JP2007047127A - Method and device for setting voltage for low battery determination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for setting voltage for low battery determination that can make an electronic device execute a predetermined operation during low battery of a secondary battery at a desired timing even if the discharge characteristic of the secondary battery used as a power source for supplying electric power to the electronic device is varied by repetition of charge and discharge, and does not require complicated calculation for calculating remaining capacity of the secondary battery. <P>SOLUTION: When the secondary battery 5 is discharged in a predetermined discharge condition from a charging completion state by a discharge means 11, a decrease time until the voltage of the secondary battery 5 measured by a voltage measuring means 8 is decreased from a first voltage in the charging completion state to a predetermined second voltage by discharge is measured by a time measuring means 9. A setting means 12 sets the voltage for low battery determination based on the decrease time measured by the time measuring means 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a low battery determination voltage setting method and setting device used in an electronic device to which power is supplied from a secondary battery.

  Conventional techniques are used in electronic devices to which power is supplied from a secondary battery. The voltage of the secondary battery decreases as the discharge time increases. When the voltage of the secondary battery decreases to a predetermined low battery determination voltage, the electronic device outputs, for example, a warning sound as a predetermined operation when the secondary battery is low battery. Since the warning sound is output before the remaining capacity of the secondary battery runs out, the operator of the electronic device operates the electronic device before the electronic device stops operating, and stores the data in use in the RAM ( Random Access Memory) can be saved to a non-volatile memory such as a hard disk. This can prevent data loss during use.

  In the conventional technique, the predetermined low battery determination voltage is set so that a secondary battery having a single charge / discharge cycle (hereinafter referred to as “charge / discharge cycle”) has a predetermined remaining capacity. is doing. This conventional technique does not take into consideration that the discharge characteristics of the secondary battery change due to repeated charging and discharging. In such a conventional technique, there is a problem in that an alarm sound cannot be output at a desired timing when the number of times the secondary battery is charged and discharged increases. In other words, there is a problem that a warning sound is output when the remaining capacity of the secondary battery is sufficiently large, or a warning sound is not output even though the remaining capacity of the secondary battery is small.

  In order to solve such a problem, the electronic device may be configured to output a warning sound when the remaining capacity of the secondary battery is measured and the measured remaining capacity falls to a predetermined remaining capacity. . A technique for measuring the remaining capacity of the secondary battery is disclosed in Patent Document 1.

  In the technique disclosed in Patent Document 1, the charge / discharge current and the temperature of the battery pack are measured at a predetermined cycle, and the charge / discharge efficiency is obtained from the measured charge / discharge current and the temperature of the battery pack. The charge / discharge current in each period is calculated by multiplying the charge / discharge current by the efficiency and the period. In a secondary battery having a large change with time, the charge / discharge current is also multiplied by a charge / discharge cycle coefficient corresponding to the number of times of charge / discharge. Then, by adding or subtracting the charge / discharge capacity from the remaining capacity calculated in the previous measurement, a new remaining capacity is obtained every time each period elapses.

  When the technique disclosed in Patent Document 1 is used, there is a problem that complicated calculation is required. Further, in this case, errors accumulate in the measured remaining capacity, and as a result, the same problem as in the conventional technique occurs.

JP 11-344544 A

  It is an object of the present invention to perform a predetermined operation when a secondary battery is in a low battery state, even if a discharge characteristic of a secondary battery used as a power source for supplying power to the electronic apparatus changes due to repeated charging and discharging. It is an object of the present invention to provide a low battery determination voltage setting method and setting device that can be executed at a desired timing and that does not require complicated calculation for calculating the remaining capacity of a secondary battery.

According to the present invention, power is supplied from the secondary battery, the voltage of the secondary battery is compared with the low battery determination voltage, and a predetermined operation at the time of the low battery of the secondary battery is performed based on the comparison result. A method for setting the low battery determination voltage in an electronic device to be executed,
The secondary battery is discharged from a fully charged state under a predetermined discharge condition, and a reduction time until the voltage of the secondary battery is reduced from a first voltage in a fully charged state to a predetermined second voltage by discharging is measured,
The low battery determination voltage setting method is characterized in that the low battery determination voltage is set based on the measured decrease time.

