Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-07-19
2002-08-27
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C323S282000
Reexamination Certificate
active
06441679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor active fuse, and particularly, to a semiconductor active fuse appropriate for a high-voltage power supply controller.
2. Description of the Related Art
FIG. 1
shows an example of a power supply controller according to a related art. This power supply controller employs a transistor QF having a temperature sensor, for selectively controlling the supply of power from a power supply
101
, such as a battery of a vehicle, to a load
102
. In the example of
FIG. 1
, the power supply
101
is of a 12-V system and supplies a voltage VBp. The power supply
101
is connected to an end of a shunt resistor RS. The other end of the shunt resistor RS is connected to a drain terminal D of the transistor QF. A source terminal S of the transistor QF is connected to the load
102
, which may be a headlight or a power-window driving motor. The power supply controller further has a control circuit
901
, an A/D converter
902
, and a microcomputer (CPU)
903
. The control circuit
901
detects a current passing through the shunt resistor RS and controls the transistor QF through hardware circuits. The A/D converter
902
and microcomputer
903
turn on and off a drive signal for the transistor QF according to the current monitored by the control circuit
901
. The transistor QF has a thermal protection function for forcibly turning off the transistor QF through an incorporated gate turn-off circuit. When detecting that the temperature of the transistor QF is above a specified temperature, the temperature sensor in the transistor QF informs the gate turn-off circuit of the high temperature, and the gate turn-off circuit forcibly turns off the transistor QF.
A Zener diode ZD
1
keeps a voltage of 12 V between the gate terminal G and source terminal S of the transistor QF, and protecting an overvoltage breakdown, bypassing between the true gate TG and the source terminal of the transistor QF. The control circuit
901
includes differential amplifiers
911
and
913
serving as a current monitor circuit, a differential amplifier
912
serving as a current limiter, a charge pump
915
, and a driver
914
. The driver
914
receives an ON/OFF control signal from the microcomputer
903
and an overcurrent signal from the current limiter
912
and drives the gate G of the transistor QF through an internal resistor RG (not shown) accordingly. The differential amplifier
912
uses a voltage drop occurring at the shunt resistor RS to detect a current flowing to the transistor QF. If the detected current is an overcurrent above an upper threshold, the differential amplifier
912
instructs the driver
914
to turn off the transistor QF. Once the detected current becomes below a lower threshold, the differential amplifier
912
instructs the driver
914
to turn on the transistor QF. 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 transistor QF to turn off the transistor QF. If the temperature of the transistor QF exceeds a predetermined level before the microcomputer
903
issues the OFF signal, the thermal protection function turns off the transistor QF.
To detect a current, the related art must have the shunt resistor RS in a power supply line. If a current flowing through the shunt resistor RS is large, the shunt resistor RS will cause a large heat loss that is not ignorable.
The thermal protection function and overcurrent control circuit of the related art may work on a dead short that occurs in the load
102
or wiring to produce a large current. However, the related art unsatisfactorily works on an incomplete short circuit failure such as a layer short having a certain extent of short-circuit resistance to produce only a weak short-circuit current. Only way for the related art to cope with such an incomplete short circuit failure 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 transistor QF by the microcomputer
903
. The microcomputer
903
, however, is slow to respond to such an abnormal current.
The shunt resistor RS, AID 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 power supply controller. When applied for a high-voltage power line, the microcomputer
903
must be protected from the high voltage, to further increase the size and cost of the power supply controller.
At present, power supply systems for vehicles are mainly of 12 volts. For the 12-V power supply system, it is sufficient to consider a maximum supply voltage of about 18 V. To reduce a power loss due to a load current, it is studied to increase the power supply system to 42 volts. To meet the 42-V supply voltage, the transistor QF and control circuit
901
must have a higher breakdown voltage.
If the supply voltage is increased to 42 V, the differential amplifiers
911
to
913
and driver
914
of the related art of
FIG. 1
must also have an increased breakdown voltage. The elements
911
to
914
are manufactured through CMOS processes or BiCMOS processes, and these processes must be modified to increase the breakdown voltage of the elements. Increasing the breakdown voltage of a given device is achievable by increasing the number of elements having the same breakdown voltage, thickening a gate insulating film, or forming a guard ring or a field plate for improving the breakdown voltage of each element. The technique of increasing the number of elements having the same breakdown voltage increases a chip area and complicates manufacturing processes to increase costs. The technique of thickening a gate insulating film deteriorates the electric characteristics such as transconductance g
m
of each semiconductor element. In addition, operating the semiconductor elements under a high voltage deteriorates the reliability of the semiconductor elements.
It is advantageous, in terms of costs and reliability, if the control circuit
901
can still employ 12-V elements even if a higher supply voltage is introduced.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the problems of the related art mentioned above and provide a semiconductor active fuse capable of quickly coping with an abnormal current caused by an incomplete short circuit failure such as a layer short without a shunt resistor.
Another object of the present invention is to provide a semiconductor active fuse capable of employing conventional 12-V elements for a comparator for comparing the potentials of the second main electrodes of first and second semiconductor elements with each other even if a 12-V power supply system is increased to, for example, a 42-V power supply system.
Still another object of the present invention is to provide a semiconductor active fuse capable of operating with a control circuit that employs a comparator of a conventional breakdown voltage, thereby avoiding a cost increase to be involved in increasing the breakdown voltage of the comparator.
Still another object of the present invention is to provide a semiconductor active fuse of improved reliability realized by a comparator of a control circuit that operates under a standard voltage, not requiring the bias condition for higher supply voltage.
In order to accomplish the objects, the present invention provides a semiconductor active fuse having a first semiconductor element that has a first main electrode connected to a DC power supply, a second main electrode connected to a load, and a control electrode, a second semiconductor element that has a first main electrode connected to the first main electrode of the first semiconductor element, a second main electrode connected to a reference circuit, and a control electrode connected to the control electrode of the f
Cunningham Terry D.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Tra Quan
Yazaki -Corporation
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