Temperature protection circuit and lithium battery

Abstract

The invention relates to the technical field of lithium battery protection, and discloses a temperature protection circuit and a lithium battery. The temperature protection circuit comprises a protection unit, a temperature detection circuit and a control switch circuit, the protection unit has a voltage detection function, the temperature detection circuit is used for detecting the temperature change of the cell assembly and outputting a corresponding voltage signal, and the control switch circuit controls the working state of the protection unit according to the voltage signal. When the temperature of the battery core assembly reaches a preset temperature, the protection unit is controlled to enter a protection state of stopping discharging; according to the invention, the temperature characteristic of the positive temperature coefficient thermistor and the voltage division circuit principle are ingeniously utilized, and the switching characteristic of the N-channel MOS tube is combined, so that the VDD voltage control of the lithium battery protection IC is realized, and the over-discharge protection function is triggered to realize temperature protection. The whole scheme can be realized only through a peripheral simple circuit without modifying the internal logic of the existing lithium battery protection IC, and is low in cost, high in reliability and suitable for large-scale production and application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery protection, in particular to a temperature protection circuit and a lithium battery. BACKGROUND

[0002] With the increasing demand for battery safety in electronic products, the overvoltage, overcurrent and other protection functions contained in conventional lithium batteries and their protection boards cannot meet the increasingly stringent use environment of electronic products. Temperature protection function will be paid more and more attention, and it is also the trend of lithium battery protection in the future.

[0003] The current main application design of lithium battery temperature protection has the following problems:

[0004] 1. There is no temperature protection circuit on the battery, and temperature detection is performed through the host end of the electronic product. This design requires the use of host end single-chip microcomputer programming, which has high development cost and long development cycle. Moreover, the battery cannot effectively protect the temperature when processing, transporting and abnormal body, and the safety level of the battery is relatively low.

[0005] 2. The lithium battery protection IC scheme containing temperature protection function on the battery. This design needs to change the internal logic circuit design of the conventional protection IC, which has a long development cycle. Moreover, the cost of lithium battery protection IC increases significantly with the addition of temperature protection function. As a very mature product and market, the logic circuit and packaging design of the lithium battery protection IC used in the lithium battery protection board has become mature and stable. Adding temperature protection function will inevitably modify the internal logic circuit wafer design and external packaging design, resulting in a significant increase in cost (about 100% increase in cost according to experimental measurement). Therefore, in the increasingly competitive cost environment and in the case where the safety policy has not been fully implemented, it cannot be effectively popularized.

[0006] 3. The battery contains temperature protection devices, which mainly include circuit breakers, temperature fuses and temperature switches. The temperature protection devices have a large size, and the operation process is troublesome, which reduces the production efficiency. The high-end circuit breaker is expensive. The temperature switch body is too large to match the trend of miniaturization of 3C digital products, and the temperature protection device needs a post-welding process, which also increases labor costs and causes the inability to popularize.

[0007] Therefore, there is an urgent need for a temperature protection circuit and a lithium battery to overcome the above-mentioned defects. SUMMARY

[0008] The purpose of the present application is to provide a temperature protection circuit and a lithium battery, which can realize temperature protection function and greatly reduce development and material cost, improve production efficiency, and also use the epitaxial structure of the flexible circuit board for design to improve temperature protection detection precision and realize more accurate temperature protection function.

[0009] To achieve the above object, the present application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a temperature protection circuit, which comprises a protection unit, a temperature detection circuit and a control switch circuit, the protection unit has a voltage detection function, the temperature detection circuit is used for detecting temperature change of the battery assembly and outputting a corresponding voltage signal, and the control switch circuit controls working state of the protection unit according to the voltage signal, when the temperature of the battery assembly reaches a preset temperature, the protection unit is controlled to enter a protection state of stopping discharging.

[0011] Preferably, the control switch circuit lowers the VDD pin voltage of the protection unit to below the over-discharge protection voltage, so that the protection unit enters the protection state of stopping discharging.

[0012] Specifically, the temperature detection circuit comprises a voltage dividing circuit, which outputs different voltage dividing voltages as the voltage signal according to temperature change of the battery assembly.

