An AC/DC PFC converter, comprising: a PFC pre-regulator, comprising: an AC input; a rectifier for rectifying a mains input voltage; a half bridge inverter comprising a high side switch and a low side switch; an LLC circuit (20,26,27) coupled to a node between the high side switch and the low side switch; and a control circuit configured to generate a gate drive signal for controlling the switching of the high side switch and the low side switch thereby to generate a controlled output voltage (vbus) at an output of the PFC pre-regulator, wherein a high gate drive signal turns on one of the high side switch and the low side switch and turns off the other one of the high side switch and the low side switch and a low gate drive signal turns off the one of the high side switch and the low side switch and turns on the other one of the high side switch and the low side switch; and an output stage connected to the PFC pre-regulator such that the controlled output voltage (vbus) becomes a bus voltage for the output stage, the output stage comprising: a DC/DC converter; and a feedback unit adapted to provide a feedback signal to the control circuit of the PFC pre-regulator for modulating the controlled output voltage (vbus) of the PFC pre-regulator; characterized in that the feedback signal is configured to modulate the controlled output voltage (vbus) of the PFC pre-regulator in dependence on the amplitude and phase of the mains input voltage and the output power of the output stage, such that a set-point for the controlled output voltage (vbus) is varied synchronously with the mains input voltage, and an imposed bus voltage variation is synchronous with the rectified mains input voltage. a PFC pre-regulator, comprising: an AC input; a rectifier for rectifying a mains input voltage; a half bridge inverter comprising a high side switch and a low side switch; an LLC circuit (20,26,27) coupled to a node between the high side switch and the low side switch; and a control circuit configured to generate a gate drive signal for controlling the switching of the high side switch and the low side switch thereby to generate a controlled output voltage (vbus) at an output of the PFC pre-regulator, wherein a high gate drive signal turns on one of the high side switch and the low side switch and turns off the other one of the high side switch and the low side switch and a low gate drive signal turns off the one of the high side switch and the low side switch and turns on the other one of the high side switch and the low side switch; and an AC input; a rectifier for rectifying a mains input voltage; a half bridge inverter comprising a high side switch and a low side switch; an LLC circuit (20,26,27) coupled to a node between the high side switch and the low side switch; and a control circuit configured to generate a gate drive signal for controlling the switching of the high side switch and the low side switch thereby to generate a controlled output voltage (vbus) at an output of the PFC pre-regulator, wherein a high gate drive signal turns on one of the high side switch and the low side switch and turns off the other one of the high side switch and the low side switch and a low gate drive signal turns off the one of the high side switch and the low side switch and turns on the other one of the high side switch and the low side switch; and an output stage connected to the PFC pre-regulator such that the controlled output voltage (vbus) becomes a bus voltage for the output stage, the output stage comprising: a DC/DC converter; and a feedback unit adapted to provide a feedback signal to the control circuit of the PFC pre-regulator for modulating the controlled output voltage (vbus) of the PFC pre-regulator; characterized in that the feedback signal is configured to modulate the controlled output voltage (vbus) of the PFC pre-regulator in dependence on the amplitude and phase of the mains input voltage and the output power of the output stage, such that a set-point for the controlled output voltage (vbus) is varied synchronously with the mains input voltage, and an imposed bus voltage variation is synchronous with the rectified mains input voltage. a DC/DC converter; and a feedback unit adapted to provide a feedback signal to the control circuit of the PFC pre-regulator for modulating the controlled output voltage (vbus) of the PFC pre-regulator; characterized in that the feedback signal is configured to modulate the controlled output voltage (vbus) of the PFC pre-regulator in dependence on the amplitude and phase of the mains input voltage and the output power of the output stage, such that a set-point for the controlled output voltage (vbus) is varied synchronously with the mains input voltage, and an imposed bus voltage variation is synchronous with the rectified mains input voltage.