US Patent 9998018 Resonant converters and methods

A multilevel LLC resonant converter comprises a first capacitor and a second capacitor connected in series providing a mid-voltage point of an input dc power source, a resonant tank connected in series with a primary side of a transformer, a first transistor and a second transistor connected in series, wherein a common node of the first transistor and the second transistor is connected to the mid-voltage point through a first isolation switch and a third transistor and a fourth transistor connected in series, wherein a common node of the third transistor and the fourth transistor is connected to the mid-voltage point through a second isolation switch.