  In the invention, it is preferable that the predetermined discharge condition is a discharge condition in which a current discharged from the secondary battery is constant or a discharge condition in which a resistance for discharging the secondary battery is constant.

  The present invention is characterized in that, when setting the low battery determination voltage, table information in which the information on the decrease time and the information on the low battery determination voltage according to the decrease time are associated is used.

In addition, the present invention provides power that is supplied from the secondary battery, compares the voltage of the secondary battery with the low battery determination voltage, and determines a predetermined operation when the secondary battery is low battery based on the comparison result. The low battery determination voltage setting device in the electronic device that executes
Discharging means for discharging the secondary battery under predetermined discharge conditions;
Voltage measuring means for measuring the voltage of the secondary battery;
When the secondary battery is discharged from the charging completion state by the discharging means under a predetermined discharging condition, the voltage of the secondary battery measured by the voltage measuring means is predetermined by the discharging from the first voltage in the charging completion state. Time measuring means for measuring the time until the voltage drops,
A low battery determination voltage setting device, comprising: setting means for setting the low battery determination voltage based on a decrease time measured by the time measurement means.

  In the invention, it is preferable that the predetermined discharge condition is a discharge condition in which a current discharged from the secondary battery is constant or a discharge condition in which a resistance for discharging the secondary battery is constant.

  According to another aspect of the present invention, there is provided storage means for storing table information in which information on a drop time and information on a low battery determination voltage according to the drop time are associated with each other for setting the low battery determination voltage by the setting means. Is further included.

  According to the present invention, electric power is supplied to the electronic device from the secondary battery. The electronic device compares the voltage of the secondary battery and the low battery determination voltage, and executes a predetermined operation when the secondary battery is low battery based on the comparison result. In the present invention, the low battery determination voltage in such an electronic apparatus is set.

  In setting the low battery determination voltage, first, the secondary battery is discharged from a fully charged state under a predetermined discharge condition, and the secondary battery voltage is predetermined by discharging from the first voltage in the fully charged state. Measure the drop time until drop. Next, the low battery determination voltage is set based on the measured decrease time.

  The discharge characteristics of the secondary battery change with repeated charging and discharging. The discharge characteristics of the secondary battery can be specified based on the decrease time. In the present invention, the low battery determination voltage is set based on the decrease time. Therefore, in the present invention, the low battery determination voltage can be set according to the discharge characteristics of the secondary battery.

  Since the low battery determination voltage can be set in this way, even if the discharge characteristics of the secondary battery change due to repeated charging and discharging, the electronic device can execute the predetermined operation at a desired timing. Can do. In order to cause the electronic device to execute the predetermined operation at a desired timing, the low battery determination voltage set as described above only needs to be compared with the voltage of the secondary battery. No complicated calculation is required to calculate the capacity.

  Further, according to the present invention, the decrease time is measured under the discharge condition that the current discharged from the secondary battery is constant or the discharge condition that the resistance for discharging the secondary battery is constant. In this case, compared with the case where the decrease time is measured under other discharge conditions, the discharge characteristics of the secondary battery can be easily specified, and therefore the low battery determination voltage can be easily set.

  Further, according to the present invention, in the table information, the information on the decrease time and the information on the low battery determination voltage corresponding to the decrease time are associated. Since the table information as described above is used when setting the low battery determination voltage, the low battery determination voltage can be easily set.

  According to the invention, electric power is supplied to the electronic device from the secondary battery. The electronic device compares the voltage of the secondary battery and the low battery determination voltage, and executes a predetermined operation when the secondary battery is low battery based on the comparison result. In the present invention, the low battery determination voltage in such an electronic apparatus is set.

