JP2002051478A - Charge control method and portable electronic device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When a notebook personal computer is used on a desktop and the battery is always used in a fully charged state, the battery is not driven because the battery is exposed to a high temperature due to heat generated from the device body. However, there is a problem that the charge / discharge capacity of the battery is deteriorated. SOLUTION: In order to solve the above-mentioned problem, a charge control circuit of the present invention controls a charge amount of a full charge to be gradually reduced according to a temperature of a secondary battery detected by a temperature detecting means. That is, when the temperature of the secondary battery is high, control is performed so that the charge amount is reduced. If it is known in advance that the battery is driven by the battery for a long time, charge control is performed so that the secondary battery is charged to the maximum amount. This makes it possible to drive the battery for a long time while extending the cycle life of the secondary battery, and to realize a portable electronic device that is excellent in usability.

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 circuit.

[0002]

2. Description of the Related Art In portable electronic equipment such as a notebook personal computer, there is a demand for a device for extending the driving time by a battery. Recently, lithium ion secondary batteries having excellent capacity density are generally used. In order to extend the operation time, when charging a lithium ion secondary battery, charging is performed to the limit of the capacity of the secondary battery. In such charging, if the charging exceeding the specified charging amount for the secondary battery is performed due to variation in charging control or the like, the cycle life of the battery itself is deteriorated.

[0003] In conventional portable electronic devices, when and under what state the portable electronic device is
Because we do not consider whether the power supply will be cut off,
In order to ensure the longest operation time regardless of when the battery is taken out, the charging control is performed so that the capacity of the lithium secondary battery is always full when the commercial power supply is connected and the battery can be charged.

[0004]

Generally, in a secondary battery such as a lithium ion battery, a discharge capacity that can be accumulated from a full charge to a complete discharge is a maximum in an initial state.
It tends to decrease with repeated charging and discharging. The decrease in capacity due to this deterioration is called cycle life deterioration. This deterioration characteristic tends to accelerate the cycle life deterioration as the state of charge of the battery is larger, that is, closer to full charge, and as the temperature of the battery itself is higher.

[0005] When a battery is always used in a fully charged state, such as when a notebook personal computer is used on a desktop with power supplied from a commercial power supply, the battery becomes hot due to heat generated from the main body of the device and is fully charged. There is a problem that the charge / discharge capacity of the battery is deteriorated even though the battery is not actually driven for portable use since the battery cannot be discharged from the battery.

[0006] Therefore, in the lithium secondary battery, the capacity is slightly smaller than the full charge, for example, 90% as compared with the full charge.
It is known that the cycle life is prolonged by keeping the capacity to about the same level or keeping the temperature rise of the secondary battery low.

SUMMARY OF THE INVENTION An object of the present invention is to extend the cycle life of a secondary battery without shortening the operation time when carrying the battery by selectively controlling the capacity at full charge.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a charge control circuit according to the present invention is provided so that a full charge amount is reduced stepwise according to a temperature of a secondary battery detected by a temperature detecting means. Control. That is, when the temperature of the secondary battery is high, the charge amount is controlled to be small, and when the temperature of the secondary battery is low, the charge amount is controlled to be large. In addition, in a state where power is supplied or supplied from an AC power source to perform operation or charging, a normal charge amount is controlled to be smaller than a rating of the secondary battery, while a user explicitly instructs. Thus, the charge amount is controlled to be high. As a result, the cycle life of the secondary battery can be prolonged, although the amount of charge is slightly smaller in normal operation. On the other hand, if there is a plan for a business trip or the like, and it is known in advance that the battery will be driven by the battery for a long time, charge control is performed so that the secondary battery is charged to the maximum amount. As a result, the battery can be driven for a long time, and a portable electronic device with excellent usability can be realized.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to a first aspect of the present invention is directed to a DC-DC converter for generating a power supply for operating an electronic device by receiving a supply of a commercial power supply, and a charging current and charging for a secondary battery. A charge control unit that controls voltage, a secondary battery and a voltage detection unit that measures a terminal voltage of the secondary battery, a current detection unit that detects a current that flows into or out of the secondary battery, A temperature detection unit that detects the temperature of the battery, a control unit that notifies the state of the secondary battery and a calculation of the remaining amount based on the information detected by the voltage detection unit and the current detection unit, and information on the control unit. A charging control method comprising: changing a voltage value of the constant voltage charging in a charging circuit including a power supply control unit that performs charging by switching to constant current charging after charging the secondary battery with constant voltage based on the voltage. And the charge capacity when fully charged In only decrease slightly, an effect that lengthening the secondary battery cycle life.

