Re: Modifying Electrophoresis Power Supply for High Voltage Microamperage

Jan Panteltje wrote:
On a sunny day (Thu, 03 Jan 2008 14:23:22 GMT) it happened
zekfrivo@xxxxxxxxxxxxxxxx (GregS) wrote in
<flir4r$i7j$1@xxxxxxxxxxxxxxxxxxxxxxxxx>:


Its nice to have an electronics shop at your institution to do stuff like this.
I would suggest getting a HV supply and using resistive current limiting
as a simple method. I would also try defeating the sense circuits on the electrophoresis supplies. Unfortunately, the supplies are likely to have noise problems
and voltage control problems with small output currents. Some voltage sinking will
probably be needed, and current control may not exist.

greg



I am not exactly sure what you want, but if I had to make one
I would use some old BW TV chassis, rob the horizontal out / HV transformer,
run it from some small 1:4 pulse, from a primary regulated 3-12 V.
That way you cam make from a few hundered volts to > 10kV.
Sensor resistor, comparator, flipflop, start button.
A PIC with LCD display (no meters) for currents and voltages.
Measure voltage exactly with some high voltage high value resistor divider.
Dunno about output capacitance, but some 100 pF is in HV triplers.
Some control loops.

power
|
3-12V DC regulator
| |
| TV ouput stage with transformer - single recifier of tripler -----------------0 +
| | | object
| PWM generator R | | | | -0 -
| ---------------)-----------------------------------------------------| --|
| | R Volt | R current
| | | sense | | sense
| | /// | ///
| | |
| -------------------- flipflop --------- comparator ----------| | | | |
|U start | |
PIC -- DISPLAY button current trip | | setpoint |
|i |
------------------------------------------------------------------------------


Or something like that, so parts perhaps 60$, and labour 5000$ only.


variac + neon transformer + rectifier & filter - the last two aint trivial at 15kV, but parts are obtainable.

Cheers
Terry
.