Audible noise on switching supply (is it bad?)

[hazuki]

Hi all. I've put together a buck switching converter for one of my projects. I noticed that there is audible noise coming from the supply (maybe around 10kHz). The high pitch whine appears to be coming from the inductor. Should I be concerned about audible noise like this? My buddy's first reaction to the sound on my circuit was "that doesn't sound healthy."

The switching frequency is actually much higher than the audible frequency (around 250kHz).

Thank you!

[Rerouter]

its either the windings or the core vibrating, though if you have access hook up the output to a scope and see if there are any repetitive patterns close to 10Khz

in general securing it better with some adhesive will make it quieter

[AndyC_772]

If a switched mode supply is making a sound you can hear, then there's some component of the switching waveform that's within the audible range. Since 250kHz is nowhere near that range, chances are your power supply is unstable and is switching in bursts, rather than producing a nice, consistent stream of pulses in which every cycle is the same.

This behaviour is generally caused by one of two things: noise, or the wrong compensation network. If the layout is poor, then the controller's sense input gets a noisy signal, and pulse widths will vary quite randomly from one cycle to the next. Or, if it's poorly compensated, then the system will tend to oscillate - pulses will get wider and then narrower, often to the point of being skipped entirely, over and over again.

A scope will show you very clearly which is the case. If your controller has an accessible compensation point (the output of the error amplifier), probe that too as it can give a better indication of whether the problem is noise or oscillation. If it looks like a sine wave, your control loop is unstable and the compensation network needs changing. If it's reasonably flat but noisy, then you need to look at your layout.

[megajocke]

Maybe it's worth mentioning that it is also common and normal for unloaded or very lightly loaded supplies to do that because there might be a lower limit on the duty cycle forcing the supply into a pulse-skipping mode creating a lower effective switching frequency. As pulse skipping/burst mode operation can be beneficial for efficiency at light loads there can be reasons to want to introduce it on purpose.

But if this is happening under load and is not by design it might not be good, causing for example higher RMS current stress on components than would be the case if every switching cycle was identical.

BTW, hi Andy!