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请问图中:R1;R2;R3与C1与D1的作用是什么,怎样计算它们的值.个人理解是一种正反馈,但还是有些不明白,请大家分析?期待着你们.500) {this.resized=true; this.width=500; this.alt='这是一张缩略图，点击可放大。\n按住CTRL，滚动鼠标滚轮可自由缩放';this.style.cursor='hand'}" onclick="if(!this.resized) {return true;} else {window.open('http://u.dianyuan.com/bbs/u/42/1149570491.gif');}" onmousewheel="return imgzoom(this);">
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