A resonant dc - dc converter for converting an input dc voltage (Vin) to an output dc voltage (Vout), the converter including: - a switching circuit (132, 134) for receiving the input dc voltage (Vin) and generating a periodic square wave voltage (Vsq) oscillating between a high value corresponding to the input dc voltage (Vin) and a low value corresponding to a fixed voltage, the square wave voltage (Vsq) oscillates at a main frequency with a main duty cycle; - a switching driving circuit for driving the switching circuit (132, 134), the switching driving circuit including a timing circuit for setting the main frequency and the main duty cycle of the square wave voltage (Vsq), 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 (110, 115, 120) based on a resonant circut for generating the output dc voltage from the square wave voltage based on the main frequency and on the main duty cycle; characterized by - a disabling circuit (525, 505) 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 (Vsq) during at least one period of the square wave voltage (Vsq) wherein: - the switching circuit (132, 134) includes a first controlled switch coupled between a terminal providing the input dc voltage (Vin) and a circuit node coupled with the conversion circuit (110, 115, 120), and a second controlled switch coupled between a terminal providing the reference voltage and the circuit node, - the switching driving circuit includes means (315, 320) for alternatively activating the first controlled switch and the second controlled switch in such a way that the square (Vsq) wave is sourced to the circuit node by the switching circuit, and - the disabling circuit (525, 505) includes means for temporarily halting the timing circuit until a resonant current (Ir) flowing from the circuit node toward the conversion circuit has changed direction. - a switching circuit (132, 134) for receiving the input dc voltage (Vin) and generating a periodic square wave voltage (Vsq) oscillating between a high value corresponding to the input dc voltage (Vin) and a low value corresponding to a fixed voltage, the square wave voltage (Vsq) oscillates at a main frequency with a main duty cycle; - a switching driving circuit for driving the switching circuit (132, 134), the switching driving circuit including a timing circuit for setting the main frequency and the main duty cycle of the square wave voltage (Vsq), 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 (110, 115, 120) based on a resonant circut for generating the output dc voltage from the square wave voltage based on the main frequency and on the main duty cycle; characterized by - a disabling circuit (525, 505) 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 (Vsq) during at least one period of the square wave voltage (Vsq) wherein: - the switching circuit (132, 134) includes a first controlled switch coupled between a terminal providing the input dc voltage (Vin) and a circuit node coupled with the conversion circuit (110, 115, 120), and a second controlled switch coupled between a terminal providing the reference voltage and the circuit node, - the switching driving circuit includes means (315, 320) for alternatively activating the first controlled switch and the second controlled switch in such a way that the square (Vsq) wave is sourced to the circuit node by the switching circuit, and - the disabling circuit (525, 505) includes means for temporarily halting the timing circuit until a resonant current (Ir) flowing from the circuit node toward the conversion circuit has changed direction.