Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Reexamination Certificate
2000-02-11
2002-05-21
Wong, Peter S. (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
Reexamination Certificate
active
06392859
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bidirectional switching device for switching alternating current and an AC semiconductor active fuse employing the bidirectional switching device.
2. Description of the Related Art
FIG. 1
shows a direct current supply/control apparatus according to a related art. The direct current supply/control apparatus has a switching element QF having a temperature sensor. The switching element QF controls the supply of power from a DC power source to a load. The DC power source
101
supplies a DC output voltage VB. The power source
101
is connected to an end of a shunt resistor RS. The other end of the shunt resistor RS is connected to a drain electrode D of the switching element QF whose source electrode S is connected to the load
102
. The load
102
is, for example, a headlight or a power window motor of a vehicle. The bidirectional switching device also has a driver
901
for detecting a current flowing through the shunt resistor RS and controlling the switching element QF accordingly, an A/D converter
902
, and a microcomputer (CPU)
903
for turning on and off a drive signal for the switching element QF according to the current detected by the driver
901
When the temperature of the switching element QF increases, the switching element QF is turned off.
A Zener diode ZD
1
is connected between the gate and source of a power element QM serving as a main semiconductor element of the switching element QF. The Zener diode ZD
1
keeps a voltage of 12 V between the gate electrode G and source electrode S of the switching element QF to bypass an overvoltage so that the overvoltage may not be applied to the true gate TG of the switching element QF. The driver
901
has differential amplifiers
911
and
913
serving as a current monitor circuit, a differential amplifier
912
serving as a current limiter, and a charge pump
915
. The driver
901
incorporates a driver
914
for receiving an ON/OFF control signal from the microcomputer
903
and an overcurrent signal from the current limiter, and according to these signals, driving the true gate TG of the switching element QF through an internal resistor RG. If an overcurrent exceeding an upper limit is detected by the differential amplifier
912
according to a voltage drop across the shunt resistor RS, the driver
914
turns off the switching element QF. If the overcurrent drops below a lower limit, the driver
914
turns on the switching element QF. On the other hand, the microcomputer
903
always monitors a current through the current monitor circuit made of the differential amplifiers
911
and
913
. Upon detecting an abnormal current exceeding a normal level, the microcomputer
903
issues an OFF signal to the switching element QF to turn off the switching element QF. If the temperature of the switching element QF exceeds a predetermined level before the microcomputer
903
issues the OFF signal, a temperature sensor
121
issues a signal to turn off the switching element QF.
To detect a current, the related art must have the shunt resistor RS in a power supply cable. If a large current flows through the shunt resistor RS, the shunt resistor RS will cause a large heat dissipation The large heat dissipation is waste of electric energy and needs a cooler, which complicates and enlarges the supply/control apparatus.
The direct current supply/control apparatus of the related art may work on a dead short that occurs in the load
102
or wiring to produce a large short-circuit current. However, the supply/control apparatus unsatisfactorily works on an incomplete short circuit failure having a certain extent of short-circuit resistance to produce a weak short-circuit current. Only way for the related art to cope with such incomplete short circuit failures is to detect an abnormal current caused by the short circuit failure with the use of the microcomputer
903
and current monitor circuit and turn off the switching element QF by the microcomputer
903
. The microcomputer
903
is expensive and is slow to respond to such an abnormal current.
The shunt resistor RS, A/D converter
902
, and microcomputer
903
that are imperative for the related art need a large space and are expensive, to increase the size and cost of the supply/control apparatus.
In addition to these problems, there is no related art that provides a bidirectional switching device or “an AC semiconductor active fuse” capable of operating on an AC power supply cable to disconnect the AC power supply cable upon detecting an abnormal current.
The reason why there is no bidirectional switching device or AC semiconductor active fuse is mainly because a control circuit for controlling a bidirectional switching device inserted in an AC power supply cable is difficult to design A control circuit for handling small signals usually operates on a voltage of, for example, 6 V, and it is very difficult to design a control circuit that withstands a commercial AC voltage of about 100-130 V Further difficulty lies in monolithically integrating a bidirectional switching device and its control circuit into a power device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a bidirectional switching device capable of serving for an AC power supply cable, detecting an abnormal current, and disconnecting the AC power supply cable accordingly.
Another object of the present invention is to provide a bidirectional switching device capable of detecting alternating current without a shunt resistor in an AC power supply cable.
Still another object of the present invention is to provide a bidirectional switching device that is easy to integrate and is manufacturable at low cost.
Still another object of the present invention is to provide an AC semiconductor active fuse capable of serving for an AC power supply cable.
Still another object of the present invention is to provide an AC semiconductor active fuse capable of suppressing heat dissipation in an AC power supply cable and efficiently supplying AC power,
Still another object of the present invention is to provide an AC semiconductor active fuse that is small and light and needs no labor for replacement.
Still another object of the present invention is to provide an AC semiconductor active fuse capable of speedily responding to an abnormal current caused by an incomplete short circuit failure having a certain extent of short-circuit resistance.
Still another object of the present invention is to provide an AC semiconductor active fuse whose breaking speed for an incomplete short circuit failure is adjustable.
Still another object of the present invention is to provide a structure for a semiconductor switch employed by an AC semiconductor active fuse, to reduce the size and cost of the fuse.
Still another object of the present invention is to provide an AC semiconductor active fuse having a control circuit that withstands the commercial AC voltage.
Still another object of the present invention is to provide a bidirectional switching device and a control circuit that controls the bidirectional switching device and withstands the commercial AC voltage, to form monolithically an AC semiconductor active fuse on a semiconductor chip.
Still another object of the present invention is to provide an AC semiconductor active fuse capable of detecting an abnormal current without intricate, expensive hardware such as a microcomputer and being small, light, and inexpensive.
Still another object of the present invention is to provide an AC semiconductor active fuse having uniform characteristics, employing no precision capacitors or resistors, and minimizing detection errors.
Still another object of the present invention is to provide an AC semiconductor active fuse that needs no external capacitor and is small and manufacturable at low cost.
Still another object of the present invention is to provide an AC semiconductor active fuse that is compact to improve space efficiency in a semiconductor chip and is manufacturable at low cost.
In order to
Tibbits Pia
Wong Peter S.
Yazaki -Corporation
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