Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-04-07
2001-06-26
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S283000
Reexamination Certificate
active
06252384
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a power-supply voltage control circuit and method. More particularly, the invention relates to a circuit for inhibiting a fluctuation in the power-supply terminal voltage of a load caused by a fluctuation in working current through the load.
BACKGROUND OF THE INVENTION
The CPUs used in recent personal computers consume ever larger amounts of power owing to higher clock speeds and a greater degree of integration. For this reason, CPUs are provided with a function for conserving power by placing the CPU in a sleep mode when there is little demand for execution of processing from the system. The function that provides the sleep (or idle) mode is referred to as a “stop-clock function”. In an actual personal computer, consumption of power is reduced by repeatedly alternating between the operating and sleep states.
Various techniques have been disclosed for performing the kind of control required for the stop-clock function.
By way of example, the specification of Japanese Patent Kokai Publication JP-A-9-237130 discloses a control method which includes determining the type of hardware interrupt that occurs when a CPU is in the sleep mode and forcibly restoring the CPU to the operating state depending upon the type of interrupt.
Also JP-A-8-6662 discloses a stop-clock control method which allows to place the CPU in the sleeping state when there is no input signal during a predetermined period of time and allows the user to set the state of CPU at his will.
The stop-clock function is such that when a CPU makes a transition from the sleep to the operating state as a result of this function, there is a sudden increase in the working current of the CPU. As a consequence, a voltage drop is produced as by impedance in the wiring of the power line that supplies the CPU with power, and the power-supply terminal voltage of the CPU temporarily falls below the allowable operating voltage of the CPU. This is a cause of CPU malfunction. Conversely, when the CPU undergoes a transition from the operating to the sleep state, the working current of the CPU declines sharply and the voltage across the power-supply terminals of the CPU rises.
FIG. 8
illustrates an example of the construction of a power-supply control circuit used in a conventional personal computer. Here a CPU
9
, which is supplied with power from a DC power supply
1
, is connected via a power-supply line
2
comprising a cable, connector and a printed circuit board, etc. The power-supply line
2
has a line impedance
4
composed of a resistance or impedance component.
The power-supply terminal voltage of the CPU
9
fluctuates when the working current of the CPU
9
fluctuates owing to the line impedance
4
. In order to prevent this, a DC-DC converter
11
is disposed in the vicinity of the CPU
9
and the output side of the converter
11
is provided with a plurality of large-capacity capacitors
10
to suppress the fluctuation across the power-supply terminals of the CPU
9
.
SUMMARY OF THE DISCLOSURE
However, the following problems have been encountered in the course of investigations toward the present invention. Namely, there is a drawback with the prior-art circuit shown in
FIG. 8
that when package space is limited, as in the case of a portable computer (personal digital assistant PDA on portable information terminal), the DC-DC converter
11
having the large capacitors cannot be placed close to the CPU and therefore cannot be applied to a computer of this kind. The reason for this is that capacitors having a large electrostatic capacity generally are necessary to inhibit a fluctuation in the terminal voltage of a CPU. These capacitors are large in size. Moreover, unless these capacitors are placed as close as possible to the CPU, a line impedance is produced between the CPU and the capacitors. This results is diminished effectiveness.
Another publication that relates to control of the power supply of a load is the specification of Japanese Patent Kokai Publication JP-A-59-89525. This discloses a terminal device having a main unit (power supply section) and a load section connected by a cable the impedance of which is not negligible, wherein it is intended no distortion is produced in a signal transmitted between the main unit and the load even if the load fluctuates. For that purpose, a dummy load is connected in parallel with the load as a device having minimal additional circuitry. By controlling the current through the dummy load, the total of the load and dummy load currents (namely the power-supply current) is rendered substantially constant. In this case the dummy load consumes a substantial amount of power.
Accordingly, an object of the present invention is to provide a circuit and a power-supply control method for inhibiting a fluctuation in a power-supply terminal voltage caused by a fluctuation in the working current of a load, whereby the load is supplied with a stabilized power-supply voltage.
It is another object of the present invention to provide a circuit and a power-supply control method in which the above object is achieved with a reduced power consumption.
It is a further object of the present invention to provide a circuit and a power-supply control method in which the circuit may be disposed in close proximity to a load requiring a minimum space.
According to a first aspect of the present invention, there is provided a circuit disposed in close proximity to a load, wherein the load is a CPU controlled between sleep (idle) and operating states by the value of a stop-clock signal input thereto. The circuit comprises a transistor connected to a DC power supply in parallel with power-supply terminals of the load, and a control circuit controlling a current, which flows into the transistor, in dependence upon a change in working current of the load, thereby inhibiting a fluctuation in voltage across the power-supply terminals of the load.
According to second aspect, a fluctuation-inhibiting circuit comprises: a CPU controlled between a sleep state and an operating state by a value of a stop-clock signal applied thereto, the CPU having power-supply terminals; a current control element inserted in parallel with the CPU across the power-supply terminals thereof; and control means for varying a current, which flows into the current control element, in dependence upon a change in power-supply current of the CPU caused by a change in the stop-clock signal, thereby inhibiting a fluctuation in voltage across the power-supply terminals of the CPU.
According to a third aspect, a fluctuation-inhibiting circuit comprises: a CPU controlled between a sleep state and an operating state by a value of a stop-clock signal applied thereto, the CPU having power-supply terminals;
a transistor inserted in parallel with the CPU across the power-supply terminals thereof; and control means for supplying the transistor with a bias voltage, comparing a predetermined voltage and a voltage proportional to a current which flows into the transistor and performing feedback control in such a manner that the current which flows into the transistor is rendered proportional to the reference voltage.
According to a fourth aspect, a fluctuation-inhibiting circuit comprises: a CPU controlled between a sleep state and an operating state by the value of a stop-clock signal applied thereto from a stop-clock terminal, the CPU having a control terminal and power-supply terminals; a transistor inserted in parallel with the CPU across the power-supply terminals thereof; an operational amplifier having an output terminal connected to the control terminal of the transistor and having, as differential inputs, a reference voltage and a voltage proportional to a current which flows into the transistor, the operational amplifier performing feedback control in such a manner that the current which flows into the transistor is rendered proportional to the reference voltage; and first and second switches serially inserted across the power-supply terminals and each having a control terminal connected to a curren
Arai Satoshi
Tohya Hirokazu
Foley & Lardner
Han Jessica
NEC Corporation
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