JP2008275524A - Battery pack and residual capacity computing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compute the residual capacity of a battery with higher accuracy by detecting current consumption in a stand-by state. <P>SOLUTION: In the normal state of an electronic device, a device operation detecting part 19 turns on a switch 18, and a normal current detecting part 14 measures voltage of a normal current detecting resistance 15. A control part 11 performs A/D conversion of the voltage of the normal current detecting resistance 15 to obtain digital voltage, and computes a normal current from this voltage and integrates the normal currents computed every predetermined time. In the stand-by state of the electronic device, the device operation detecting part 19 turns off the switch 18, and a micro current detecting part 16 measures voltage of a micro current detecting resistance 17. The control part 11 performs A/D conversion of the voltage of the micro current detecting resistance 17 to obtain digital voltage, and computes a micro current from this voltage and integrates micro currents computed every predetermined time. The control part 11 adds the integrated normal current and micro current to compute the residual capacity of the battery based on a ratio to the available current amount of the battery pack. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a battery pack for a secondary battery and a battery pack remaining capacity calculation method.

  In recent years, in portable electronic devices such as notebook PCs (Personal Computers) and PDAs (Personal Digital Assistants), secondary battery packs are widely used as power sources. In such electronic devices, functions have been diversified, and recently, for example, a plurality of different electronic devices such as a PC with a TV function in which a PC and a receiving device capable of receiving television broadcasting are integrated. It has device functions and can be used by switching devices according to the purpose.

  In an electronic apparatus having a plurality of different device functions, when the functions of the respective devices are used, current consumption may be different. Further, when using the same device, there is a large difference in current consumption between a normal state in which the device is activated and a standby state such as a low power consumption mode.

  Specifically, for example, in the above-described PC with a TV function, even when the PC is used or in a normal state where a television broadcast is viewed, and even when the PC and the TV are turned off, the user However, the amount of current consumption differs from the standby state in which the television is turned on by operating a remote control commander (hereinafter referred to as a remote controller as appropriate). For example, the current consumption in a normal state where the PC is activated is about 1 [A]. Further, the current consumption in a standby state in which the television is waiting for the user's operation of the remote control is about 5 [mA].

  Normally, when the power of the electronic device is OFF, almost no power is consumed. However, when the electronic device is in a standby state, a small amount of power is consumed due to the flow of a minute current. Therefore, when actually using an electronic device, it is possible that the battery remaining capacity of the battery pack has decreased.

  Therefore, for example, as described in Patent Document 1 below, it is detected whether or not an electronic device that uses a battery pack is in a standby state. Technology to suppress has been proposed.

JP 2001-118607 A

  By the way, in a portable electronic device such as a notebook PC, if the remaining battery capacity is insufficient and the power supply is suddenly shut down, there is a possibility that data in use may be damaged. It is very important to be able to recognize how much remaining battery capacity of the battery pack remains. Therefore, in the conventional battery pack, the remaining battery capacity is calculated in the battery pack, and the calculated remaining battery capacity can be displayed on the display unit or the like of the electronic device.

  As shown in FIG. 5, the conventional battery pack 100 includes a battery cell 110, a control unit 111, a switch circuit 112, a voltage detection unit 113, a current detection unit 114, a current detection resistor 115, and communication terminals 102a and 102b. The positive electrode terminal 103 and the negative electrode terminal 104 are connected to the positive electrode terminal and the negative electrode terminal of an electronic device or a charger, respectively, and charging / discharging is performed.

  For example, the voltage detection unit 113 detects the voltage of the battery cell 110 in which one or a plurality of secondary batteries are connected in series, and supplies the detection result to the control unit 111. The current detection unit 114 detects the magnitude and direction of the current using the current detection resistor 115 and supplies the detection result to the control unit 111.

  The switch circuit 112 includes a charge control FET (Field Effect Transistor) 121 and a discharge control FET 122. When the battery voltage becomes the overcharge detection voltage, the charge control FET 121 is turned off by the control signal from the control unit 111, and only discharge is possible through the parasitic diode 121a. Further, when the battery voltage becomes the overdischarge detection voltage, only the charge can be performed by turning off the discharge control FET 122 by the control signal from the control unit 111 and via the parasitic diode 122a.

  Based on the detection result from the voltage detection unit 113, the control unit 111 controls the switch circuit 112 when the voltage of the battery cell 110 becomes the overcharge detection voltage or when the voltage becomes lower than the overdischarge detection voltage. Prevent overcharge and overdischarge.

