Abstract: An operation coil drive device includes a drive control unit to perform control to set, for a semiconductor switching element to switch on and off the source voltage applied to an operation coil of a magnetic contactor, a larger ON/OFF time ratio for a circuit-closing control and a smaller ON/OFF time ratio for a holding control, wherein the drive control unit includes: a circuit-closing-control inductance calculation unit to calculate an inductance of the operation coil immediately after a start of the circuit-closing control; a circuit-closing-control resistance value calculation unit to calculate a direct current resistance value of the operation coil based on the calculation result; and a circuit-closing-control switching correction unit to correct the ON/OFF time ratio of the semiconductor switching element for the circuit-closing control based on the calculation result.

Abstract: An operation coil drive device includes a drive control unit to perform control to set, for a semiconductor switching element to switch on and off the source voltage applied to an operation coil of a magnetic contactor, a larger ON/OFF time ratio for a circuit-closing control and a smaller ON/OFF time ratio for a holding control, wherein the drive control unit includes: a circuit-closing-control inductance calculation unit to calculate an inductance of the operation coil immediately after a start of the circuit-closing control; a circuit-closing-control resistance value calculation unit to calculate a direct current resistance value of the operation coil based on the calculation result; and a circuit-closing-control switching correction unit to correct the ON/OFF time ratio of the semiconductor switching element for the circuit-closing control based on the calculation result.

Abstract: The present invention provides a snubber circuit for a switching power supply that generates rectified direct current power from an inductive load cyclically connected and disconnected by two switching means fed by a direct current power supply. To reduce turn-on and turn-off loss of the switching means and increase switching frequency by reducing power loss in the snubber circuit, the snubber circuit according to the present invention absorbs counter-electromotive force generated during turn-off of the switching means. Turn-on loss of the switching means is reduced because a current from the switching means does not flow through the snubber circuit when the switching means are turned on.

Abstract: In a switching power supply, electric current is supplied through a switching device to a load located away from the switching power supply. The electric current at the load is detected by a remote detecting device at remote detecting terminals. The remote detecting device includes a differential amplifier and a comparator connected to an output terminal of the differential amplifier. The comparator compares an output voltage of the differential amplifier with a reference voltage and outputs an alarm signal when the output voltage of the differential amplifier is lower than the reference voltage. A control device is connected to the switching device, the output terminal of the remote detecting device and a first reference voltage supply device. The control device changes ON-OFF duty ratio of the switching device by comparing the output voltage of the differential amplifier with the first reference voltage to control an output voltage of the switching device at a predetermined value.