FEEDFORWARD ACTIVE-FILTER FOR OUTPUT RIPPLE CANCELLATION

An active filter for DC-DC converter ripple cancellation is described and demonstrated. The feed-forward technique used applies to any converter with an output filter inductor. The technique is inherently stable, performs in both continuous and discontinuous conduction modes, and applies to both square-wave and resonant converters. A suitable linear amplifier, combined with a current transformer, implements it with low loss. An adaptive tuning scheme compensates for inductance variation and drift. Operation is demonstrated with buck, push-pull, and boost converter topologies. The result is output ripple below 10mV RMS, effective on converters with outputs as low as 2V and currents above 30 A.