  The discharging means discharges the secondary battery under predetermined discharge conditions. The voltage measuring means measures the voltage of the secondary battery. The time measuring means discharges the voltage of the secondary battery measured by the voltage measuring means from the first voltage in the charging completed state when the secondary battery is discharged from the charging completed state by the discharging means under a predetermined discharge condition. The time until the voltage drops to the predetermined second voltage is measured. The setting means sets the low battery determination voltage based on the decrease time measured by the time measuring means.

  The discharge characteristics of the secondary battery change with repeated charging and discharging. The discharge characteristics of the secondary battery can be specified based on the decrease time. In the present invention, the low battery determination voltage is set based on the decrease time. Therefore, in the present invention, the low battery determination voltage can be set according to the discharge characteristics of the secondary battery.

  Since the low battery determination voltage can be set in this way, even if the discharge characteristics of the secondary battery change due to repeated charging and discharging, the electronic device can execute the predetermined operation at a desired timing. Can do. In order to cause the electronic device to execute the predetermined operation at a desired timing, the low battery determination voltage set as described above only needs to be compared with the voltage of the secondary battery. No complicated calculation is required to calculate the capacity.

  Further, according to the present invention, the decrease time is measured under the discharge condition that the current discharged from the secondary battery is constant or the discharge condition that the resistance for discharging the secondary battery is constant. In this case, compared with the case where the decrease time is measured under other discharge conditions, the discharge characteristics of the secondary battery can be easily specified, and therefore the low battery determination voltage can be easily set.

  According to the invention, the storage unit stores table information. In the table information, the information on the drop time is associated with the information on the low battery determination voltage corresponding to the drop time. The setting means can easily set the low battery determination voltage by using the table information as described above when setting the low battery determination voltage.

  FIG. 1 is a block diagram showing a configuration of an electronic device 2 including a low battery determination voltage setting device 1 according to an embodiment of the present invention. The electronic device 2 according to the present embodiment is supplied with power from the AC power source 3 via the AC adapter 4 and also with power from the secondary battery 5. The electronic device 2 operates with power from the AC power source 3 when power is supplied from the AC power source 3, and operates with power from the secondary battery 5 when power is not supplied from the AC power source 3. The electronic device 2 includes a charging circuit 6 and supplies power from the AC power source 3 to the secondary battery 5 via the charging circuit 6, thereby charging the secondary battery 5. In the present embodiment, secondary battery 5 is realized by a lithium ion secondary battery.

  The electronic device 2 compares the voltage of the secondary battery 5 and the low battery determination voltage, and executes a predetermined operation when the secondary battery 5 is low battery based on the comparison result. Specifically, when the voltage of the secondary battery 5 decreases and reaches the low battery determination voltage, the electronic device 2 executes the predetermined operation. In the present embodiment, the predetermined operation is a warning operation for warning that the remaining capacity of the secondary battery 5 has decreased. The “low battery” is a state in which the voltage of the secondary battery 5 has decreased from the completion of charging due to power consumption by the operation of the electronic device 2, and the voltage of the secondary battery 5 is the low battery determination voltage as described above. It means the state when it reaches. For example, the electronic device 2 outputs a warning sound as the warning operation. Since the warning sound is output before the remaining capacity of the secondary battery 5 runs out, the operator of the electronic device 2 operates the electronic device 2 before the electronic device 2 stops operating, data in use, etc. Can be saved from the volatile memory to the nonvolatile memory. This can prevent data loss during use.

  The low battery determination voltage setting device 1 according to the present embodiment is used to set the low battery determination voltage in the electronic device 2. The low battery determination voltage setting device 1 includes a system circuit 7, a voltage measurement unit 8, a time measurement unit 9, and a storage unit 10. In the present embodiment, the system circuit 7 functions as the discharging unit 11 and the setting unit 12. The system circuit 7 is realized by a central processing unit (abbreviated as CPU).

