HF switcher supply construction and voltage multiplication

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
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Dennis P Brown
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Re: HF switcher supply construction and voltage multiplication

Post by Dennis P Brown » Fri Jul 17, 2020 11:48 am

Don't get discouraged. Learning electronics can be very difficult. That for a voltage multiplier (V.M.) is no different but to make one that can power a fusor isn't something that many (if any) here have achieved. There is a reason those expensive power supplies that are sold are so complex when they use V.M. instead of a big transformer. High frequency circuits are not easy to design - calculating the capacitors required and final voltage are not simple procedures and EE types spend a lot of time doing that. By the way, there are many designed (with all required components listed) circuits to drive and control voltage output for V.M.'s. Just search the internet.

To get started I'd suggest you just build a simple V.M. and measure its parameters. Best to start with a low current 60 Hz supply. This way you get hands on experience with a real and simple system. Then move on to higher frequency (but low current) systems. Finally, once your calculations agree with your designs, then move up to trying the real thing. Attempting to build a full sized, high frequency fusor level power supply by a novice isn't likely to happen until one gains a great deal of real experience with such circuits.

A circuit diagram is just a map that shows the gross behavior of a given electrical circuit (does not give performance values; that requires real valued components) - that is, unless you copy someone else's system complete with their list of components. Just trying to build from a schematic isn't likely to succeed since correct caps, diodes, x-formers, and driver circuits must be selected and modeled before performance gets close to what one requires.

My two cents from someone who started that route, and built a few very high voltage systems - one with very high current (at 60 Hz so the actual power wasn't known - good for my accelerator but not likely to be a good fusor P.S.)

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Nicolas Krause
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Re: HF switcher supply construction and voltage multiplication

Post by Nicolas Krause » Fri Jul 17, 2020 7:23 pm

Hi Pierre, I just thought I would add my two cents, I've been working on my fusor for a very long time. I think I found this site back in 2010 initially, and couldn't understand anything here. I only started buying actual parts for my device in 2015, when I went back to school for electrical engineering. With work and school and everything else, it's only now that I've got the vacuum chamber close to being done, and the pumping and pressure control well underway. I can understand more of the site now, but there's still lots left to learn! Which is great! I find it a lot more fun to look forward to all the things I'm going to learn than to get discouraged by all the things I can't do. I started learning electronics with simple kits, and then moved onto designing my own simple circuits in class and in my spare time. Designing a switch-mode power supply, especially a high voltage one, would be beyond my abilities right now. Dennis' advice of picking a simpler version to start is great, it's basically how I've learned to do anything that I couldn't do initially.

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Richard Hull
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Re: HF switcher supply construction and voltage multiplication

Post by Richard Hull » Sat Jul 18, 2020 5:18 am

Nicolas, you, once again, point out the proper path to the learning and knowing, be it a sprint or takes place over a long period. It is drive, study and the doing that allows us to own and function actively to good effect in all that we encounter. As we study, work and grow, we acquire skill sets. Some are for ornament and self-satisfaction. Others are of a value that can sustain us through life and result in a productive path into old age. The fusor and amateur fusion effort can teach in a way that will impact much that we do in future, even if that future has nothing to do with fusion, engineering or science. One has to learn to take on tasks and develop what skills are needed to see the task through to fruition.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault » Sat Jul 18, 2020 10:31 am

Thank you very much for your support, your advices and your personal experience. So I’m going to break apart my circuit and learn, design and build every piece of my original circuit. I have a book for beginners about logic gates and chips so I think I’m going to start with this. Then I’ll follow Dennis’s advice and do a VM. So little by little I’ll get closer to my goal.

Again thank you guys for the support ;)

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Re: HF switcher supply construction and voltage multiplication

Post by Chris Giles » Sun Jul 19, 2020 4:45 pm

Hi Pierre, I'd recommend using a dedicated driver IC for this rather than designing it totally from scratch. Earlier in this thread the an Infineon IC is shown. Alternatively you could rip-off large parts of the circuit from a commercial design, for instance see the manual in this post. You might also be able to modify a driver circuit from a lower voltage PSU (i.e. find on eBay etc) and then use a different transformer and voltage multiplier. When constructing & testing, please bear in mind that even the low voltage side of these circuits have lethal voltages present.

Here is an explanation of how the transformer core size reduces with frequency. You also have to bear in mind that many characteristics of electronic components derate from the theoretical ideal with frequency, typically at about the frequencies used in SMPS (~50kHz), so some critical components need to be carefully chosen - specifically the capacitors.
HTH!

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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault » Sun Jul 19, 2020 8:51 pm

Thank you for your advices,

Yes I will go for a dedicated driver IC for the buck and H bridge but for now it is too complex to me so that’s why I have said I will learn logic gates and chips.

For the explanation of the link between the size of the transformer I’ve already looked for it (thanks Wikipedia). But in your link It looks more explained and detailed so thank you for sharing it

My goal is to step down the price and learn electronics so it’s not in my plan to buy a design and modify it else I would just directly buy a transformer and a variac et voilà as we say in my country. But I might consider it for the driver if it becomes a real nightmare.

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Nathan Marshall
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Re: HF switcher supply construction and voltage multiplication

Post by Nathan Marshall » Tue Jul 21, 2020 9:06 pm

Hello Pierre:

I built a high voltage switching power supply with a beefy AC to DC supply, ZVS driver, large flyback-style transformer, and a voltage tripler. Since I used a cheap ZVS driver off eBay, I didn't have to bother with any driver circuitry. You can see pictures of my supply and a circuit diagram on this thread: viewtopic.php?f=18&t=13340&start=10

I wish you luck with this project. I'm interested to see what you are able to build!

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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault » Fri Jul 24, 2020 10:00 pm

Thank you for your answer Nathan,

Your thread is very interesting, your diagram is very similar to mine except you use a variac instead of a buck and a full wave CW multiplier instead of a half ( by the way I thought the only advantage of a full wave was the smaller ripple but are there any others ?)

Ti instrument have some advanced high power buck that work around the voltage of your ZVS driver so I may be able to use one.

Could you give me the reference of the ZVS driver ? And why do you call your transformer a flyback ?

I’ve read quickly the 5 pages of your thread tonight ( I will read it more focused tomorrow) and thank you very much for providing that much data, it will help me a lot.

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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault » Sat Jan 16, 2021 7:26 pm

Hello everyone,

I’m back with a bit of experience with HV transformers ( I did a couple of experiments with a microwave oven transformer) But most importantly with a 400W ZVS driver and it’s power supply ( 24VDC). I approximate the inductance of the coil to 0.47 uH and the capacitance to be roundly 132 uF which give us a resonnant frequency of 20.2 KHz so it sounds plausible. I would like my transformer to have a 1:100 turns ratio to get a nice 7.5kV at the ouput. Then rectify it to have finally 30kV 15mA output for my fusor.

But I have a problem designing the transformer because I need the primary to have an inductance around 0.47 uH with the ferrite core in order to not change the frequency. But meantime I need my 1:100 ratio and also respect the number of turns require for such a frequency.

I’ve seen Nathan that you use 8 - 9 turns in your primary. Do you think it would match with my need ?

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