The **BC548C** (commonly referred to as LC548C in some regional labeling or transcription errors) is a widely used NPN epitaxial silicon phototransistor/general-purpose transistor. It belongs to the BC54x series and is a staple in low-power amplification and switching circuits. --- ### 1. General Specifications The "C" suffix in BC548C refers specifically to the **DC Current Gain ($h_{FE}$)** classification, representing the highest gain range for this transistor model. | Parameter | Value | | :--- | :--- | | **Type** | NPN Transistor | | **Package** | TO-92 (Plastic) | | **Collector-Emitter Voltage ($V_{CEO}$)** | 30V | | **Collector-Base Voltage ($V_{CBO}$)** | 50V | | **Collector Current ($I_C$)** | 100mA (Continuous) | | **Power Dissipation ($P_{tot}$)** | 500mW | | **DC Current Gain ($h_{FE}$)** | 420 to 800 | | **Transition Frequency ($f_T$)** | 300 MHz | --- ### 2. Pinout Configuration When looking at the flat side of the TO-92 package with the leads pointing down, the pin configuration is 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 to the ground or common rail. --- ### 3. Key Characteristics * **High Gain:** Because it is the "C" variant, it can amplify very small input signals significantly. * **Low Noise:** It is designed to provide a high signal-to-noise ratio, making it ideal for audio pre-amplifiers. * **Fast Switching:** With a transition frequency of 300MHz, it handles high-frequency oscillation and fast pulse switching efficiently. --- ### 4. Common Applications Due to its versatility, the BC548C is used in: * **Signal Amplification:** Boosting weak signals from sensors or microphones. * **Switching:** Driving small loads like LEDs, relays, or logic gates (up to 100mA). * **Darlington Pairs:** Combined with another transistor to create extremely high gain. * **PWM Circuits:** Used in pulse width modulation for brightness or speed control. --- ### 5. Equivalent Alternatives If the BC548C is unavailable, the following transistors are common replacements: | Part Number | Relation | Notes | | :--- | :--- | :--- | | **BC547** | Higher Voltage | Rated for 45V instead of 30V. | | **BC549** | Ultra Low Noise | Better for sensitive audio stages. | | **2N3904** | Equivalent (USA) | Different pinout (E-B-C instead of C-B-E). | | **BC558** | PNP Complement | Used for push-pull amplifier configurations. |