Interesting (but disappointing) Mini Buck Boards

I needed some cheap little vregs recently and had run out of and/or lost all of my useful-value 780x linear parts, so I decided to look at what people in this century use. 

I found some little buck boards roughly the size of a TO-220 package that looked exciting. These particular ones are QSKJ Mini DC-DC Buck Step Down Module model “QS-1205CME-3A”, Vendor page here, mine were 5pcs/$9 from Amazon.

Upon analysis they have serious issues with regulating under load, so the hunt for something decent continues, but the form-factor and advertised feature set are really compelling.


  • High-efficiency high-frequency synchronous buck instead of a linear heater^H^H regulator.
  • Solder-jumpers for 1.8,2.5,3.3,5,9,12V or a default (fiddly, tiny) adjustment pot output so you only have to stock one device – one easy-to-cut trace to disable adjustable mode.
  • Tolerates 4.5-24V input as long as out < in or so.
  • Good stability to input voltage variation.
  • ~0.25V drop-out.
  • Does appear to have a cutoff for over-current.
  • No perceptible ripple under various load conditions.


  • Voltage regulation manages maybe 600mA at 5V before droop becomes unacceptable (<4.8v).

…and that makes it basically useless for most applications. Test data below the fold.

Maybe it could be resolved with appropriate external capacitors and/or offsetting the adjustable to regulate right at a known load or something, but not being drop-in really reduces their charm.

Anyone know of a similar offering that doesn’t suck at output regulation?
(Rel: Anyone know if any of the low-end electronic loads are worthwhile? I’m not looking to spend real-lab-instrument money, but it’s come up often enough lately that I want to be able to dissipate a couple 10s of Watts through a at least stepwise-controllable resistive load).


Input stability and drop-out test:
Set 5V fixed output jumper
Input hooked to a gigantic bench supply
Output voltage and stability from a Tektronix MDO3012 oscilloscope showing both the bare waveform and DMM mode.
Output current by running through a BK 5492B bench meter
50Ω of resistors as a load

Input – Output
20 – 5.013
12 – 5.013
9 – 5.013
5 – 4.762
(and it doesn’t boost, so much under 5 cuts off)

Large load test:
Input hooked to bench supply at 12V
Abomination USB AF-AF adapter to connect a USB to Alligator Clip cable to a “1A/2A” load for testing USB Power supplies. Hand DMMs in series and parallel for voltage/current.

12V input, dummy load for nominal 1A (apparently 5.33Ω) and 2A (apparently 2.75Ω) at 5v
(1A setting) 700mA@4.2V
(2A setting) 1A@2.3V (LOL)

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2 Responses to Interesting (but disappointing) Mini Buck Boards

  1. Jcrist90 says:

    I got these today and tested. First, it’s a buck converter so the input voltage shouldn’t be lower than the output + ~1.5v.
    Second, I cannot confirm your results under load. I tested on 12.6 input and 5V fixed output – got honest 5.44V 1A without any issue. Did you measure the output voltage on the converter output directly, or on the load? It could happen that your alligator wire is the issue.

    • pappp says:

      I did just do the test with “Whatever was on the bench” including a pretty sketchy test load and some alligator clips of unknown provenance, so it’s possible there was a setup artifact.
      They’ve been sitting in my parts bin since, because I distrust them, next time I need a regulator I’ll have to try them again.

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