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Phototransistor optocoupler

PC817 Internal Circuitry

Explore the internal circuitry and functional stages of PC817.

Package view

Inside PC817

Infrared emitter and phototransistor inside the four-pin body.

PC817 cutaway: anode1 and cathode2 feed infrared LED; light crosses insulating barrier toward NPN transistor with collector4 and emitter3.
Functional cutaway, not the physical die layout. Light arrows illustrate invisible infrared radiation.

Explore the circuit

Select a stage to see its role and connections

Input emitter

Pins 1 and 2 form the infrared LED. A series resistor sets its current.

Insulating barrier

The input and output have no internal electrical connection.

Output detector

Pins 4 and 3 expose the phototransistor collector and emitter. The base is internal.

Component view