Audible Noise

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We have been designing LED drivers with TNY series, particularly TNY280 since long.

 

Recently I made a 25V, 700mA LED driver with TNY280.

It has a transistor current limiting at output.

 

Otherwise ok with a small heat sink, but there is always an audible noise ( though mild), which I just could not eliminate.

 

What is the source & reason of this noise?

How can I eliminate this sound totally?

 

Please HELP.

 

Somen Ghosh

Kolkata 

 

Please check if the design is sound by monitoring the voltage and current waveforms and check if there is excessive ringing.

You may also try to varnish the magnetics. This usually helps eliminate audible noise if it's the magnetics that is causing the noise.