Cleaning up Switching PS output

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I bought a couple of cheap (read crappy - it's the only thing available in China) 5V/2A switching power supplies the other day, and the output is terribly noisy.

Any way to easily clean these things up? At $6 each, I'll toss them if there is no way to salvage them. I've tried a 2.2F cap, but no great improvement, and that's the limit of my meager knowledge.

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Cheers,

Tom

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Quote:
I've tried a 2.2F cap, but no great improvement,
These large cap's have a rather high impedance, so it's not surprising it doesn't clean up the output.

I suggest you add an inductor to the output, and 2 capacitors to ground: one capacitor 10 uF tantalum, and one ceramic fo 0.1 uF. Keep the groundleads as short as possible.
For the inductor: find one that can handle the 2 Amp DC, and has 100 uH as inductance.

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

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Nard's suggestion is a good one.

A 2.2F capacitor (SuperCap) is NOT a very good capacitor, at all. Its good for energy storage but it has a rather high effective series resistance that makes it very poor for this.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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My guess is that a low-esr switching capacitor across the rails, and 100nF ceramic, will do something, but not a lot.
The resonance is around 4MHz - I would have expected much higher even for china-caps. What I suspect is happening is that the supply lacks a shield between the input and output winding (such a shield costs money), and what you're seeing is the voltage across the ground lead (of the scope when the additional capacitors are on) when the primary drives a 300V square wave into the input-output parasitic capacitance.
The way to help that is a common mode filter; Salvage a ferrite tube from a monitor cable or other such, and run a wire pair through that as many times at it will fit.

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Thanks, all. I'll see if I can find a 100uH/2A inductor in the electronics market. Everything in China will be shut down next week, so I'll probably have to wait a while on this. I'll update this topic as soon as I have news.

Cheers,

Tom

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Quote:
Everything in China will be shut down next week, so I'll probably have to wait a while on this.
Again Chinese New Year ?? :)

Find a ferrite too, KKP's suggestion.

Quote:
I'll update this topic as soon as I have news.
We would appreciate that. Cheers !

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Nard,

China has two week-long holidays per year. One in the fall - The Autumn Festival/Mooncake Festival in October - and Chinese New Year in January/February. They are both Lunar Calendar based, so the week they occur changes every year.

Zài Jiàn!

Cheers,

Tom

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Learned again something today. Thanks tblough. Happy holidays !

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Isn't much of the ringing caused by the scope ground lead?