Filters with active tuning for power applications

Passive filters for switched-mode power converters rely on low-pass networks - with corner frequencies well below the ripple fundamental - to attenuate switching harmonics over a range of frequencies. The filters explored in this report provide extra attenuation at discrete frequencies, easing the filtering requirement of accompanying low-pass networks. When a converter's switching frequency is tuned to a filter resonance using a novel phase-lock control scheme, a resonant filter can match the ripple-attenuation performance of a low-pass network for less volume, weight, and expense. The applications and limitations of resonant filters and active-tuning control are discussed, and experimental results from the input filter and power stage of a prototype DC-DC converter are presented.