I am beginning a project that requires the sensing of a very small current (in the nA range) from a 3000V supply. The application is such that it can only be done on the high side. The data needs to be transmitted via I2C, ultimately, so the voltage drop across the sense resistor needs to be in the range of 5V, but it will be sensed up at the 3000V level. If I float an op-amp up there to amplify the dynamic voltage across the sense resistor, the output is still up in the 3000V range with respect to the system ground, so this needs to be scaled down to 5V. I guess this is the crux of the problem. I've found devices that do this type of thing for the 100V range, but does anyone know of anything that will be able to work with 3000V?
Any suggestions would be greatly appreciated.
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