Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2000-02-11
2001-07-31
Patel, Rajnikant D. (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S089000, C323S908000, C361S093500
Reexamination Certificate
active
06269011
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply cable preferable for use in a vehicle to supply electric power from the battery of the vehicle to each section thereof. More specifically, the present invention relates to a power supply cable having “a semiconductor active fuse” which can detect an abnormal current and/or short-circuit failure and if necessary, can cut off the conduction of the current. The present invention also relates to a power supply system having a plurality of the power supply cables.
2. Description of the Related Art
FIG. 1
is a diagram showing a conventional power supply system provided with an overcurrent controller installed in a vehicle, where electric power is selectively supplied from the battery to each load of the vehicle, and a transistor QF, having a temperature sensor, controls the supply of the electric power. In the conventional overcurrent controller shown in
FIG. 1
, the power supply cable extending from a power source
101
for supplying an output voltage VB is connected to an end of a shunt resistor RS and a drain terminal D of the transistor QF, having the temperature sensor, is connected to the second end of the shunt resistor RS. To a source terminal S of the transistor QF, a load
102
is connected. The load
102
is, for example, a headlight or a driving motor for power windows of the vehicle. The overcurrent controller used for the power supply cable shown in
FIG. 1
further includes a driver
701
for detecting a current which flows through the shunt resistor RS and controlling the operation of the transistor QF, and A/D converter
702
for converting the analogue value of the current monitored by the driver
701
into the digital values, and a microcomputer (CPU)
703
. The transistor QF has a thermal protection function such that it can turn off when its junction temperature increases to a predetermined temperature or higher. In this case, a temperature sensor incorporated therein detects the increase of the temperature of the semiconductor chip, and then a flip-flop circuit (or a latch circuit) is triggered by the temperature sensor to turn on the thermal cutoff transistor which cause the transistor QF compulsorily to be turned off.
In
FIG. 1
, a Zener diode ZD
1
keeps the voltage between the gate terminal G and the source terminal S of the transistor QF at 12 V. When an overvoltage is applied to a true gate TG of the transistor QF, the Zener diode ZD
1
bypasses the overvoltage. The driver
701
includes differential amplifiers
711
,
713
as current monitors, a differential amplifier
712
as a current limiter, a charge pump
715
, and a driver
714
. The driver
714
drives the true gate TG of the transistor QF through an internal resistor RG based on an ON/OFF control signal from the microcomputer
703
and the result of the judgment from the differential amplifier
712
as the current limiter whether or not an overcurrent is generated. When the differential amplifier
712
detects the over current more than the predetermined, by means of the voltage drop across the shunt resistor RF, the driver
714
turns off the transistor QF. After that, when the current value decreases less than a lower criterion, the driver
714
turns on the transistor QF, again. The microcomputer
703
always monitors the current via the current monitors (i.e. the differential amplifiers
711
,
713
). When the flow of an abnormal current exceeding the normal value is monitored, the microcomputer
703
outputs a signal for turning off the transistor QF. Upon receiving the signal, the transistor QF is turned off. However, if the temperature sensor installed in the transistor QF detects that the temperature exceeds the predetermined value before the microcomputer
703
outputs the signal for turning off the transistor QF, the temperature sensor outputs a signal for making the thermal protection function of the transistor QF to work. Upon receiving the signal, the transistor QF is turned off.
As described above, the overcurrent controller employed for the conventional power supply cable requires the shunt resistor RS connected to a power supply path in series in order to detect the current. Thus structure, however, has a problem as follows. Since larger and larger current flows in the load in recent years, it becomes impossible to ignore the heat dissipation of the shunt resistor, and the conduction loss of the power supply cable becomes large. This problem is especially serious when larger current is passed through the power supply cable, and in such a case, it is required to install a cooler to the overcurrent controller.
In addition, there is another problem. That is, in the case of using the conventional power supply cable having the thermal protection function, the over current control circuit successfully works when the load
12
or the power supply cable would be short-circuited completely so that a large current flows therethrough. However, such functions do not work when a layer short-circuit, or an imperfect short-circuit having some degree of short-circuit resistance occurs so that a low short-circuit current flows through the power supply cable. As the only method to cover this drawback, the monitor must diagnose the current flowing through the power supply cable so that the microcomputer
703
recognizes an abnormal current. When the microcomputer
703
detects an abnormal current, it turns off the transistor QF. However, this method has a problem that, the current detection of the microcomputer
703
is not so fast that shutting down of the transistor QF may be delayed.
There is also a problem that, in accordance with the necessity to mount the shunt resistor RS, the A/D converter
702
, and the microcomputer
703
or the like, a large space is required for the power supply device. In addition, since these elements are relatively expensive, the cost of the apparatus provided with them becomes high.
SUMMARY OF THE INVENTION
The present invention has been contrived to solve the problems of the above-described prior arts, and an object thereof is to provide a power supply system, having a small conduction loss by eliminating the shunt resistor employed by conventional power supply system, the shunt resistor was directly connected to the power supply path in order to detect an abnormal current flowing through the power supply cable.
Another object of the present invention is to provide a power supply system with high reliability and safety, implementing quick response even when an imperfect short-circuit having some degree of short-circuit resistance occurs in a power supply cable.
Still another object of the present invention is to provide a power supply system including a plurality of the power supply cables comprising intermediate wires. When a short-circuit failure occurs at one or some of the power supply cables, the short-circuited cable is immediately cutoff, thereby avoiding the influence of the short-circuit failure to the remaining cables and/or loads.
Still another object of the present invention is to provide a power supply system where, even if a trouble such as a breaking failure, or an open circuit failure in a cable occurs, the remaining cables work, thereby easily increasing reliability and safety.
Still another object of the present invention is to provide a power supply system where two power sources are easily available at a low cost.
In regard of above objects, a feature of the present invention inheres in a power supply system including a first wire having m branches (m≧2), m first semiconductor active fuses connected to the respective branches of the first wire, m intermediate wires, each of the intermediate wires having first and second ends, the first end is connected to one of the first semiconductor fuses, m second semiconductor active fuses respectively connected to the second end of the intermediate wires, and a second wire having m branches respectively connected to the second semiconductor active fuses. Each of the first semiconductor active fuses i
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Patel Rajnikant D.
Yazaki -Corporation
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