| 摘要 |
A power supply for supplying a substantially square wave of current to a welding arc and including a source of A.C. power having a succession of positive and negative portions forming an input voltage cycle; first switch means for initiating a positive output current pulse at a selected first switching point during the positive portion of the input voltage cycle; second switch means for initiating a negative output current pulse at a selected second switching point during the negative portion of the input voltage cycle; means for sensing the output current through the arc; means responsive to the output current for creating a command signal as a voltage level which varies according to the desired instantaneous output current through the arc; and, control means for automatically selecting the first and second switching points in response to the voltage level. The control means comprises a first circuit for creating a first voltage ramp signal, a second circuit for creating a second voltage ramp signal with the voltage ramp signals having generally the same final voltage but different slopes. The ramp signals as they are being created are compared with the voltage level. The comparing means creating the first switching signal when the first ramp signal progresses to the voltage level and creating the second switching signal when the second ramp signal progresses to the voltage level, whereby the current pulses are automatically unbalanced at high selected output current and progressively approaches balanced as the selected output current decreases.
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