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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
7 comments
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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