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I am having trouble coming up with a solution to a problem engineering a DC circuit that can take a single line input (Vin) and split into two outputs (Vout1 & Vout2).

The goal of the circuit is to take a high voltage line and supply two parallel electrodes connected to Vout1 and Vout2. By changing the potentiometer setting (R1) one should be able to adjust |Vout1-Vout2| between 0-9V or 0-18V depending on the switch (SW1) settings. The circuit should be able to handle high voltage inputs (Vin: 0-4000 VDC, 1000 VDC typically). The electrodes are floating in ultrahigh vacuum.

The current circuit setup is shown below; however, this circuit does not perform as desired.

schematic

simulate this circuit – Schematic created using CircuitLab

The current configuration allows one to change electrode voltages (Vout1 & Vout2) 0-9V or 0-18V by adjusting the potentiometer; however the potential difference between the two electrodes (|Vout1-Vout2|) is always constant (either 9V or 18V depending on SW1 settings). I would like to be able to use the potentiometer to "tune" one electrode relatively. For example, I might wish to use a 1000 VDC input voltage (Vin) and get output voltages of: Vout1= 1000 VDC, Vout2= 1005 VDC.

Does anyone know of a way to modify this circuit or adapt a simple design to implement this idea?

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  • \$\begingroup\$ This is not simple -- not at this voltage level! Is whatever is generating this variable HV capable of providing a fixed HV supply as well? \$\endgroup\$ – ThreePhaseEel Feb 2 '16 at 20:15
  • \$\begingroup\$ You clearly have no clue of what you are getting into, the circuit diagram doesn't even remotely do what you describe. Leave these voltages to experienced and properly HV trained people. An electronics hobby is supposed to be fun, keep it that way. \$\endgroup\$ – jippie Feb 2 '16 at 20:16
  • \$\begingroup\$ I smell some XY problem here \$\endgroup\$ – PlasmaHH Feb 2 '16 at 20:19
  • \$\begingroup\$ @ThreePhaseEel I agree that it is not a simple problem, as I have exhausted most of the resources that I would first turn to in troubleshooting. The input voltage is being supplied by a stable HV supply. The high voltage DC power supply has a relatively slow response time, but that is a nonissue for my application. I don't even need any speed considerations when trying to implement the above circuit either. The DC level is designed to be adjusted some level and left there. \$\endgroup\$ – lplath13 Feb 2 '16 at 20:19
  • \$\begingroup\$ Also, can you explain more about how you got into this pickle? \$\endgroup\$ – ThreePhaseEel Feb 2 '16 at 20:23
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I think this may do what you want:

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Electrode 2 positive-only with respect to Electrode 1.

schematic

simulate this circuit

Figure 2. Switchable polarity version.

Note that while the batteries, switches and potentiometer have a maximum of 18 V across them they are possibly all at high voltage (1,000 to 4,000 V) with respect to ground and you. All need to be properly insulated. The metal case of the potentiometer should not be grounded (as you're unlikely to find one with a 4,000 V rating between the carbon track and the case) but should be mounted totally inside the enclosure with only the plastic shaft protruding through the case with a knob on the outside.

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  • \$\begingroup\$ That's a nice take on the question and I didn't understand what the OP asked. I've taken the liberty of adding the polarity reversal version which was part of the specification rather than a separate answer which might steal some of the credit for the original insight. Feel free to edit ... \$\endgroup\$ – Transistor Feb 2 '16 at 21:10
  • \$\begingroup\$ Thank you all very much for the nice answer. I just got done building your circuits on a low voltage scale and they work exactly as I would hoped that it would. What a life-saver! \$\endgroup\$ – lplath13 Feb 2 '16 at 22:42
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I designed one of these for a gas mass spectrometer back in the 90s and it was fairly complex because there was also a 12V heater circuit involved that had to be floated up to the HT voltage (up to 5 kV from memory). 5 kV isn't too much of a problem providing you apply sufficient insulation - I used switching power supplies (home spun) and very-well insulated ferrite transformers (hand made) for transferring power up to the HT voltage. I also used pots and very long plastic spindles connected to the knobs on the front fascia of the box.

There were some logic controls to the HT board from ground level and I used 10 kV rated opto-isolaters. For feedback of the voltages I used a parallel ADC and a bunch of optos but these days I'd use serial ADCs. Watch your hands - I once got a 5kV shock from it and it hurt and flung me a couple of yards.

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