The PC817 is an optically isolated isolator (optocoupler) consisting of an infrared emitting diode (IRED) optically coupled to a phototransistor. This component provides 5,000V of isolation between the input and output, making it essential for protecting sensitive microcontrollers from high-voltage spikes or electrical noise in the load circuit. Because the signal is transferred via light rather than electricity, there is no direct physical connection between the two sides, preventing ground loops and protecting your hardware from catastrophic failure in the event of a high-voltage short.
PC817 Pinout (DIP-4)
The PC817 is a compact 4-pin IC. Pin 1 is identified by a small dot on the surface of the package.
| Pin | Terminal | Function |
| 1 | Anode (+) | Positive input for the internal IR LED |
| 2 | Cathode (–) | Negative input for the internal IR LED |
| 3 | Emitter | Emitter of the internal phototransistor |
| 4 | Collector | Collector of the internal phototransistor |
Technical Specifications
- Input Forward Current (IF): 50mA
- Collector-Emitter Voltage (VCEO): 80V (Maximum)
- Collector Current (IC): 50mA
- Isolation Voltage (Viso): 5,000 Vrms
- Current Transfer Ratio (CTR): 50% to 600%
- Response Time (tr): 4μs to 18μs
- Power Dissipation (PD): 200mW
Key Features & Benefits
- High Isolation: Safely separates low-voltage logic from high-voltage AC or DC power.
- Noise Immunity: Effectively blocks electrical noise and EMI from reaching the MCU.
- Compact Footprint: The 4-pin DIP/SMD package saves significant PCB space.
- Versatile Speed: Fast enough for most digital switching and feedback loop applications.
Common Applications
- Microcontroller Protection: Isolating Arduino/ESP32 pins from relays or motors.
- Switching Power Supplies: Providing feedback for voltage regulation while maintaining isolation.
- System Isolation: Preventing ground loops in complex industrial systems.
- AC Mains Detection: Safely detecting the presence of high-voltage AC signals.
PC817 Equivalent & Substitutes
- EL817 (Direct equivalent from Everlight)
- SFH615 (High-reliability alternative)
- 4N25 (6-pin alternative with base connection)
- PC814 (AC input version)
Related Tutorials on ElxHub
- Basics: Learn more in Integrated Circuits – Basics and Working
- Transistor Basics: Understand the output stage in Transistors – Basics, Types, and Working
- Selection Guide: Compare interface options in our Ultimate IC Selection Guide
Conclusion
The PC817 is the ultimate “safety valve” for electronic circuits. Its ability to pass data via light while keeping high voltages physically separated is indispensable for modern embedded systems. If you are working with inductive loads or high-voltage power supplies, including a PC817 in your design is the most effective way to ensure the longevity and safety of your control electronics.
Download the IC’s Datasheet pdf
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