  In addition, the control unit 111 measures the voltage value and integrates the current value based on the detection results supplied from the voltage detection unit 113 and the current detection unit 114, and calculates the remaining battery capacity. Then, information on the remaining battery capacity is transmitted to the device via the communication terminals 102a and 102b, and the remaining capacity rate, remaining usable time, etc. are displayed on a display unit such as a liquid crystal provided on the electronic device side that has received this information. Is displayed.

  An example of a method for calculating the remaining battery capacity of the battery pack is a current integration method. In the current integration method, the current flowing through the current detection resistor 115 is measured and integrated every predetermined time, and the remaining battery capacity of the battery pack is calculated from the ratio between the discharge current amount of the battery pack and the integrated current amount.

  However, when the remaining battery capacity is calculated using the conventional current detection resistor 115, the current measurement accuracy by the current detection resistor 115 is low, and the minute current flowing in the standby state cannot be accurately detected. An error occurs in the amount of current that is generated. Therefore, the remaining battery capacity cannot be calculated accurately. Therefore, conventionally, for example, immediately after starting an electronic device, the remaining battery capacity is about 50% even though the remaining battery capacity is displayed as 100%. There was a difference between the calculation result and the actual remaining battery capacity.

  As described above, the conventional battery pack cannot accurately detect the current consumption of the battery pack in the standby state, and it is difficult to accurately calculate the remaining battery capacity.

  Accordingly, an object of the present invention is to provide a battery pack capable of detecting current consumption in a standby state and calculating the remaining battery capacity more accurately, and a battery pack remaining capacity calculating method.

  In order to solve the above-described problem, a first invention is a battery pack of a secondary battery, wherein the first current detection resistor provided in the current path and the first current detection resistor are connected in series. A second current detection resistor connected and having a resistance value larger than that of the first current detection resistor, a switch connected in parallel to the second current detection resistor, and an operating state received from an external device are shown. Based on the information, when the external device is in a normal state, the switch is turned on to bypass the second current detection resistor, and when the external device is in a standby state, the switch is turned off. , An operation detection unit that controls the switch, a first detection unit that detects a current flowing through the first current detection resistor when the switch is ON, and a second current detection when the switch is OFF Detect the current flowing through the resistor A second detection unit, a battery pack and having a computing unit that calculates a remaining capacity based on the detected current by the first detector and the second detector.

  Further, the second invention is based on the information indicating the operating state received from the external device, and the external device is in a normal state with respect to the first current detection resistor provided in the current path. A second current detection resistor connected in series and having a resistance value greater than that of the first current detection resistor is set to ON to bypass the second current detection resistor by turning on a switch connected in parallel to the second current detection resistor. When the external device is in a standby state, an operation detection step for controlling the switch so that the switch is turned OFF, and when the switch is ON, the current flowing through the first current detection resistor is detected. Detected by the first detection step, the second detection step for detecting the current flowing through the second current detection resistor when the switch is OFF, the first detection step, and the second detection step. A remaining capacity calculating method characterized by having a calculation step of calculating a remaining capacity based on current was.

  As described above, in the first and second inventions, when the external device is in the normal state based on the information indicating the operation state received from the external device, the first provided in the current path A second current detection resistor connected in series to the current detection resistor and having a resistance value larger than that of the first current detection resistor is set to ON by setting a switch connected in parallel to the second current detection resistor. Since the switch is controlled so that the current detection resistor is bypassed and the switch is turned off when the external device is in the standby state, the first current detection resistor is set in the normal state. The current flowing through the second current detection resistor can be detected when the flowing current is detected and in the standby state.

  In the present invention, the current flowing through the second current detection resistor having a resistance value larger than that of the first current detection resistor used in the normal state is detected in the standby state. The remaining battery capacity can be calculated.

  In the present invention, the first current detection resistor and the second current detection resistor are connected in series, and the switch is connected in parallel to the second current detection resistor. There is an effect that the current path is not interrupted when switching between.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the battery pack according to one embodiment of the present invention, the operation state of the connected electronic device is detected, and the current consumption is changed according to the operation state. The current is measured accurately. In the following, the state in which the electronic device is activated and various processes are performed is referred to as a normal state, and the state in which the process is not performed but a command to turn on the power from outside is awaited. This will be described as a state.

  As shown in FIG. 1, in the battery pack 1, when the electronic device is used, the positive electrode terminal 3 and the negative electrode terminal 4 are connected to the positive electrode terminal and the negative electrode terminal of the electronic device, respectively, and discharging is performed. In addition, the battery pack is attached to the charger during charging, and the positive electrode terminal 3 and the negative electrode terminal 4 are connected to the positive electrode terminal and the negative electrode terminal of the charger, respectively, as in the case of using the electric device, and charging is performed.

