Recoil protection circuit for charging power battery

Abstract

The invention relates to a recoil 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, and is characterized in that the charging sampling module is connected to a charged battery pack to obtain a voltage signal when the battery pack is charged, and outputs the voltage signal 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, the output end of the primary protection module is connected to the charging management module, and the primary protection module is used for judging whether the voltage input of the positive end of the external charging circuit is abnormal or not; the input end of the secondary protection module is connected to the forward end of the battery pack, the output end of the secondary protection module is connected to the charging management module, and the secondary protection module is used for acquiring an output signal of the battery pack. By arranging the primary protection module and the secondary protection module, the power battery anti-recoil protection circuit can be protected.

Description

Technical Field

[0001] The present application relates to the technical field of power battery charging management, and in particular to a recoil protection circuit for power battery charging. Background Art

[0002] With the increasing popularity of new energy vehicles, the use of power batteries is also increasing day by day. When testing or repairing batteries, there is a risk of reverse connection between the positive and negative poles of the battery pack and the external charging circuit, which can easily cause 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. Summary of the invention

[0003] Based on this, it is necessary to provide a power battery charging recoil protection circuit for the above technical problems, including a charging management module, a primary protection module, a secondary protection module and a charging sampling module, wherein: A charging sampling module is connected to the battery pack to obtain a voltage signal when the battery pack is charged, and outputs the voltage signal to the charging management module; A primary protection 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, for determining whether there is an abnormality in the voltage input of the positive end of the external charging circuit; A secondary protection module, 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, for obtaining the output signal of the battery pack.

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

[0005] In one embodiment, the primary protection module includes a charging MOS tube and a discharging MOS tube, the source of the charging MOS tube is connected to the secondary protection module, the drain of the charging MOS tube is connected to the drain of the discharging MOS tube, and the drains of the charging MOS tube and the discharging MOS tube are connected to the charging management module, the source of the discharging MOS tube is connected to the positive end PACK+ of the external charging circuit, and a cut-off resistor is arranged between the gate and source of the charging MOS tube and the discharging MOS tube, the gate of the charging MOS tube is connected to the charging management module, and the gate of the discharging MOS tube 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 MOS tube and the source of the discharging MOS tube.

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

[0008] In one of the embodiments, the drain of the charging MOS tube and the drain of the discharging MOS tube are both connected to the VCC pin of the charging management IC, a driving resistor is arranged between the gate of the charging MOS tube and the charging management IC, the gate of the charging MOS tube is connected to one end of the driving resistor, and the other end of the driving resistor is connected to the CHG pin of the charging management IC, a driving resistor is also arranged between the discharging MOS tube and the charging management IC, the gate of the discharging MOS tube is connected to one end of the driving resistor, and the other end of the driving 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 MOS tube and / or the discharging MOS tube and the driving resistor.

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

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

[0012] In one embodiment, the power battery charging recoil protection circuit 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 respectively connected to the differential resistor R27 and the differential resistor R28, 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 end of the battery pack, and the other end of the sampling resistor is connected to a common ground.

[0013] The above-mentioned power battery charging recoil protection circuit can protect the power battery recoil protection circuit by setting a primary protection module and a secondary protection module. In particular, an anti-reverse connection unit is set in the primary protection module. When reverse connection occurs, the negative end of the external charging circuit mistakenly input into the PACK+ end makes the anti-reverse connection MOS tube Q5 meet the conduction condition, so that the negative end of the external charging circuit is grounded, thereby preventing a large current from entering the subsequent circuit, playing a role in protecting the circuit during reverse connection. Moreover, since the other end of the current limiting resistor is connected to the common ground, the gate of the anti-reverse connection MOS tube Q5 also always maintains a potential equal to the common ground, so that it can be correctly triggered during reverse connection, thereby ensuring that the anti-reverse connection function can remain effective for a long time, and avoiding the failure of the anti-reverse connection function due to the inability of the anti-reverse connection MOS tube to stably meet the conduction condition due to incorrect grounding (for example, the negative output end of the power battery connected to the non-common ground end). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The topology diagram of a recoil protection circuit for charging a power battery in one embodiment.

