A dual protection circuit for lithium batteries

Abstract

This invention discloses a dual protection circuit for lithium batteries. An isolation circuit for protecting the second control chip circuit is connected between the discharge control terminal of the second control chip circuit and the gate terminal of the second MOS transistor circuit. The discharge control terminal of the second control chip circuit is connected to a control signal sampling circuit and a step-down circuit. The control signal sampling circuit is connected to a drive control circuit for controlling the rapid switching on and off of the second MOS transistor circuit. The step-down circuit is connected to a power storage circuit. A MOS energy discharge circuit is connected between the gate terminal and the source terminal of the second MOS transistor circuit. A voltage regulation control circuit for protecting the fourth MOS transistor circuit is connected between the gate terminal and the source terminal of the fourth MOS transistor circuit. By adopting a dual IC + dual MOS scheme, dual protection functions are achieved. Even if the first-level circuit fails, the second circuit can still protect the battery cell, improving the safety and reliability of the battery pack system.

Description

[Technical Field]

[0001] This invention relates to a dual protection circuit for lithium batteries. [Background Technology]

[0002] Due to their inherent chemical properties, existing lithium batteries pose a risk of thermal runaway, fire, or explosion if used beyond their specifications. Therefore, a circuit board is needed in battery packs composed of individual cells to protect and manage each cell, ensuring that no serious safety accidents occur during use.

[0003] For battery packs used in general applications, a single-level circuit board protection scheme is typically used. If the single-level protection circuit fails due to uncontrollable factors, all protection functions will fail, and the battery cells will be at risk of being used beyond specifications at any time. For applications with more stringent requirements, a dual-level protection circuit scheme is typically used. That is, if the single-level protection circuit board fails, there is a second-level circuit to protect the battery, increasing the redundancy of the system and improving the safety of the system.

[0004] There are currently three types of dual-protection hardware protection circuits commonly used in the market:

[0005] The first type is a hardware protection circuit consisting of an IC controller, MOS, and either a fuse or a PTC. However, it has the following drawbacks: 1. Incomplete protection functions, lacking dual voltage protection; 2. Current PTC technology cannot handle high voltage and high current, and after multiple protection cycles, the PTC's internal resistance increases, presenting certain limitations; 3. Fuse selection is difficult. If the fuse is too small, it will activate before the MOS during a short circuit, causing the battery pack to become unusable. If the fuse is too large, the MOS and sampling resistor will fail before the fuse during safety certification, posing a fire risk. Furthermore, the fuse itself has significant individual parameter variations, making design and selection difficult; 4. In terms of design, it is difficult to provide overcurrent protection for the battery pack during charging and discharging using a fuse.

[0006] The second type is a hardware protection circuit consisting of an IC controller, a secondary controller, a MOS, and a three-terminal fuse. However, it has the following disadvantages: 1. Incomplete functionality, lacking over-discharge secondary protection, temperature dual protection, and basically no current dual protection; 2. The three-terminal fuse also presents difficulties in selection. Refer to points 3 and 4 in the first scheme.

[0007] The third type is a hardware protection circuit composed of IC controller + IC controller + MOS + MOS. However, it has the following drawbacks: under extreme conditions such as high current charging and discharging or short circuit, the charging and discharging MOS and IC may fail.

[0008] Conventional dual protection circuit structure such as Figure 1As shown, when the discharge overcurrent is too large or there is a short circuit, due to the parasitic equivalent inductance of the circuit, the induced voltage U = L*DI / DT, therefore, when the current is large enough, the induced voltage across the DS terminals of the discharge MOS transistor in the first MOS circuit will reach several times the voltage of the battery pack itself when it is turned off. For example, if the battery pack is 12V, the induced voltage when the discharge MOS transistor in the first MOS circuit is turned off will be as high as 30-50V.

[0009] Figure 1 In the circuit, if a large current occurs during the discharge process, and the discharge MOSFET in the first MOSFET circuit is turned off at this time, according to U=L*DI / DT, an extremely high induced voltage will be generated across the drain and source terminals of the discharge MOSFET. This induced voltage will cause the Vgs of the charging MOSFET in the second MOSFET circuit to exceed ±20V, leading to the risk of failure of the charging MOSFET in the second MOSFET circuit. At the same time, the induced energy will flow into the control IC in the second control chip circuit in the direction of the red curve arrow in the figure below, causing damage to the charging control terminal of the control IC.