  The discharge means 11 discharges the secondary battery 5 under predetermined discharge conditions. The predetermined discharge condition is a discharge condition in which a current discharged from the secondary battery 5 is constant. The discharge means 11 discharges the secondary battery 5 under the discharge conditions by repeatedly executing a predetermined calculation. The predetermined calculation is, for example, addition, specifically, addition of adding 1.

  The voltage measuring unit 8 measures the voltage of the secondary battery 5. The voltage measuring means 8 is realized by an A / D (Analog to Digital) converter.

  The time measuring means 9 is configured such that the voltage of the secondary battery 5 measured by the voltage measuring means 8 when the secondary battery 5 is discharged from the charging completion state by the discharging means 11 under the above-mentioned discharging condition. The reduction time until the voltage drops to a predetermined second voltage by discharging from one voltage is measured. The predetermined second voltage is within a range in which a predetermined difference is generated in the decrease time when the number of repetitions of charging and discharging of the secondary battery 5 (hereinafter referred to as “the number of charging / discharging”) differs by a predetermined number. To be elected. As an example, the predetermined second voltage is selected in such a range that the decrease time is reduced to about 50% when the number of charge / discharge cycles is increased by 500 times. Specifically, in the case of a lithium ion secondary battery having discharge characteristics as shown in FIG. 4 to be described later, the predetermined second voltage is selected in the vicinity of 3.5V. The time measuring means 9 is realized by a timer function mounted on the CPU.

  The setting unit 12 sets the low battery determination voltage based on the decrease time measured by the time measurement unit 9. In the present embodiment, the setting unit 12 sets the low battery determination voltage based on the decrease time measured by the time measuring unit 9 so that the secondary battery 5 has a predetermined remaining capacity. The predetermined remaining capacity is selected according to the discharge characteristics of the secondary battery 5. The predetermined remaining capacity is selected according to the type of the electronic device 2.

  The storage means 10 stores table information 13 for setting the low battery determination voltage by the setting means 12. The storage means 10 stores low battery determination voltage information 14 set by the setting means 12 and also stores the predetermined second voltage information 15. The storage means 10 is realized by a non-volatile memory such as a flash memory.

  FIG. 2 is a diagram illustrating a configuration of the table information 13 stored in the storage unit 10. In the table information 13, the drop time information 16 and the low battery determination voltage information 17 corresponding to the drop time are associated with each other.

  FIG. 3 is a flowchart for explaining the setting operation of the low battery determination voltage by the system circuit 7. The electronic device 2 has a low battery determination voltage setting mode for setting a low battery determination voltage as one of operation modes. When the operator of the electronic device 2 determines that the driving time of the electronic device 2 has become shorter, for example, he / she operates the electronic device 2 to select a low battery determination voltage setting mode, and to the cradle having the AC adapter 4 The electronic device 2 is attached. The drive time is a time for which the electronic device 2 is driven by one charge.

  When the setting mode of the low battery determination voltage is selected by an operation input by the operator of the electronic device 2, the electronic device 2 is mounted on the cradle and charging of the secondary battery 5 is started, the low voltage by the system circuit 7 is started. The battery determination voltage setting operation is started. When the setting operation of the low battery determination voltage is started, the process proceeds to step a1.

  In step a1, it is determined whether or not the secondary battery 5 is in a fully charged state. In the present embodiment, the secondary battery 5 is a lithium ion secondary battery, and a constant current / constant voltage charging method is used for charging the lithium ion secondary battery. In this case, in step a1, when the charging voltage reaches a predetermined voltage and becomes constant and the charging current stops flowing, it is determined that the secondary battery 5 is in a charging completed state. The operation of step a1 is repeatedly executed until the secondary battery 5 is in a fully charged state. If it is determined that the secondary battery 5 is in a fully charged state, charging of the secondary battery 5 is terminated and the process proceeds to step a2.

