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I have a voltage multiplier connected to an X-ray tube, but when I I set the filament too high, the voltage on the multiplier drops, but it goes up when lower the filament, but sometimes it would not output any voltage, is it the diodes or the caps that are failing? and how can I test them since it only fail at HV around 50KV 70KV?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
If the filament current is higher, you are drawing more of a load on the cathode, so yes, when the voltage multiplier is loaded more, the voltage should decrease.
However, you should be running your x-ray tube at the manufacturer recommend filament current. There shouldn't be a need to vary the filament current.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
It doesn't seem like your multiplier is broken - they are load dependant, if the output resistance drops (hotter filament) then the output voltage will also drop. At short-circuit a multiplier's output voltage is zero and its current is limited by the size of its capacitors.
Be careful not to burn out the filament by taking it outside of the datasheet specs. Also beware of the obvious X-Ray hazard, but that should go without saying (if the tube is conducting enough to cause the multiplier's voltage to drop, then it's most likely emitting X-rays and cooking you).
To test a HV diode, place it in series with a resistor and LED, then use a LV power supply to visually see if its conducting in the correct direction. A HV capacitor should read open circuit on a DMM (>20M Ohm)
thanks for the info guys, but this is a HV multiplier it does not fail at 1KV it fails at around 40KV when you apply a bit of current,lets put the x-ray out of the picture for a minute.
the multiplier is already damage because of my previews test with the xray and I'm trying to fix it. I have 15KV caps I think thats where the problem is, does anyone know how can I test them because it does not show any problems when I check with a fluke meter..
Registered Member #3343
Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
Provide a complete schematic, bill of all material with data, pics from your apparatus and them you may receive precise advice...to help you solve the trouble.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Andre wrote ...
thanks for the info guys, but this is a HV multiplier it does not fail at 1KV it fails at around 40KV when you apply a bit of current
I think we'll need a complete schematic to help out properly.
Most importantly: What is the input frequency and voltage? What is the capacitance of each stage, and how many stages in total?
If the multiplier is built with small caps and has many stages, then there will be a significant voltage drop as soon as a small current is drawn from the output.
If you leave the multiplier's output unconnected and energize it to its full input voltage, is there any audible corona?
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the voltage drops on my multiplier
