JP2008259386A - Battery protection circuit and battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery protection circuit, along with a battery pack with the circuit, capable of reducing a difference between the voltage at which a secondary battery is protected by a protection circuit at the first stage and that at which a secondary battery is protected by the protection circuit at the second stage. <P>SOLUTION: A comparator M1 and an A/D converter 231 that detect a common input voltage is provided. The comparator M1 detects an overvoltage if the input voltage exceeds a reference voltage Ref1. A first reference voltage acquiring part 211 acquires a voltage detected by the A/D converter 231 as a first reference voltage Vref1 when the overvoltage is detected by the comparator M1. A second reference voltage setting part 212 sets a second reference voltage Vth1 by subtracting a differential voltage Vd from the first reference voltage Vref1. The protection of the first stage is made at the second reference voltage Vth1, and that of the second stage is made at the first reference voltage Vref1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a battery protection circuit that protects a secondary battery from overcharging, and a battery pack including the same.

  Conventionally, in a charging circuit of a secondary battery such as a lithium ion secondary battery or a nickel hydride secondary battery, the terminal voltage of the secondary battery is monitored, and when the terminal voltage of the secondary battery exceeds a certain determination voltage, A battery protection circuit is provided for protecting the secondary battery from overcharging by turning off the switching elements provided in series on the charging path of the secondary battery. In addition, the determination voltage is set in two stages in advance, and the first-stage protection circuit that turns off the switching element when the terminal voltage of the secondary battery exceeds the first-stage first determination voltage, and the first-stage protection When a fault occurs in the circuit and the switching element does not turn off, and the terminal voltage of the secondary battery exceeds the second determination voltage of the second stage, the fuse is blown to interrupt the charging path. A battery protection circuit that improves the safety of a secondary battery by including a second-stage protection circuit that protects the battery is known (see, for example, Patent Documents 1, 2, and 3). .

In this case, the first-stage protection circuit and the second-stage protection circuit each include a voltage detection circuit that detects the terminal voltage of the secondary battery, so that the voltage detection circuit in the first-stage protection circuit fails. Even so, the second-stage protection circuit can operate.
JP-A-9-233713 JP 2000-323175 A JP-A-10-51962

  However, as described above, when the first-stage protection circuit and the second-stage protection circuit each include a voltage detection circuit, considering the accuracy and characteristic variation of the voltage detection circuit included in each protection circuit, In order to prevent the second-stage protection circuit from operating before the first-stage protection circuit, the first determination voltage at which the first-stage protection circuit operates and the second-stage protection circuit operate. It is necessary to set a voltage difference larger than the accuracy and characteristic variation of the voltage detection circuit between the second determination voltage and the second determination voltage. In addition, even if the terminal voltage of the secondary battery exceeds the first determination voltage, if the switching element is not turned off by the first-stage protection circuit due to a failure or the like, the fuse is quickly Therefore, it is preferable that the difference between the first determination voltage and the second determination voltage is smaller. In particular, lithium ion secondary batteries that have been widely used in recent years have a feature that a difference between a terminal voltage in a normal use state and a voltage that causes a safety risk is small. The first determination voltage and the second determination voltage It is desirable to reduce the difference between the first protection circuit and the second protection circuit as soon as possible when the first protection circuit does not operate.

  However, as described above, since it is necessary to provide a voltage difference larger than the accuracy and characteristic variation of the voltage detection circuit between the first determination voltage and the second determination voltage, the difference between the first determination voltage and the second determination voltage. There was an inconvenience that it was difficult to reduce the difference.

  The present invention is an invention made in view of such circumstances, and includes a voltage at which the secondary battery is protected by the first-stage protection circuit and a voltage at which the secondary battery is protected by the second-stage protection circuit. It is an object of the present invention to provide a battery protection circuit capable of reducing the difference, and a battery pack including the same.

  The battery protection circuit according to the present invention includes a battery voltage acquisition unit that acquires a terminal voltage of a secondary battery, a pair of first and second voltage detection units that detect a common input voltage, and the first voltage detection unit. The detected voltage is compared with a preset first reference voltage, and when the detected voltage exceeds the first reference voltage, an overvoltage detector that detects an overvoltage and the overvoltage detector Is detected, the first reference voltage acquisition unit that acquires the voltage detected by the second voltage detection unit as the first reference voltage, and the first reference voltage acquired by the first reference voltage acquisition unit A second reference voltage setting unit that sets a second reference voltage that differs by a preset differential voltage, and the voltage acquired by the battery voltage acquisition unit to the pair of first and second voltage detection units As input voltage A mode switching unit for switching to a normal mode for supplying, a first protection control unit for prohibiting charging of the secondary battery when an overvoltage is detected by the overvoltage detection unit during the normal mode, and during the normal mode. A second protection control unit for prohibiting charging of the secondary battery when a voltage detected by the second voltage detection unit exceeds a second reference voltage set by the second reference voltage setting unit; Prepare.

  According to this configuration, the input voltage to the pair of first and second voltage detection units increases, the detection voltage detected by the first voltage detection unit increases, and the detection voltage exceeds the first reference voltage. Thus, an overvoltage is detected by the overvoltage detection unit. Further, when the first reference voltage acquisition unit detects an overvoltage by the overvoltage detection unit, the voltage detected by the second voltage detection unit is acquired as the first reference voltage. Then, the voltage at which the overvoltage is actually detected by the first voltage detection unit and the overvoltage detection unit is acquired by the first reference voltage acquisition unit. In addition, the second reference voltage setting unit sets a second reference voltage that differs from the first reference voltage acquired by the first reference voltage acquisition unit by a preset differential voltage. Then, the mode switching unit supplies the voltage acquired by the battery voltage acquisition unit as an input voltage to the pair of first and second voltage detection units, that is, the terminal voltage of the secondary battery is supplied to the first and second voltage detection units. Is switched to the detectable normal mode. Further, when an overvoltage is detected by the overvoltage detection unit during the normal mode, charging of the secondary battery is prohibited by the first protection control unit, and the voltage detected by the second voltage detection unit during the normal mode is the second voltage. When the second reference voltage set by the reference voltage setting unit is exceeded, charging of the secondary battery is prohibited by the second protection control unit.

  In this case, the first reference voltage that is actually prohibited from charging the secondary battery by the first protection control unit is acquired by the first reference voltage acquisition unit, and the first reference voltage acquired by the first reference voltage acquisition unit. Since the secondary protection control unit prohibits charging of the secondary battery at the second reference voltage set to a voltage different from the voltage by a preset differential voltage, the first reference voltage is not affected regardless of the accuracy and variation of the circuit. As a result of being able to reliably provide a preset differential voltage between the voltage at which the secondary battery is protected by the protection control unit and the voltage at which the secondary battery is protected by the second protection control unit, It is no longer necessary to set a differential voltage larger than the range of variation, and the differential voltage is the difference between the voltage at which the battery is protected by the first-stage protection circuit and the voltage at which the battery is protected by the second-stage protection circuit. It can be reduced.

  In addition, an inspection voltage generation unit that generates a predetermined inspection voltage, a voltage acquired by the battery voltage acquisition unit, and a voltage generated by the inspection voltage generation unit are used as the input voltage as the pair of pairs. A voltage switching unit that supplies the first and second voltage detection units; and the first reference voltage acquisition unit is configured to supply the inspection voltage generated by the inspection voltage generation unit by the voltage switching unit. When the overvoltage is detected by the overvoltage detection unit by gradually increasing the inspection voltage by the inspection voltage generation unit while supplying the first and second voltage detection units, and when the overvoltage is detected The voltage detected by the second voltage detection unit is acquired as the first reference voltage, and the mode switching unit is connected to the battery voltage acquisition unit by the voltage switching unit. By supplying the obtained voltage to the first and second voltage detecting unit, it is preferable to perform the switching to the normal mode.

  According to this configuration, the voltage switching unit supplies the inspection voltage generated by the inspection voltage generation unit to the pair of first and second voltage detection units, and the inspection voltage generation unit gradually increases the inspection voltage. Since it is increased, the input voltage of the pair of first and second voltage detectors can be gradually increased. The mode switching unit can switch to the normal mode by causing the voltage switching unit to supply the voltage acquired by the battery voltage acquisition unit to the first and second voltage detection units.

  The battery voltage acquisition unit acquires voltages at both ends of a plurality of secondary batteries connected in series, and the pair of first and second voltage detection units correspond to the plurality of secondary batteries. A plurality of pairs are provided, and the overvoltage detection unit detects an overvoltage by comparing the detection voltages detected by the plurality of first voltage detection units with the first reference voltage, respectively, and the first reference voltage acquisition unit Is a voltage detected by each of the second voltage detectors when the overvoltage is detected by the overvoltage detector according to an increase in each input voltage of the plurality of pairs of first and second voltage detectors. The second reference voltage setting unit obtains a first reference voltage corresponding to each second voltage detection unit, and the second reference voltage setting unit varies the first reference voltage corresponding to each second voltage detection unit by the difference voltage. A plurality of second voltage detectors corresponding to the second voltage detectors; The second protection control unit sets a voltage detected by each of the second voltage detection units corresponding to each of the second voltage detection units during the normal mode. When the voltage exceeds 2 reference voltages, it is preferable to prohibit charging of the secondary battery.

