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Is there any solution to sense high differential voltages using operational amplifiers (without using resistive voltage divider) ?

The input voltage range is [-30, 80] Volts.

I've searched on all operational amplifiers and no one fill this range.

I can't use a normal attenuator (Differential amplifier with gain < 1 ) since the common mode input voltage of the op amp is limited, and the input votlage has an independant ground ( I will not be sure if the CMIV will not be exceeded )

Thank you.

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  • \$\begingroup\$ Why is a prescaling not an option? What precision do you need on this? And what do you mean with sense, as in, where is the output of your circuit going? \$\endgroup\$ Commented May 8, 2017 at 14:55
  • \$\begingroup\$ Are you saying that the independent ground could be hundreds or thousands of volts different to the ground for a circuit that might be useful in sensing? \$\endgroup\$
    – Andy aka
    Commented May 8, 2017 at 14:56
  • \$\begingroup\$ Show us some schematic of source of voltage signal - there is always a possibility to measure any voltage, even when DM is in millivolts range and CM in kilovolts (I've designed such circuits which are now in production). \$\endgroup\$ Commented May 8, 2017 at 15:13
  • \$\begingroup\$ Use a gold-leaf-foil sensor, with laser interferometer readout of the tilt-angle of the two leaf's separation angle. The Interferometer needs OpAmps to process and recover the laser optical beat notes. \$\endgroup\$ Commented May 8, 2017 at 15:36
  • \$\begingroup\$ The precision i need in the global sensing is 0,5%. For the independant ground, i don't have any information about it so i can not assume that the common mode voltage at V+ and V- will not be exceeded using a differential amplifier. \$\endgroup\$ Commented May 9, 2017 at 15:37

1 Answer 1

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You know the inputs are in the (+80V, -30V) range. So, you could apply a battery-powered voltmeter and read the difference directly.

Yes, of course it can be also be done with low-voltage op amps. The high voltage can be turned into a modest current, and with a few (-30, -35, -40V) power rails to power an op amp, one can generate a ground-referenced (negative) voltage from each input. Do it twice, and you can apply a normal difference amplifier on the translated/scaled voltages.

schematic

simulate this circuit – Schematic created using CircuitLab

The scheme (1) reduces the voltages to something less, (2) applies an offset to near-ground levels. $$A_{scaled} = -(A + 30) *( R8*R4)/(R1*R7) $$

so (80V, -30V) inputs are changed to (-0.550V, 0V) outputs

(There's some linearity errors near the (-30V) value, if that end of the range is important, moving the power supplies down by ten volts will clean it up).

Actually, though, voltage dividers aren't so bad; the proliferation of power supplies is rather a nuisance, doing it this way.

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  • \$\begingroup\$ Thank you very much for your quick answer. I'm trying to understand this schematic. I will get back to you once i will have a fixed idea about it. \$\endgroup\$ Commented May 9, 2017 at 15:48

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