JPH04366781A - Device for detecting life of battery - Google Patents

Abstract

PURPOSE:To perform detection to see whether or not a battery can be used normally after charging is completed. CONSTITUTION:A pulse generating circuit 1 supplies pulses of short time to a constant current circuit 2 in response to signals which are generated from a charge control circuit 3a when charging is completed. The constant current circuit 2 passes a relatively large current from a battery 4 and changes in battery voltage as measured before and after the current flows are detected by a peak value detecting circuit 5 and, if larger than a predetermined value, this detected value is detected by a voltage comparison circuit 6 so as to judge the life of the battery.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery life detection device for detecting the life of a battery used in, for example, a portable computer or a portable television set.

0002

2. Description of the Related Art Generally, rechargeable batteries cannot be used indefinitely, and when their lifespan reaches the end, they cannot be used even if they are charged. Conventionally, the lifespan of a battery has been determined by detecting whether the battery is open or short-circuited.

0003

[Problem to be Solved by the Invention] However, when a battery is overcharged for an abnormally long time or when the number of charging and discharging exceeds a predetermined number of times, when the battery is started to be used after charging is completed, the battery becomes unusable at first. Even if it is possible, the battery will become unusable in a much shorter time than the battery can be used for. In other words, the device can only be used for a much shorter time than the original usable time. Conventionally, there was no means to detect such a state, so there was a problem in that the only option was to start using the battery after charging was completed, and if the usable time was extremely short, it was necessary to determine that the battery had reached the end of its life.

The present invention has been made in view of the above situation, and provides a device for detecting whether or not a battery can be used normally after charging is completed.

[0005]

[Means for Solving the Problems] In order to solve such problems, the battery life detection device of the present invention includes a current circuit that flows a predetermined current from the battery at the end of charging, and a battery voltage that detects the battery voltage before and after the current flows. , and a voltage comparison circuit that generates an output signal when the output voltage difference of the peak value detection circuit is equal to or greater than a predetermined value.

[0006]

[Operation] In the battery life detecting device constructed as described above, a relatively large current is passed at the end of charging, and the life of the battery is determined based on the change in battery voltage before and after the current flows.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the structure of an embodiment of a battery life detection device to which the present invention is applied. First, to explain the outline of the circuit, the pulse generation circuit 1 in FIG.
Each time the control signals shown in (c) and (d) are supplied, a pulse of, for example, 70 μS is generated, and the constant current circuit (load means) 2
Each time a pulse signal is supplied from the pulse generating circuit 1, it acts as a load on the battery 4, causing a relatively large current to flow therethrough as will be described later.

A peak value detection circuit 5 detects the difference in the terminal voltage of the battery 4 before and after the current flows through the constant current circuit 2. If the value of the difference is larger than a certain level, it is detected by the voltage comparison circuit 6, and the detection signal is input to the CPU 10 via the OR circuit 9, and the L
The CD11 is designed to display that the battery life has run out.

Furthermore, when an overcurrent is detected by the overcurrent detection circuit 8 and an open state of the battery is detected by the open detection circuit 7, the detection output is sent to the LCD 11 via the OR circuit 9 and the CPU 10. A message appears indicating that the battery life is running out.

Next, the detailed operation of this device will be explained. AC 100V commercial power supplied via the transformer 12 is rectified by the rectifier circuit 13, converted to a predetermined DC voltage by the DC-DC converter 14, and supplied to the charging control circuit 3a. When the charging start switch 3c is momentarily pressed as shown in FIG. 2(a), the charging control circuit 3a generates a charging voltage for the time required to charge the battery 4 as shown in FIG. 2(b). This is supplied to the battery 4 via the overcurrent detection circuit 8, and the battery 4 is charged.

The charging control circuit 3a also generates a pulse signal when the charging start switch 3c is pressed, as shown in FIG. 2(c), and at the end of charging, as shown in FIG. 2(d). It is connected to the pulse generating circuit 1 via the OR circuit 3b.
is being supplied to. The signal is supplied to a one-shot multivibrator 1a of a pulse generating circuit 1, which generates a pulse signal whose duration (70 μS in this example) is determined by a resistor 1b and a capacitor 1c.

The constant current circuit 2 is configured to allow a relatively large current to flow from the battery 4 while a pulse is being generated from the one-shot multivibrator 1a. This current is not used for the actual operation of the device, but is used only to detect battery life, and since it is a relatively large current, it should be passed for as short a time as possible to avoid putting a burden on the battery. This is desirable. Therefore, in this example, the duration of the pulse signal generated from the one-shot multivibrator 1a is selected to be 70 μs, and the pulse is supplied to the constant current circuit 2 for that period.

