JPH0864256A - Charging method and device - Google Patents

Abstract

PURPOSE: To prevent dispersion of charging conditions and deterioration in performance of a secondary battery by means of a simple structure by arranging a current detecting circuit and the like and detecting charging current in the secondary battery so as to finish charging when the detected value reaches the predetermined value or less. CONSTITUTION: A current detecting circuit 4 detects charging current It so as to output the detected value to a controlling circuit 5. In the controlling circuit 5, a charging finish current value is previously set, and the set value and the detected current It are compared with each other, so that ON/OFF control in a switch circuit 1 is carried out In this way, actual charging current is detected, and when the detected value is lowered below the predetermined value, a finish of charging is determined. Therefore, after a finish of charging, a uniform charging condition can be obtained no matter how an initial charging condition of the secondary battery is. On the other hand, excessively long constant voltage charging can be prevented as a finish of charging is determined by comparing the charging current with the set value, so that deterioration in battery performance such as battery capacity and a cycle life can be prevented even in a lithium ion battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery charging method and charging device.

[0002]

2. Description of the Related Art A secondary battery or a storage battery is an indispensable power source for portable devices such as mobile phones and cordless phones, and battery performance such as voltage and life has become an increasingly important technical item. In particular, it is necessary to consider charging the secondary battery so as not to deteriorate the battery performance.

FIG. 6 is a block diagram showing an example of a conventional constant voltage constant current charging device. The secondary battery B is connected to the output terminals T1 and T2 of the charging device for charging. The charging current It is the switching circuit 101 and the constant current circuit 102.
Is supplied to the secondary battery B through the constant current circuit 102 and its current value is limited to the control current value Ic. Further, the terminal voltage Vt between the output terminals T1 and T2 connected to the secondary battery B is controlled by the constant voltage circuit 103 by the control voltage value Vt.
Limited to c. The switch circuit 101 is the control circuit 1
ON / OFF is controlled by 04 and the timer circuit 105.

In the above conventional charging device, as shown in FIG. 7, when the secondary battery B is connected and charging is started, the timer circuit 105 starts (S201). Timer circuit 1
When the set time Ts of 05 has elapsed, the control circuit 104 turns off the switch circuit 101 to end the charging (S2
02).

FIG. 8 is a graph showing charge characteristics when the terminal voltage Vt of the secondary battery has not reached the constant voltage control voltage Vc. As shown in the figure, the charging current It is the constant current control value Ic and the constant current charging is performed until the terminal voltage Vt reaches the constant voltage control voltage value Vc after starting the charging. When the terminal voltage Vt reaches the control voltage value Vc, constant voltage charging is performed in which the terminal voltage Vt is constant and the charging current It gradually decreases. Then, when the time Ts set in advance in the timer circuit 105 has elapsed, the switch circuit 101 turns off.
It becomes FF and charging is completed.

FIG. 9 is a graph showing the charging characteristics when the terminal voltage Vt of the secondary battery has reached the constant voltage control voltage Vc. In this case, since constant voltage charging is performed from the start of charging, the charging current It gradually decreases from the start as shown in FIG. 7B, and constant voltage charging continues until the timer set time Ts elapses. To do. Therefore, the charging current It after the set time Ts has a smaller value than in the case of FIG.

A charging device in which the charging time is set in advance by such a timer circuit is disclosed in Japanese Patent Laid-Open No. 1-321826. In this charging device, the charging current is detected, and the time when the detected current value starts to decrease is set as the start time of the timer.

Further, the charging device disclosed in Japanese Patent Laid-Open No. 1-321827 is provided with a circuit for detecting the charging current to determine the charging state of the secondary battery and setting the charging time suitable for the charging state. ing.

[0009]

However, in the device in which the charging time is preset as in the prior art, since the charging is performed for a certain period of time regardless of the state of charge of the secondary battery, there is a variation in the battery capacity after the end of charging. It could happen. Particularly in the lithium ion battery, there is a problem that the battery capacity and the cycle life are deteriorated depending on the application time of the constant voltage control voltage.

