A backflush protection circuit for charging a power battery

Abstract

The application relates to a backflow protection circuit for charging a power battery, which comprises a charging management module, a primary protection module, a secondary protection module and a charging sampling module, wherein the charging sampling module is connected to the battery pack to be charged to obtain a voltage signal when the battery pack is charged and is output to the charging management module; the input end of the primary protection module is connected to the positive end PACK+ of the external charging circuit, and the output end of the protection module is connected to the charging management module, which is used for judging whether the voltage input of the positive end of the external charging circuit is abnormal; the input end of the secondary protection module is connected to the positive end of the battery pack, and the output end of the secondary protection module is connected to the charging management module, which is used for obtaining an output signal of the battery pack. The primary protection module and the secondary protection module can protect the backflow protection circuit for the power battery.

Description

Technical Field

[0001] This application relates to the field of power battery charging management technology, and in particular to a backflush protection circuit for power battery charging. Background Technology

[0002] With the increasing popularity of new energy vehicles, the usage of power batteries is also increasing day by day. When conducting battery testing or maintenance, there is a risk that the positive and negative terminals of the battery pack may be reversed with the external charging circuit. Reverse connection can easily lead to damage to the BMS (Battery Management System). Therefore, there is an urgent need for a circuit that can protect the BMS system after reverse connection. Utility Model Content

[0003] Therefore, it is necessary to provide a reverse charge protection circuit for power battery charging to address the above-mentioned technical problems, including a charging management module, a primary protection module, a secondary protection module, and a charging sampling module, wherein: The charging sampling module is connected to the battery pack being charged to obtain the voltage signal of the battery pack during charging and output it to the charging management module. The primary protection module has its input terminal connected to the positive terminal PACK+ of the external charging circuit, and its output terminal connected to the charging management module. It is used to determine whether there is an abnormality in the voltage input of the positive terminal of the external charging circuit. The secondary protection module has its input connected to the positive terminal of the battery pack and its output connected to the charging management module to obtain the output signal of the battery pack.

[0004] In one embodiment, the primary protection module includes a reverse connection protection unit, which includes a reverse connection protection MOSFET Q5. The drain of the reverse connection protection MOSFET Q5 is connected to the charging management module, the gate of the reverse connection protection MOSFET Q5 is connected to a current-limiting resistor, the other end of the current-limiting resistor is connected to a common ground terminal, and the source of the reverse connection protection MOSFET Q5 is connected to the positive terminal PACK+ of the external charging circuit.

[0005] In one embodiment, the primary protection module includes a charging MOSFET and a discharging MOSFET. The source of the charging MOSFET is connected to the secondary protection module, the drain of the charging MOSFET is connected to the drain of the discharging MOSFET, and the drains of the charging MOSFET and the discharging MOSFET are connected to the charging management module. The source of the discharging MOSFET is connected to the positive terminal PACK+ of the external charging circuit. A cutoff resistor is provided between the gate and source of both the charging MOSFET and the discharging MOSFET. The gate of the charging MOSFET is connected to the charging management module, and the gate of the discharging MOSFET is connected to the charging management module.

[0006] In one embodiment, a protection capacitor C1 and a protection capacitor C2 are connected in series between the source of the charging MOSFET and the source of the discharging MOSFET.

[0007] In one embodiment, the charging management module uses a charging management IC of model BQ4050 or BQ40Z50.

[0008] In one embodiment, the drains of both the charging MOSFET and the discharging MOSFET are connected to the VCC pin of the charging management IC. A drive resistor is provided between the gate of the charging MOSFET and the charging management IC. The gate of the charging MOSFET is connected to one end of the drive resistor, and the other end of the drive resistor is connected to the CHG pin of the charging management IC. A drive resistor is also provided between the discharging MOSFET and the charging management IC. The gate of the discharging MOSFET is connected to one end of the drive resistor, and the other end of the drive resistor is connected to the DSG pin of the charging management IC.

[0009] In one embodiment, a precision resistor with a resistance of 10Ω is further provided between the charging MOSFET and / or the discharging MOSFET and the driving resistor.

