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?