  The battery pack 1 mainly includes a battery cell 10, a control unit 11 as a calculation unit, a switch circuit 12, a voltage detection unit 13, a normal current detection unit 14 as a first detection unit, and a normal as a first current detection resistor. Current detection resistor 15, minute current detection unit 16 as second detection unit, minute current detection resistor 17 as second current detection resistor, switch 18, device operation detection unit 19, detection terminal 5, communication terminals 2a and 2b It consists of The battery cell 10 is, for example, a secondary battery of a lithium ion battery, and one or a plurality of secondary batteries are connected in series.

  The voltage detection unit 13 detects the voltage of the battery cell 10 and supplies the detection result to the control unit 11. The normal current detection unit 14 detects the magnitude and direction of the current using the normal current detection resistor 15 and supplies the detection result to the control unit 11. As the normal current detection resistor 15, for example, a resistor of about 5 [mΩ] is used in order to suppress power loss due to a voltage drop.

  The minute current detection unit 16 detects the magnitude and direction of the current using the minute current detection resistor 17 and sends the detection result to the control unit 11. The minute current detection resistor 17 is connected in series to the normal current detection resistor 15 and has a resistance value smaller than that of the normal current detection resistor 15. Specifically, for example, a resistance of about 20 [mΩ] or more is used.

  The switch 18 is provided in parallel to the minute current detection resistor 17 and turns on / off the switch based on control of a device operation detection unit 19 described later. When the switch 18 is turned on, the minute current detection resistor 17 is bypassed, current flows through the switch 18, and no current flows through the minute current detection resistor 17. The device operation detection unit 19 receives information indicating the operation state from the electronic device via the detection terminal 5, controls the switch 18 based on the received information indicating the operation state, and switches the current path. For example, the control is performed so that the switch 18 is turned on when the electronic device is in a normal state such as an activated state, and the switch 18 is turned off when the electronic device is in a standby state with low current consumption.

  The switch circuit 12 includes a charge control FET (Field Effect Transistor) 21 and a discharge control FET 22. When the battery voltage becomes the overcharge detection voltage, the charge control FET 21 is turned off by the control signal from the control unit 11 so that the charging current does not flow. Note that after the charge control FET 21 is turned off, only discharge is possible via the parasitic diode 21a. Further, when the battery voltage becomes the overdischarge detection voltage, the discharge control FET 22 is turned off by the control signal from the control unit 11 and the discharge current is controlled not to flow. Note that after the discharge control FET 22 is turned off, only charging is possible through the parasitic diode 22a.

  Based on the detection result from the voltage detection unit 13, the control unit 11 switches when the voltage of the battery cell 10 becomes an overcharge detection voltage or when the voltage of the battery cell 10 becomes equal to or lower than the overdischarge detection voltage. By sending a control signal to the circuit 12, overcharge and overdischarge are prevented. Further, the control unit 11 includes, for example, an A / D (Analog / Digital) converter therein, and the detection result supplied from the voltage detection unit 13, the normal current detection unit 14, and the minute current detection unit 16 is converted into a digital signal. Convert to Based on the detection result converted into a digital signal, the voltage value is measured and the current value is integrated to calculate the remaining battery capacity. A method for calculating the remaining battery capacity will be described later.

  The detection results detected by the voltage detection unit 13, the normal current detection unit 14, and the minute current detection unit 16 are stored in a nonvolatile memory such as an EEPROM (Electrically Erasable and Programmable Read Only Memory) (not shown). The non-volatile memory may be built in the control unit 11, for example, or may be provided outside.

  When the communication terminals 2a and 2b are attached to an electronic device, the communication terminals 2a and 2b transmit information on the remaining battery capacity to the device using a predetermined communication protocol. On the electronic device side receiving this information, the remaining capacity ratio, the remaining usable time, etc. are displayed on a display unit such as a liquid crystal display. For example, an SM bus (System Management Bus) can be used for communication with the electronic device.

  Next, a method for calculating the remaining battery capacity will be described. Examples of a method for calculating the remaining battery capacity of the battery pack include a voltage method based on the voltage of the battery cell 10 and an integration method based on an integrated value of the voltage and current of the battery cell 10. In the voltage method, the voltage of the battery cell 10 is measured, and the remaining battery capacity is calculated based on the correlation between the voltage of the secondary battery and the battery capacity (remaining capacity ratio). By doing so, for example, in the case of a lithium ion battery, it is possible to determine that the battery voltage is fully charged at 4.2 V / cell and to be overdischarged when it reaches 2.4 V / cell, and measurement is easy.

