPN | Can handle higher current |
| 2N3904 | NPN | Common low-power transistor alternative |
| S8050 | NPN | Similar switching performance |
Applications
- Audio preamplifiers and small signal amplifiers
- Switching LED and relay circuits
- Sensor signal conditioning
- Oscillator and pulse circuits
- Microcontroller output drivers
- General-purpose low current switching
- Digital logic circuits and timers
Conclusion
The BC547 transistor is one of the most versatile and widely used general-purpose NPN transistors. Its combination of low noise, moderate voltage rating, and good gain makes it perfect for educational and professional circuits alike. It is ideal for signal amplification, switching, and small load driving, making it a must-have component for electronics hobbyists, engineers, and circuit designers.
