Lithium battery protection system and mobile power supply

Abstract

The invention relates to the field of power supplies, in particular to a lithium battery protection system and a mobile power supply. Comprising a battery end, a power supply circuit, a primary protection circuit, an interface end and a secondary protection circuit, the primary protection circuit comprises a control chip, the secondary protection circuit comprises a voltage division module, a comparator, a reference voltage module, a first MOS tube and a fuse, the fuse is connected with the positive electrode of the battery end, the positive electrode of the interface end and the drain electrode of the first MOS tube, and the grid electrode of the first MOS tube is connected with the output end of the comparator. The voltage dividing module is connected with a battery end and the in-phase input end of the comparator. The reference voltage module is connected with the power supply circuit and the reverse input end of the comparator. According to the scheme, the battery overcharge protection threshold can be accurately set by adjusting the parameters of the voltage division module, the reference voltage of the comparator can be accurately set by adjusting the parameters of the reference voltage module, different overcharge protection requirements can be met without replacing a core protection device, and the adaptation cost of product research and development and production is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of power supply, specifically to a lithium battery protection system and a portable power supply. Background Technology

[0002] With the rapid development of the new energy industry, especially lithium battery technology, and the widespread use of mobile power supplies, energy storage products, and other related products, cell safety has become a top priority for the industry. In multi-cell battery applications, the increased voltage after series connection exacerbates the risk of overvoltage during charging. As the core guarantee for the normal operation of lithium batteries, the market's requirements for cell protection mechanisms are constantly being upgraded. It is clearly required that, in addition to the protection of the DC-DC stage, the cell section must have two levels of protection functions. Currently, most solutions for two-level cell protection adopt a two-level lithium protection structure, that is, using two identical sets of devices for protection. This solution is challenging in terms of device selection and has low accuracy. It is prone to misjudgment due to parameter conflicts, resulting in repeated on / off charging. In addition, the two sets of charge and discharge protection MOS will cause the internal resistance of the two lithium protection stages to be superimposed, affecting charging efficiency.

[0003] Therefore, designing a flexible and more accurate lithium battery protection system and mobile power supply is of great importance to those skilled in the art. Summary of the Invention

[0004] This invention provides a flexible and more accurate lithium battery protection system and power bank to solve the problems of difficult selection and easy misjudgment in the prior art.

[0005] This invention discloses a lithium battery protection system, comprising: a battery terminal, a power supply circuit, a primary protection circuit, an interface terminal, and a secondary protection circuit. The input terminal of the power supply circuit and the interface terminal are both connected to the battery terminal. The output terminal of the power supply circuit is connected to both the primary and secondary protection circuits. The primary protection circuit includes a control chip. The secondary protection circuit includes a voltage divider module, a comparator, a reference voltage module, a first MOSFET, and a fuse. The first terminal of the fuse is connected to the positive terminal of the battery terminal, the second terminal of the fuse is connected to the positive terminal of the interface terminal, the drain of the first MOSFET is connected to the third terminal of the fuse, the source of the first MOSFET is grounded, and the gate of the first MOSFET is connected to the output terminal of the comparator. The voltage divider module is connected to the positive terminal of the battery terminal and the non-inverting input terminal of the comparator. The reference voltage module is connected to both the power supply circuit and the inverting input terminal of the comparator.

[0006] Optionally, the voltage divider module includes a first voltage divider resistor and a second voltage divider resistor. One end of the first voltage divider resistor is connected to the positive terminal of the battery, and the other end of the first voltage divider resistor is connected to the non-inverting input terminal of the comparator and one end of the second voltage divider resistor, respectively. The other end of the second voltage divider resistor is grounded.

[0007] Optionally, the reference voltage module includes a first resistor and a second resistor. One end of the first resistor is connected to the output terminal of the power supply circuit, and the other end of the first resistor is connected to the inverting input terminal of the comparator and one end of the second resistor, respectively. The other end of the second resistor is grounded.

