Abstract: In each odd-numbered unit current-supplying period of a plurality of unit current-supplying periods making up a set current-supplying time, a control unit subjects only positive switching elements to continuous switching operations at an inverter frequency while keeping negative switching elements in an OFF state, whereas in each even-numbered unit current-supplying period, the control unit subjects only the negative switching elements to continuous switching operations while keeping the positive switching elements in an OFF state. This allows a secondary current having a substantially trapezoidal current waveform to flow through a secondary circuit of a power supply apparatus in the positive direction in each odd-numbered unit current-supplying period but in the negative direction in each even-numbered unit current-supplying period.

Abstract: In odd-numbered current-supplying periods of a plurality of current-supplying periods constituting a gross current-supplying time, a control unit 42 allows continuous switching actions of only a first set of switching elements at an inverter frequency, with a second set of switching elements remaining OFF. In even-numbered current-supplying periods, the control unit 42 allows continuous switching actions of only the second set of switching elements at the inverter frequency, with the first set of switching elements (24, 28) remaining OFF. As a result of this, a secondary circuit of the power supply apparatus allows a secondary current i2, namely a fusing current I having a substantially trapezoidal current waveform to flow in a positive direction in the odd-numbered current-supplying periods, and to flow in a negative direction in the even-numbered current-supplying periods.

Abstract: This reflow soldering apparatus comprises a heater tip 10 for soldering sites to be soldered of a workpiece W by reflow method, a power supply unit for supplying an electric power for heat generation or heating to the heater tip, a control unit for providing a control of the supplied current in the power supply unit, and a pressing unit 16 for pressing the heater tip against the sites to be soldered of the workpiece W. An inverter of the power supply unit has four transistor switching elements. By the control unit by way of a driving circuit, the first set of switching elements and are simultaneously switching (ON/OFF) controlled at a predetermined inverter frequency (e.g., 10 kHz) in response to in-phase inverter control signals G1 and G3, whereas the second set of switching elements are simultaneously switching controlled at the inverter frequency in response to in-phase inverter control signals G2 and G4.

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: In each odd-numbered unit current-supplying period of a plurality of unit current-supplying periods making up a set current-supplying time, a control unit subjects only positive switching elements to continuous switching operations at an inverter frequency while keeping negative switching elements in an OFF state, whereas in each even-numbered unit current-supplying period, the control unit subjects only the negative switching elements to continuous switching operations while keeping the positive switching elements in an OFF state. This allows a secondary current having substantially a trapezoidal current waveform to flow through a secondary circuit of a power supply apparatus in the positive direction in each odd-numbered unit current-supplying period but in the negative direction in each even-numbered unit current-supplying period.

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: This reflow soldering apparatus comprises a heater tip 10 for soldering sites to be soldered of a workpiece W by reflow method, a power supply unit for supplying an electric power for heat generation or heating to the heater tip, a control unit for providing a control of the supplied current in the power supply unit, and a pressing unit 16 for pressing the heater tip against the sites to be soldered of the workpiece W. An inverter of the power supply unit has four transistor switching elements. By the control unit by way of a driving circuit, the first set of switching elements and are simultaneously switching (ON/OFF) controlled at a predetermined inverter frequency (e.g., 10 kHz) in response to in-phase inverter control signals G1 and G3, whereas the second set of switching elements are simultaneously switching controlled at the inverter frequency in response to in-phase inverter control signals G2 and G4.

Abstract: When a second switching element Q.sub.2 is changed over from ON state to OFF state for each switching cycle while a first switching element Q.sub.1 remains ON in a unit weld period T.sub.a for example, a primary current I.sub.1 does not come to a stop at once under the influence of inductance of a welding transformer 16 but it flows as a transient current i through a primary circuit until it is off. The transient current i makes a closed circuit through which it flows from a primary coil of the welding transformer 16 via a third diode D.sub.3 and then a first switching element Q.sub.1 again into the primary coil of the welding transformer 16. More specifically, due to the first switching element Q.sub.1 being kept ON, the transient current i which has passed through the third diode D.sub.3 flows through the first switching element Q.sub.1, without passing through a capacitor 12, and comes back into the primary coil of the welding transformer. Little or substantially no current flows through the capacitor 12.

Abstract: An inverter resistance welding control or power supply apparatus includes a clock generator which generates a clock signal defining a switching cycle of an inverter in a resistance welding machine, a device for preselecting a predetermined reference value corresponding to a desired current peak, a current sensor for detecting primary or secondary current of the welding machine, and an inverter control for controlling the inverter on a switching cycle-by-cycle basis. Specifically, the apparatus turns on the inverter in response to a leading edge of the clock signal, and turns the inverter off either when the current detected signal has reached the reference value or when the clock signal has reached a trailing edge. The control apparatus further includes a magnitude evaluator for measuring a magnitude of the current from the detected signal, which magnitude is expressed in root mean square, arithmetic mean or averaged peak value.