JPS61231472A - Circuit for detecting voltage of battery - Google Patents

Abstract

PURPOSE:To reduce the current consumption of a battery for measurement and to eliminate the adjustment work of each circuit part, by simple constitution such that voltage is connected to a battery only at the time of voltage and compared with a preliminarily stored value as an initial voltage value. CONSTITUTION:An integrator circuit consisting of a resistor 12 and a condenser 13 is connected to the switch 12 connected to a battery 9 and a switch 11 is connected between the connection point of the resistor 12 and the switch 10 and the earth and turned OFF and ON by turning the switch ON and OFF. When the output level of the integrator circuit reaches a predetermined value or more, the output of a comparator 15 changes to be applied to a microcomputer (MPU) 1. MPU 1 measures the time before the output of the comparator 15 is turned ON after the ON-control of the switch 10 on the basis of a microprogram to store the same in RAM 3 as the initial voltage value of the battery and subsequently compares the value measured by turning the controlled switch 10 ON with the value of RAM 3 to detect the voltage of the battery.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a battery voltage detection circuit for detecting a voltage drop in a battery used in electronic equipment and the like.

(Prior Art) Conventionally, this type of battery voltage detection circuit has been comprised of a precise reference voltage generator and a comparator for voltage comparison.

(Problems to be Solved by the Invention) Therefore, there is a drawback that adjustment work is required to absorb variations in individual reference voltages, level variations in comparators, and variations in elements such as capacitors and resistors.

Also, since the voltage of the reference voltage generator is generally lower than the battery voltage, the battery voltage is lowered using a voltage divider circuit to match the reference voltage, but since a small amount of current flows through the voltage divider circuit, the battery is wasted. The disadvantage was that it was consumed. Another disadvantage is that it requires relatively precise analog electronic circuits that are difficult to obtain, making it expensive as a whole.

The purpose of the present invention is to solve the above-mentioned drawbacks.By connecting to the battery output only when voltage is detected, it is possible to prevent unnecessary consumption of battery capacity and to set a value corresponding to the battery voltage when a new battery is installed in advance. By storing it in memory and using it as a comparison standard, we can eliminate the adjustment work for each circuit, element, etc., and by replacing voltage detection with digitally measuring the charging time of the integrating circuit. It is an object of the present invention to provide a battery voltage detection circuit that does not require the use of relatively expensive analog circuits.

(Means for Solving the Problems) In order to achieve the above object, a battery voltage detection circuit according to the present invention includes a first switch connected to the battery, and a first switch connected to the battery. is connected to the switch, and is connected between an integrating circuit consisting of a resistor and a capacitor, and a connection point between the resistor of this integrating circuit and a first switch, and ground, and is turned off when the first switch is turned on, and turned on when turned off. a second switch that operates in such a relationship; a comparator that detects that the voltage of the integrating circuit has exceeded a predetermined level; It includes a time measuring circuit that stops measuring time based on the detection output of the comparator, and a nonvolatile memory, and the output of the time measuring circuit, which is measured by turning on the first switch, is used as the initial voltage value of the battery. The battery voltage is stored in a non-volatile memory and is configured to detect the battery voltage by completely comparing the value measured by the time measuring circuit when the first switch is turned on which is controlled later with the value in the non-volatile memory. ing.

(Function) According to the above configuration, adjustment work can be eliminated, unnecessary consumption of battery capacity can be prevented, and a low-cost circuit can be realized, so that the objects of the present invention can be completely achieved.

(Example] Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a battery voltage detection circuit according to the present invention.

This diagram shows the case of detecting a voltage drop in a battery used to back up a watch, etc. when the power is turned off.
The entire battery voltage detection circuit is controlled by a microcomputer. A bus 2 of a microcomputer that controls the entire device includes a non-volatile memory 3 consisting of EEPROM, etc., a main memory 4 that stores instructions and data to be executed by the non-volatile memory, and input/output for exchanging data with the outside. A section 5, an output port for outputting control data of the voltage detection circuit/circuit, and an input port for inputting the state of the voltage detection circuit are connected.

The voltage detection circuit includes a first switch 1G, a second switch 11, which is opened and closed according to the control data of the output port, and an integrating circuit consisting of a resistor 12 and a capacitor 13. The detection output 33, which is the output of the comparator 15, is passed through the input port door and its state can be read by the microcomputer 1.