  In step a2, repetition of a predetermined calculation is started, thereby starting discharge of the secondary battery 5 under a discharge condition that the current discharged from the secondary battery 5 is constant, and the process proceeds to step a3. In step a3, the time measuring operation by the time measuring means 9 is started, and the process proceeds to step a4. In step a4, it is determined whether or not the voltage of the secondary battery 5 measured by the voltage measuring means 8 has dropped to the second voltage. For this determination, the second voltage information 15 stored in the storage means 10 is used.

  If it is determined in step a4 that the voltage of the secondary battery 5 measured by the voltage measuring means 8 has dropped to the second voltage, the discharging of the secondary battery 5 by the discharging means 11 and the time measuring operation by the time measuring means 9 are terminated. Then, the process proceeds to step a5. In step a5, a low battery determination voltage is set based on the decrease time measured by the time measuring means 9. The decrease time is the time from when the time measuring means 9 starts the time measuring operation to when it ends. In setting the low battery determination voltage, the table information 13 stored in the storage unit 10 is used. Further, the storage unit 10 stores low battery determination voltage information 14 set by the setting unit 12. After setting the low battery determination voltage in this way, the low battery determination voltage setting operation is terminated.

  If it is determined in step a4 that the voltage of the secondary battery 5 measured by the voltage measuring unit 8 has not decreased to the second voltage, the process proceeds to step a7. In step a7, it is determined whether or not the discharge under the discharge condition that the current discharged from the secondary battery 5 is constant is continued. For example, when the discharge condition is changed by an operation input by the operator of the electronic device 2, it is determined in step a7 that the discharge is not continued.

  If it is determined in step a7 that the discharge is continued, the process returns to step a4. If it is determined in step a7 that the discharge is not continued, the discharge of the secondary battery 5 by the discharging means 11 and the time measuring operation by the time measuring means 9 are ended, and the setting operation of the low battery determination voltage is ended. . If it is determined that the discharge is not continued in this manner, the setting operation of the low battery determination voltage is terminated without setting the low battery determination voltage, so that an incorrect low battery determination voltage is set. Can be prevented.

  The electronic device 2 is for informing the operator of the electronic device 2 that the low battery determination voltage is being set, for example, from the start to the end of the low battery determination voltage setting operation. You may be comprised so that a screen can be displayed. In this case, it is possible to avoid the inconvenience that the operator of the electronic device 2 erroneously operates the electronic device 2 during the setting operation of the low battery determination voltage.

  In the present embodiment, if it is determined in step a1 that the secondary battery 5 is in a fully charged state, charging of the secondary battery 5 is terminated and the process proceeds to step a2, but in another embodiment of the present invention, In step a1, after determining that the secondary battery 5 is in a charged state, when the operator of the electronic device 2 releases the electronic device 2 from the cradle, the charging of the secondary battery 5 is terminated. You may proceed to step a2.

  FIG. 4 is a diagram illustrating an example of discharge characteristics of a lithium ion secondary battery. In FIG. 4, the horizontal axis indicates the discharge time, and the vertical axis indicates the voltage of the lithium ion secondary battery. FIG. 4 shows discharge characteristics under a discharge condition in which the current discharged from the lithium ion secondary battery is constant. The current discharged from the lithium ion secondary battery corresponds to the current discharged from the secondary battery 5 by the discharging means 11. In FIG. 4, the solid line 21 shows the discharge characteristics of the lithium ion secondary battery when the number of times of charging and discharging is one, and the broken line 22 shows the discharge of the lithium ion secondary battery when the number of times of charging and discharging is 500 times. Show the characteristics.

  The voltage of the lithium ion secondary battery decreases as the discharge time increases. Specifically, the voltage of the lithium ion secondary battery rapidly decreases immediately after the start of discharge, then decreases gradually for a while, and finally decreases slightly abruptly.

