Effect of geometrical factors on copper loss in high-frequency low-profile transformers

The relationship between the copper loss and geometrical factors of high-frequency low-profile transformers is in investigated with the aid of finite-element method, and some practical design guidelines, which are useful for minimizing the copper loss, are presented. It has been shown that the winding geometry and arrangement are significant factors to determine the copper loss and leakage inductance; magnetic cores with lumped air-gaps can cause excessive AC loss in the windings; and windings with variable-width turns can have lower AC and DC losses than those with constant-width turns. The sandwich structure, in which the secondary is positioned between the two series-connected portions of the primary, is an effective approach to reduce the copper loss and leakage inductance. Optimal winding thicknesses are given for both the two-layered and sandwich-structured transformers