According to a second aspect of the present invention, there is provided a DC-DC power supply for generating a power supply for operating an electronic device by receiving a supply of a commercial power supply.
A converter, a charging control unit for controlling a charging current and a charging voltage to the secondary battery, a voltage detecting unit for measuring a terminal voltage of the secondary battery and the secondary battery, and an inflow or outflow of the secondary battery A current detection unit that detects current, a temperature detection unit that detects the temperature of the secondary battery, a calculation of the remaining amount based on information detected by the voltage detection unit and the current detection unit, and a state of the secondary battery. In the charging circuit including a control unit for notifying and a power supply control unit for charging the secondary battery with constant current based on the information of the control unit and then switching to constant voltage charging to perform charging, switching to the constant current charging is performed. The charge control method is characterized in that the value of the charging current until the completion of charging is made variable, and the charging time can be reduced by only slightly reducing the charging capacity when fully charged, and the secondary battery Extend cycle life It has the effect of.

According to a fifth aspect of the present invention, there is provided a temperature detecting section for detecting a temperature of the secondary battery, and when the temperature detected by the temperature detecting section is higher than a predetermined temperature, the voltage value of the constant voltage charging is changed. 2. The method according to claim 1, wherein the control is performed so as to be lower.
Alternatively, the charge control method according to claim 3 has an effect of suppressing a deterioration in the cycle life of the secondary battery when the use environment of the battery changes and the battery is used in a high-temperature environment.

According to a sixth aspect of the present invention, there is provided a temperature detecting unit for detecting a temperature of the secondary battery, and when the temperature detected by the temperature detecting unit is higher than a predetermined temperature, the charging at the time of the constant voltage charging is performed. 5. The charge control method according to claim 2, wherein the value of the discontinuation current is controlled to be high, and when the battery is used in a high-temperature environment due to a change in a use environment of the battery. This has the effect of suppressing the deterioration of the cycle life of the battery.

According to a seventh aspect of the present invention, there is provided a portable electronic device provided with a charge control method obtained by combining one or more of the charge control methods according to the first to sixth aspects. Even if the battery is used for a long period of time, the cycle life of the secondary battery is hardly deteriorated, and an electronic device having an excellent service life with less frequent battery replacement is provided.

An embodiment of the present invention will be described below in detail with reference to FIGS.

(Embodiment 1) FIG. 1 is a block diagram of an electronic apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 100 denotes an electronic device main body, which corresponds to, for example, a notebook personal computer main body. Details of these internal configurations are omitted. A power switch 110 instructs on / off control of the electronic device body. 111
A power control unit controls the power supply unit 112 by detecting the operation of the power switch 110 and the state of the battery pack 120.
Reference numeral 112 denotes a power supply unit, which receives a supply of commercial power from the AC plug 113 or a temporarily reduced voltage to generate a power supply to be consumed by the main unit, and charges the battery pack. It comprises a charging control unit 115 for supplying electric power. Reference numeral 120 denotes a battery pack, which includes a cell 121 of a lithium ion secondary battery, a voltage detection unit 122 that measures the voltage of the cell 121, a current detection unit 123 that detects a current flowing into or out of the cell 121, A temperature detecting unit 124 for detecting a temperature, a voltage,
The control unit 125 evaluates the remaining amount of the battery in the cell 121 and the appropriate charging voltage and charging current based on the information on the current and the temperature. The control unit 125 and the power supply control unit 111 have signal lines for exchanging data, and are generally connected by serial data.
Send to 11 A charge control composed of these components will be described.

In general, in charging control using a lithium ion secondary battery, when the remaining amount of the secondary battery is small, the charging current is set higher to charge the battery in a short time. In addition, when the charging is advanced and the battery is approaching full charge, the charging current is controlled to be small in order to prevent stress on the secondary battery due to overcharging. This will be described in detail with reference to FIG.

