The PC817 / EL817 is a general-purpose 4-pin optocoupler that provides electrical isolation between its input and output. It is commonly used to:

• Transfer signals between circuits with different voltage levels

• Protect microcontrollers from high-voltage spikes

• Isolate noisy power electronics from sensitive control logic

• Implement signal switching, voltage sensing, and feedback loops

Internally, it contains:

• An infrared LED on the input side

• A phototransistor on the output side
  When current flows through the LED, it emits IR light that activates the phototransistor, conducting or switching the output, without direct electrical contact between the sides.

• Input Forward Voltage (VF): ~1.2V typical

• Input Current (IF): 5–20mA for full activation

• Collector-Emitter Voltage (VCEO): 35V max

• Current Transfer Ratio (CTR): ~50–600% (depends on model bin and current)

• Isolation Voltage: 5,000 Vrms (between input and output)

• PC817 and EL817 are functionally equivalent and interchangeable.

• The difference lies in manufacturer:

  • PC817 – by Sharp

  • EL817 – by Everlight
    Both conform to similar specs and pinouts.