Gregory's ServerThyristors arrived. Standard TO-220 packages, but they should be okay for a oneshot pulse up to 100+ amps, good enough for my surge generator to blow things up without blowing up itself. ⚡ #electronics
 29 comments
Galvanic isolation turned out to be the correct decision. Just had an electrical breakdown. The SCR was completely destroyed, feeding high voltage back to the gate, then the gate drive transistor arced, high voltage kept going back further to destroy the optocoupler. ⚡💥 The sacrificial optocoupler did its job to stop damages from propagating further... #electronics What killed my SCR? :blobcatthinking2: Either an arc over caused by low creepage & clearance, or max di/dt violation. Need to try again tomorrow... #electronics Problem solved, a n00b mistake. The SCR was incorrectly wired as a high-side switch, not a low-side one. As the load was switched on, the gate and cathode would rise to 200 volts, an exploding gate drive transistor was guaranteed... ⚡ 💥 Replaced it with a high-voltage one as a temporary fix, now it works fine. :blobfacepalm: #electronics The next long-term goal is converting this "Improvised Electronic Device" to a proper impulse generator that can produce a proper 8/20 µs surge per IEC 61000-4-5. The 4000 V / 2000 A Class 4 test is difficult to implement, but the basic 500 V / 250 A surge should be easy. #electronics IGBTs are not really much better it seems... Common discrete devices only exist below 2000 volts, roughly the same range. #electronics Pulse capacitors also become hugely expensive at 2000 volts... 2000 volts really looks like a barrier in power electronics. Beyond this point components suddenly become either hugely expensive or come with inconvenient packages... But if you stay at 1500 or 1700 V, it's much easier... #electronics Now I need 1500-volt, 6 µF pulse capacitors, what are my options.... :blobcatthinking2: It turned out the choices are pretty limited, basically three: Kemet R75 & R76 series, Vishay MKP385 series, and Cornell-Dubilier 940C & 941C series (this one seems to have a cult following by Tesla coil builders). 941C is currently the cheapest, 1.5 µF for just $11. But I need FOUR and only THREE are in stock until 2023. :blobfacepalm: #electronics High-voltage flyback transformers look like a dying breed these days. All the experimenters seem to get them either from old CRTs or random eBay surplus sources. But my project needs to be replicable from standard parts on the product catalog of a big vendor, so random components are unacceptable. CCFL lightning transformers seemed to be a good source in the past decade, but most are discontinued in this LED age. I guess I'll just stop wasting time and use a pre-made SIP DCDC module instead. #electronics The datasheet says the pulse resistors I'm using to build a 8/20 µs surge generator are themselves tested by a 8/20 µs surge generator by the vendor. Now the cycle is complete. :blobcatgiggle: #electronics You know pulse resistors are specialized when a manufacturer in China sells them at a higher price than Vishay in the US... And the official website shows zero stock. #electronics Huge pulse capacitor is huge. Cornell-Dubilier 941C series #electronics 0.1 Ω pulse resistors arrived. Time to do more test on the original quick-and-dirty HV pulser before building a proper one: 31.2 A short circuit, 200 V open-circuit, so the effective ESR is 6.4 Ω, a bit on the high side. The di/dt is high, 10-90 rise time is just 400.0 ns, it's 65 A/µs - I'm already violating the absolute maximum of the SCR. #electronics Saying I'm building a "8/20 μs impulse surge protector tester" sounds boring, I think I'll start calling it a "0.3 megawatt pulser" instead. I hope I can rightfully call it a "megawatt pulser" when I break the 2000-volt barrier one day... :blobcatgiggle: #electronics Just found a workable solution to switch 4000 volts and 2000 amps. Time to go old-school!!! Except there are three problems. The tube has no trigger electrode, only free running is possible. Each tube costs over $200. Also, each tube is filled with 5.44 MBq of radioactive tritium ☢️ ! #electronics Just finished the construction of my new 8/20 μs impulse generator. Its output surge should be in compliance with IEC 61000-4-5 now, but I haven't checked it yet. Need to get some sleep and continue the test tomorrow. Working with lethal voltage at midnight is definitely not a good idea... #electronics My impulse generator's current output failed to meet the standard waveform requirement. The rise time is 50% too short. I think I didn't wind that inductor correctly. Just ordered a simple LCR meter to continue the experiment (trimming an inductor with a oscilloscope or VNA is just too awkward). #electronics LCR meter arrived, indeed, the inductor I winded was 50% too low. I pushed the windings together while looking at the readings, within 10 seconds I brought it within design specification. Time for a test... Then I immediately blow the entire circuit up by connecting 200 V to 5 V input... ⚡💥 :doge: #electronics Success, the output waveform of my 8/20 μs impulse generator prototype is now IEC 61000-4-5 compliant! Peak current: 200 A New plan: abusing a MOSFET gate driver to drive a SCR's gate to get high-side switching. Now I need to figure out how much Common Mode Transient Immunity do I need. My circuit is *literally* a surge generator. #electronics Rewired the isolated DC-DC converter to float on top of the high voltage instead of ground. No more explosions, even a small-signal transistor can drive the gate with ease. #electronics Look at my gate turn-on waveform... Man-made horrors beyond comprehension. #electronics In electronics, everything is an LC resonator if your layout is bad enough. #electronics |
still waiting for the new isolated DC/DC converters to arrive (I already have some but cannot find them anymore) before I can start the pulsed power experiments... It's not technically required but I assume allowing 200 volts to flow back into your logic circuits really isn't a good idea... #electronics