Electronics > Repair
strange low frequency switching noice from diy sg3525 smps
<< < (3/5) > >>
Herschel:

--- Quote from: T3sl4co1l on September 18, 2024, 08:07:18 pm ---I would be inclined to suspect EMI.  Try permutations of 'Y' capacitors. In particular, the one to bridge '-' is probably wrong, but one from there to output may be helpful.  Additional filtering (another CMC?), shielding (stuff everything into a box and filter all wires that pass through it) and testing are likely to prove fruitful.

Tim

--- End quote ---

I tried using the Y capacitors, and it did improved the noise under one "condition":

I was testing my smps with a 400 watt class D amplifier board, which is locally assembled one, I found out that the noise is created by that class D amplifier when I connect it to my smps. Does class D amplifers oscillates to create noise?, but after replacing that with a class AB amplifier, which I made, the noise just vanished! (still audiable when I hold my ears really close, covering the tweeters which I'm happy with)

So the *condition, only applies for the class ABs not Ds. And yes, the Y caps helped a lot

Is it a good idea to use a CMC with .1uf mylar filter caps only for the classD amp does it improves the performance and reduce noise?
ftg:
Could you post a picture of the full SMPS and your test setup?
The rectifier and electrolytic capacitor board looked like it was a separate unit at the end of cables.
Even on 60kHz the wires will have some inductances and currents will flow in funny ways.
T3sl4co1l:
Yes... a class D amp is itself an SMPS, to which all the same filtering considerations also apply.

In particular, the speaker output may not be well filtered, which puts EMI onto that lead, and by reaction, inversely onto the board itself, and thus up connecting cables to other equipment (and through all these cables, as antennas, into the air).

Filtering options are a bit more limited, because you need to know if the output is filtered at all for one (some class D amps have direct drive to the speaker, depending on coil inductance for SMPS filtering; this requires short wires and usually a ground connection to the speaker frame, and must only be done in self-powered speakers, not over any lead length), and thus whether to provide filtering specific to the outputs; and because the audio input itself cannot be filtered arbitrarily low, because of the audio itself; a common-mode choke can be useful here, filtering the input ground with respect to the shield/enclosure (EMI reference plane) while leaving the signal conductor alone (other than by effect of the CMC, and a little RFI filtering say 1nF + ferrite beads).

Tim
Herschel:

--- Quote from: T3sl4co1l on September 19, 2024, 08:13:13 am ---Yes... a class D amp is itself an SMPS, to which all the same filtering considerations also apply.

In particular, the speaker output may not be well filtered, which puts EMI onto that lead, and by reaction, inversely onto the board itself, and thus up connecting cables to other equipment (and through all these cables, as antennas, into the air).

Filtering options are a bit more limited, because you need to know if the output is filtered at all for one (some class D amps have direct drive to the speaker, depending on coil inductance for SMPS filtering; this requires short wires and usually a ground connection to the speaker frame, and must only be done in self-powered speakers, not over any lead length), and thus whether to provide filtering specific to the outputs; and because the audio input itself cannot be filtered arbitrarily low, because of the audio itself; a common-mode choke can be useful here, filtering the input ground with respect to the shield/enclosure (EMI reference plane) while leaving the signal conductor alone (other than by effect of the CMC, and a little RFI filtering say 1nF + ferrite beads).

Tim

--- End quote ---

the class D amp I'm using have an inductor + capacitor at its output, This is just a simple IR2153 class D amp


this is the most similar circuit I could find, also the maker of this amp have added some more components to it at the audio input side... and yes, ICs for powersupplies/inverters are used here
T3sl4co1l:
Ok, output filter choke, that's a start.

Looks to be single-side layout, which means no ground plane, and all the stray inductances wreak havoc on the EMI response in the 10s of MHz where those traces cease being good conductors but stray inductance takes over.

Tim
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod