Abstract: The number of cycles R of a fundamental frequency <SET>F (Hz) for a set value Tw (ms) of a set weld time [WELD] is first found as a real number. The number of cycles R conforms to the number of times (real number) of repetition of the fundamental frequency <SET>F cycle in the interval of the set weld time Tw and is given as Tw×<SET>F (step B1). An AC waveform cycle set value Ns (integer) for the set weld time Tw is then determined as an integer Min [N] that is equal to the number of cycles R or to the least one (i.e., the integer closest to R) of larger integers (N) than R (step B2). An AC waveform cycle set frequency Fs (Hz) and a period Ts (ms) for the set weld time Tw is then found from the set number of cycles Ns. The set frequency Fs and the period Ts are given as Fs=1/Ts and Ts=Tw/Ns, respectively (step B3).

Abstract: Disclosed is a resistance-welding power supply apparatus comprising a large-capacitance capacitor for storing a welding energy in the form of electric charge, a charging unit for charging the capacitor up to a predetermined voltage, a transistor group electrically connected between the capacitor and a welding electrode on one hand, and a control unit for causing a switching action of the transistor group at a predetermined frequency during the weld time to provide a control of a welding current I. The charging unit includes a charging transformer and a rectifying circuit. The control unit includes a main control unit for providing a control of the switching action of the transistor group by way of a drive circuit. The control unit further includes various sensors, measuring circuits and an arithmetic circuit, for providing a feedback control of the welding current, an interelectrode voltage or a welding power.

Abstract: The number of cycles R of a fundamental frequency <SET>F (Hz) for a set value Tw (ms) of a set weld time [WELD] is first found as a real number. The number of cycles R conforms to the number of times (real number) of repetition of the fundamental frequency <SET>F cycle in the interval of the set weld time Tw and is given as Tw×<SET>F (step B1). An AC waveform cycle set value Ns (integer) for the set weld time Tw is then determined as an integer Min [N] that is equal to the number of cycles R or to the least one (i.e., the integer closest to R) of larger integers (N) than R (step B2). An AC waveform cycle set frequency Fs (Hz) and a period Ts (ms) for the set weld time Tw is then found from the set number of cycles Ns. The set frequency Fs and the period Ts are given as Fs=1/Ts and Ts=Tw/Ns, respectively (step B3).

Abstract: A main control unit can be for example a microprocessor (CPU) or a dedicated logic circuit.

Abstract: When each weld period starts, a control feeds e.g., a high-level ON signal to switching elements having the associated polarity of an inverter so that the switching elements go on and remain on (step S2). This allows the current to start to flow and rise with a sharp gradient on the primary and secondary sides of a welding transformer. When a current detection signal <I.sub.1 > from a sensor reaches a preset current value I.sub.F for current build-up in that weld period (steps S3 and S4), the control stops the on signal and instead issues a PWM signal to provide a high-frequency (e.g., 10 kHz) switching control of the switching elements (steps S5 to S9).

Abstract: A capacitor type welding power unit incorporates a constant-current charging control circuit which serves to control a charging current being supplied to a capacitor so as to be substantially constant during the charging. By such a control circuit, which typically performs a thyristor firing control, the charging voltage of the capacitor is made to follow a reference signal, which is preferably set to change linearly with time, and it reaches a preset target value in a predetermined time regardless of fluctuations in the supply voltage. Furthermore, such a control circuit enables the capacitor to be directly connected to the output terminals of a rectifier circuit with no charging resistor being provided so as to reduce resistance heating and so as to lower power consumption in charging the capacitor.