Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
1999-12-28
2001-04-24
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S289000
Reexamination Certificate
active
06222355
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a power supply control device and a method of controlling the same. More particularly, the invention relates to a power supply control device with a semiconductor switch for controlling the supply of electric power from a power supply to a load by its switching control in response to a control signal, and a power supply control method for controlling the same.
2. Related Art
A power supply control device with a semiconductor switch as shown in
FIG. 19
is known. This conventional power supply control device supplies electric power from a battery selectively to each load in a motor vehicle, and controls the power supply to the load.
As seen from the figure, the power supply control device is arranged such that a shunt resistor RS and the drain (D)—source (S) path of a thermal FET QF are connected in series in a path for applying an output voltage VB of a power source
101
to a load
102
, such as head lamps and drive motors for power windows. The power supply control device includes a driver
901
for detecting a current flowing through the shunt resistor RS and controlling the drive of the thermal FET QF by a hardware circuit, an A/D converter
902
for performing an on/off control of a drive signal to the thermal FET QF in accordance with a current value monitored by the driver
901
, and a microcomputer (CPU)
903
.
The thermal FET QF, containing a temperature sensor (not shown) therein, has such an overheat cut-off function that when a temperature of the thermal FET QF rises to a predetermined temperature or higher, a gate cut-off circuit contained therein forcibly turns off the thermal FET QF. In the figure, RG represents a resistor RG, and ZD
1
is a Zener diode which keeps a voltage across the gate (G)-source (S) path at 12V, and when an overvoltage will reach the gate G, provides a by path for the overvoltage.
The conventional power supply control device has also a protection function against an overcurrent flowing through the load
102
or the drain-source path of the thermal FET QF. The power supply control device includes a driver
901
, differential amplifiers
911
and
913
as current monitoring circuits, another differential amplifier
912
as a current restriction circuit, a charge pump circuit
915
, and a drive circuit
914
for driving the gate G of the thermal FET QF in accordance with an on/off control signal from the microcomputer
903
and an overcurrent judging result signal from the current restriction circuit.
When it is judged through the differential amplifier
912
that the current exceeds a judging value (upper limit) of current, by a voltage drop across the shunt resistor RS, viz., an overcurrent is detected, the drive circuit
914
turns off the thermal FET QF, and when the current decreases below a judging value (lower limit), it turns on the thermal FET QF.
The microcomputer
903
always monitors the current by use of the current monitoring circuit (differential amplifiers
911
and
913
). If an abnormal current flows which is in excess of a normal current in value, it interrupts the drive signal to the thermal FET QF to turn off the thermal FET QF. Before the microcomputer
903
outputs a drive signal for an off control, when a temperature of the thermal FET QF exceeds a predetermined value of temperature, the thermal FET QF is turned off by the overheat cut-off function.
In the conventional power supply control device, the shunt resistor RS connected in series to the power supplying path is required for the current detection. The on-resistance of the recent thermal FET QF reduces, so that the load current is large. For this reason, a heat loss by the shunt resistor amounts to a quantity not negligible.
The overheat cut-off function and the overcurrent restriction circuit effectively function when a large current flows because of a dead short in the load
102
or wirings. When an imperfect short-circuit, such as a layer short-circuit, having a certain amount of short resistance occurs, and a small short-circuit current flows, the overheat cut-off function and the overcurrent restriction circuit fail to function. In this case, only one optional way permitted is that the microcomputer
903
detects an abnormal current by the current monitoring circuit and turns off the thermal FET QF. However, the control by the microcomputer has a disadvantage of slow response to the abnormal current.
The use of the shunt resistor RS, the microcomputer
903
and the like indispensably requires a large mounting space. Further, those components are relatively expensive, so that cost to manufacture the power supply control device is high.
SUMMARY OF INVENTION
Accordingly, an object of the present invention is to provide a power supply control device in which there is no need of using the shunt resistor connected in series to the power supply path for detecting current, to thereby reduce the heat loss, and it quickly responds to an abnormal current when an imperfect short-circuit, such as a layer short-circuit, having a certain amount of short-circuit resistance occurs, and it may be fabricated into an integrated circuit and has a reduced cost to manufacture, and a method of controlling such a power supply control device.
According to the present invention, there is provided a first power supply control device comprising:
a semiconductor switch which responds to a control signal applied to a control signal input terminal to be switched and controls the supply of electric power from a power supply to a load;
reference voltage generating means for generating a reference voltage having a voltage characteristic substantially equivalent to that of a voltage between the terminals of the semiconductor switch;
detecting means for detecting a difference between the voltage between the terminals of the semiconductor switch and the reference voltage;
control means for performing an on/off control of the semiconductor switch in accordance with the difference between the voltage between the terminals of the semiconductor switch and the reference voltage.
A second power supply control device of the invention corresponds to the first power supply control device specified such that the reference voltage generating means includes a circuit connected in parallel with the semiconductor switch and the load, the circuit containing a series circuit consisting of a second semiconductor switch and a second load, and generates a voltage between the terminals of the second semiconductor switch as the reference voltage.
A third power supply control device of the invention corresponds to the first or second power supply control device specified such that a voltage characteristic of the reference voltage of the reference voltage generating means is substantially equivalent to a voltage characteristic in a state that a target current, which is in excess of a maximum current within a normal operation range, flows into the semiconductor switch and the load.
A fourth power supply control device of the invention corresponds to the second or third power supply control device specified such that a transient voltage characteristic of a voltage between the terminals of the semiconductor switch when the semiconductor switch shifts its state from an off state to an on state is equivalent to the corresponding one when the second semiconductor switch shift its state so.
A fifth power supply control device of the invention corresponds to any of the second to fourth power supply control device specified such that a current capacity of the second semiconductor switch is smaller than that of the semiconductor switch, and a resistance ratio of the load and the second load is substantially inversely proportional to a current capacity ratio of the semiconductor switch and the second semiconductor switch.
A sixth power supply control device of the invention corresponds to any of the first to fifth power supply control device which further comprises second reference voltage generating means including a circuit, connected in paral
Ohshima Shouzou
Watanabe Mitsugu
Berhane Adolf Deneke
Sughrue Mion Zinn Macpeak & Seas, PLLC
Yazaki -Corporation
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