For example, in the case where a charging device is provided on a telephone stand for a mobile phone or a cordless telephone, charging is started every time a handset containing a secondary battery is set on the telephone stand. As a result, the fully charged secondary battery is charged many times, which deteriorates the battery capacity and life as described above.

A method of determining the charging state of the secondary battery and setting the charging time (Japanese Patent Laid-Open No. 1-321827).
Then, it is necessary to set a charging time suitable for the charging state, and there is a problem that the device configuration and operation control become complicated.

It is an object of the present invention to provide a charging method and device capable of preventing variations in the charging state of secondary batteries and performance deterioration with a simple structure.

[0013]

The charging method according to the present invention is characterized in that the charging current of a secondary battery is detected and the charging is terminated when the detected value falls below a preset value.

Further, the charging device according to the present invention includes a detecting means for detecting the charging current of the secondary battery, and a controlling means for outputting a charging end signal when the detected value of the charging current falls below a preset value. And switch means for stopping the supply of the charging current to the secondary battery in response to the charging end signal.

[0015]

[Function] When the charging current drops below the set value, the fully charged state of the secondary battery is judged, and charging is stopped.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a charging device according to the present invention. The present embodiment is a constant voltage constant current charging device, and a secondary battery B is connected to its output terminals T1 and T2 for charging. The switch circuit 1 is provided on the input power source side, and the start / end control of charging is performed by turning on / off the switch circuit 1. Charging current I
t is supplied to the secondary battery B through the switch circuit 1 and the constant current circuit 2, and its current value is limited to the control current value Ic by the constant current circuit 2. Further, the terminal voltage Vt between the output terminals T1 and T2, to which the secondary battery B is connected, is limited to the control voltage value Vc by the constant voltage circuit 3.

The current detection circuit 4 detects the charging current It,
The detected value is output to the control circuit 5. A charge end current value Is is preset in the control circuit 5, and the set value I
ON / OFF control of the switch circuit 1 is performed by comparing s with the detected charging current It.

FIG. 2 is a flow chart for explaining the charging operation of this embodiment. First, 2 at terminals T1 and T2
When the secondary battery B is connected, the control circuit 5 switches to the switch circuit 1
Is turned on to start charging (S11). When the charging is started, the charging current It flows through the constant current circuit 2 and the secondary battery B, and its magnitude is detected by the current detection circuit 4 (S12).

The control circuit 5 compares the set value Is with the detected charging current value It (S13). If the charging current It is larger (Is <It), the charging is continued and the charging current It is set. When the value Is is reached (Is ≧ It),
The switch circuit 1 is turned off to end the charging (S1
4).

FIG. 3 is a graph showing the charging characteristics of this embodiment when the terminal voltage Vt of the secondary battery has not reached the constant voltage control voltage Vc. As shown in the figure, the charging current It is the constant current control value Ic and the constant current charging is performed until the terminal voltage Vt reaches the constant voltage control voltage value Vc after starting the charging. When the terminal voltage Vt reaches the control voltage value Vc, constant voltage charging is performed in which the terminal voltage Vt is constant (Vc) and the charging current It gradually decreases. Then, when the charging current It drops to the charging end set value Is, the control circuit 5 turns off the switch circuit 1 to end the charging as described above.

FIG. 4 is a graph showing the charging characteristics of this embodiment when the terminal voltage Vt of the secondary battery has reached the constant voltage control voltage Vc. In this case, since constant-voltage charging is performed from the start of charging, the charging current It gradually decreases from the start as shown in FIG. 7B, and when the charging current setting value Is decreases, the control circuit 5 switches the switch. The circuit 1 is turned off to end the charging. Therefore, when the secondary battery B is charged to some extent, the charging time is short as shown in FIG. Of course, if the secondary battery B is sufficiently charged, the charging current It is less than or equal to the set value Is, so the switch circuit 1 is immediately turned off and charging is not performed.

