Patent ID: 8391026

Claim:
A resonant dc-dc converter for converting an input dc voltage to an output dc voltage, the converter comprising: a switching circuit configured to receive the input dc voltage and generate 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 oscillating at a main frequency with a main duty cycle; a switching driving circuit configured to drive the switching circuit, the switching driving circuit including a timing circuit configured to set the main frequency and the main duty cycle of the square wave voltage, the timing circuit being configured to set the value of the main duty cycle to about 50% when the converter operates in steady state; a conversion circuit configured to generate the output dc voltage from the square wave voltage based on the main frequency and on the main duty cycle, wherein the switching circuit is configured to produce a resonant current flowing from an output node of the switching circuit to the conversion circuit; a sense circuit configured to produce a direction signal that changes value in response to detecting that the resonant current has changed direction; and a disabling circuit configured to temporarily halt 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, wherein the disabling circuit is coupled to the sense circuit and is configured to re-start the timing circuit in response to the direction signal indicating that the resonant current has changed direction.