Automatic Current Sharing of Paralleled Windings for LLC Resonant Converter With Secondary-Side Resonant Inductors

The current sharing issue of paralleled secondary windings of the transformer is a major concern of LLC resonant converters. Matrix transformers solve this issue by connecting primary windings in series and secondary windings in parallel, but the volume and loss of magnetic cores increase dramatically. This letter proposes a modified LLC resonant converter, which can achieve automatic current sharing of secondary windings by distributing the resonant inductor to each secondary winding. Theoretical analysis indicates that the current balance of each paralleled secondary winding only depends on the inductance of distributed resonant inductors, whereas the tolerance of resonant inductors can be guaranteed easily in practice. An experimental prototype is built and tested to verify the effectiveness of the proposed method.