JP2012009327A - Battery pack and power tool having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery pack consisting of five battery blocks and capable of stably protecting the battery blocks from an over-voltage, an over-discharge and an overload without requiring a complicated circuit, and to provide a power tool.SOLUTION: The battery pack includes: a battery cell set 31 obtained by connecting five lithium ion battery cells 31A to 31E in series; and a protection IC32 for detecting each battery voltage of all the battery cells 31A to 31E constituting the battery cell set 31.

Description

  The present invention relates to a battery pack composed of a secondary battery and an electric tool including the battery pack.

  In recent years, a further increase in capacity and weight has been demanded as a secondary battery serving as a drive source for electric tools. In response to this demand, lithium ion batteries having a high output density have become widespread.

  Lithium-ion batteries may be overcharged, overdischarged, overloaded, etc., resulting in deterioration or failure of the battery. Generally, a dedicated protection IC or microcomputer is installed in the battery pack to overcharge the battery. -Overdischarge / overload is monitored, and a dedicated protection IC or microcomputer is used when the battery voltage of the lithium ion battery falls below or above the specified voltage value, or when a current exceeding the specified value flows through the lithium ion battery. A countermeasure is taken for safety, such as outputting a signal from, and blocking the charge / discharge path based on the output signal.

JP-A-6-141479

  When protecting a battery pack using a protection IC dedicated to lithium ion batteries, there is a limit to the number of cells (number of cells) that can be monitored, and each cell of a battery pack configured with cells exceeding the limit number There are various problems in monitoring the condition.

  Currently, protection ICs are mainly used for voltage monitoring up to 4 cells. For example, when monitoring 5 cell batteries, ie 18V (3.6V / cell x 5 cells) battery pack, 4 cell protection IC and 1 cell The battery pack is protected by using two protection ICs. In such a method, a 4-cell protection IC and a 1-cell protection IC, for example, of 4 cells, four cells at the higher potential are monitored by the 4-cell protection IC, and the remaining one is used for 1-cell. It will be monitored by the protection IC. In this case, the ground level of the 4-cell protection IC is different from that of the 1-cell protection IC, that is, the ground of the 4-cell protection IC is the positive side of the fifth battery cell from the top with the lowest potential. Since the cell protection IC has the same fifth negative side, a circuit for adjusting the ground level is required.

  In addition, for example, when the logic of a signal output from the protection IC at the time of overvoltage (at the time of overcharge) differs depending on the protection IC, a circuit for matching the logic is also necessary. Furthermore, if there is a difference in current consumption between the two protection ICs, it is necessary to correct this. Thus, when two or a plurality of protection ICs are used, a complicated circuit is required.

  Then, this invention aims at providing the battery pack which can protect a battery cell from overdischarge etc. without requiring a complicated circuit, the electric tool provided with a battery pack, and the charger which charges a battery pack. To do.

  In order to achieve the above object, the present invention includes a battery cell set in which five lithium ion battery cells are connected in series, and a protection IC for detecting each battery voltage of all the battery cells constituting the battery cell set. It is characterized by that.

  By adopting such a configuration, five battery cells can be monitored by one protection IC, so that a lithium ion battery cell can be reliably protected with a simple configuration without requiring a complicated circuit.

  Here, it is preferable that the protection IC outputs an overcharge signal when detecting that even one of the voltages of the battery cells constituting the battery cell set has reached an overcharge threshold. Further, it is preferable that the protection IC outputs an overdischarge signal when detecting that even one of the voltages of the battery cells constituting the battery cell set has reached an overdischarge threshold.

  By adopting such a configuration, it is possible to reliably detect that the battery cell is overdischarged or overcharged, and thus it is possible to suppress deterioration of the battery cell.

  Further, it has a current detection means for detecting a current flowing through the battery cell set, and the protection IC detects an overcurrent signal when detecting that the current value from the current detection means exceeds an overcurrent threshold. Is preferably output. By adopting such a configuration, it is possible to reliably detect that an overcurrent has flowed through the battery pack, and thus it is possible to suppress deterioration of the battery cell.

  Further, the current detection means is preferably a shunt resistor connected to the negative side of the battery cell having the lowest potential in the battery cell set, and the protection IC preferably detects a current based on a potential difference generated in the shunt resistor. . With such a configuration, it is possible to detect the load current with high accuracy without being affected by the voltage variation of the battery cell set due to the load variation.

