Analysis and design of an active ripple filter for DC-DC applications

When low ripple is required from a DC-DC converter, active filters offer an alternative to passive LC and coupled inductor filters. A simple experimental active ripple filter is presented, which employs a pair of current transformers as sensors for feedforward and feedback control and two MOSFETs as cancellation current drivers. Measurements demonstrate good ripple attenuation: more than 70 dB at 100 kHz, and 23 dB at 1 MHz. The overall efficiency was measured as 95%, but could be improved by attention to the auxiliary supplies to around 98%. The filter is suitable for input and output smoothing in aerospace and other critical applications.<
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