Magnetic control of DC-DC resonant converters provides constant frequency operation

A solution to operate DC-DC resonant converters at constant frequency is proposed. A variable inductor is used to achieve output voltage control and regulation without changing the switching frequency of the converter. The output voltage characteristic of the parallel resonant converter operating under this so-called magnetic control is briefly analysed. A 48 V input, 5 V output, 500 kHz, 25 W prototype is presented to prove the feasibility of the proposed control method.