Ordinary photocouplers can only transmit digital signals (switch signals), not suitable for analog signals. Linear optocoupler is a new type of photoelectric isolation device, which can transmit continuously changing analog voltage or current signal, so that the corresponding optical signal will be generated with the change of the input signal strength, so that the conduction degree of the phototransistor is also different , The output voltage or current is also different.
PC817 photoelectric coupler can not only play a feedback role but also play a role in isolation.

PC817X Specifications
Voltage-Output (Max): 80V
Voltage-Isolation: 5000Vrms
Voltage-Forward (Vf) (Typ): 1.2V
Vce Saturation (Max): 200mV
Turn On / Turn Off Time (Typ):-
Supplier Device Package: 4-DIP
Rise / Fall Time (Typ): 4µs, 3µs
Packaging: Tube
Package / Case: 4-DIP (0.300", 7.62mm)
Output Type: Transistor
Other Names: 425-1464-5
Operating Temperature: -30°C ~ 100°C
Number of Channels: 1
Mounting Type: Through Hole
Moisture Sensitivity Level (MSL): 1 (Unlimited)
Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
Input Type: DC
Detailed Description: Optoisolator Transistor Output 5000Vrms 1 Channel 4-DIP
Current Transfer Ratio (Min): 50% @ 5mA
Current Transfer Ratio (Max): 600% @ 5mA
Current-Output / Channel: 50mA
Current-DC Forward (If) (Max): 50mA

PC817 photoelectric couplers are widely used in computer terminals, thyristor system equipment, measuring instruments, photocopiers, automatic ticketing, household appliances, such as fans, heaters and other circuits for signal transmission, so that the front end is completely isolated from the load. The purpose is to increase safety, reduce circuit interference, and simplify circuit design.