Low-Loss Segmented Shielding Technique for PCB-Winding Planar Transformers

Printed-circuit-board (PCB) winding planar transformers have been widely adopted in isolated high-efficiency and high-power-density converters. Inserting the shielding layer is an effective method to attenuate the common-mode noise induced by the large interwinding capacitance of PCB winding. This letter identifies that a part of the magnetic flux will pass through the shielding layer due to the planarized structure of the planar transformer. Furthermore, the generation mechanism and the distribution of eddy current and related loss in the shielding layer are revealed. In order to reduce the eddy current loss in the shielding layer, a segmented shielding technique is proposed. The shielding layer is divided into multiple segments to reduce the coupled flux and the eddy current loss in each segment of the shielding layer. The experimental results on a 300 kHz 1000 W/28 V output resonant converter validate that, compared with the conventional shielding method, the proposed shielding technique can improve the efficiency by 0.15% at full load.