Designing a -5KV pulse, (10 watt) Power supply working on mains (230VAC)  - Page 1
Forum section: electronics / projects

author: pravin.ladde
author_rank: Newbie
timestamp: October 25, 2023, 08:26:06 am
content: Hello electronics enthusiast !This is my first post. I am a beginner as an electronics hardware designer (at least here on EEV-blog) and I am seeking some help here for one of my current hardware project.I want to design power supply for a lamp (UV). As per specifications of the UV tube, we need negative 5KV pulse of around 2uSec with switching frequency of 25k. (Manufacturer of the UV-tube found optimum UV generation at this supply pulse voltage and frequency)I have used "SG3525" to generate gate pulse of above frequency and ON time, but struggling to calculate required transformer and snubber calculations, I have hand wound 2 different transformers but they are getting hot, though I was able to turn on the UV tube.load of the tube is around 7watt (600mA at primary side maximum for 100nS). flat top of the pulse is not very crucial. looking forward for someone to save me through this black hole. Please let me know if you want any additional information.looking for help regarding choosing right topology for SMPS, transformer core and winding calculations or any reference circuit.Pravinppladde@gmail.com

author: p.larner
author_rank: Frequent Contributor
timestamp: October 25, 2023, 08:53:26 am
content: just interested to know what project requires that,is it a ultra fast tanning lamp?.

author: pravin.ladde
author_rank: Newbie
timestamp: October 25, 2023, 09:12:19 am
content: Its a mercury free UV lamp used for disinfection... particularly in small household water purifiers. (RO+UV)

author: moffy
author_rank: Super Contributor
timestamp: October 25, 2023, 09:18:24 am
content: Quote from: pravin.ladde on October 25, 2023, 08:26:06 amThat is going to be a little tricky as the high voltage secondary, with a largish number of turns will have a proportional self capacitance which will tend to limit the bandwidth for the pulse, it will have a self resonant frequency low enough to interfere with the pulse without special techniques. What is your starting voltage? And you might need to use a much larger core and litz wire so that you can space the turns out and use thicker insulation between windings to reduce winding capacitance.

author: pravin.ladde
author_rank: Newbie
timestamp: October 25, 2023, 09:41:45 am
content: Thanks for your interest,I am envisioning to make it work on mains voltage directly. (i.e. 230VAC here in India).I have added bridge rectifier + capacitor to get DC output voltage of around 320VDC. This will be the constant DC voltage available at the primary of the transformer (I am still not considering voltage fluctuation at mains which might reach up to 250VAC ). I have used flyback configuration during my prototype.

author: mk_
author_rank: Regular Contributor
timestamp: October 25, 2023, 09:45:35 am
content: Quote from: pravin.ladde on October 25, 2023, 09:12:19 am5kV @ 25kHz UV-transparent in a mostly wet environment, running for months in small housholds, this looks - at least from my experiences in India - not only a challenge for the puls-generator.Good luck.

author: pravin.ladde
author_rank: Newbie
timestamp: October 25, 2023, 10:00:31 am
content: oh.. I have never thought it that way.. Thanks.Still I think we might come to know about its environmental reliability once we develop it electronically.

author: moffy
author_rank: Super Contributor
timestamp: October 25, 2023, 10:08:59 am
content: Flyback seems a good way to go it will mostly be designing the transformer and keeping its resonant frequency high.

author: Marco
author_rank: Super Contributor
timestamp: October 25, 2023, 10:31:24 am
content: I'd try something similar to a two switch forward converter, with the output diode but without the output inductor. That way you get core reset and recover the magnetizing current. Flyback gets nowhere near a flat topAs for designing the pulse transformer, no idea.

author: pravin.ladde
author_rank: Newbie
timestamp: October 25, 2023, 10:51:47 am
content: Quote from: Marco on October 25, 2023, 10:31:24 amLately, I was also thinking like that, and if flyback is getting actual bottleneck. Anyways I was thinking to start working on Transformer and schematic for this approach.

author: mk_
author_rank: Regular Contributor
timestamp: October 25, 2023, 10:54:28 am
content: Quote from: Marco on October 25, 2023, 10:31:24 amDischarging into a plasma is a lot of fun, specialy because plasma detracts sometimes any prediction.... so there could be a lot of current, even during that 1µs - which is even higher on the primary side. Switching off a lot of current and being back in business 40µs later into the next plasma ....That's the reason why I do this kind of stuff only with fullbridge, there is no problem with freewheeling currents - as long as the brigde isn`t overloaded when powerd on again.

author: Marco
author_rank: Super Contributor
timestamp: October 25, 2023, 11:15:24 am
content: Full bridge doesn't really get you anything here because the secondary current is unipolar.Two of the switches in the full bridge would serve the same function as the diodes in two switch forward, except more expensive and needing to be driven (unless you really just use them as expensive diodes, then you don't need to drive them).

