I am building a DC energy generating device that at the moment generated DC power at 15K-50k Volts at 1 microampere.

I am considering using a high impedance ADC (1G ohm, 0.3V range, 2 nanoamperes current, 32 bits.)

When I plan out a voltage divider circuit to work with this ADC my voltage or current is always out of range.

I would ideally like to tune my circuit so current is between 0-0.3V and I have 2 nanoamperes for the ADC to sample. It also requires a very expensive 100G ohm or more resistor.

Is there a way (with op amps perhaps) to reduce the voltage but keep the current high and be more cost effective?

32 bits is far more precision than I need so even if the range becomes more like 0-0.003V that is acceptable.

  • 2
    \$\begingroup\$ Use a lot of cheap, lower value resistors in series to make a big resistor. \$\endgroup\$
    – user69795
    Nov 21, 2021 at 6:31
  • \$\begingroup\$ Before you design your first prototype I suggest you to read norm UL 60950 for your own safety. \$\endgroup\$ Nov 21, 2021 at 8:58
  • \$\begingroup\$ Is the problem that the current is at high potential relative to ground, or that the current is small relative to the converter error currents? Does a battery-powered current monitor that sends its measurements via bluetooth to a cell phone app fit the need? \$\endgroup\$
    – Whit3rd
    Nov 21, 2021 at 9:09
  • \$\begingroup\$ "When I plan out a voltage divider circuit to work with this ADC....", you do need a shunt, not a divider if you want to measure the current. Post a schematics of what you have done. I would rather buffer the shunt voltage with a very high 100G electrometer opamp, not a cheap way. \$\endgroup\$ Nov 21, 2021 at 9:44

1 Answer 1


A shunt of 2M would produce 2V for 1uA. The series resisor limits the current into the opamp. If accidentally a voltage of 15kV is applied on input, then a current of 15kV/100MOhm = 15uA flows into the opamp.

When either input of the ADA4530-1 exceeds one of the supply rails by more than 300 mV, the input ESD diodes become forward-biased and large amounts of current begin to flow through them. Without current limiting, this excessive fault current causes permanent damage to the device. If the inputs are expected to be subject to overvoltage conditions, insert a resistor in series with each input to limit the input current to 10 mA maximum. However, consider the resistor thermal noise effect on the entire circuit.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ I would be tempted to use an electrostatic divider. Depends on the mechanical setup. \$\endgroup\$
    – colintd
    Feb 3 at 0:27

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