Abstract: A transformer assembly suitable for use in very high frequency (VHF) switching power supplies that maintains a low leakage inductance between critical transformer windings while complying with the physical and electrical requirements imposed by standards for primary to secondary isolation. The transformer includes a telescopic bobbin assembly with an inner and an outer section that telescope together to form an interior clearance space or chamber between the two sections. The interior chamber has a narrow conduit exiting to the exterior of the bobbin assembly. Described are two embodiments for a transformer used in a forward-averaging type converter and a third embodiment for a transformer used in a frequency modulated converter.