#8: A Unified Board | Details | Hackaday.io

<p>It's been a busy couple of months behind the scenes -- this project is basically finished! I'll be breaking the final few updates into a couple posts, while I wrangle loans of camera equipment for the beauty shots. </p> <h1>Circuit Unification</h1> <p>Taking the different prototyped modules and banging them together:</p> <figure><img class="lazy" data-src="https://cdn.hackaday.io/images/4564281716833141406.png"></figure> <p><em>(you might have to click to embiggen)</em><br>I've paralled the mosfets for better heat dissipation. This doesn't help quite as much as one would like (since a lot of the losses are switching and not resistive), but it does help. The mosfet gate resistors are also paralled since they get <em>quite</em> hot before the arc is struck. I'm not sure why that behavior is occurring -- if you know, drop me a line!<br><br>The 4.3V zener diode (D5) for regulating gate bias is a carefully chosen value for this particular mosfet and circuit. Cranking the knob full-clockwise guarantees oscillations start, but doesn't set the bias so high as to cause excessive power draw and heating. The use of full knob range also makes adjustments more precise and controllable.</p> <p>A bank of four 33pF capacitors is a balance between heat distribution and board space. While the board itself has plenty of room (see below), I ran into

#9: Black FR-4 and transparent soldermask, by PCBWay | Details | Hackaday.io

<p>For the final build of this project, I wanted something special.</p> <figure><img class="lazy" data-src="https://cdn.hackaday.io/images/1192521717273710046.jpg"></figure> <p>Typical PCBs use a olive-green fiberglass core, layers of copper, and a (traditionally green) soldermask layer to protect the copper and define areas where solder/component pads should stick.  This board instead has a dyed-black fiberglass core and a transparent soldermask layer. This means that all traces are visible as their natural copper color, which is delightfully high-contrast against the black substrate. Component pads and other areas left uncovered by the transparent mask are plated (ENIG) gold. <br><br>This order of circuitboards was <em><strong>(partially) </strong><strong></strong></em><strong>Sponsored by <a href="https://www.pcbway.com/" target="_blank">PCBWay</a>! </strong>They covered about 60% of the cost of these boards, and I paid the remainder out-of-pocket. <br><br>There's <em></em>very few photos out there of real PCBs made using this stackup, so I'm taking the time to write out a review. <br><br>(Transparency: being partially sponsored will likely bias my opinions, but I did also pay enough to feel like I have skin in the game. I have not given PCBWay any editorial control and they will not have seen this review prior to publication. Photos have been lightly post-processed and are broadly representative of how things look irl under good lighting. An order number [visible on the unpopulated

Files | Plasma Toroid (sky-guided PCB edition) | Hackaday.io

Files | Plasma Toroid (sky-guided PCB edition) | Hackaday.io

#11: Design deficiencies, and what you can improve | Details | Hackaday.io

<p>I'm considering this project Completed, at least for the time being. I'm <strong><em>incredibly</em> </strong>proud of what I've created -- every design goal was achieved, and it looks even better than I'd dared to hope. <br><br>However, this is far, far from perfect. If I were to continue this project, I have a real hit-list of what could be improved.</p><h1>Overall System</h1><p>The biggest issue is that controlling drive intensity by adjusting mosfet feedback bias voltage is janky and unstable. A proper system would leave a bias voltage set with a trimmer, and use high-side limiting on the primary input current for primary drive control. I realized this kinda late in the design process, and wanted to reach "done" rather than do another round of prototyping.<br><br>Also, having a breakout board for the USB-PD trigger module is pretty inelegant. Having a trigger module on-board would be better, but when I started this project I was having trouble finding a suitable IC with decent availability in the US. Several folks have since suggested good candidate ICs. </p><h1>MOSFET and driving</h1><p>A straightforward error is that the gate-drive resistors have been undersized. The design shown in the video uses two 10-ohm 1206-size resistors in parallel (per mosfet), and they get incineratingly hot if

#12: v2, current control | Details | Hackaday.io

<p>After a year away, I'm returning to this project. It's time to come back and fix the deficiencies of Version 1.<br><br></p> <h1>The Problem</h1> <p>Version 1 of the plasma toroid controlled drive intensity with a potentiometer that adjusted oscillator mosfet bias voltage, which in turn changed the switching duty cycle. This isn't a great method of control. Changing the duty cycle introduces a variable phase delay which is harder to tune for. Also, since the drive is a sine wave running a low duty cycle leaves the mosfet in an intermediate half-switched state for longer, which isn't great for efficiency. Finally, low duty cycles would often result in loss of oscillation if the plasma was extinguished for any reason.<br><br>The better method is a dynamic high-side current limit. </p> <p>I'm accomplishing this with a buck converter based on TI's "Simple Switcher" line of ICs, specifically LMR14030SDDAR. This chip is a monolithic buck converter with integrated mosfet, and it really is simple to implement. It's also capable of running at up to 97% duty cycle which is perfect for a low minimum dropout.  Here's the reference circuit from their datasheet:</p> <figure><img class="lazy" data-src="https://cdn.hackaday.io/images/6500541758392745491.png"></figure> <p>This is a perfectly normal buck converter topology. Most buck converters are designed to hold a fixed

#13: v2, pushbutton arc start that isn't terrible | Details | Hackaday.io

<p>The <a href="https://hackaday.io/project/194683-plasma-toroid-sky-guided-pcb-edition/log/228419-7-how-to-ionize-xenon-the-arc-start-module">pushbutton arc start in version 1</a> was cool, but also kinda trash. First, it was super inconsistent with starting ionization on a cold xenon globe, and often took several seconds of button-pressing to do so. Secondly, the subcircuit had a bill of materials that was way<em></em> too expensive and was over-reliant on specialty components. The photoflash IC in particular both cost >6USD each (at quantity ten) and is an out-of-production last-time-buy part. The arc start module also needed two different specialty transformers and a particular model of gas discharge tube. Ridiculous. </p> <h1>Design for Production</h1> <p>What the arc start module <em>actually needs to do</em> is produce several kilovolts. A pulse of DC is fine, a few milliseconds of HV AC is fine, whatever.</p> <p>It took me a weirdly convoluted series of steps, but the end solution is easy: a donkey-simple flyback converter using one of the same xenon trigger transformers as the last design. </p> <figure><img class="lazy" data-src="https://cdn.hackaday.io/images/7232371758401906734.png"></figure> <p> MIC1551 (U1) is a spinoff from the classic 555 timer but reconfigured to generate a 50% duty square wave with only two external components. The values shown here run at ~43kHz which was chosen as an arbitrary ultrasonic frequency. This hasn't been optimized at all, and doesn't really