[0008] Optionally, the secondary protection circuit further includes a second MOSFET and a first transistor. The source of the second MOSFET is connected to the positive terminal of the battery, the drain of the second MOSFET is connected to the voltage divider module, the gate of the second MOSFET is connected to the collector of the first transistor, the base of the first transistor is connected to the output terminal of the power supply circuit, and the emitter of the first transistor is grounded.

[0009] Optionally, the primary protection circuit further includes an AFE module, which is connected to both the battery terminal and the control chip.

[0010] Optionally, the primary protection circuit further includes a charging MOSFET and a discharging MOSFET, which are disposed between the battery terminal and the interface terminal, and the gates of the charging MOSFET and the discharging MOSFET are both connected to the control chip.

[0011] Optionally, the power supply circuit includes a voltage regulator chip, the input terminal of which is connected to the positive terminal of the battery, and the output terminal of which is connected to the first-level protection circuit and the second-level protection circuit respectively.

[0012] Optionally, the power supply circuit further includes a third MOSFET, a second transistor, and a third transistor. The drain of the third MOSFET is connected to the positive terminal of the battery, the source of the third MOSFET is connected to the input terminal of the voltage regulator chip, the gate of the third MOSFET is connected to the collector of the second transistor, the emitters of the second transistor and the third transistor are both grounded, the base of the second transistor is connected to the collector of the third transistor, and the base of the third transistor is connected to the control chip.

[0013] Optionally, the first MOS transistor is an NMOS transistor.

[0014] To address the problems existing in the prior art, the present invention also provides a portable power bank, wherein the portable power bank includes the lithium battery protection system described above.

[0015] The beneficial effects of this invention are as follows: By designing a lithium battery protection system, a dual protection system of software protection and hardware protection is constructed, avoiding the risk of overcharge caused by the failure of a single protection link. The voltage divider module of the secondary protection circuit can accurately set the battery overcharge protection threshold through parameter adjustment, and the reference voltage module can accurately set the reference voltage of the comparator through parameter adjustment. Compared with the fixed and unadjustable protection parameters of fuses and PTCs in traditional two-level protection schemes, this system can adapt to the overcharge protection requirements of different models and capacities of lithium battery packs. It can meet the diverse product design requirements without replacing the core protection components, reducing the adaptation costs of product development and production. Attached Figure Description

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a circuit diagram of the secondary protection circuit in an embodiment of the present invention; Figure 2 This is a circuit diagram of the primary protection circuit in an embodiment of the present invention; Figure 3 This is a circuit diagram of the power supply circuit in an embodiment of the present invention.

[0017] The labels for the attached figures are as follows: 1. Battery terminal; 2. Power supply circuit; 4. Interface terminal; 5. Secondary protection circuit; U2. Control chip; 51. Voltage divider module; 52. Reference voltage module; F1. Fuse; Q1. First MOSFET; R22. First voltage divider resistor; R32. Second voltage divider resistor; R23. First resistor; R33. Second resistor; Q4. Second MOSFET; Q7. First transistor; U1. AFE module; U3. Voltage regulator chip; Q5. Third MOSFET; Q8. Second transistor; Q9. Third transistor. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] like Figures 1 to 3 As shown, the present invention provides a specific embodiment of a lithium battery protection system.

[0020] A lithium battery protection system, reference Figures 1 to 3The lithium battery protection system includes a battery terminal 1, a power supply circuit 2, a primary protection circuit, an interface terminal 4, and a secondary protection circuit 5. The input terminal and the interface terminal 4 of the power supply circuit 2 are both connected to the battery terminal 1, and the output terminal of the power supply circuit 2 is connected to the primary protection circuit and the secondary protection circuit 5, respectively.