  According to this configuration, the both-end voltages of the plurality of secondary batteries connected in series are acquired by the battery voltage acquisition unit, and the pair of first and second voltage detection units is provided for each of the number of secondary batteries. Correspondingly, multiple pairs are provided. In addition, the overvoltage detection unit detects the overvoltage by comparing the detection voltages detected by the plurality of first voltage detection units with the first reference voltage. Then, when an overvoltage is detected by the overvoltage detection unit according to an increase in each input voltage of the plurality of pairs of the first and second voltage detection units by the first reference voltage acquisition unit, it is detected by each second voltage detection unit. Is acquired as the first reference voltage corresponding to each of the second voltage detectors, the voltage at which the overvoltage is actually detected by each of the first voltage detectors and the overvoltage detector is the first reference voltage. Acquired by the acquisition unit. In addition, a plurality of second reference voltages that differ from the first reference voltage corresponding to each second voltage detection unit by a differential voltage are set by the second reference voltage setting unit corresponding to each second voltage detection unit. Is done. Then, when the voltage detected by each second voltage detector during the normal mode by the second protection controller exceeds the second reference voltage set corresponding to each second voltage detector, Secondary battery charging is prohibited.

  In this case, the voltage at which the secondary battery is actually protected by the first protection control unit is acquired as the first reference voltage in each first voltage detection unit, and the first reference voltage in each first voltage detection unit and Since charging of the secondary battery is prohibited by the second protection control unit at the second reference voltage that is set to a voltage that differs by a preset differential voltage, a plurality of pairs of the first and second voltage detection units Regardless of the accuracy and variation of the circuit, a preset differential voltage between the voltage at which the secondary battery is protected by the first protection controller and the voltage at which the secondary battery is protected by the second protection controller is ensured. As a result, it is not necessary to set a differential voltage larger than the range of accuracy and variation of the circuit, and the voltage that protects the battery by the first-stage protection circuit and the second-stage protection circuit It is possible to reduce the difference voltage which is the difference between voltages pond is protected.

  The battery voltage acquisition unit acquires voltages at both ends of a plurality of secondary batteries connected in series, and the pair of first and second voltage detection units correspond to the plurality of secondary batteries. A plurality of pairs are provided, and the overvoltage detection unit detects an overvoltage by comparing the detection voltages detected by the plurality of first voltage detection units with the first reference voltage, respectively, and the first reference voltage acquisition unit The plurality of pairs of the first and second voltage detection units are sequentially selected by the voltage switching unit, and the test generated by the test voltage generation unit to the selected pair of the first and second voltage detection units. The overvoltage is detected by the overvoltage detection unit by supplying the operation voltage and gradually increasing the inspection voltage by the inspection voltage generation unit. When the overvoltage is detected, each second voltage detection unit By The detected voltage is acquired as a first reference voltage corresponding to each second voltage detection unit, and the second reference voltage setting unit determines the first reference voltage corresponding to each second voltage detection unit as the difference. Different voltages are set as a plurality of second reference voltages corresponding to the second voltage detection units, and the second protection control unit is detected by the second voltage detection units during the normal mode. When the voltage exceeds a second reference voltage set corresponding to each of the second voltage detectors, it is preferable to prohibit charging of the secondary battery.

  According to this configuration, a plurality of pairs of first and second voltage detection units are sequentially selected by the voltage switching unit, and generated by the inspection voltage generation unit to the selected pair of the first and second voltage detection units. Since the inspection voltage is supplied and the inspection voltage is gradually increased by the inspection voltage generation unit, the overvoltage detection unit detects the overvoltage, so that the voltage actually detected by each first voltage detection unit is Based on this, the first reference voltage at which an overvoltage is detected by the overvoltage detection unit is detected by the second voltage detection unit paired with each first voltage detection unit. The second reference voltage setting unit sets a plurality of second reference voltages that differ from each first reference voltage by a difference voltage in correspondence with each second voltage detection unit. The input voltage of each of the first and second voltage detectors can be increased by the test voltage generator and the voltage switching unit without increasing the input voltage of the second voltage detector, and the first protection controller Thus, the voltage at which the secondary battery is actually protected can be acquired as the first reference voltage in each first voltage detector.

  In addition, the battery voltage acquisition unit is configured to change the voltage at the connection point between the positive electrode and the negative electrode between the plurality of secondary batteries connected in series to the secondary battery on the high potential side of the connection point. A plurality of voltages supplied as a negative side voltage to the second voltage detection unit pair and supplied as a positive side voltage to the pair of the first and second voltage detection units corresponding to the secondary battery on the low potential side at the connection point Including a supply path, wherein the voltage switching unit includes a selector switch capable of selecting the plurality of voltage supply paths every other one, and the first reference voltage acquisition unit includes a voltage supply path selectable by the selector switch. When acquiring the first reference voltage of the second voltage detection unit to which the voltage is supplied as the negative side voltage, the first switch paired with the second voltage detection unit and the second voltage detection unit by the changeover switch. Supply the negative voltage to the voltage detector The voltage supply path to be selected and the voltage of the selected voltage supply path is gradually reduced by the inspection voltage generation unit, thereby supplying the supply voltage to the first and second voltage detection units of the selected pair. When acquiring the first reference voltage of the second voltage detector that is gradually increased and the voltage of the voltage supply path that can be selected by the selector switch is supplied as the positive voltage, the second switch is used to obtain the second reference voltage. A voltage supply path that supplies the positive voltage to the first voltage detection section that is paired with the voltage detection section and the second voltage detection section is selected, and the voltage of the selected voltage supply path is selected by the inspection voltage generation section. It is preferable to gradually increase the supply voltage to the first and second voltage detectors of the selected pair by gradually increasing.

  According to this configuration, the voltage at the connection point between the positive electrode and the negative electrode between the plurality of secondary batteries connected in series by the voltage supply path corresponds to the first and second secondary batteries on the high potential side of the connection point. The negative voltage is supplied to the pair of second voltage detectors as the positive voltage to the pair of first and second voltage detectors corresponding to the secondary battery on the low potential side at the connection point. In addition, there is provided a selector switch capable of selecting every other plurality of voltage supply paths. And when the 1st reference voltage of the 2nd voltage detection part with which the voltage of the voltage supply path which can be chosen with a changeover switch by the 1st reference voltage acquisition part is supplied as a negative side voltage is acquired by the changeover switch, A voltage supply path for supplying a negative voltage to the second voltage detection section and the first voltage detection section paired with the second voltage detection section is selected, and the voltage of the selected voltage supply path is selected by the inspection voltage generation section. By gradually decreasing, the supply voltage to the first and second voltage detectors of the selected pair is gradually increased. In addition, when the first reference voltage of the second voltage detector that is supplied as the positive voltage is the voltage of the voltage supply path that can be selected by the changeover switch by the first reference voltage acquisition unit, the changeover switch A voltage supply path for supplying a positive voltage to the second voltage detection section and the first voltage detection section paired with the second voltage detection section is selected, and the voltage of the selected voltage supply path is selected by the inspection voltage generation section. By gradually increasing, the supply voltage to the first and second voltage detectors of the selected pair is gradually increased.

  In this case, the first and the second corresponding to each secondary battery using a changeover switch capable of selecting every other plurality of voltage supply paths connected to connection points between the plurality of secondary batteries connected in series. Since the supply voltage to each of the two voltage detection units can be increased, it is easy to simplify the circuit by reducing the number of changeover terminals of the changeover switch to be less than the number of secondary batteries.

  In addition, when the charging voltage is supplied by a charging circuit that supplies a charging voltage for charging the secondary battery according to an instruction from the outside, the second voltage detection unit detects the charging voltage during the normal mode. When the terminal voltage of the recharged secondary battery exceeds an upper limit voltage set in advance as an upper limit of the charge voltage, a charge voltage adjustment unit that outputs an instruction to the charge circuit to reduce the charge voltage is further provided It is preferable.

  According to this configuration, when the terminal voltage of the secondary battery detected by the second voltage detection unit during the normal mode exceeds the upper limit voltage preset as the upper limit of the charging voltage, the charging voltage adjustment unit causes the charging circuit to An instruction to reduce the charging voltage is output, and the charging voltage can be reduced to the charging circuit. For example, when a charging voltage exceeding the upper limit voltage is output from the charging circuit due to accuracy or variation of the charging circuit. Even if it exists, as a result of being able to make a charging voltage fall and not exceeding an upper limit voltage, a possibility that a secondary battery may deteriorate by an overvoltage is reduced.

  Further, when the charging voltage is supplied by a charging circuit that supplies a charging voltage for charging the plurality of secondary batteries according to an instruction from the outside, the second voltage detection unit during the normal mode Charge that outputs an instruction to lower the charging voltage to the charging circuit when the maximum voltage among the plurality of both-end voltages detected by the battery exceeds an upper limit voltage set in advance as an upper limit of the charging voltage. It is preferable to further include a voltage adjustment unit.

  According to this configuration, when the maximum voltage among the voltages across the plurality of secondary batteries connected in series exceeds the upper limit voltage set in advance as the upper limit of the charging voltage, the charging voltage adjustment unit causes the charging circuit to An instruction to reduce the charging voltage is output, and the charging voltage can be reduced by the charging circuit. For example, the characteristics of a plurality of secondary batteries connected in series are unbalanced and deteriorated compared to other batteries. Even if the voltage at both ends of a rechargeable secondary battery exceeds the upper limit voltage, the charging voltage can be lowered so that the upper limit voltage is not exceeded. The risk of further accelerating degradation is reduced.

