适用于宽电压恒流输出的半桥LLC谐振变换器研究

Research on Half-bridge LLC Resonant Converter Suitable for Wide Voltage and Constant Current Output

半桥LLC谐振变换器以其结构简单、效率高等特点在开关电源领域得到了广泛运用。针对宽电压恒流输出的应用需求,分析并比较了半桥LLC谐振变换器的3种工作方式特点,选用了开关频率大于谐振频率的工作状态,控制方式采用了固定死区的互补调频方式,利用了变压器的励磁电感和外置谐振电感与谐振电容发生谐振,此时原边MOSFET实现ZVS,输出整流管为连续模式,适合用于恒流输出场合,次级整流部分采用全波整流方式,选用了智能同步整流驱动芯片的同步整流技术,降低了低压大电流输出场合下副边整流管的导通损耗,进一步提高了变换器效率。结合LLC控制芯片L6599和同步整流芯片TEA1795AT,设计了一款240 W\36 V输出的半桥LLC谐振变换器原理样机,最高效率达到93.4%,仿真和实验验证了设计方案的正确性。

Half bridge LLC resonant converter has been widely used in the field of switching power supply because of its simple structure and high efficiency.According to the application requirements of wide voltage and constant current output,the characteristics of three working modes of half-bridge LLC resonant converter were analyzed and compared.The working state in which the switching frequency was greater than the resonant frequency was selected.The complementary frequency modulation mode with fixed dead time was used as the control mode,and the excitation inductance and external resonant inductance of the transformer resonate with the resonant capacitor.The primary MOSFET realized ZVS,and the output rectifier was in continuous mode,which was suitable for constant current output.The secondary rectifier adopted full wave rectification,and the synchronous rectification technology of intelligent synchronous rectification driving chip was selected.In the case of low voltage and high current output,the conduction loss of the secondary rectifier was reduced and the converter efficiency was further improved.Combined with LLC control chip L6599 and synchronous rectifier chip TEA1795AT,a principle prototype of 240 W\36 V output half bridge LLC resonant converter was designed,and the maximum efficiency was 93.4%.Simulation and experiments verify the correctness of the design scheme.