[0010] In one embodiment, the secondary protection module includes a three-terminal fuse, a fusible MOSFET, and a secondary protection IC. The first terminal of the three-terminal fuse is connected to the positive terminal of the battery pack, the third terminal is connected to the primary protection module, the second terminal is connected to the drain of the fusible MOSFET, the source of the fusible MOSFET is connected to the negative terminal of the battery pack, the gate of the fusible MOSFET is connected to the FUSE pin of the charging management IC, and the gate of the fusible MOSFET is also connected to the secondary protection IC.

[0011] In one embodiment, the secondary protection IC is model MM3284. The VSS pin of the secondary protection IC is connected to the negative terminal of the battery pack, the V1, V2, and V3 terminals of the secondary protection IC are respectively connected to the three voltage sampling points of the battery pack, and the VDD pin of the secondary protection IC is connected to the positive terminal of the battery pack.

[0012] In one embodiment, the reverse charge protection circuit for charging the power battery further includes a current detection module. The current detection module includes a sampling resistor, a differential resistor R27, a differential resistor R28, and a differential capacitor C11. The two ends of the sampling resistor are connected to the differential resistors R27 and R28, respectively. The other end of the differential resistor R27 is electrically connected to the SRP pin of the charging management IC. The other end of the differential resistor R28 is connected to the SRN pin of the charging management IC. The differential capacitor C11 is connected in series between the SRP pin and the SRN pin of the charging management IC. One end of the sampling resistor is connected to the negative terminal of the battery pack, and the other end of the sampling resistor is connected to the common ground.

[0013] The aforementioned reverse charge protection circuit for power battery charging, by setting a primary protection module and a secondary protection module, can protect the power battery from reverse charge. In particular, the primary protection module includes a reverse connection protection unit, which, when a reverse connection occurs, prevents the external charging circuit's negative terminal (PACK+) from being mistakenly connected, causing the reverse connection protection MOSFET Q5 to meet the conduction condition. This grounds the negative terminal of the external charging circuit, preventing large current from entering subsequent circuits and protecting the circuit during reverse connection. Furthermore, since the other end of the current-limiting resistor is connected to the common ground, the gate of the reverse connection protection MOSFET Q5 always maintains the same potential as the common ground, ensuring correct triggering during reverse connection. This ensures that the reverse connection protection function remains effective for a long time and prevents the reverse connection protection function from failing due to incorrect grounding of the reverse connection protection MOSFET (e.g., connected to the negative output terminal of the power battery that is not connected to the common ground). Attached Figure Description

[0014] Figure 1 This is a topology diagram of a reverse charge protection circuit for power battery charging in one embodiment.

[0015] Figure 2 This is a schematic diagram of a reverse charge protection circuit for power battery charging in one embodiment.

[0016] Figure 3 This is a partial circuit diagram of the primary protection module in one embodiment.

[0017] Figure 4 This is a partial circuit diagram of the secondary protection module in one embodiment.

[0018] Figure 5 This is a partial circuit diagram of the charging sampling module in one embodiment.

[0019] Figure 6 This is a partial circuit diagram of the current detection module in one embodiment.

[0020] Reference numerals in the attached diagram: 1. Primary protection module; 11. Reverse connection protection unit; 2. Secondary protection module; 3. Charging sampling module; 4. Current detection module; 5. Charging management module. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] In one embodiment, such as Figure 1As shown, a reverse charge protection circuit for power battery charging is provided, including a charging management module, a primary protection module, a secondary protection module, a charging sampling module, and a current detection module, wherein: The charging sampling module is connected to the battery pack being charged to obtain the voltage signal of the battery pack during charging and output it to the charging management module. The primary protection module has its input terminal connected to the positive terminal PACK+ of the external charging circuit, and its output terminal connected to the charging management module. It is used to determine whether there is an abnormality in the voltage input of the positive terminal of the external charging circuit. The secondary protection module has its input connected to the positive terminal of the battery pack and its output connected to the charging management module to acquire the output signal of the battery pack. One end of the current sensing module is connected to the negative terminal of the battery pack, and the other end of the current sensing module is connected to the common ground.

[0023] After the aforementioned anti-reverse protection circuit for charging the power battery is powered on, the charging sampling module will sample the input or output voltage of the battery pack during operation and output it to the charging management module. The primary protection module and the secondary protection module are used to protect the anti-reverse protection circuit for charging the power battery powered by the battery or an external power source. The current monitoring module is used to sample the charging and / or discharging current of the battery pack and output it to the charging management module so that the charging management module can monitor the charging and discharging status of the power battery.