  Moreover, it is preferable to have a common terminal to which the overdischarge signal and the overcurrent signal output from the protection IC are transmitted. With such a configuration, the number of terminals of the battery pack can be reduced, and the cost can be suppressed.

  A motor, a battery pack serving as a drive source of the motor, a trigger for turning on / off power supply from the battery pack to the motor, and a switch element provided between the motor and the battery pack; The battery pack is the battery pack according to any one of claims 1 to 6, wherein the switch element is preferably cut off by a signal from a protection IC of the battery pack. With this configuration, the switch element is cut off by a signal from the protection IC, so that the discharge path can be cut off when the battery cell is overdischarged or overcurrent, thus protecting the battery cell. can do.

  According to the present invention, a battery cell can be stably protected from at least one of overvoltage, overdischarge, and overload without requiring a complicated circuit. In particular, it is most effective in protecting a lithium ion battery pack composed of five battery blocks.

It is a side view which shows the electric tool used as this invention. It is a circuit block diagram of the battery pack which becomes this invention. It is a circuit block diagram of the battery pack in the examination stage.

  First, the power tool of the present invention will be described with reference to FIG. The impact driver 1 serving as a cordless electric tool includes a main body 1a that houses a motor and a speed reduction mechanism (not shown), and a handle 1b that extends from the main body and is held by an operator. A chuck 2 is provided on one end side of the main body 1a for mounting a bit serving as a tip tool (not shown). A battery pack 30 serving as a motor drive source (not shown) is detachably attached to the handle portion 1b by a latch mechanism 30a. The battery pack 30 is composed of a lithium ion battery having a voltage of 3.6 V per cell, and is configured such that five lithium ion batteries (unit cells or cells) are connected in series to obtain a rated voltage of 18 V. . Furthermore, as will be described later, the battery pack 30 monitors the battery state of each lithium ion battery cell, and outputs an abnormal signal when the battery cell is in an abnormal state, that is, overdischarge, overcharge, or overload. A protection IC for stopping the motor is provided.

  The impact driver 1 rotates a bit (not shown) attached to the chuck 2 by supplying electric power from the battery pack 30 to a motor (not shown) by the operator holding the handle 1B and operating the trigger 3 (ON). Can be screwed. The motor is configured so that the rotation direction can be selected by the forward / reverse selector switch 4. A hook 5 is attached to the handle portion 1b so that the impact driver 1 can be hooked on an operator's belt or the like.

  Next, the battery pack according to the present invention and the battery pack at the examination stage will be described with reference to FIGS. FIG. 2 is a circuit block diagram of a battery pack according to the present invention, in which five lithium ion battery cells of 3.6 V / cell are connected in series, and a rated voltage of 18 V can be obtained. FIG. 3 is a circuit block diagram of the battery pack in the examination stage, and a rated voltage of 18 V can be obtained as in FIG.

  First, before describing the battery pack according to the present invention, the battery pack at the examination stage will be described with reference to FIG. The battery pack of FIG. 3 is provided with two protection ICs, a 4-cell protection IC and a 1-cell protection IC, in order to protect 5 lithium ion battery cells from overvoltage, overdischarge, and overcurrent. Further, a shunt resistor serving as a current detection means for overload protection is provided between the plus terminal of the battery cell having the highest potential and the load (plus terminal of the battery pack).

  The battery pack 10 has a battery cell set 11 including five lithium ion battery cells 11A to 11E having a rated voltage of 3.6V per cell, and the rated voltage is 18V. The battery cell set 11 includes five lithium ion battery cells 11A, 11B, 11C, 11D, and 11E connected in series in the order of connection from the highest potential. Two or more battery cells may be connected in parallel to each battery cell, and connecting two in parallel doubles the battery capacity. Here, the case where the battery cells are not connected in parallel as shown in FIG. 3 and the case where two or more battery cells are connected in parallel are collectively referred to as a battery block.

  The 4-cell protection IC 12 monitors the voltages of the four battery blocks of the battery blocks 11A to 11D in descending order of the potential among the battery blocks 11A to 11E of the battery cell set 11, and the plus terminal and the load of the battery block 11A. The overload is monitored by detecting a voltage drop between the shunt resistor 14 provided between the (plus terminals 20 and 21 of the battery pack 10). The protection IC 12 determines that it is an overvoltage (overcharge) when at least one voltage in the four battery blocks to be monitored reaches a first predetermined voltage or more, and determines the first predetermined signal (overvoltage signal). ) Is output. Further, when at least one voltage in the four battery blocks to be monitored reaches a second predetermined voltage or less, it is determined that the battery is overdischarged, and a second predetermined signal (overdischarge signal) is output. It has a configuration. In addition, when an overload (overcurrent) is detected by the shunt resistor 14, a third predetermined signal (overload signal) is output.

