JPS6440182A - Power source controller for inverter type resistance welding machine - Google Patents

Abstract

PURPOSE:To prevent a welding transformer from being damage by magnetic saturation by detecting a primary current of the welding transformer and finding an error between an expected value and an actual value on the middle part of each pulse of the primary current to control switching of an inverter according to the error. CONSTITUTION:A current sensor 38 is provided between a primary coil of the welding transformer 20 and an output terminal of an inverter circuit 18. An output signal of the sensor 38 is supplied to a primary current detection circuit 40 which supplies a signal SI corresponding to the primary current Ip to a magnetic saturation detection circuit 42. The circuit 42 calculates the error between a value D of the latter half part expected from plural sample values A-C of the first half part on the middle part of each pulse and an actual value P of the latter half part and supplies an output signal according to the error to a pulse width control circuit 32 as a magnetic saturation detection signal MS. The circuit 32 controls a switching action of the inverter circuit 18 so as to regulate the pulse width of the primary current Ip when the magnetic saturation is generated according to the signal MS.