[0024] The charging management module uses a charging management IC of model BQ4050 or BQ40Z50. Specifically, in this embodiment, BQ4050 is selected as the charging management IC.

[0025] In one specific implementation, such as Figure 2 As shown, the primary protection module includes a charging MOSFET and a discharging MOSFET. The source of the charging MOSFET is connected to the secondary protection module, and the drain of the charging MOSFET is connected to the drain of the discharging MOSFET. The drains of the charging MOSFET and the discharging MOSFET are connected to the charging management module, and the source of the discharging MOSFET is connected to the positive terminal PACK+ of the external charging circuit. A cutoff resistor is provided between the gate and source of both the charging MOSFET and the discharging MOSFET. The gate of the charging MOSFET is connected to the charging management module, and the gate of the discharging MOSFET is connected to the charging management module.

[0026] Furthermore, the charging MOSFETs include charging MOSFETs Q1 and Q3, and the discharging MOSFETs include discharging MOSFETs Q2 and Q4. The sources of charging MOSFETs Q1 and Q3 are connected to the secondary protection module, while the sources of discharging MOSFETs Q2 and Q4 are connected to the positive terminal PACK+ of the external charging circuit. Protection capacitors C1 and C2 are connected in series between the sources of charging MOSFETs Q1 and Q3 and the sources of discharging MOSFETs Q2 and Q4. The drains of charging MOSFETs Q1, Q3, Q2, and Q4 are connected to the same equipotential point and are connected to a resistor R14. The other end of resistor R14 is connected to the VCC terminal of the charging management IC. The charging MOSFETs Q1 and Q3 are connected to the charging management IC. A turn-off resistor R4 is provided between the source and gate of MOSFET Q3, and a turn-off resistor R1 is provided between the source and gate of discharge MOSFETs Q2 and Q4. The resistance values ​​of turn-off resistors R1 and R4 are set to 10MΩ to ensure that the charging or discharging MOSFETs can be smoothly turned off when the conduction condition is not met. A drive resistor R13 is provided between the gate of charging MOSFETs Q1 and Q3 and the CHG terminal of the charging management IC, and a drive resistor R15 is provided between the gate of discharging MOSFETs Q2 and Q4 and the DSG terminal of the charging management IC. The resistance values ​​of drive resistors R13 and R15 are both set to 5.1KΩ. Charging MOSFETs Q1, Q3, Q2, and Q4 have sufficient switching speed.

[0027] In some embodiments, an adjusting resistor R3 is connected in series between the gate of the charging MOSFET Q1 and the driving resistor R13; an adjusting resistor R8 is connected in series between the gate of the charging MOSFET Q3 and the driving resistor R13; an adjusting resistor R5 is connected in series between the gate of the discharging MOSFET Q2 and the driving resistor R15; and an adjusting resistor R9 is connected in series between the gate of the discharging MOSFET Q4 and the driving resistor R15. All adjusting resistors R3, R5, R8, and R9 are precision resistors with a resistance of 10Ω. By setting these adjusting resistors, the switching speed can be further improved, thereby enhancing the protection capability of the primary protection circuit for the reverse charge protection circuit used for charging the power battery.

[0028] In one specific implementation, such as Figure 3 As shown, the primary protection module includes a reverse connection protection unit, which includes a reverse connection protection MOSFET Q5. The drain of the reverse connection protection MOSFET Q5 is connected to the charging management module, and the gate of the reverse connection protection MOSFET Q5 is connected to a current-limiting resistor R16. The other end of the current-limiting resistor R16 is connected to the common ground terminal GND, and the source of the reverse connection protection MOSFET Q5 is connected to the positive terminal PACK+ of the external charging circuit.

[0029] In this embodiment, by setting a reverse connection protection MOSFET Q5, the source of the reverse connection protection MOSFET Q5 is connected to the positive terminal PACK+ of the external charging circuit, and the drain is connected to the charging management module. When the positive terminal PACK+ of the external charging circuit is correctly connected, the conduction condition is not met, and the discharge MOSFETs Q2 and Q4 can work normally. However, when the positive terminal PACK+ of the external charging circuit is reverse connected, that is, when a voltage of volt is applied, the reverse connection protection MOSFET meets the conduction condition and conducts, thereby short-circuiting the discharge MOSFETs Q2 and Q4, thus protecting the discharge MOSFETs and the subsequent circuits.

