An apparatus comprising: a first switch leg (210,215,218,240) connected between a first input terminal and a first output terminal, the first switch leg comprising a first plurality of serially connected switches; a second switch leg (211,216,219,242) connected between a second input terminal and the first output terminal, the second switch leg comprising a second plurality of serially connected switches; a third switch leg connected between an input voltage midpoint and the first output terminal; and a controller configured to: disable the second switch leg during first half-periods of periodic reference waveforms of first and second consecutive switching periods, and alternately enable and disable the first switch leg and the third switch leg, and disable the first switch leg during second half-periods of periodic reference waveforms of the first and second consecutive switching periods, and alternately enable and disable the second switch leg and the third switch leg characterized in that the controller is configured to: control, during the first half-period of the periodic reference waveform of the first switching period, a first switch of the first switch leg to be ON and a second switch of the first switch leg to be alternately ON and OFF, and control, during the first half-period of the periodic reference waveform of the second switching period, the second switch of the first switch leg to be ON and the first switch of the first switch leg to be alternately ON and OFF. a first switch leg (210,215,218,240) connected between a first input terminal and a first output terminal, the first switch leg comprising a first plurality of serially connected switches; a second switch leg (211,216,219,242) connected between a second input terminal and the first output terminal, the second switch leg comprising a second plurality of serially connected switches; a third switch leg connected between an input voltage midpoint and the first output terminal; and a controller configured to: disable the second switch leg during first half-periods of periodic reference waveforms of first and second consecutive switching periods, and alternately enable and disable the first switch leg and the third switch leg, and disable the first switch leg during second half-periods of periodic reference waveforms of the first and second consecutive switching periods, and alternately enable and disable the second switch leg and the third switch leg disable the second switch leg during first half-periods of periodic reference waveforms of first and second consecutive switching periods, and alternately enable and disable the first switch leg and the third switch leg, and disable the first switch leg during second half-periods of periodic reference waveforms of the first and second consecutive switching periods, and alternately enable and disable the second switch leg and the third switch leg characterized in that the controller is configured to: control, during the first half-period of the periodic reference waveform of the first switching period, a first switch of the first switch leg to be ON and a second switch of the first switch leg to be alternately ON and OFF, and control, during the first half-period of the periodic reference waveform of the second switching period, the second switch of the first switch leg to be ON and the first switch of the first switch leg to be alternately ON and OFF. control, during the first half-period of the periodic reference waveform of the first switching period, a first switch of the first switch leg to be ON and a second switch of the first switch leg to be alternately ON and OFF, and control, during the first half-period of the periodic reference waveform of the second switching period, the second switch of the first switch leg to be ON and the first switch of the first switch leg to be alternately ON and OFF.