BUCK充电电路中MOS管在关断时有振荡!有原理图+波形!!!

图中BUCK充电电路开关频率120KHz,采用NMOS高端驱动.在充电初期大电流充电时,NMOS的DS间波形还算正常,没有明显振荡;而到了充电过程后期,充电电流小到200mA左右时,NMOS的DS间波形则有明显的振荡,不确定这段振荡是如何产生的?怎样才可以消除呢?
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