A module (40; 160) adapted for use in a DC-DC power conversion circuit having a step down conversion ratio of at least 12 to 1, comprising: a hybrid transformer adapted to transfer stored inductive and capacitive energy to a load, the hybrid transformer comprising a magnetic core (28; 83) and a primary winding electrically coupled in series with a secondary winding, an output of the primary winding being resistively connected to an input of the secondary winding at a node, wherein the primary winding and the secondary winding are further magnetically coupled by the magnetic core (28; 83); a synchronous rectifier coupled between the node between the primary winding and the secondary winding and ground; an output capacitor coupled between an output of the secondary winding and ground, wherein the primary winding and the secondary winding of the hybrid transformer are provided by a winding module comprising: a primary winding electrically coupled in series with a secondary winding, an output of the primary winding being resistively connected to an input of the secondary winding at the node, wherein the primary winding comprises a first conductive trace arranged on a planar support and the secondary winding comprises a second conductive trace arranged on the planar support, wherein the first conductive trace and the second conductive trace are arranged in a stack and the planar support comprises an aperture for accepting the magnetic core, wherein the primary winding has a number of turns N1 and the secondary winding has a number of turns N2, wherein the number of turns N1 and the number of turns N2 are selected to provide the step-down conversion ratio of at least 12:1, wherein the primary winding comprises a plurality of conductive primary layers (54, 56, 58, 59, 61, 63) and the secondary winding comprises a plurality of conductive secondary layers (53, 55, 57, 60, 62, 64), the conductive primary layers (54, 56, 58, 59, 61, 63) and the conductive secondary layers (53, 55, 57, 60, 62, 64)being arranged on the planar support in a stack, wherein the conductive primary layers (54, 56, 58, 59, 61, 63) each comprise a planar spiral (91, 94) with at least one turn, wherein the conductive secondary layers (53, 55, 57, 60, 62, 64) are coupled in parallel by a common conductive via extending substantially perpendicularly to the planar support and the planar spirals (91, 94) of the primary layers (54, 56, 58, 59, 61, 63) are coupled in series by one or more conductive vias extending between adjacent ones of the planar spirals (91, 94), and wherein the magnetic core comprises a central protruding portion and two outer arms (121, 122), wherein the central protruding portion protrudes into the aperture in the planar support of the winding module and the two outer arms (121, 122) extend adjacent two opposing side faces of the planar support of the winding module. a hybrid transformer adapted to transfer stored inductive and capacitive energy to a load, the hybrid transformer comprising a magnetic core (28; 83) and a primary winding electrically coupled in series with a secondary winding, an output of the primary winding being resistively connected to an input of the secondary winding at a node, wherein the primary winding and the secondary winding are further magnetically coupled by the magnetic core (28; 83); a synchronous rectifier coupled between the node between the primary winding and the secondary winding and ground; an output capacitor coupled between an output of the secondary winding and ground, wherein the primary winding and the secondary winding of the hybrid transformer are provided by a winding module comprising: a primary winding electrically coupled in series with a secondary winding, an output of the primary winding being resistively connected to an input of the secondary winding at the node, wherein the primary winding comprises a first conductive trace arranged on a planar support and the secondary winding comprises a second conductive trace arranged on the planar support, wherein the first conductive trace and the second conductive trace are arranged in a stack and the planar support comprises an aperture for accepting the magnetic core, wherein the primary winding has a number of turns N1 and the secondary winding has a number of turns N2, wherein the number of turns N1 and the number of turns N2 are selected to provide the step-down conversion ratio of at least 12:1, wherein the primary winding comprises a plurality of conductive primary layers (54, 56, 58, 59, 61, 63) and the secondary winding comprises a plurality of conductive secondary layers (53, 55, 57, 60, 62, 64), the conductive primary layers (54, 56, 58, 59, 61, 63) and the conductive secondary layers (53, 55, 57, 60, 62, 64)being arranged on the planar support in a stack, wherein the conductive primary layers (54, 56, 58, 59, 61, 63) each comprise a planar spiral (91, 94) with at least one turn, wherein the conductive secondary layers (53, 55, 57, 60, 62, 64) are coupled in parallel by a common conductive via extending substantially perpendicularly to the planar support and the planar spirals (91, 94) of the primary layers (54, 56, 58, 59, 61, 63) are coupled in series by one or more conductive vias extending between adjacent ones of the planar spirals (91, 94), and wherein the magnetic core comprises a central protruding portion and two outer arms (121, 122), wherein the central protruding portion protrudes into the aperture in the planar support of the winding module and the two outer arms (121, 122) extend adjacent two opposing side faces of the planar support of the winding module.