Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2001-02-01
2002-04-09
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S285000
Reexamination Certificate
active
06369556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply control device and method. More particularly, the invention relates to a power supply control device having a semiconductor switch which is controlled in accordance with a control signal supplied to a control signal input terminal to control the supply of electric power from a power supply to a load under the switching control, and a power supply control method in use for the power supply control device.
2. Related Art
The power supply control device with a semiconductor device, which arranged as shown in
FIG. 8
is known. This power supply control device, which is used in a vehicle, selectively supplies electric power source from a battery to respective loads, and controls the power supply to the load.
As shown, the related power supply control device is arranged such that a shunt resistor RS and a drain (D)—source (S) path of a thermal FET QF are connected in series in a power supply path for supplying an output voltage VB of a power supply
101
to a load
102
including headlights, power windows and others. The power supply control device includes a driver
901
which detects a current flowing through the shunt resistor RS and controls the drive of the thermal FET QF by a hardware circuit, an A/D converter
902
for translating the analogue value of a current monitored by the driver
901
into the digital value, and a microcomputer (CPU)
903
.
The thermal FET QF is contained with a thermosensor (not shown). The thermal FET QF as a semiconductor switch has an overheat shut-off function to forcibly shut off the thermal FET QF by a gate shut-off circuit contained therein when temperature of the thermal FET QF rises in excess of a predetermined temperature. In the figure, RG is a resistor, and ZD
1
is a Zener diode which keeps the voltage between the gate G and the source S of the thermal FET QF at 12V, and when overvoltage is applied to the gate G of the FET, forms a bypass for a current caused by the overvoltage.
This related power supply control device has a protecting function against an over current flowing through the load
102
or the drain-source path of the thermal FET QF. The driver
901
includes differential amplifiers
911
and
913
, which serves as a current monitoring circuit, a differential amplifier
912
as a current restricting circuit, a charge/pump circuit
915
, and a drive circuit
914
which drives the gate G of the thermal FET QF through the resistor RG based on an on/off control signal from the microcomputer (referred to as MICROCOMPUTER)
903
and the overcurrent judgement result output from the current restricting circuit.
When the differential amplifier
912
judges on a voltage drop through the shunt resistor RS that the current exceeds a reference value (upper limit), viz., it detects overcurrent, the drive circuit
914
turns off the thermal FET QF. Thereafter, when the current decreases to below another reference value (lower limit), it turns on the FET again.
The MICROCOMPUTER
903
monitors the current by the current monitor circuit (differential amplifiers
911
and
913
) at all times. When an abnormal current in excess of a normal value flows, the MICROCOMPUTER
903
stops the drive current for the thermal FET QF to turn off the FET. When temperature of the thermal FET QF exceeds a prescribed value before a drive signal for the off control is output from the MICROCOMPUTER
903
, the overheat shut-off function operates to turn off the thermal FET QF.
The related power supply control device mentioned above needs the shunt resistor RS connected in series to the power supply path, in order to make the current detection. In the recent trend of large load currents, which induces reduction of the resistance of the thermal FET QF, the heat loss by the shut resistor is not negligible.
The overheat shut-off function and the overcurrent restricting circuit operate when an almost perfect short occurs in the load
102
or the wiring, and large current flows. However, those fail to operate when a layer short, e.g., an imperfect short having some short resistance, occurs and small short current flows. A possible measure taken for the layer short is that the MICROCOMPUTER
903
detects an abnormal current by only using the monitor circuit and turns off the thermal FET QF. A response of the MICROCOMPUTER basis control to such an abnormal current is poor.
Since the shunt resistor RS, the MICROCOMPUTER
903
and the like are indispensably used in the related power supply control device, a large packaging space is required. Additionally, those part and component are relatively expensive, so that the resultant device is high in cost.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to solve the above problems and to eliminate the inconvenient circumstances, and has an object to provide a power supply control device and method which eliminates the shunt resistor connected in series to the power supply path in order to detect the current, thereby repressing the heat loss, quickly responses to an abnormal current flowing when a layer short, e.g., an imperfect short having some resistance, occurs, and is easy to integrate and is low in cost.
According to the present invention, there is provided a power supply control device comprising: a semiconductor switch being controlled in accordance with a control signal supplied to a control signal input terminal to control the supply of electric power from a power supply to a load under the switching control; a reference current generating device for generating a reference current; a reference voltage generating device for generating a reference voltage based on the reference current; a detector for detecting a difference between a voltage between terminals of the semiconductor switch and the reference voltage; and a controller for on/off controlling the semiconductor switch in accordance with a detected difference between the terminal-terminal voltage and the reference voltage.
In the power supply control device, the reference voltage generating device includes a second semiconductor switch controlled in accordance with the control signal, and the second semiconductor is connected in series to the reference current generating device to form a series circuit, which is connected in parallel to the semiconductor switch and the load, whereby the terminal-terminal voltage of the second semiconductor switch is generated in the form of the reference voltage.
In the power supply control device, the reference current generating device generates a reference current dependent on an output voltage of the power supply.
In the power supply control device, the reference current generating device is a constant current source.
In the power supply control device, a voltage characteristic of the reference voltage of the reference voltage generating device is substantially equal to a voltage characteristic in a state that a target current flows, which is in excess of a maximum current within a range where the semiconductor switch and the load are normally operable.
In the power supply control device, the semiconductor switch and the second semiconductor switch are equivalent to each other in a transient voltage characteristic of the terminal-terminal voltage when each semiconductor switch shifts its state from an off state to an on state.
The power supply control device further includes overheat protector operating such that when the semiconductor switch is overheated, the overheat protector turns off the semiconductor switch, to thereby protect the semiconductor switch.
In the power supply control device, the semiconductor switch, the reference voltage generating device, the detector, the controller, and the overheat protector are formed on a same chip.
In the power supply control device, the reference current generating device is located outside the chip.
The power supply control device further comprises prohibiting device for prohibiting the controller from turning on and off the semiconductor switch for a fixe
Laxton Gary L.
Sughrue & Mion, PLLC
Wong Peter S.
Yazaki -Corporation
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