Transistor

 

A transistor like BC546–BC550 is a small NPN device used to amplify or switch signals. It has three pins: Emitter (E), Base (B), and Collector (C). A small current at the base controls a larger current flowing from collector to emitter.

These transistors look similar but differ in voltage rating and noise performance:

BC546: Handles higher voltage (up to ~65 V)

BC547 / BC550: Medium voltage (~45 V)

BC548 / BC549: Lower voltage (~30 V)

BC549 / BC550 are preferred for low-noise audio circuits

Current gain (hFE) shows how much amplification you get:

A: 110–220 (low gain)

B: 200–450 (medium gain)

C: 450–800 (high gain)

Key limits:

Max current ≈ 100 mA

Max power ≈ 500 mW

Frequency range up to ~300 MHz

In simple terms, use:

BC547/548 for general circuits

BC549/550 for audio (less noise)

Pick A/B/C depending on how much amplification you need