author: jonpaul
author_rank: Super Contributor
timestamp: October 25, 2023, 11:55:52 am
content: Lamp mfg? Spec sheet?UV 1849 Angstroms?Beware of ozone.Check latest UV LEDsj

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 25, 2023, 12:54:22 pm
content: I would look at the CRT TV technology, what you need is a flyback configuration with a transformer similar to a LOPT (Line Output Transformer) used there, I think, the frequency is close to the HR TV line frequency and the voltage could be high enough.CheersAlex

author: Marco
author_rank: Super Contributor
timestamp: October 25, 2023, 03:16:05 pm
content: EDN has an article how to design a pulse transformer, I guess you have to use 250 khz for fhttps://www.edn.com/design-high-performance-pulse-transformers-in-easy-stage/

author: mk_
author_rank: Regular Contributor
timestamp: October 25, 2023, 04:23:29 pm
content: Quote from: Marco on October 25, 2023, 11:15:24 amHm...as long as the tube-supplier specifies unipolar only there is no reason to pulse the tube unipolar.So - as it seems that there is no ignition transformer for this tube required bipolar pulsing should be possible without degrading the tube, making the magnetic part easier to handle as it is only a somehow transformer.

author: Marco
author_rank: Super Contributor
timestamp: October 25, 2023, 05:43:02 pm
content: If you put a diode on the secondary, the magnetics work fine even with an unipolar current on the secondary.That's howtwo switch forwardwork. The magnetizing current goes through the diodes back into the power supply, which puts exactly the inverse voltage on the primary, as well as secondary though blocked by the diode. That's enough to reset the core.Only difference here would be that you would leave out the inductor and free wheeling diode on the secondary, just one diode and the load.

author: p.larner
author_rank: Frequent Contributor
timestamp: October 25, 2023, 07:30:25 pm
content: What about using a car or motorbike ignition coil?.

author: moffy
author_rank: Super Contributor
timestamp: October 25, 2023, 09:40:31 pm
content: Quote from: p.larner on October 25, 2023, 07:30:25 pmThey couldn't handle the 25kHz pulse repetition rate nor provide a 2us pulse, 25kHz is equivalent to 1.5 million RPM, the coils would burn out well before that.

author: LaserSteve
author_rank: Super Contributor
timestamp: October 26, 2023, 03:36:45 am
content: :such lamps often have a seperate "series" trigger transformer and a pulse forming network to peak the inverter output or to. give a high "Q" to make the system resonant. This might be as simple as a series capacitor on the coil output.I've seen other crazy designs such as a transformer opposite in phase at each end of the lamp or a transformer with dual secondaries. Exciplex lamps often prefer pulses measured in nanoseconds.Core materials or inductors with magnetic materials chosen for pulse compression might be in play.Make sure you test with both a fresh and weak/dying lamp.Also test a totally dead lamp. As the other poster has noted, plasmas can be difficult to model and have highly varying characteristics, especially with temperature, humidity, and nearby charged or grounded objects. Sometimes a grounded or charged external wire or reflector is often added to insure triggering.As the lamp maker what they develop and test with.The late Jim Willams has app notes about CCFL or CFL circuitsSteve

author: jonpaul
author_rank: Super Contributor
timestamp: October 26, 2023, 07:28:34 am
content: Hello Pravin:The reply you made re mercury free UV lamp for disinfection...Please research your Project more carefully.According to Oshio, Sylvania and other lamp mfg, this lamp DOES NOT YET EXIST and requires extensive research and development.The so called "mercury free UV lamps" (especially from China) are FAKES.They may light but will NOT product the expected 2537 nor 1849 A UV rays needed to disinfect.Similar for so called UV LEDs also from China.Finally note that UV short wave is VERY hard to accurately measure and requires a special and expensive SW UV radiation meter.Thus I question the project basis.Very sorry,Jon

author: Marco
author_rank: Super Contributor
timestamp: October 26, 2023, 11:00:45 am
content: Ushio Excimer seems available right now, as well as ech20 from Merck though that might be a rebrand.There is some questionable shit on aliexpress though, like this one put together with hoseclamps.https://ae01.alicdn.com/kf/S6370ac1207ad4f9199f0eb0bf818175dn/Uvc-222-nm-led-uv-c-excimer-uvc-50-uv-222nm.jpg_.webpPS. if these Chinese barrier discharge lamps work, they will need a bipolar power supply BTW. It's not a classical discharge lamp, you can't push DC through it. So indeed a full bridge driven pulse transformer is the most appropriate.PPS. Flyback doesn't work for the same reason.PPPS. these should really be driven resonantly, even with a full bridge you're burning up way too much power due to the mostly capacitive load. Might not even need a transformer, using an inductor and relying on resonant ring up might be enough.