  The 1-cell protection IC 13 monitors the voltage of the battery block 11E. Moreover, when the voltage of the battery block 11E to be monitored reaches a third predetermined voltage or higher, it is determined that the voltage is overvoltage (overcharge), and a fourth predetermined signal (overvoltage signal) is output. . Furthermore, when the voltage of the battery block 11E to be monitored reaches a fourth predetermined voltage or less, it is determined that the battery is overdischarged, and a fifth predetermined signal (overdischarge signal) is output.

  As described above, the current detection unit 14 is a shunt resistor that is provided between the battery block 11A and the load and detects the load current. The temperature sensing element 17 is provided in the vicinity of the battery cell set 11 and is configured by a thermistor or the like for monitoring the battery temperature. The identification resistor 18 is provided to identify the type of the battery cell. For example, the battery pack (14.4V) constituted by four battery blocks and the battery pack (18V) constituted by five battery blocks are provided. When both are connected to a rechargeable charger, it is necessary to perform charge control according to the battery type (number of battery blocks, etc.) identified by the identification resistor 18. The thermal protector 19 is provided in the vicinity of the battery cell set 11 in order to protect the battery cells from overcurrent, abnormally high temperature, and the like when the battery pack 11 is charged. For example, when an overcurrent flows into the battery cell due to some failure of the charger, the thermal protector provided near the battery becomes hot as the battery becomes hot. And when a certain predetermined temperature is reached, a thermal protector will be in an open state, A current path (charge path) can be interrupted | blocked and a battery cell can be protected.

  The terminal 20 is a discharge terminal that connects a plus terminal of the battery cell set 11 (a plus terminal of the battery block 11A) and a load such as a motor of an electric tool (for example, the impact driver 1) connected to the battery pack 10. The terminal 21 is a charging terminal for connecting a plus terminal of the battery cell set 11 (a plus terminal of the battery block 11A) and a plus terminal of a charger (not shown). That is, the battery pack 10 has a configuration including two plus terminals.

  The terminal 22 is a discharge stop signal terminal for transmitting a signal for stopping discharge from the protection ICs 12 and 13 to the power tool 1 side at the time of overdischarge and overload. The electric power tool 1 is configured to receive a discharge stop signal and cut off a discharge path (current path). For example, the switch element 6 such as an FET is provided in the discharge path between the motor and the battery pack 10 in the handle portion 1b, and the discharge path is interrupted by turning off the FET 6 by receiving a discharge stop signal. Is configured to do. A terminal 23 is a charge stop signal terminal for transmitting a signal for stopping charging from the protection ICs 12 and 13 to the charger side during overcharge. The charger is configured to receive a charge stop signal and to block the charging path. For example, a switching element such as a relay is provided in the charging path, and the charging path is blocked by turning off the relay or the like by receiving a charging stop signal.

  The terminal 24 is a temperature detection terminal for transmitting temperature information of the battery cell based on the thermistor 17 which is a temperature sensitive element to the charger. The charger side is configured to stop charging when it is determined that the battery pack (battery cell) is at a high temperature when the battery temperature detected via the temperature detection terminal 24 reaches a predetermined value or more. The temperature detection terminal 24 is connected to the charger but not to the electric tool. The terminal 25 is a battery type detection terminal for transmitting battery type information based on the identification resistor 18 to the charger side. The charger side is configured to set a charging method according to the battery type information detected via the battery type determination terminal 25. The terminal 26 is a minus terminal and is connected to the electric tool 1 and the minus terminal of the charger.

  At the time of overcharge, a predetermined signal (overcharge signal) is output from the 4-cell protection IC 12 or the 1-cell protection IC 13, but the ground of the 4-cell protection IC 12 is fourth from the highest potential. The potential of the positive terminal of the battery block 11D, and the ground of the protection IC 13 for one cell is the potential of the negative terminal of the battery block 11E having the lowest potential. On the other hand, as described above, the charger is configured to receive a signal from the protection IC 12 and / or the protection IC 13 at the time of overcharging, but the ground line of the charger is connected to the negative terminal 26. This is a potential of the negative terminal of the battery block 11E. As described above, since the ground of the 4-cell protection IC 12 that outputs the overcharge signal and the charger on the receiving side are different, the first additional circuit 15 for adjusting the ground level is required.

