Research On A Synchronous Rectification Half-Bridge LLC Reasonant Converter With High Power Factor

With the explosive increase in consumer electronics and IT equipment, the demand for high-power-density and high-efficiency Switching Mode Power Supply (SMPS) is growing. SMPS usually uses classical two-stage circuit topology, the first stage is a power factor correction (PFC) circuit which helps reduce the current harmonics on the power grid, and the second is a DC-DC converter.For a Boost-type PFC, interleaving architecture can be a practical way in order to improve the power density, since it can reduce the input-output ripple current and the current stress of the switch. The constant on-time approach, which is based on the critical mode (CRM) operation of Boost inductor current, is adopted to simplify the circuit structure, meanwhile the switching losses and electromagnetic interference (EMI) can be reduced. The LLC resonant converter is a promising circuit topology for a DC-DC converter, due to its soft-switching characteristics, high switching frequency, wide input voltage range and good dynamics. To further improve the efficiency in low output conditions, the synchronous rectifiers (SR) are employed, since the conduction loss is much lower than that of the diode rectifiers. The driving method of SR is based on sensing its drain to source voltage.Then, the operation principle of the SR half-bridge LLC resonant converter with high power factor is analyzed in detail, and the specific design consideration and procedure is described. Finally, a300W PFC and a240W SR half-bridge LLC experimental prototype are implemented respectively, and the relevant experimental waveforms are also presented. The results reveal that the unity power factor and high efficiency are acquired.