JPH10248177A - Charging circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct safe charging without fear for over-charging within a short period of time with the quick charging method, by conducting the complete charging with a third charging current which is smaller than the second charging current, after a battery voltage during the charging has reached the second predetermined value lower than the first predetermined value. SOLUTION: A power source 1 can switch a charging current in the three stages. Namely, the charging current can be switched to the rate current (3C) three times, rate current (2C) two times the nominal capacity of battery and rate current (1C) equal to the nominal, capacity of battery. Here, IC means a current value which can supply the charging amount equal to the nominal capacity in an hour when the battery is charged with a constant current value. Therefore, the higher the rate is, the larger the charging current is and thereby charging amount can be increased within a short period of time. A microcomputer 2 switches a charging current supplied from the power source 1 and also switches the quick charging and trycle charging. Therefore, there is no fear for over-charging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit for rapidly charging a secondary battery.

[0002]

2. Description of the Related Art Secondary batteries are widely used in portable devices and battery-driven toys. If the battery runs out during use of these devices and toys, the devices and toys can be used again by charging and reusing the batteries or replacing them with spare batteries. Even if you use extra batteries,
In the meantime, it is necessary to charge the battery that has run out of battery and charge it in advance so that it can be used again. In particular, when secondary batteries are used in toys, children often handle them, so it is necessary to have quick charging that can be charged in a short time so that they can be used immediately and repeatedly even if the batteries run out. come. However, rapid charging has a drawback that the charging current is large, so that the battery temperature rises, and that overcharging tends to cause deterioration of the battery. Therefore, it is necessary to perform charging in a short period of time and without any special attention during charging, which is safe and less likely to cause deterioration of the battery.

[0003] For this reason, for example, Japanese Patent Application Laid-Open No. 60-24173 is disclosed.
As disclosed in Japanese Patent Application Laid-Open No. 9-209, there is known a charging circuit including a current reducing unit that performs charging with a large current at an initial stage of charging and then gradually reduces the charging current as the battery approaches full charge. This charging circuit performs rapid charging with a large current and gradually reduces the charging current so that the charging amount approaches 100% with a smaller safe current. For this reason, the charging amount can be brought close to 100% while charging is performed in a short time, and deterioration due to overcharging can be prevented by reducing the charging current.

[0004] However, the charging circuit disclosed in this publication may cause danger or degrade the battery by generating heat when charging with a large current until switching to the safe current. FIG. 1 is a diagram illustrating the operation of the charging circuit disclosed in this publication. This charging circuit switches the charging current when the battery voltage at the time of charging reaches a predetermined value. The charging current changes in four stages and gradually decreases from the initial large current, and finally becomes the safe current. When the charging current is switched, the battery voltage at the time of charging is detected, and switching is performed when the battery voltage reaches a predetermined value. At this time,
As shown in FIG. 1, the battery voltage is set to a single constant value. That is, the charging current switched in four stages is switched when the battery voltage reaches the same value, even when switching from the initial charging current to the next charging current or finally when switching to the safe current. I have.

When charging is performed by rapid charging, it is necessary to stop charging or switch to a safe current when full charge is reached. This is because if the charging is continued with a large current, the battery will be overcharged and cause deterioration of the battery. In order to detect that the battery has reached a full charge, a peak value of the battery voltage is detected, or a so-called -Δ voltage slightly lowered from the peak value is detected.
This is done by detecting V.

However, in the case of the charging circuit, since the charging current is switched according to the absolute value of the battery voltage, there is a disadvantage that the full charge cannot be detected accurately.
Also, since the set voltage in the battery voltage detection circuit is constant regardless of the initial, middle, and end stages of charging,
In the middle and late stages of charging, charging is progressing as much as compared to the initial stage of charging, so as in the early stage of charging, if the charging current is switched at the same set voltage in the middle and end stages,
There is a danger that overcharging may occur due to exceeding the full charge. Further, if the set voltage is reduced so as not to cause overcharging, the charging current is reduced without obtaining a sufficient charge amount in the initial stage of charging, and there is a disadvantage that charging cannot be performed in a short time.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a charging circuit capable of performing safe charging without fear of overcharging, even though charging is performed in a short time by rapid charging.

[0008]

According to the present invention, in order to solve the above-mentioned problems, a secondary battery is charged with a first charging current, and after the battery voltage at the time of charging reaches a first predetermined value, the secondary battery is charged. The battery is charged with the second charging current smaller than the first charging current, and after the battery voltage at the time of charging reaches the second predetermined value lower than the first predetermined value, the second charging current is further smaller than the second charging current. And a current reducing means for performing charging up to full charge with the charging current of No. 3.

