PC817 optocoupler

An optocoupler (also called an optoisolator) is a tiny component that lets one part of a circuit talk to another without an electrical connection — instead it uses light to transfer the signal. This protects sensitive electronics (like microcontrollers) from high voltages, noise, and spikes.

Inside the PC817:

Infrared LED on the input side

Phototransistor on the output side

When the LED lights up, the phototransistor switches — without any metal‑to‑metal electrical path between input and output.

📊 Typical Specifications (for PC817)
Parameter Typical Value
Package 4‑pin DIP (through‑hole)
Isolation Voltage ~5,000 Vrms between input/output
Max Collector‑Emitter Voltage ~80 V
Max Output Current (Collector) ~50 mA
Forward Voltage (LED) ~1.2 V
Current Transfer Ratio ~50 % – 600 %
Operating Temp ~ ‑30 °C to +100 °C
Rise/Fall Time ~18 µs