Achieving constant frequency operation in DC-DC resonant converters through magnetic control

In this paper a new solution to operate dc-dc resonant converters at constant frequency is investigated. The proposed converter is based on the use of a variable inductor to achieve output voltage control and regulation at constant switching frequency. The output voltage characteristics for two typical dc-dc resonant converters operating under this so-called magnetic control are analyzed. As an example, the design of a 48V input 5V/10A output, 500 kHz prototype was carried out. Also, the dynamic behavior of this prototype was investigated by performing a step response test. From this result, a compensator for operating in closed loop was designed and experimented. The obtained results showed that the proposed control method could be a good possibility to achieve constant frequency operation in dc-dc resonant converters.