Since the pulse signal is supplied to the non-inverting input terminal of the operational amplifier 2a, the constant current circuit 2 outputs an H level signal, and this signal is supplied to the base of the transistor 2c via the resistor 2b. . Therefore, transistor 2
c is turned on and current flows through the resistor 2d, so a voltage is generated across the resistor 2d, which is supplied to the inverting input terminal of the operational amplifier 2a.

As a result, the operational amplifier 2a sends out an output such that the voltage at the inverting input terminal is the same as the voltage at the non-inverting input terminal, and in this state the output level is balanced. Therefore, the current flowing through the transistor 2c becomes a constant current determined by the resistor 2d. In other words, at the start and end of charging, the constant current determined by the resistor 2d for 70 μS is applied to the battery 4.
Flows into the constant current circuit 2 from there.

[0015] This current should be relatively large in order to detect changes in the internal impedance of the battery 4. However, as described above, the current flows only for detecting the battery life and is not the current flowing for the original purpose of the device, so it is better to keep it as small as possible. Therefore, the maximum value is a value that does not place much burden on the battery 4, and the minimum value is a value that allows the internal impedance of the battery 4 to be detected, and the value is determined within this range.

When current is extracted from the battery 4, its terminal voltage changes in accordance with the internal impedance, and this voltage change is detected by the peak value detection circuit 5. When a nickel-cadmium battery starts to be used after being fully charged, it generally exhibits terminal voltage characteristics as shown in FIG. That is, in the section indicated by symbol A, the terminal voltage slightly decreases as the usage time increases. However, as shown by symbol B, when used after a certain point, the terminal voltage suddenly decreases. This is because the internal impedance increases rapidly when the battery 4 is discharged beyond a certain point, and the change in internal impedance of the battery 4 increases rapidly in section B.

[0017] Also, both sections A and B are connected to the battery 4.
While the current drawn from is small, although its value is different,
There is a corresponding battery terminal voltage, but when a certain amount of current flows, that voltage drops significantly. However, as shown in FIG. 3, there are two types of the amount of decrease. The solid line is section A in Figure 4, where sufficient charge remains in the battery 4 and the internal impedance of the battery 4 is small, so even if a large current flows, the voltage drop will be limited to a certain level. .

On the other hand, in the section shown by the two-dot chain line in FIG. 3, ie, section B in FIG. 4, the internal impedance of the battery 4 becomes large, and the voltage drop when a large current flows becomes large. However, when the battery 4 has not reached the end of its life, the internal impedance can be lowered by charging. That is, when the battery 4 has not reached the end of its life, the internal impedance of the battery can be lowered by charging, and the internal impedance of the battery exhibits a reversible value.

However, as described above, if the battery is left in an overcharged state for an abnormally long time, or if the number of charging and discharging times exceeds a predetermined value, the internal impedance of the battery cannot be lowered even if the battery is sufficiently charged. That is, a non-reversible state is exhibited, and the terminal voltage is also lower than the specified voltage. This state is the same as the characteristic indicated by the chain double-dashed line in FIG. 3, which was previously shown as the characteristic in section B in FIG.

[0020] That is, if the battery 4 is left in an overcharged state for an abnormally long time, or if the number of times of charging and discharging exceeds a predetermined value, the battery 4 undergoes a chemical change and its internal impedance becomes irreversible. Even if it is charged, the internal impedance cannot be lowered, so the state will be the same as the state in section B of FIG. 4, and when a relatively large current is passed, the terminal voltage of the battery 4 will drop significantly.

The peak value detection circuit 5 in FIG. 1 is a circuit that performs this detection, and changes in the terminal voltage of the battery 4 are detected by an operational amplifier 5a.
The signal is supplied to the non-inverting terminals of operational amplifiers 5d and 5e via a buffer circuit consisting of diodes 5b and 5c. The hold circuit including the operational amplifier 5d, the diode 5e, and the capacitor 5f holds the voltage when the voltage is high, that is, before the current flows through the constant current circuit 2. In the hold circuit consisting of the operational amplifier 5g, the diode 5h, and the capacitor 5i, when the voltage is low, that is, the constant current circuit 2
The voltage when current flows through is held.