[0013] Further, the voltage dividing circuit comprises a positive temperature coefficient thermistor and a third resistor connected in series, the voltage dividing circuit is electrically connected between the positive electrode and the negative electrode of the battery assembly, and the negative electrode of the battery assembly is grounded.

[0014] Preferably, the control switch circuit comprises a switching element, a control end of the switching element is electrically connected to a voltage dividing point between the positive temperature coefficient thermistor and the third resistor, and an output end of the switching element is electrically connected to the VDD pin of the protection unit.

[0015] Preferably, the switching element is a second field effect transistor, a triode or a thyristor.

[0016] Specifically, the switching element is a second field effect transistor, the second field effect transistor is an N-channel MOS transistor, a gate of the second field effect transistor is electrically connected to the voltage dividing point between the positive temperature coefficient thermistor and the third resistor, a drain is electrically connected to the VDD pin of the protection unit, and a source is electrically connected to the negative electrode of the battery assembly.

[0017] Preferably, the temperature protection circuit further comprises a charging and discharging switch field effect transistor group connected in series in a charging and discharging loop of the battery assembly, the charging and discharging switch field effect transistor group comprises two first field effect transistors connected in back-to-back, sources of the two first field effect transistors are connected, drains are respectively electrically connected to the negative electrode of the battery assembly, a gate of one of the two first field effect transistors is electrically connected to the OD pin of the protection unit, and a gate of the other is electrically connected to the OC pin of the protection unit.

[0018] Preferably, one end of the positive temperature coefficient thermistor is electrically connected to the positive electrode of the battery cell assembly, and the other end is electrically connected to the negative electrode of the battery cell assembly through the third resistor.

[0019] The gate of the second field effect transistor is connected to the connection point of the positive temperature coefficient thermistor and the third resistor, the source is electrically connected to the negative electrode of the battery cell assembly, and the drain is electrically connected to the VDD pin of the protection unit, and the VSS pin of the protection unit is electrically connected to the negative electrode of the battery cell assembly.

[0020] Preferably, the temperature protection circuit further comprises a filter capacitor, a first resistor and a second resistor, the filter capacitor is electrically connected between the VDD pin and the VSS pin of the protection unit, and the filter capacitor is used for filtering the power supply voltage of the protection unit.

[0021] The VDD pin of the protection unit is electrically connected to the positive electrode of the battery cell assembly through the first resistor.

[0022] One end of the second resistor is electrically connected to the CS pin of the protection unit, and the other end is electrically connected to the negative electrode of the battery cell assembly.

[0023] Preferably, the positive temperature coefficient thermistor is a positive temperature coefficient thermistor made of ceramic material.

[0024] Preferably, the protection unit further has an over-discharge hibernation function, and the temperature protection circuit has an automatic recovery function, and when the temperature decreases to a safe range, the normal working state can be restored through external charging.

[0025] In a second aspect, the present application provides a lithium battery comprising a battery cell assembly, a flexible circuit board and a temperature protection circuit as described above, wherein the temperature protection circuit is arranged on the flexible circuit board.

[0026] Preferably, when the temperature detection circuit comprises a positive temperature coefficient thermistor, the positive temperature coefficient thermistor is arranged on the flexible circuit board by using a SMD packaging process, and the flexible circuit board is attached to the surface of the battery cell assembly.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1. Based on the conventional lithium battery protection circuit, by uniquely adding a pure hardware temperature protection circuit, the over-discharge protection function of the existing protection IC is ingeniously used to realize temperature protection. The voltage divider circuit composed of positive temperature coefficient thermistor and fixed resistor drives N-channel MOS tube, which pulls down the VDD voltage of protection IC to trigger over-discharge protection when the temperature is abnormal, without modifying the internal logic circuit and wafer design of protection IC, avoiding the high cost (cost reduction of more than 50%) caused by the need to customize special temperature protection IC in traditional scheme, and greatly shortening the development cycle;

