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Noisy PWM regulator revisited


Robert Latest

Jan 1, 1970
A few days ago I posted about a PWM controller in a WLAN router that emitted
acoustic noise and got a few good hints. Unlike I wrote at first, however,
the effect is not a thermal one but has to do with the fact that the power
consumption of the device changes after boot-up of the embedded processor. I
checked the switch-side node of the coil with an oscilloscope, and indeed
when the things makes its noise the PWM pulses are all over the place. No
two traces look alike. To see if this had anything to do with the output
capacitance I soldered various caps (electrolytic and foil) in parallel to
the output but found no change at all.

Now I'm going to have to look at their feedback loop and see if I can do
anything about that.