Resonant converters are often considered ideal solution for fixed conversion ratio applications. They can achieve better efficiency and lower level of noise generation as compared to other popular non-resonant topologies, such as phase shift full bridge. However, resonant converters are not able to handle a wide conversion ratio because optimal operation cannot be maintained. In this digest, a multilevel pulse width modulation method is proposed for resonant topologies to achieve a wide conversion ratio under fixed switching frequency operation. The advantageous features of resonant converters are retained while achieving wide range of conversion ratio with fixed switching frequency. This method can be used with various resonant topologies. 240W experiment prototype had been built and tested to validate the proposed method. Excellent efficiency had been obtained under a wide 4: 1 ratio input voltage range.
