JPH06351164A - Battery voltage monitor - Google Patents

Abstract

(57) [Abstract] [Purpose] Battery voltage monitoring that accurately detects battery voltage drop before the battery is completely exhausted, prompts battery replacement, and prevents memory backup operation from being interrupted due to battery exhaustion. It is to realize the device. A device for monitoring an output voltage of a battery for memory backup, which is connected in parallel with the battery and forms a load current path sufficiently larger than a load current in a memory backup operation state, and a switch element. Of the series circuit, a switch drive circuit for selectively turning on and off the switch element of the series circuit in the main power-on state, and a voltage measuring unit for measuring the output voltage of the battery in the state where the switch element of the series circuit is turned on. It is characterized by the provision of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery voltage monitoring device for monitoring the output voltage of a battery for memory backup, and more particularly to improving the accuracy of voltage monitoring.

[0002]

2. Description of the Related Art In an electronic device having a rewritable memory, a battery is used to back up the memory in order to prevent the data stored in the memory from being lost when the main power supply is turned off. There is. By the way, even if the battery for memory backup is provided in this way, if the battery is exhausted and the output voltage drops, the original memory backup operation may not be performed and valuable data may be lost. .

Therefore, conventionally, for example, a battery voltage monitoring circuit as shown in FIG. 3 has been used. In the figure, 1
Is a main power supply, which supplies power to the entire device, and the power is also supplied to the memory 3 via the diode 2. The main power supply 1 is on / off controlled by a power switch (not shown). Reference numeral 4 is a battery for backing up the memory 3 when the main power supply 1 is off, and for example, a lithium battery is used. The output voltage of the battery 4 is constantly supplied to the memory 3 via the diode 5. Reference numeral 6 is an operational amplifier that functions as a battery open circuit that detects the open state of the battery 4. The inverting input terminal is connected to the output terminal of the battery 4, and the non-inverting input terminal is connected to the output terminal of the voltage dividing circuit. ing. Reference numeral 7 denotes an operational amplifier that functions as a voltage drop detection circuit that detects a drop state of the output voltage of the battery 4. The output terminal of the battery 4 is connected to the non-inverting input terminal and the output of the voltage dividing circuit is connected to the inverting input terminal. The terminals are connected. Here, assuming that the rated value of the backup voltage of the memory 3 by the battery 4 is, for example, 3 V, the operational amplifier 6 is set to output an alarm when a voltage of 5 V or more is detected, and the operational amplifier 7 is, for example, 2.5 V.
It is set to output an alarm when the following voltage is detected.

[0004]

However, as shown in FIG. 5, the output voltage characteristic of the lithium battery used as the battery 4 for memory backup sharply changes from a certain point after a certain period of several years has passed. descend. On the other hand, the current consumption for backing up the memory 3 is 1 μA to 1
It is extremely small, 0 μA.

In combination with these, at the time when the voltage drop is detected by the operational amplifier 7, the battery 4 is almost completely depleted, and the backup operation of the memory 3 may not be performed properly. Further, when the battery 4 is exhausted, the internal resistance of the battery 4 becomes high, and when the main power supply 1 is on, the battery 4 is charged by the leak voltage as shown in FIG. Rises,
There is also a problem that an accurate voltage detection operation cannot be performed.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to accurately detect a voltage drop of the battery before the battery is completely consumed and to promptly replace the battery. It is to realize a battery voltage monitoring device in which the backup operation of the memory is not interrupted due to exhaustion of the battery.

[0007]

A battery voltage monitoring device of the present invention is a device for monitoring the output voltage of a battery for memory backup, which is connected in parallel with the battery and provides a load current in a memory backup operating state. A series circuit of a resistor and a switch element that form a load current path that is sufficiently larger than that of the switch circuit, a switch drive circuit that selectively turns on and off the switch element of the series circuit in a main power-on state, and the switch element of the series circuit. A voltage measuring unit for measuring the output voltage of the battery in the ON state is provided.