FIG. 2 shows the change over time of the charging voltage, charging current, and charging rate of the lithium ion secondary battery. When the remaining amount of the secondary battery is low, the control unit 125 requests the power supply control unit 111 to apply a constant current to the secondary battery. The control unit 125 counts the remaining amount of the cell 121 by integrating the information of the current detection unit 123. As charging progresses, cell 1
The terminal voltage of 21 gradually increases. Voltage detector 12
2 detects the voltage of the cell 121, and when the terminal voltage reaches a predetermined value, for example, 4.2V, the control unit detects that the full charge is approaching, and instructs the power supply control unit 111 to keep the voltage at 4.2V. Is supplied. The power supply control unit 111 controls the charge control unit 115 to maintain the charge voltage at 4.2V.

As the charging proceeds further, the charging current to the cell 121 gradually decreases. When the charging current falls below a certain value, for example, when the charging current falls below 10% of the charging current at the time of constant current charging, the charging is stopped.

Thus, from the beginning of charging to just before full charging, a constant current is applied to quickly fill the cell 121, thereby shortening the charging time, and performing constant voltage charging near the time of full charging. To prevent overcharging. The above voltage value is a voltage per cell of the lithium ion secondary battery. When a plurality of cells are connected in series and used, it is needless to say that an integral multiple of the voltage is applied.

Assuming that the fullness of the lithium secondary battery charged in this way is 100%, the cycle life in this case is the number of times defined by the specifications of the secondary battery, for example, 300 times.
It has a cycle life of times.

Next, consider a case where the voltage at the time of switching to constant voltage charging is changed from 4.2 V to 4.1 V. The basic charge control is the same as described above, and the voltage value when switching from constant current charging to constant voltage charging is changed to 4.1V. Thereafter, similarly, when the charge current of the constant current charge drops to 10%, the charge is terminated. With this control, the sufficiency is reduced, but the cycle life is about 5
It becomes as long as 00 times. This relationship is illustrated in FIG.

As described above, since the cycle life of the secondary battery can be extended by lowering the charging rate, the life of the secondary battery is prolonged for users who carry the battery less frequently. The effect that can be expected can be expected.

(Embodiment 2) The charging control of an electronic device according to Embodiment 2 of the present invention will be described. Since the circuit configuration and the like are the same as those in the first embodiment, a description thereof will be omitted, and specific charging control will be described.

When the remaining amount of the secondary battery is low, the control unit 1
Reference numeral 25 denotes a power control unit 1 for applying a constant current to the secondary battery.
Make a request to 11. The control unit 125 counts the remaining amount of the cell 121 by integrating the information of the current detection unit 123. As charging proceeds, the terminal voltage of the cell 121 gradually increases. When the voltage of the cell 121 is detected by the voltage detection unit 122 and the terminal voltage reaches a predetermined value, for example, 4.2 V, the control unit detects that the full charge is approaching, and instructs the power supply control unit 111 as it is. Instruct to supply a voltage of 4.2V. The power control unit 111 is a charge control unit 1
15 is controlled so that the charging voltage is maintained at 4.2V.

As the charging proceeds further, the charging current to the cell 121 gradually decreases. When the charging current falls below a certain value, for example, when the charging current falls below 60% of the charging current at the time of constant current charging, the charging is stopped. By increasing the current value of the charge termination in this way, the filling rate can be reduced. This makes it possible to extend the cycle life as in the above embodiment.

(Embodiment 3) In Embodiments 1 and 2, a method of extending the cycle life of a secondary battery by lowering the sufficiency in charging the secondary battery has been described. Since the operation time in battery driving is affected by the decrease, the switching method of these will be described.

Although it is a portable notebook personal computer, the notebook personal computer is frequently used on a desk. Rather, it is generally used on a desk and carried only when needed. Therefore, there is usually no problem even if charging is performed at a low charging rate.

