Fuji Electric Co., Ltd.

Koichi Ueki

Yasuo Kobayashi

Kimitada Ishikawa

Masahiro Motonobu

Conventionally, a non-conductive period is provided in a region in the vicinity of zero of an AC power voltage via a voltage detection circuitto turn off reliably. The FETmaintains the ON state within several switching cycles after the non-conductive interval to rapidly restore the magnetizing coil current, so that the magnetizing coil current rapidly increases. An object is to suppress beat noise in the electromagnetic device. Within a prescribed interval following the non-conductive interval, a partial voltage at a resistorof an output Vof a mono-stable circuitis added as a bias voltage to a detection voltage of a magnetizing coil current at a resistorand is detected by the ICThe ICdrives a FETwith a constant switching period after the non-conductive interval, thereby preventing the increase in the magnetizing coil current and resolving the problem.

Electromagnetic apparatus drive apparatus

A power transformer is formed of a pair of cores having wiring storage portions, at least one primary winding formed of a spirally wound flat ring having a pair of primary leading portions, at least one secondary winding formed of a flat plate, at least one spacer interposed between the flat ring and the flat plate, and an insulation member mounted in the wiring storage portions of the cores. The flat ring, flat plate and at least one spacer for insulating the flat ring and the flat plate are housed in the insulation member. The insulation member has an opening for allowing the primary leading portions to pass therethrough. In order to insulate the primary leading portions from burrs of the secondary winding, a protrusion may be formed on an outer periphery of the spacer to be located under the primary leading portions, or a cut-out portion may be formed in the flat plate.

Power transformer

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. A first overvoltage protecting device is connected to the control device for protecting the load from overvoltage by monitoring the output of the switching device.

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Tokyo, Japan

Koichi Ueki