A Novel Buck-Boost Control Technique for Push-Pull Parallel-Resonant Converters

This paper presents a new control technique by which the voltage gain of a push-pull parallel resonant converter can be varied. The technique operates the converter either in buck or boost mode by varying the switching frequency above and below its natural resonance frequency, respectively. A split-capacitor topology is used and a variable phase-shift, modulated into the switch signals at damped resonance frequency, generates the desired switching frequency. The operation of the circuit under all three modes is discussed in detail using a simplified model. Experimental results of a 50 W prototype converter, which indicate that the output can be varied from 75 to 135% of its nominal value, are compared with simulated results to show the validity of the proposed concept