AN EFFICIENT ACTIVE RIPPLE FILTER FOR USE IN DC-DC CONVERSION

When low ripple is required from a switched mode dc-dc converter, diss ipative active filters offer an alternative to passive LC and coupled inductor filters. Analytical and experimental results are presented fo r a simple active ripple filter. The filter employs a pair of current transformers as sensors for feedforward and feedback control and two m etal-oxide-semiconductor held-effect transistors (MOSFETs) as cancella tion current drivers. Measurements demonstrate good ripple attenuation up to 5 MHz, more than 70 dB being obtained at 100 kHz, the switching frequency of a test converter. The overall efficiency was measured as 95%, with room for further improvement. The filter is suitable for in put and output smoothing in dc-dc converters for aerospace and other c ritical applications.