电子变压器磁环发热问题

最近调试一块电子变压器的电路板,半桥自激拓扑结构,磁环和功率管发热比较严重,观察高压边开关管导通时磁环变压器的电压与电流波形如图所示.从图中发现磁环变压器在Ton/2时饱和,并没有翻转,却开始正向激磁,不知是何缘故?是否磁环有问题,还请各位大侠指教!
电路原理图如图2所示
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