Efficiency Optimized Design Procedure of low-Q LLC Resonant Converter for Wide Input Voltage and Load Range Application

Abstract

LLC resonant dc-dc converter has become a de-facto resonant topology in many emerging industrial applications. This paper proposes a simple to implement design approach for LLC dc-dc resonant converter suitable for operation under wide input voltage and load range for fixed output voltage applications. For such applications, selecting a design with low inductance ratio (K) and high-quality factor (Q) ensures narrow switching frequency variation but at the cost of efficiency and power density. However, maximizing power efficiency throughout the required range of line and load conditions with output voltage regulation requires optimal selection of K and Q. The proposed design approach is compared with two other existing design approaches and tested on an experimental prototype of 300W LLC converter for 2:1 input voltage range (20-40V). The proposed design shows rated efficiency improvement of 3% over existing methods.