[0029] 2. The positive temperature coefficient thermistor is made of ceramic material, which has more stable and regular temperature-resistance characteristics than high polymer material PTC, and the protection temperature point can be accurately designed according to the temperature-resistance curve. In addition, combined with the design of flexible circuit board, the positive temperature coefficient thermistor can be directly attached to the surface of the battery cell, greatly improving the temperature detection accuracy and response speed, and realizing more accurate temperature protection function;

[0030] 3. Compared with the traditional need to increase circuit breaker, temperature fuse, temperature switch and other large volume temperature protection devices, the present application only needs to add a few SMD components (PTC, resistor, MOS tube), without post-welding process, and can be directly assembled on the SMT production line, greatly improving the production efficiency and reducing the labor cost, and the SMD packaged positive temperature coefficient thermistor is small in size, which fully meets the miniaturization trend of 3C digital products;

[0031] 4. The over-discharge sleep function of the protection IC is used, when the temperature is abnormal, the circuit enters a stable sleep state. When the temperature decreases to a safe range, the resistance value of the positive temperature coefficient thermistor decreases, and the N-channel MOS tube is automatically turned off. At this time, the protection state can be removed by external charging without manual intervention or replacement of components, which ensures the reusability of the circuit and the battery, and improves the reliability and service life of the product;

[0032] 5. It can be used with various existing lithium battery protection ICs, and the protection IC used is a general pin, which only needs to have over-discharge sleep function, without special customization, and has strong universality and compatibility. At the same time, by adjusting the resistance parameters in the voltage divider circuit, different protection temperature points can be flexibly set to meet the needs of different application scenarios.

[0033] The present application has other characteristics and advantages, which will be apparent or will be described in detail in the accompanying drawings and subsequent specific embodiments incorporated herein, which together serve to explain the specific principles of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0035] Figure 1 is a temperature protection circuit circuit diagram provided by the embodiment of the present application.

[0036] Figure 2 is a temperature resistance curve diagram of the positive temperature coefficient thermistor of ceramic material provided by the embodiment of the present application.

[0037] Figure 3 is a second field effect tube Q2 gate-source voltage VGS calculation schematic diagram of the positive temperature coefficient thermistor of ceramic material when the resistance value is 10KΩ at 25℃.

[0038] Figure 4 is a second field effect tube Q2 gate-source voltage VGS calculation schematic diagram of the positive temperature coefficient thermistor of ceramic material when the resistance value is 200KΩ at 65℃.

[0039] Figure 5 is a structural schematic diagram of one angle of the lithium battery provided by the embodiment of the present application.

[0040] Figure 6 is a structural schematic diagram of another angle of the lithium battery provided by the embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0042] Embodiment one:

[0043] Please refer to Figures 1-4 The temperature protection circuit 100 of the embodiment includes a protection unit U1, a temperature detection circuit and a control switch circuit, the protection unit U1 is a common lithium battery protection IC on the market, which has a voltage detection function. The protection unit U1 and the charge-discharge switch field effect tube group 20 constitute a conventional lithium battery protection circuit, which realizes the conventional protection functions such as battery overvoltage and overcurrent. The protection unit U1 here has OC, OD, VSS, VDD and CS pins, which are respectively used for overcharge or overcurrent control, open drain output, power ground, power positive and current detection.

[0044] The temperature detection circuit is used for detecting temperature change of the battery cell assembly 200 which is the core part of the lithium battery and outputting corresponding voltage signal.

[0045] The control switch circuit controls the working state of the protection unit U1 according to the voltage signal, and when the temperature of the battery cell assembly 200 reaches the preset temperature, the control switch circuit controls the protection unit U1 to enter the protection state of stopping discharging. It can be understood that the preset temperature can be flexibly adjusted by combining and setting the parameters of various electronic components in the temperature protection circuit 100 of the embodiment.

[0046] The core innovation of the application is to add a pure hardware temperature protection circuit based on the conventional lithium battery protection circuit, without modifying the internal logic of the protection IC, which greatly reduces the cost.

