An electronic power supply circuit for a load composed of at least two independent circuit branches connected in parallel to each other, where a first branch requires a different power supply voltage from the power supply voltage of a second branch. The circuit includes a step-up converter, a timer circuit connected to the step-up converter so that the converter generates, alternately, at least a first output voltage able to power the first circuit branch and a second output voltage able to power a second circuit branch, a regulation circuit able to regulate the overvoltages at the ends of an output capacitor of the converter during commutations between the different output voltages; and a commutation circuit able to activate the step-up converter, according to the timer signals coming from the timer circuit, when the output voltage at the ends of the output capacitor has reached the level needed to power the activated branch and regulate the current flowing thereto.