  The discharge characteristics of the lithium ion secondary battery vary depending on the number of charge / discharge cycles. Specifically, the time from the start of discharge to the end of discharge becomes shorter as the number of charge / discharge cycles increases. Further, the voltage when the same discharge time has elapsed from the start of discharge becomes lower as the number of charge / discharge cycles increases. Furthermore, the time from the time when the change in voltage changes from a gradual drop to a somewhat sudden drop until the end of discharge becomes longer as the number of charge / discharge increases, and the change in voltage at this time increases as the number of charge / discharge increases. , Get loose.

  The discharge characteristics of the lithium ion secondary battery can be specified based on the decrease time. When the discharge characteristics of the lithium ion secondary battery are specified, the relationship between the remaining capacity of the lithium ion secondary battery and the voltage of the lithium ion secondary battery is known. If the relationship between the remaining capacity of the lithium ion secondary battery and the voltage of the lithium ion secondary battery is known, the low battery determination voltage can be set so that the lithium ion secondary battery has a predetermined remaining capacity.

  Based on this point, the table information is created in advance based on the discharge characteristics of the lithium ion secondary battery as described above. In the present embodiment, a drop time and a low battery determination voltage are respectively obtained for a plurality of discharge characteristics when the number of times of charging and discharging is different, and the table is based on the drop time and the low battery determination voltage. Information 13 is created. The decrease time is a time until the voltage of the lithium ion secondary battery decreases from the first voltage V1 to the second voltage V2. The low battery determination voltage is a voltage of a lithium ion secondary voltage when the lithium ion secondary battery has a predetermined remaining capacity.

  As an example, regarding the discharge characteristics indicated by the solid line 21, the time T1 until the voltage of the lithium ion secondary battery decreases from the first voltage V1 to the second voltage V2 is the decrease time, and the lithium ion secondary battery is The voltage V11 of the lithium ion secondary voltage when having a predetermined remaining capacity is the low battery determination voltage. Regarding the discharge characteristics indicated by the broken line 22, the time T2 until the voltage of the lithium ion secondary battery decreases from the first voltage V1 to the second voltage V2 is the decrease time, and the remaining capacity determined by the lithium ion secondary battery in advance The lithium-ion secondary voltage V12 is a low battery determination voltage.

  As described above, the time from the point at which the voltage change changes from a gradual drop to a slight sudden drop until the end of discharge becomes longer as the number of charge / discharge cycles increases, and the voltage change at this time is the number of charge / discharge cycles. As it increases, it becomes milder. In consideration of this point, the predetermined remaining capacity for determining the low battery determination voltage is lowered as the change of the voltage in the time becomes gentler.

  In setting the low battery determination voltage, the setting means 12 uses the table information 13 prepared in advance as described above, and the low battery determination voltage according to the drop time measured by the time measurement means 9. Select. Therefore, the setting means 12 can set the low battery determination voltage so that the lithium ion secondary battery has a predetermined remaining capacity.

  Referring again to FIG. 1, the electronic device 2 includes the low battery determination voltage setting device 1, a voltage measuring unit 8 that measures the voltage of the secondary battery 5, and a secondary measured by the voltage measuring unit 8. When the voltage of the battery 5 drops to the low battery determination voltage set by the low battery determination voltage setting device 1, the control unit 31 executes a warning operation.

  In the present embodiment, the voltage measuring means 8 in the electronic device 2 is the same as the voltage measuring means 8 in the low battery determination voltage setting device 1. The voltage measuring means 8 in the electronic device 2 may be provided separately from the voltage measuring means 8 in the low battery determination voltage setting device 1. In the present embodiment, the control means 31 is one of the functions of the system circuit 7. The control unit 31 may be realized by a circuit different from the system circuit 7.

  The electronic device 2 is realized as a mobile phone, a personal digital assistant (abbreviated as PDA), a personal computer, or a portable music device.

