Abstract: Single-phase AC resistance welder provides alternating current similar to sine-wave． Due to the long zero-crossing time and high peak current，welding heating becomes discontinuous and splash occurs easily． In order to solve these problems，a control system for AC resistance welding，which takes DSP(Digital Signal Processor) as the controlling core and is composed of information detection，PWM (Pulse Width Modulation) output control，human-computer interaction，I/O (Input/Output) interface and fault detection circuits，is developed，and the correspond-ing software is also designed to assure system function． By employing PWM control to adjust the primary voltage of welding transformer，a relative continuous output in wide current range is ensured． The control system possesses three feedback control modes respectively in terms of current，voltage and power，provides several output frequen-cies，and implements quick and stable output control in half a period． Thus，both high control precision and adaptive welding process can be achieved．

Key words: resistance welding, welding power source, digital signal processor, AC inverter, control system