Fuji Electric Co., Ltd.

Kimitada Ishikawa

Takahiro Kudo

Yujiro Kitaide

Junzo Tanaka

Minoru Ishikawa

Koichi Ueki

An over-current protection device is constituted of a current detection unit for detecting a current from a power-supply source to a load having a magnetism detection element with a magnetic impedance (MI) effect, an AC-current supply device for supplying an AC current to the detection element, a bias-current supply device for supplying a bias current to a bias coil, a peak detection device for detecting a peak of impedance of the magnetism detection element as a variation of voltage, and a switch corresponding to a phase for selecting an output of the peak detection device. In the current detection unit, a holding device for holding a switch output and an amplifier are disposed in common for detecting the current in each phase, thereby expanding a current detectable range and reducing power consumption and cost.

Over-current protection device

An overload current protection device for cutting off power applied from a power supply to a load () such as a motor by means of a contactor (switch) () at overloading. With the configuration, an element () having a magnetic impedance effect as current detection units () is used to thereby expand a current detection range by eliminating magnetic saturation due to a core, a problem with a conventional current transformer, thereby providing at low costs an overload current protection device having a wide current detection range.

Overload current protection device using magnetic impedance element

In an overload current protection device for cutting off power from a power supply to a load () such as a motor by means of a contactor (switch) () at overloading, an MI element having a magnetic impedance (MI) effect as current detectors (, and) is installed at a position capable of detecting a current flowing through the secondary winding of power supply transformers (, and) that generate a control power supply to thereby reduce costs without using a constant voltage power supply and expand a current detection range by eliminating magnetic saturation due to a core, a problem with a conventional current transformer, thereby providing at low costs a high-precision overload current protection device having a wide current detection range.

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 current sensor which constitutes an overload protection apparatus and senses a current supplied from a power source to a load is constituted by providing a magnetic sensor having the effect of magnetic impedance (MI), an AC supply means which impresses AC on this sensor, a bias current supply means which supplies a bias current to a bias coil, a peak sensing means which senses the peak or a change in impedance of the magnetic sensor as a change in voltage, and a switch which selects the output of the peak sensing means in accordance with each phase. A holding means which holds switch outputs one after another and an amplification means are provided in common to enable current sensing for each phase. Thus, a range of current sensing is enlarged to reduce power consumption and cost.

Overload current protection apparatus

A small, low-cost, wide-range current sensor excellent in environmental resistance and noise resistance and high in accuracy, and an application device, a DC magnetic field is applied to two magnetic elements () having a magnetic impedance effect by means of a magnet (), while a negative feedback magnetic field is applied to both elements by means of a coil (). The variation of the magnetic field depending on the external magnetic field applied to the magnetic elements () is detected by detection units (). The difference between the output is amplified by a differential amplifier unit (). Thus, detection is achieved in a wide range while eliminating the influence of the noise.

Current sensor and overload current protective device therewith

A drive circuit of an electromagnetic contactor including a series circuit of a surge absorber and a diode connected in parallel with the coil of the contactor, and a transistor connected in parallel with the surge absorber. There are two operation modes. In a first operation mode, the contactor is opened immediately after the contactor has been closed by a starting pulse. In a second operation mode, the contactor is opened after the contactor has been closed by a starting pulse and held by holding pulses following the starting pulse. In the first operation mode, the transistor is kept in an on state for a delay time after starting the contactor. This prevents the current due to counter electromagnetic force of the coil from flowing through the surge absorber before the current is reduced below the allowable level of the surge absorber by the transistor. This makes it possible to protect the surge absorber from being overheated. In the second operation mode, the transistor is turned off immediately after the DC power supply is removed. This makes it possible to open the contactor with little delay.

Drive circuit of an electromagnetic device

A DC electromagnet apparatus that can prevent an excessive making coil current caused by changes in a power supply voltage. The electromagnet has an operation coil, a switching device, and a current detecting resistor connected in series. A one-shot pulse generating circuit produces a one-shot pulse having a pulse width corresponding to the duration of the making coil current flowing through the operation coil to close the electromagnet. A Miller circuit generates, based on the one-shot pulse, a trapezoidal pulse having a predetermined rising rate, a predetermined peak value, and a pulse width substantially equal to that of the one-shot pulse. A comparator produces an ON control signal that controls the switching device in such a manner that the making coil current becomes proportional to the trapezoidal pulse.

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Saitama, Japan

Kimitada Ishikawa