[0030] A resistor R2, a diode D1, a capacitor C14, and a capacitor C15 are also provided between the source of the reverse-connection MOSFET Q5 and the positive terminal PACK+ of the external charging circuit. One end of the resistor R2 is connected to the reverse-connection MOSFET Q5, and the other end of the resistor R2 is connected to the cathode of the diode D1. The anode of the diode D2 is electrically connected to the common ground terminal. The capacitors C14 and C15 are connected in series between the source of the reverse-connection MOSFET Q5 and the common ground terminal.

[0031] In one specific implementation, such as Figures 4-5As shown, the secondary protection module includes a three-terminal fuse F1, a fusible MOSFET Q6, and a secondary protection IC ICU2. The first terminal of the three-terminal fuse F1 is connected to the positive terminal B+ of the battery pack, the third terminal is connected to the source of charging MOSFET Q1 and / or charging MOSFET Q3, and the second terminal is connected to the drain of the fusible MOSFET. The source of the fusible MOSFET Q6 is connected to the negative terminal B- of the battery pack, and the gate of the fusible MOSFET Q6 is connected to the FUSE pin of the charging management IC ICU2. The gate of the fusible MOSFET is also connected to the secondary protection IC. A resistor R17 and a capacitor C6 are connected in series between the gate and source of the fusible MOSFET Q6. Specifically, in this embodiment, the secondary protection IC ICU2 is model MM3284. The VSS pin of the secondary protection ICU2 is connected to the negative terminal of the battery pack. The V1, V2, and V3 pins of the secondary protection ICU2 are connected to the three voltage sampling points of the battery pack, respectively. The VDD pin of the secondary protection ICU2 is connected to the positive terminal B+ of the battery pack. Specifically, a current-limiting resistor R6 is connected in series between the VDD pin of the secondary protection ICU2 and the positive terminal B+ of the battery pack. An isolation capacitor C3 is connected in series between the VDD pin of the secondary protection ICU2 and the negative terminal B- of the battery pack. In addition to the positive terminal B+ and the negative terminal B-, the battery pack also has three voltage sampling nodes: the primary voltage sampling node B1+, the secondary voltage sampling node B2+, and the tertiary voltage sampling node B3+. The primary voltage sampling node B1+ is electrically connected to the V1 pin of the secondary protection ICU2. Connect the first-level voltage sampling node B1+ and the V1 terminal of the second-level protection ICU2 with a current-limiting resistor R12 in series. Connect the second-level voltage sampling node B2+ and the V2 terminal of the second-level protection ICU2 with a current-limiting resistor R10 in series. Connect the third-level voltage sampling node B3+ and the V3 terminal of the second-level protection ICU2 with a current-limiting resistor R7 in series. Connect the V1 and V2 terminals of the second-level protection ICU2 with an isolation capacitor C5 in series. Connect the V2 and V3 terminals of the second-level protection ICU2 with an isolation capacitor C4 in series. Connect the VSS and V1 terminals of the second-level protection ICU2 with an isolation capacitor C7 in series. After the reverse charge protection circuit for the power battery is powered on, the secondary protection ICU2 monitors the output voltage of the battery pack's positive terminal B+, as well as the output voltages of the first-level voltage sampling node B1+, the second-level voltage sampling node B2+, and the third-level voltage sampling node B3+. When any of these voltages becomes abnormal, the 0V terminal of the secondary protection ICU2 outputs a high level to turn on the fusible MOSFET Q6, which in turn blows the three-terminal fuse F1, thereby protecting the charging MOSFETs Q1 and Q3 and the preceding circuit, thus playing the role of a protection circuit.