[0021] The primary protection circuit includes a control chip U2, and the secondary protection circuit 5 includes a voltage divider module 51, a comparator U4, a reference voltage module 52, a first MOSFET Q1, and a fuse F1. The first terminal of the fuse F1 is connected to the positive terminal B+ of the battery terminal 1, the second terminal of the fuse F1 is connected to the positive terminal PACK+ of the interface terminal 4, the drain of the first MOSFET Q1 is connected to the third terminal of the fuse F1, the source of the first MOSFET Q1 is grounded, and the gate of the first MOSFET Q1 is connected to the output terminal of the comparator U4. The voltage divider module 51 is connected to the positive terminal B+ of the battery terminal 1 and the non-inverting input terminal of the comparator U4, respectively. The reference voltage module 52 is connected to the power supply circuit 2 and the inverting input terminal of the comparator U4, respectively.

[0022] Specifically, refer to Figures 1 to 3 Battery terminal 1 is connected to the battery pack and is used to provide the output voltage and current of the lithium battery pack. Battery terminal 1 serves as a monitoring object for overcharge, over-discharge and other protection risks, and provides a real-time voltage sampling source for the first-level protection circuit and the second-level protection circuit 5. Interface terminal 4 serves as the connection port between the battery pack and the external load, realizing the switching of the charging and discharging path of the battery pack. The positive terminal PACK+ of interface terminal 4 forms a series circuit with fuse F1 and the positive terminal of battery terminal 1, which is a key node for the protection circuit to cut off abnormal paths. The input terminal of power supply circuit 2 is connected to battery terminal 1 and is used to convert the voltage of battery terminal 1 into the stable operating voltage required by the first-level protection circuit and the second-level protection circuit 5, powering the active devices such as control chip U2 and comparator U4, and ensuring the normal operation of the first-level protection circuit and the second-level protection circuit 5.

[0023] The primary protection circuit is a conventional protection circuit, which includes the control chip U2 and the AFE front-end acquisition. It is responsible for collecting parameters such as voltage, current and temperature at battery terminal 1 in real time, and judging whether the battery is in an abnormal state such as overcharge, over-discharge or overcurrent based on the real-time voltage, current and temperature at battery terminal 1. When an abnormality is detected, the control signal is output to cut off the charging and discharging circuit in time.

[0024] The secondary protection circuit 5 is activated after the normal overcharge and overcurrent protection functions of the lithium battery protection system fail. The secondary protection circuit 5 includes a voltage divider module 51, a comparator U4, a reference voltage module 52, a first MOSFET Q1, and a fuse F1. The voltage divider module 51 is connected to the positive terminal B+ of battery terminal 1, accurately dividing the real-time voltage of battery terminal 1 and converting the high-voltage signal into a low-voltage sampling signal recognizable by comparator U4. The protection threshold can be flexibly set by adjusting the parameters of the voltage divider resistors. The reference voltage module 52 is powered by the power supply circuit 2 and outputs a stable reference voltage signal to the inverting input of comparator U4 as a reference standard for determining whether the battery voltage exceeds the limit. Comparator U4, as the core judgment device of the secondary protection, converts in-phase... The voltage divider sampling signal at the input terminal is compared with the reference voltage signal at the inverting input terminal in real time. When the sampling signal exceeds the reference voltage, the output state is immediately reversed, and a drive signal is output. The first MOSFET Q1 acts as a switching device, with its drain connected to the third terminal of the fuse F1, its source grounded, and its gate controlled by the output signal of the comparator U4. When the drive signal of the comparator U4 is received, the first MOSFET Q1 is turned on, triggering the fuse F1 to operate. The fuse F1 adopts a three-terminal structure and is connected in series between the positive terminal of battery terminal 1 and the positive terminal of interface terminal 4. It is the hardware-level circuit breaking execution element of the secondary protection circuit 5. When the first MOSFET Q1 is turned on, the internal circuit of the fuse F1 triggers the turn-off action and cuts off the series circuit between battery terminal 1 and interface terminal 4.