  The integration method can be further classified into a current integration method and a power integration method. In the current integration method, the amount of discharge current is calculated by measuring the current and integrating the current every predetermined time, and the remaining battery capacity of the battery pack is calculated from the ratio to the available current amount of the battery. The power integration method measures the voltage and current, calculates the amount of power by multiplying them, calculates the amount of discharge power by integrating the amount of power every fixed time, and the usable power of the battery The remaining battery capacity of the battery pack is calculated from the ratio with the amount. By doing so, stable remaining capacity detection can be performed without being affected by fluctuations in the voltage of the battery pack.

  In battery packs used in portable electronic devices such as notebook PCs, an accurate display of remaining battery capacity is required, and therefore, a remaining battery capacity calculation method using a current integration method is usually used. In the embodiment of the present invention, a method for calculating the remaining battery capacity will be described by taking the case of using the current integration method as an example.

  When calculating the remaining battery capacity using the current integration method, the current based on the voltage of the normal current detection resistor 15 in the normal state is calculated, and the current based on the voltage of the minute current detection resistor 17 in the standby state is calculated. . Then, the calculated currents are integrated, and the remaining battery capacity is calculated based on the ratio to the usable current amount of the battery pack. In the following description, the current flowing through the normal current detection resistor 15 in the normal state is referred to as a normal current, and the current flowing through the minute current detection resistor 17 in the standby state is referred to as a small current.

  When the electronic device is in a normal state, the device operation detection unit 19 turns on the switch 18 and bypasses the minute current detection resistor 17 so that a normal current does not flow. By doing so, it is possible to prevent the heat from being generated due to the power loss caused by the normal current flowing through the minute current detection resistor 17, and the occurrence of breakage or ignition. The normal current detection unit 14 measures the voltage of the normal current detection resistor 15. The control unit 11 performs A / D conversion on the voltage of the normal current detection resistor 15 using the built-in A / D converter, and converts the analog voltage into a digital voltage. Then, the normal current is calculated based on the digital voltage and the normal current detection resistor 15, and the calculated normal current is integrated every predetermined time.

  When the electronic device is in a standby state, the device operation detection unit 19 turns off the switch 18 so that a minute current flows through the minute current detection resistor 17. The minute current detection unit 16 measures the voltage of the minute current detection resistor 17. The control unit 11 performs A / D conversion on the voltage of the minute current detection resistor 17 using an A / D converter, and converts an analog voltage into a digital voltage. Then, a minute current is calculated based on the digital voltage and the minute current detection resistor 17, and the minute current calculated every predetermined time is integrated.

  The control unit 11 adds the normal current and the minute current accumulated in this way, and calculates the remaining battery capacity based on the ratio between the added current and the usable current amount of the battery pack.

  In the standby state, since the current flows not only through the minute current detection resistor 17 but also through the normal current detection resistor 15, a voltage drop due to the normal current detection resistor 15 also occurs. However, the voltage of the normal current detection resistor 15 is measured. If not, it is preferable. As described above, the control unit 11 needs to control the current detection operation in the normal current detection unit 14 and the minute current detection unit 16 in accordance with the operation state of the electronic device. Information indicating the operation state may be directly received or may be received via the device operation detection unit 19.

  By the way, when an analog voltage is converted into a digital voltage using an A / D converter as described above, and a current is calculated from the converted digital voltage, the current range per bit differs depending on the resistance value, This will affect the current measurement accuracy.

Here, as an example, consider a case where a current is calculated from an analog voltage using an A / D converter having a bit number of 15 [bit] and a reference voltage of 0.309 [V]. In this case, the voltage range per bit is the weight of one bit, the number of division by the number of bits from the range of 2 ^15, is calculated based on equation (1).
Voltage range per bit = reference voltage / number of divisions
= 0.309 [V] / 2 ¹⁵ = 9.43 [μV] (1)

As a result, the current range per bit is calculated based on Equation (2) according to Ohm's law, where R [Ω] is the current detection resistor.
Current range per bit = Voltage range per bit / Current detection resistor
= 9.43 [μV] / R [Ω] (2)

  Therefore, the current range per bit when the current detection resistance is 5 [mΩ] is 9.43 [μV] / 5 [mΩ] = as shown in FIG. 2 based on the above equation (2). It becomes 1.886 [mA]. On the other hand, the current range per bit when the current detection resistance is 20 [mΩ] is 9.43 [μV] / 20 [mΩ] = 0.472 [mA] as shown in FIG.

