Is optocoupler only suited for switcing applications???

[ajoseph88]

Can an opto-coupler be used to provide isolation in feedback circuits...
eg. say in my case, where the input voltage of 0 to 200V D.C is from the armature of a dc motor, is passed through low pass filter and a voltage divider, and the final output is 0 to 5V D.C, but i did not provide any kind of isolation... what can we use to provide isolation. can we use a opto-coupler, but the output voltage after isolation should vary linearly from 0 to 5V as the input varies from 0 to 5V.

Or is buffer-opamp a good choice... What can I use to provide isolation...

I searched on the internet and found some DC/DC isolators like "recom r1s 0505", but the problem with that is, the output is a constant 5V, and is useless for feedback applications....       

[Tomorokoshi]

A couple options:

1. Analog linear optoisolator:
https://www.digikey.com/product-detail/en/HCNR201-500E/516-1773-1-ND/1894317

2. Use a separate micro at the motor and run communications through a digital optoisolator to the other side.

[Kleinstein]

An Optokcoupler can also be used in alalog feedback applications.  Many switched mode supplys use this to control the voltage.
However one should keep im mind that normal optocouplers are not very linear, not temperarure stable and can age. So feedback should only transfer a signal that is not that sensitve. Often that means havening the reference value on the sender side, and integrate the transfered signal. So dirft of the optocoupler will silghtly alter the speed, but not the final value.

So direct transfer of the 0-5 VsSignal would require a special linear optocoupler or a different isolation.

[ajoseph88]

How about buffer or unity gain op-amp configuration... They call it isolation amplifier...
I have the op-amp ready at my place, so is it a good option or High linear analog optoisolator HCNR201-500E as said by one of the gentleman... Which one should I go for...

[macboy]

How about buffer or unity gain op-amp configuration... They call it isolation amplifier...
I have the op-amp ready at my place, so is it a good option or High linear analog optoisolator HCNR201-500E as said by one of the gentleman... Which one should I go for...

Both at the same time actually. Download, read, and understand the data sheet for the analog optocoupler. Generally they have two outputs; one goes inside the feedback loop of an op-amp on the non-isolated side, and the other goes on the isolated side.  This is necessary to provide a linear transfer function.