Accurate Design of Output Filter for DC–DC PWM Buck Converter and Derived Topologies

This paper presents an analysis of an LCR second-order low-pass filter capacitor to achieve a specified ripple output voltage in Buck, forward, Zeta, and Ćuk PWM DC-DC power converters for continuous-conduction mode (CCM). Current and voltage waveforms across output filter components are derived. Using the waveform of the ac component of the output voltage, an expression for the ripple voltage is developed in terms of the filter capacitance and equivalent series resistance. The results can be used for all PWM converters with the LCR output filter, such as Buck, forward, Zeta, and Ćuk PWM DC-DC converters. Theoretical results were in good agreement with simulation and experimental results.