An Active Ripple Filtering Technique for Improving Common-Mode Inductor Performance

Abstract

Active ripple filtering is the replacement of large passive components in power filter circuits with smaller passive components and active control circuitry. This letter focuses on common-mode filters, where a large common-mode inductor (choke) is replaced by two smaller chokes and active op-amp control. The technique is appropriate when improved attenuation is required at relatively low frequencies and the high-frequency filtering requirements are easily met. Smaller chokes save significantly in material and winding costs. The technique is more advantageous if wire-wound chokes can be replaced by planar printed circuit board chokes. The use of the technique in an automotive electromagnetic interference (EMI) filter application is explored in detail.