The **BC548C** is a widely used NPN epitaxial silicon phototransistor, primarily utilized for general-purpose switching and amplification tasks. It is part of the BC54x family of transistors. --- ### 1. Technical Specifications The BC548C is characterized by its high current gain (hFE). Below are the absolute maximum ratings and electrical characteristics: | Parameter | Symbol | Value | Unit | | :--- | :--- | :--- | :--- | | Collector-Emitter Voltage | $V_{CEO}$ | 30 | V | | Collector-Base Voltage | $V_{CBO}$ | 50 | V | | Emitter-Base Voltage | $V_{EBO}$ | 5 | V | | Collector Current (Continuous) | $I_C$ | 100 | mA | | Total Device Dissipation | $P_D$ | 625 | mW | | **DC Current Gain** | **$h_{FE}$** | **420 – 800** | - | --- ### 2. Pin Configuration The BC548C typically comes in a **TO-92** plastic package. When looking at the flat side with the leads pointing downwards, the pins are arranged as follows: 1. **Collector (C):** Current enters the transistor here. 2. **Base (B):** The trigger that controls the flow between Collector and Emitter. 3. **Emitter (E):** Current exits the transistor here. --- ### 3. Key Features * **High Gain:** The "C" suffix indicates the highest gain group in the BC548 series (A: 110-220, B: 200-450, C: 420-800). * **Low Noise:** Suitable for the first stages of audio pre-amplifiers. * **Low Cost:** Very economical and easy to source globally. * **Complementary Pair:** The PNP counterpart to the BC548C is the **BC558C**. --- ### 4. Typical Applications * **Switching:** Driving small loads like LEDs, relays, or logic gates (up to 100mA). * **Amplification:** Boosting weak signals from sensors or microphones. * **Oscillators:** Used in signal generation circuits. * **Pulse Width Modulation (PWM):** Controlling motor speed or light intensity at low power. --- ### 5. Simple Circuit Example: LED Switch This code-like representation shows how to calculate the base resistor for a simple switch: ```text Input (5V) ---> [Resistor Rb] ---> Base Collector ---> [LED] ---> [Resistor Rc] ---> VCC (9V) Emitter ---> GND Calculation for Rb: Rb = (V_input - V_be) / I_b Where V_be is approx 0.7V. ```