Transformer

Do you have an idea of the current you will expect (or how big a capacitor you need to charge in how much time)?

Do you need isolation between the 12 volt source and the 800 volt DC output?

I suspect that a flyback converter may be good for this sort of thing, since it handles big voltage variations in the output (like starting with a fully discharged capacitor load that ramps from zero to 800 volts).

This type also reduces the turns ratio required, because it can produce more than 12 volts across the primary.

An old TV or monitor flyback transformer (and built in high voltage rectifier) might serve.

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John Popelish

First they learn about the circuit configurations available and pick one or two good candidates. (I mentioned the need for an ability to handle loads that vary from nearly zero volts to 800 volts as an example.) Then they study the design of the magnetic components needed.

I suggest you study the flyback converter (or boost regulator) from several sources, till you have a basic understanding of the concepts. You might start with this reference on switching converters:

When this study has allowed you to have a specification for the inductive components (inductance, current levels, magnetic energy storage capability, etc.) you need to read up on the design of the magnetics, themselves. Many core manufacturers have tutorials at their web sites. Lots of the design formulas are in the back of the catalog (page 163) from Fair-Rite:

but you may need a lot more hand holding than this brief reference to understand all the design process.

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John Popelish

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Sorry, I accidently hit the send button on my last message.

I don't really know what the current requirements are. The capacitor bank is around 800V @ 700uF. The time it takes to charge is not really an issue. If it takes a while then that is fine.

I do own a flyback transformer (from a computer monitor), but I would rather make my own transformer (more fun and I would learn more).

I guess it would be better to make a transformer which can generate 200V and then use a voltage quadruppler (diodes and caps). Hopefully the voltage quadruppler would give me 800V.

I don't know how many turns to use or which wire gauge to use. The best frequency to use is a bit of a mystery as well. Surely some formulas (or simulators) exist, which will allow me to work out what I need. How do people normally go about working these things out?

one of the nice things of resonant circuits using transformers is that they can go pretty high on the secondary side. try using your transformer in an oscillator circuit, OR

another way is using a 12V to 220V transformer (standard 220V to 12V but using it reversed), and use a simple tripler-circuit to "amplify" the secondary side. regulating the 12V side voltage will regulate the 800V side then

tripler schematic (view using notepad and fixed font) extending the tripler can be done by adding more of the same on the dots (gives higher voltage then) enlarging capacitors allows more current choose a frequency for the 12V side giving you some "resonant upswing" in the transformer (but don't overdo it or it breaks down...)

12V ac in and doubling the secondary side gets you about 600V already, so be carefull please !

o--||--+------+--||--+.....--o V+ | | | --- --- --- ac in / / / --- --- --- | | | 0------+--||--+------+.....--o V-

I would like to make a 800V DC power supply, which will be used to charge a capacitor bank. The power supply will run of a 12V battery. To make the power supply I am thinking of making an oscillator, which will generate a

12V AC signal. The 12V AC signal will then be fed to a transformer, which will step the 12V AC signal upto 800V. I will then use diodes to convert the 800V AC signal to approx. 800V DC.

I would like to make my own transformer (I can't find any suitable premade transformers). I understand that the transformer will need a ratio of

800/12. But how do I determine how many turns I should have on the primary coil? Also, how do I determine the best frequency for the transformer? Should the frequency be as high as possible? And what about wire thickness, how thick should it be? Do any calculators exist which will tell me all this?

Can anyone point me in the right direction (websites or answers)?

Thanks.

Yes, you need a copy of a book called the 'Coil Design and Construction Manual', published by Babani Press in Britain for just 4 pounds Sterling. The chapter on power transformers in conjunction with the tables in the back cover *everything* (and I mean everything - former, core type, turns, turns ratio, wire size, winding spacing; you name it!) you need to know. You should be able to get this excellent book even cheaper on e-bay. Good luck!

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Fat, sugar, salt, beer: the four essentials for a healthy diet.

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Greetings Jim.

You ask all very good questions. The answers to your questions however can be quite lengthy. There are entire books dedicated to answering just some of your questions.

That said, I highly recommend reading (and/or watching the narrated slides) of the Magnetics Design Handbook that Texas Instruments is generous enough to provide to the world for free. You can get the goods here:

If you are serious about fully learning the answers to your questions, you will want to download, save, and eventually read the whole handbook in the slup222.zip file which can be downloaded from the above link. Although the handbook is pretty comprehensive and contains most of the answers to your questions, you will likely need to read it more than once while simultaneously supplementing that reading with other books (perhaps from your local university's science library) and personal experimentation before fully understanding the answers to your questions.

Good luck Mr. Jim.

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?

Actually, that nat'l doc looks ok.

And free design/selector tools. Same for the controller chips - Nat'l, TI, Maxim, LTI ... LTI - friggin' amazing company. A new controller every month in EDN or wtf mag it is.

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Best Regards,
Mike