Design consideration for high frequency LLC resonant converter with matrix transformer

Abstract

This paper analyzes application of a matrix transformer structure in high frequency LLC resonant converter. Soft-switching condition for primary switches has been derived considering the parasitic capacitance of elements in resonant circuit. A comparison is made between characteristics of cascade GaN and state-of-the-art Si switching devices and its effect on the value of resonant current. The concept of matrix transformer has been described and applied in the design of LLC resonant converter. Area product method for selecting appropriate size of ferrite core is presented in respect to the value of the transformer magnetizing current and zero voltage turn-on condition for primary switches. As shown, additional core losses due to the use of matrix transformer structure is negligible compared to reduced conduction and switching losses. Design of 400V/24V 500W high frequency LLC converter with matrix transformers is presented, and experimental model is made in order to verify the analysis. Experimental results recorded on a LLC converter prototype are provided to verify fulfilling of the soft-switching condition for primary switches in specified switching frequency range.