Novel Control Method for Ultra-High Step-Down Converter

Abstract

A novel dual PWM control method for achieving an ultra-high step-down DC-DC converter is proposed. Both high-frequency and low-frequency PWM waveform generators are used in synthesizing the dual PWM control of buck converters. This resulting PWM waveform will lead to various switching cycles, and five operation modes of the buck converter can be defined accordingly. The operation principle of the proposed converter and its small-signal switched model are studied in details. One salient feature of the proposed design is that if the duty cycle of the high-frequency PWM is exactly equal to that of the low-frequency PWM, by exploring the volt-sec balance condition, the voltage gain can be expressed as the quadratic formula of the duty cycle. Thus, an ultra-high step-down conversion ratio and significant reductions of the inductor current ripple can be ensured simultaneously. Since no modifications of the conventional circuit topology are made, the proposed scheme is very cost effective. Simulation studies and hardware prototype circuit implementations are conducted to validate the proposed design with satisfactory performance.