  In addition, a signal output during overcharge, overdischarge, or overload is, for example, a high signal or a low signal. The logic of this signal may differ depending on the protection IC. . On the other hand, the logic in the tool and the charger that receives the signal is naturally one, such as a high signal during overcharge. That is, when the logics of the 4-cell protection IC 12 and the 1-cell protection IC 13 are different, the second additional circuit 16 is required to match the logic. Also, the current consumed by different protection ICs is different. Since the difference in current consumption causes voltage imbalance between battery cells, a separate circuit is required to correct this. Thus, when different types of protection ICs are used, the circuit configuration becomes complicated, which is disadvantageous in terms of installation location and cost associated with an increase in the number of components.

  Further, the protection IC generally has a function of protecting an overload to the battery cell. As described above, the shunt resistor 14 for detecting the load current is installed, and the shunt resistor 14 is installed. The value of the voltage drop of the shunt resistor 14 is detected by the protection IC 12 when the current flows through the current, and when the value exceeds a predetermined value, it is determined that the load is overloaded (overcurrent). At this time, the place where the shunt resistor 14 is installed becomes a problem. For example, as shown in FIG. 3, consider a case where the shunt resistor 14 is provided between the plus terminal of the battery block 11 </ b> A having the highest potential in the battery cell set 11 and the load. In the case of a device such as a power tool that has a particularly heavy load fluctuation and a large current flow, the voltage fluctuation of the battery cell set 11 is severe, and the potential of the positive terminal of the battery block 11A having the highest potential fluctuates. For this reason, the potential between both ends of the shunt resistor 14 also fluctuates greatly. In such a detection, it is desirable to detect the fluctuation on the other end side at a position where the one end side of the shunt resistor 14 does not fluctuate. However, when both ends of the shunt resistor 14 fluctuate as shown in FIG. Is disadvantageous in terms of stability of load current detection.

  In contrast, the present invention improves the complexity and cost of the circuit configuration and the lack of stability of load current detection, and can stably perform overcurrent detection without complicating the circuit configuration. And a power tool can be provided. Of course, overcharge detection and overdischarge detection can also be performed accurately. An embodiment according to the present invention will be described below with reference to FIG.

  The battery pack 30 has a battery cell set 31 including five (5 cells) of lithium ion battery cells 31A to 31E having a rated voltage of 3.6V per cell, and the rated voltage is 18V. The battery cell set 31 includes five lithium ion battery blocks 31A, 31B, 31C, 31D, and 31E in the order of connection from the higher potential. Here, the battery block has a configuration in which one and two or more battery cells are connected in parallel.

  The battery pack 30 of the present invention is different from the battery pack 10 shown in FIG. 3 in that five battery blocks are monitored by one protection IC. The protection IC 32 for the lithium ion battery monitors battery states, for example, battery voltages, of the five battery blocks 31A to 31E of the battery cell set 31. That is, the protection IC 32 is a protection IC for 5 cells. Further, the protection IC 32 detects a load current, that is, an overload, by detecting a voltage drop of the shunt resistor 33 provided between the negative terminal of the battery block 31E and the load (negative terminal of the battery pack). The protection IC 32 determines that the voltage is overvoltage (overcharge) when at least one voltage in the five battery blocks to be monitored reaches a predetermined voltage or higher, and outputs a predetermined signal, that is, an overvoltage signal. It has become. Further, when at least one of the five battery blocks to be monitored reaches a predetermined voltage or less, it is determined that the battery is overdischarged, and a predetermined signal, that is, an overdischarge signal is output. Further, when an overload (overcurrent) is detected by the shunt resistor 33, a predetermined signal, that is, an overload signal is output.

  As described above, the current detection means 33 is a shunt resistor that is provided between the battery block 31E and the load and detects an overload current. The temperature sensing element 34 is provided in the vicinity of the battery cell set 31 and is configured by a thermistor or the like for monitoring the battery temperature. The identification resistor 35 is provided to identify the type of battery cell. For example, the identification resistor 35 is a charger that can charge both a battery pack composed of four battery blocks and a battery pack composed of five battery blocks. When connected, it is necessary to perform charge control according to the battery type (number of battery blocks, etc.) identified by the identification resistor 35. The thermal protector 36 is provided in the vicinity of the battery cell set 31 in order to protect the battery cells from overcurrent and abnormally high temperature when the battery pack 30 is charged. For example, when an overcurrent flows into the battery cell due to some failure of the charger, the thermal protector provided near the battery becomes hot as the battery becomes hot. Then, when the battery cell (battery cell set 31) reaches a certain temperature, the thermal protector 36 is opened, so that the current path (charging path) can be cut off and the battery cell can be protected.

