Abstract: The decreasing time of free-wheeling current is relative to duty cycle in the exiting FB-ZVZCS-PWM soft-switching inverter arc welding power supply with the block capacitor,and it is hard to achieve zero current switching(ZCS) for lagging leg with low duty cycle.By adopting auxiliary transformer in the primary side of main transformer,the decreasing time of free-wheeling current is independent of duty cycle,which is proportion to the peak current in the primary side of main transformer.A new FB-ZVZCS-PWM soft-switching inverter arc welding power supply was introduced,which adopted the auxiliary transformer and limited bipolar control mode.The principles of realizing zero voltage switching(ZVS) for leading leg by capacitor and ZCS for lagging leg by auxiliary transformer were explained.Simulation and experimental results showed that the soft-switching could be realized under all loads as long as the auxiliary transformer was designed by the maximum peak current in the primary side of main transformer.