The LLC resonant converter that controls the output voltage via the frequency control of the DC / DC converter developed for the medium capacity class power supply system has various advantages. For example, it is robust against EMI noise, soft switching operation on the primary side and secondary side is possible, the frequency variation range is narrow and it has wide input / output voltage conversion ratio.
Meanwhile, as demand for distributed power supply systems and communication rectifiers recently increases, high-quality power supplies are required for power supply devices. In addition, a charging technique for maintaining the performance and life of the battery used for the power supply device is required. However, since the power system using the existing Center-Tab type LLC resonant converter transmits the electric energy via resonance, the charging current ripple inevitably occurs. The charging ripple current induces temperature rise and overcharging of the battery, and shortens battery life. In order to overcome this problem, this paper proposes an LLC resonant converter that reduces output current ripple by using a differential coupled inductor on the secondary side. The proposed circuit (1) can obtain the output current with reduced ripple current using two transformers and one coupled inductor. The proposed circuit (2) can obtain an output current in which the ripple current is reduced by using one transformer and two coupled inductors. Therefore, the proposed resonant converter circuits do not require an additional hardware filter to reduce the output ripple current. In addition, since it does not affect the resonance network designed using the coupled inductors of differential coupling with high coupling ratio, complicated design method is not required.
In this paper, preferentially analyze the existing technology and in order to verify the validity of the proposed circuit, presented the operation principle, mathematical analysis and design procedure. Finally, in order to confirm the theoretical characteristics of the proposed technique, simulation experiments and prototypes are produced and the superiority of the proposed technique is verified.