Design Methodology to Reduce the Lumped Winding Capacitance of Spiral Winding Transformer in LLC converters

In LLC converters, the transformer's lumped winding parasitic capacitance degrades the zero-voltage-switching performance as well as power delivery capability. However, the literature survey indicates that there is still a lack of a systematic methodology to guide the optimal winding of the transformer. In this paper, a method to reduce the parasitic capacitance is proposed. The mechanism of the parasitic lumped winding capacitance in spiral winding transformer is detailed. A performance comparison between the conventional winding and proposed winding is conducted experimentally. The experimental results show that using the proposed design, the lumped winding capacitance is reduced from 14.40pF/turn to 1.76pF/turn.