  And a switching element provided in series with the charging path of the secondary battery, a thermal fuse provided in series with the charging path of the secondary battery, and a heater for blowing the thermal fuse, The first protection control unit prohibits charging of the secondary battery by blowing the thermal fuse by the heater, and the second protection control unit charges the secondary battery by turning off the switching element. It is preferable that the second reference voltage setting unit sets the second reference voltage by subtracting the differential voltage from the first reference voltage acquired by the first reference voltage acquisition unit.

  According to this configuration, the second reference voltage setting unit sets the second reference voltage by subtracting the differential voltage from the first reference voltage acquired by the first reference voltage acquisition unit. As a result of the second reference voltage being lower than the voltage, the second protection control unit functions as a first-stage protection circuit, and the first protection control unit functions as a second-stage protection circuit. The second protection control unit, which is the first-stage protection circuit, prohibits charging of the secondary battery by turning off the switching element. Therefore, if the terminal voltage of the secondary battery decreases, the second protection control unit turns on the switching element. It is possible to resume the charging of the secondary battery. In addition, when charging is prohibited by the first protection control unit, which is the second-stage protection circuit, it is considered that some abnormality has occurred that the first-stage protection circuit does not work. By doing so, charging of the secondary battery is permanently prohibited and safety is improved.

  A battery pack according to the present invention includes the above-described battery protection circuit and the secondary battery. According to this configuration, in the battery pack, a battery that can reduce a differential voltage that is a difference between a voltage at which the battery is protected by the first protection circuit and a voltage at which the battery is protected by the second protection circuit. Since the secondary battery is protected by the protection circuit, if the charging of the secondary battery is not prohibited by the first-stage protection circuit by reducing the differential voltage, the secondary-stage protection circuit promptly recharges the secondary battery. As a result of prohibiting charging of the battery, it is easy to improve safety.

  In the battery protection circuit and the battery pack having such a configuration, the first reference voltage acquisition unit acquires the first reference voltage that is actually prohibited from charging the secondary battery by the first protection control unit. In the second reference voltage set to a voltage different from the first reference voltage acquired by the voltage acquisition unit by a preset differential voltage, charging of the secondary battery is prohibited by the second protection control unit. Regardless of the accuracy and dispersion of the voltage, a differential voltage set in advance between the voltage at which the secondary battery is protected by the first protection control unit and the voltage at which the secondary battery is protected by the second protection control unit is ensured. As a result, it is not necessary to set a differential voltage larger than the range of accuracy and variation of the circuit, the voltage that protects the battery by the first-stage protection circuit and the battery by the second-stage protection circuit It is possible to reduce the difference voltage is the difference between the voltage to be protected.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a block diagram illustrating an example of a configuration of a battery pack including a battery protection circuit according to the first embodiment of the present invention. The battery pack 1 shown in FIG. 1 includes control ICs (Integrated Circuits) 2 and 3, external connection terminals 11, 12, 13, and 14, secondary batteries B1, B2, B3, and B4, switching elements Q1, Q2, and Q3, resistors R1, R2, thermal fuse F1, F2, and heater Rh are comprised.

  The secondary batteries B1, B2, B3, B4 are not particularly limited, but are, for example, lithium ion secondary batteries. Secondary batteries B1, B2, B3, and B4 are connected in series to form an assembled battery B. Note that the secondary batteries B1, B2, B3, and B4 may each have a plurality of secondary batteries connected in parallel. The switching elements Q1, Q2, and Q3 are switching elements such as FET (Field Effect Transistor), for example.

  The external connection terminals 11, 12, 13, and 14 are connected to a charging device for charging the assembled battery B, or are connected to a mobile phone, a digital camera, a portable personal computer, or the like driven by a discharge current from the assembled battery B It is a connection terminal for connecting a battery drive apparatus. The external connection terminal 11 is connected to the positive electrode of the assembled battery B via the temperature fuses F1, F2 and the switching elements Q1, Q2, and the external connection terminal 12 is connected to the negative electrode of the assembled battery B, that is, the circuit ground. The external connection terminals 13 and 14 are communication terminals for performing data transmission / reception with a charging device or a battery driving device connected to the battery pack 1.

  The switching element Q1 is in a direction in which the anode of the parasitic diode is on the assembled battery B side, and the switching element Q2 is in the direction in which the anode of the parasitic diode is on the external connection terminal 11 side. The switching element Q1 is used as an overcharge protection switch that cuts off the charging current when the battery pack B is overcharged, and the switching element Q2 is used when the discharge current of the battery pack B becomes excessive. It is used as an overdischarge protection switch that cuts off the discharge current.

  Further, the connection point between the thermal fuse F1 and the thermal fuse F2 is connected to the negative electrode of the battery pack B via the heater Rh and the switching element Q3. The gate of the switching element Q3 is connected to the control IC 3 via the resistor R3. When the switching element Q3 is turned on according to the control signal S1 from the control IC 3, the heater Rh generates heat and the thermal fuses F1 and F2 are blown.

  The control IC 2 turns off the switching elements Q1 and Q2 to protect the secondary batteries B1, B2, B3 and B4 when the terminal voltage of the secondary batteries B1, B2, B3 and B4 is overvoltage. It is a protection circuit. The control IC 2 includes, for example, a control unit 21, A / D (analog / digital) converters 231, 232, 233, 234 (second voltage detection unit), and D / A (digital / analog) converter 22 (inspection voltage generation unit). The switch SW1 and the EEPROM (Electrically Erasable and Programmable Read Only Memory) 25 are provided.

  In addition, the control IC 3 does not perform the first-stage protection operation due to a failure of the control IC 2, the switching elements Q1, Q2, etc., and the second-stage protection voltage is set to a voltage higher than the first-stage protection voltage. When each terminal voltage of the secondary batteries B1, B2, B3, B4 rises, a control signal S1 for turning on the switching element Q3 is output, the heater Rh is heated and the thermal fuses F1, F2 are blown. This is a second-stage protection circuit that protects the secondary batteries B1, B2, B3, and B4. The control IC 3 includes a logic circuit 31 (first protection control unit), comparators M1, M2, M3, M4 (first voltage detection unit, overvoltage detection unit) and reference voltage sources E1, E2, E3, E4. The reference voltage sources E1, E2, E3, and E4 generate first reference voltages Ref1, Ref2, Ref3, and Ref4, which are second-stage protection voltages. The first reference voltages Ref1, Ref2, Ref3, and Ref4 are set to 4.25 V, for example, and correspond to an example of a preset first reference voltage.

  The A / D converter 231 and the comparator M1 are paired to detect the voltage across the secondary battery B1, and the A / D converter 232 and the comparator M2 detect the voltage across the secondary battery B2. The A / D converter 233 and the comparator M3 are paired to detect the voltage across the secondary battery B3, and the A / D converter 234 and the comparator M4 are secondary. A pair is formed to detect the voltage across the battery B4.

  The positive electrode of the secondary battery B1 is connected in parallel to the positive input terminal of the A / D converter 231 and the positive input terminal of the comparator M1, and the negative electrode of the secondary battery B1 and the positive electrode of the secondary battery B2 are connected. The point P1 is connected to a connection point P11 between the negative input terminal of the A / D converter 231, the positive input terminal of the A / D converter 232, and the positive input terminal of the comparator M2 via the resistor R1. Further, the connection point P11 is connected to the negative electrode of the reference voltage source E1, and the positive electrode of the reference voltage source E1 is connected to the negative electrode side input terminal of the comparator M1.

  Further, the connection point P2 between the negative electrode of the secondary battery B2 and the positive electrode of the secondary battery B3 is the negative input terminal of the A / D converter 232, the positive input terminal of the A / D converter 233, and the positive input of the comparator M3. Further, the connection point P2 is connected to the negative electrode of the reference voltage source E2, and the positive electrode of the reference voltage source E2 is connected to the negative input terminal of the comparator M2.

  The connection point P3 between the negative electrode of the secondary battery B3 and the positive electrode of the secondary battery B4 is connected to the negative input terminal of the A / D converter 233, the positive input terminal of the A / D converter 234, and the comparator via the resistor R2. It is connected to a connection point P31 with the positive input terminal of M4. Further, the connection point P31 is connected to the negative electrode of the reference voltage source E3, and the positive electrode of the reference voltage source E3 is connected to the negative electrode side input terminal of the comparator M3.

  The negative electrode of the secondary battery B4 is connected to the negative input terminal of the A / D converter 234 and the negative electrode of the reference voltage source E4, and the positive electrode of the reference voltage source E4 is connected to the negative input terminal of the comparator M4. Yes. In this case, connection terminals and wirings for connecting the secondary batteries B1, B2, B3, B4, the A / D converters 231, 232, 233, 234 and the comparators M1, M2, M3, M4, and resistors R1, R2 are provided. This corresponds to an example of a voltage supply path.

  By connecting in this way, the voltage V1 between the connection point P11 and the positive electrode of the secondary battery B1 is converted into a digital value by the A / D converter 231 and output to the control unit 21 and also by the comparator M1. When compared with the first reference voltage Ref1 and the voltage V1 exceeds the first reference voltage Ref1, a high level signal indicating the detection of the overvoltage is output from the comparator M1 to the logic circuit 31.

