INVERTER TYPE RESISTANCE WELDING POWER UNIT

摘要

PROBLEM TO BE SOLVED: To improve quality control of resistance welding by monitoring an actually flowing electric current value while executing constant electric current control of current peak value. SOLUTION: CPU 40 starts up a control pulse CA or CB at the start end of each unit energizing cycle to turn on transistors 18, 24 or 20, 22. Successively, CPU 40 causes the control pulse CA or CB to fall in response to the output signal of comparing circuit 59 or in response to the end of internal clock to turn off transistors 18, 24 or 20, 22. At the same time, CPU 40 makes an integrated value SIn of the electric current detected signal SI at that time hold in a sampling/hold circuit 56 and take in through A-D converter 58. An electric current average value is obtained from this electric current integrated value SIn and energizing pulse width Tn. After welding energizing is completed, an electric current average value for total cycle is obtained from the electric current average value for each cycle accumulated in a memory part 64 and then discrimination of normal/defective welding is executed based on this electric current average value.