Trap for young players... If you're disabling another...

Trap for young players... If you're disabling another interrupt within an interrupt, that disabled interrupt source may have already set its flag just before you've disabled it, causing a TACTOU situation. When the ISR returns, that supposedly-disabled IRQ is immediately invoked. I just spent an hour trying to debug a strange problem because of this race condition... :woozy_baa: #electronics

Like 31 Oct 2022 at 22:55 | Open on mk.absturztau.be

4 comments

niconiconi replied to niconiconi

Success. High-voltage supply and regulation are now fully functional. My fatally flawed analog power supply problem has been fixed in software. The burst-ON hack turned out to not "just a software hack" but kind of an optimal solution given the circuit components constraints. If I need a real hardware solution I'd just implement exactly the same control with RC timers and AND gates instead of an interrupt service routine. #electronics

Oscilloscope screenshots showing the ON signal and the regulated output voltage. The flyback converter is turned on in small 50 milliseconds bursts. The output voltage is a 550 V sawtooth waveform with 10 V ripple above and below the set point.

1 Nov 2022 at 17:49 | Open on mk.absturztau.be

niconiconi replied to niconiconi

More progress on the high-voltage impulse generator. The huge capacitors, resistors and inductors for pulse shaping are now installed for testing. They mostly work. But this test uncovered a serious problem - each time the circuit fires, I can hear an arcing noise, the oscilloscope also shows a weird glitch, likely caused by arcing. The generator is supposed to destroy the device-under-test, not itself! Now my suspect is the isolated DC-DC module. Just ordered a better one for another try... #electronics

Photo of the same circuit board, now with huge capacitors, inductors, resistors, and huge banana socket connector installed.

8 Nov 2022 at 12:46 | Open on mk.absturztau.be

niconiconi replied to niconiconi

Problem solved. The "arcing" sound during the impulse current discharge is NOT a fault. It's actually a common phenomenon in all high-current pulse circuits. The "snap" noise was caused by sudden physical deformations of the circuit board itself, due to Lorentz force from the intense current. #electronics

14 Nov 2022 at 21:16 | Open on mk.absturztau.be

niconiconi replied to niconiconi

Success! My first circuit board prototype of the IEC 61000-4-5 Combination Wave Generator (aka Lightning Surge Generator, aka Impulse Generator) is working after a month of development. This PCB has greatly improved safety and usability compared to the original perfboard. #electronics

Surge waveforms are compliant to IEC 61000-4-5's 1.2/50 μs & 8/20 μs requirements.
⚡ Open-Circuit Voltage:
- 1.02 kV, Front time: 1.33 μs, Duration: 53.60 μs
⚡ Short-Circuit Current:
- 484 A, Front time: 7.53 μs, Duration: 21.51 μs

Photo of the PCB prototype.

On the left there's a 120x160 LCD screen, four pushbuttons. USB power connector, a debug header, a microcontroller.

At the middle there's an isolation barrier, separating the low-voltage side and high-voltage side by a few centimeters for reinforced isolation. An isolated optocoupler and a isolation transformer are used for signal and power transmissions.

On the right there are various subcircuits. Most visible ones are a thyristor, massive capacitors, resistors, two toroidal inductors, and two large banana connector / binding post. Other supporting components includes a microcontroller, a flyback high-voltage power supply, a normally-on high-voltage SiC FET transistor for safety discharge, a floating high-side gate driver, among other things.

Oscilloscope screenshot of the output voltage and current waveform, showing the device is in conformance to the IEC 61000-4-5 requirements.

Comparison of the old and crude hand-built perfboard prototype and the new fancy PCB prototype.

14 Nov 2022 at 21:39 | Open on mk.absturztau.be