Next, if it is known that the portable personal computer is to be used in the future, it instructs the notebook personal computer to increase the filling rate and perform 100% charging. Specifically, an instruction is given to the power supply control unit through an application program on a notebook personal computer. Immediately after receiving this instruction, charging is controlled so that the charging rate becomes 100%. As a result, the operation time during carrying can be prevented from being shortened. Usually, it is known in advance that you will carry it with you, so you will not lose your convenience. Even if it is decided in a hurry, the operation time will not be extremely short because the sufficiency rate of about 90% is satisfied.

(Embodiment 4) FIG. 4 is a diagram showing that the relationship between the filling rate and the cycle life is affected by temperature. As the battery temperature increases, the cycle life decreases.
For this reason, the filling rate is reduced according to the value of the temperature detection unit 124. The specific control method of the filling rate is the same as the method shown in the first embodiment and the second embodiment, and the description is omitted.

Although the control method of the sufficiency rate has been described in two stages, it is needless to say that finer control can be performed by performing control using more stages.

[0031]

According to the present invention, the user can select the charging rate of the charged amount of the secondary battery, and the cycle life of the battery can be extended by lowering the charging rate except when the secondary battery is used. Users who mainly use notebook personal computers on office desks with power supplied from an AC adapter, and in rare cases use batteries on the go, do not need to keep the batteries fully charged, and use them in portable applications. If the battery can be fully charged only when the battery is used, the battery driving time is not reduced and the battery life is improved.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram in charge control of a lithium ion secondary battery.

FIG. 3 is a characteristic diagram showing a filling rate and a cycle life of a secondary battery.

FIG. 4 is a characteristic diagram showing a filling rate and a cycle life of a secondary battery.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 main unit 110 power switch 111 power control unit 112 power supply unit 113 AC plug 114 DC-DC converter 115 charge control unit 120 battery pack 121 cell 122 voltage detection unit 123 current detection unit 124 temperature detection unit 125 control unit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01M 10/48 H01M 10/48 P

Claims (7)

[Claims] A DC-DC converter for generating a power supply for operating an electronic device in response to a supply of a commercial power supply; a charging control unit for controlling a charging current and a charging voltage for a secondary battery;
A secondary battery and a voltage detector that measures a terminal voltage of the secondary battery; a current detector that detects a current flowing into or out of the secondary battery; and a temperature detector that detects the temperature of the secondary battery. And a control unit that calculates the remaining amount based on the information detected by the voltage detection unit and the current detection unit and notifies the state of the secondary battery, and charges the secondary battery at a constant voltage based on the information of the control unit. A charging control method comprising: changing a voltage value of the constant-voltage charging in a charging circuit including a power supply control unit that performs charging by switching to constant-current charging after the charging. 2. A DC-DC converter for generating a power supply for operating an electronic device in response to a supply of a commercial power supply, a charge control unit for controlling a charge current and a charge voltage for a secondary battery,
A secondary battery and a voltage detector that measures a terminal voltage of the secondary battery; a current detector that detects a current flowing into or out of the secondary battery; and a temperature detector that detects the temperature of the secondary battery. A control unit for calculating the remaining amount based on the information detected by the voltage detection unit and the current detection unit and for notifying the state of the secondary battery; and charging the secondary battery with a constant current based on the information of the control unit. And a power supply control unit that performs charging by switching to constant voltage charging after the charging, wherein the value of a charging current that reaches charging completion after switching to the constant voltage charging is variable. Control method. 3. The charge control method according to claim 1, wherein the constant voltage value is switched to be higher when a user explicitly gives an instruction. 4. The charging control method according to claim 2, wherein the switching is performed so as to reduce the current value when a user explicitly gives an instruction. 5. A temperature detecting section for detecting a temperature of the secondary battery, wherein when the temperature detected by the temperature detecting section is higher than a predetermined temperature, control is performed such that the voltage value of the constant voltage charging is reduced. The charge control method according to claim 1 or 3, wherein 6. A temperature detecting unit for detecting a temperature of the secondary battery, wherein when the temperature detected by the temperature detecting unit is higher than a predetermined temperature, a value of the charge termination current at the time of constant voltage charging increases. The charge control method according to claim 2, wherein the control is performed as follows. 7. A portable electronic device comprising a charge control method obtained by combining one or more of the charge control methods according to claim 1.