  According to the present embodiment as described above, the setting means 12 can set the low battery determination voltage so that the secondary battery 5 has a predetermined remaining capacity. Since the low battery determination voltage can be set in this way, even if the discharge characteristics of the secondary battery 5 change due to repeated charging and discharging, the electronic device 2 can execute a warning operation at a desired timing. Can do. In order to cause the electronic device 2 to perform a warning operation at a desired timing, the low battery determination voltage set by the setting unit 12 is simply compared with the voltage of the secondary battery 5 measured by the voltage measuring unit 8. In many cases, a complicated calculation for calculating the remaining capacity of the secondary battery 5 is not required.

  Here, description will be made assuming that a lithium ion secondary battery whose discharge characteristics change as shown in FIG. When the low-battery determination voltage is kept constant, when the number of charge / discharge cycles increases and the discharge characteristics of the lithium-ion secondary battery change, a warning sound is generated even though the remaining capacity of the lithium-ion secondary battery is sufficiently large. The problem of output occurs. On the other hand, when the low battery determination voltage is set as in the present embodiment, even if the number of times of charging / discharging increases and the discharge characteristics of the lithium ion secondary battery change, the remaining lithium ion secondary battery remains. A warning sound is output when the capacity reaches the predetermined remaining capacity.

  Further, since the decrease time is measured under a discharge condition in which the current discharged from the secondary battery 5 is constant, the discharge characteristics of the secondary battery 5 can be easily specified, and thus the low battery determination voltage can be easily set. Can be set.

  Further, table information 13 is stored in the storage means 10, and in this table information 13, information 16 on the drop time and information 17 on the low battery determination voltage corresponding to the drop time are associated with each other. The setting means 12 can easily set the low battery determination voltage by using the table information 13 as described above when setting the low battery determination voltage.

  Further, the second voltage is selected in such a range that a predetermined difference occurs in the decrease time when the number of times of charging / discharging the secondary battery 5 differs by a predetermined number. As a result, the discharge characteristics of the secondary battery 5 can be accurately specified based on the decrease time, and thus the low battery determination voltage can be set accurately.

  The above-described embodiment is merely an example of the present invention, and the configuration can be changed within the scope of the present invention. For example, the predetermined operation is not limited to the warning operation, and may be a series of operations in which data in use after the warning is saved from the volatile memory to the nonvolatile memory and the power is turned off. In this case, when a lithium ion secondary battery is used as the secondary battery 5, when the number of times of charging / discharging increases and the discharge characteristics of the lithium ion secondary battery change, the low battery determination voltage as described above. Is set, the driving time of the electronic device 2 can be extended.

  The discharging means 11 may be realized by a constant current circuit. When the electronic device 2 includes a display unit including a backlight, a discharge condition in which a current discharged from the secondary battery 5 is constant by turning on the backlight may be realized. In addition, a discharge condition in which the current discharged from the secondary battery 5 is constant may be realized by maintaining the predetermined mode, for example, when the electronic device 2 has the call mode, the call mode is maintained.

  The current discharged from the secondary battery 5 by the discharge means 11 may be equal to the current during actual use, or may be higher than the current during actual use. The current during actual use is, for example, a current required for a call when the electronic device 2 is a mobile phone. By making the current discharged from the secondary battery 5 by the discharging means 11 equal to the current in actual use, the low battery determination voltage can be set accurately. Further, by setting the current discharged from the secondary battery 5 by the discharging means 11 higher than the current during actual use, the time required for setting the low battery determination voltage can be shortened. The former is preferable when the time zone in which the electronic device 2 is used is determined, and the latter is preferable when it is not determined when the electronic device 2 is used.

  The predetermined discharge condition may be a discharge condition in which a current discharged from the secondary battery 5 is constant and a resistance for discharging the secondary battery 5 is constant. Even in this case, it is possible to achieve the same effect as the above-described embodiment.

  The second voltage is selected as close to the first voltage as possible within a range in which a predetermined difference occurs in the drop time when the number of times of charging / discharging differs by a predetermined number. As a result, the time required for measuring the drop time can be shortened, and the time required for setting the low battery determination voltage can be shortened.

