Electrical transmission or interconnection systems – Plural load circuit systems – Plural sources of supply
Reexamination Certificate
2000-02-11
2002-01-01
Wong, Peter S. (Department: 2838)
Electrical transmission or interconnection systems
Plural load circuit systems
Plural sources of supply
C307S064000
Reexamination Certificate
active
06335577
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply control unit and a power supply control method, and more particularly to a power supply control unit having a semiconductor switch for controlling a power supply from a power source to a load by switching control depending on a control signal.
2. Description of the Related Art
FIG. 1
shows a conventional power supply control unit having a semiconductor switch. This conventional power supply control unit supplies a power from a battery to each load selectively and controls the power supply to the load.
In this conventional power supply control unit shown in the same Figure, a shunt resistor RS and a drain D and source S of a thermal FET QF are connected in series in a path for supplying an output voltage VB of a power source
101
to a load
102
such as a head lamp and a power window driving motor. Further, this power supply control unit comprises a driver
901
for detecting a current flowing in the shunt resistor RS so as to control a driving of the thermal PET QF by a hardware circuit , an A/D converter
902
for carrying out ON/OFF control of a driving signal of the thermal FET QF based on a current value monitored by a driver
901
, a microcomputer (CPU)
903
. The thermal FET QF acting as a semiconductor switch contains an over-heat shut-off function for turning itself OFF by an incorporated gate shut-off circuit when an incorporated temperature sensor (not shown) detects that a temperature of the thermal FET QF rises up to a temperature above a predetermined one. A symbol RG in the same FIG. indicates an incorporated resistor and ZD
1
denotes a Zener diode which maintains 12 V between gate G and source S and bypasses when an overvoltage is about to be applied to the gate G.
Further, this conventional power supply control unit also includes a protective function for an overcurrent on the load
102
or between the drain D and source S of the thermal FET. Namely, the driver
901
comprises differential amplifiers
911
,
913
as a current monitor circuit, a differential amplifier
912
as a current control circuit, a charge pump circuit
915
and a driving circuit
914
for driving the gate G of the thermal FET QF via an internal resistor RG based on an ON/OFF control signal from the microcomputer
903
and a result of overcurrent determination from a current control circuit.
When a voltage different from the output voltage VB of the power source 101 is used, for example, VB is 42 V while the other necessary voltage is 12V, it is necessary to provide a new power supply control unit including the aforementioned charge pump
915
. By providing the power supply control unit for 12 V, 12 V can be obtained as well as 42 V.
When an overcurrent is detected via the differential amplifier
912
based on a voltage drop in the shunt resistor RS by determining that the currant exceeds its predetermined (upper limit) value, the thermal FET QF is turned OFF by the driving circuit
914
and when the current drops below a predetermined (lower limit) value, the thermal FET is turned ON.
On the other hand, the microcomputer
903
always monitors a current via current monitor circuits (differential amplifiers
911
,
913
). When an abnormal current exceeding a normal value flows, it turns OFF the thermal FET QF by turning OFF a driving signal to the thermal FET QF. When the temperature of the thermal FET QF exceeds its predetermined value before the driving signal for OFF control is outputted from the microcomputer
903
, the operation of the thermal FET QF is turned OFF by the overheat shut-off function.
However, in the above-mentioned conventional power supply control unit, a charge pump is necessary for that control. Because generally, the charge pump circuit is large in size, reduction of the size of the charge pump and its production cost are difficult.
Further, when the charge pump is necessary, the total number of components of the power supply control unit increases and the circuit thereof becomes complicated. Thus, a reliability of such a power supply control unit is not so satisfactory.
Further, to detect a current, a shunt resistor RS connected to a power supply path in series is necessary. Because, in recent years, current flowing to the load has been increased with a reduction of ON resistance of the thermal FET QF, heat loss of the shunt resistor cannot be neglected.
Although the aforementioned overheat shut-off function and overcurrent limiting circuit function when a substantially complete short-circuit occurs in the load
102
and wiring so that a large current flows, they do not function when a rare short-circuit such as incomplete short-circuit having some extent of short-circuit resistance occurs so that a small short-circuit current flows. Therefore, there is no way but turning OFF the thermal FET QF by detecting an abnormal current by a microcomputer
903
via a current monitor circuit. However, according to the conventional art, a response of microcomputer control to the abnormal current is not satisfactory.
Further, because the shunt resistor RS. A/D converter
902
, microcomputer
903
and the like are necessary, a large installation space is necessary. Thus, there is a problem that the cost for the unit is increased by these relatively expensive components.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above described conventional problems and therefore, an object of the invention is to provide a power supply control unit having a simple circuit structure and a high reliability in which a charge pump circuit can be eliminated,
Another object of the invention is to provide a power supply control unit and power supply control method in which a shunt resistor connected to a power supply path for detecting a current in series is unnecessary so as to suppress heat loss and a quick response is enabled against an abnormal current generated when a rare short-circuit such as incomplete short-circuit having some extent of short-circuit resistance occurs, the power supply control unit being easy to integrate and not expensive.
To achieve the above object, there is provided a power supply control unit comprising: a power transmission means for supplying a power from a power source to a first load; an auxiliary power means for generating at least a kind of voltage different from a voltage of the power source; a semiconductor switch for controlling a power supply to a second load from the auxiliary power means by switching control depending on a control signal supplied to a control signal input terminal thereof; a reference voltage generating means for generating a reference voltage having a voltage characteristic equivalent to the voltage characteristic of a voltage between terminals of the semiconductor switch when a predetermined load is connected thereto; a detecting means for detecting a difference between a voltage between the terminals of the semiconductor switch and the reference voltage: a control means for controlling ON/OFF of the semiconductor switch depending on a difference between the detected voltage between the terminals and the reference voltage; and a control reference voltage supply means for supplying a voltage serving for a reference of control to the control means.
According to the present invention, an electric power is supplied to both the first load requiring a predetermined voltage of a power source and a second load requiring a voltage different from the predetermined voltage. The power supply to the second load is carried out through a current vibration type shut-off function provided switching circuit. As a result, an abnormal current such as a rare short-circuit, ordinary short-circuit and excessive current can be detected by monitoring current. When the abnormal current is detected, the power supply can be Interrupted.
According to a preferred embodiment of the present invention, the reference voltage generating means comprises a circuit which is connected in parallel to the semiconductor switch and the second loa
Luk Lawrence
Wong Peter S.
Yazaki -Corporation
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