| 摘要 |
PROBLEM TO BE SOLVED: To improve a welding electric power efficiency by reducing a heat generation or exhaustion of a condenser to be connected between a rectification circuit and an inverter. SOLUTION: For example, at a unit energizing term Ta, if the second switching element Q2 is changed into OFF status form ON status at every switching cycle, while the first switching element Q1 is maintained at ON status, the primary current 11 does not stop immediately due to an inductance action of a welding transformer 16 and runs through the primary side circuit as an excess current i until it is cut off. This excess current i flows, as shown by a dotted chain line, from the primary side coil of the welding transformer 16→the third diode D3→the first switching element Q1→the primary side coil closed circuit of the welding transformer 16. That is, since the first switching element Q1 is kept in ON status, the excess current i passed through the third diode D3 returns to the primary side coil of the welding transformer 16 through the switching element Q1, instead of the condenser 12 side. Virtually, no current flow in the condenser 12.
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