IL300 and linear amplifier for DC voltage sensing

[mohansaini]

Referred to the attached circuit from the same forum i need to convert DC 0-60V to 0-5Vdc. As it is shown at the input of op-amp we need to connect 0-10V at the input for that purpose i have connected a voltage divider of 100K and 200K POT which will give 10V at 60V input
i have connected R3=100K but i am getting 3.9V max at the output of second op-amp. and its same at the 30V input as well. what could be the problem? and please suggest any solution.
The idea was taken from here
https://www.edaboard.com/threads/217799/

 

[BradtheRad]

Just to give some helpful suggestion...

The IL300 is an optocoupler. To get predictable levels from the internal photosensors D2 & D3, you may need to carefully adjust the current going into D1, until you get the results you want from D2 & D3.

At no time should you exceed the specs for current going into any of the terminals.

 

[godfreyl]

Did you check the voltage at the output of the first opamp? Perhaps it is limited. You may need bigger resistors for R3 and R4.

 

[mohansaini]

@ godfreyl can you please suggest any working circuit voltage at output of op-amp was arround 5.12V.

 

[godfreyl]

I do not understand all of this:

...i have connected a voltage divider of 100K and 200K POT which will give 10V at 60V input
i have connected R3=100K but i am getting 3.9V max at the output of second op-amp. and its same at the 30V input as well.

I have added some labels to your schematic.
Were the 10V and 30V inputs measured at A or at B?

To find the problem:

• If the voltage at C is not the same as the voltage at B, then opamp OA1 has a problem.
• If the voltage at D is not the same as the voltage at C, then there is a problem with the optocoupler.
• If the voltage at E is not the same as the voltage at D, then there is a problem with opamp OA2.