  The predetermined remaining capacity for determining the low battery determination voltage may be constant regardless of the discharge characteristics of the secondary battery 5. As an example, the predetermined remaining capacity is selected to be about 10% of the capacity of the secondary battery 5 when the number of charge / discharge cycles is one.

  In setting the low battery determination voltage, information of a relational expression indicating the relationship between the reduction time and the low battery determination voltage may be used instead of the table information 13. Even in this case, it is possible to achieve the same effect as the above-described embodiment.

The system circuit 7 may count the number of times of charging / discharging, and may execute the setting operation of the low battery determination voltage when the number of times of charging / discharging reaches a predetermined number. As an example, the system circuit 7 may perform the setting operation of the low battery determination voltage once per 100 charge / discharge cycles.
The secondary battery 5 is not limited to the lithium ion secondary battery 5 but may be another secondary battery.

It is a block diagram which shows the structure of the electronic device 2 provided with the setting device 1 of the low battery determination voltage which is one Embodiment of this invention. It is a figure which shows the structure of the table information 13 memorize | stored in the memory | storage means 10. FIG. 5 is a flowchart for explaining a setting operation of a low battery determination voltage by the system circuit 7; It is a figure which shows an example of the discharge characteristic of a lithium ion secondary battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Low battery determination voltage setting device 2 Electronic device 3 AC power source 4 AC adapter 5 Secondary battery 6 Charging circuit 7 System circuit 8 Voltage measurement means 9 Time measurement means 10 Storage means 11 Discharge means 12 Setting means 13 Table information 14 Low Information on battery determination voltage 15 Information on second voltage 16 Information on drop time 17 Information on low battery determination voltage according to drop time 31 Control means

Claims (6)

An electronic device that is supplied with power from a secondary battery, compares the voltage of the secondary battery with a low battery determination voltage, and executes a predetermined operation when the secondary battery is low battery based on the comparison result A method for setting the low battery determination voltage in
The secondary battery is discharged from a fully charged state under a predetermined discharge condition, and a reduction time until the voltage of the secondary battery is reduced from a first voltage in a fully charged state to a predetermined second voltage by discharging is measured,
A low battery determination voltage setting method, wherein the low battery determination voltage is set based on the measured decrease time.   2. The low battery determination according to claim 1, wherein the predetermined discharge condition is a discharge condition in which a current discharged from the secondary battery is constant or a discharge condition in which a resistance for discharging the secondary battery is constant. Voltage setting method.   3. The table information in which the information on the drop time and the information on the low battery decision voltage according to the drop time are associated with each other when the low battery determination voltage is set. To set the low battery determination voltage. An electronic device that is supplied with power from a secondary battery, compares the voltage of the secondary battery with a low battery determination voltage, and executes a predetermined operation when the secondary battery is low battery based on the comparison result The low battery determination voltage setting device in
Discharging means for discharging the secondary battery under predetermined discharge conditions;
Voltage measuring means for measuring the voltage of the secondary battery;
When the secondary battery is discharged from the charging completion state by the discharging means under a predetermined discharging condition, the voltage of the secondary battery measured by the voltage measuring means is predetermined by the discharging from the first voltage in the charging completion state. Time measuring means for measuring the time until the voltage drops,
A low battery determination voltage setting device, comprising: setting means for setting the low battery determination voltage based on a decrease time measured by the time measurement means.   5. The low battery determination according to claim 4, wherein the predetermined discharge condition is a discharge condition in which a current discharged from the secondary battery is constant or a discharge condition in which a resistance for discharging the secondary battery is constant. Voltage setting device.   And further comprising storage means for storing table information in which the information on the reduction time and the information on the low battery determination voltage according to the reduction time are associated with each other for setting the low battery determination voltage by the setting means. 6. The low battery determination voltage setting device according to claim 4, wherein the low battery determination voltage is set.

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