A new structure of LLC with primary current driven synchronous rectifier

LLC resonant converter has become an excellent candidate for front-end dc-dc converter because of its high efficiency and capability of optimizing the converter for normal operation condition over a wide input voltage and load range. However, lack of suitable driving scheme for the synchronous rectifier (SR) limits the efficiency improvement of LLC in the wide input voltage condition. Although corporations like International Rectifier (IR) and STMicroelectronics (ST) have offered some so-called idea SR driver like IR1167, the 500 kHz switching frequency restriction and the cost pressure of IR1167 limit its application. In this paper, a new structure for LLC converter which enables self-driven for its synchronous rectification is proposed. A 400 kHz, 1 kW LLC resonant converter with wide input voltage range (300 V to 400 V) and 12 V output is designed and simulated to verify the function of the proposed circuit.