How do I achieve 5kV from mainstream components? - Page 1
Forum section: electronics / beginners

author: nsled
author_rank: Contributor
timestamp: October 01, 2024, 10:04:22 am
content: I've been struggling with something, how do I create ~5kV from parts available from mainstream sources (like Mouser/Digikey etc.). It's an easy task if you care to source your components from Aliexpress but the big western component retailers don't seem to have anything at all in the small HV transformer category.I only require about 50mA at the very most and less is fine. It's easy enough to make a PWM driver but do you really have to wind your own transformer? Am I just missing that subsection of their websites?ps. I tried a 1:100 current sense transformer from Digikey but it only achieved 1.8kV when driven with 16V 20kHz 50% duty and got very hot, it is just too small with a single turn primary.I really require components that have a manufacturer number etc. not some generic Chinese thing.

author: Refrigerator
author_rank: Super Contributor
timestamp: October 01, 2024, 10:33:34 am
content: Well first things first, 50mA at 5kV is 250W, so i'm not sure how you can achieve that with a small transformer. That's big SMPS territory right there.Second, make use of a Cockroft-Walton multiplier, because it's an easy way to get very high DC voltages.If you're having trouble getting HV with a single transformer then just use two in series.Also, using a CST is pretty smart, because they're potted most of the time.Moreover, 20kHz is a pretty low switching frequency, so just bump it up to 50kHz and you should be fine.The way i see it: bump frequency to 50k, add 5x to 10x Cockroft-Walton multiplier and then add feedback to regulate voltage (i assume that's what you want?)One more thing: flyback topology will get you stupidly high voltages if you want. I mean i can build a boost converter that will step up 3.7V to 160V with just an inductor, now imagine that gain combined with a HV transformer.PS: 5kV at 50mA continuous is basically asking for deathIt will hurt the whole time you're dying!

author: Refrigerator
author_rank: Super Contributor
timestamp: October 01, 2024, 10:42:11 am
content: And here's a HV transformer for CCFL backlights, rated for up to 1340V at the secondary and 2kV breakdown, very easily can be stepped up to 5kV with a multiplier.https://www.digikey.lt/en/products/detail/eaton-electronics-division/CTX210609TR-R/1762290

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 01, 2024, 12:37:23 pm
content: Good Morning Nsled, How about a neon sign transformer

author: nsled
author_rank: Contributor
timestamp: October 01, 2024, 01:31:53 pm
content: That transformer Refrigerator, and every other one like it on Digikey are not stocked/obsolete. I find it extremely hard to search their transformers as they rarely give turn ratio etc. Using a pulsed DC source isn't it 10 capacitor multiplier to go from say 1kV to 5kV? that's larger and more awkward than ideal. I'm just finding it so frustrating that I can easily find exactly what I need on Aliexpress but nothing at all in Western retailers.250W is about a fist sized transformer, and yeh its very much the upper limit here, I just wanted to place an upper limit so people didn't recommend microwaves etc. At high frequency it doesn't hurt too much though. Half a thumb sized transformer would be ideal.No BILLPOD, I'm very specifically after components from Digikey/Mouser etc. I can do this easily if I just search for any individual component on google and cobble something together however I want to be able to create a BOM and send it off to PCBWay etc. and have it sent back complete and working.Pic shows my test driver (11-200kHz 16V) the perfect Aliexpress 1:64 transformer, and the smaller current sense transformer for Digikey which I'd have to run maybe 4 in parallel than multiply it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 01, 2024, 06:16:54 pm
content: The problem isn't whether it can be done, it's whether it's available. The suppliers you mention, cater to the mass market; while they do carry many specialty items, the more special you go, the more spotty is the availability of any particular kind of item.There are few mainstream applications for high voltages, at more than tiny currents.Even CCFLs are falling out of use now, and they only deliver small currents (~mA?).You're almost certainly going to need some windings in series, and then a voltage multiplier. High voltage diodes have never gone out of style, and even regular diodes can be wired in series if needed.That leaves the transformer. You may well be better off with an iron-core power transformer, or an SMPS type would be equally usable at high frequency, wired in reverse so that e.g. 12V AC at the input is stepped up to 240V at the output, a few of these wired in series, and then enough of a multiplier used to go the final distance. If regulation is required, you'll need some sort of primary-side control (PWM? frequency control + resonance?) and a feedback voltage divider. Notably: you must find transformers with "REINFORCED" isolation, over 5kV obviously: preferably 8kV, a level commonly available for medical-grade devices. The parts will be somewhat expensive (more insulation, more approvals), but you only stipulated availability, not cost, so this seems acceptable.More esoteric items are available on Ali and etc. where no one cares about safety, practicality or application; the quantities don't need to be large, necessarily: remember those products come from low cost-of-living countries where your mere $3 purchase price, say, means a lot more over there than it does here. (Though still not actually that much; there's competition even between in niche products, driving prices down, and the CoL multiplier isn't actually all that big, maybe 3-5x these days, depending on where.) In particular, such a transformer might be made for unsafe (to handle, or environmentally to operate) products such as spark generators (generically; take your pick as to application), corona (ozone) generators, UV, NOx, whatever. The sorts of infamous things BigClive takes apart, y'know. Some of these might have industrial application (sterilization, spark ignition?), but putting them in consumer products ("ion purifier"!) is reckless, and there's very little mainstream, western market for parts like that. (Besides, the few applications/companies that do need such ratings, are happy to custom-order a transformer of such spec -- they're simply not buying them through distributors anyway, there's hardly any widespread, multi-use market for such products, hence they aren't offered on DK/M.)Tim

