TNY264 - hisses when isn't load significantly

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Recently I designed a power supply based on TNY264 datasheet schematic and tested it.

It works perfectly but at small loads the TNY generates a loud hissing sound.
Only after load of about 100-120mA does the hiss fall to an acceptable level.
It becomes audible propably, when the power-supply stops an restarts several times per second because the load is too light to have it run continuously.

Please tell me what can I change to need a smaller load works correctly without hissing.


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Hi maghost,

Thank you for considering Power Integrations for your solution.
Is the transformer you are using varnished?
Applying varnish to the transformer generally reduces audible noise.
If audible noise is still present even with the varnished transformer, can you share an image of the PCB and the transformer construction so that we can help you more?

Best Regards,

Hi am replacing the TNY267 with TNY266 or 268 in the attached circuit diagram. The transformer core being EE20 , primary is 140turns of 0.15mm, secondary is 15 turns of 0.4mm for 12v o/p. Will it work or any further calculation is required.

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Hi Ch@r@n,

Please kindly raise a separate ticket or post for this one since you are referring to a different question.

Thanks and Regards,

Lupin The Third