Three stage power source for electric ARC welding

A three stage power source comprising an input first stage having an AC input and a first DC output signal, a second stage in the form of an unregulated DC to DC converter having an input connected to said first DC output signal, a network of switches switched at a high frequency with a given duty cycle to convert said input into a first internal AC signal, an isolation transformer with a primary winding driven by said first internal high frequency AC signal and a secondary winding for creating a second internal AC signal and a rectifier to convert said second internal AC signal into a second DC output signal of said second stage, with the magnitude related to said duty cycle of said switches, wherein said input first stage includes a power switch having a soft switching circuit and a three stage to convert said DC output signal of said second stage into a current suitable for welding.

A three stage power source comprising an input first stage having an AC input and a first DC output signal with a DC to DC converter having a power switch with an active soft switching circuit, a second stage in the form of an unregulated DC to DC inverter having a plurality of power switches, said plurality of switch operated by a PWM set at a given duty cycle, and a third stage to convert the DC output of said unregulated inverter into a current suitable for welding.

An active soft switching circuit for controlling switching losses of a switching element in a boost converter at the input of a power source for a welder or plasma cutter, said boost converter having a main inductance, a main switching device, and a main rectifier with a cathode, said active softswitching circuit comprising:

• an auxiliary switching device and a tank circuit closed by said auxiliary switching device, said tank circuit comprising a resonant inductance coupled in series with said auxiliary switch, and a resonant capacitance coupled across said main switching device, said resonant capacitance having a first resonant capacitor portion coupled across said resonant inductance and a second resonant capacitor portion coupled across said auxiliary switching device.