  Further, the voltage V2 between the negative electrode of the secondary battery B2 and the connection point P11 is converted into a digital value by the A / D converter 232 and output to the control unit 21 and compared with the first reference voltage Ref2 by the comparator M2. When the voltage V2 exceeds the first reference voltage Ref2, a high level signal indicating the detection of the overvoltage is output from the comparator M2 to the logic circuit 31.

  Further, the voltage V3 between the connection point P31 and the positive electrode of the secondary battery B3 is converted into a digital value by the A / D converter 233 and output to the control unit 21, and compared with the first reference voltage Ref3 by the comparator M3. When the voltage V3 exceeds the first reference voltage Ref3, a high level signal indicating the detection of the overvoltage is output from the comparator M3 to the logic circuit 31.

  Then, the voltage V4 between the negative electrode of the secondary battery B4 and the connection point P31 is converted into a digital value by the A / D converter 234 and output to the control unit 21 and compared with the first reference voltage Ref4 by the comparator M4. When the voltage V4 exceeds the first reference voltage Ref4, a high level signal indicating the detection of the overvoltage is output from the comparator M4 to the logic circuit 31.

  In addition, although the example using the same number of A / D converters 231, 232, 233, and 234 as the secondary battery has been shown, for example, one A / D converter is used and the input signal of the A / D converter is switched by a switch. The voltage V1, V2, V3, V4 may be detected by switching.

  When the output signal level of any one of the comparators M1, M2, M3, and M4 becomes a high level, the logic circuit 31 outputs a control signal S1 for turning on the switching element Q3 to the switching element Q3 and the control unit 21.

  The D / A converter 22 outputs a voltage corresponding to the voltage instruction signal from the control unit 21 to the changeover switch SW1. The changeover switch SW1 switches the output destination of the D / A converter 22 to any one of the terminals CN1 and CN2 and the terminal OFF in accordance with a control signal from the control unit 21. The terminal CN1 is connected to the connection point P11, the terminal CN2 is connected to the connection point P31, and the terminal OFF is in an open state. That is, the changeover switch SW1 can select every other connection point P11, P21, P31 on the voltage supply path that connects the connection points P1, P2, P3 to the A / D converters 231, 232, 233, 234. Yes.

  Then, when the changeover switch SW1 is switched to the terminal OFF, the voltages V1, V2, V3, V4 are equal to the voltages at both ends of the secondary batteries B1, B2, B3, B4, respectively. On the other hand, when the changeover switch SW1 is switched to the terminal CN1, the voltage V1 is equal to the difference between the output voltage of the D / A converter 22 and the positive voltage of the secondary battery B1, and the voltage V2 is the secondary battery B2. Is equal to the difference between the negative electrode voltage and the output voltage of the D / A converter 22. In this case, the selector switch SW1 and the resistors R1 and R2 correspond to an example of a voltage switching unit.

  Therefore, the control unit 21 switches the changeover switch SW1 to the terminal CN1, increases the voltage V1 by decreasing the output voltage of the D / A converter 22, and increases the output voltage of the D / A converter 22. V2 can be increased. Further, the control unit 21 switches the changeover switch SW1 to the terminal CN2, increases the voltage V3 by decreasing the output voltage of the D / A converter 22, and increases the output voltage of the D / A converter 22. V4 can be increased.

  The control unit 21 includes, for example, a CPU (Central Processing Unit) that executes predetermined arithmetic processing, a ROM (Read Only Memory) that stores a predetermined control program, and a RAM (Random Access Memory) that temporarily stores data. A first reference voltage acquisition unit 211, a second reference voltage by executing a control program stored in the ROM, and an I / O port, a communication interface circuit, and peripheral circuits thereof. It functions as a setting unit 212, a mode switching unit 213, a second protection control unit 214, and a charging voltage adjustment unit 215.

  The first reference voltage acquisition unit 211 sequentially increases the voltages V1, V2, V3, and V4 as described above by the D / A converter 22 and the changeover switch SW1. The voltages detected by the A / D converters 231, 232, 233 and 234 when the control signal S 1 for turning on the switching element Q 3 is output from the logic circuit 31, respectively. , 233, 234 corresponding to the first reference voltages Vref1, Vref2, Vref3, Vref4.

  The second reference voltage setting unit 212 subtracts a preset differential voltage Vd, for example, 0.01 V, from the first reference voltages Vref1, Vref2, Vref3, and Vref4 to obtain second reference voltages Vth1, Vth2, Vth3, and Vth4. Is calculated and stored in the EEPROM 25.

  When the second reference voltages Vth1, Vth2, Vth3, and Vth4 are stored in the EEPROM 25 by the second reference voltage setting unit 212, the mode switching unit 213 switches the changeover switch SW1 to the terminal OFF so that the secondary batteries B1 and B2 are switched. , B3, B4 are switched to a normal mode in which the voltages at both ends of B1, B4 can be detected as voltages V1, V2, V3, V4 by the A / D converters 231, 232, 233, 234 and the comparators M1, M2, M3, M4.

  When the voltage detected by the A / D converters 231, 232, 233, and 234 exceeds the second reference voltages Vth1, Vth2, Vth3, and Vth4 during the normal mode, the second protection control unit 214 switches the switching element Q1. , Q2 are turned off to prohibit charging of the secondary batteries B1, B2, B3, B4.

  The charging voltage adjustment unit 215 has a maximum voltage among the terminal voltages of the secondary batteries B1, B2, B3, and B4 detected by the A / D converters 231, 232, 233, and 234 during the normal mode. When the voltage exceeds a preset upper limit voltage, for example, 4.2 V, the charging voltage is reduced via the external connection terminals 13 and 14 to the charger connected to the external connection terminals 11, 12, 13, and 14. A communication signal to the effect is output.

  In the battery pack 1 shown in FIG. 1, connection terminals and wirings connected to the secondary batteries B1, B2, B3, B4, resistors R1, R2, comparators M1, M2, M3, M4, A / D converters 231, 232, 233, 234, reference voltage sources E1, E2, E3, E4, D / A converter 22, changeover switch SW1, first reference voltage acquisition unit 211, second reference voltage setting unit 212, mode switching unit 213, logic circuit 31, The second protection control unit 214, the charging voltage adjustment unit 215, the switching elements Q1 and Q2, the temperature fuses F1 and F2, and the heater Rh correspond to an example of a battery protection circuit.

  FIG. 2 shows a state where the battery pack 1 shown in FIG. 1 is connected to the charger 4. In addition, in FIG. 2, the structure of the battery pack 1 is simplified and shown. The charger 4 shown in FIG. 2 includes external connection terminals 41, 42, 43, 44, a DC power supply circuit 45, a DC-DC converter 46, a charge control unit 47, a D / A converter 48, an error amplifier (error amplifier) 49, 50, reference voltage sources 51, 52, and 53, and a current detection resistor RS. The external connection terminals 41, 42, 43, 44 are connected to the external connection terminals 11, 12, 13, 14 of the battery pack 1, respectively.

  The DC power supply circuit 45 converts, for example, a commercial AC power supply voltage into a DC voltage and outputs it. The high potential side output terminal of the DC power supply circuit 45 is connected to the external connection terminal 41 via the switching element Q4 and the coil L1, the low potential side output terminal is connected to the ground, and the current detection resistor RS is connected to the ground. Are connected to the external connection terminal 42.

  The DC-DC converter 46 includes, for example, an FET switching element Q4, a coil L1, a diode D1, a capacitor C1, and a PWM (Pulse Width Modulation) signal generation circuit 461. The connection point between the switching element Q4 and the coil L1 is connected to the cathode of the diode D1, and the anode of the diode D1 is connected to the ground. A capacitor C1 is connected in parallel with the series circuit of the diode D1 and the coil L1. The PWM signal generation circuit 461 outputs a PWM control signal whose pulse width is changed according to the control signal from the charging control unit 47 to the gate of the switching element Q4 to turn on and off the switching element Q4. A DC power supply voltage corresponding to a control signal from the charging control unit 47 is generated and supplied to the battery pack 1 via the external connection terminals 41 and 42.

  The charging control unit 47 controls the charging voltage and charging current for charging the battery pack 1 connected to the external connection terminals 41, 42, 43, 44, and performs, for example, CCCV (constant current constant voltage) charging. It is a control circuit.

  The error amplifier 49 compares the voltage across the current detection resistor RS with the reference voltage Ve1 output from the reference voltage source 51. If the voltage across the current detection resistor RS is equal to or lower than the reference voltage Ve1, the error amplifier 49 detects a low level current detection. If the voltage across the resistor RS exceeds the reference voltage Ve1, a high level signal is output to the charge control unit 47. The reference voltage Ve1 is set to a voltage across the current detection resistor RS when a current Ic preset as a charging current for constant current charging flows through the current detection resistor RS. Then, if the output voltage of the error amplifier 49 is at a low level, the charging control unit 47 outputs a control signal to the PWM signal generation circuit 461 to increase the output voltage of the DC-DC converter 46, while the error amplifier 49 If the output voltage is high, a control signal is output to the PWM signal generation circuit 461 to reduce the output voltage of the DC-DC converter 46, thereby supplying a constant current Ic as a charging current to the battery pack 1. Perform current charging.

