Electricity: electrical systems and devices – Safety and protection of systems and devices – Voltage regulator protective circuits
Reexamination Certificate
2000-02-11
2001-04-24
Nguyen, Matthew (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Voltage regulator protective circuits
C323S282000
Reexamination Certificate
active
06222709
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The subject application is related to subject matter disclosed in the Japanese Patent Application No.Heill-074260 filed in Feb. 14, 1999 in Japan, to which the subject application claims priority under the Paris Convention and which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an improvement of a device and method for supplying electric power to a load, and more particularly, to a device and method for switchingly supplying electric power to loads from a battery.
2. Prior Art
FIG. 1
is a circuit diagram showing an exemplary prior art electric power supply control device provided with a semiconductor switch. The electric power supply control device of this prior art example is provided for supplying electric power from a battery selectively to the respective loads located in a motor vehicle.
In the same figure, the electric power supply control device of this prior art example includes a temperature sensor FET QF and a shunt resistor RS connected in series and located upon the electric current path provided for supplying the output voltage VB of an electric power source
101
to a load capacitance
102
such as a headlamp, a driving motor for controlling the open/close operation of a power window. Also, the electric power supply control device is provided with a driver circuit
901
for detecting the electric current flowing through the shunt resistor RS and taking control of the operation of the temperature sensor FET QF by means of a hardware circuit, the analog-digital converter
902
for taking control of on/off operation of the temperature sensor FET QF on the basis of the electric current level as monitored by the driver circuit
901
, and a microcomputer (CPU)
903
.
Furthermore, the temperature sensor FET QF is equipped with a built-in temperature sensor (not shown in the figure) and functions as a semiconductor switch which forcibly turns off the temperature sensor FET QF itself by means of a built-in gate shutdown circuit when the temperature of the temperature sensor FET QF elevates beyond a predetermined level. In the same figure, the reference RG designates an internal resistor while the reference ZD
1
designates a zener diode for maintaining the voltage between the gate G and the source S in order to enable an excessive voltage as applied to the gate G to bypass the gate G.
In the case of the electric power supply control device of this prior art example, there is provided with a protection mechanism for protecting the temperature sensor FET QF and/or the load capacitance
102
from suffering from an excessive electric current. Namely, the driver circuit
901
is composed of differential amplifiers
911
and
913
functioning as an electric current monitoring circuit, a differential amplifier
912
functioning as an electric current limiting circuit, a charge pump circuit
915
, a driving circuit
914
for driving the gate G of the temperature sensor FET QF through the internal resistor RG on the basis of the judgment signal of an excessive electric current given from the electric current limiting circuit and the control signal of the on/off operation given from the microcomputer
903
.
When the electric current passed through the electric power supply control device exceeds a reference level (the upper limit) followed by detecting an excessive electric current, the temperature sensor FET QF is turned off by means of the driving circuit
914
. The temperature sensor FET QF is then turned on when the electric current level has dropped below a reference level (the lower limit).
On the other hand, the electric current is continuously monitored through the electric current monitoring circuit (the differential amplifiers
911
and
913
) under the control of the microcomputer
903
. If an abnormal electric current flows beyond the normal level, the temperature sensor FET QF serves to turn off the driving signal in order to turn off the temperature sensor FET QF. Meanwhile, if the temperature of the temperature sensor FET QF exceeds a predetermined level before the microcomputer
903
outputs the driving signal to turn off the temperature sensor FET QF, the temperature sensor FET QF is turned off by means of an overheat shutdown mechanism.
However, in the case of the prior art electric power supply control device as explained above, there are shortcomings that the shunt resistor RS has to be provided in series with the electric power supplying line in order to detect an abnormal electric current passing therethrough, and therefore the heat dissipation of the shunt resistor becomes problematic because the electric current passing through the load has increased, while the on resistance of the temperature sensor FET QF has currently decreased in the recent years.
Also, while the overheat shutdown mechanism and the excessive electric current limiting circuit as explained above can function properly when there is formed a typical short-circuit in the load
102
or the related wirings resulting in a large electric current, they no longer can properly function when the short-circuit is formed imcomplete, i.e., rare shorting, resulting in a certain short-circuit resistance. In this case, the abnormal electric current has to be detected by means of the microcomputer
903
through the electric current monitor circuit in order to turn off the temperature sensor FET QF. However, the responsibility to the abnormal electric current is not sufficient.
Also, there are further shortcomings that the circuit has tube provided with the shunt resistor RS, the analog-digital converter
902
, the microcomputer
903
and the like, resulting in a large volume the circuit. These elements are relatively expensive so that the production cost of the device is elevated.
Furthermore, the excessive electric current limiting circuit serves also to detect an excessive electric current which is not originating from a trouble of the hardware so that the electric current supply is unnecessarily halted resulting in damage to the usability.
The present invention has been made in order to solve the shortcomings as described above. It is an object of the present invention to provide an electric power supply control device and the electric power supply control method for awaiting for recovery of the normal condition of the electric power supply control device, when an excessive electric current which is not originating from a trouble of the hardware is flowing, rather than immediately shutting down the current path of the excessive electric current, in addition to the function for detecting an excessive electric current due to occurrence of a short-circuit originating from a trouble of the hardware.
SUMMARY OF THE INVENTION
In brief, the above and other objects and advantages of the present invention are accomplished by a new and improved electric power supply control device for supplying electric power to a load from a battery comprising: a semiconductor switch connected between said electric power source and said load in order to control the power supply to said load; an excessive electric current detecting circuit for detecting an excessive electric current flowing through said load; a protection circuit connected to said semiconductor switch for turning off said semiconductor switch if said excessive electric current detecting circuit detects an excessive electric current; and a control circuit for disabling said protection circuit from turning off said semiconductor switch if the rate of increase of the electric current as flowing through said load is smaller than a predetermined rate.
Furthermore, in accordance with a preferred embodiment of the present invention, the rate of increase of the electric current is detected by measuring the level of the electric current a predetermined time after the supply of the electric power to said load is initiated.
Furthermore, in accordance with a preferred embodiment of the present invention, said control circuit serves to enable said protectio
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Nguyen Matthew
Yazaki -Corporation
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