DC-DC SMPS Inductor got sound!

[mongater]

HI,
Sorry ,if there is similar topic somewhere in this forum, I've tried search but no match found!
This is the first DC/DC 12-19V SMPS I've build,but when I first boot up no smoke! *Lucky* , then I tried to load to 5A using dummy load.. sound comes out from the inductor i think so.. *heeeeeeeee.....* sound continuously.
Is it normal? How to make the sound disappear?

http://www.peony888.com/VS/DSCI1267.JPG

[luka]

Hi

wire on toroid is vibrating, some kind of varnish over it. It could be too because of unstable feedback, rapid changing duty cycle would do that too

[mongater]

Thanks man . I got that!

[odnaizutra]

if the core is broken anywhere,vibration also occurs.As Luka said,some varnish is good for vibration.Feedback compensation.

[chimi]

Seeing the pic you posted, like the boys already said, and for the problems i have myself, it's the compensation, that noise is due to fast-changing duty cycle no doubt!!! the questions are: is it current or voltage mode? is the current sense resistor the right size? has the design single point ground for the control logic? if it is a flyback type converter, at 5A the peak currents must be big so, have you used any kind of switching transcient snubber?

Cheers!!

[Tolik]

As Luka mentoined - unstable, or wrong (to high) filtered feedback loop. Feedback cut out frequency should to be 5-8% of Fsw, & & should not exeed 10% of Fsw.
Elese check you traffo & inductor for saturation.