Post AlMIn8qNjsx3KCOjlg by skyguided@cathode.church
(DIR) More posts by skyguided@cathode.church
(DIR) Post #AfRA6YrnHBYFMZhESe by skyguided@cathode.church
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presenting without elaboration
(DIR) Post #AfRA6Z5GT6KK2LzzSS by skyguided@cathode.church
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best hope that this design is solid, because the board and components are getting ordered rn
(DIR) Post #AfRA6ZIjf16Oi8IkSG by skyguided@cathode.church
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that 1k through-hole resistor is there becaussse it was either have a resistor do double-duty as a jumper wire, or switch to a four-layer board just for one trace. not a good solution but maybe the least-bad.
(DIR) Post #AfRA6ZRx6kTVAic6oy by skyguided@cathode.church
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update:realized wait, LTspice can totally calculate power dissipation; I ought to see if my components are gonna cook.fine: MOSFET drawing somewhere like 12-15W which is A Lot but I planned for a heatsink.probably not-fine: >10W on an 1808 capacitor, 400mW on a 0603 resistor🌶️ ♨️ 😅
(DIR) Post #AfRA6ZZOf4QhXo63QO by skyguided@cathode.church
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prototype board for only run short durations i guess
(DIR) Post #AfRA6ZgUEi6JtnPiTY by skyguided@cathode.church
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me: i need to think very carefully about this board layout and I want things to be clean as possible.other folks, with apparent success:
(DIR) Post #AfRA6ZoHliL6Hz3wdE by skyguided@cathode.church
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(and I'm running way less power than that)
(DIR) Post #AfRA6ZvjK2IIf4XtEe by skyguided@cathode.church
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Boards arrived!
(DIR) Post #AfRA6a2otfxv13rYHo by skyguided@cathode.church
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The field-wiggler is operational, at least partially.Pictured: wirelessly lighting an ampoule of neon.
(DIR) Post #AfRA6a9uTJdXN3BDKy by skyguided@cathode.church
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Problems: - getting some higher frequency noise on the mosfet gate, probably some sort of parasitic resonance. May or may not be significant.- drive coil gets *really* hot, fast. 18ga wire apparently isn't adequate for this much RF power?- I've blown up three out of my five mosfets (and that's not an inexpensive component). Worse, I'm not sure exactly *why* they've failed.
(DIR) Post #AfRA6aHi0JsJlEpRUe by skyguided@cathode.church
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Also I'm still waiting on my larger xenon globe.
(DIR) Post #AfRA6aNjduhC3veFt2 by skyguided@cathode.church
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Here's what the board looks like with the lights on.
(DIR) Post #AfRA6aVXAuvyS7IU2i by skyguided@cathode.church
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Right, of course, my intuition for "how thick wire do I need for a given amperage" is totally wrong because the skin effect depth at ~10MHz is like 20 micrometers. No wonder my 18ga coil got ✨toasty✨
(DIR) Post #AfRA6adKhvAkqIwiCO by skyguided@cathode.church
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I could buy litz wire.(Thanks @Hearth for offhand mentioning litz wire years ago!)Ultimately though I do want this to be a PCB coil which should be fine? 1oz copper traces are 35μm thick so standard current-capacity calculator tools should be applicable.
(DIR) Post #AfRA6al8EvPXEUawM4 by skyguided@cathode.church
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Decided to play with this device a bit more. Characterized my inductors, made another inductor with only two turns instead of three. I don't have an LCR meter so uhh used the 1kHz calibration output on my scope to ring a little parallel-LC resonator circuit and measured the frequency.To my great surprise, I also found that the device performs much better at ~12v than the ~20 that other folks have run previously. Still not sure what exactly is causing the ~100mhz ringing.
(DIR) Post #AfRA6asvlveJcgFAVk by skyguided@cathode.church
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heck I keep pulling my own posts back up to see how cool this photo is :blob_ooh:
(DIR) Post #AfRA6azJOCklwTEGSO by skyguided@cathode.church
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update on the ~100mhz ringing:thought about it some more, and did some more poking at LTspice. While the previously highlighted axial resistor might well be inductive, it's hardly conducting any current. Not nearly enough to produce that kind of oscillation. My new suspect: the parasitics on the mosfet itself (plus a bit of pcb trace) are acting as resonant LC circuit. Turns out this is totally a known phenomenon if external gate resistance is too low. I had been thinking of my 2Ω2 gate resistor as part of a phase-shift RC circuit (that's how it was presented in previous work I'm referencing), but it also is dampening the parasitic LC resonance.Here's a video of a lovely gentleman going in-depth on mosfet gate ringing and necessary resistor valueshttps://www.youtube.com/watch?v=6plZ2iOI0d4
(DIR) Post #AfRA6b5h0TrEGGDMP2 by skyguided@cathode.church
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should be able to test this tomorrow. and I'm... having this feeling like I've rapidly departed from "dabbling at some electronics" and entering territory of "this legitimately qualifies as electrical engineering".it's a funny feeling.
