Integrated Matrix Transformer with Optimized PCB Winding for High-Efficiency High-Power-Density LLC Resonant Converter

Abstract

Both server and telecom power supply prefers LLC resonant converter with matrix transformer as DC/DC stage due to its high efficiency and high power density. With reduced labor intensive and lower profile, print circuit board (PCB) winding based matrix transformer is gaining more and more attention. A 4 layer PCB structure, with two layers for secondary side winding and another two layers for primary side winding, is general practice. In the case with even number of turns in primary side, each layer has half of the turns. However, with odd number of turns in primary side, it is impossible to physically get half of one turn. This paper proposes a novel winding structure that allows odd number of turns arranged in two layer PCB. Besides, four elemental transformers are integrated into a single planar magnetic core by flux cancellation. The winding width and core dimension are optimized to achieve lower loss and footprint. A 3 kW matrix transformer with 4 layer PCB winding is built up. Turns ratio of 3:1 is demonstrated as an example in each elemental transformer. The proposed winding layout method has simple structure, but shows low winding loss and good current sharing. The matrix transformer is demonstrated on a 500 kHz switching frequency wide band-gap device based LLC resonant converter. The prototype achieves a peak efficiency of almost 98.5% and a power density of 24.4 kW/L (400 W/in3).