[0015] Figure 2 The schematic diagram of a recoil protection circuit for charging a power battery in one embodiment.

[0016] Figure 3 FIG. 4 is a partial circuit schematic diagram of a primary protection module in an embodiment.

[0017] Figure 4 FIG. 4 is a partial circuit schematic diagram of a secondary protection module in an embodiment.

[0018] Figure 5 FIG. 4 is a partial circuit schematic diagram of a charging sampling module in an embodiment.

[0019] Figure 6 FIG. 4 is a partial circuit schematic diagram of a current detection module in an embodiment.

[0020] Figure numerals: 1. Primary protection module; 11. Anti-reverse connection unit; 2. Secondary protection module; 3. Charging sampling module; 4. Current detection module; 5. Charging management module. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0022] In one embodiment, Figure 1As shown, a recoil 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: A charging sampling module is connected to the battery pack to obtain a voltage signal when the battery pack is charged, and outputs the voltage signal to the charging management module; A primary protection 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, for determining whether there is an abnormality in the voltage input of the positive end of the external charging circuit; A secondary protection module, 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, for obtaining the output signal of the battery pack; One end of the current detection module is connected to the negative end of the battery pack, and the other end of the current detection module is connected to the common ground.

[0023] After the above-mentioned anti-recoil protection circuit for charging the power battery is powered on, the charging sampling module will sample the input or output voltage of the working battery pack and output it to the charging management module. The first-level protection module and the second-level protection module are used to protect the anti-recoil protection circuit for charging the power battery powered by a battery or an external power supply. 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 the embodiment of the present application, BQ4050 is selected as the charging management IC.

[0025] In a specific embodiment, Figure 2 As shown, the primary protection module includes a charging MOS tube and a discharging MOS tube, the source of the charging MOS tube is connected to the secondary protection module, the drain of the charging MOS tube is connected to the drain of the discharging MOS tube, and the drains of the charging MOS tube and the discharging MOS tube are connected to the charging management module, the source of the discharging MOS tube is connected to the positive end PACK+ of the external charging circuit, and a cut-off resistor is arranged between the gate and source of the charging MOS tube and the discharging MOS tube, the gate of the charging MOS tube is connected to the charging management module, and the gate of the discharging MOS tube is connected to the charging management module.

[0026] Furthermore, the charging MOS tube includes a charging MOS tube Q1 and a charging MOS tube Q3, and the discharging MOS tube includes a discharging MOS tube Q2 and a discharging MOS tube Q4. The source electrodes of the charging MOS tube Q1 and the charging MOS tube Q3 are connected to the secondary protection module, and the source electrodes of the discharging MOS tube Q2 and the discharging MOS tube Q4 are connected to the positive end PACK+ of the external charging circuit. The source electrodes of the charging MOS tube Q1 and the charging MOS tube Q3 and the source electrodes of the discharging MOS tube Q2 and the discharging MOS tube Q4 are connected in series with protection capacitors C1 and C2. The drain electrodes of the charging MOS tube Q1, the charging MOS tube Q3, the discharging MOS tube Q2 and the discharging MOS tube Q4 are connected to the same equipotential point and are connected to a resistor R14. The other end of the resistor R14 is connected to the VCC end of the charging management IC. The charging MOS tube Q1 and the charging MOS tube Q3 are connected to the VCC end of the charging management IC. A turn-off resistor R4 is arranged between the source and the gate of the MOS tube Q3, and a turn-off resistor R1 is arranged between the source and the gate of the discharge MOS tube Q2 and the discharge MOS tube Q4. The resistance values ​​of the turn-off resistor R1 and the turn-off resistor R4 are set to 10MΩ, so that the charging MOS tube or the discharge MOS tube can be smoothly turned off when the conduction condition is not met; a driving resistor R13 is arranged between the gates of the charging MOS tube Q1 and the charging MOS tube Q3 and the CHG terminal of the charging management IC, and a driving resistor R15 is arranged between the gates of the discharge MOS tube Q2 and the discharge MOS tube Q4 and the DSG terminal of the charging management IC. The resistance values ​​of the driving resistor R13 and the driving resistor R15 are both set to 5.1KΩ. The charging MOS tube Q1, the charging MOS tube Q3, the discharge MOS tube Q2, and the discharge MOS tube Q4 have sufficient switching speed.