author: TimFox
author_rank: Super Contributor
timestamp: October 01, 2024, 06:37:48 pm
content: The suggestion for a Cockroft-Walton voltage multiplier does not require very high insulation on the transformer, since one side of a "reasonable" secondary winding can be grounded.Here's a technical note from a manufacturer:https://www.voltagemultipliers.com/wp-content/uploads/2018/08/Multiplier-Design-Guideline.pdfReasonable-size diodes and capacitors can be mounted on an insulating board at these voltages.For 50/60 Hz operation, Mouser does have some Hammond transformers designed for vacuum-tube amateur radio, some of which have a center-tapped secondary (watch for insulation questions).In that datasheet, note that "ICAS" means "intermittent commercial and amateur service", but "CCS" means "continuous commercial service".You may need to contact Hammond directly for this series.These transformers can be lethal!https://www.mouser.com/datasheet/2/177/pwdahl-2934065.pdfOf course, the secondary current in a voltage-multiplier is much higher than the DC output current of the rectifier: see the proper electronics texts for details.(Historical note: see the very interesting bookhttps://www.atomicarchive.com/resources/book-reviews/0374530262.htmlabout how Cockroft and Walton achieved 1 MV in 1932.However, when they tried to patent the voltage-multiplier rectifier, it had already been patented by Greinacher in 1919 for similar purposes.)

author: Xena E
author_rank: Frequent Contributor
timestamp: October 01, 2024, 06:45:45 pm
content: Line powered ignition transformer for a gasoil burner, as used in industrial boilers...Just a thought.And yeah, bloody lethal.X

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 01, 2024, 10:02:10 pm
content: Quote from: TimFox on October 01, 2024, 06:37:48 pmDepends on design -- a single-ended (half wave) multiplier this is true, it can be common-ground. A full wave, symmetrical design may be preferred here -- giving better regulation / not needing as large capacitors, making better use of the transformer. That would still strictly be only 2.5kV (average, plus winding end-to-end voltage) with one or the other side grounded, but I would air on the side of caution, as with sparks likely inevitable, discharge waveforms and transmission line effects can double the peak easily, and pushing 10kV isolation starts to look attractive. (Granted, that's a long-term spec, and a lower spec might handle more impulse for a few hits. Where "few" might be one, a dozen, a thousand... who knows.)50mA out of a, say, quadrupler, is kind of like 200mA out of a half-wave rectifier, but actually the peak currents are even worse (current distributes along the chain, it adds up triangularly) so it's more like a 400, 800mA, maybe even more, rectifier in comparison -- the required cap values, and transformer capacity, go up quickly, and you can see a 1250V 1A supply is no joke! This is in compromise with regulation, so if you can afford poor regulation (perhaps solving it with a controlled inverter as mentioned), that relaxes everything a bit, perhaps at the cost of another stage (to make up for being on the charge-limited slope of operation) but not increasing capacity demands much.Incidentally, I may be taking "5kV DC" too literally. Normally we mean a fixed supply, approaching an ideal voltage source. Maybe it's just to charge capacitors, or to have fun with sparks and the voltage doesn't matter at all. A cap charger isn't too concerned with charge slope, as long as it reaches the desired end point within the required time (and charging can just stop abruptly when it gets there, trivial hysteretic (on-off / bang-bang) control).Tim

author: BrokenYugo
author_rank: Super Contributor
timestamp: October 01, 2024, 10:12:50 pm
content: Car ignition coil is probably cheapest, look at 90s-00s cars with wasted spark two tower coils if you want a fully isolated secondary.

author: amyk
author_rank: Super Contributor
timestamp: October 02, 2024, 12:11:28 am
content: Quote from: BrokenYugo on October 01, 2024, 10:12:50 pmVoltage may be too high, although the current is about right.Why not a microwave oven inverter?