(DIR) Post #AfRA6bEuSDEKiqWilk by skyguided@cathode.church
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goddammit blew up my last FET.What I'm tempted to do is order more of them and keep fucking around.What I should actually do is redesign this board based on lessons learned and include some more self-protection features.
(DIR) Post #AfRA6bM01qtx4pqNou by skyguided@cathode.church
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problem: no overvoltage protection on the mosfet gateplan: add zener/TVS clamping diodeproblem: mosfet failure to oscillate creates possible overcurrent conditionplan: current-measuring shunt + op-amp + etc to force mosfet gate low if device overcurrentproblem: layout is kinda bad for parasitics.plan: make the layout less bad.
(DIR) Post #AfRA6bT5bUZZQpA2s4 by skyguided@cathode.church
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swear someday I'm gonna do my best to explain wtf is going on for all the non-electronics critters who so kindly follow mein the meantime this is raw projectblogging
(DIR) Post #AfRA6baBB8FBmoThvE by skyguided@cathode.church
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rawblogging.
(DIR) Post #AfRA6bhyi8TyB07w4u by skyguided@cathode.church
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me: what's the deal with HV creepage (arcing/breakdown) distances under surface-mount capacitors? Seems to violate IEC design guidelines for minimum spacehigh-spec capacitor mfg: Hey here's some information about this exact question.https://www.johansondielectrics.com/impact-of-pad-design-and-spacing-on-ac-breakdown-performance
(DIR) Post #AfRA6brC9rr4daRIRc by skyguided@cathode.church
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like this is something that seems particular for electronics part manufacturers, even moreso than most industrial products: they go out of their way to show you *exactly* how best to use their shit. It makes learning about how to actually make stuff so, so much easier. You might need to wade through a forest of datasheets and application notes, but information is the opposite of obscured.
(DIR) Post #AfRA6byzgs5r1m5WbI by skyguided@cathode.church
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what people think electronics design is: routing pcb traces, brandishing a soldering ironwhat it actually is (much of the time): squinting at poorly-photocopied performance curves in AZ23C51OMGWTF.pdf with calc.exe open on the 2nd monitor.
(DIR) Post #AfRA6c8D8bSxUMOsy0 by skyguided@cathode.church
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All right, so, I have this mosfet which I expect to be dissipating a fair bit of power (several watts, potentially >10W). In the previous prototype I used a THT part (SO-247) with a bolt-on heatsink, which worked pretty well.Ultimately I'd prefer to use a surface mount part, and the device is also available in D2pak-7. My plan was attach the tab to an oversized pad, drop an array of thermal vias to the ground plane on the opposite side, and mount the entire (single-sided) board's ground plane on a shared heatsink.The problem is the thermal tab on this device isn't connected to ground, but instead is the pin for Drain. So I can't drop thermal vias to the ground plane. Is the expectation that I use a top-mount heatsink, dissipate heat through a big power plane for Drain on the board's front, or what?datasheet https://www.qorvo.com/products/d/da008707
(DIR) Post #AfRA6cOABIE6Hprcpc by skyguided@cathode.church
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Here we go, a Revision 2 of the board! I think it's ready to send to the fab, but inevitably I'm gonna find some small things to tweak after posting.Light blue rectangle is the outline of a big heatsink on the back side of the board.Thanks to @gsuberland and @electronic_eel for their input on thermals :)
(DIR) Post #AfRA6cchJFqv0ufEUC by skyguided@cathode.church
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new boards already arrived!ngl I'm a bit spooked by how fast and I inexpensive it was, even though there's pretty explicitly some kind of promotional/loss-leader pricing going on.Also these are 0.8mm boards (half of "standard" thickness) which should help with both front-back thermal conductivity and make the two-layer inductor a little more inductor -y.
(DIR) Post #AfRA6craPtlJl5d7h2 by skyguided@cathode.church
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oh yeah, seen in action here is a hot tip I'm only recently internalizing:if you're making a thing and it has screw and/or mounting holes, mark the screw size/spacing directly on the object if at all possible.
(DIR) Post #AfRA6cyK0r9M5ymVBw by skyguided@cathode.church
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it is with profound excitement that I'm able to finally unshroud the project I've been working on:xenon plasma toroid
(DIR) Post #AfRA6jMIGdtFu42jOC by skyguided@cathode.church
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(also I had to duck the volume in this clip because my "let's gooo" was too loud)
(DIR) Post #AfRA6mX2T9GfkG5r3Q by skyguided@cathode.church
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tried to run the toroid off of my beefier bench supply and blew a mosfet. It's looking like the driver is probably drawing a lot more current than simulated. The miniware psu (and the USB-PD supply) I used yesterday handles brownout pretty gracefully, but I suspect the bargain bin bench PSU is less graceful. Part of the higher power draw could be due to messy switching, but if I lower the primary cap values in the sim to 66pF (from the nominal 99pF) I get results more similar to the observed circuit. I don't think the frequency or temperature is high enough to cause that kind of de-rating but who knows, could be as simple as one of the three capacitors has failed. Going to order some more caps, this time explicitly marked as low-ESL. Still not sure what's up with the coil getting blazing hot.