The difference between the voltages held in operational amplifiers 5d and 5g is determined by a differential amplification circuit consisting of resistors 5j to 5n and operational amplifier 5p. This value is the difference between the voltage before and after the voltage decreases in FIG. 3, that is, the difference between the terminal voltage of the battery 4 before and after the current flows from the battery 4 to the constant current circuit 2. This difference is small if the battery 4 has not reached the end of its life, as shown by the solid line in FIG. However, when the battery reaches the end of its life, it becomes larger as shown by the two-dot chain line.

This voltage difference is supplied to a voltage comparison circuit 2 consisting of a Zener diode 6a, a resistor 6b, and an operational amplifier 6c. Therefore, if the avalanche voltage of the Zener diode 6a is set to be larger than the voltage change shown by the solid line in FIG. 3 and smaller than the voltage change shown by the two-dot chain line, the Voltage comparator circuit 6 to H
A level output signal is sent out. This signal is OR circuit 9
When this signal is input, the CPU 10 controls the LCD 11 to display that the battery 4 has reached the end of its life.

[0024] When the battery 4 reaches the end of its life, in addition to the state in which the internal impedance becomes irreversibly large, it may also become in a short-circuit or open state. When a short circuit occurs, the overcurrent detection circuit 8 outputs an H level signal. Therefore, the signal is supplied to the LCD 11 via the CPU 10 to display that the battery has reached the end of its life.

[0025] In addition to this, when the battery reaches the end of its life, it may become open. In this case, when current is extracted from the battery 4, the terminal voltage of the battery 4 becomes 0 volts. Therefore, when current flows through the constant current circuit 2, it is detected by the open detection circuit 7. The open detection circuit 7 includes a Zener diode 7a, a resistor 7b, and an operational amplifier 7c, and the avalanche voltage of the Zener diode 7a is set lower than the terminal voltage when the battery 4 is normal.

For this reason, when the battery 4 is normal, the open detection circuit 7 outputs an L level signal, so no output signal is generated from the OR circuit 9. However, when the battery 4 becomes open, the terminal voltage drops to 0 volts when current flows, so the open detection circuit 7 generates an H-level output signal. This signal is sent to the OR circuit 9 and the CPU.
10 to the LCD 11 to display that the battery 4 has reached the end of its life.

Since the battery 4 becomes open regardless of the state of charge, the determination may be made in any state. Therefore, in the present invention, when the charging start switch 3c is turned on and the pulse shown in FIG. 2(c) is generated from the charging control circuit 3a, the one-shot multivibrator 1a is operated as shown in FIG. 2(e). A current is caused to flow through the constant current circuit 2 to make a determination.

On the other hand, if the internal impedance of the battery becomes irreversibly large, it is necessary to make a determination at the time of completion of charging. That is, if the internal impedance is measured immediately after charging is completed, if the battery is normal, the internal impedance will be small because charging has already been completed. However, in the case of a battery that has reached the end of its lifespan, its internal impedance increases even immediately after charging is completed. Therefore, in this detection, as shown in FIG. 2(d), the one-shot multivibrator is driven by a pulse generated from the charging control circuit 3a upon completion of charging.

[0029]

As described above, according to the battery life detection device of the present invention, a predetermined current is applied when charging is completed, and an output signal is output when the difference between the battery terminal voltages before and after the current flows exceeds a predetermined value. Since this occurs, you can know the battery life immediately after charging is finished, and unlike the conventional situation where you can't know until you use it, you can know it in advance, so you can use it normally before you start using it. This makes it possible to replace the battery, which has the effect of eliminating the loss of time required to replace the battery after the start of use.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of a device constructed by applying the present invention.

[Figure 2] Timing chart explaining the operation of the device in Figure 1

[Figure 3] Graph showing changes in detection voltage detected by the peak value detection circuit before and after the battery internal impedance increases

[Figure 4] Graph showing changes in battery voltage versus battery usage time

[Explanation of symbols]

1 Pulse generation circuit 2 Constant current circuit 3a Charging control circuit 4 Battery 5 Peak value detection circuit 6 Voltage comparison circuit 7 Open detection circuit 8 Overcurrent detection circuit 10 CPU 11 LCD

Claims (1)

[Claims] 1. A current circuit that causes a predetermined current to flow from the battery at the end of charging, a peak value detection circuit that maintains the battery voltage before and after the current flows, and an output voltage difference between the peak value detection circuit and the battery voltage that is a predetermined value. A battery life detection device comprising a voltage comparator circuit that generates an output signal when the above conditions occur.