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I've got a need to measure the integral of voltage with respect to time.

I'm measuring a 25V AC power source through one of these voltage dividers to get it down to a workable 5I. I then rectify it as my microcontroller can't read negative voltages.

When I look at my oscilloscope after the rectifier, I'm seeing peaks of over 100V. Upstream of the rectifier, I'm seeing a nice 5V sine wave.

Post rectifier

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Upstream

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Circuit Diagram

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Is the "25v AC power source" the secondary of a transformer (isolated)? Could you please post a schematic of the rectifier and how the voltage divider is connected? \$\endgroup\$
    – devnull
    Mar 25, 2022 at 21:21
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    \$\begingroup\$ Yes, it is the secondary of a transformer. I'm working on a schematic now. \$\endgroup\$
    – MikeSchem
    Mar 25, 2022 at 21:22
  • \$\begingroup\$ @devnull uploaded a hand drawn diagram, let me know if that works. \$\endgroup\$
    – MikeSchem
    Mar 25, 2022 at 21:53
  • \$\begingroup\$ Thanks. Any other scope ground clips connected anywhere else in the circuit? Maybe even not explicitly, like through the ground pin at the primary. \$\endgroup\$
    – devnull
    Mar 25, 2022 at 21:57
  • \$\begingroup\$ Also, unrelated to the problem, since this is for measurement you may find that the voltage drop due to the diodes is excessive, specially rectifying after the voltage division, and handle the negative cycles differently. \$\endgroup\$
    – devnull
    Mar 25, 2022 at 22:05

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