So I built this power supply kit from Banggood:
https://www.banggood.com/0-28V-0_01-2A-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-Short-Circuit-Current-Limiting-Protection-p-1060253.htmlNow, I wasn't expecting it to be amazing or anything-- I mostly got it because I wanted a kit to start with and I needed a power supply anyways. The only real issue I had with the kit was that when I first powered it on, one of the diodes let out the smoke and tripped the breaker on the transformer (and before you ask, yes it was in the correct orientation), but when I replaced it with another of the same kind, it worked with no other obvious problems.
Everything seemed all well and good until I tried to power something with it (it was a cheap DMM) and... RIP. The meter died without any real warning. No smoke or anything.
Cut to a few days later and I had the bright idea to start troubleshooting with my USB Scope, and I found something I can't really explain. At three
specific voltage settings, the output is suddenly spiking to 32-38V.
At 3.9-4V the voltage spikes and exponentially decays back to the correct voltage in about 2.5ms.
At 12.4-12.5V it also spikes and returns in a similar curve, taking about 840 us.
Finally, at 20.9V the spike returns to normal in about 410 us.
The spikes can almost always be triggered by moving from a higher voltage down to the troubled one, with the spike happening right as I hit it, however sometimes the voltage will spike repeatedly if I leave it at that set level. The 12.5V level seems particularly susceptible to this kind of behavior.
These spikes ONLY occur at these three voltages, and the time I gave to return to normal is actually pretty consistent. There are some hints of a pattern in the timing (3x voltage normalizes in 1/3 the time). This suggested to me that whatever is happening is not a random glitch, but then-- why these specific voltages? I feel like there's a pattern I'm missing.
Note that I am NOT really asking for help fixing it or making it somehow not cheap junk. I've already bought a prebuilt power supply (the Korad KA3005 that people seem to think isn't too awful). I'm far more interested in learning what components and designs might be the culprit.
Does anyone have any hints or suggestions about what causes spikes like these? I'm still very much a beginner at this, so I'd appreciate any advice!