A circuit in a power system for suppressing an AC ripple superimposed on a bus signal on a bus includes a first circuit for producing first and second signals having a frequency substantially equal to the AC ripple frequency wherein the second signal is a phase quadrature of the first signal, a second circuit for combining these signals with a signal representing the bus signal having the AC ripple superimposed thereon so as to derive a control signal having substantially the same frequency and phase as the AC ripple, and a third circuit responsive to this control signal so as to substantially suppress the AC ripple on the bus.