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120kv 10-20mA SMPS

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Linas

Fri Apr 22 2011, 10:15PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Hello.
I am trying to make x ray generator, but can't get enough power from 8x multiplier.
so i decided to use half bridge smps (IR2153) and some huge HF transformer
i get very massive very high power ferrite core capable to give up to 30V per turn with low stand by current
for diode bridge i will use 500x SUF4007 (125kv per diode string)
and i have two questions:
first, if i reach up to 125kv, diodes will behave like zener diode, and don't die ?
second, how to wind secondary col , and how to isolate windings ? ( i need around 6000T )
i have 12*9cm ferrite U shape core (12x9 is inside window)
thank you for any help :)

James

Fri Apr 22 2011, 10:59PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I've been working on the same thing, but have not got past the brainstorming stage. I think you will have a lot of trouble insulating a transformer at such high voltages. You might try a compromise, using a 2 or 4 stage multiplier, or a pair of multipliers fed by a transformer with a grounded center tap. Most iron transformer x ray generators are wired like this too, with the center tap grounded and the anode and cathode driven by opposing positive and negative supplies. The advantage is you only have half as much voltage to ground at any point in the circuit.

If you want to try a single high voltage winding, you will probably need a sectioned bobbin and wind a string of series connected pancake secondaries. Obviously the whole transformer will have to be immersed in oil or you will not be able to prevent corona.

Dr. ISOTOP

Sat Apr 23 2011, 01:44AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

You'll still need a multiplier for 100kV+.
UF4007's are not avalanche rated; you'll want to use strings rated to 2x the voltage they'll see.

Adam Munich

Sat Apr 23 2011, 04:02AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

SF4007's are avalanche rated, but since you only need 10mA I'd just get some 20mA HV diodes. It'd cost less than a bunch of SF4007s and take up less space.

And yes you'll need a multiplier. A 2stage one ought to do it. There is no way you are going to be able to make a 120kV HF transformer, it's just no feasible. If it was then GE medical would have beat you to the punch long ago.

Linas

Sat Apr 23 2011, 06:58AM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Well, for insulator i will use paraffin ( because it can heal himself after brake )
Also i will use enamel wire with silk insulation ( which will absorb the paraffin for even better isolation)
after each 5cm long layer, i will coat windings with liquid paraffin, and let it harden, then apply paper/lexan insulator between the layers, and repeat process for 15-20 times.
after that i will cook transformer in boiling paraffin, and hopefully i will get mono-block secondary.
Here is some pictures ( primary 8T and rectifying capacitors for more stable voltage )

Dr. Dark Current

Sat Apr 23 2011, 08:01AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Maybe you would find the replies in my thread useful

Linas

Sat Apr 23 2011, 09:08AM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Dr. Kilovolt wrote ...

Maybe you would find the replies in my thread useful

well, i don't want to use multipliers any more, because they don't work with SUF4007 diodes, and buy new one cost to much (for 80kv 0,1A 100ns more than 20$ :( )
ok, i made some experiments, and find out, that my biggest enemy right now is heat generated by corona effect.
( but i made test at 15-20khz, will heat be greater in 60KHz? )
so, i get best results with laser printer slide sheet.it can stand quite high voltage and don't burn until critical temperature is reached, after that i just brake it in one dot.
Does any one tried Teflon for insulator ? it can stay at very high temperatures, and also can hold very high voltages. i guess is ideal material for the job, but i can't easy get it in my pore country :(

Ok, i found this:

So if i use more than 3-4 layers of this tape, it will hold temperature and voltage for quite long time.
and other question, will corona effect will be reduced by applying load on transformer output ? or it depend only on voltage gradient ?

Wolfram

Sat Apr 23 2011, 11:06AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

The problem you're going to have is that the high self-capacitance of the secondary will give it a very low Fres, this will limit the driving frequency. Then, because of the low driving frequency, you won't get enough volts per turn (because of core saturation), and you won't reach the desired output voltage. I know of several people who have tried, and all of them have ended up going with voltage multipliers instead.

Personally, I would make two voltage multipliers, one +60kV and one -60kV, and drive them off one transformer. Each multiplier could be two stages, each diode could be two of these

in series, and each capacitor could be two of these

in series.

Dr. Dark Current

Sat Apr 23 2011, 11:19AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Why don't multipliers work with SUF4007 diodes ?

Ps. In the circuit diagram I posted in my original post, the total diode rating could be only 1x output voltage while in your configuration it must be 4x output voltage. Of course the downside of my circuit is that the output is HF-modulated.
For ringing and safety reasons, you should design your diodes to stand at least 2X the calculated voltage from transformer ratio, and have a safety gap on the output.

Linas

Sat Apr 23 2011, 12:22PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Dr. Kilovolt wrote ...

Why don't multipliers work with SUF4007 diodes ?

Ps. In the circuit diagram I posted in my original post, the total diode rating could be only 1x output voltage while in your configuration it must be 4x output voltage. Of course the downside of my circuit is that the output is HF-modulated.
For ringing and safety reasons, you should design your diodes to stand at least 2X the calculated voltage from transformer ratio, and have a safety gap on the output.

they just don't work, maybe they are to much powerful, so they don't work at low current, i don't know
I used 10nF 30KV capacitors and 37kv suf4007 diode for each stage, and output was even smaller than input. all diodes was in right direction ( i tested that)

so i spend lot of money for multipliers and they just don't work, so i move on single stage transformer to get it done. i know i probably kill transformer because of corona effect o something like that , but i have no options right not. i just don't want to go in to multiplier stuff again

FYI- ferrite core was from original 60KW 140KV power supply unit for huge x ray tube power supply, no multipliers, just 20kv diode in series for secondary each layer of insulation,i don't know why they do that... ( diodes was BYV26E )

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