## PC813 Photocoupler: Electronic Components and Specifications The **PC813** is a high-density mounting type optoisolator (photocoupler) that consists of an **AC Input** side and a **Transistor Output** side. Unlike standard photocouplers that only accept DC, the PC813 is designed to handle alternating current or bidirectional DC inputs. --- ### 1. Internal Structure The PC813 contains two primary electronic components integrated into a single 4-pin package: | Component | Description | Function | | :--- | :--- | :--- | | **Input: LED Pair** | Two Gallium Arsenide (GaAs) infrared emitting diodes connected in **inverse parallel**. | Converts AC or bidirectional DC electrical signals into light. | | **Output: Phototransistor** | A silicon NPN phototransistor. | Detects light from the LEDs and converts it back into an electrical current. | --- ### 2. Key Technical Specifications Below are the typical absolute maximum ratings and characteristics for the PC813 series: | Parameter | Symbol | Rating/Value | | :--- | :--- | :--- | | **Forward Current** | $I_F$ | $\pm 50\text{ mA}$ | | **Collector-Emitter Voltage** | $V_{CEO}$ | $35\text{ V}$ (Min) | | **Isolation Voltage** | $V_{iso}$ | $5,000\text{ Vrms}$ | | **Current Transfer Ratio (CTR)** | $CTR$ | $20\%$ to $400\%$ (at $I_F = \pm 1\text{mA}$) | | **Response Time (Rise)** | $t_r$ | $4\mu\text{s}$ (Typical) | --- ### 3. Pin Configuration The PC813 usually comes in a 4-pin DIP or SMD package: 1. **Pin 1:** Anode / Cathode (Input) 2. **Pin 2:** Cathode / Anode (Input) 3. **Pin 3:** Emitter (Output) 4. **Pin 4:** Collector (Output) --- ### 4. Distinctive Features * **AC Input Capability:** Because the internal LEDs are in inverse parallel, the device can conduct on both the positive and negative cycles of an AC signal. * **High Isolation:** Provides a physical air gap and transparent dielectric between the input and output, protecting sensitive microcontrollers from high-voltage surges. * **Compact Footprint:** Often used in space-constrained power supply designs. ### 5. Common Applications * **AC Line Monitoring:** Detecting if a mains voltage is present. * **Programmable Controllers:** Interfacing between industrial AC sensors and DC logic. * **Telephone Line Interfacing:** Handling ring signals which are AC in nature. * **System Appliances:** Controlling power in washers, heaters, or fans. ---