Ölbaum2d ago

I bought these buck converters to power a 12V fan with the 24V power supply of my soldering iron, and when I powered one on with 24 V, it immediately smoked. I’m pretty sure I didn’t reverse the polarity (unfortunately, I desoldered it, now,) but I didn’t connect anything to the output, and now I notice that one of the pictures say not to use with no or light load (< 10% of output power.)

Is that really a thing? #Electronics

https://www.amazon.de/dp/B0FZK4249L

Pack of 6 DC-DC Buck Converter, 4.5-28V to 0.8-20V Step Down Converter, MP1584EN 3A Power Downward Adjustable Voltage Regulator Module, Adjustable Converter 24V to 12V, 9V, 5V : Amazon.de: Business, Industry & Science

Pack of 6 DC-DC Buck Converter, 4.5-28V to 0.8-20V Step Down Converter, MP1584EN 3A Power Downward Adjustable Voltage Regulator Module, Adjustable Converter 24V to 12V, 9V, 5V : Amazon.de: Business, Industry & Science

Show threadrawe

@oscherler the datasheet I found states: "At no load or light load, the converter may operate in pulse skipping mode in order to maintain the output voltage in regulation. "

It should not self-destruct, but the output voltage might be more unstable as desired. Unless whoever built that module did some questionable component selection which is entirely possible for those cheap boards.

One thing that can lead to smoked SMPS ICs is series inductance in the supply lines combined with small input capacitance with low losses (ceramic capacitors) and running it near the maximum voltage. I did some measurements on such a board and the 48V supply had 30V ringing on it (series resonant circuit of parasitic input inductance and input capacitance) with an absolute maximum rating of 60-odd volts that's a big no no and was the cause of that specific issue. Parallel input electrolytic capacitor = oscillations gone = chip survived. (I am a big fan of derating and safety margins so stuff lives longer....)

Apr 1 at 8:31pmWeb
Show threadÖlbaum7h ago

@stereo4x4 So I put a small load on a new board, a 1.6 V LED with a 1.2 kΩ resistor, which results in 15 mA at 20 V. I tried it with the lab power supply up to 26 V, no problem. I transferred it to my 24 V power supply, turned it on, it smoked immediately.

I checked on the oscilloscope for peaks at power on, but there aren’t. Anyway, I used a switch on the 24 V side when it smoked. >>

cc @diver300

Show threadÖlbaum7h ago

@stereo4x4 @diver300 For the third one, I powered it on the lab power supply up to 30 V with the load. Tuned the output to 12 V. Tested power on and off several times with and without the load. Transferred it to the other supply. It works.

I suspect the culprit is the combination of (1) steep input voltage increase when switching on the 24 V with a rocker switch, compared to turning on the lab PS, (2) low output voltage (around 5 V) at factory settings, and (3) small or no load at the output.

Show threadMalin Dixon5h ago
@oscherler @stereo4x4
I have seen a buck regulator that didn't like a slow rise of input.
The regulator that is in an Arduino MKR CANbus shield is quite crude and can spike to 7 V on a 5 V line if the voltage rises slowly. If maybe that your buck regulators manage to be sensitive to fast rise.
Show threadrawe1h ago
@diver300 @oscherler just FYI: had the same behavior (rocker switch with lots of contact bounce = blown up IC, lab PSU no issue) with the 48V dcdc mentioned earlier