Resistance welding power supply apparatus

A resistance welding power supply apparatus having a pair of welding electrodes through which a welding current flows, said pair of welding electrodes adapted to come into pressure contact with workpieces to resistance weld said workpieces, said resistance welding power supply apparatus comprising:

• a capacitor for storing resistance welding energy in the form of electric charges;
• charging means arranged to charge said capacitor;
• first switching means having a first terminal electrically connected to one electrode of said pair of welding electrodes and having a second terminal electrically connected to a first electrode of said capacitor;
• second switching means having a first terminal electrically connected to the other electrode of said pair of welding electrodes and having a second terminal electrically connected to a second electrode of said capacitor;
• third switching means having a first terminal electrically connected to said other electrode of said pair of welding electrodes and having a second terminal electrically connected to said first electrode of said capacitor;
• fourth switching means having a first terminal electrically connected to said one electrode of said pair of welding electrodes and having a second terminal electrically connected to said second electrode of said capacitor;
• and
• control means electrically connected to respective control terminals of said first, second, third and fourth switching means, said control means providing a switching control of said first and second switching means while keeping said third and fourth switching means OFF in a first current-supplying mode where said welding current flows through said workpieces in a first direction, said control means providing a switching control of said third and fourth switching means while keeping said first and second switching means OFF in a second current-supplying mode where said welding current flows through said workpieces in a second direction, said control means upon switching between said first and second current-supplying modes initiating a switching control of the following current-supplying mode in the course of decrease of said welding current based on the preceding current-supplying mode.