Im curious about optocoupler.

What is optocoupler,why and how it is used in electronic circuits ?

  • 3
    \$\begingroup\$ What research have you already done? What do you already know abou this topic, and what specific question about it can we help you with? \$\endgroup\$
    – The Photon
    Oct 26, 2018 at 22:27
  • \$\begingroup\$ I read about it a little on google,but I do not get it really. I want to know how it is used in circuits and why. \$\endgroup\$ Oct 26, 2018 at 22:31
  • \$\begingroup\$ Possible duplicate of How do I select the accompanying components for an optocoupler? \$\endgroup\$ Oct 29, 2018 at 9:16

2 Answers 2


an optocoupler is a device used when you want to electrically isolate a circuit from another circuit that you want to send an electric signalenter image description here

when you turn on the led it sends photons to the phototransistor, these phototransistor which is like a normal transistor but its "base current" is the light emitted by the led, in this way you can use it as an isolated switch between two circuits

 image from https://electronics.stackexchange.com/questions/294744/mosfet-switch-using-an-optocoupler using an optocoupler to control a 12v load with a 3v3 signal

  • \$\begingroup\$ Is there a reason they usualy put the R1 at pin 2 instead of pin 1? \$\endgroup\$
    – floppy380
    Oct 27, 2018 at 18:15
  • \$\begingroup\$ i dont see a particular reason, in this circuit instead of the internal LED lighting up with a 3.3V signal it will light up with a 0V signal. a more experienced user could point out a better reason for this but i think is an inheritance from the old bjt transistor low side switching circuits. \$\endgroup\$ Oct 28, 2018 at 2:34

What is an optocoupler?

It's a device that couples an electronic signal from an input to an output optically. In practice, that means it has an LED for an input, a photodiode or phototransistor for a detector, and possibly some logic or other devices conditioning the output.

How is it used in electronic circuits?

It's used when you need to communicate between two circuits while maintaining electrical isolation, either as a safety isolation or as a designer convenience.


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