A　novel　inverter　power　source　is　developed　characterized　with　constant　output　current　and　unit　power　factor　input.　Digital　signal　processor　(DSP)　is　used　to　realize　power　factor　correction　and　control　of　back-stage　inverter　bridge　of　the　arc　welding　inverter.　The　fore-stage　adopts　double　closed　loop　proportion　and　integration　(PI)　rectifier　technique　and　the　backstage　adopts　digital　pulse　width　modulation　(PWM)　technique.　Simulated　waves　can　be　obtained　in　Matlab/Simulink　and　validated　by　experiments.　Experiments　of　the　prototype　showed　that　the　total　harmonic　distortion　(THD)　can　be　controlled　within　10%　and　the　power　factor　is　approximate　to　1.