Design Of LC Harmonic Notch Filter for Ripple Reduction in Step-Down DC-DC Buck Converter

Abstract

This paper proposes the design of an LC harmonic notch filter to improve the output ripple in an inductor type step-down DC-DC buck converter. To examine the overshoot voltage of the converter, the transfer function and its self-loop function of the power stage were analyzed. The LC network was designed at the 180 kHz harmonic frequency and added at the output node of the power stage of the converter. As a result, the ripple was reduced by 3 dB (from -35 dBV to -42 dBV at 180 kHz). The ripple level was kept below 5 mVpp, which is small enough compared to 5 V desired voltage.