[0027] In some embodiments, an adjusting resistor R3 is connected in series between the gate of the charging MOS tube Q1 and the driving resistor R13, an adjusting resistor R8 is connected in series between the gate of the charging MOS tube Q3 and the driving resistor R13, an adjusting resistor R5 is connected in series between the gate of the discharging MOS tube Q2 and the driving resistor R15, and an adjusting resistor R9 is connected in series between the gate of the discharging MOS tube Q4 and the driving resistor R15, and the adjusting resistors R3, R5, R8 and R9 are all precision resistors with a resistance value of 10Ω. By setting the adjusting resistors, the switching speed can be further improved, thereby improving the protection capability of the primary protection circuit to the recoil protection circuit for charging the power battery.

[0028] In a specific embodiment, Figure 3 As shown, the primary protection module includes an anti-reverse connection unit, the anti-reverse connection unit includes an anti-reverse connection MOS tube Q5, the drain of the anti-reverse connection MOS tube Q5 is connected to the charging management module, the gate of the anti-reverse connection MOS tube 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 anti-reverse connection MOS tube Q5 is connected to the positive terminal PACK+ of the external charging circuit.

[0029] In this embodiment, by providing an anti-reverse connection MOS tube Q5, the source of the anti-reverse connection MOS tube 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 MOS tube Q2 and the discharge MOS tube Q4 can work normally. However, when the positive terminal PACK+ of the external charging circuit is reversely connected, that is, a volt voltage is connected, the anti-reverse connection MOS tube meets the conduction condition and is turned on, thereby short-circuiting the discharge MOS tube Q2 and the discharge MOS tube Q4, thereby protecting the discharge MOS tube and the subsequent circuit.