  The terminal 37 is a discharge terminal for connecting a plus terminal of the battery cell set 31 (a plus terminal of the battery block 31 </ b> A) and a load such as a motor of the electric tool 1. The terminal 38 is a charging terminal for connecting a positive terminal of the battery cell set 31 (a positive terminal of the battery block 31A) and a positive terminal of a charger (not shown). The battery pack 30 in the present embodiment has a configuration including two plus terminals for charging and discharging, but may be one.

  The terminal 39 is a discharge stop signal terminal for transmitting a signal for stopping the discharge from the protection IC 32 to the power tool 1 side at the time of overdischarge and overload. The electric power tool 1 is configured to receive a discharge stop signal and cut off a discharge path (current path). For example, the switch element 6 such as an FET is provided in the discharge path between the motor and the battery pack 30 in the handle portion 1b, and the discharge path is interrupted by turning off the FET 6 by receiving a discharge stop signal. Is configured to do. The terminal 40 is a charge stop signal terminal for transmitting a signal for stopping charging from the protection IC 32 to the charger side during overcharge. The charger is configured to receive a charge stop signal and to block the charging path. For example, a switching element such as a relay is provided in the charging path, and the charging path is blocked by turning off the relay or the like by receiving a charging stop signal.

  The terminal 41 is a temperature detection terminal for transmitting temperature information of the battery cell based on the thermistor 34 which is a temperature sensitive element to the charger. The charger side is configured to stop charging when it is determined that the battery pack (battery cell) is at a high temperature when the battery temperature detected via the temperature detection terminal 41 reaches a predetermined value or more. Although the temperature detection terminal 41 is connected to the charger, it is not connected to the power tool 1. The terminal 42 is a battery type detection terminal for transmitting battery type information based on the identification resistor 35 to the charger side. The charger side is configured to set a charging method according to battery type information detected via the battery type discrimination terminal 42. The terminal 43 is a minus terminal and is connected to the electric tool 1 and the minus terminal of the charger.

  When charging such a battery pack 30, the charging terminal (plus terminal) 38, the minus terminal 43, the charging signal transmission terminal 40, the temperature detection terminal 41, and the battery type detection terminal 42 of the battery pack 30 correspond to the charger. Connect to the terminal. The protection IC 32 monitors the voltage of each battery block of the battery cell set 31, and if one of the battery blocks detects that the voltage exceeds the predetermined voltage (overvoltage threshold), the protection IC 32 charges from the charge stop signal terminal. The overcharge is prevented by outputting a stop signal, that is, an overvoltage signal and cutting off the charging path. Further, when the battery temperature becomes high, a high temperature signal is output from the temperature detection terminal to cut off the charging path. The charger monitors the overall voltage of the battery cell set 31, and is configured to stop charging even when the overall voltage exceeds the overcharge threshold.

  On the other hand, when the battery pack 30 is connected to the power tool, the discharge terminal (plus terminal) 37, the minus terminal 43, and the discharge stop signal transmission terminal 39 of the battery pack 30 are connected to corresponding terminals of the power tool 1. By operating the trigger 3 of the electric power tool 1, electric power is supplied from the battery pack 30 (battery cell set 31) to the motor of the electric power tool 1, and the motor rotates. At this time, the battery state, that is, the battery voltage of the five battery blocks 31A to 31E of the battery cell set 31 is monitored by one protection IC 32. When the protection IC 32 determines that one of the battery blocks is in an overdischarged state, the protection IC 32 outputs a discharge stop signal to the discharge stop signal terminal 39 and is connected to the discharge stop signal terminal 39 on the electric tool 1 side terminal. A switch stop signal, for example, an FET connected in series with the motor is shut off by inputting a discharge stop signal. As a result, the discharge path is interrupted, and overdischarge of the battery cell can be prevented.

