Optocoupler circuit design

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a.singh123

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I need to design a optocoupler circuit as shown in the attached datasheet of IL300 optocoupler IC. I designed the circuit as shown in the first page of pdf. I used OPAMP OP-07. I did'nt used the output OPAMP in the circuit. I applied a sine wave of few hundred hertz at the input. It gets reflected at the output. Problem is that if I give sine wave at the input from 0V to 1V, the output gets clipped from negative side. If I give a DC shift of 0.3V, then output comes faithfully.
I want the output should follow input if input is from 0 to 1V. But output is getting clipped. please suggest me.

Abhishek
 

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  • IL300.pdf
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The datasheet for the old OP-07 opamp shows that its output cannot go closer than about 2V from its negative supply that is ground in your circuit. The OP-07 needs to have an additional negative supply voltage, or use an opamp that has an output voltage that goes lower.
 

I connected a negative bias at the -V pin of OPAMP instead of ground, and it is working perfectly. The circuit image is attached. For a input of 0 to 1V, it gives a output of 0 to 1V exactly. Thanks dear for your kind support. Thank you very much.
But one issue is that if I increase input above 1V, output gets clipped from above. I need input range from 0 to 2V. What should I do? I tried increasing power supply from 12v to 15v but it did'nt worked.

Regards,
Abhishek
 

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  • Optocoupler_finalckt.png
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Hi,

R1 and R4 should have the same value to get best performance.

If you need higher input voltage range, then add a resistor between VG1 and R3, so it forms a voltage divider with R3.

Klaus
 

Easy to see that output photodiode saturates with 2V input due to large R4 value. Won't happen with R4=10k.
 

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