Abstract: Taking advantage of the SG3524 chip a sort of wire feeder timing circuit of the CO₂ arc welding machine was designed.The SG3524 is a kind of special PWM chip with fine performance and most in common use.Through it we can control the on-off of the wire feeder,negative feedback of the armature voltage and adjust the speed.Compared with the traditional silicon controlled rectifier timing circuit,this circuit has more simple structure and better timing performance.By the experiments of electric network voltage fluctuatiuon,the cold-heat state special property variation of electrical machinery and the obstruction inside welding torch,the trustiness of this timing circuit has been verified.In the three conditions,wire feed rate variety are within 10%,and accord with the JB/T8748-1998,MIG/MAG arc welding machine standard demands.This circuit has been used in NBC-500KR welding machine.