I need to measure a floating high voltage in my DC/DC converter. See image below of the schematic which outlines in very basic terms the output of my converter.
I am able to measure the -6kV with a simple voltage resistance chain, as you would expect. I originally had attempted the exact same with the -3kV voltage and kept realising the results were not as I expected. This is because my control circuitry, of course, is referenced to ground - as will be my DSP which has a maximum 3VDC input before tripping a fault condition and turning off all switches.
My question is fairly basic and I am almost embarassed to ask it. But what is the best way to measure such a voltage, if it is not referenced to a ground point? As can be seen, the high voltage is already "referenced" to ground through a high voltage 250K load. There should be -3kV across both of these loads under steady-state. This confugration may look strange but gives the direction of current flow required to emulate the behaviour of my DC loads.
I have tried using a differential amplifier to measure the voltage drop across an additional series resistor in the feedback chain across the -3kV voltage, to no avail. I have scoured the internet but have either missed a solution or tried it to no avail again.
Please do let me know if anyone has a solution to this. I have already figured out how I shall isolate the 3kV and 6kV signals, but not how to get an accurate reading to my DSP ADC of the floating voltage. Another solution could be the use of an isolated error amplifier such as https://www.mouser.co.uk/ProductDetail/Analog-Devices-Inc/ADUM4190ARIZ?qs=sMtB33eOQTIXR4llky2wIA%3D%3D&gclid=Cj0KCQiA34OBBhCcARIsAG32uvOXJ_v8Re_2o49-YBgnN7ZVRP4OQS_o2UBEGdcpuoNERIbt00whGQ8aAnBWEALw_wcB - since we can connect it to ground through the isolator. I am confused as to how best set up the primary side of the device, however. Possibly this is where a diffferential amplfiier may be handy.
Any advice appreciated.