Novel L-R modulation resonant converter with wide output range and low output voltage ripple

The disadvantage of resonant converter with pulse frequency modulation in applications with wide voltage gain is that the frequency modulation range is wide, which causes difficulty in optimizing the design of transformer and increases the high-frequency switching loss. In the light load condition, the resonant converter with pulse width modulation has a large circulating current loss. In this paper, a soft-switching converter with linear-resonant composite modulation is proposed. It has two operation modes and can adjust the voltage gain in a wide range with narrow frequency variation range. In the fixed frequency mode, no circulating current is present in the full load range, and the light load efficiency is improved. In variable frequency mode, the feedback loop of the converter is simple, which reduces the loss in the feedback loop. The operation principle and voltage gain characteristics of the two modes are analyzed in detail, and the parameter design steps are given. An experimental prototype based on constant current and constant voltage charging is built to demonstrate its feasibility.