Abstract: By utilizing the transformer magnetizing inductor, DC block capacitor,leakage inductance and the auxiliary inductor, a full-bridge LLC soft-switching welding power supply with constant output voltage was proposed. Because the converter was operated between the two resonant frequency in the whole load range,the zero voltage switching(ZVS) turn-on can be achieved for primary side power switch,and the zero current switching(ZCS) turn-off can be achieved for secondary rectifier diodes. The converter can be operated in higher frequency,with high density,lower losses and high efficiency,hence it is especially suitable for the high power applications. Moreover,the operation principles were discussed as well. Finally,a 3.2 kW welding power supply prototype had been implemented,and the experimental results were also presented.