  The output voltage Ve3 of the reference voltage source 53 is variable, and the charging control unit 47 applies the control voltage to the reference voltage source 53 via the D / A converter 48, thereby outputting the output voltage of the reference voltage source 53. Ve3 is controlled. The output voltage Ve3 is set to 0V in the initial state.

  The error amplifier 49 adds (Vout + Ve3) the output voltage Ve3 to the output voltage Vout between the external connection terminals 41 and 42, which is the charging voltage of the battery pack B, and the reference voltage Ve2 output from the reference voltage source 52. In comparison, if (Vout + Ve3) is equal to or lower than the reference voltage Ve2, a low level signal is output to the charge control unit 47 if the voltage across the current detection resistor RS exceeds the reference voltage Ve2. The reference voltage Ve2 is, for example, an end voltage for ending constant current charging, and a charging voltage for constant voltage charging is set in advance, and is an upper limit value of the charging voltage. In the case of a lithium ion secondary battery, since the upper limit value of the charging voltage, that is, the charging voltage in constant voltage charging is, for example, 4.2 V per cell, the reference voltage Ve2 is obtained by multiplying 4.2 V by 4 cells. .8V is preset.

  If the output voltage of the error amplifier 49 becomes high level during constant current charging, the charging control unit 47 shifts to constant voltage charging. When the charging control unit 47 shifts to constant voltage charging, if the output voltage of the error amplifier 49 is low level, the charging control unit 47 outputs a control signal to the PWM signal generation circuit 461 to increase the output voltage of the DC-DC converter 46. If the output voltage of the error amplifier 49 is at a high level, a control signal is output to the PWM signal generation circuit 461 and the output voltage of the DC-DC converter 46 is lowered, so that the output voltage Vout is (Ve2-Ve3). A constant voltage charge is performed for constant control.

  In this case, since the output voltage Ve3 is set to 0 V in the initial state, constant voltage charging is performed with the charging voltage of the reference voltage Ve2 output from the reference voltage source 52 in the initial state.

  In addition, the charging control unit 47 and the control unit 21 are synchronized using a data signal D transmitted by the external connection terminals 13 and 43 and a synchronization signal CL transmitted by the external connection terminals 14 and 44, respectively. A communication interface circuit is provided.

  And the charge control part 47 will receive the output voltage Ve3 of the reference voltage source 53, if the communication signal to the effect of reducing a charge voltage is received from the charge voltage adjustment part 215 in the control part 21 via the external connection terminals 43 and 44. By increasing the output voltage Vout, the output voltage Vout is decreased.

  In addition, although the example in which the battery protection circuit is configured in the battery pack is shown, the above-described battery protection circuit may be configured to be built in the charger. Further, the configuration included in the battery pack 1 and the charger 4 shown in FIG. 2 may be a charging system that is integrally configured without being separated into the battery pack 1 and the charger 4. Such a charging system may be built in a battery-driven device such as a portable personal computer, a digital camera, or a mobile phone driven by a battery.

  Next, the operation of the battery pack 1 configured as described above will be described. First, in the initial state, the first reference voltages Ref1, Ref2, Ref3, and Ref4 are set to, for example, 4.25 V in the reference voltage sources E1, E2, E3, and E4 as voltages for performing the second-stage protection. . Moreover, the upper limit value of the charging voltage supplied from the charger 4 is set to 4.2 V per cell, for example. Then, the second reference voltage at which the control IC 2 performs the first stage protection is (upper limit value of charging voltage per cell) <(second reference voltage (first stage)) <(first reference voltage (second stage)). Therefore, the second reference voltages Vth1, Vth2, Vth3, and Vth4 must be set to voltages exceeding 4.2V and not exceeding 4.25V.

  However, due to the accuracy and characteristic variations of the reference voltage sources E1, E2, E3, and E4 and the comparators M1, M2, M3, and M4, the voltage that is actually protected at the second stage by the control IC 3 is the set first reference. There may be an error between the voltages Ref1, Ref2, Ref3, and Ref4. Similarly, if the second reference voltage to be protected by the control IC 2 is set in advance, the voltage at which the control IC 2 is actually protected by the control IC 2 due to variations in accuracy and characteristics of the control IC 2. May cause a difference from the set second reference voltage. Furthermore, the output voltage Vout output from the charger 4 also exceeds a preset upper limit voltage of 4.2 V due to variations in accuracy and characteristics of the reference voltage source 53, the error amplifier 49, the DC-DC converter 46, and the like. There is a fear.

  Thus, in consideration of the accuracy and characteristic variation of each part, the difference between the upper limit value of the charging voltage per cell and the first reference voltage (second stage) is slight (4.25V-4.2V = 0.05V). Is set to satisfy the condition of (upper limit value of charging voltage per cell) <(second reference voltage (first stage)) <(first reference voltage (second stage)). Have difficulty. Therefore, the battery pack 1 detects the first reference voltages Vref1, Vref2, Vref3, and Vref4 that are actually protected by the control IC 3 and detects the difference voltages from the first reference voltages Vref1, Vref2, Vref3, and Vref4, respectively. By setting the second reference voltages Vth1, Vth2, Vth3, Vth4 for subtracting Vd and performing the first stage protection, (second reference voltage (first stage)) <(first reference voltage (second stage) )) Is satisfied.

  Further, when the voltage across each of the secondary batteries B1, B2, B3, B4 exceeds a preset upper limit value (4.2 V) per cell, the charging voltage adjustment unit 215 causes the charger 4 to By giving an instruction to lower the output voltage, the condition of (upper limit value of charging voltage per cell) <(second reference voltage (first stage)) is satisfied.

  Hereinafter, the operation will be described in detail. First, the changeover switch SW1 is switched to the terminal CN1 in accordance with the control signal from the first reference voltage acquisition unit 211, and the output voltage of the D / A converter 22 is gradually reduced. As a result, the voltage V1 gradually increases. When the voltage V1 exceeds the reference voltage Ref1, the output voltage of the comparator M1 becomes high level, and the control signal S1 is turned to high level, for example, to turn on the switching element Q3 from the logic circuit 31, and the switching element Q3 It is output to the control unit 21.

  Then, the voltage detected by the A / D converter 231 when the first reference voltage acquisition unit 211 detects that the control signal S1 becomes high level is acquired as the first reference voltage Vref1. Then, in response to the control signal from the first reference voltage acquisition unit 211, the changeover switch SW1 is switched to the terminal OFF, so that the voltage V1 drops below the reference voltage Ref1 and the control signal S1 output from the logic circuit 31. Is set to low level.

  At this time, the first reference voltage Vref1 is acquired by the first reference voltage acquisition unit 211 after the control signal S1 is set to the high level, and the switching element Q3 is turned on until the control signal S1 is set to the low level. Although a current flows through the heater Rh, it takes about 30 seconds until the heater Rh generates heat and the thermal fuses F1 and F2 are blown, whereas the processing time of the first reference voltage acquisition unit 211 is the thermal fuse F1. , F2 which is much shorter than the fusing time of F2, the thermal fuses F1 and F2 are not blown. Hereinafter, the temperature fuses F1 and F2 are prevented from being blown in the same manner when the first reference voltage acquisition unit 211 acquires the first reference voltages Vref2, Vref3, and Vref4.

  Next, the changeover switch SW1 is switched to the terminal CN1 according to the control signal from the first reference voltage acquisition unit 211, and the output voltage of the D / A converter 22 is gradually increased. As a result, the voltage V2 gradually increases. When the voltage V2 exceeds the reference voltage Ref2, the output voltage of the comparator M2 becomes high level, and the control signal S1 output from the logic circuit 31 is set to high level, for example, and the switching element Q3, the control unit 21, Is output.

  Then, the voltage detected by the A / D converter 232 when the first reference voltage acquisition unit 211 detects that the control signal S1 has become high level is acquired as the first reference voltage Vref2. Then, in response to the control signal from the first reference voltage acquisition unit 211, the changeover switch SW1 is switched to the terminal OFF, so that the voltage V1 drops below the reference voltage Ref2 and the control signal S1 output from the logic circuit 31. Is set to low level.

  Next, the changeover switch SW1 is switched to the terminal CN2 according to the control signal from the first reference voltage acquisition unit 211, and the output voltage of the D / A converter 22 is gradually reduced. As a result, the voltage V3 gradually increases. When the voltage V3 exceeds the reference voltage Ref3, the output voltage of the comparator M3 becomes high level, the control signal S1 output from the logic circuit 31 is set to high level, for example, and the switching element Q3, the control unit 21, Is output.

  Then, the voltage detected by the A / D converter 233 when the first reference voltage acquisition unit 211 detects that the control signal S1 has become high level is acquired as the first reference voltage Vref3. Then, in response to the control signal from the first reference voltage acquisition unit 211, the changeover switch SW1 is switched to the terminal OFF, so that the voltage V1 drops below the reference voltage Ref3 and the control signal S1 output from the logic circuit 31. Is set to low level.

  Next, the changeover switch SW1 is switched to the terminal CN2 according to the control signal from the first reference voltage acquisition unit 211, and the output voltage of the D / A converter 22 is gradually increased. As a result, the voltage V4 gradually increases. When the voltage V4 exceeds the reference voltage Ref4, the output voltage of the comparator M4 becomes high level, the control signal S1 output from the logic circuit 31 is set to high level, for example, and the switching element Q3, the control unit 21, Is output.

