A battery pack having a secondary battery; a measurement unit measuring a terminal voltage and a current of the secondary battery; a protection unit preventing the secondary battery from being overcharged when the terminal voltage measured by the measurement unit is equal to or higher than an overcharge detection voltage; and a control unit receiving the terminal voltage and current measured by the measurement unit, the control unit having a first mode and a second mode in which current is less consumed than the first mode. A voltage in a range of from a full charge voltage to less than the overcharge detection voltage is defined as a voltage threshold. The control unit changes from the first mode to the second mode when a state in which a transition requirement is satisfied lasts for a predetermined period of time.
1. A battery pack comprising:
a secondary battery;
a measurement unit for measuring a terminal voltage and a current of the secondary battery;
a protection unit for preventing the secondary battery from being overcharged when the terminal voltage measured by the measurement unit is equal to or higher than an overcharge detection voltage; and
a control unit to which the terminal voltage and current measured by the measurement unit are input, the control unit having a first operating mode and a second operating mode in which the consumed current is small, as compared to that in the first operating mode, wherein:
a voltage in a range of from a full charge voltage of the secondary battery to less than the overcharge detection voltage is defined as a voltage threshold,
the control unit changes from the first operating mode to the second operating mode when a state in which a transition requirement is satisfied lasts for a predetermined period of time, and
the transition requirement is that the current measured by the measurement unit be smaller than a current threshold and the terminal voltage measured be equal to or smaller than the voltage threshold.
2. The battery pack according to claim 1 , wherein:
the second operating mode is intermittently changed to the first operating mode so that the measurement unit measures the current, and
the second operating mode is changed to the first operating mode when a transition requirement that the current measured be equal to or higher than the current threshold is satisfied.
3. The battery pack according to claim 1 , wherein the control unit calculates the remaining capacity of the secondary battery in the first operating mode.
4. The battery pack according to claim 1 , wherein:
the control unit is a microcomputer, and
the second operating mode is achieved by stopping the operation of a clock oscillator in the microcomputer.
5. The battery pack according to claim 1 , wherein:
the control unit is a microcomputer,
the microcomputer is capable of communicating with an external device, and
the transition requirement for changing the first operating mode to the second operating mode includes a requirement that the microcomputer receive no command from the external device.
6. The battery pack according to claim 2 , wherein:
the control unit is a microcomputer,
the microcomputer is capable of communicating with an external device, and
the second operating mode is changed to the first operating mode when the microcomputer receives a command from the external device.
7. The battery pack according to claim 1 , further comprising a switching unit in a power source line on the positive side connecting a +terminal and a positive electrode of said secondary battery, wherein:
the switching unit includes a first field effect transistor and a second field effect transistor connected in series,
the first field effect transistor and the second field effect transistor have a first parasitic diode and a second parasitic diode, respectively, between the respective drain and source,
the first parasitic diode has a polarity in a direction opposite to a direction of a charging current flowing toward the battery from the +terminal and in the same direction as a direction of a discharging current, and
the second parasitic diode has a polarity in the same direction as the direction of the charging current and in the direction opposite to the direction of the discharging current.
8. The battery pack according to claim 7 , wherein:
the first field effect transistor is a charge control switching element,
the second field effect transistor is a discharge control switching element,
a charge control signal is fed to a gate of the first field effect transistor from the protection circuit, and
a discharge control signal is fed to a gate of the second field effect transistor from the protection circuit.
9. The battery pack according to claim 7 , wherein:
each of the first field effect transistor and the second field effect transistor is of a P-channel type, and is turned ON by a gate potential lower than a source potential by a predetermined value or more.
10. The battery pack according to claim 1 , wherein:
a measurement result of the terminal voltage and current measured by the measurement circuit and a measurement result detected by a temperature detector are fed to the protection unit, and
the first field effect transistor and the second field effect transistor are controlled to be turned ON/OFF depending the results of measurement, to control charging or discharging of the secondary battery.
11. The battery pack according to claim 1 , wherein:
the protection unit has a protection function to protect the secondary battery from overcharge, over-discharge, or over-current.