no load & full load both causes audible noise how can I fix ? Nobody knows?

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I have designed a 24V 1.5 A output power supply with top HX 257 YN. I have an audible noise problem especially at no load condition.

When I investigate the drain-source waveform I see pulse punching operation. I thing this is the main reason for the noise.. How can I fixed the problem without changing the transformer design? I tried to change I limit of the IC but it doesn't make any help.. I also applied to change the feedback circuit in accordance to the notes on PI university in "how to fix... audible noise" section.

At full load condition the noise increases with increasing load current, at over current condition for 220V AC input the noise is very high and top switch does not turn off. As I try to use power limiting circuit PI expert says no need any power limiting resistors for this design..

Can Any body help?

Hi,

Our device will enter into Burst mode of operation in order to minimize the no load power consumption.

However if the correct transformer construction techniques are not used the transformer may produce audible noise sometimes. Please follow the transformer construction techniques suggested in the below mentioned application note

http://www.powerint.com/sites/default/files/product-docs/an24.pdf

Some types of ceramic capacitors used in primary clamp circuitry can be very noisy. Replace the ceramic capacitor with a plastic film capacitor or use a Zener clamp.

Please verify if any component on the board has got damaged physically.

Could you please share the schematics, Layout and PIExpet files in order to analyze the issue further.

Regards,

PI-NANO

Hi,

Please visit Fixing a Flyback Supply that has Audible Noise video at the following location

http://www.powerint.com/en/pi-university/courses/fixing-flyback-supply-has-audible-noise

This video should help in resolving your issue.

Regards,

PI-NANO