A buck-boost converter comprising: input terminals for connection to a power supply supplying an alternating input voltage; output terminals for outputting an output voltage; a first group of devices and a second group of devices, each group of devices comprising: a first switch, a second switch, and a third switch or diode connected in series; a first node (18, 20) located between the first switch and the second switch; and a second node (19, 21) located between the second switch and the third switch or diode; an inductor; a capacitor; and a controller for controlling the switches of the first group of devices and the second group of devices, wherein: a first of the input terminals is connected to the first node of the first group of devices; a second of the input terminals is connected to the first node of the second group of devices; the inductor is connected between the second node of the first group of devices and the second node of the second group of devices; the first group of devices, the second group of devices, and the capacitor are connected in parallel across the output terminals; the first switch of each group of devices has an OFF state in which the switch is non-conductive in both directions; the second switch of each group has an ON state in which the switch is conductive in both directions; the third switch or diode of each group of devices provides a path for inductive current when charging the capacitor; and the controller configures the switches in (i) a configuration in which the first switch of one group of devices is OFF, the first switch of the other group of devices is ON, and the second switches of both groups of devices are ON, thereby causing the inductor to be energised by the power supply, and (ii) a further configuration in which the first and second switches of one group of devices are OFF, and the first and second switches of the other group of devices are ON, thereby causing energy stored in the inductor to be transferred to the capacitor. input terminals for connection to a power supply supplying an alternating input voltage; output terminals for outputting an output voltage; a first group of devices and a second group of devices, each group of devices comprising: a first switch, a second switch, and a third switch or diode connected in series; a first node (18, 20) located between the first switch and the second switch; and a second node (19, 21) located between the second switch and the third switch or diode; an inductor; a capacitor; and a controller for controlling the switches of the first group of devices and the second group of devices, wherein: a first of the input terminals is connected to the first node of the first group of devices; a second of the input terminals is connected to the first node of the second group of devices; the inductor is connected between the second node of the first group of devices and the second node of the second group of devices; the first group of devices, the second group of devices, and the capacitor are connected in parallel across the output terminals; the first switch of each group of devices has an OFF state in which the switch is non-conductive in both directions; the second switch of each group has an ON state in which the switch is conductive in both directions; the third switch or diode of each group of devices provides a path for inductive current when charging the capacitor; and the controller configures the switches in (i) a configuration in which the first switch of one group of devices is OFF, the first switch of the other group of devices is ON, and the second switches of both groups of devices are ON, thereby causing the inductor to be energised by the power supply, and (ii) a further configuration in which the first and second switches of one group of devices are OFF, and the first and second switches of the other group of devices are ON, thereby causing energy stored in the inductor to be transferred to the capacitor. a first of the input terminals is connected to the first node of the first group of devices; a second of the input terminals is connected to the first node of the second group of devices; the inductor is connected between the second node of the first group of devices and the second node of the second group of devices; the first group of devices, the second group of devices, and the capacitor are connected in parallel across the output terminals; the first switch of each group of devices has an OFF state in which the switch is non-conductive in both directions; the second switch of each group has an ON state in which the switch is conductive in both directions; the third switch or diode of each group of devices provides a path for inductive current when charging the capacitor; and the controller configures the switches in (i) a configuration in which the first switch of one group of devices is OFF, the first switch of the other group of devices is ON, and the second switches of both groups of devices are ON, thereby causing the inductor to be energised by the power supply, and (ii) a further configuration in which the first and second switches of one group of devices are OFF, and the first and second switches of the other group of devices are ON, thereby causing energy stored in the inductor to be transferred to the capacitor.