有源钳位正激变换器寄生参数对软开关和直流偏磁的影响

本文考虑有源钳位正激变换器原边MOS管寄生电容、变压器激磁电感及漏感的影响,推导了钳位管ZVS开通的能量条件和时间匹配条件;建立了正激变压器直流偏磁与寄生参数的定量关系;指出了小漏感、大激磁感、大寄生电容条件会导致钳位MOS管无法实现ZVS开通,降低整机效率,影响控制器的可靠工作;同时还指出大漏感条件会导致变压器负向偏磁严重,降低磁心利用率。最后完成了50W有源钳位正激模块电源的仿真和实验验证,证明了理论分析的正确性。

Influence of parasitic parameters on soft switching and DC magnetic bias for active-clamp forward converter

The parasitic capacitor of MOSFET,and magnetizing and leakage inductances of transformer are taken into account for the analysis of active-clamp forward converter in this paper.The conditions for zero-voltage switching of clamp MOSFET are derivated.Based on the conditions,it is pointed out that small leakage inductance,large magnetizing inductance and large parasitic capacitor tend to result in hard switching of clamp MOSFET,which degrades efficiency,and even disturbs the proper functions of controller.The quantitative relation between DC magnetic bias current and parasitic parameters is also given in this paper.The larger is the leakage inductance,the larger is the DC magnetic bias current,and the lower is the utilization of ferrite core.The simulation results agree with the theoretical analysis.Finally,a 50W prototype was built in the lab.Experimental results coincide well with the theoretical analysis.