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LM51551-DSS, 隔离方案,DC 24V TO 12V/5A

Other Parts Discussed in Thread: LM51551, TL431

参考WEBENCH设计的LM51551-DSS隔离方案,24V输入,12V/5A输出;

现在输出达不到 12V; 我把开关MOS下的保护电阻改为0 OHM,输出也只能到10V左右;输出是明显的锯齿波,频率1.13S,隔离变压器在相同的频率啪啪的响;

下面是电路图与12V输出波形:

12V输出波形:

问题:

1,变压器是根据WEBENCH参考设计定制的,是否有改善建议?

2,空载时输出是上图的波形;输出加一个 轻载(20 OHM电阻),输出就变成0 V左右了;

3,LM51551的手册上说VCC是芯片输出?接变压器的辅助级对吗?

4,LM51551的GATE输出是250KHZ,  约7~8V,但是DUTY很小;