[0025] During the normal monitoring phase, power supply circuit 2 supplies power to reference voltage module 52, which outputs a stable reference voltage to the inverting input of comparator U4. The real-time voltage from battery terminal 1 is input to voltage divider module 51, and after voltage division, it is input to the non-inverting input of comparator U4. At this time, the battery voltage is within a safe range, the voltage divided sampling voltage is less than or equal to the reference voltage, the output state of comparator U4 remains constant, the gate of the first MOS transistor has no drive signal and is in the cutoff state, the fuse F1 conducts normally, and the charging and discharging circuit between battery terminal 1 and interface terminal 4 is unobstructed.

[0026] During the overvoltage triggering phase, i.e., when battery terminal 1 is overcharged, the voltage of battery terminal 1 continues to rise. The sampled voltage after being processed by the voltage divider module 51 rises synchronously and exceeds the reference voltage threshold. The comparator U4 detects that the voltage at the non-inverting input terminal is higher than that at the inverting input terminal, and the output state immediately reverses, outputting a high-level drive signal to the gate of the first MOS transistor Q1.

[0027] During the circuit breaker protection phase, after the first MOSFET Q1 receives the drive signal and turns on, the drain and source of the first MOSFET Q1 form a path (source grounded), triggering the action mechanism of the three-terminal fuse F1. The fuse F1 quickly turns off, cutting off the series circuit between battery terminal 1 and interface terminal 4, preventing the battery from continuing to charge, limiting the battery voltage within a safe range, and completing the secondary hardware protection.

[0028] In this embodiment, a lithium battery protection system is designed, constructing a dual protection system that combines software protection and hardware protection. The first-level protection circuit realizes intelligent monitoring of multiple parameters such as battery voltage, current, and temperature and software logic protection through the control chip U2. The second-level protection circuit 5 adopts a pure hardware architecture and operates independently without relying on software programs and control chip U2. When the first-level software protection fails due to program failure, signal interference, etc., the second-level hardware protection can be triggered independently, avoiding the overcharging risk caused by the failure of a single protection link, and significantly improving the safety of lithium battery packs in scenarios such as power banks and energy storage products.

[0029] Furthermore, the voltage divider module 51 of the secondary protection circuit 5 can accurately set the battery overcharge protection threshold by adjusting the resistance parameters. Compared with the fixed and unadjustable protection parameters of the fuse F1 and PTC in the traditional two-level protection scheme, this system can adapt to the overcharge protection requirements of different models and capacities of lithium battery packs. It can meet the diverse product design requirements without replacing the core protection device, thereby reducing the adaptation cost of product development and production.

[0030] Furthermore, the secondary protection circuit 5, based on the real-time voltage comparison mechanism of comparator U4, eliminates the need for algorithm calculations and signal processing by control chip U2. When the battery voltage exceeds the threshold, comparator U4 can instantly reverse its output state and drive the first MOSFET Q1 to trigger fuse F1. The response speed is much faster than protection schemes that rely on software calculations, and it is also superior to traditional fuse F1 and PTC protection, which are limited by physical characteristics. It can quickly cut off the circuit in the early stage of overcharge risk, effectively preventing problems such as capacity loss, overheating, bulging, or even explosion and fire of the battery cell due to continuous overvoltage. Moreover, the secondary protection circuit 5 consists of voltage divider module 51, comparator U4, reference voltage module 52, MOSFET, and fuse F1. The components are universally selected, the circuit topology is simple, and there is no need for complex external auxiliary circuits. It is easy to integrate with the hardware architecture of existing BMS battery packs and meets the process requirements of mass production, which helps to improve the market competitiveness of the product.

[0031] In one embodiment, reference Figures 1 to 3The voltage divider module 51 includes a first voltage divider resistor R22 and a second voltage divider resistor R32. One end of the first voltage divider resistor R22 is connected to the positive terminal B+ of the battery terminal 1. The other end of the first voltage divider resistor R22 is connected to the non-inverting input terminal of the comparator U4 and one end of the second voltage divider resistor R32. The other end of the second voltage divider resistor R32 is grounded.