  Then, the voltage detected by the A / D converter 234 when the first reference voltage acquisition unit 211 detects that the control signal S1 becomes high level is acquired as the first reference voltage Vref4. Then, in response to the control signal from the first reference voltage acquisition unit 211, the changeover switch SW1 is switched to the terminal OFF, so that the voltage V1 drops below the reference voltage Ref4 and the control signal S1 output from the logic circuit 31. Is set to low level.

  In this way, the first reference voltage acquisition unit 211 acquires the first reference voltages Vref1, Vref2, Vref3, and Vref4 that are actually protected by the control IC 2 in the first stage.

  The switching unit, for example, connects the connection points of the paired A / D converters 231, 232, 233, 234 and the comparators M 1, M 2, M 3, M 4 to the secondary batteries B 1, B 2, B 3, B 4 and D / A converter 22 may be configured using a selector switch that is selectively connected to either one, but in this case, as many selector switches as the number of secondary batteries connected in series are required. In the battery pack 1 shown in FIG. 1, the A / D converter is connected to the secondary battery via a resistor, and the output voltage of the D / A converter 22 is applied to the connection point between the resistor and the A / D converter. Thus, there is no need to disconnect the secondary battery, and the number of changeover switches is reduced.

  Further, the changeover switch SW1 is not limited to an example in which every other connection point P11, P21, P31 can be selected, and for example, a pair of A / D converters 231, 232, 233, 234 and comparators M1, M2 , M3, M4 are all connected to the secondary batteries B1, B2, B3, B4 through resistors, and paired A / D converters 231, 232, 233, 234 and comparators M1, M2, A changeover switch that can select all the connection points with M3 and M4 may be provided, but by using the changeover switch SW1 that can select every other connection point P11, P21, and P31, the number of changeover terminals of the changeover switch It is possible to reduce the number of resistors and simplify the circuit.

  Next, the second reference voltage setting unit 212 subtracts a differential voltage Vd, for example, 0.01 V from the first reference voltages Vref1, Vref2, Vref3, and Vref4 acquired by the first reference voltage acquisition unit 211 to obtain a second value. Reference voltages Vth1, Vth2, Vth3, Vth4 are calculated and stored in the EEPROM 25.

  When the first determination voltage at which the first-stage protection circuit operates and the second determination voltage at which the second-stage protection circuit operates are fixedly set in advance as in the background art described above, Considering the accuracy and characteristic variation of the voltage detection circuit included in the protection circuit, a voltage difference larger than the accuracy and characteristic variation of the voltage detection circuit is set between the first determination voltage and the second determination voltage. For example, the upper limit value of the charging voltage is 4.2V, whereas the first determination voltage of the first stage is 4.3V, and the second determination voltage of the second stage is 4.4V. It was necessary to provide a difference between the eye protection voltage and the second protection voltage of about 0.1V.

  However, in the battery pack 1 shown in FIG. 1, the control IC 3 that performs the second-stage protection detects the voltages that actually detect the overvoltage and change the control signal S1 as the first reference voltages Vref1, Vref2, Vref3, and Vref4. Then, by subtracting the differential voltage Vd from the first reference voltages Vref1, Vref2, Vref3, and Vref4, the second reference voltages Vth1, Vth2, Vth3, and Vth4 that perform the first-stage protection are calculated. Therefore, regardless of the accuracy and variation of the control ICs 2 and 3, the voltage at which the control IC 2 performs first-stage protection (switching elements Q1 and Q2 are turned off) and the control IC 3 perform second-stage protection (temperature fuses F1 and F2). Therefore, it is easy to set the difference voltage Vd to a voltage difference smaller than that of the background art, for example, 0.01V.

  Next, the changeover switch SW1 is switched to the terminal OFF by the mode switching unit 213, and the voltages at both ends of the secondary batteries B1, B2, B3, and B4 are converted into voltages V1, V2, V3, and V4 as A / D converters 231 and 231, respectively. 232, 233, 234 and comparators M1, M2, M3, and M4 are set to a normal mode that can be detected, and the secondary battery B1, B2, B3, and B4 can be protected by the battery protection circuit. A charging start instruction is transmitted from the mode switching unit 213 to the charging control unit 47.

  Then, as described above, the output voltage Vout of the DC-DC converter 46, that is, the charging voltage of the assembled battery B is output according to the control signal from the charging control unit 47, and the assembled battery B is charged.

  During the normal mode, the maximum voltage among the terminal voltages V1, V2, V3, V4 of the secondary batteries B1, B2, B3, B4 detected by the A / D converters 231, 232, 233, 234 is When the voltage exceeds an upper limit voltage, for example, 4.2 V, the charging voltage adjusting unit 215 outputs a communication signal indicating that the charging voltage is reduced to the charging control unit 47 of the charger 4. Then, the output voltage Vout of the DC-DC converter 46 is reduced by the charging control unit 47, and the terminal voltages of the secondary batteries B1, B2, B3, B4 during charging are reduced from exceeding the upper limit voltage. Deterioration of the secondary batteries B1, B2, B3, B4 is reduced.

  In this case, the possibility that the upper limit of the charging voltage exceeds the upper limit voltage of 4.2 V is reduced regardless of the accuracy and characteristic variations of the reference voltage source 53, the error amplifier 49, the DC-DC converter 46, and the like of the charger 4. It is easy to set the second reference voltages Vth1, Vth2, Vth3, and Vth4 such that (upper limit value of charging voltage per cell) <(second reference voltage (first stage)).

  Then, in the battery protection circuit according to the background art, for example, the upper limit value of the charging voltage is 4.2V, whereas the first determination voltage at the first stage needs to be 0.1V, such as 4.3V. In contrast, in the battery pack 1 shown in FIG. 1, the upper limit voltage during charging is set to 4.2 V, whereas the second reference voltages Vth1, Vth2, Vth3, and Vth4 are set to 4.24V ( = 4.25V-0.01V), it becomes easy to reduce the difference between the upper limit value of the charging voltage and the second reference voltages Vth1, Vth2, Vth3, Vth4 to about 0.04V. Thus, when each terminal voltage of the secondary batteries B1, B2, B3, B4 exceeds the upper limit (4.2V) of the charging voltage, it is applied to the battery until the charging is prohibited by the first protection circuit. As a result, the deterioration of the secondary batteries B1, B2, B3, B4 is reduced.

  By the way, each terminal voltage of the secondary batteries B1, B2, B3, B4 exceeds the upper limit value of the charging voltage, not only due to the accuracy or characteristic variation of the charger 4. Even if the output voltage Vout of the charger 4 is maintained at 16.8V, if imbalance occurs in the secondary batteries B1, B2, B3, B4, the terminal voltage may exceed 4.2V.

  FIG. 3 is an explanatory diagram for explaining a case where the terminal voltage exceeds 4.2 V due to imbalance of the secondary batteries B1, B2, B3, and B4. FIG. 3A shows an example in which the secondary batteries B1, B2, B3, and B4 have the same degree of deterioration and are balanced. As shown in FIG. 3A, when the secondary batteries B1, B2, B3, and B4 are balanced, the output voltage 16.8V of the charger 4 is set to the secondary batteries B1, B2, B3, and B3. The voltage is equally divided by B4 and 4.2V is applied to each secondary battery.

  On the other hand, the secondary batteries B1, B2, B3, and B4 have different levels of deterioration each time they pass through a charge / discharge cycle, and the capacity of the batteries that have deteriorated decreases. FIG. 3B shows an example in which the deterioration of the secondary battery B3 progresses more than the other secondary batteries B1, B2, B4 and the capacity decreases. When the capacity of the secondary battery B3 is smaller than that of the other secondary batteries B1, B2, B4, the terminal voltage of the secondary battery B3 becomes higher than that of the other secondary batteries. For example, the secondary batteries B1, B2, B4 However, the terminal voltage of the secondary battery B3 is 4.23V, which exceeds the upper limit voltage and further deteriorates.

  However, in the battery pack 1, the maximum voltage among the terminal voltages V1, V2, V3, V4 of the secondary batteries B1, B2, B3, B4 detected by the A / D converters 231, 232, 233, 234 is the highest. When the voltage exceeds an upper limit voltage, for example, 4.2 V, the charging voltage adjustment unit 215 outputs a communication signal indicating that the charging voltage is reduced to the charging control unit 47 of the charger 4, and the output voltage Vout of the charger 4 decreases. In addition, since any terminal voltage of the secondary batteries B1, B2, B3, and B4 does not exceed the upper limit voltage, it is reduced that the deterioration of the deteriorated secondary battery is further accelerated. , (Upper limit value of charging voltage per cell) <(second reference voltage (first stage)) is easily maintained.

  Further, when the charging voltage continues to increase without decreasing the output voltage Vout regardless of the communication signal for decreasing the charging voltage from the charging voltage adjusting unit 215 due to, for example, a failure of the charger 4, A / When the voltages detected by the D converters 231, 232, 233, and 234 exceed the second reference voltages Vth1, Vth2, Vth3, and Vth4, the second protection control unit 214 turns off the switching elements Q1 and Q2, and the secondary Charging of batteries B1, B2, B3, B4 is prohibited.

