Audible noise in CCIM
We designed 17V6A with TOP258YN. Audible noise appears after the transition from DCIM to CCIM. Some minor random harmonics are noticable in output ripple voltage at that moment. Any changes in regulation loop elements does not affect this noise. During DCIM converter is stable and silent. Can we reduce the noise by improving regulation loop? Is the only solution to lower magnetic flux?
We use regulator in attached JPG.
Thank you for your answer.
Best regards.
Comments
There are 2 things that you should do
1) Check to see if your loop is stable. The "harmonics" in the ripple that you mention. What is the frequency of these in the output ripple?. When you transition from DCM to CCM there is an increase in the loop gain. This increase can cause loop instability of the loop is not properly designed. Try to reduce the gain of the circuit by increasing the value of the resistor in series with the opto diode. Attach a copy of your schematic so I can comment further...
2) Once supply is stable, dip varnish your transformer. This should reduce audible noise.
According to AN-24 - good gloing and dip varnishing reduced audible noise to acceptable level.
Thank you for all answers.
