Medium voltage (~800v) SMPS

logjam · 2007-10-02T08:06:57+00:00

I am interested in constructing a SMPS suitable for connecting to acascade diode multiplier to get around 80,000@~3mav. I will needabout 800v at 30-50ma for the project. I would be happy to get1ma@80,000, but hey! ; )Most of the website links I've found are for much lower voltagesupplies. Does anyone have any suggestions on what type of SMPS Ishould use? Any tips/hints? Any web resources I can study? I wouldlove to find a reference schematic or project on the net to look at.I will probably end up having to wind my own transformer unless thereare companies out there willing to do it for under $80 or so.I'm still going through some schematics on commercial units. I'mtrying to figure out how they measure the output of the cascadedoubler using a resistor divider when it seems there is no commonconnection. Its using a series of 100Mohm resistors for a total ofabout 2Gohms. I will do some more research on that and try to contactthe manufacture about it. Its not a secret (to the industry) sohopefully they will help me out. I will see if I can extract themanual pages and upload them.This is for a hobby project involving an x-ray tube. Don't worry, Ihave all the safety gear required... : )Thanks,Grant

Oct 02, 2007 24 Replies

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Robert Baer 18 years ago

Well, you should now be aware of a few probelms with the transformer:

1) lots of leakage inductance, as you cannot interwind so many output turns to so few input turns. 2) Lots of capacitance to drive, as the inter-winding capacitance of the secondary is going to severely reflect back to the primary. After all, a 5KV secondary is going to have a *lot* of turns. Be careful with insulation, you will need some between the secondary and the coer itself. Have you picked a core and determined volts per turn for a "final" prototype?

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logjam 18 years ago

I still haven't come up with a way to find the ultimate minimum turns per volt for the primary.

I've been rethinking the secondary output voltage. 10kV capacitors are expensive but 6.3kV capacitors are more affordable. I may want to build a 3kV secondary with more cascade sections than use larger more expensive capacitors and fewer stages. More stages with a 3kV input will result in less output ripple too.

I still have not made the SPICE simulation work. I need to choose a capacitor value and fill in all of the characteristic information in.

If I use a form and a split core then will the form be the insulation I would need?

Grant

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Frithiof Andreas Jensen 18 years ago

"logjam" skrev i en meddelelse news: snipped-for-privacy@d55g2000hsg.googlegroups.com...

Usually, what one does to measure HV is to feed a *current* into a buffer amplifier.

You cannot get a transformer that small to work: *if* it does not arc over, you will loose all the power in inter-winding capacitances (before it arcs over).

However, there is a much easier way: Use an automotive ignition transformer in either a flyback topology (easiest) or a resonant converter (more efficient). Ingnition transformers are cheap and available (unlike attractive wimmen)

An typical ignition transformer should be good for about 100 W at 25 kHz and probably give you 25 kV!! Enough to require EHT diodes (BYW 95 ??) and oil & silicone potting for the rectifier stack. And deadly, really it is!!

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Robert Baer 18 years ago

Sorry; all else being equal, the number of stages is not related to amount of ripple. Try load current, stage capacitance, load capacitance for starters.

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