Cost optimize voltage sense board

[npetersen2]

The present design of the voltage sensor board is built around the Voltage Transducer LV 25-P from LEM.

This requires a (large) burden resistor across the HV input. The current through the burden resistor flows through the LEM device, is isolated, and a proportional current output is produced. Then, this goes across a load resistor where the voltage produced is measured.

The LEM device costs $60-$68 in low quantities from Digi-Key... see: https://www.digikey.com/en/products/detail/lem-usa-inc/LV-25-P/409832

For our applications, we do not need this LEM device... there are much cheaper, smaller devices we could use to measure high voltages. We simply need a voltage divider resistance network! However, the isolation is the harder part.

Potential Ideas

An obvious idea is to simply use a small SMD resistor network to divide the input voltage to a low range: 0V to 2V. Then, use an isolated amplifier with unity gain to feed the existing ADC on the board. E.g. the TI AMC1311 part would be perfect for this: https://www.ti.com/lit/ds/symlink/amc1311.pdf -- in fact, it is designed specifically for this. And it costs $6 in low quantity on Digi-Key... 10x less than the LEM! The only thing we would require is a small isolated power supply to drive the HV side of the AMC1311, which is not too hard.

There are many other options and devices which are designed for HV sensing which are much cheaper than the LEM device.

TI sells integrated isolated delta-sigma ADCs which can directly sense and digitize the voltage divider output... However, this is not compatible with the SAR ADC architecture on the AMDS.