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

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exe:

--- Quote from: blueskull on April 03, 2019, 10:05:33 am ---100Hz=50Hz*2, sounds familiar? When you full bridge rectify a 50Hz signal, you get 100Hz.

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That's not the point I'm trying to make :). I sort of understand where 100Hz comes from. But I question the regulation of this power supply.

exe:

--- Quote from: mikerj on April 03, 2019, 12:21:36 pm ---Capacitors across bridge rectifier diodes certainly are helpful.  Despite the mains frequency being low, the rectifiers still switch on and off quickly, generating high frequency harmonics.  As I said, you will find these capacitors in linear supplies where low noise is important.

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I've never seen people providing measurements of this "improvement". Looks like a cargo cult to me. So far I only found one attempt to measure it and the result was not in favor of added capacitance.

floobydust:
I think 72mVpp of mains freq. ripple is normal, assuming there is a load on the power supply and the filter cap is not a fake.
Every second peak being lower I have seen as crappy power quality where the mains sine-wave is distorted. A lop-sided third harmonic.

The very high freq. pulses could be caused by many things. Whether it's the PSU oscillating or a mains power quality issue, or both- need more tests.

exe:

--- Quote from: floobydust on April 03, 2019, 06:08:52 pm ---I think 72mVpp of mains freq. ripple is normal

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I wouldn't call this normal. No regulator or linear psu I've seen so far had such horrible ripple (unless broken). Just compare this to specs of 7505 or lm317.

I like the idea to check the power quality. Can be "modified sine" or something. But still, normally regulators have 100kHz+ loop bandwidth, so it should be a different waveform. So, I think something is wrong with it.

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