A welding power source connected to an AC input and having two output terminals , the welding power source comprises: a rectifying and wave-filtering unit configured for transforming an input AC into a high voltage DC; a first inverter unit configured for inverting the high voltage DC output by the rectifying and wave-filtering unit into a high voltage high frequency AC; a transformer configured for transforming the high voltage high frequency AC output by the first inverter unit into a low voltage high frequency AC, the transformer comprising on the low voltage side a winding with a center tap and first and a second terminal; the welding power source further comprises a hybrid inverter unit connected to the low voltage side of the transformer configured for performing a rectification or a frequency converting process on the low voltage high frequency AC output by the transformer , and arranged to provide a low voltage DC or a low voltage low frequency AC at an output to the welding workpiece; the hybrid inverter unit comprises four IGBTs, referred to as IGBT Q1, IGBT Q2, IGBT Q3, and IGBT Q4 respectively; each IGBT comprises an integrated Fast Recovery Diodes, FRD and an emitter and a collector, the emitter of the IGBT Q1 is connected to the first transformer terminal and the collector of the IGBT Q3 is connected to the second transformer terminal, the collector of the IGBT Q1 and the collector of the IGBT Q2 are connected, the emitter of the IGBT Q3 and the emitter of the IGBT Q4 are connected , the emitter of the IGBT Q2 and the collector of the IGBT Q4 are connected to form a first output terminal of the welding power source, the center tap of the transformer forming a second output of the welding power source; the hybrid inverter unit is PWM controlled. a rectifying and wave-filtering unit configured for transforming an input AC into a high voltage DC; a first inverter unit configured for inverting the high voltage DC output by the rectifying and wave-filtering unit into a high voltage high frequency AC; a transformer configured for transforming the high voltage high frequency AC output by the first inverter unit into a low voltage high frequency AC, the transformer comprising on the low voltage side a winding with a center tap and first and a second terminal; the welding power source further comprises a hybrid inverter unit connected to the low voltage side of the transformer configured for performing a rectification or a frequency converting process on the low voltage high frequency AC output by the transformer , and arranged to provide a low voltage DC or a low voltage low frequency AC at an output to the welding workpiece; the hybrid inverter unit comprises four IGBTs, referred to as IGBT Q1, IGBT Q2, IGBT Q3, and IGBT Q4 respectively; each IGBT comprises an integrated Fast Recovery Diodes, FRD and an emitter and a collector, the emitter of the IGBT Q1 is connected to the first transformer terminal and the collector of the IGBT Q3 is connected to the second transformer terminal, the collector of the IGBT Q1 and the collector of the IGBT Q2 are connected, the emitter of the IGBT Q3 and the emitter of the IGBT Q4 are connected , the emitter of the IGBT Q2 and the collector of the IGBT Q4 are connected to form a first output terminal of the welding power source, the center tap of the transformer forming a second output of the welding power source; the hybrid inverter unit is PWM controlled. <EOS>