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/55/664461184400138.bmp');}" onmousewheel="return imgzoom(this);">单断反激电源求教
电路如图,变压器磁芯为EI25,现在为输出电压只有14V,A点振荡波形正常,不过频率过高,一个开关周期只有2US,PC817 1脚有一个正负3V的振荡波形,减小R10,增大C20,R20,C14后,输出电压能上到24V,不过很快烧毁PF40,不知道为何原因,请教高手指点.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/55/664461184400138.bmp');}" onmousewheel="return imgzoom(this);">
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/55/664461184400138.bmp');}" onmousewheel="return imgzoom(this);">