[0032] Specifically, the voltage divider module 51 adopts a topology structure in which the first voltage divider resistor R22 and the second voltage divider resistor R32 are connected in series. One end of the first voltage divider resistor R22 is directly connected to the positive terminal B+ of the battery terminal 1 to receive the real-time voltage of the battery pack. The other end of the first voltage divider resistor R22 is connected to the non-inverting input terminal of the comparator U4 and one end of the second voltage divider resistor R32. The other end of the second voltage divider resistor R32 is grounded, forming a complete series voltage divider circuit.

[0033] This design enables precise adjustment of the protection threshold. When adjusting the protection threshold, simply adjust the resistance value of the first voltage divider resistor R22 or the second voltage divider resistor R32 to flexibly change the voltage division ratio, thereby accurately setting the overcharge protection threshold of the battery pack. Compared with the fixed protection threshold of fuse F1 and PTC in the traditional two-stage protection scheme, this module does not require replacement of core components and can adapt to the protection requirements of different models and capacities of lithium battery packs, greatly reducing product development and adaptation costs and improving the versatility of the product in multiple scenarios such as power banks and energy storage products.

[0034] Furthermore, by employing a pure resistor series voltage divider, the circuit topology is simple, with no active components involved in sampling. It is less affected by external factors such as temperature and electromagnetic interference, and can stably output a sampling signal that is linearly related to the voltage at battery terminal 1. Compared with other complex sampling circuits, this module can avoid signal distortion or drift problems, ensuring that the comparator U4 accurately judges the overcharge voltage and effectively preventing false or missed protection triggers due to sampling errors. The voltage divider module 51 consists of only two resistors, with universally applicable components and low procurement costs. The circuit layout is simple and requires no additional auxiliary circuits. It can be directly integrated into the PCB board of the existing BMS battery pack and seamlessly cooperates with the comparator U4, MOSFETs, and other components of the secondary protection circuit 5.

[0035] In one embodiment, reference Figures 1 to 3 The reference voltage module 52 includes a first resistor R23 and a second resistor R33. One end of the first resistor R23 is connected to the output terminal of the power supply circuit 2, and the other end of the first resistor R23 is connected to the inverting input terminal of the comparator U4 and one end of the second resistor R33. The other end of the second resistor R33 is grounded.

[0036] Specifically, the reference voltage module 52 adopts a series voltage divider topology with a first resistor R23 and a second resistor R33. Its function is to provide a stable reference voltage for the inverting input of the comparator U4. One end of the first resistor R23 is connected to the output of the power supply circuit 2 to receive the stable operating voltage output by the power supply circuit 2. The other end of the first resistor R23 is connected to both the inverting input of the comparator U4 and one end of the second resistor R33. The other end of the second resistor R33 is grounded, forming a complete series voltage divider circuit.

[0037] This design enables precise adjustment of the reference voltage. When adjusting the reference voltage, simply adjust the resistance value of the first resistor R23 or the second resistor R33 to precisely change the voltage division ratio, thereby flexibly setting the reference voltage threshold of the comparator U4. Combined with the parameter adjustment of the voltage divider module 51, it can achieve dual precise matching of the battery overcharge protection threshold, adapting to the protection needs of lithium battery packs with different voltage specifications and capacities, and solving the problem of poor adaptability of traditional fixed reference source solutions.