FIG. 5 is a block diagram showing another embodiment of the charging device according to the present invention. In this embodiment, the control circuit 5
The current value comparison operation of is realized by an analog circuit.

In the figure, a comparator 6 receives a voltage value Vi corresponding to the charging current It from the current detection circuit 4 and compares it with a reference voltage value Vref corresponding to a preset charging end set value Is. Then, FIG. 3B and FIG.
As shown in (b), when Vref ≧ Vi,
The comparator 6 outputs a stop signal to the switch circuit 1 to end the charging. In this embodiment, the secondary battery B can be uniformly charged with a simple configuration using the comparator 6, and the performance deterioration can be prevented.

[0025]

As described in detail above, the charging method and device according to the present invention detect the actual charging current and determine the end of charging when the detected value falls below a predetermined value. Therefore, after charging is completed, a uniform charge state can be obtained regardless of the initial charge state of the secondary battery. Further, since the end of charging is determined by comparing the charging current with the set value, excessively long constant voltage charging can be avoided, and deterioration of battery performance such as battery capacity and cycle life can be prevented even with a lithium ion battery.

For example, when the present invention is applied to a charging device for a mobile phone or a cordless phone, charging is not performed if the secondary battery on the handset side is fully charged, so the handset is repeatedly placed on the telephone stand. However, the performance of the secondary battery is not deteriorated.

Further, in the present invention, since the charging end time is determined by comparing the charging current with the set value, it is not necessary to set the charging time by the timer as in the conventional case, and the configuration and control are much simpler than the conventional case. become.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a charging device according to the present invention.

FIG. 2 is a flowchart for explaining a charging operation of this embodiment.

FIG. 3 is a diagram showing that the terminal voltage Vt of the secondary battery is a constant voltage control voltage Vc.
6 is a graph showing the charging characteristics of the present embodiment when the charging rate has not reached

FIG. 4 is a diagram illustrating a terminal voltage Vt of a secondary battery as a constant voltage control voltage Vc.
7 is a graph showing the charging characteristics of the present embodiment when the charging rate has reached.

FIG. 5 is a block diagram showing another embodiment of the charging device according to the present invention.

FIG. 6 is a block diagram showing an example of a conventional charging device.

FIG. 7 is a flowchart for explaining a conventional charging operation.

FIG. 8 is a diagram illustrating a terminal voltage Vt of a secondary battery as a constant voltage control voltage Vc.
7 is a graph showing a conventional charging characteristic when the charging speed has not reached the value.

FIG. 9 is a diagram showing that the terminal voltage Vt of the secondary battery is a constant voltage control voltage Vc.
6 is a graph showing a conventional charging characteristic when the battery has reached the limit.

[Explanation of symbols]

 1 Switch Circuit 2 Constant Current Circuit 3 Constant Voltage Circuit 4 Current Detection Circuit 5 Control Circuit 6 Comparator B Secondary Battery T1, T2 Output Terminal

Claims (5)

[Claims] 1. A method of charging a secondary battery, wherein the charging current of the secondary battery is detected, and the charging is terminated when the detected charging current becomes equal to or less than a preset value. How to charge. 2. The charging method according to claim 1, wherein charging is not performed if the charging current of the secondary battery is equal to or less than the set value from the start of charging. 3. A device for charging a secondary battery, comprising: a detection unit for detecting a charging current of the secondary battery; and a charging end signal when a detected value of the charging current drops below a preset value. A charging device comprising: a control unit that outputs and a switch unit that stops the supply of a charging current to the secondary battery in response to the charging end signal. 4. The charging device according to claim 3, wherein the control means is composed of a comparator. 5. The charging device according to claim 2, wherein the secondary battery is charged with a constant voltage and a constant current.