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LM5145方案50V转7.4V空载噪声过大(示波器全带宽)

1.原理图:

1.issue:

7.4Vout空载/满载时噪声高达408mV-见下图(示波器全带宽,接地弹簧),当示波器切换到20Mhz带宽时,噪声消失,纹波PP值正常

2.噪声和VSW(测试点为L1输入端)的上升沿同步,而且VSW方波有上冲,如图

3.尝试增加100Mhz磁珠、增加滤波电容、增大L1路径(想减小等效感性),没有效果

感觉像是MOS导通瞬间,由于等效电感和电容的关系,形成boost效应造成。

请问各位有没有遇到过类似情况,整改思路如何?