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Old 10-26-2010, 01:05 PM
Lundin Lundin is offline
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Originally Posted by Coily View Post
If it is an inductor making the noise:

Noise is usually due to a mechanical resonance in the component that is excited by the electrical conditions of the circuit, a phenomenon known as magnetostriction, and does not indicate a defect in the part. It is very dependent on the application conditions and not always possible to eliminate by changes to the inductor alone. Changing the switching frequency is often the best way eliminate the noise.

Applying a dampening material (electronic-grade encapsulant, potting compound, etc.) may decrease the sound level produced or the increased mass of a larger inductor may dampen or shift the resonance to a different frequency.

Yes but when doing a proper EMC test at a 3rd party notified body, they don't give a darn whether the phenomenon appearing affects the output voltage or not. If they can conjure an unintended side-effect caused by an external frequency, the device won't pass the test.