刚开始是设计的输出电压12V,调试出来,带负载能正常工作;后来改变输出电压到18V(调整tl431的电阻为5.1k和33.2k),用开关电源输入的50V,空载情况下输出18V,正常;带上负载,刚开始正常(接90欧电阻,电流0.2A,电压18V),过了有几十秒,然后电流为0,芯片已经烧坏,不知道有没人遇到这种情况?是什么原因呢?
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您将需要重新设计18V输出的电源转换器。为了适应新的输出电压,你可能需要对你的变压器和副侧电路进行修改,而不仅仅是反馈电路。我建议可以参考设计指南:http://www.ti.com/lit/an/slva305c/slva305c.pdf