This paper analyzes the runaway phenomenon and its causes of the single-phase half-controlled-bridge commutated circuit, describes the functions of the fly-wheel diode, and puts forward some corresponding measures according to the features of the trigger circuit of double-base diode and the peculiarities of thyristor. 分析了单相半控桥整流电路的失控现象及产生原因,说明了续流二极管的作用,提出了根据单结晶体管触发电路特点和晶闸管特性采取的应对措施。