Patent ID: 7336512

Claim:
A method of providing welding power, comprising the steps of: rectifying an input line voltage; pre-regulating the input line voltage to provide a dc bus; and converting the dc bus to a welding output; wherein pre-regulating includes SCT switching a boost convertor; maintaining a boost converter switch off, and allowing current to flow through a boost inductor, a snubber inductor, and a first diode, to the dc bus; turning the switch on and diverting current from the snubber inductor to the switch; reversing the current in the snubber inductor; discharging a second capacitor through a first capacitor, a third diode, and the snubber inductor, thereby transferring energy from the second capacitor to the snubber inductor; diverting current through a fourth diode, the third diode and the first capacitor when the second capacitor is discharged, thereby transferring energy from the snubber inductor to the first capacitor; turning the switch off and diverting current through the fourth diode and into the second capacitor; allowing the voltage on the second capacitor to rise until current begins to flow from the snubber inductor to the first capacitor; diverting current from the second capacitor through a third diode to the second diode; allowing the current flowing from the boost inductor to the snubber inductor to increase until all of the current from the boost inductor flows into the snubber inductor; and diverting current from the first capacitor to the first diode; and repeating these steps.