[0047] Preferably, the control switch circuit triggers the over-discharge protection function by pulling down the VDD pin voltage of the protection unit U1 to below the over-discharge protection voltage, so that the protection unit U1 enters the protection state of stopping discharging. The over-discharge protection function is a function of the protection unit U1, which ingeniously uses the existing over-discharge protection function of the lithium battery protection IC to realize temperature protection, without modifying the internal logic of the IC, which greatly reduces the cost. When the VDD voltage is pulled down, the protection unit U1 triggers the over-discharge protection function, outputs a control signal to shut down the charging and discharging circuit, and stops the battery from discharging.

[0048] The temperature detection circuit includes a voltage dividing circuit 10 which outputs different voltage dividing voltages as voltage signals according to the temperature change of the battery cell assembly 200. By using the characteristics of the voltage dividing circuit 10, when the temperature of the battery cell assembly 200 changes, the resistance of the temperature sensitive element changes, thereby changing the voltage value of the voltage dividing point, realizing the conversion of the temperature of the battery cell assembly 200 to the voltage signal. The temperature here is generally the temperature of the surface of the battery cell assembly 200, of course, according to the placement position of the temperature sensitive element, the temperature protection according to the temperature change of other positions of the battery cell assembly 200 can be realized.

[0049] Specifically, the voltage dividing circuit 10 includes a positive temperature coefficient thermistor P1 and a third resistor R3 connected in series. The voltage dividing circuit 10 is electrically connected between the positive electrode B+ and the negative electrode B- of the battery cell assembly 200, and the negative electrode B- of the battery cell assembly 200 is grounded. The resistance value of the third resistor R3 is a fixed value, and 820KΩ is selected in the embodiment.

[0050] The control switch circuit comprises a switch element, a control end of the switch element is electrically connected to a voltage division point between the positive temperature coefficient thermistor P1 and the third resistor R3, and an output end of the switch element is electrically connected to a VDD pin of the protection unit U1. Through this connection mode, with the change of temperature, the resistance value of the positive temperature coefficient thermistor P1 also changes synchronously in the same direction, so that the voltage change of the voltage division point can control the on-off state of the switch element. The on-off of the switch element is controlled by using the characteristics of the voltage division circuit 10.

[0051] Specifically, the switch element can be a second field effect transistor Q2, a triode or a silicon controlled rectifier. These switch devices can realize the switching function according to the voltage signal of the control end, and have good versatility and replaceability. In other embodiments, appropriate switch devices can be selected according to specific application requirements.

[0052] Preferably, the switch element of the embodiment is the second field effect transistor Q2, which is an N-channel MOS transistor. The gate of the second field effect transistor Q2 is electrically connected to the voltage division point between the positive temperature coefficient thermistor P1 and the third resistor R3, the drain is electrically connected to the VDD pin of the protection unit U1, and the source is electrically connected to the negative pole B- of the battery cell assembly 200.

[0053] It can be understood that the selection of the N-channel MOS transistor is critical, and its conduction threshold voltage is 0.7V. When it is turned on, the VDD pin detection voltage of the protection unit U1 can be pulled down below the over-discharge protection voltage, so that the battery cell assembly 200 is forced to enter the over-discharge protection state, and the battery cannot continue to discharge, thereby playing a temperature protection role.

[0054] The temperature protection circuit of the embodiment further comprises a charge-discharge switch field effect transistor group 20 connected in series in the charge-discharge circuit of the battery cell assembly 200. The charge-discharge switch field effect transistor group 20 comprises two first field effect transistors Q1 connected in back-to-back, the sources of the two first field effect transistors Q1 are connected, and the drains are respectively electrically connected to the negative pole B- of the battery cell assembly 200.

[0055] Specifically, the gate of one of the two first field effect transistors Q1 is electrically connected to the OD pin of the protection unit U1 for discharge control, and the gate of the other is electrically connected to the OC pin of the protection unit U1 for charge control.

[0056] This back-to-back connection of MOS transistors can realize independent control of charging and discharging through the respective body diode directions. By controlling the current flow direction through the respective body diode directions, the protection unit U1 can control the gates of the two MOS transistors respectively, thereby realizing independent control of charging and discharging.

