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cheap chinese adjustable lab power supply kit on ebay ( 3AG1 , xiaolin )

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voltlog:
I assembled this power supply and also did some basic tests. I think there are some things that are not right with this power supply so I don’t think I will be using it in any project. For the full story please watch the video below.


For those who don't want to watch the full video I'm gonna list the problems I found: First I don’t like the overshoot behavior were seeing on power-on and I certainly don’t like that double drop waveform were seeing on power off.  Then there is the 50Hz oscillation that we can see on the output and I’m not sure if that’s caused by insufficient filtering on the rectified input or if it’s something else but I don’t like having that on the output of the power supply.

qu1ck:

--- Quote from: voltlog on March 21, 2018, 07:28:20 pm ---For those who don't want to watch the full video I'm gonna list the problems I found: First I don’t like the overshoot behavior were seeing on power-on and I certainly don’t like that double drop waveform were seeing on power off.  Then there is the 50Hz oscillation that we can see on the output and I’m not sure if that’s caused by insufficient filtering on the rectified input or if it’s something else but I don’t like having that on the output of the power supply.


--- End quote ---

So why not rule out insufficient filtering by measuring with a scope what's after the bridge rectifier and try and eliminate that part by providing stable DC from good power source? You will also have to provide another voltage for the upper rail, measure what is it's potential with standard AC input first.

voltlog:
Here is a measurement taken at the output of the bridge rectifier right on the 4700uF capacitor.

schmitt trigger:
Sorry for resurrecting an old thread but...
What are those oscillations?

exe:

--- Quote from: schmitt trigger on April 02, 2019, 01:20:04 pm ---Sorry for resurrecting an old thread but...
What are those oscillations?

--- End quote ---

Looks like ringing to me. Normally due to excessive inductance (including your oscilloscope probes), incorrect routing, and too sharp signal edges.

Or stability issues, as ringing tends to fade. Hard to say without zooming in and know how measurement was done.

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