The invention describes a split transformer assembly (1) comprising a first partial assembly (10) comprising a primary winding arrangement (10W) shaped to accommodate a first core half (10C); a second partial assembly (20) comprising a secondary winding arrangement (20W) shaped to accommodate a second core half (20C); and wherein the first partial assembly (10) is realized for mounting on one side of a circuit board (3) and the second partial assembly (20) is realized for mounting on the opposite side of the circuit board (3) such that the core halves (10C, 20C) of the partial assemblies (10, 20) are completely isolated by the material of the circuit board (3). The invention further describes a switching converter circuit arrangement (2), and a method of assembling a split transformer (1).