Optimizing the performance of planar transformers

Planar transformers are a good solution for high frequency switching-mode power supplies (SMPS). Since these kind of transformers have some advantages that improve the SMPS performance, their use is growing. Some of the high frequency parasitics can be drastically reduced due to their planar geometry and the proximity of the windings. This work presents a study of different structures and winding strategies using a standard procedure to build planar transformers. This standard method makes easier and cheaper the transformer construction by means of a standard set of layers. The paper presents a study of the influence of the parasitic effects, the advantage of the interleaving technique depending on the magnetic component role, the advantage of these transformers in multiwinding applications and the use of planar transformers in different topologies. The study is carried out by means of a finite element analysis (FEA) procedure, not only by the inspection of the flux and current distribution, but generating models that take into account all the geometry and frequency effects. Design guidelines and some experimental results are also included in this paper.