Transformer Cores with Low Common Mode Currents for LLC Converters

This work proposes an innovative design for reducing common-mode noise in LLC converter transformers and meeting electrical safety regulations. Conventional designs are often prone to common-mode noise current paths due to parasitic capacitance and the typical characteristics of the transformer core. This study introduces the concept of dividing and insulating the core structure of the transformer to effectively break the common-mode noise current path, thereby substantially diminishing the common-mode current path resulting from the parasitic capacitances of the primary and secondary windings, as well as the core. The experimental results of the study revealed significant performance enhancement in minimizing the conducted electromagnetic interference (EMI) using the new design. Furthermore, the proposed scheme offers advantages in terms of simplicity and practicality. This design presents an efficient and electrically safe solution for LLC converters that require high power density and low EMI levels.