A half-bridge converter is controlled by a circuit including a differential circuit receiving a reference signal and a feedback signal which is a function of an output signal from the converter. The half-bridge converter includes high-side and low-side electronic switches. A comparator generates a PWM-modulated signal for controlling the converter as a function of the duty cycle of the PWM-modulated signal in response to a signal at an intermediate node between the high-side and low-side electronic switches and an output of the differential circuit. A gain circuit block coupled between the intermediate node and the input of the comparator applies a ramp signal to the input of the comparator which is a function of the signal at the intermediate node. A variable gain is applied by the gain circuit block in order to keep a constant value for the duty cycle of said PWM-modulated signal irrespective of converter operation.