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Design of a 3-5kV Supply

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Revky27:
Hi all,

I am interested if anyone is familiar with other technieques of obtaining a high voltage output and prefferably quite low noise ( few mV noise)

Currently I am using the classic 1:100 transformer with a few voltage doublers after in a royer configuration.
I have also used a configuration where I am driving a few transformers in parallel ( 1:20 * 3) and then adding the voltages on top of eachother.

But both configurations have their trade-offs. Is there another way to generate high voltages or if anyone has come across transformer 1:100 arond 20-30W that are off the shelf?

Thanks

ejeffrey:
A flyback converter could do this. Meeting that noise/ripple spec is going to be difficult for any design.  Consider that a few mV noise at 5 kV is the same proportion as a few uV at 5 V.  That is a major challenge, especially at 30 W.

sandalcandal:
Since you mentioned you're using a Royer, I'm guessing you might have already seen this classic Jim Williams app note going over 5V to 1000V with 100uVpp noise (thank god ADI has kept the LT app notes)
https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdf

I was also trying to make a low noise HV PSU in the past but didn't get to finish the project. I used an LT1683 with some CCFL transformers from Coilcraft. https://www.coilcraft.com/en-us/products/transformers/power-transformers/ccfl-transformers/fl/ (nothing near your required 30W however).

Berni:
Royer is one of the lowest noise switchmode designs you can find. Something along the lines of flyback is going to be noisy as heck.

The downside of Royer is that the transistors operate in the linear region a lot so they might get fairly toasty once you scale it up to 10s of Watts. One alternative is the ZVS aka Mazzilli oscillator that is so commonly used in simple induction heaters. The circuit also produces a smooth sinewaveish current trough the transformer, so its also low noise while using the resonant nature of the circuit to switch transistors at zero crossing, making it very efficient even at larger powers.

As for the transformer one place to look is indeed CCFL driver transformers as they are some of the rare use cases for high voltage continuous operation transformers at a decent power. Another place worth looking at are TV flyback transformers (You can find them as spare parts) those have a benefit of already having the HV rectification built in and a high voltage cable already coming out of it. They do not have to be driven by an actual flyback circuit, they can be driven by royer or ZVS just fine.

Revky27:
Yeah I know of both. I think there are plenty of applications to get to 1kV no problem - check LT8304 with Sumida 0399-T208.
https://www.analog.com/en/technical-articles/1000-v-output-no-opto-isolated-flyback-converter.html

And yes I am familiar with the coilcraft transofrmer however they are 6W at best. The problem is a lot of CCFL transofrmers are becoming obsolete hence the availability is going down massively.

I was just asking whether there is another technique apart the ones I already know that I am missing but it seems those are the only ways.

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