Flyback transformers and HV generation - Page 1
Forum section: electronics / beginners

author: MaxSimmonds
author_rank: Contributor
timestamp: November 17, 2018, 09:16:25 am
content: Hi all!I'll apologise now for the brevity, I'm on my phone but I have a few burning questions that have been bothering me for a few days. (If anyone wants to see any datasheet, photos, or schematics it'll have to wait until I'm home!)So, I'd like to make a plasma speaker. The principal is pretty simple, as I'm sure you all know. Generate HV with frequency somewhere above 20Khz, and then modulate this with audio.Currently, I have make the plasma and all is well (using a 555 timer, IR2110 driver, and IGBT and a transformer).The arcs are not large, maybe only half a cm at best. But this is not my concern at the moment, it's driven from a 12v supply so they're going to be small.What I've started to realise is that I don't understand my transformer (that I made) very well, and I was hoping someone can clear a few things up for me.I first set out to make a "flyback transformer", I have one of those DIY inductors laying around (made by a company called ferrox cube, you basically chose a ferrite with a certain al value and wind accordingly). But, it seems to me that there's no such thing as a "flyback transformer" unless it contains the blocking diode. It's more how the transformer is driven that makes it a flyback? IE, the sudden discontinuous current?I wound thin gauge wire around the plastic bobbin to the top, then, I taped around, put the wire at the bottom of the bobbin, and started going to the top again. My reason for this (please correct me if I'm wrong!) Is that I want the electric field lines all in the same direction so that they don't cancel out, which is what I assume would happen if I went from bottom to top to bottom ect.? Then I wound a few turns of larger gauge around the inner (small gauge) coil.Can I ask what type of transformer I have made and whether it can be considered a flyback, or is it a coupled inductor (which would be used for a flyback converter?!?)?I really don't care what transformer I make, but I'd like to drive this differently (currently, the IGBT is the lowside switch which excited the primary coil, however this is heating the IGBT up a lot) using a half or full bridge topology, and since the ir2110 is a low and high side driver, I might as well. I'd also like to do some calculations to determine the amount of current through the primary and make sure the IGBTs won't fail, but that should be trivial. I just want to understand the transformer first!Can anyone help shed some light on this?Many thanks!Max

author: ArthurDent
author_rank: Super Contributor
timestamp: November 17, 2018, 02:43:46 pm
content: Google turns up lots of videos and DIY stuff.

author: Stray Electron
author_rank: Super Contributor
timestamp: November 17, 2018, 06:31:16 pm
content: I've made several flame speakers over the years. I build my first one for a high school science project in about 1968. You need to use a conventional (preferably audio frequency) transformer and not a flyback transformer. FB transformers are made to run at a fixed frequency (used to be TV sweep rate or about 16khz.)I don't understand why you're using a 555 timer for a speaker circuit, unless you just want a fixed frequency output. The ones I built took an audio signal and run it trough a fair size audio amplifier, then feed the output into a step up transformer (sometimes a filament transformer wired in reverse) and then to the electrodes. One big difference though, I actually placed my electrodes in a flame from a bunsen burner. The flame was much more conductive than just a simple arc. Feeding a solution of sodium or potassium nitrate or a similar chemical into the flame provided an ionized conductive path but it would work without it. I also found that wiring a 400 VDC source in series with the amplifier output and the electrodes helped. I used pieces or 1/8" brass welding rod for the electrodes and spaced them about 2" apart in the flame. The nitrate solution was held in a test tube and feed into the flame via an asbestos wick placed a couple of inches below the electrodes.If you're making a speaker then you need to feed it an AC signal so you're not going to be able to use any kind of transformer that has a blocking diode in it. That said, a friend of mine uses old FB transformers for some of his circuits and he blasts the diodes out of them by charging up a large cap to about 400 volts and then shorting it through the transformer and blowing out the blocking diodes.The flame speakers that I made actually worked quite well and the sound quality was at least as good as most of the cheap speakers that were on the market. Without the flame and the ionization you could get some sound out of an arc but it was barely recognizable and had a LOT of hiss in it.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 17, 2018, 09:20:29 pm
content: A lot of designs can be seen athttp://www.plasmatweeter.de/also in English. He uses a tube-based circuit with a TV sweep tube, I tried it and it works.