[0038] Furthermore, the module consists of only two passive resistors, eliminating the need for a dedicated reference voltage chip. This significantly reduces component procurement costs and circuit design complexity. The resistors are small and highly compatible, allowing direct integration into the PCB of the secondary protection circuit 5. They seamlessly integrate with components such as the voltage divider module 51 and comparator U4, meeting the miniaturization design requirements of portable power banks and small energy storage products. The voltage output from the power supply circuit 2 itself has voltage regulation characteristics. Based on this, a reference voltage is generated through pure resistor voltage division, eliminating noise interference from active components and minimizing the impact of external factors such as temperature fluctuations and electromagnetic interference. This provides a stable reference threshold for comparator U4. Compared to solutions using dedicated reference chips, this module avoids reference voltage drift caused by chip temperature drift, ensuring the consistency and accuracy of protection trigger thresholds and effectively preventing false or missed triggers. The static current of the resistor voltage divider circuit is extremely small, resulting in negligible energy consumption for the power supply circuit 2. It does not consume additional energy from the battery pack and does not affect the battery pack's output capacity or charging / discharging efficiency.

[0039] In one embodiment, reference Figures 1 to 3 The secondary protection circuit 5 also includes a second MOSFET Q4 and a first transistor Q7. The source of the second MOSFET Q4 is connected to the positive terminal B+ of the battery terminal 1, the drain of the second MOSFET Q4 is connected to the voltage divider module 51, the gate of the second MOSFET Q4 is connected to the collector of the first transistor Q7, the base of the first transistor Q7 is connected to the output terminal of the power supply circuit 2, and the emitter of the first transistor Q7 is grounded.

[0040] Specifically, when the power supply circuit 2 outputs a stable voltage, the voltage signal is input to the base of the first transistor Q7, causing Q7 to conduct. The collector and emitter of the first transistor Q7 are connected, pulling the collector potential of Q7 down. At this time, the positive voltage of battery terminal 1 is input to the voltage divider module 51 through the second MOSFET Q4, and the secondary protection circuit 5 enters the working state. When the system experiences undervoltage or other conditions, and the power supply circuit 2 stops outputting, the first transistor Q7 and the second MOSFET Q4 are disconnected to cut off the secondary protection circuit 5. The secondary protection circuit 5 stops operating and enters a low-power mode. This design can significantly reduce the standby power consumption of the battery pack when the system is undervoltage, extending the battery pack's storage life and battery life.

[0041] In one embodiment, reference Figures 1 to 3 The primary protection circuit also includes an AFE module U1, which is connected to both the battery terminal 1 and the control chip U2. The primary protection circuit also includes a charging MOSFET Q2 and a discharging MOSFET Q3, which are positioned between the battery terminal 1 and the interface terminal 4. The gates of both the charging and discharging MOSFETs Q2 and Q3 are connected to the control chip U2. This design primarily employs conventional battery protection, using the AFE module U1 to collect parameters such as voltage, current, and temperature at the battery terminal 1 and send them to the control chip U2. The control chip U2 determines whether the battery is in an abnormal state such as overcharge, over-discharge, or overcurrent based on the real-time voltage, current, and temperature at the battery terminal 1. When an abnormality is detected, it outputs a control signal to promptly cut off the charging and discharging circuit.

[0042] In one embodiment, reference Figures 1 to 3 The power supply circuit 2 includes a voltage regulator chip U3, a third MOSFET Q5, a second transistor Q8, and a third transistor Q9. The output terminal of the voltage regulator chip U3 is connected to the first-level protection circuit and the second-level protection circuit 5, respectively. The drain of the third MOSFET Q5 is connected to the positive terminal B+ of the battery terminal 1. The source of the third MOSFET Q5 is connected to the input terminal of the voltage regulator chip U3. The gate of the third MOSFET Q5 is connected to the collector of the second transistor Q8. The emitters of the second transistor Q8 and the emitters of the third transistor Q9 are both grounded. The base of the second transistor Q8 is connected to the collector of the third transistor Q9. The base of the third transistor Q9 is connected to the control chip U2. The input terminal of the voltage regulator chip U3 is connected to the positive terminal B+ of the battery terminal 1.

[0043] Among them, the voltage regulator chip U3 is mainly used to convert the voltage output from the battery terminal 1 into the working voltage required by the first-level protection circuit and the second-level protection circuit 5. The third MOSFET Q5, the second transistor Q8, and the third transistor Q9 are all used to cut off the power supply circuit 2 when the system experiences undervoltage or other situations, so that it can enter the low-power module.