Further, the current reducing means includes a temperature compensating circuit for changing the first predetermined value and the second predetermined value according to an ambient temperature of the secondary battery.

[0010]

According to the present invention, in the early stage of charging, the battery is rapidly charged by the first charging current, and the amount of charge is obtained in the early stage of charging, which is less likely to cause overcharging. Eventually, when the battery voltage reaches a first predetermined value, charging is performed with a second charging current smaller than the first charging current. Since the charging by the second charging current ends when the battery voltage reaches a second predetermined value lower than the first predetermined value, the battery may be overcharged beyond the full charge, The battery temperature is prevented from rising abnormally. When the battery voltage reaches the second predetermined value, charging is performed with a smaller third charging current until the battery is fully charged. Since the third charging current is smaller than the first and second charging currents, detection of the peak voltage and-
It is easy to detect full charge such as ΔV detection, and there is no fear of overcharging.

Further, the current reducing means includes a temperature compensating circuit for changing the first predetermined value and the second predetermined value in accordance with the ambient temperature of the secondary battery. Since the battery is liable to be deteriorated when charging is performed, the first predetermined value and the second predetermined value can be set low according to the rise in the ambient temperature by the temperature compensation circuit. For this reason, it is possible to further prevent the battery from deteriorating and charge the battery safely.

[0012]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a block circuit diagram of the charging circuit according to the present invention.
In this figure, a charger drawn on the left side and a battery pack drawn on the right side constitute a charging circuit for a secondary battery. The battery pack includes a nickel-metal hydride storage battery B and a thermistor T provided in the battery pack in close contact with the battery B. The thermistor T is arranged to detect the ambient temperature of the battery B. The battery pack has three terminals, a + terminal, a-terminal and a T terminal, respectively.
On the other hand, the charger incorporates a power source 1 for supplying a charging current to the battery B and a microcomputer 2 including a current reducing means and a temperature compensating circuit, which will be described later. And a T terminal.

The power supply 1 can switch the charging current in three stages. That is, it is possible to switch to a rate current (3C) that is three times the nominal capacity of the battery B, a rate current (2C) that is twice the rate, and a rate current (1C) that is the same as the nominal capacity of the battery B. Where 1C
Is a current value that can supply a charge amount equal to the nominal capacity in one hour when the battery is charged with a constant current value. Therefore, the higher the rate is, the larger the charging current is, and the more the charging amount can be increased in a short time.

The microcomputer 2 is connected between the power supply 1 and the + and-terminals, and can input a battery voltage from the + terminal and a temperature signal from the T terminal. The microcomputer 2 can calculate and control the input battery voltage and temperature signals, and can generate a predetermined output based on the calculation results. That is, a current switching signal is output to the power supply 1 to switch the charging current supplied from the power supply 1, and a switching signal of a resistor inserted in the charging current path is output to perform rapid charging and trickle charging. Switch. Further, the state of charge of the battery B can be determined and the state of charge can be displayed.

The operation of the charging circuit according to the present invention will be described with reference to the flowcharts shown in FIGS. First, FIG.
(1) When the battery B is not connected to the charger 1, the charge display indicates that there is no battery, and the switches for quick charge and trickle charge are turned off. (2) When the battery B is connected, the battery voltage is detected. Since the voltage of the nickel-metal hydride battery does not exceed 2 V per cell, when a voltage of less than 2 V is detected, it is determined that the battery is present. (3) Next, it is determined whether or not the voltage exceeds 1.1 V per cell. (4) When the voltage is less than 1.1 V, it is determined that the battery B is in an inactive state, and the trickle charge is turned on at the same time as the quick charge is turned off, thereby indicating that charging is in progress. (5) The battery voltage remains at 1.
If the voltage does not recover to 1 V or more, the charging is stopped and an abnormality of the battery is displayed. (6) For a battery satisfying 1.1 V per cell,
Start charging. At this time, quick charging at the 3C rate is performed, and a message that charging is being performed is displayed. This rapid charging is performed for 4.9 seconds and then pulsed for 0.1 seconds. (7) Thereafter, it is determined whether or not the battery temperature rise from the start of charging is 20 ° C. or more. (8) If the temperature exceeds 20 ° C., in order to protect the battery from deterioration due to heat generation, quick charge is turned off and trickle charge is switched. At this time, the display of the full charge is performed. (9) For the battery B not exceeding 20 ° C., the rapid charging at the 3C rate is continued, and the battery voltage is detected during the off-time of the pulse. The 3C rate fast charge requires the battery voltage to be the first
Exceeds the predetermined value V1 (T), or the charging time is 10
Continued until minutes have passed. Incidentally, when measuring the battery voltage, during the period of the pulse off, if the measurement is performed while the charging current is supplied, the influence of the internal resistance of the battery is large, it is impossible to measure the battery voltage accurately, This is to prevent this. (10) If the determination in (9) is YES, the current reduction means in the microcomputer 2 operates to switch to the 2C rate quick charge. Pulse charging is performed as in the case of the 3C rate. (11) The same determination as in (7) is performed.