[0057] One end of the positive temperature coefficient thermistor P1 of the embodiment is electrically connected to the positive electrode B+ of the battery cell assembly 200, and the other end is electrically connected to the negative electrode B- of the battery cell assembly 200 through the third resistor R3. The gate of the second field effect tube Q2 is connected to the connection point of the positive temperature coefficient thermistor P1 and the third resistor R3, the source is electrically connected to the negative electrode B- of the battery cell assembly 200, and the drain is electrically connected to the VDD pin of the protection unit U1. The VSS pin of the protection unit U1 is electrically connected to the negative electrode B- of the battery cell assembly 200.

[0058] When the second field effect tube Q2 is turned on, the VDD pin of the protection unit U1 is connected to the negative electrode of the battery cell assembly 200 through the second field effect tube Q2, so that the voltage of the VDD pin is pulled down, realizing the temperature protection function. This connection mode ensures the reliability and stability of the circuit.

[0059] The temperature protection circuit of the embodiment further comprises a filter capacitor C1, a first resistor R1 and a second resistor R2.

[0060] The filter capacitor C1 is electrically connected between the VDD pin and the VSS pin of the protection unit U1, which is used to filter the power supply voltage of the protection unit U1, improve the stability of the circuit, and reduce the influence of voltage fluctuation on the operation of the protection unit U1. The capacitance value of the filter capacitor C1 is preferably 0.1 μF to 10 μF.

[0061] The VDD pin of the protection unit U1 is electrically connected to the positive electrode B+ of the battery cell assembly 200 through the first resistor R1, which is used for current limiting and voltage sampling to protect the VDD pin from overcurrent impact.

[0062] One end of the second resistor R2 is electrically connected to the CS pin of the protection unit U1, and the other end is electrically connected to the negative electrode B- of the battery cell assembly 200. The second resistor R2 is used to set the working parameters of the protection unit U1, such as the overcurrent protection threshold. By adjusting the resistance value of R2, different overcurrent protection points can be set.

[0063] Preferably, the positive temperature coefficient thermistor P1 is a ceramic positive temperature coefficient thermistor. The unique selection of ceramic positive temperature coefficient thermistor is different from the high molecular polymer material PTC. When the resistance value increases with the increase of temperature, the resistance value is more stable and regular, and the temperature coefficient is more linear. Figure 2 The temperature-resistance curve of the ceramic positive temperature coefficient thermistor is shown, which can be easily designed for temperature circuit.

[0064] In this embodiment, the positive temperature coefficient thermistor P1 selected has a resistance of 10KΩ at 25℃ and a resistance of 200KΩ at 65℃. In order to better understand the technical solution of this embodiment, the resistance variation rule at different temperatures can be obtained according to the temperature curve of the positive temperature coefficient thermistor P1. Taking the battery voltage of 4V as an example for calculation:

[0065] 1. Normal temperature working state (25℃): as shown in the figure, the resistance of the positive temperature coefficient thermistor P1 is 10KΩ at 25℃, and the gate-source voltage VGS of the second field effect transistor Q2 is the voltage at the voltage dividing point, so according to the voltage dividing formula, the voltage at the voltage dividing point is: Figure 3

[0066] VGS=4V×R3 / (P1+R3)=4V×820 / (10+820)≈0.048V,

[0067] This voltage at the voltage dividing point is much lower than the conduction threshold value 0.7V of the N-channel second field effect transistor Q2, and the second field effect transistor Q2 remains in the off state, the VDD pin of the protection unit U1 maintains the normal voltage, and the battery assembly 200 is in the normal working state.

[0068] 2. High temperature protection state (65℃): as shown in the figure, when the temperature of the battery assembly 200 rises to 65℃, the resistance of the positive temperature coefficient thermistor P1 increases to 200KΩ. At this time, the voltage at the voltage dividing point is: Figure 4

[0069] VGS=4V×R3 / (P1+R3)=4V×820 / (200+820)≈0.78V,

[0070] This voltage at the voltage dividing point is greater than the minimum conduction threshold value 0.7V of the second field effect transistor Q2, and the second field effect transistor Q2 is turned on, connecting the VDD pin of the protection unit U1 to the negative electrode of the battery assembly 200 through the second field effect transistor Q2, and the VDD voltage of the protection unit U1 is pulled down to below the over-discharge protection voltage. The protection unit U1 detects that the VDD voltage is too low, triggers the over-discharge protection function, outputs a control signal to turn off the charge-discharge switch field effect transistor group 20, and the battery assembly 200 stops discharging, realizing the temperature protection function.