  In this case, as described above, in the battery pack 1, it is easy to make the difference between the upper limit value of the charging voltage and the second reference voltages Vth1, Vth2, Vth3, Vth4 smaller than the background art, for example, about 0.04V. For example, even if the battery 4 exceeds the secondary batteries B1, B2, B3, B4 due to a failure of the charger 4, the terminals of the secondary batteries B1, B2, B3, B4 with a slight voltage increase As a result of the voltage reaching the second reference voltages Vth1, Vth2, Vth3, and Vth4, the switching elements Q1 and Q2 are quickly turned off by the control IC2 and charging of the secondary batteries B1, B2, B3, and B4 is prohibited. Deterioration of the batteries B1, B2, B3, B4 can be reduced.

  Furthermore, the terminal voltages of the secondary batteries B1, B2, B3, B4 rise beyond the second reference voltages Vth1, Vth2, Vth3, Vth4 due to the failure of the control IC2, the switching elements Q1, Q2, etc., and the voltages V1, V2 , V3, V4 exceed the first reference voltage Vref1, Vref2, Vref3, Vref4, the output voltages of the comparators M1, M2, M3, M4 become high level and an overvoltage is detected. Then, the control signal S1 is set to the high level by the logic circuit 31, the heater Rh generates heat, and the temperature fuses F1, F2 are blown to protect the secondary batteries B1, B2, B3, B4.

  In this case, since the differential voltage Vd is reduced from the background art, the terminal voltages of the secondary batteries B1, B2, B3, and B4 are reduced to the second reference voltages Vth1, Vth2, and the like due to a failure of the control IC 2, the switching elements Q1, Q2, and the like. If the charging voltage is not interrupted even if Vth3 and Vth4 are exceeded, the terminal voltages of the secondary batteries B1, B2, B3, and B4 reach the first reference voltages Vref1, Vref2, Vref3, and Vref4 with a slight voltage increase and quickly. Further, since the thermal fuses F1 and F2 are blown by the control IC 3 and the secondary battery is protected, safety risk can be reduced.

  Although the control IC 2 performs the first-stage protection and the control IC 3 performs the second-stage protection, for example, the control IC 2 controls on / off of the switching element Q3, and the control signal S1 output from the control IC 3 The second reference voltage setting unit 212 adds the differential voltage Vd to the first reference voltages Vref1, Vref2, Vref3, and Vref4 by turning on and off the switching elements Q1 and Q2 in response to the second reference voltages Vth1 and Vth2. , Vth3, Vth4 may be set as the protection voltage for the second stage. In this case, the control IC 2 performs the second stage protection, and the control IC 3 performs the first stage protection.

(Second Embodiment)
Next, the battery pack 1a provided with the battery protection circuit according to the second embodiment of the present invention will be described. FIG. 4 is a block diagram showing an example of the configuration of the battery pack 1a according to the second embodiment of the present invention. The battery pack 1a shown in FIG. 4 differs from the battery pack 1 shown in FIG. 1 in the following points. That is, the battery pack 1a shown in FIG. 4 does not include the D / A converter 22 and the changeover switch SW1. Further, the operation of the first reference voltage acquisition unit 211a is different as described later.

  The positive electrode of the secondary battery B1 is connected in parallel to the positive electrode side input terminal of the A / D converter 231 and the positive electrode side input terminal of the comparator M1 via the resistor R11, and the positive electrode of the secondary battery B2 is connected to the resistor R12. Are connected in parallel to the positive input terminal of the A / D converter 232, the positive input terminal of the comparator M2, and the negative terminal of the reference voltage source E1, and the positive terminal of the reference voltage source E1 is connected to the negative input terminal of the comparator M1. Has been.

  In addition, the positive electrode of the secondary battery B3 is connected in parallel to the positive electrode side input terminal of the A / D converter 233, the positive electrode side input terminal of the comparator M3, and the negative electrode of the reference voltage source E2 via the resistor R13. The positive electrode of E2 is connected to the negative input terminal of the comparator M2. The positive electrode of the secondary battery B4 is connected in parallel to the positive input terminal of the A / D converter 234, the positive input terminal of the comparator M4, and the negative electrode of the reference voltage source E3 via the resistor R14. The positive electrode of E3 is connected to the negative input terminal of the comparator M3.

  In addition, although illustration is abbreviate | omitted, the negative electrode terminal of secondary battery B1, B2, B3, B4 is each connected to the negative electrode side input terminal of A / D converter 231,232,233,234.

  A connection point between the resistor R11 and the A / D converter 231 is connected to the connection terminal TP1, a connection point between the resistor R12 and the A / D converter 232 is connected to the connection terminal TP2, and the resistor R13 and the A / D are connected to each other. The connection point with the converter 233 is connected to the connection terminal TP3, the connection point between the resistor R14 and the A / D converter 234 is connected to the connection terminal TP4, and the negative electrode of the secondary battery B4 is connected to the connection terminal TPG. ing.

  A jig 5 for setting the second reference voltages Vth1, Vth2, Vth3, Vth4 by the first reference voltage acquisition unit 211a is connectable to the connection terminals TP1, TP2, TP3, TP4, TPG. .

  The jig 5 includes a series circuit of variable voltage sources E51, E52, E53, and E54, and switches SW51, SW52, SW53, and SW54. The positive terminal of the variable voltage source E51 is connected to the connection terminal TP1 through the switch SW51, the connection point of the variable voltage sources E51 and E52 is connected to the connection terminal TP2 through the switch SW52, and the variable voltage sources E52 and E53 are connected. The connection point is connected to the connection terminal TP3 via the switch SW53, the connection point of the variable voltage sources E53 and E54 is connected to the connection terminal TP4 via the switch SW54, and the negative electrode of the variable voltage source E54 is connected via the switch SW55. It is connected to the terminal TPG.

  Next, the operation of the battery pack 1a shown in FIG. 4 will be described. As described above, in the battery pack 1 shown in FIG. 1, the voltages V1, V2, V3, and V4 are forcibly increased by using the D / A converter 22 and the changeover switch SW1, and the protection operation is artificially performed by the control IC 3. By doing so, the first reference voltages Vref1, Vref2, Vref3, and Vref4 are detected.

  However, since the first reference voltages Vref1, Vref2, Vref3, and Vref4 depend on the accuracy and variation of the control ICs 2 and IC3, once they are detected, they rarely change afterwards. Especially in the case of a battery pack, the cycle life of the secondary battery is unavoidable, so the period of continuous use is relatively short, and the first reference voltages Vref1, Vref2, Vref3, Vref4 change due to aging of the control IC2, the control IC3, etc. The need to consider doing is low.

  Therefore, in the battery pack 1a shown in FIG. 4, when the battery pack 1a is shipped or the like, the jig 5 is attached to the battery pack 1a to forcibly increase the voltages V1, V2, V3, and V4, and the control IC 3 simulates them. By performing the protection operation, the first reference voltages Vref1, Vref2, Vref3, and Vref4 are detected. Thereby, the battery pack 1a shown in FIG. 4 does not require the D / A converter 22 and the changeover switch SW1, can simplify the circuit, and can reduce the cost.

  Hereinafter, an operation of acquiring the first reference voltages Vref1, Vref2, Vref3, and Vref4 in the battery pack 1a illustrated in FIG. 4 will be described. First, the jig 5 is connected to the battery pack 1a, for example, at the time of manufacturing the battery pack 1a or at the time of product inspection before shipment. On the other hand, the first reference voltage acquisition unit 211a monitors the control signal S1. Then, the switches SW51 and SW52 are turned on in the jig 5, the output voltage of the variable voltage source E51 is gradually increased, and the voltage V1 is gradually increased.

  When the voltage V1 exceeds the reference voltage Ref1, the output voltage of the comparator M1 becomes high level, and the control signal S1 is made high level by the logic circuit 31, and is output to the switching element Q3 and the control unit 21. . Then, the voltage detected by the A / D converter 231 when the first reference voltage acquisition unit 211a detects that the control signal S1 becomes high level is acquired as the first reference voltage Vref1.

  Next, when the switch SW51 is turned off in the jig 5, the voltage V1 drops below the reference voltage Ref1, and the control signal S1 output from the logic circuit 31 is set to the low level. Then, the first reference voltage acquisition unit 211a detects that the control signal S1 has become low level, and enters a state of waiting for acquisition of the first reference voltage Vref2.

  Next, the switch SW53 is turned on in the jig 5, the output voltage of the variable voltage source E52 is gradually increased, and the voltage V2 is gradually increased. When the voltage V2 exceeds the reference voltage Ref2, the output voltage of the comparator M2 becomes high level, and the control signal S1 is set to high level by the logic circuit 31, and is output to the switching element Q3 and the control unit 21. . Then, the voltage detected by the A / D converter 232 when the first reference voltage acquisition unit 211a detects that the control signal S1 becomes high level is acquired as the first reference voltage Vref2.

  Thereafter, the first reference voltages Vref1, Vref2, and Vref3 are similarly controlled by the first reference voltage acquisition unit 211a by repeatedly turning on and off the switches SW53, SW54, and SW55 and adjusting the output voltage of the variable voltage sources E53 and 54. , Vref4 is acquired.

  The on / off of the switches SW51, SW52, SW53, SW54 in the jig 5 and the adjustment of the output voltage of the variable voltage sources E51, E52, E53, E54 may be performed manually by an operator, for example. You may perform automatically using the control circuit using a microcomputer.

