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I'm trying to implement a half-wave rectifier using just a diode. I'm using a unity gain opamp for isolation from the mains. At the output of the opamp, I'm using a smoothing capacitor to get a DC voltage across 1K load resistor.

But for some reason, I can't get rid of the ripples. Any idea why?enter image description here

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  • \$\begingroup\$ I sense XY problem. What is your end goal? \$\endgroup\$
    – winny
    Commented May 18, 2020 at 17:23

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I don't know what you mean here with isolation, but the opamp does not isolate from mains, don't be lured into false sense of safety.

You have an ideal simulator, the op-amp will buffer whatever voltage there is at the input, and it will do that no matter how big capacitor you put at the op-amp output, it will get charged and discharged by the op-amp.

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  • \$\begingroup\$ If the capacitor is charging and discharging by the opamp, shouldn't we get a constant voltage across the load? \$\endgroup\$
    – varun
    Commented May 18, 2020 at 16:40
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    \$\begingroup\$ No, because the opamp wants the output to have identical waveform than there is on the input, so the circuit works precisely as it should. You just expect something else. Either change the diode location to output side, or change the capacitor to the input side. \$\endgroup\$
    – Justme
    Commented May 18, 2020 at 17:03
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Thank you so much.

I moved the diode after the opamp. Technically, The -ve of the opamp is connected to the ground. So the opamp itself should rectify (No diode needed). But without the diode, I was running into the previous problem where the smoothing capacitor is not worth the way it supposes to work.

With the Diode, it simulates just the way I want it to. Attached the screenshot. Thank you.enter image description here

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