[0071] ​​3. Automatic recovery process: when the surface temperature of the battery assembly 200 reaches the protection temperature, the discharge is stopped, and as the temperature decreases, the resistance of the positive temperature coefficient thermistor P1 also decreases, and the gate-source voltage VGS of the second field effect transistor Q2 decreases. When the gate-source voltage VGS of the second field effect transistor Q2 is lower than the threshold value of 0.7V, the second field effect transistor Q2 is turned off, and the VDD pin of the protection unit U1 is no longer pulled low. At this time, the battery assembly 200 can be charged by an external charger to restore the VDD voltage of the protection unit U1 to normal, so that the protection unit U1 is removed from the over-discharge protection state, and the battery assembly 200 returns to normal operation, ensuring the reusability of the circuit and the battery.

[0072] In this embodiment, the protection unit U1 must be selected with an over-discharge sleep function, which can ensure that the circuit can enter a stable protection state after the temperature protection is triggered, and the protection can be removed by charging when the temperature returns to normal.

[0073] Based on the temperature protection circuit design, when the surface temperature of the battery reaches the protection temperature, the battery stops discharging. As the temperature decreases, the resistance of the positive temperature coefficient thermistor P1 also decreases, and the gate-source voltage VGS of the second field effect transistor Q2 decreases. When the gate-source voltage VGS of the second field effect transistor Q2 is lower than the threshold value of 0.7V, the conduction channel of the second field effect transistor Q2 is closed, so the second field effect transistor Q2 is disconnected. At this time, the battery assembly 200 is charged by an external charger to remove the protection state, ensuring the reusability of the temperature protection circuit and the battery assembly 200, achieving the automatic recovery function, and effectively reducing the use cost and recovery cost.

[0074] Please refer to Figure 1 and Figure 2 The lithium battery of the present embodiment includes a battery assembly 200, a flexible circuit board 300, and the temperature protection circuit 100 described above. The temperature protection circuit 100 is arranged on the flexible circuit board 300, and all components can be completed by SMT process at one time, without the need for post-soldering process, greatly improving the production efficiency.

[0075] When the temperature detection circuit 100 includes a positive temperature coefficient thermistor P1, the positive temperature coefficient thermistor P1 is arranged on the flexible circuit board 300 using a surface mount packaging process, and the flexible circuit board 300 is attached to the surface of the battery assembly 200 or the internal battery.

[0076] Based on the temperature protection circuit design, the related battery application can be extended. By using the miniaturization characteristics of the positive temperature coefficient thermistor P1 patch, the flexible circuit board 300 can be directly attached to the surface of the battery cell assembly 200, thereby greatly improving the temperature detection accuracy and realizing more accurate temperature protection function. This structure design enables the temperature sensor to directly contact the surface of the battery cell, the temperature response is faster, and the detection is more accurate. Moreover, through this structure design, the production operation is more convenient, the efficiency is higher, and batch production is possible.

[0077] In combination Figures 1-6 , the present application has the following beneficial effects:

[0078] By skillfully utilizing the temperature characteristics of the positive temperature coefficient thermistor and the principle of the voltage divider circuit 10, and combining the switching characteristics of the N-channel MOS tube, the VDD voltage control of the lithium battery protection IC is realized, thereby triggering the over-discharge protection function to realize temperature protection. The whole scheme does not need to modify the internal logic of the existing lithium battery protection IC, and can be realized by only a simple peripheral circuit, with low cost, high reliability, and suitable for large-scale production application.

[0079] The above-described and above-mentioned embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A temperature protection circuit, characterized in that: It includes a protection unit, a temperature detection circuit and a control switch circuit. The protection unit has a voltage detection function. The temperature detection circuit is used to detect the temperature change of the battery cell assembly and output a corresponding voltage signal. The control switch circuit controls the working state of the protection unit according to the voltage signal. When the temperature of the battery cell assembly reaches a preset temperature, the protection unit is controlled to enter a protection state of stopping discharge.

