Basic Information Type: NPN transistor Package: TO-92 (plastic, small size) Complementary PNP: BC557 ⚙️ Key Specifications Collector–Emitter Voltage (Vceo): 45V Collector–Base Voltage (Vcbo): 50V Emitter–Base Voltage (Vebo): 6V Collector Current (Ic): 100mA max Power Dissipation: 500mW (0.5W) DC Current Gain (hFE): 110 – 800 (depends on variant: A, B, or C) Transition Frequency (ft): ~300 MHz (good for audio and RF use) 📌 Pin Configuration (TO-92, flat side facing you) Pin 1 – Collector (C) Pin 2 – Base (B) Pin 3 – Emitter (E) 🛠️ Working Principle Since it’s an NPN transistor: A small current at the base (B) controls a larger current from collector (C) to emitter (E). The transistor turns ON when the base is ~0.7V higher than the emitter. It can work as: Switch → to drive LEDs, relays, or small loads. Amplifier → to amplify weak signals in audio and RF circuits. ⚙️ Applications LED driver circuits Audio amplification Switching small relays or motors Sensor interface (signal amplification) General-purpose low-power switching 🔋 Example Circuit (Switching an LED) Collector (C) → one side of LED → resistor → +5V Emitter (E) → Ground Base (B) → Arduino/microcontroller pin via 10kΩ resistor When the base gets a HIGH signal (~5V), the transistor conducts and the LED turns ON.