[0030] In a specific embodiment, Figure 4-Figure 5As shown, the secondary protection module includes a three-terminal fuse F1, a fuse MOS tube Q6 and a secondary protection ICU2, the first end of the three-terminal fuse F1 is connected to the positive end B+ of the battery pack, the third end is connected to the source of the charging MOS tube Q1 and / or the charging MOS tube Q3, the second end is connected to the drain of the fuse MOS, the source of the fuse MOS tube Q6 is connected to the negative end B- of the battery pack, the gate of the fuse MOS tube Q6 is connected to the FUSE pin of the charging management ICU2, the gate of the fuse MOS tube is also connected to the secondary protection IC, a resistor R17 is connected in series between the gate and the source of the fuse MOS tube Q6, and a capacitor C6 is also connected in series between the gate and the source of the fuse MOS tube Q6. Specifically, in this embodiment, the model of the secondary protection ICU2 is MM3284. The VSS pin of the secondary protection ICU2 is connected to the negative end of the battery pack, the V1, V2, and V3 terminals of the secondary protection ICU2 are respectively connected to the three-level voltage sampling points of the battery pack, and the VDD pin of the secondary protection ICU2 is connected to the positive end B+ of the battery pack. Specifically, a current-limiting resistor R6 is connected in series between the VDD terminal of the secondary protection ICU2 and the positive end B+ of the battery pack, and an isolation capacitor C3 is connected in series between the VDD terminal of the secondary protection ICU2 and the negative end B- of the battery pack. In addition to the positive end B+ and the negative end B-, the battery pack is also provided with three voltage sampling nodes, namely, 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 terminal of the secondary protection ICU2. The first-level voltage sampling node B1+ is electrically connected to the V1 end of the second-level protection ICU2, and a current-limiting resistor R12 is connected in series between the first-level voltage sampling node B1+ and the V1 end of the second-level protection ICU2, the second-level voltage sampling node B2+ is electrically connected to the V2 end of the second-level protection ICU2, and a current-limiting resistor R10 is connected in series between the second-level voltage sampling node B2+ and the V2 end of the second-level protection ICU2, the third-level voltage sampling node B3+ is electrically connected to the V3 end of the second-level protection ICU2, and a current-limiting resistor R7 is connected in series between the third-level voltage sampling node B3+ and the V3 end of the second-level protection ICU2, an isolation capacitor C5 is connected in series between the V1 end and the V2 end of the second-level protection ICU2, an isolation capacitor C4 is connected in series between the V2 end and the V3 end of the second-level protection ICU2, and an isolation capacitor C7 is connected in series between the VSS end and the V1 end of the second-level protection ICU2. After the power battery charging recoil protection circuit is powered on, the secondary protection ICU2 monitors the output voltage of the positive terminal B+ of the battery pack, as well as the output voltages of the primary voltage sampling node B1+, the secondary voltage sampling node B2+, and the tertiary voltage sampling node B3+. When any of the voltages is abnormal, the OV terminal of the secondary protection ICU2 outputs a high level to turn on the fuse MOS tube Q6, and then blow the three-terminal fuse F1, thereby protecting the charging MOS tubes Q1, Q3 and the previous stage circuit, thereby playing a role in protecting the circuit.

[0031] In addition, the primary voltage sampling node B1+, the secondary voltage sampling node B2+, and the tertiary 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 primary voltage sampling node B1+, and a limited current single group R30 is connected in series between the VC1 terminal and the primary voltage sampling node B1+, the VC2 terminal of the charging management IC is electrically connected to the secondary voltage sampling node B2+, and a limited current single group R26 is connected in series between the VC2 terminal and the secondary voltage sampling node B2+, the VC3 terminal of the charging management IC is electrically connected to the tertiary voltage sampling node B3+, and the VC3 terminal is connected to the tertiary voltage sampling node B3 +, the VC4 terminal of the charging management IC is electrically connected to the positive terminal B+ of the battery pack, and the limited current single group 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 primary voltage sampling node B1+, an isolation capacitor C12 is connected in series between the primary voltage sampling node B1+ and the secondary voltage sampling node B2+, an isolation capacitor C10 is connected in series between the secondary voltage sampling node B2+ and the tertiary voltage sampling node B3+, and an isolation capacitor C9 is connected in series between the tertiary voltage sampling node B3+ and the positive terminal B+ of the battery pack.

[0032] In one embodiment, if Figure 6 As shown, the power battery charging recoil protection circuit 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 sampling resistor includes a sampling resistor RS1 and a sampling capacitor RS2 connected in parallel. The two ends of the sampling resistor are respectively connected to the differential resistor R27 and the differential resistor R28. The other end of the differential resistor R27 is electrically connected to the SRP pin of the charging management IC, and 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 end B- of the battery pack, and one end of the sampling resistor connected to the differential resistor R28 is connected to the common ground GND.

