Stackable and cost-reduced transformer with embedded emi filters

Abstract

A transformer (FIG. 1) optimized for surface-mount vacuum-pickup automated circuit assembly eliminates the expense of a transformer housing. The transformer has a ferrite body (100) that defines a pair of wells (208, 209) each opening onto an opposite face (108, 109) of the ferrite body. Transformer primary and secondary windings are wound in a coil (103) through slots (210, 211) around a transformer core (204) at the bottom of the wells. The windings do not protrude from the wells beyond the faces, resulting in flat faces. A first plurality of conductive vias (104-106), one pair for each winding, are completely embedded in the ferrite body and extend to both of the faces. Each pair of vias serves at one face to attach to the winding and at the other face to attach to solder pods of a PC board. The embedded vias also serve as EMI filters. A plate (107) covers the one face and provides a surface for vacuum pickup and for labeling of the transformer. The ferrite body (500) of a first transformer (FIG. 5) adapted for stacked mounting of transformers dispenses with the flat plate and further defines a second plurality of pairs of conductive vias (104-106). These vias are not connected to the first transformer's windings, but rather are positioned for connection to the winding-connected first pairs of vias of a second transformer that is positioned orthogonally to and mounted on the first transformer at the one of the faces.