A multi-layered printed circuit board, PCB, for providing first windings for a primary side of a planar magnetic transformer and second windings for a secondary side of the planar magnetic transformer, the multi-layered PCB comprising: a plurality of conductive layers (2, 4, 6, 8, 10, 12) configured to provide the first windings; a plurality of conductive layers (22, 14, 16, 18, 20, 24) configured to provide the second windings; and a plurality of layers of an isolation material; wherein: each layer of isolation material is arranged between two conductive layers so as to provide electrical isolation between said two conductive layers; a first group of two or more adjacent conductive layers (6, 8) are all conductive layers of the first windings and are all arranged between conductive layers (16, 18) of the second windings, wherein the thickness of the isolation material between at least a pair of adjacent conductive layers (6, 8) in the first group of layers of the first windings is less than the thickness of the isolation material between a conductive layer of the second windings and a conductive layer of the first windings; and a second group of two or more adjacent conductive layers (14, 16) are all conductive layers of the second windings and are all arranged between conductive layers (4, 6) of the first windings, wherein the thickness of the isolation material between at least a pair of adjacent conductive layers in the second group of layers (14, 16) of the second windings is less than the thickness of the isolation material between a conductive layer of the first windings and a conductive layer of the second windings. a plurality of conductive layers (2, 4, 6, 8, 10, 12) configured to provide the first windings; a plurality of conductive layers (22, 14, 16, 18, 20, 24) configured to provide the second windings; and a plurality of layers of an isolation material; wherein: each layer of isolation material is arranged between two conductive layers so as to provide electrical isolation between said two conductive layers; a first group of two or more adjacent conductive layers (6, 8) are all conductive layers of the first windings and are all arranged between conductive layers (16, 18) of the second windings, wherein the thickness of the isolation material between at least a pair of adjacent conductive layers (6, 8) in the first group of layers of the first windings is less than the thickness of the isolation material between a conductive layer of the second windings and a conductive layer of the first windings; and a second group of two or more adjacent conductive layers (14, 16) are all conductive layers of the second windings and are all arranged between conductive layers (4, 6) of the first windings, wherein the thickness of the isolation material between at least a pair of adjacent conductive layers in the second group of layers (14, 16) of the second windings is less than the thickness of the isolation material between a conductive layer of the first windings and a conductive layer of the second windings. each layer of isolation material is arranged between two conductive layers so as to provide electrical isolation between said two conductive layers; a first group of two or more adjacent conductive layers (6, 8) are all conductive layers of the first windings and are all arranged between conductive layers (16, 18) of the second windings, wherein the thickness of the isolation material between at least a pair of adjacent conductive layers (6, 8) in the first group of layers of the first windings is less than the thickness of the isolation material between a conductive layer of the second windings and a conductive layer of the first windings; and a second group of two or more adjacent conductive layers (14, 16) are all conductive layers of the second windings and are all arranged between conductive layers (4, 6) of the first windings, wherein the thickness of the isolation material between at least a pair of adjacent conductive layers in the second group of layers (14, 16) of the second windings is less than the thickness of the isolation material between a conductive layer of the first windings and a conductive layer of the second windings.