[0032] In addition, the first-level voltage sampling node B1+, the second-level voltage sampling node B2+, and the third-level voltage sampling node B3+ are also connected to the charging management IC. The VC1 terminal of the charging management IC is electrically connected to the first-level voltage sampling node B1+, and a current-limiting single-group resistor R30 is connected in series between the VC1 terminal and the first-level voltage sampling node B1+. The VC2 terminal of the charging management IC is electrically connected to the second-level voltage sampling node B2+, and a current-limiting single-group resistor R26 is connected in series between the VC2 terminal and the second-level voltage sampling node B2+. The VC3 terminal of the charging management IC is electrically connected to the third-level voltage sampling node B3+, and the VC3 terminal is connected in series with the third-level voltage sampling node B3+. A current-limiting single-group resistor R21 is connected in series between the + terminals. The VC4 terminal of the charging management IC is electrically connected to the positive terminal B+ of the battery pack, and a current-limiting single-group resistor R20 is connected in series between the VC4 terminal and the positive terminal B+ of the battery pack. An isolation capacitor C13 is connected in series between the negative terminal B- of the battery pack and the first-level voltage sampling node B1+. An isolation capacitor C12 is connected in series between the first-level voltage sampling node B1+ and the second-level voltage sampling node B2+. An isolation capacitor C10 is connected in series between the second-level voltage sampling node B2+ and the third-level voltage sampling node B3+. An isolation capacitor C9 is connected in series between the third-level voltage sampling node B3+ and the positive terminal B+ of the battery pack.

[0033] In one embodiment, such as Figure 6 As shown, the reverse charge protection circuit for power battery charging also includes a current detection module. The current detection module includes a sampling resistor, a differential resistor R27, a differential resistor R28, and a differential capacitor C11. The sampling resistor includes a sampling resistor RS1 and a sampling capacitor RS2 connected in parallel. The two ends of the sampling resistor are connected to the differential resistor R27 and the differential resistor R28, respectively. The other end of the differential resistor R27 is electrically connected to the SRP pin of the charging management IC. The other end of the differential resistor R28 is electrically connected to the SRN pin of the charging management IC. The differential capacitor C11 is connected in series between the SRP pin and the SRN pin of the charging management IC. One end of the sampling resistor connected to the differential resistor R27 is connected to the negative terminal B- of the battery pack. One end of the sampling resistor connected to the differential resistor R28 is connected to the common ground terminal GND.

[0034] Since the two ends of the sampling resistor are connected to the common ground GND and the negative terminal B- of the battery pack respectively, there is a potential difference between the common ground GND and the negative terminal B- of the battery pack. The direction of this potential difference is uncertain. Therefore, it is necessary to emphasize again the grounding state of the reverse connection protection MOSFET Q5 in the reverse connection protection unit. That is, the gate of the reverse connection protection MOSFET Q5 is connected to the current limiting resistor R16, and the other end of the current limiting resistor R16 is connected to the common ground GND. This connection method can keep the gate of the reverse connection protection MOSFET Q5 at zero potential. When a reverse connection occurs, the conduction condition of the reverse connection protection MOSFET Q5 can be met, and the reverse connection protection function can be successfully triggered. If the gate of the reverse connection protection MOSFET Q5 is connected to the negative terminal B- of the battery pack, and the negative terminal B- of the battery pack is negative relative to the common ground GND, then the reverse connection protection MOSFET Q5 may not meet the conduction condition, and the reverse connection protection function will not be successfully triggered, resulting in circuit damage. Therefore, connecting the other end of the current-limiting resistor to the common ground terminal ensures that the gate of the reverse-connection MOSFET Q5 always maintains the same potential as the common ground, thus guaranteeing that it can be correctly triggered in reverse connection and thereby realizing the protection circuit function.

[0035] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0036] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A reverse charge protection circuit for charging a power battery, characterized in that, It includes a charging management module, a primary protection module, a secondary protection module, and a charging sampling module, among which: The charging sampling module is connected to the battery pack being charged to obtain the voltage signal of the battery pack during charging and output it to the charging management module. The primary protection module has its input terminal connected to the positive terminal PACK+ of the external charging circuit, and its output terminal connected to the charging management module. It is used to determine whether there is an abnormality in the voltage input of the positive terminal of the external charging circuit. The secondary protection module has its input connected to the positive terminal of the battery pack and its output connected to the charging management module to acquire the output signal of the battery pack. The primary protection module includes a reverse connection protection unit, which includes a reverse connection protection MOSFET Q5. The drain of the reverse connection protection MOSFET Q5 is connected to the charging management module, the gate of the reverse connection protection MOSFET Q5 is connected to a current limiting resistor, the other end of the current limiting resistor is connected to the common ground terminal, and the source of the reverse connection protection MOSFET Q5 is connected to the positive terminal PACK+ of the external charging circuit. A resistor R2, a diode D1, a capacitor C14, and a capacitor C15 are also provided between the source of the reverse-connection MOSFET Q5 and the positive terminal PACK+ of the external charging circuit. One end of the resistor R2 is connected to the reverse-connection MOSFET Q5, and the other end of the resistor R2 is connected to the cathode of the diode D1. The anode of the diode D2 is electrically connected to the common ground terminal. The capacitors C14 and C15 are connected in series between the source of the reverse-connection MOSFET Q5 and the common ground terminal.

