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UCC28780启动时的VDD问题

Other Parts Discussed in Thread: UCC28780EVM-021, UCC28780

Hi,

我想请教一下当接入220V时,VDD是断断续续的(下面附上两张波形图和原理图),断电时的瞬间,VDD的波形就变得连续了,像是和50Hz的220V市电有关系。不太能理解VDD为什么是这样的波形。电路参考的是UCC28780EVM-021,空载时得到的下面的波形。

schdoc.pdf