[SI-LIST] Re: Damped voltage oscillation

> Changing the inductor to a resistor helps to dampen the oscillation and
> ringing.  However, the effectiveness of filtering at low frequencies also
> goes down.

Actually, changing to a resistor improves the effectiveness of the low
frequency filtering, which is why a resistor may sometimes be a better
choice.  But it also degrades the voltage stability or regulation at low
frequencies, which can increase the low frequency ripple and/or voltage
droop seen on the filtered side, caused by the load current.

Ringing can happen even if the LC resonant frequency is nowhere near the
oscillator's frequency or a harmonic of it.  All it takes is spikes in the
current (at any suitably low frequency), and a high-Q LC filter.  The
ferrite bead, or resistor, reduces the Q.

Regards,
Andy



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