In FIG. 4, (12) the battery voltage and the second predetermined value V
2 (T). (13) When the determination in (12) is YES, the current reduction means in the microcomputer 2 operates to switch to the 1C rate quick charge. In this case, the pulse charging is not performed, and the current is always on. (14) Thereafter, the same determination as in (7) is performed. (15) Then, full charge detection is performed by a peak sensor, a -ΔV sensor, or a 60-minute timer. (16) When full charge is detected, the mode is switched from quick charge to trickle charge, and a full charge is displayed. (17) Then, it is determined whether or not the trickle charge has passed for 8 hours. (18) After 8 hours, trickle charging is stopped.
Note that the charge display maintains the full charge display.

In the above operation, transitions of the charging current and the battery voltage during charging are shown in FIG.
FIG. 6 shows an example of voltage setting based on a change in the ambient temperature between the predetermined value V1 (T) and the second predetermined value V2 (T). The first predetermined value V1 (T) and the second predetermined value V2 (T) of the battery voltage are 5
In the normal ambient temperature range of 0 ° C. or less, V1
(T) is set higher. As shown in FIG. 6, these predetermined values are set by a temperature compensation circuit in the microcomputer 2 so as to decrease stepwise as the ambient temperature increases. Further, in a high temperature environment of 50 ° C. or more, in order to prevent the battery from deteriorating due to charging at a high rate current in the initial stage of charging or to cause an abnormal heat generation and a dangerous state, the initial charging is performed. The set value V1 (T) is reduced.

[0018]

According to the present invention, in the early stage of charging, the battery is rapidly charged by the first charging current, and the amount of charge is obtained in the early stage of charging, which is less likely to cause overcharging. Eventually, when the battery voltage reaches a first predetermined value, charging is performed with a second charging current smaller than the first charging current. Since the charging by the second charging current ends when the battery voltage reaches a second predetermined value lower than the first predetermined value, the battery may be overcharged beyond the full charge, The battery temperature is prevented from rising abnormally. When the battery voltage reaches the second predetermined value, charging is performed with a smaller third charging current until the battery is fully charged. The third charging current is the first
And the second charging current is smaller than the second charging current, it is easy to detect the full charge such as the detection of the peak voltage and the detection of -ΔV, and there is no fear of overcharging.

Further, the current reducing means includes a temperature compensating circuit for changing the first predetermined value and the second predetermined value in accordance with the ambient temperature of the secondary battery. Since the battery is liable to be deteriorated when charging is performed, the first predetermined value and the second predetermined value can be set low according to the rise in the ambient temperature by the temperature compensation circuit. For this reason, it is possible to further prevent the battery from deteriorating and charge the battery safely.

As a result, according to the present invention, although charging is performed in a short time by rapid charging, charging can be performed safely without fear of overcharging or battery deterioration. Therefore, for example, it is most suitable for charging a secondary battery used for a toy or the like often handled by children.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change characteristic of a charging current in a conventional charging circuit.

FIG. 2 is a block circuit diagram of a charging circuit of the present invention.

FIG. 3 is a charge control flowchart.

FIG. 4 is a charge control flowchart.

FIG. 5 is a change characteristic diagram of a charging current and a battery voltage.

FIG. 6 is a diagram showing an example of setting a charging current switching voltage.

[Explanation of symbols]

 1 power supply 2 microcomputer B nickel-metal hydride storage battery T thermistor

Claims (2)

[Claims] A secondary battery is charged with a first charging current, and after a battery voltage during charging reaches a first predetermined value, the secondary battery is charged with a second charging current smaller than the first charging current. After the battery voltage at the time of charging reaches a second predetermined value lower than the first predetermined value, a current reducing unit that performs charging with a third charging current smaller than the second charging current until full charging is performed. A charging circuit, comprising: 2. The apparatus according to claim 1, wherein said current reducing means includes a temperature compensation circuit for changing said first predetermined value and said second predetermined value according to an ambient temperature of a secondary battery.
The charging circuit as described.