On Sat, 23 Oct 2010 00:58:17 -0700, Robert Baer
wrote:

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?

The current regulator loop dynamics changes radically as you change
the shunt resistors. With 50K and 4.7 uF, the corner frequency is
under 1 Hz, so any ripple in the DUT current is hugely attenuated
before it gets to the error amp.

It would be better to use a single shunt and adjust the voltage
reference, so you can better tune loop dynamics and reduce ripple.
You'll need a pretty fast loop (and maybe a little feed-forward hum
nulling) to supress that power supply ripple.

Can't you filter the supply better, too?

Some caps across your 100M resistors might help.

Spicing is in order!


John