FIG. 2 shows the output waveforms of each circuit section to explain the operation of FIG. The switch control signal 33 indicates the output waveform of the comparator 15, respectively.

In the initial state, the input of an integrating circuit consisting of a resistor] 2 and a capacitor 13 is grounded by a second switch 11. Then analog signal 32 is zero. Here, it is assumed that a signal is sent to the microcomputer lf output port and the switch control signal 31 is turned on. The first switch 1G is on, the second switch 11 is controlled via the inverter 14, so it is not off, and the battery voltage 30 of the battery 9 is charged to the capacitor 13 via the resistor 12t. The analog signal 32 of the capacitor 13 is 3 in FIG.
2, and when it exceeds the detection level VTi of the comparator 15, the detection output 33 turns on. The microcomputer l has this detection output 33 inputted to it.
Read through. The higher the voltage of the battery 9, the steeper the charging curve of the capacitor 13 and the faster the charging speed.
The time T from when the microcomputer 1 turns on the switch control signal 311 to when the detection output 33 turns on becomes shorter. That is, the time T is a function of the battery voltage level 30, and the battery voltage level 30 can be measured depending on the magnitude of T. This time T can be easily and fairly accurately measured by a counter (not shown) serving as a time measuring circuit or by a microprogram of the microcomputer I.

Although the absolute value of the battery voltage 30 cannot be measured, changes can be measured with sufficient precision.

In order to detect a drop in the battery voltage 30 and issue an alarm, first, when setting the battery 9, a time To corresponding to the initial voltage of the battery is read and stored in the nonvolatile memory 3.

Thereafter, the time Tt-
The battery voltage 30 is measured, and if the time T becomes longer than a certain value compared to the time To in the nonvolatile memory, an alarm is output as a result of the battery voltage 30 decreasing.

First switch 10 used in this circuit. The second switch 11, the resistor 2, the capacitor 13, and the comparator 15 do not require any precision as long as they do not change over time.

Since the microcomputer 1 normally operates with a crystal oscillator, time can be measured with sufficient precision.

Since this circuit and the battery 9 are disconnected from each other when no measurement is being performed with the first switch 10 turned off, there is no wasteful consumption of current.

Further, the current consumed for measurement is negligible if a capacitor 13f with a small capacity is selected.

The first switch IO and the second switch 11 can be electronic switches such as FETs. Although a discharge path for the capacitor 3 is required, it is not necessarily necessary to provide one since the capacitor 13 generally discharges naturally due to leakage.

A nonvolatile memory 3 is provided in such a device to store various parameters, etc., and is commonly used as a nonvolatile memory used in the present invention.

(Effects of the Invention) As explained in detail above, the present invention converts the analog value of the battery voltage into a digital value by using an integrating circuit, and converts the analog value of the battery voltage into a digital value that is stored in advance in a non-volatile memory. By comparing this digital value with the value corresponding to This has the effect of reducing current consumption and eliminating the need for complete assembly of each circuit section.

[Brief explanation of drawings]

11i9 is a block diagram showing an embodiment of the battery voltage detection circuit according to the present invention, and FIG. 2 is a time chart for explaining the operation of the circuit of FIG. 1. 1... Microcomputer (MPU) 2... Bus (BU8-3-... Not issued memo IJ (NV FLAM) 4-
・・Main memory (MgM-5...input/output section Cl10)

Claims (1)

[Claims] A detection circuit that detects a decrease in battery voltage includes a first switch connected to the battery, an integrating circuit connected to the first switch and consisting of a resistor and a capacitor, and a resistor of the integrating circuit and the first switch. and a second switch connected between the connection point of the first switch and the ground and operated in such a manner that it turns off when the first switch is turned on and turns on when it turns off, and the voltage of the integrating circuit reaches a predetermined level or higher. a time measurement circuit that starts measuring time when the first switch is turned on and stops measuring time at the detection output of the comparator; and a nonvolatile memory, the first switch The output of the time measuring circuit measured by turning on the first switch is stored in the non-volatile memory as an initial voltage value of the battery, and the output is measured by the time measuring circuit by turning on the first switch which is controlled later. A battery voltage detection circuit characterized in that the battery voltage detection circuit is configured to detect a battery voltage by comparing a value stored in the nonvolatile memory with a value stored in the nonvolatile memory.