LLC轻载下输出特性分析及保持输出电压可控的解决方案

Analysis on LLC Light-load Output Characteristics and Solution to Maintaining Controllable Output Voltage

LLC拓扑广泛应用于各种功率转换设备中,然而LLC拓扑在轻载及空载情况下,即使工作频率范围很宽,往往仍然出现输出电压超出规格要求的现象。本文从理论上对引起该问题的原因进行深入分析,证明变压器原边等效并联电容和原边MOSFET输出电容是造成该问题的根本原因,并针对性地提出了减小等效电容、原边MOSFET并联电容、谐振电感并联电容、增加变压器原副边匝比、变换器工作于打嗝模式等措施来应对该问题。

LLC topology is widely applied in various power conversion equipment.Yet,under the light-load and no-load circumstance,a phenomenon that the output voltage exceeds specification requirements will still arise sometimes in spite of a very wide operating frequency range.The paper focuses on conducting an in-depth analysis on the reason for the problem theoretically to prove that the underlying cause of the problem is the equivalent parallel capacitance on primary side of transformer and MOSFET output capacitance on primary side.In addition,the countermeasures on the problem including reduction of equivalent capacitance,primary-side MOSFET parallel capacitance,and parallel capacitance of resonant inductance,increase of primary and secondary turn ratio,converter work on a hiccup mode are proposed.