SG3525+IR3205,EI40磁心,满占空比是发热正常,占空比小时发热严重

我做的300w DC12V/DC220V逆变器,3525加8050.8550驱动IR3205*4,EE40磁心
满载时开关管及磁心温度正常.在40%占空比一下时开关管严重发热,谐波严重把
220v/150w假负载接在整流管前,输出波形正常,发热正常.无谐波,(下图)
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把负载接在整流管后滤波电容上,波形崎变,开关管严重发热,
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占空比40%上负载接整流管前,波形平整发热较小.
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负载接滤波电容波形变为
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不知道是什么原因请高手指点一下[url=/bbs/u/67/1888731216521270.doc] 1888731216521270.doc