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Switching power supply whistling ??

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hameeds01

hameeds01

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I have a switching power supply 12v 50A, it runs perfect but the problem with that is it produces a loud whistling sound when a load is attached to it, I know that sound comes from a Transformer bcz of high frequency switching, is there any way to suppress this noise ??
 

If the switching frequency is above audible range, it's most likely a problem of controller instability, or possibly subharmonics of a current mode controller. If so, the controller has to be redesigned.

Some switch-mode controllers are changing to discontinous operation with low load, in this case the problem is "by design".

Or the switching frequency is basically audible, then you can't do much against it.
 

I've heard powers supplies make noise when going to discontinuous mode but this seems different.

There could be something loose in the coils and the magnetics are causing vibration.
 

You should replace the power inductor with a big one.
 

ilikebbs said:
You should replace the power inductor with a big one.
Click to expand...

y should i spend my money on it, My Power supply is running perfect other then the whistling sound, is there any cheap way to supress the sound
 

If it is iron core transformer, the sound could be due to vibration of the stampings, that results in loss of power as well. If it is so, you can try putting some varnish, that should solve the problem. Be sure that you dont have problems like excess heating due to execss load etc.
Raoof
 

I think you have two options:

- Wait for more funny suggestions. Sound absorbing enclosures haven't been mentioned yet...
- Try to understand the nature of the interfering sound. This requires at least to watch the SMPS operation with an oscillospe and
determine the switching fundamental and if the device is operating continously in the said situation. If you don't want to measure
in the circuit, a few windings pick-up coild near the transformer should be sufficient.

I assume that you already excluded loose core parts and similar trivial issues.
 

hameeds01,
You might try vacuum impregnating the transformer with transformer varnish. This involves:
1) Completely immersing the transformer in a container of varnish.
2) Placing the container under a bell jar connected to a vacuum source.
3) Running the vacuum pump until bubbles no longer appear.
.
This is often done in the aerospace industry fror small prototype runs of magnetic devices.
Regards,
Kral
 

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