  INDUSTRIAL APPLICABILITY The present invention is suitably used for battery protection circuits and battery packs that are used as power sources for battery-mounted devices such as portable personal computers, digital cameras, mobile phones, and other electronic devices, vehicles such as electric cars and hybrid cars. Can do.

It is a block diagram which shows an example of a structure of the battery pack provided with the battery protection circuit which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the state in which the battery pack shown in FIG. 1 was connected to the charger. It is explanatory drawing for demonstrating the case where a terminal voltage exceeds 4.2V by the imbalance of a secondary battery. It is a block diagram which shows an example of a structure of the battery pack which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

1,1a Battery pack 2,3 Control IC
DESCRIPTION OF SYMBOLS 4 Charger 5 Jig 11, 12, 13, 14 External connection terminal 21 Control part 22 D / A converter 31 Logic circuit 46 DC-DC converter 47 Charge control part 211, 211a 1st reference voltage acquisition part 212 2nd reference voltage Setting unit 213 Mode switching unit 214 Second protection control unit 215 Charging voltage adjustment unit 231, 232, 233, 234 A / D converter B assembled battery B1, B2, B3, B4 secondary battery CN1, CN2, OFF terminals E1, E2 , E3, E4 Reference voltage source E51, E52, E53, E54 Variable voltage source F1, F2 Thermal fuse M1, M2, M3, M4 Comparator P1, P2, P3, P11, P31 Connection point Q1, Q2, Q3, Q4 Switching element R1, R2, R3, R11, R12, R13, R14 Resistance RS Current detection resistance Ref , Ref2, Ref3, Ref4 Reference voltage Rh Heater S1 Control signal SW1 Changeover switch SW51, SW52, SW53, SW54, SW55 Switch TP1, TP2, TP3, TP4, TPG Connection terminals V1, V2, V3, V4 Voltage Vd Differential voltage Ve1, Ve2 reference voltage Vout output voltage Vref1, Vref2, Vref3, Vref4 first reference voltage Vth1, Vth2, Vth3, Vth4 second reference voltage

Claims (9)

A battery voltage acquisition unit for acquiring a terminal voltage of the secondary battery;
A pair of first and second voltage detectors for detecting a common input voltage;
An overvoltage detection unit that compares the detection voltage detected by the first voltage detection unit with a preset first reference voltage and detects an overvoltage when the detection voltage exceeds the first reference voltage;
A first reference voltage acquisition unit configured to acquire, as the first reference voltage, a voltage detected by the second voltage detection unit when the overvoltage is detected by the overvoltage detection unit;
A second reference voltage setting unit that sets a second reference voltage that differs from a first reference voltage acquired by the first reference voltage acquisition unit by a preset differential voltage;
A mode switching unit that switches the voltage acquired by the battery voltage acquisition unit to a normal mode that supplies the voltage to the pair of first and second voltage detection units as the input voltage;
A first protection control unit that prohibits charging of the secondary battery when an overvoltage is detected by the overvoltage detection unit during the normal mode;
In the normal mode, when the voltage detected by the second voltage detection unit exceeds the second reference voltage set by the second reference voltage setting unit, charging of the secondary battery is prohibited. A battery protection circuit comprising a protection control unit. An inspection voltage generator for generating a predetermined inspection voltage;
A voltage switching unit that supplies either the voltage acquired by the battery voltage acquisition unit or the voltage generated by the inspection voltage generation unit as the input voltage to the pair of first and second voltage detection units; In addition,
The first reference voltage acquisition unit includes:
The voltage switching unit supplies the inspection voltage generated by the inspection voltage generation unit to the pair of first and second voltage detection units, and gradually increases the inspection voltage by the inspection voltage generation unit. Thus, the overvoltage detection unit detects the overvoltage, and when the overvoltage is detected, the voltage detected by the second voltage detection unit is acquired as the first reference voltage,
The mode switching unit
The switching to the normal mode is performed by causing the voltage switching unit to supply the voltage acquired by the battery voltage acquisition unit to the first and second voltage detection units. Battery protection circuit. The battery voltage acquisition unit
Obtain the voltage across each of a plurality of secondary batteries connected in series,
The pair of first and second voltage detectors includes:
A plurality of pairs are provided corresponding to the plurality of secondary batteries,
The overvoltage detector is
Detecting an overvoltage by comparing the detected voltages detected by the plurality of first voltage detectors with the first reference voltage,
The first reference voltage acquisition unit includes:
When the overvoltage is detected by the overvoltage detection unit in response to an increase in each input voltage of the plurality of pairs of first and second voltage detection units, the voltage detected by each second voltage detection unit is Obtained as the first reference voltage corresponding to the second voltage detector,
The second reference voltage setting unit includes:
The first reference voltage corresponding to each of the second voltage detection units is set as a plurality of second reference voltages corresponding to each of the second voltage detection units by making the difference voltage different.
The second protection controller is
When the voltage detected by each of the second voltage detectors exceeds the second reference voltage set corresponding to each of the second voltage detectors during the normal mode, the secondary battery is charged. The battery protection circuit according to claim 1, wherein the battery protection circuit is prohibited. The battery voltage acquisition unit
Obtain the voltage across each of a plurality of secondary batteries connected in series,
The pair of first and second voltage detectors includes:
A plurality of pairs are provided corresponding to the plurality of secondary batteries,
The overvoltage detector is
Detecting an overvoltage by comparing the detected voltages detected by the plurality of first voltage detectors with the first reference voltage,
The first reference voltage acquisition unit includes:
The plurality of pairs of first and second voltage detection units are sequentially selected by the voltage switching unit, and the test voltage generated by the test voltage generation unit to the selected pair of the first and second voltage detection units. And the inspection voltage generation unit gradually increases the inspection voltage so that the overvoltage detection unit detects the overvoltage, and the second voltage detection unit detects the overvoltage when the overvoltage is detected. Is acquired as a first reference voltage corresponding to each second voltage detector,
The second reference voltage setting unit includes:
The first reference voltage corresponding to each of the second voltage detection units is set as a plurality of second reference voltages corresponding to each of the second voltage detection units by making the difference voltage different.
The second protection controller is
When the voltage detected by each of the second voltage detectors exceeds the second reference voltage set corresponding to each of the second voltage detectors during the normal mode, the secondary battery is charged. The battery protection circuit according to claim 2, wherein the battery protection circuit is prohibited. The battery voltage acquisition unit
The voltage at the connection point between the positive electrode and the negative electrode among the plurality of secondary batteries connected in series is transferred to the pair of the first and second voltage detectors corresponding to the secondary battery on the high potential side of the connection point. Including a plurality of voltage supply paths that supply a positive voltage to the pair of the first and second voltage detectors corresponding to the secondary battery on the low potential side of the connection point,
The voltage switching unit is
Including a selector switch capable of selecting every other voltage supply path;
The first reference voltage acquisition unit includes:
When acquiring the first reference voltage of the second voltage detector that is supplied as a negative voltage, the voltage of the voltage supply path that can be selected by the selector switch, the second voltage detector and the A voltage supply path that supplies the negative voltage to the first voltage detection section paired with the second voltage detection section is selected, and the voltage of the selected voltage supply path is gradually reduced by the inspection voltage generation section. By gradually increasing the supply voltage to the first and second voltage detectors of the selected pair,
When acquiring the first reference voltage of the second voltage detector supplied with the voltage of the voltage supply path selectable by the selector switch as the positive side voltage, the second voltage detector and the A voltage supply path for supplying the positive voltage to the first voltage detection section paired with the second voltage detection section is selected, and the voltage of the selected voltage supply path is gradually increased by the inspection voltage generation section. 5. The battery protection circuit according to claim 4, wherein the supply voltage to the first and second voltage detection units of the selected pair is gradually increased. Detected by the second voltage detection unit during the normal mode when the charging voltage is supplied by a charging circuit that supplies a charging voltage for charging the secondary battery according to an instruction from the outside When the terminal voltage of the secondary battery exceeds an upper limit voltage set in advance as the upper limit of the charging voltage, the battery further includes a charging voltage adjusting unit that outputs an instruction to reduce the charging voltage to the charging circuit. The battery protection circuit according to claim 1 or 2, characterized in that: Detected by the second voltage detector during the normal mode when the charging voltage is supplied by a charging circuit that supplies a charging voltage for charging the plurality of secondary batteries according to an instruction from the outside A charging voltage adjustment that outputs an instruction to the charging circuit to lower the charging voltage when a maximum voltage of the plurality of both-end voltages exceeds a predetermined upper limit voltage as an upper limit of the charging voltage. The battery protection circuit according to claim 3, further comprising a unit. A switching element provided in series in the charging path of the secondary battery;
A thermal fuse provided in series with the charging path of the secondary battery;
A heater for fusing the thermal fuse;
The first protection control unit includes:
Prohibiting charging of the secondary battery by fusing the thermal fuse with the heater;
The second protection controller is
Prohibiting charging of the secondary battery by turning off the switching element;
The second reference voltage setting unit includes:
The said 2nd reference voltage is set by subtracting the said differential voltage from the 1st reference voltage acquired by the said 1st reference voltage acquisition part, The any one of Claims 1-7 characterized by the above-mentioned. Battery protection circuit. The battery protection circuit according to any one of claims 1 to 8,
A battery pack comprising the secondary battery.

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