(DIR) Post #AfRA6onm1tqImjwFPs by skyguided@cathode.church
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Good news is, @x44203 was totally right about the apparent higher-frequency jigglyness of the mosfet gate trace being due to my scope probe having too long a ground lead. Using the spring-probe shows much cleaner waveform!
(DIR) Post #AfRA6rxSIMMyZdUWQK by skyguided@cathode.church
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still not the clean sine-wave I'm hoping for, but better.
(DIR) Post #AfRA6uQF8IaMDUyXZY by skyguided@cathode.church
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...not the exact capacitors I have installed, but similar.Using a bank of only three is *definitely* asking too much, even if I think things aren't quite as bad as 300°C/W. Note the log scale on x-axis.
(DIR) Post #AfRA6xxfyS6xC3dmbI by skyguided@cathode.church
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Sincerely though, does anycritter have ideas on why the two-turn 1.9uH PCB coil gets so dang hot? According to the saturnPCB calculator / IPC 2152, I'd expect less than 30°C rise to steady-state even taking skin effect into consideration, based on my ltspcie sims expecting ~12 peak amps at ~13MHz (sinusoidal). I see like 70°+ temperature rise within a minute. Guessing there's something going on with inductor energy getting dumped as heat, so resistive load calcs go out the window. But I have no idea how to reason about those possible effects.
(DIR) Post #AfRA70NH0Fm6g1dFmC by skyguided@cathode.church
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...I suppose the board is taking like 40W input so clearly the power needs to go *somewhere*. I was hoping that most of the somewhere would either be making the xenon get all bright, or else drifting away as legally iffy radio.
(DIR) Post #AfRA72rpjbPOPNwggi by skyguided@cathode.church
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lol so ended up just using I^2 *R just given DC resistance of a few tenths of a ohm and amperages in the 6-10A range...that's multiple tens of watts of heat.Very rough estimates of thermal mass give many degrees per second rise. ...yep there's a problem.So the standard trace width calculations just aren't remotely applicable here apparently!
(DIR) Post #AfRA75WfqjGWed4Kci by skyguided@cathode.church
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I now slightly better understand why other folks haven't used PCB inductors here. I suspect I might still be able to donut with much lower amperages though! If I get down below 3A in the inductor, that's only like four watts heat rather than dozens.
(DIR) Post #AfRA77y2lwLaE5tDYu by skyguided@cathode.church
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Here's a li'l gif of my inductor coil trying very hard to burn itself to a crisp. Spot-point temperatures come on-screen near the end.
(DIR) Post #AfRA7ASxTyGRyYMw1g by skyguided@cathode.church
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~130°C in about 30 seconds.
(DIR) Post #AfRA7CtyQV3vWv1XPc by skyguided@cathode.church
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writeup updatedhttps://hackaday.io/project/194683-plasma-toroid-sky-guided-pcb-edition/log/227533-i-would-like-my-circuit-to-not-cook-itself
(DIR) Post #AfRA7FwD8ddOwj5roe by skyguided@cathode.church
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More progress on the plasma toroid! More videos! Less overheating!!Writeup at https://hackaday.io/project/194683-plasma-toroid-sky-guided-pcb-edition/log/227790-tweakinHigher-quality vid at https://www.youtube.com/watch?v=rEc76ckTJcg
(DIR) Post #AlMIn8WsuNM6LjHANU by skyguided@cathode.church
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UPDATE:I've finally released KiCAD source files for the plasma toroid driver.still need to flesh out documentation.https://hackaday.io/project/194683/files
(DIR) Post #AlMIn8iEECQguuaE3k by skyguided@cathode.church
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and I don't think I'd actually posted the full schematic here yet :3
(DIR) Post #AlMIn8qNjsx3KCOjlg by skyguided@cathode.church
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(feel free to roast)
(DIR) Post #AlMIn8xpICuFhHsgN6 by skyguided@cathode.church
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video status is: still need to shoot one more bit of pick-up footage, do a bit of polish on graphics, finalize the edit, sound cleanup, color grade. So coming a lot closer to done, at last.
(DIR) Post #AlMIn95cpD925TWuWm by skyguided@cathode.church
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the actual dang build was done in like, May.
(DIR) Post #AlMIn9DQMDNoTfB8gS by skyguided@cathode.church
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AND IT IS DONE"A plasma toroid for the modern era."https://www.youtube.com/watch?v=Bl3zHuih_CY