A multiple output DC-DC converter comprising: a transformer having a primary winding and at least one secondary winding; a primary circuit comprising: an input for connecting to a DC power supply source; the primary winding of the transformer; a primary switch connected in series with the primary winding; a plurality of secondary circuits (21, 22, 23), wherein each secondary circuit comprises the secondary winding of the transformer or a respective winding of a plurality of secondary windings of the transformer, and an output stage for providing a DC power supply output, wherein at least one of the secondary circuits (21, 22, 23) comprises a secondary switch (25, 26, 27); a digital controller which is arranged to monitor a respective output signal of each of the secondary circuits (21, 22, 23) wherein the digital controller is arranged to receive one bit of feedback data for each respective output signal per monitoring period and to control operation of the primary switch and the at least one secondary switch (25, 26, 27) based on the monitored signals, wherein the digital controller is arranged to co-ordinate operation of the at least one secondary switch (25, 26, 27) with the primary switch, such that the primary switch and the at least one secondary switch (25, 26, 27) are switched on with a controlled offset, such that the combined operation of the first switch and at least one secondary switch provides an on-off duty cycle matched to the load demands of the respective secondary circuit (21, 22, 23), wherein the controlled offset is selectable per secondary circuit (21, 22, 23) by the digital controller and may be zero. a transformer having a primary winding and at least one secondary winding; a primary circuit comprising: an input for connecting to a DC power supply source; the primary winding of the transformer; a primary switch connected in series with the primary winding; an input for connecting to a DC power supply source; the primary winding of the transformer; a primary switch connected in series with the primary winding; a plurality of secondary circuits (21, 22, 23), wherein each secondary circuit comprises the secondary winding of the transformer or a respective winding of a plurality of secondary windings of the transformer, and an output stage for providing a DC power supply output, wherein at least one of the secondary circuits (21, 22, 23) comprises a secondary switch (25, 26, 27); a digital controller which is arranged to monitor a respective output signal of each of the secondary circuits (21, 22, 23) wherein the digital controller is arranged to receive one bit of feedback data for each respective output signal per monitoring period and to control operation of the primary switch and the at least one secondary switch (25, 26, 27) based on the monitored signals, wherein the digital controller is arranged to co-ordinate operation of the at least one secondary switch (25, 26, 27) with the primary switch, such that the primary switch and the at least one secondary switch (25, 26, 27) are switched on with a controlled offset, such that the combined operation of the first switch and at least one secondary switch provides an on-off duty cycle matched to the load demands of the respective secondary circuit (21, 22, 23), wherein the controlled offset is selectable per secondary circuit (21, 22, 23) by the digital controller and may be zero.