[0044] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Those skilled in the art can modify the technical solutions described in the above embodiments, or make equivalent substitutions for some of the technical features; and all such modifications and substitutions should fall within the protection scope of the appended claims of the present invention.

Claims

1. A lithium battery protection system, characterized in that, include: The system comprises a battery terminal, a power supply circuit, a primary protection circuit, an interface terminal, and a secondary protection circuit. The input terminal of the power supply circuit and the interface terminal are both connected to the battery terminal. The output terminal of the power supply circuit is connected to both the primary and secondary protection circuits. The primary protection circuit includes a control chip. The secondary protection circuit includes a voltage divider module, a comparator, a reference voltage module, a first MOSFET, and a fuse. The first terminal of the fuse is connected to the positive terminal of the battery terminal, the second terminal of the fuse is connected to the positive terminal of the interface terminal, and the third terminal of the fuse is connected to the drain of the first MOSFET. The source of the first MOSFET is grounded, and the gate of the first MOSFET is connected to the output terminal of the comparator. The voltage divider module is connected to the positive terminal of the battery terminal and the non-inverting input terminal of the comparator. The reference voltage module is connected to the output terminal of the power supply circuit and the inverting input terminal of the comparator.

2. The lithium battery protection system according to claim 1, characterized in that: The voltage divider module includes a first voltage divider resistor and a second voltage divider resistor. One end of the first voltage divider resistor is connected to the positive terminal of the battery. The other end of the first voltage divider resistor is connected to the non-inverting input terminal of the comparator and one end of the second voltage divider resistor, respectively. The other end of the second voltage divider resistor is grounded.

3. The lithium battery protection system according to claim 1, characterized in that: The reference voltage module includes a first resistor and a second resistor. One end of the first resistor is connected to the output terminal of the power supply circuit, and the other end of the first resistor is connected to the inverting input terminal of the comparator and one end of the second resistor, respectively. The other end of the second resistor is grounded.

4. The lithium battery protection system according to claim 1, characterized in that: The secondary protection circuit further includes a second MOSFET and a first transistor. The source of the second MOSFET is connected to the positive terminal of the battery, the drain of the second MOSFET is connected to the voltage divider module, the gate of the second MOSFET is connected to the collector of the first transistor, the base of the first transistor is connected to the output terminal of the power supply circuit, and the emitter of the first transistor is grounded.

5. The lithium battery protection system according to claim 1, characterized in that: The primary protection circuit also includes an AFE module, which is connected to both the battery terminal and the control chip.

6. The lithium battery protection system according to claim 5, characterized in that: The primary protection circuit also includes a charging MOSFET and a discharging MOSFET, which are disposed between the battery terminal and the interface terminal. The gates of both the charging MOSFET and the discharging MOSFET are connected to the control chip.

7. The lithium battery protection system according to claim 1, characterized in that: The power supply circuit includes a voltage regulator chip, the input terminal of which is connected to the positive terminal of the battery, and the output terminal of which is connected to the first-level protection circuit and the second-level protection circuit respectively.

8. The lithium battery protection system according to claim 7, characterized in that: The power supply circuit further includes a third MOSFET, a second transistor, and a third transistor. The drain of the third MOSFET is connected to the positive terminal of the battery. The source of the third MOSFET is connected to the input terminal of the voltage regulator chip. The gate of the third MOSFET is connected to the collector of the second transistor. The emitters of the second transistor and the third transistor are both grounded. The base of the second transistor is connected to the collector of the third transistor. The base of the third transistor is connected to the control chip.

9. The lithium battery protection system according to claim 8, characterized in that: The first MOS transistor is an NMOS transistor.

10. A portable power bank, characterized in that: The power bank includes a lithium battery protection system as described in any one of claims 1-9.

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