PWM控制LLC谐振变换器一种常见MOSFET失效分析及对策

在宽范围输出电压及负载变化范围较大的应用场合，LLC谐振变换拓扑的高频区不单调现象及考虑过高开关频率的限制，单纯的调频控制难以满足要求，业界常用的解决方案是在PFM基础上引入PWM控制。这种混合控制模式的LLC电路在PWM工作模态特定条件下桥式电路出现的“上管MOSFET体二极管反向恢复、下管开通”的瞬时直通现象将引起MOSFET电压电流应力超标而失效。分析了失效模式机理、提出了解决方案并进行了实验验证。

A Common MOSFET Failure Analysis and Solution About LLC Resonant Converter in PWM State

In wide output voltage and load range applications, since the non-monotonic phenomenon in high frequency region of the LLC resonant converter and considering of limiting the too high switching frequency, a simple frequency control is difficult to satisfy need and the usual approach is to introduce PWM control on the basis of PFM. The LLC resonant converter exists such a operating state under certain conditions of PWM control mode, that is, during body diode reverse recovery of the upper MOSFET of bridge circuit, the lower MOSFET is turned on simultaneously, the instantaneous pass-through phenomenon will cause excessive voltage and current stress and lead to MOSFET failure. Analyzes failure mechanism, proposes the solution and makes experimental test.