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schematic

simulate this circuit – Schematic created using CircuitLab

In the past, I have worked with high voltage projects, but seldom with HV rectifiers. Thus, I was curious how I could build a rectifier that could take 70 kV AC and 10 mA to put out a continuous, negative DC voltage with minimal ripples. The frequency for the input is 60 Hz and is provided by a X-ray transformer that provides adjustable voltage from 0-70 kV AC.

Note on image below: There was not an option for a variable transformer image, so I used a non-center tapped transformer to depict it.

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  • \$\begingroup\$ I corrected the diagram. Basically, the first transformer is a variable transformer for adjusting the voltage from 0-130 VAC. The second one (the one recently added) is the 70 kV AC X-ray transformer. Sorry about that, I was a bit tired at the time of the diagram's drawing. \$\endgroup\$ Aug 8 '18 at 0:35
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    \$\begingroup\$ a rectifier produces a pulsed putput .... filtering capacitors and a regulator would be needed to produce a DC output \$\endgroup\$
    – jsotola
    Aug 8 '18 at 0:36
  • \$\begingroup\$ Certainly, but how could I make the rectifier itself? What ratings would I need on the components? \$\endgroup\$ Aug 8 '18 at 0:39
  • \$\begingroup\$ Also, I would not be able to use a typical voltage regulator, as the voltage is to be adjusted from 0-70 kV (hence, the purpose of the variac). \$\endgroup\$ Aug 8 '18 at 0:41
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    \$\begingroup\$ That would appear to leave you with a rectifier and an RLC filter. You will probably have to find the highest blocking voltage diodes you can, and string them in series with carefully chosen parallel resistors to build each of the diodes of the rectifier. Run the output through an RLC filter. You are aware of how potentially dangerous your project is? \$\endgroup\$
    – K H
    Aug 8 '18 at 1:24
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The frequency for the input is 60 Hz and is provided by a X-ray transformer that provides adjustable voltage from 0-70 kV AC

Some more modern X-ray machines generate a high frequency (10 kHz to 100 kHz) variable AC voltage of several kV magnitude and then use a Cockcroft Walton multiplier like below: -

enter image description here

This both performs AC to DC rectification and, each stage need only be rated for the peak voltage from the AC source hence 10 kV rated diodes and capacitors can be used.

I was curious how I could build a rectifier that could take 70 kV AC and 10 mA to put out a continuous, negative DC voltage with minimal ripples.

If you can't find diodes rated at over 100 kV DC then a good option is to scrap the X-ray transformer method and use the multiplier shown above. Minimal ripple is meaningless but if you are driving a tungsten target X-ray tube then a few volts p-p isn't going to be a problem.

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