Optimized Design of Integrated Planar Matrix Transformer for LLC Converter in Consumer Electronics

LLC resonant converter gets more and more applications in consumer electronics as it can convert the high voltage-low current state induced by wireless power transfer (WPT) into a low voltage-high current state effectively and efficiently. In this work, a planar matrix transformer structure and a new winding method are proposed in an LLC resonant converter to achieve a voltage conversion of 40-5 V after WPT in consumer electronics. This article focuses on modeling such a transformer and finding an optimal size to minimize the copper loss and the core loss with a total thickness of 2 mm. The theoretical analysis shows that the proposed winding method can minimize magnetomotive force (MMF) in both positive and negative periods and reduce the fringing magnetic fields' influence around air gaps. The winding's ac resistance can be reduced dramatically by such a printed circuit board (PCB) winding method. Meanwhile, such a structure can decrease copper loss by integrating the secondary winding in the UI core. An 80-W prototype is built to validate the proposed method's feasibility with 1.5-MHz operating frequency, 40-V input voltage, and 5-V output voltage. The system owns the efficiency of 93.1% at full load condition.