[0010] Figure 1 In the circuit, if an abnormally high voltage and current occur during charging, and the charging MOSFET in the third MOSFET circuit is turned off at this time, a high negative voltage will appear between P- and GND. If the discharging MOSFET in the fourth MOSFET circuit is not turned off at this time, the VGS voltage of the discharging MOSFET will exceed ±20V, causing the MOSFET to fail. [Summary of the Invention]

[0011] This invention overcomes the shortcomings of the prior art and provides a dual protection circuit for lithium batteries, which solves the problem of protection failure under extreme conditions in existing dual protection circuits for lithium batteries and realizes comprehensive dual voltage protection function for lithium batteries.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A dual protection circuit for a lithium battery includes a first MOSFET circuit and a second MOSFET circuit for controlling discharge, a third MOSFET circuit and a fourth MOSFET circuit for controlling charging, a first control chip circuit, and a second control chip circuit. The first and second control chip circuits can detect lithium battery temperature, voltage, and current information, and control the charging and discharging of the lithium battery. The negative terminal of the lithium battery is connected to the source terminal of the first MOSFET circuit through a resistor R1. The drain terminal of the first MOSFET circuit is connected to the source terminal of the second MOSFET circuit. The drain terminal of the second MOSFET circuit is connected to the drain terminal of the third MOSFET circuit. The source terminal of the third MOSFET circuit is connected to the drain terminal of the fourth MOSFET circuit. The source terminal of the fourth MOSFET circuit is connected to the negative output terminal of the load. The discharge control terminal of the first control chip circuit is connected to the gate terminal of the first MOSFET circuit, and the charging control terminal of the first control chip circuit is connected to the gate terminal of the third MOSFET circuit. The second control chip circuit's charging control terminal is connected to the gate terminal of the fourth MOS transistor circuit. The circuit is characterized by: an isolation circuit for protecting the second control chip circuit being connected between the discharge control terminal of the second control chip circuit and the gate terminal of the second MOS transistor circuit; a control signal sampling circuit for sampling the discharge control signal of the second control chip circuit and a step-down circuit for reducing the output voltage of the discharge control terminal of the second control chip circuit being connected to the discharge control terminal of the second control chip circuit; a drive control circuit for controlling the rapid switching of the second MOS transistor circuit being connected to the control signal sampling circuit; a power storage circuit for storing energy and supplying power to the drive control circuit being connected to the step-down circuit; a MOS energy discharge circuit for protecting the second MOS transistor circuit being connected between the gate terminal and the source terminal of the second MOS transistor circuit; and a voltage regulation control circuit for protecting the fourth MOS transistor circuit being connected between the gate terminal and the source terminal of the fourth MOS transistor circuit.

[0014] The lithium battery dual protection circuit described above is characterized in that: the second MOS transistor circuit includes a MOS transistor Q6, the source terminal of the MOS transistor Q6 is connected to the drain terminal of the first MOS transistor circuit and one end of the resistor R37, the drain terminal of the MOS transistor Q6 is connected to the drain terminal of the third MOS transistor circuit, the gate terminal of the MOS transistor Q6 is connected to the other end of the resistor R37 and one end of the resistor R40, and the other end of the resistor R40 is connected to the discharge control terminal of the second control chip circuit through the resistor R35.

[0015] The lithium battery dual protection circuit described above is characterized in that: the isolation circuit is a diode D2, the positive terminal of the diode D2 is connected to the discharge control terminal of the second control chip circuit, and the negative terminal of the diode D2 is connected to a resistor R35.

[0016] The lithium battery dual protection circuit described above is characterized in that: the drive control circuit includes a MOSFET Q9 and a MOSFET Q10, the drain terminal of the MOSFET Q9 is connected between resistors R40 and R35, the source terminal of the MOSFET Q9 is grounded, the gate terminal of the MOSFET Q9 is connected to one end of resistor R41 and one end of resistor R49, the other end of resistor R41 is grounded, the other end of resistor R49 is connected to the drain terminal of the MOSFET Q10, the source terminal of the MOSFET Q10 is connected to one end of resistor R50 and the power storage circuit, and the gate terminal of the MOSFET Q10 is connected to the other end of resistor R50 and the control signal sampling circuit.

[0017] The lithium battery dual protection circuit described above is characterized in that: the control signal sampling circuit includes a diode D8, the negative terminal of the diode D8 is connected to the discharge control terminal of the second control chip circuit, and the positive terminal of the diode D8 is connected to the gate terminal of the MOS transistor Q10 through a resistor R52.

