METHOD AND CIRCUIT FOR AVOIDING HARD SWITCHING IN RESONANT CONVERTERS

摘要

A resonant dc-dc converter for converting an input dc voltage to an output dc voltage is provided. The converter includes a switching circuit for receiving the input dc voltage and generating a periodic square wave voltage oscillating between a high value corresponding to the input dc voltage and a low value corresponding to a fixed voltage. The square wave voltage oscillates at a main frequency with a main duty cycle. The converter further includes a switching driving circuit for driving the switching circuit. The switching driving circuit includes a timing circuit for setting the main frequency and the main duty cycle of the square wave voltage. The timing circuit is configured to set the value of the main duty cycle to about 50% when the converter operates in steady state. The converter includes a conversion circuit based on a resonant circuit for generating the output dc voltage from the square wave voltage based on the main frequency and on the main duty cycle. The converter further includes a disabling circuit for temporarily halting the timing circuit after a power on of the converter in such a way to temporarily vary the main duty cycle of the square wave voltage during at least one period of the square wave voltage.