  Thus, since the voltage range per bit is determined by the reference voltage and the number of bits of the A / D converter, the current range per bit varies depending on the current detection resistor. The size of the current range per bit is a current measurement error. That is, by increasing the value of the current detection resistor, the measurement range of the entire current is narrowed and the maximum measurement current is reduced. However, the measurement error can be reduced by reducing the current range per bit. Therefore, when detecting a minute current in the standby state, the current can be measured with high accuracy by using a current detection resistor having a larger value than the current detection resistor used in the normal state.

  Next, information indicating an operation state will be described. The device operation detection unit 19 receives information indicating the operation state from the electronic device, and controls ON / OFF of the switch 18 based on this information to switch the current path, but indicates the operation state supplied from the electronic device. Examples of the information include information indicating current consumption of the electronic device. Specifically, for example, the electronic device outputs information indicating the current consumption, and the device operation detection unit 19 receives the information indicating the current consumption via the detection terminal 5. Then, assuming that the current consumption in the standby state is about 5 [mA], the device operation detection unit 19 uses the electronic device based on the information indicating the current consumption when the actual current consumption is, for example, 5 [mA] or less. Is determined to be in a standby state, and if the current consumption exceeds 5 [mA], it is determined that the electronic device is in a normal state.

  Further, as another information indicating the operation state, for example, information indicating the ON / OFF state of the power supply of an electronic device such as a PC or a television can be cited. For example, a signal that rises when the power of the electronic device is turned on is detected, and when this signal is “H (high)”, the device operation detection unit 19 determines that it is in a normal state. On the other hand, when the power of the electronic device is turned off, if the signal is “L (low)”, it is determined that the electronic device is in a standby state.

  Next, a method for switching the current path by the device operation detection unit 19 will be described. First, the flow of current path switching processing when the operation state of the electronic device is switched from the normal state to the standby state will be described with reference to the flowchart shown in FIG. Unless otherwise specified, the following processing is assumed to be performed under the control of the device operation detection unit 19.

  In step S11, when the operation state of the electronic device is in the standby state and the current consumption is low, the process proceeds to step S12. On the other hand, when the operation state of the electronic device is not the standby state, the process returns to step S11 until the operation state becomes the standby state.

  In step S12, the device operation detection unit 19 receives information indicating the operation state from the electronic device via the detection terminal 5, and the operation state of the electronic device is determined based on the received information. If it is determined that the operation state of the electronic device is the standby state, the process proceeds to step S13. On the other hand, when it is determined that the operation state of the electronic device is the normal state, the process returns to step S12, and the determination of the operation state of the electronic device is performed again.

  In step S13, based on the ON / OFF state of the switch 18, it is determined whether or not the current path is for normal current. If the switch 18 is ON, it is determined that the current path is for a normal current, and the process proceeds to step S14, where the switch 18 is turned OFF to switch to a current path for a minute current, and the minute current detection resistor 17 is turned on. A series of processing is completed so that a current flows through

  On the other hand, if the switch 18 is OFF in step S13, it is determined that the current path is for a minute current, and a series of processing ends.

  As described above, in a standby state in which a minute current flows through the current path, the current path is switched by turning off the switch 18 so that the current flows through the minute current detection resistor 17. By doing so, a minute current is measured by the minute current detection resistor 17, and the battery capacity can be accurately detected.

  Next, the flow of the current path switching process when the operation state of the electronic device is switched from the standby state to the normal state will be described with reference to the flowchart shown in FIG. In step S21, when the operation of the electronic device is in a normal state and the current consumption increases, the process proceeds to step S22. On the other hand, when the operation state of the electronic device is the standby state, the process returns to step S21 until the operation state becomes the normal state.

  In step S22, the operating state of the electronic device is determined based on the information indicating the operating state. If it is determined that the operation state of the electronic device is the normal state, the process proceeds to step S23. On the other hand, when it is determined that the operation state of the electronic device is the standby state, the process returns to step S22, and the determination of the operation state of the electronic device is performed again.

  In step S23, based on the ON / OFF state of the switch 18, it is determined whether or not the current path is for a minute current. If the switch 18 is OFF, it is determined that the current path is for a minute current, the process proceeds to step S24, the switch 18 is turned ON to switch to a current path for a normal current, and the minute current detection resistor 17 is turned on. Is bypassed so that no current flows, and a series of processing ends.