2. The reverse charge protection circuit for charging a power battery according to claim 1, characterized in that, The primary protection module includes a charging MOSFET and a discharging MOSFET. The source of the charging MOSFET is connected to the secondary protection module. The drain of the charging MOSFET is connected to the drain of the discharging MOSFET, and the drains of both the charging and discharging MOSFETs are connected to the charging management module. The source of the discharging MOSFET is connected to the positive terminal PACK+ of the external charging circuit. A cutoff resistor is provided between the gate and source of both the charging and discharging MOSFETs. The gate of the charging MOSFET is connected to the charging management module, and the gate of the discharging MOSFET is also connected to the charging management module.

3. The reverse charge protection circuit for power battery charging according to claim 2, characterized in that, A protection capacitor C1 and a protection capacitor C2 are connected in series between the source of the charging MOSFET and the source of the discharging MOSFET.

4. The reverse charge protection circuit for charging a power battery according to claim 3, characterized in that, The charging management module uses a charging management IC of model BQ4050 or BQ40Z50.

5. The reverse charge protection circuit for charging a power battery according to claim 4, characterized in that, The drains of both the charging MOSFET and the discharging MOSFET are connected to the VCC pin of the charging management IC. A drive resistor is provided between the gate of the charging MOSFET and the charging management IC. The gate of the charging MOSFET is connected to one end of the drive resistor, and the other end of the drive resistor is connected to the CHG pin of the charging management IC. A drive resistor is also provided between the discharging MOSFET and the charging management IC. The gate of the discharging MOSFET is connected to one end of the drive resistor, and the other end of the drive resistor is connected to the DSG pin of the charging management IC.

6. The reverse charge protection circuit for charging a power battery according to claim 5, characterized in that, A precision resistor with a resistance of 10Ω is also provided between the charging MOSFET and / or the discharging MOSFET and the driving resistor.

7. The reverse charge protection circuit for charging a power battery according to claim 1, characterized in that, The secondary protection module includes a three-terminal fuse, a fusible MOSFET, and a secondary protection IC. The first terminal of the three-terminal fuse is connected to the positive terminal of the battery pack, the third terminal is connected to the primary protection module, and the second terminal is connected to the drain of the fusible MOSFET. The source of the fusible MOSFET is connected to the negative terminal of the battery pack, and the gate of the fusible MOSFET is connected to the FUSE pin of the charging management IC. The gate of the fusible MOSFET is also connected to the secondary protection IC.

8. The reverse charge protection circuit for charging a power battery according to claim 7, characterized in that, The secondary protection IC is model MM3284. The VSS pin of the secondary protection IC is connected to the negative terminal of the battery pack. The V1, V2, and V3 terminals of the secondary protection IC are respectively connected to the three voltage sampling points of the battery pack. The VDD pin of the secondary protection IC is connected to the positive terminal of the battery pack.

9. The reverse charge protection circuit for charging a power battery according to claim 1, characterized in that, It also includes a current detection module, which includes a sampling resistor, a differential resistor R27, a differential resistor R28, and a differential capacitor C11. The two ends of the sampling resistor are connected to the differential resistors R27 and R28 respectively. The other end of the differential resistor R27 is electrically connected to the SRP pin of the charging management IC. The other end of the differential resistor R28 is connected to the SRN pin of the charging management IC. The differential capacitor C11 is connected in series between the SRP pin and the SRN pin of the charging management IC. One end of the sampling resistor is connected to the negative terminal of the battery pack, and the other end of the sampling resistor is connected to the common ground.

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