JPH01127983A - Battery service life detecting device - Google Patents

Abstract

PURPOSE:To detect in advance a fact that the battery reached a service life by providing a timer means for driving periodically a switching element of an overload means for a prescribed time, a voltage detector for detecting a voltage drop and a latching circuit, etc. CONSTITUTION:To both ends of a lithium battery 1, a battery service life detecting device 3 is connected. This device 3 is provided with an overload means consisting of a resistance R1 and a transistor. A base of this transistor is connected to a timer means 5, and the means 5 generates periodically a short pulse, for instance, about 100ms once per day, and drives intermittently a means 4 through a resistance R2. A voltage detector 6 connected to both ends of the battery 1 detects a drop of its terminal voltage, and a prescribed threshold level is set. An output of the detector 6 is provided to a latching circuit 7, and the circuit 7 holds a detection output, and its output is provided to an indicator 8. In such a way, for instance, as the discharge quantity of the battery 1 increases, its terminal voltage drops gradually, this variation is detected by the detector 6 and displayed by the indicator 8, and it can be known that the battery 1 reached its service life.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a battery life detection device that is attached to a device equipped with a battery and detects the life of the battery.

[Prior art and its problems]

(Prior Art) Conventionally, as electronic devices have become lower in power consumption and smaller in size, systems equipped with batteries have come into widespread use in order to eliminate power cords and back up memory. As such batteries, for example, lithium batteries and mercury batteries, which have a long life due to their high energy density and little self-discharge, are often used.As long as lithium batteries and mercury batteries are used under light loads, the terminal voltage will be low. The characteristics of the battery do not depend on the discharge rate, and the terminal voltage can be maintained at a nearly constant level until the end of its life.

(Problems to be Solved by the Invention) However, in electronic devices using such lithium batteries, especially thionyl chloride-based lithium batteries, etc., it is not possible to predict the battery life in advance because the internal resistance is low.
There is a problem in that when the life span is reached, the terminal voltage drops rapidly, causing the electronic device to suddenly stop working.

Particularly when a memory is provided in an electronic device, there is a drawback that the data therein disappears rapidly.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional electronic devices, and a technical problem is to make it possible to detect in advance that the battery has reached the end of its life even when using such a battery. shall be.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention is a battery life detection device that is attached to a device including a battery and detects the battery life using an internal resistance.
As shown in the figure, overload means is connected in parallel to the battery and causes an overcurrent sufficiently larger than the load current to flow when the switching element is driven, and timer means periodically drives the switching element of the overload means for a predetermined period of time; It has a voltage detector that detects a voltage drop in the terminal voltage of the battery to a predetermined level, a latch circuit that holds the voltage level drop detection output from the voltage detection means, and a display means that displays the output of the latch circuit. It is characterized by:

(Function) According to the present invention having such characteristics, the switching element of the overload means is periodically driven for a predetermined period of time to cause an overcurrent larger than the normal load current to flow from the battery to the overload means. . As the remaining capacity of the battery decreases, its internal resistance gradually increases, and the terminal voltage decreases accordingly.

As the battery approaches the end of its life, the internal resistance becomes much larger than its original value. Therefore, if an excessive current is allowed to flow near the end of its life, the terminal voltage will drop accordingly. Therefore, by detecting this drop in terminal voltage with a voltage detector, it is determined whether the battery has reached the end of its life. If it is determined that the battery has reached the end of its life, it is held by a latch circuit and the life of the battery is displayed on the display. ing.

(Effects of the Invention) Therefore, according to the present invention, even when the battery life cannot be determined until it is almost completely discharged due to changes in terminal voltage because the battery is used with low current consumption, by periodically passing an overcurrent for a short time, Its lifespan can be determined.

If the terminal voltage drops when an overcurrent is applied, the latch circuit will hold the battery and the display will indicate that the battery has almost no life left. The terminal voltage will not suddenly drop at an unexpected point and the equipment will not stop working.

Therefore, even when a memory is used as a load, there is no possibility that the data will be damaged.

[Explanation of Examples]

FIG. 1 is a block diagram showing the configuration of a battery life detection device according to an embodiment of the present invention. In the figure, a load 2 is connected to a lithium battery 1 which is a power source of the electronic device. Here, it is assumed that the load 2 has a low current consumption. Now, a battery life detection device 3 of the present invention is connected to both ends of the lithium battery 1. As shown in the figure, the battery life detection device 3 has overload means 4 consisting of a resistor R1 and a transistor Tri. The base of the transistor Tri is connected to the timer means 5 as shown in the figure.
It is connected to the. The timer means 5 periodically e.g.
A short pulse of about 100 m5 is generated once a day, and is applied to the transistor Trl via a resistor R2 to drive the overload means 4 intermittently. Here, the resistor R1 is set to a value such that the internal resistance of the lithium battery is large so that when it reaches the end of its life, an overcurrent can flow through the lithium battery and the terminal voltage will be lowered.
It is assumed that a value of about 00 is set. For example, even if the normal current consumption of the load 2 is about several tens of microamperes, a current value of about 300 mA is selected as the overcurrent. Now, the battery life detection device 3 has a voltage detector 6 connected to both ends of the lithium battery 1. The voltage detector 6 detects a drop in the terminal voltage, and is set to a predetermined dark value level.