[0033] Since the two ends of the sampling resistor are respectively connected to the common ground terminal GND and the negative end B- of the battery pack, there is also a potential difference between the common ground terminal GND and the negative end B- of the battery pack, and the direction of the battery difference is uncertain, so it is necessary to emphasize once again the grounding state of the anti-reverse MOS tube Q5 in the anti-reverse connection unit, that is, the gate of the anti-reverse MOS tube 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 terminal GND. Such a connection method can keep the gate of the anti-reverse MOS tube Q5 at zero potential all the time. When reverse connection occurs, the conduction condition of the anti-reverse MOS tube Q5 can be met, and the anti-reverse connection function is successfully triggered. If the gate of the anti-reverse MOS tube Q5 is connected to the negative end B- of the battery pack, and the negative end B- of the battery pack is a negative voltage relative to the common ground terminal GND, the anti-reverse MOS tube Q5 may not meet the conduction condition, and the anti-reverse connection function cannot be successfully triggered, resulting in damage to the circuit. Therefore, connecting the other end of the current limiting resistor to the common ground terminal can ensure that the gate of the anti-reverse connection MOS tube Q5 always maintains a potential equal to the common ground, so as to ensure that it can be correctly triggered in the case of reverse connection to achieve the protection circuit function.

[0034] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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.

[0035] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A recoil protection circuit for power battery charging, characterized in that: It includes charging management module, primary protection module, secondary protection module and charging sampling module, among which: A charging sampling module is connected to the battery pack being charged to obtain a voltage signal of the battery pack when being charged, and outputs the voltage signal to the charging management module; A primary protection 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, for determining whether there is an abnormality in the voltage input of the positive end of the external charging circuit; A secondary protection module, 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, for obtaining the output signal of the battery pack; The primary protection module includes an anti-reverse connection unit, which includes an anti-reverse connection MOS tube Q5, a drain of which is connected to the charging management module, a gate of which is connected to a current limiting resistor, the other end of which is connected to a common ground, and a source of which is connected to a positive end PACK+ of an external charging circuit.

2. A power battery charging recoil protection circuit according to claim 1, characterized in that: The primary protection module includes a charging MOS tube and a discharging MOS tube, the source of the charging MOS tube is connected to the secondary protection module, the drain of the charging MOS tube is connected to the drain of the discharging MOS tube, and the drains of the charging MOS tube and the discharging MOS tube are connected to the charging management module, the source of the discharging MOS tube is connected to the positive end PACK+ of the external charging circuit, and a cut-off resistor is arranged between the gate and source of the charging MOS tube and the discharging MOS tube, the gate of the charging MOS tube is connected to the charging management module, and the gate of the discharging MOS tube is connected to the charging management module.

3. A power battery charging recoil protection circuit 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 MOS tube and the source of the discharging MOS tube.

4. A power battery charging recoil protection circuit according to claim 3, characterized in that: The charging management module uses a charging management IC of type BQ4050 or BQ40Z50.

5. A power battery charging recoil protection circuit according to claim 4, characterized in that: The drain of the charging MOS tube and the drain of the discharging MOS tube are both connected to the VCC pin of the charging management IC, a driving resistor is arranged between the gate of the charging MOS tube and the charging management IC, the gate of the charging MOS tube is connected to one end of the driving resistor, and the other end of the driving resistor is connected to the CHG pin of the charging management IC, a driving resistor is also arranged between the discharging MOS tube and the charging management IC, the gate of the discharging MOS tube is connected to one end of the driving resistor, and the other end of the driving resistor is connected to the DSG pin of the charging management IC.

6. A power battery charging recoil protection circuit according to claim 5, characterized in that: A precision resistor with a resistance of 10Ω is also arranged between the charging MOS tube and / or the discharging MOS tube and the driving resistor.

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

8. A power battery charging recoil protection circuit according to claim 7, characterized in that: The model of the secondary protection IC is MM3284. The VSS pin of the secondary protection IC is connected to the negative end of the battery pack, the V1, V2, and V3 terminals of the secondary protection IC are respectively connected to the three-level voltage sampling points of the battery pack, and the VDD pin of the secondary protection IC is connected to the positive end of the battery pack.

9. A power battery charging recoil protection circuit 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 respectively connected to the differential resistor R27 and the differential resistor R28, 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 end of the battery pack, and the other end of the sampling resistor is connected to a common ground.

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