[0008]

[Function] By turning on the switch element of the series circuit of the resistor and the switch element, the load circuit has a load current sufficiently larger than the load current in the memory backup operation state in the series circuit of the resistor and the switch element during the period. Flows.
As a result, when the battery is depleted considerably, the output voltage of the battery will drop significantly compared to the normal memory backup state, and it is necessary to prompt the replacement of the battery before it is completely consumed. An alarm can be output.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.
The same parts as those in FIG. 3 are designated by the same reference numerals. In the figure, a series circuit of a resistor 8 and a switch element 9 is connected in parallel to the output terminal of the battery 4. A pulse generator 10 outputs a drive pulse for selectively driving the switch element 9, and intermittently outputs the drive pulse while the main power supply 1 is turned on. The operational amplifier 11 functions as a voltage measuring unit that measures the output voltage of the battery 4. The inverting input terminal is connected to the output terminal of the battery 4, and the non-inverting input terminal is connected to the output terminal of the voltage dividing circuit. Has been done. Here, the series circuit of the resistor 8 and the switch element 9 has a load current (1 μA to
The load current is set to be 10 to 100 times as large as that of 10 μA). Further, as the pulse generator 10 for driving the switch element 9 on and off, a drive pulse that is selectively turned on for a sufficient time (for example, about several tens of μS) for the operational amplifier 11 to detect a change in battery voltage. It is only necessary to be able to output, and for example, it may be an output pulse of a microprocessor.

FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, in which (A) shows the on / off state of the main power supply 1,
(B) shows a change in the output voltage of the battery 4, (C) shows an on / off state of the switch element 9, and (D) shows an alarm signal generated based on the output of the operational amplifier 11. If the internal resistance of the battery 4 is high due to the progress of consumption, the battery 4 is charged by the leak when the main power supply 1 is turned on as shown in (A), and the output voltage of the battery 4 is as shown in (B). Apparently rises. In this state, when the switch element 9 is turned on as shown in (C), the output voltage of the battery 4 drops sharply as shown in (B) and is set and input to the non-inverting input terminal of the operational amplifier 11. The voltage becomes lower than the alarm voltage, and the operational amplifier 11 outputs a detection signal corresponding to the state. Then, based on such a detection signal of the operational amplifier 11, an alarm notifying that the consumption of the battery 4 has progressed to a state requiring replacement as shown in FIG. Is output.

As a result, it is possible to know the replacement time of the battery 4 before the battery 4 is completely consumed, so that the battery 4 can be replaced at an appropriate time, and continuous backup operation of the memory 3 by the battery 4 can be realized. It should be noted that in the above-described embodiment, the battery 4 is provided by using the comparator with the operational amplifier as the voltage measuring unit.
Is detected digitally, the analog output voltage of the battery 4 is directly converted into a digital signal by using, for example, an A / D converter, and the measured data is sequentially stored in a memory of a microprocessor or the like. Alternatively, the progress status of the consumption of the battery 4 may be determined based on the transition of the stored measurement data. According to such a configuration,
It is possible to measure the output voltage of the battery 4 in more detail and with higher accuracy than in the case where the measurement is performed using a comparator including an operational amplifier.

Further, a series circuit of a resistance forming a load current path and a switch element is provided with a plurality of systems with different load currents, and the switch element is appropriately switched to check the progress of battery consumption. You may do it.

[0013]

As described above, according to the present invention,
It is possible to realize a battery voltage monitoring device that accurately detects a low battery voltage before the battery is completely exhausted, prompts battery replacement, and prevents the memory backup operation from being interrupted due to battery exhaustion. It is effective for various kinds of electronic devices that it has.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating the operation of FIG.

FIG. 3 is a block diagram showing an example of a conventional battery voltage monitoring circuit.

FIG. 4 is a diagram showing an output characteristic example of a lithium battery.

FIG. 5 is a waveform diagram illustrating the operation of FIG.

[Explanation of symbols]

 1 main power supply 2, 5 diode 3 backup memory 4 memory backup battery 8 resistance 9 switch element 10 pulse generator 11 operational amplifier (comparator)

Claims (1)

[Claims] 1. A device for monitoring an output voltage of a battery for memory backup, the resistor and the switch connected in parallel with the battery and forming a load current path sufficiently larger than a load current in a memory backup operation state. A series circuit with an element, a switch drive circuit for selectively turning on and off the switch element of the series circuit in a main power-on state, and a voltage for measuring the output voltage of the battery when the switch element of the series circuit is turned on A battery voltage monitoring device comprising a measuring unit.