Very High Voltage potentiometer

[Ravaner]

Hello. I need 3 adjustable HV power supplies (0-10 kV). I built one and as currents needed by the 2 others are very low (in the order of 1 µA). I try to avoid building PS #2 & #3. That means that I'm looking for a device which looks like a kind of HV potentiometer but of course which is not one (don't exist for these voltages). If there is a solution please tell me. I really don't want to multiply the HVPS.

 

[yungman]

I afraid there is no easy way. The solution is more complicate than the problem. You can't exactly use a potentiometer because in order not to draw too much power, the resistance value has to be high. So even drawing 1uA will cause inaccurate result.

I designed a 5KV descrete op-amp. I am sure by stacking up more transistors I can get 0 to 10KV. BUT this solution is much harder than to build a low current supply. It is not even that expensive for something that is 1uA!

 

[Ravaner]

Thanks for your answer. Unfortenately it confirms my concern. The only HVPS working correctly I've built uses a TV flyback tranformer with filtering and regulation. For the 2 other HVPS I've tried CCFL inverter with multiplier, but the result is very poor, large drop and huge ripple so I believed it was possible to use the main HVPS with voltage dividers ...

 

[skeptic2]

Could you make a potentiometer from a number of high value resistors in series and a multiple position selector switch which would switch between nodes of the resistors? It would have to be a selector switch suitable for HV of course.

 

[yungman]

Unfortunately my experience is we adjust full range and it is very inconvenient to have to drop the voltage, then switch tapes and power up. HV switches cost a lot of money also, so putting a switch is out of the question.

Small low current supply is not that expensive. It is not worth monkeying around. In HV, very simple relay and switches and resistors can cost an arm and a leg and they add up. At 10KV, you need to pot a lot of things, the money circuit, the more trouble you can get.

 

[skeptic2]

Okay then, what is the input voltage to your flyback transformer? Could you vary the voltage of your input to get a variable voltage on the output?

 

[Ravaner]

My main HVPS is continuously adjustable and regulated for an output from 0 to 16 kV. It produces several tens of mA. The 2 other supplies I need have also to be adjustable and regulated up to 10 kV but they have to deliver very low currents. CCFL with multiplier seemed to be a good solution, but as I told over 4 kV multiplication almost stops and ripple is out of acceptance.

 

[yungman]

We use EMCO before here is the link for some small little thingy:

http://emcohighvoltage.com/proportional.html

At 10KV, don't monkeying around. It is at the edge of what people consider "black magic"! I remember the days when we had to trouble shoot where is the little arc and little corona that cause problem. Unless you are just doing it in the garage and whatever goes go. There are a lot of things you have to worry if you do anything that is more formal( developing a product) way. You can get into situation that it work one day when the humidity is low and totally screw up otherwise. It is getting into the region like RF, unless you know what you are doing, it is like black magic. All the creepage distance, floating piece of conductor, unclean surface....

 

[Ravaner]

Many thanks for this link. I hope they have representative in Europe ... I used to work with very high voltages (in my garage !) Marx generators, Tesla coils ... After having developped my own Mass Spectrometer, for the time being I'm building a Scanning Electron Microscope.

 

[yungman]

Many thanks for this link. I hope they have representative in Europe ... I used to work with very high voltages (in my garage !) Marx generators, Tesla coils ... After having developped my own Mass Spectrometer, for the time being I'm building a Scanning Electron Microscope.

I work 14 years in mass spectrometers, semi-conductor testing equipments. I have been working with a lot of HV power supplies. Also design a lot of high speed high voltage pulsing circuits. I am sure you are familiar with those also. Part of the Time of Flight SIMS electronics that I designed for can be used as scanning electron microscope.

I hope you can get EMCO, they are about the smallest and cheapest I found at the time. We use a lot of them, some of them are as small as 15mmX15mm.

 

[dlgoff]

We use EMCO before here is the link for some small little thingy:

http://emcohighvoltage.com/proportional.html

Nice DX series. Makes me want one to play with :)