See attached PDF.
Basically, current thru the DUT is set by adjusting a series resistor
to get one volt.
The average reading of voltage is fairly decent, but the actual
voltage across the DUT is not so nice (to be polite); the 200V ripple in
the 2800V supply shows across the DUT (10Meg resistor used for analysis).
Believe it or not, using the capacitor values shown for C1 and C2
appear to be optimum for that average reading..
It would be nice to get the opamp + FET chain to work for a constant
current instead.
Useful comments please?