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niconiconi

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

The high current discharge tube GXH series double electrode spark gap is a gas discharge tube, sealed in a glass/metal casing. It can provide tubes with a DC breakdown voltage ranging from 0.50KV to 5kV. This is represented by the number or number following the letter and is expressed in hundreds of volts.
Description of High Energy Ignition Spark Gap Tubes: The GXH Series of 2-electrode spark gaps are gas discharge tubes, hermetically sealed in a glass/metal envelope. Tubes with a DC breakdown voltage in the range 0.50KV to 12 kV are available. This is signified by a numeral or numerals following the type letters and is expressed in hundreds of volts. Applications of High Energy Ignition Spark Gap Tubes: • Single-shot pulse generators • Turbine engine ignition circuits • Medical lithotripsy • High energy switches Physical Characteristics of High Energy Ignition Spark Gap Tubes: All ratings given in this data sheet a reab solute, nonsimultaneous ratings. It is the equipment designer’s responsibility to ensure that they are not exceeded. The spark gap life depends on circuit conditions such as peak discharge current and duration, charge transfer per discharge and the repetition rate. Charge transfer, single discharge (8/20 ms waveshape): 0.5C max Cumulative charge transfer: 6000C at 0.81 mC per discharge at 1 Hz Operating temperature: -55 to +125 C. Mechanical shock, half-sine (to B.S. 2011 Es): 40g for 4ms Mounting: screw mounted Radioactivity: tritium (3H), 5.44 MBq (147 mCi) max per device.
21 Jul 2022 at 7:28 | Open on cybre.space
11 comments
niconiconi replied to niconiconi

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

24 Jul 2022 at 16:21 | Open on cybre.space
niconiconi replied to niconiconi

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

25 Jul 2022 at 8:24 | Open on cybre.space
niconiconi replied to niconiconi

I found the solution for switching 2000 volts - two thyristors in series should be able to handle it. I was worriying about off-state leakage current due to voltage balancing resistors in the original capacitor discharging circuit. But this problem disappears in the standard 8/20 μs impulse generator, it already has two 20 Ω resistive loads, this diverts leakage mostly to the ground instead of the load, making the series switch connection feasible again.

Capacitor size and cost are still the problem. Using non-pulse rated capacitors is perhaps an acceptable workaround if I'm willing to replace them once in a while. A lifetime of 10,000 shots is practically infinite for my purpose. #electronics

I found the solution for switching 2000 volts - two thyristors in series should be able to handle it. I was worriying about off-state leakage current due to voltage balancing resistors in the original capacitor discharging circuit. But this problem disappears in the standard 8/20 μs impulse generator, it already has two 20 Ω resistive loads, this diverts leakage mostly to the ground instead of the load, making the series switch connection feasible again.

26 Jul 2022 at 16:04 | Open on cybre.space
niconiconi replied to niconiconi

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

27 Jul 2022 at 10:54 | Open on cybre.space
niconiconi replied to niconiconi

Success, the output waveform of my 8/20 μs impulse generator prototype is now IEC 61000-4-5 compliant!

Peak current: 200 A
Front time: 7.05 μs
Duration: 21.24 μs #electronics

A homebrew perfboard with four huge HV capacitors, some large HV power resistors, an air-core inductor coil, and a TO-220 thyristor at the center. At the left, there's a big red button, galvanic isolated from the HV power domain, for triggering the surge. At the leftmost side is a ready-mode HV power supply module.
The standard 8/20 μs impulse current waveform in IEC 61000-4-5. [Figure 3 – Waveform of short-circuit current (8/20 µs) at the output of the generator with no CDN connected] Front time: T f = 1,25 × Tr = 8 µs ± 20 % Duration: T d = 1,18 × Tw = 20 µs ± 20 % Undershoot: 0% to 30%. NOTE 1 The value 1,25 is the reciprocal of the difference between the 0,9 and 0,1 thresholds. NOTE 2 The value 1,18 is derived from empirical data.
Oscilloscope measurement of the output waveform of the actual surge generator. Rise time is 5.363 μs, peak current 194 A, no undershoot.
Same oscilloscope trace with cursor measurement of time interval between the instant at which the surge voltage rises to 0,5 of its peak value, and then falls to 0,5 of its peak value. Duration is 18.00 μs.
27 Jul 2022 at 14:34 | Open on cybre.space
niconiconi replied to niconiconi

The only problem I need to solve now is that the entire circuit exploded after firing the first shot. ⚡💥 I believe it was the same mistake and failure mode - the thyristor was wired as a high-side switch this time deliberately for convenience. As soon as the thyristor is turned on, the gate voltage rises to 500 volts.

I thought the transistor was protected by the new diode I added in series, but no, it's again a n00b mistake. The base-collector junction of a BJT is also a diode, and you can't connect any diodes in series without an RC snubber to balance the voltage. Without balancing, series diodes simply break down one after another. #electronics

The only problem I need to solve now is that the entire circuit exploded after firing the first shot. ⚡💥 I believe it was the same mistake and failure mode - the thyristor was wired as a high-side switch this time deliberately for convenience. As soon as the thyristor is turned on, the gate voltage rises to 500 volts.

27 Jul 2022 at 15:00 | Open on cybre.space
niconiconi replied to niconiconi

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

27 Jul 2022 at 17:17 | Open on cybre.space
niconiconi replied to niconiconi

CMTI: 100 kV/μs. Oh, it's more than enough... #electronics

27 Jul 2022 at 17:21 | Open on cybre.space
niconiconi replied to niconiconi

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

29 Jul 2022 at 14:31 | Open on cybre.space
niconiconi replied to niconiconi

Look at my gate turn-on waveform... Man-made horrors beyond comprehension. #electronics

A step signal, with extremely large overshoots and ringings for several microseconds at the rising edge.
29 Jul 2022 at 14:35 | Open on cybre.space
niconiconi replied to niconiconi

In electronics, everything is an LC resonator if your layout is bad enough. #electronics

29 Jul 2022 at 14:38 | Open on cybre.space
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