DPA426反激电源出现的问题,急求解答!!!

本人用PI的DPA426设计了一个输入24VDC,输出5V/5A,24V/0.5A的电源,用反激作的,调试的时候,发现空载是DS两段波形很正常,也比较稳,随负载加大,波形越来越不稳,在3.5A时,输出电压就开始出现不稳状态,出现打嗝,求PI工程师解答!
1)空载时波形
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2)1A时的波形
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3)2A时候波形
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4)3A时的波形
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5)3.5A时出现打嗝
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原理图如下:
337471209350909.sch

盼望大家给我帮助阿!!!