L6562使用的问题

使用L6562做了一个LED电源.现在效率很低,240VAC时才75%.
电源如下:输入100V---240VAC  50/60HZ
        输出 40VDC/350MA   (即负载是12个1W的LED串接)
        
测试:240VAC/73MA  37VDC/0.359MA  EFF=75%

     120VAC/142MA  37VDC/0.367MA  EFF=80%

变压器参数:初级电感量1.1MH  
初级匝数100匝 φ0.21MM*1P
次级40匝 φ0.31MM*2P
供电20匝 φ0.21MM*1P500) {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/69/471071220940898.jpg?x-oss-process=image/watermark,g_center,image_YXJ0aWNsZS9wdWJsaWMvd2F0ZXJtYXJrLnBuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzQwCg,t_20');}" 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/69/471071220940948.jpg?x-oss-process=image/watermark,g_center,image_YXJ0aWNsZS9wdWJsaWMvd2F0ZXJtYXJrLnBuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzQwCg,t_20');}" onmousewheel="return imgzoom(this);">
请高手指教.特别是变压器,我觉得这种电源理论应该可以做到90%(240VAC输入).