View attachment 86000I am trying to isolate input(0-5v) from output(V4) by using optocoupler but the circuit is not linear I need to make V4 the same like (0-5v), i need to do the circuit without using transformer so is there any suggestion to make the circuit work
Thanks

 

If you want to optically couple a linear signal you should use a Linear Optocoupler. Do a Google of "linear optocoupler" to get started.

Ron

 

If you want to optically couple a linear signal you should use a Linear Optocoupler. Do a Google of "linear optocoupler" to get started.

Ron

thanks so much

 

Would a linear analog opto-isolator be an appropriate solution? http://www.avagotech.com/pages/en/o...igh_linearity_analog_optocoupler/gate_driver/
http://www.avagotech.com/pages/en/o...igh_linearity_analog_optocoupler/gate_driver/

This publication has some ideas for using couplers that are not particularly linear
www.imsasafety.org/journal/ja12/21.pdf

If you don't mind building a little more complex circuit, you can use the approach outlined in the Silicon Labs application note.
www.silabs.com/Support%20Documents/TechnicalDocs/AN614.pdf

 

Driving a standard opto coupler with a current rather than a voltage will significantly improve the input to output linearity since it eliminates the non-linear input voltage to current relationship.

Below is the LTspice simulation of such a circuit.

Op amp U3 is configured as a current driver for the opto input, generating a current proportional to the voltage input.

As you can see the output is quite linear with respect to the input.
The simulation results are somewhat idealized of course, and the real linearity will depend upon the actual characteristics of the opto coupler used, but hopefully will still be adequate for your application.
The linearity degrades at higher operating currents due to reduction in the CTR of the opto but it should be fairly good if the maximum current is kept to no more than a few mA (2.5mA in this simulation).

R3 will likely need to be tweaked to get the desired voltage output depending upon the gain of the particular opto isolator you have (you could make it a 5kΩ pot).
A higher value increases the gain.

The opamps are rail-rail types.