Voltage Gain Improvement of a High-Step-Down Converter With Coupled-Inductor Core Size Reduction Based on Flux Linkage

As compared with the buck converter, the ultrahigh step-down converter can achieve a much higher step-down gain, which can be determined by not only the duty cycle, but also the turns ratio of the coupled inductor. However, this converter suffers from some problems, such as pulsating output current and large dc magnetizing inductance current, which will degrade the core utilization. As compared with the ultrahigh step-down converter, the coupled-inductor-based high step-down converter features a nonpulsating output current and a zero dc magnetizing inductance current. Therefore, the output current ripple is lower and the core utilization can be upgraded. Since the core size is proportional to the square of the applied flux-linkages, an improved coupled-inductor-based high step-down converter is presented herein. By employing an auxiliary circuit, consisting of a small capacitor and a mosfet, the flux linkage of the coupled inductor can be decreased, and hence the required core size can be reduced. In addition, due to the auxiliary circuit, the voltage spike across the tapped switch can be reduced. Above all, the step-down gain can be improved. Finally, detailed theoretical analyses and experimental results are provided to verify the feasibility and effectiveness of the proposed converter.