For example, assuming that the terminal voltage of a lithium battery during normal operation is 3.6V, a detection output is output when the voltage falls below 2.6V. The output of voltage detector 6 is given to latch circuit 7. The latch circuit 7 holds this detection output, and the output is given to the display 8. The display 8 is a display means for displaying the detection signal held in the latch circuit 7. In this way, for example, as the discharge amount of the lithium battery 1 increases, its terminal voltage gradually decreases.

FIG. 2 shows an example of the change in terminal voltage with respect to the amount of discharge of a lithium battery, and curve A shows the change in terminal voltage when the overload means 4 is not driven by the timer means 5 and only the load 2 is connected. It shows change. Here, assuming that the load 2 consumes a minute current of about several tens of microamperes, its terminal voltage hardly changes and remains at 3.6V until the discharge amount reaches 100%. Here B1-B8
The range indicated by is the range of terminal voltage when multiple lithium batteries are used and overcurrent is applied, and indicates a state in which the terminal voltage decreases significantly as the amount of discharge increases. In the figure, it is known that the internal resistance of the lithium battery gradually increases because the terminal voltage at the time of overcurrent decreases as the discharge amount increases.Then, when the discharge amount exceeds 90%, the overcurrent By selecting the overload current, that is, the resistance value of the resistor R1, in advance so that the terminal voltage is below the dark value set in the voltage detector 6 when the voltage is applied, a discharge amount exceeding 90% can be detected. be able to.

FIG. 3 is a time chart of each part of the battery life detection device according to this embodiment. In this figure, the timer means 5 outputs a pulse signal at predetermined intervals as described above. For example, as shown in FIG. 3, time 1. ~t2 and t
A pulse signal is output between 3 and t4. However, if the discharge rate of the lithium battery 1 is low, the terminal voltage will hardly decrease as shown from time t1 to t2, but at time t3 to t4.
As shown in the figure, when the discharge rate approaches 100%, the terminal voltage drops significantly.

Therefore, as shown in FIG. 3 (C1), voltage detector 6 detects this change and provides its output to latch circuit 7.

As shown in FIGS. 3(d) and 3(e), the latch circuit 7 provides a signal to the display 8 by holding this output. Therefore, if the discharge amount exceeds 90%, the display 7 will continue to display the battery, indicating that the battery is nearing the end of its service life and needs to be replaced as soon as possible.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention. In this embodiment, the same parts as in the first embodiment are given the same reference numerals. In this embodiment, a voltage holding circuit 10 consisting of a resistor R4 and a capacitor C1 is provided so that the terminal voltage applied to the load 2 does not drop when the transistor Tri is driven by the timer means 5 and an overcurrent flows. It is something. In this way, the overload means 4 is intermittently driven by the timer means 5, causing the terminal voltage of the lithium battery 1 to drop rapidly, but during this time, the capacitor CI
Since the voltage is bank-amplified by the load 2, the voltage supplied to the load 2 is prevented from dropping suddenly to avoid affecting the load 2. In this case, it is preferable to provide a diode D1 in series with the resistor R4, as shown by the broken line in the figure, to prevent current from flowing from the capacitor C1 to the voltage detector 6, thereby preventing the voltage detector 6 from malfunctioning.

In this embodiment, the overload means is driven intermittently by the timer means, but for example, a switch or the like may be installed in parallel with this, so that the load means is driven for a certain period of time by the switch output, so that the user can operate the overload means. The lifespan of the battery may be determined at this point.

Although the battery in this embodiment is a lithium battery, the present invention can be applied to various batteries whose discharge characteristics maintain a constant terminal voltage until the end of discharge and then rapidly decrease, such as mercury batteries and silver oxide batteries. Needless to say, it can be used.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the configuration of an electronic device having a battery life detection device according to an embodiment of the present invention, and Fig. 2 shows changes in terminal voltage depending on the amount of discharge of a lithium battery and terminal voltage when overcurrent is applied. FIG. 3 is a time chart showing waveforms of various parts of this embodiment, and FIG. 4 is a circuit diagram showing a second embodiment of the present invention. 1-1-Lithium battery 2--One load 3--
- Battery life detection device 4 - Overload means 5
−・−111~Timer means 6・・・−・・・Voltage detector 7−−−−Latch circuit patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person) Figure 3

Claims (1)

[Claims] (1) A battery life detection device that is attached to a device containing a battery and detects the battery life using an internal resistance, which is connected in parallel to the battery and has an overload that causes an overcurrent that is sufficiently larger than the load current to flow when the switching element is driven. means, a timer means for periodically driving the switching element of the overload means for a predetermined period of time, a voltage detector for detecting a voltage drop of the terminal voltage of the battery to a predetermined level, and a voltage level detection means for detecting a voltage drop of the terminal voltage of the battery to a predetermined level. A battery life detection device comprising: a latch circuit that holds a fall detection output; and a display means that displays the output of the latch circuit.