Electricity: measuring and testing – Testing potential in specific environment
Reexamination Certificate
2002-01-28
2004-05-18
Le, N. (Department: 2858)
Electricity: measuring and testing
Testing potential in specific environment
C341S141000
Reexamination Certificate
active
06737850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply voltage detection circuit and a power supply voltage detection method.
2. Description of the Related Art
An application, such as a micro computer driven by a battery or a computer installed in a car, in which a power supply voltage is changed, is operated on a system in which a power supply voltage is changed since a battery is used as a power supply, as disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-136579), Japanese Laid Open Patent Application (JP-A-Heisei 11-223860) and the like. In recent years, a function of not only judging an allowance or rejection with regard to a voltage at one point, but also detecting a continuous power supply voltage is required in detecting a power supply voltage. For example, it is an essential function to indicate in detail the condition that a battery is an empty state, a full state, a middle state and a state close to an exhausted state. A voltage that can be detected by a known constant voltage detection circuit used to detect a power supply voltage is a voltage at only one point. It is difficult to monitor the change in the power supply voltage or its shift. In order to cope with a request of detecting the power supply voltages at a plurality of points necessary for the monitoring of the change and the shift in the power supply voltage, a plurality of detection circuits must be added and installed in a micro computer, in a case of the known circuit. Also, the detection voltage is only set at a time of a design. Thus, it is impossible to satisfy the usage environments and conditions of all users.
In a market in recent years, it is required to monitor the change and the shift in the power supply voltage. However, the conventional detection of the power supply voltage has been performed only on a voltage at one point. It is impossible to monitor the change and the shift in the power supply voltage.
Japanese Laid Open Patent Application (JP-A-Heisei 9-49868) discloses the following apparatus for detecting an exhausted battery. The apparatus for detecting the exhausted battery includes: a constant voltage generator for generating a constant voltage until a usage limit voltage of a battery; and an A/D converter for receiving an operational electric power from an electric power supply line in which it is dropped on the basis of an electric power exhaustion degree of the battery, and performing an A/D conversion on the constant voltage from the constant voltage generator, and it determines that the battery is exhausted if a digital data value into which the constant voltage is converted, on receipt of the A/D conversion value obtained from this A/D converter, is changed by a predetermined value or more.
Japanese Laid Open Patent Application (JP-A-Heisei 11-51985) discloses the following apparatus for detecting a power failure. In this apparatus for detecting the power failure, an A/D converter converts an instantaneous voltage of an alternating power supply into a digital value. A magnitude comparator, if the digital value is equal to or greater than a predetermined threshold, outputs it. An edge detector detects a rising edge and a trailing edge of an output wave form. A timer and an instantaneous power failure detection processor, if a period from the rising edge to the trailing edge (a voltage drop period) exceeds a first time limit T
1
, determine that it is the instantaneous power failure, and interrupt a main service. If the voltage drop period exceeds a second time limit T
2
(T
2
>T
1
), they determine that it is the power failure, and carry out a predetermined power failure process. When the electric power is recovered during the instantaneous power failure or the power failure, the process before the power failure is resumed.
Japanese Laid Open Patent Application (JP-A-Heisei 11-250940) discloses the following method of detecting a full charge in a battery charging operation. The method of detecting the full charge in the battery charging operation is carried out by using a |V| detection method of judging, on the basis of a voltage change amount, a process for detecting the full charge based on a software. In any measurement after a detection of a peak voltage in the charging operation, when a battery voltage is dropped from the peak voltage by |V| or more, it is assumed that the full charge is detected. At this time, a time from the detection of the peak voltage to the detection of the full charge is no matter. Also, after the detection of the peak voltage, if the battery voltage is dropped continuously a plurality of times in a periodical measurement, it is assumed to be the detection of the full charge, irrespectively of a drop width. Due to those operations, the detection change width of the battery voltage is expanded, which leads to the easy detection of the full charge. Thus, it is possible to relax an accuracy of an A/D converter for converting the battery voltage.
SUMMARY OF THE INVENTION
The present invention is accomplished in view of the above mentioned problems. Therefore, an object of the present invention is to provide a power supply voltage detection circuit and a power supply voltage detection method that can monitor a change and a shift in a power supply voltage by using an A/D converter as a circuit for detecting a power supply voltage.
Another object of the present invention is to provide a power supply voltage detection circuit and a power supply voltage detection method, in which a potential of a power supply voltage to be detected can be freely set, differently from a constant voltage detection circuit in which the potential is set when it is designed.
In order to achieve an aspect of the objects of the present invention, a power supply voltage detection circuit, includes: a constant voltage generator generating a first voltage of a constant voltage; an A/D converting unit performing an A/D conversion on the first voltage inputted through an analog input channel as a reference voltage of a second voltage of a power supply voltage; and an A/D conversion result register storing an A/D conversion result obtained by the A/D converting unit.
In this case, the power supply voltage detection circuit further includes: a selector selecting the analog input channel of a plurality of analog input channels.
Also in this case, the power supply voltage detection circuit further includes: a result comparison register setting an expectation value of a power supply voltage to be detected; and a judging circuit comparing the A/D conversion result with the expectation value to generate an interruption signal if a detection condition of the power supply voltage is satisfied.
Further in this case, the power supply voltage detection circuit further includes: a result comparison register setting an expectation value of a power supply voltage to be detected; and a judging circuit comparing the A/D conversion result with the expectation value to generate an interruption signal if a detection condition of the power supply voltage is satisfied.
In order to achieve another aspect of the objects of the present invention, a power supply voltage detection circuit, includes: a constant voltage generator generating a first voltage of a constant voltage; and an A/D converting unit inputting the first voltage and a second voltage whose voltage is detected to perform an A/D conversion on the first voltage based on the second voltage, and wherein the power supply voltage detection circuit detects the second voltage based on an A/D conversion result obtained by the A/D converting unit.
In order to achieve still another aspect of the objects of the present invention, a power supply voltage detection circuit, includes: a constant voltage generator generating a first voltage of a constant voltage; a first analog input channel; a second analog input channel, one of the first and second analog input channels inputting the first voltage from the constant voltage generator; a selector selecting an analog inpu
Lair Donald M
Le N.
NEC Electronics Corporation
Young & Thompson
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