Steady State Characteristics of Two-Phase Isolated Converter for Step-down Applications.

Abstract

This paper presents a method of minimizing the smoothing capacitor of the buck converter with isolated transformers and synchronous rectifiers, which is used for the low voltage-high current applications. The principle is to remove the ripple voltage by applying two-phase configuration of asymmetry switching. A detailed analysis is given using averaging method and cleared the operations of the circuit. Especially the smoothing capacitor can be shifted to the high voltage side, as a results the capacity is extremely lessened to be few μF. In this circuit, small capacitor of several hundred μF is necessary to use in the output (low voltage side). The capacitors in the primary and secondary sides being both small, the ceramic capacitors of low ESR are possible to use. From the experimental result, the efficiency of about 92% was obtained under the conditions of the input 140V and the output 1.5V/20A with the primary capacity of 0.33μF, the secondary capacity of 200μF and the switching frequency of 100kHz.