Power supply apparatus for resistance welder including means for preventing polarized transformer excitation

A power supply apparatus for a resistance welder comprising:

• first and second gate controlled rectifiers connected in inverse-parallel relationship and inserted between an AC power source and a transformer for supplying, during a predetermined time interval, a welding current from the AC power source to a pair of welding electrodes via the transformer;
• a synchronizing signal generating circuit for generating a synchronizing signal based on the voltage wave form of said AC power source;
• a first ignition pulse forming circuit responsive to said synchronizing signal and a setting level, for supplying a first ignition pulse to said first gate controlled rectifier when said synchronizing signal reaches said setting level;
• a current deviation sensor circuit responsive to the welding current or voltage and producing, based on said welding current or voltage, a current deviation signal representative of the deviation between positive and negative halves of the welding current;
• and
• a second ignition pulse forming circuit responsive to said synchronizing signal, said first ignition pulse and said current deviation signal for supplying to said second gate controlled rectifier a second ignition pulse.

A power supply apparatus for a resistance welder comprising:

• first and second gate controlled rectifiers connected in inverse-parallel relationship and inserted between an AC power source and a transformer, for supplying, during a predetermined time interval, a welding current from the AC power source to a pair of welding electrodes via the transformer;
• a synchronizing signal generating circuit for generating a synchronizing signal based on the voltage wave form of said AC power source;
• a first ignition pulse forming dircuit responsive to said synchronizing signal and a setting level, for supplying a first ignition pulse to said first gate controlled rectifier when said synchronizing signal reaches said setting level;
• a current deviation sensor circuit responsive to the welding current or voltage and producing, based on said welding current or voltage, a current deviation signal representative of the deviation between positive and negative halves of the welding current;
• a controlling angle command circuit for selectively delivering a controlling angle command signal in accordance with the phase difference between said synchronizing signal and said first ignition pulse;
• and
• a second ignition pulse forming circuit responsive to said synchronizing signal, said first ignition pulse, said current deviation signal and said controlling angle command signal, for supplying to said second gate controlled rectifier a second ignition pulse.