2. The temperature protection circuit according to claim 1, wherein: The control switch circuit pulls down the voltage of the VDD pin of the protection unit to below the over-discharge protection voltage, so that the protection unit enters a protection state of stopping discharge.

3. The temperature protection circuit according to claim 2, wherein: The temperature detection circuit includes a voltage divider circuit, and the voltage divider circuit outputs different divided voltages as the voltage signal according to the temperature change of the battery cell assembly.

4. The temperature protection circuit according to claim 3, wherein: The voltage divider circuit includes a positive temperature coefficient thermistor and a third resistor connected in series in sequence. The voltage divider circuit is electrically connected between the positive electrode and the negative electrode of the battery cell assembly, and the negative electrode of the battery cell assembly is grounded.

5. The temperature protection circuit according to claim 4, wherein: The control switch circuit includes a switch element, a control end of the switch element is electrically connected to a voltage dividing point between the positive temperature coefficient thermistor and a third resistor, and an output end of the switch element is electrically connected to a VDD pin of the protection unit.

6. The temperature protection circuit according to claim 5, wherein: The switch element is a second field effect tube, a triode or a thyristor.

7. The temperature protection circuit according to claim 6, wherein: The switching element is a second field effect transistor, which is an N-channel MOS transistor. The gate of the second field effect transistor is electrically connected to the voltage divider point between the positive temperature coefficient thermistor and the third resistor, the drain is electrically connected to the VDD pin of the protection unit, and the source is electrically connected to the negative electrode of the battery cell assembly.

8. The temperature protection circuit according to claim 7, wherein: The temperature protection circuit also includes a charge and discharge switch field effect transistor group connected in series in the charge and discharge circuit of the battery cell assembly, and the charge and discharge switch field effect transistor group includes two first field effect transistors electrically connected back to back, the sources of the two first field effect transistors are connected, and the drains are electrically connected to the negative electrode of the battery cell assembly respectively, the gate of one of the two first field effect transistors is electrically connected to the OD pin of the protection unit, and the gate of the other is electrically connected to the OC pin of the protection unit.

9. The temperature protection circuit according to claim 7, wherein: One end of the positive temperature coefficient thermistor is electrically connected to the positive electrode of the battery core assembly, and the other end is electrically connected to the negative electrode of the battery core assembly through the third resistor; The gate of the second field effect transistor is connected to the connection point of the positive temperature coefficient thermistor and the third resistor, the source is electrically connected to the negative electrode of the battery cell assembly, the drain is electrically connected to the VDD pin of the protection unit, and the VSS pin of the protection unit is electrically connected to the negative electrode of the battery cell assembly.

10. The temperature protection circuit according to claim 8 or 9, characterized in that: It also includes a filter capacitor, a first resistor and a second resistor, wherein the filter capacitor is electrically connected between the VDD pin and the VSS pin of the protection unit, and the filter capacitor is used to filter the power supply voltage of the protection unit; The VDD pin of the protection unit is electrically connected to the positive electrode of the battery cell assembly through the first resistor; One end of the second resistor is electrically connected to the CS pin of the protection unit, and the other end is electrically connected to the negative electrode of the battery cell assembly.

11. The temperature protection circuit according to claim 4, wherein: The positive temperature coefficient thermistor is a positive temperature coefficient thermistor made of ceramic material.

12. The temperature protection circuit according to claim 1, wherein: The protection unit also has an over-discharge sleep function, and the temperature protection circuit has an automatic recovery function. When the temperature drops to a safe range, the normal working state can be restored through external charging.

13. A lithium battery, characterized in that: It comprises a battery cell assembly, a flexible circuit board and a temperature protection circuit according to any one of claims 1 to 12, wherein the temperature protection circuit is arranged on the flexible circuit board.

14. The lithium battery according to claim 13, wherein When the temperature detection circuit includes a positive temperature coefficient thermistor, the positive temperature coefficient thermistor is arranged on the flexible circuit board by using a surface mount packaging process, and the flexible circuit board is attached to the surface of the battery core assembly.

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