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SMPS noise sound

Posted by: ni.amir on Mon, 05/31/2021


I used TNY280 in 12V-2.2A power supply. In light loads for example in 70mA, it makes annoying noise sound in treble range (high frequency noise sound ).

But in high load the noise sound changes from high frequency to lower freq. that is not very annoying.

How can I remove or decrease this noise? Should I change transformer construction method or feedback or  ...?

With Best Regards



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Submitted by PI-Radiant on Thu, 06/10/2021

Hello Amir

 Thank you for considering our product for your application.

Could you please clarify if the transformer is varnished?

Would it be possible to share with us the Primary drain to source voltage waveform which would help us figure out the switching frequency for some of the test conditions where the noise is felt?

If possible, could you please share more information regarding the design such as magnetizing, leakage inductance?

Could you please let us know if the design was made as per suggestions in PIXls spreadsheet?





I used a Two-component polyester adhesive for varnishing. We immerse the transformers in the polyester liquid three times and in the end we put them in oven for 30 minutes for baking.  Could you please introduce best way and materials for dip varnishing to reduce audible noise of SMPS ??

I attached light load and full load state of drain-source voltage waveforms. In no load or light load or even in full load conditions IC skips the switching cycles and the frequency is decreased. In full load there are no skipping cycle very much but the audible noise is listened.

Also I changed the transformer structure from 1 layer primary to sandwich mode (two layers primary) and the noise decreased but it is not zero.

I checked the snubber capacitors for audible noise problem but they do not contribute in audible noise.

Unfortunately I didn't use the PIXLs but primary inductance is 1230 uH, leakage inductance is about 20 uH and maximum
flux density in the core is 2500 Gauss.

Thank you for helping