zxd414:
沒有錯,詳細請看我的帖子,有個附件,說得很明白,高手就是這么煉成的:http://bbs.dianyuan.com/topic/593343------------------------------------------------------------Theboardisequippedwithafeedbacklooptoregulatetheoutputcurrent.ThisfeedbackloopsensestheLEDcurrentoversenseresistorR10,andacurrentmirrorismadefromtransistorsQ10a/Q10b.UsingR18,thecurrentlevelcanthenbeset.Thesamefeedbackloopisalsousedtoprovideovervoltageprotection.IftheLEDvoltageexceeds33V,acurrentthroughR17andD11,D12andD13willstartrunning.ThecurrentthroughtheoptocouplerIC2willpulluptheREGpin.Atvaluesabove2.7V,the‘ontime’oftheinternalMOSFETiszero.Thefeedbackloophasaproportional,andpartiallyintegratedaction.ThegainiscriticalduetothephaseshiftcausedbytheconverterandtheoutputcapacitorC10.Increasedgainwillmakethefeedbackloopintrinsicallyunstable.