  On the other hand, if the switch 18 is ON in step S23, it is determined that the current path is for a normal current, and a series of processing ends.

  Thus, in the normal state where the normal current flows through the current path, the current path is switched by turning on the switch 18 and the minute current detection resistor 17 is bypassed so that no current flows. Then, the normal current is measured by the normal current detection resistor 15, and the battery capacity can be accurately detected.

  In one embodiment of the present invention, the current detection resistor is switched according to the operating state of the electronic device, and when in the standby state, the current flowing through the minute current detection resistor having a resistance value larger than that of the normal current detection resistor. Therefore, the remaining battery capacity can be calculated more accurately. Further, in the normal state, the minute current detection resistor is bypassed so that no current flows, so that the minute current detection resistor can be prevented from being damaged or ignited by heat generation.

  Furthermore, since the minute current detection resistor is connected in series with the normal current detection resistor, the current path is prevented from being interrupted when the current path is switched according to the operation state of the electronic device. Can do.

  The embodiment of the present invention has been described above. However, the present invention is not limited to the embodiment of the present invention described above, and various modifications and applications can be made without departing from the gist of the present invention. Is possible. For example, in the battery pack 1, the voltage between the electrode terminals (closed circuit voltage) when the current is flowing to the electronic device and connected to the electronic device is not connected to the electronic device, or It is known that the voltage between the electrode terminals (Open Circuit Voltage) when the current is not flowing, such as when the power of the electronic device is turned off but connected to the electronic device, is different. Therefore, for example, the device operation detection unit 19 controls the ON / OFF of the switch 18 by judging the operation state of the electronic device by comparing the closed circuit voltage and the open circuit voltage based on the voltage between the electrode terminals. May be.

It is a block diagram which shows the structure of an example of the battery pack by one Embodiment of this invention. It is a basic diagram for demonstrating the precision by A / D conversion. It is a flowchart which shows the flow of the switching process of an electric current path when the operation state of an electronic device switches from a normal state to a standby state. It is a flowchart which shows the flow of the switching process of an electric current path when the operation state of an electronic device switches from a standby state to a normal state. It is a block diagram which shows the structure of an example of the conventional battery pack.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery pack 2a, 2b Communication terminal 3 Positive terminal 4 Negative terminal 5 Detection terminal 10 Battery cell 11 Control part 12 Switch circuit 13 Voltage detection part 14 Normal current detection part 15 Normal current detection resistance 16 Minute current detection part 17 Minute current detection resistance 18 switch 19 device operation detector

Claims (6)

A secondary battery pack,
A first current detection resistor provided in the current path;
A second current detection resistor connected in series to the first current detection resistor and having a resistance value larger than that of the first current detection resistor;
A switch connected in parallel to the second current detection resistor;
When the external device is in a normal state based on the information indicating the operating state received from the external device, the second current detection resistor is bypassed by turning on the switch, and the external device is on standby. If it is in a state, an operation detection unit that controls the switch so as to turn off the switch;
A first detector that detects a current flowing through the first current detection resistor when the switch is ON;
A second detector for detecting a current flowing through the second current detection resistor when the switch is OFF;
A battery pack comprising: a calculation unit that calculates a remaining capacity based on the current detected by the first detection unit and the second detection unit. The battery pack according to claim 1,
The battery pack according to claim 2, wherein the second current detection resistor has a resistance value of 20 mΩ or more. The battery pack according to claim 1,
The battery pack according to claim 1, wherein the information indicating the operation state is information indicating a current consumption of the external device. The battery pack according to claim 3,
The information indicating the operation state indicates that the battery pack is in a standby state when the current consumption is 5 mA or less. The battery pack according to claim 1,
The battery pack characterized in that the information indicating the operation state is information indicating ON / OFF of the power supply of the external device. Based on the information indicating the operating state received from the external device, when the external device is in a normal state, the external device is connected in series with the first current detection resistor provided in the current path, and A second current detection resistor having a resistance value larger than that of the first current detection resistor, a switch connected in parallel to the second current detection resistor is turned on to bypass the second current detection resistor, and the external device Is in a standby state, an operation detecting step for controlling the switch so as to turn off the switch;
A first detection step of detecting a current flowing through the first current detection resistor when the switch is ON;
A second detection step of detecting a current flowing through the second current detection resistor when the switch is OFF;
A remaining capacity calculation method comprising: a calculation step of calculating a remaining capacity based on the current detected by the first detection step and the second detection step.

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