Abstract: A welding power source controlled by Z-80 single-board microcomputer has been developed.A computer was introduced into the QH-ARC welding arc control system.Various types of desirable characteristics may be obtained by only changing the software.In this paper the hardware diagram and the features of extended interfaces were carefully briefed,such as A/D and D/A convertors,PIO,electronic switch and some logic circuits.The design method of the gain in some blocks is given,and the effect of "converse equivalence" on system accuracy is discussed.In the nonlinear discrete control,a sampling period T=100μs is adopted.The P and PI regulation with threshold and the experimental results of constant voltage,constant current and dual-step static characteristics are described.The results show that ±1bit static accuracy and satisfactory dynamic response can be obtained with the constant value regulation system.This enables the power source control to be more accurate and versatile.Doubtlessly,this system should be n effective means of realizing the fully automatic welding process.