  Further, the protection IC 32 detects the current flowing through the battery cell set 31 by a shunt resistor 33 provided between the minus terminal of the lowest battery block 31E of the battery cell set 31 and the minus terminal of the battery pack 30. As described above, in the case of a device such as the electric power tool 1 where the load fluctuation is particularly large and the flowing current is large, the voltage fluctuation of the battery cell set 31 is severe. For this reason, by providing the shunt resistor 33 on the negative terminal side of the battery pack 30, the load current can be stably detected without being affected by the voltage fluctuation of the battery cell set 31 even when the load fluctuation is severe. can do.

  As described above, according to the present invention, in a battery pack having a battery voltage of 18 V, that is, five battery blocks, all the battery blocks are monitored by one protection IC 32. Therefore, as shown in FIG. This eliminates the need for an additional circuit for adjusting the ground level, which is necessary when the protective IC is used. Furthermore, an additional circuit for matching the logic of output signals output from two or more protection ICs is not required. In addition, a circuit for correcting the voltage imbalance between the battery cells due to the consumption current generated in two or more different types of protection ICs is also unnecessary. Therefore, compared with the battery pack of FIG. 3, the present invention can reduce the number of parts of the battery pack, so that the cost of parts can be reduced, and the shunt resistor for current detection has a ground line of the battery pack 30. Therefore, stable current detection can be realized without being affected by voltage fluctuations.

  As described above, a battery pack comprising lithium ion battery cells is provided with a protection circuit for preventing overcharge, overdischarge, overload, etc., but instead of a protection IC dedicated to lithium ion battery cells. It is also possible to use a microcomputer.

  As an overcharge prevention method, monitoring is generally performed so that the voltage of a 3.6 V rated lithium-ion battery cell per cell does not exceed 4.25 V per cell (overcharge threshold). On the other hand, when charging with constant current / constant voltage control, which is a general method for charging lithium ion battery cells, it is necessary to control the charging voltage with high accuracy around 4.20 V per cell, The difference from the overcharge threshold of 4.25 V is very small. For this reason, when monitoring the voltage of the battery cell with respect to the overcharge threshold of 4.25 V determined to be overcharge, it is necessary to detect the cell voltage with extremely high accuracy. When high-accuracy voltage monitoring is performed by a microcomputer, it is necessary to devise a method for correcting detection accuracy and peripheral circuit variations at the A / D port of the microcomputer, and the circuit tends to be complicated.

  On the other hand, in the present invention, since voltage monitoring is performed by the protection IC, high-accuracy voltage monitoring can be performed without providing an additional circuit. In addition, although embodiment demonstrated the battery pack which has five lithium ion battery blocks, it is not limited to this. Further, the switch element 6 may be provided not in the electric power tool 1 but in the battery pack 30.

  1 is an electric tool, 30 is a battery pack, 31 is a battery cell set, 32 is a protection IC for 5 cells, 33 is a shunt resistor, 34 is a thermistor, 35 is an identification resistor, 36 is a thermal protector, 37 is a discharge terminal (plus terminal) , 38 is a charge terminal (plus terminal), 39 is a discharge stop signal transmission terminal, 40 is a charge stop signal transmission terminal, 41 is a temperature detection terminal, 42 is a battery type detection terminal, and 43 is a minus terminal.

Claims (7)

A battery cell set in which five lithium ion battery cells are connected in series;
A battery pack comprising: a protection IC for detecting each battery voltage of all battery cells constituting the battery cell set.   The said protection IC outputs an overcharge signal, when it detects that the voltage of one battery cell which comprises the said battery cell group has reached the overcharge threshold value. Battery pack.   The protection IC outputs an overdischarge signal when it detects that even one of the voltages of the battery cells constituting the battery cell set has reached an overdischarge threshold. Item 3. The battery pack according to Item 2. Current detection means for detecting current flowing in the battery cell set;
4. The protection IC outputs an overcurrent signal when detecting that the current value from the current detection means exceeds an overcurrent threshold. The battery pack described. The current detection means comprises a shunt resistor connected to the negative side of the battery cell having the lowest potential of the battery cell set,
The battery pack according to claim 4, wherein the protection IC detects a current based on a potential difference generated in the shunt resistor.   6. The battery pack according to claim 3, further comprising a common terminal to which the overdischarge signal and the overcurrent signal output from the protection IC are transmitted. A motor,
A battery pack as a drive source of the motor;
A trigger for turning on and off the power supply from the battery pack to the motor;
A switching element provided between the motor and the battery pack;
The battery pack is the battery pack according to any one of claims 1 to 6,
A power tool characterized in that the switch element is cut off by a signal from a protection IC of the battery pack.