Ron H said:Because the load is a square wave, which has harmonics that extend far beyond the fundamental. If one of the harmonics is at the resonant frequency of the filter, it will ring.
EDIT:
You sucked me in there. You read something wrong in my sim. The square wave is at the resonant frequency of the filter.
What I said about harmonics is true, but the amplitude of the 15th harmonic will be 1/15th the amplitude of the fundamental.
Opps sorry... youre right.
Even with the addition to an LC filter, if you design the feedback compensation to have a bandwidth of a frequency much less than the transient load frequency (for example, I design the feedback to have a bandwith of 10k and the load transient is 151k in your example), wouldnt you not see the oscillation like in your example?