Series Resonant Converter with Wide Load Range

A modification of the series resonant converter topology is presented which extends converter operation from no-load to full-load. This result is accomplished by adding two switches at the secondary-side bridge rectifier, thus improving output voltage control. The resonant inverter can be operated either at constant switching frequency, even for the half-bridge topology, or at variable switching frequency. With constant switching frequency, the output voltage is regulated by controlling the switches of the rectifier stage. Soft-switching commutations of all switches are maintained in any operating condition, thus optimizing overall efficiency. The secondary-side control of the output voltage adds another interesting feature to the basic converter, i.e. the step-up and step-down regulation capability which allows the use of this topology in high power factor rectification, too. Simulated and experimental results confirm proper converter operation in the range from no-load to full-load.