A High Step-Down DC–DC Converter With Reduced Inductor Current Ripple and Low Voltage Stress

This article presents a buck converter with a large step-down voltage conversion ratio, reduced ripple in inductor current and low semiconductor voltage stress. The proposed converter produces a lower output voltage at a sufficiently higher duty ratio compared to the conventional buck converter. The step-down voltage conversion ratio is modified by a series-parallel transition of two identical capacitors of a switch-capacitor cell. Two parallelly placed switches and two cross-connected identical capacitors are utilized to design the cell. An extra inductor is placed at the input side to oppose the sudden change in input current due to the series-parallel transition of the two identical capacitors. Therefore, two inductors are required to design the converter. These two inductors are coupled directly. The modified voltage conversion ratio reduces the ripple in inductor currents and output voltage. Direct coupling between the two inductors helps to further reduce the ripple in inductor currents and output voltage. The operating principle, analysis of ripple in inductor currents, and ripple in output voltage are discussed. The analysis of small-signal modeling is carried out and a voltage mode PI-controller is designed to enable the closed-loop operation. Finally, the proposed converter is implemented in hardware and the performance of the proposed converter is verified experimentally.