[0018] The lithium battery dual protection circuit described above is characterized in that: the power supply circuit includes a storage capacitor C5, one end of the storage capacitor C5 is connected to one end of the resistor R48 and the source terminal of the MOSFET Q10, the other end of the resistor R48 is connected to the step-down circuit, and the other end of the storage capacitor C5 is grounded.

[0019] The lithium battery dual protection circuit described above is characterized in that: the step-down circuit is a diode D7, the positive terminal of the diode D7 is connected to the discharge control terminal of the second control chip circuit, and the negative terminal of the diode D7 is connected to a resistor R48.

[0020] The lithium battery dual protection circuit described above is characterized in that: the MOS energy discharge circuit is a diode D6, the positive terminal of the diode D6 is connected to the source terminal of the MOS transistor Q6, and the negative terminal of the diode D6 is connected to the gate terminal of the MOS transistor Q6.

[0021] The lithium battery dual protection circuit described above is characterized in that: the fourth MOS transistor circuit includes a MOS transistor Q8, the drain terminal of the MOS transistor Q8 is connected to the source terminal of the third MOS transistor circuit, the source terminal of the MOS transistor Q8 is connected to the negative output terminal of the load, the gate terminal of the MOS transistor Q8 is connected to the collector terminal of the transistor Q12, the base terminal of the transistor Q12 is grounded through a resistor R39, and the emitter terminal of the transistor Q12 is connected to the charging control terminal of the second control chip circuit through a resistor R32.

[0022] The lithium battery dual protection circuit described above is characterized in that: the voltage regulation control circuit is a Zener diode D5, the positive terminal of the Zener diode D5 is connected to the source terminal of the MOSFET Q8, and the negative terminal of the Zener diode D5 is connected to the gate terminal of the MOSFET Q8.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention adopts a dual IC + dual MOS scheme to achieve dual protection function. Even if the primary circuit fails, the secondary circuit can protect the battery cell, thereby improving the safety and reliability of the battery pack system.

[0025] 2. This invention eliminates the need for traditional solutions to select Fuse, three-terminal Fuse, and PTC, simplifying design and testing and saving a significant amount of design and testing time.

[0026] 3. This invention solves the problem of high current easily burning out fuses in traditional circuits, thereby completely solving the problem of permanent damage to battery packs caused by fuses.

[0027] 4. This invention solves the problem that PTC cannot be used in high-voltage, high-current scenarios due to its limitations, and also solves the problem of excessive internal resistance caused by the use of PTC.

[0028] 5. This invention solves the problem of chip and MOS failure when there is a large current abnormality in traditional dual protection circuits, completely solves various problems in safety certification, and improves product reliability. [Image Description]

[0029] Figure 1 This is a schematic diagram of a dual protection circuit for existing lithium batteries.

[0030] Figure 2 This is a schematic diagram of the invention;

[0031] Figure 3 This is one of the circuit diagrams of the present invention;

[0032] Figure 4 This is the second circuit diagram of the present invention. [Detailed Implementation]

[0033] The technical solutions in the embodiments of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0034] It should be noted that all directional indications in the embodiments of the present invention, such as up, down, left, right, front, back, etc., are only used to explain the relative positional relationship and movement of the components in a specific posture as shown in the accompanying drawings. If the specific posture changes, the directional indication will also change accordingly. Furthermore, descriptions involving "preferred," "second-best," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "preferred" or "second-best" may explicitly or implicitly include at least one of those features.

[0035] like Figure 2-4As shown, a dual protection circuit for a lithium battery includes a first MOSFET circuit 1 and a second MOSFET circuit 2 for controlling discharge, a third MOSFET circuit 3 and a fourth MOSFET circuit 4 for controlling charging, a first control chip circuit 5 and a second control chip circuit 6. The first control chip circuit 5 and the second control chip circuit 6 can detect lithium battery temperature, voltage and current information, and control the charging and discharging of the lithium battery. The negative terminal of the lithium battery is connected to the source terminal of the first MOSFET circuit 1 through a resistor R1. The drain terminal of the first MOSFET circuit 1 is connected to the source terminal of the second MOSFET circuit 2. The drain terminal of the second MOSFET circuit 2 is connected to the drain terminal of the third MOSFET circuit 3. The source terminal of the third MOSFET circuit 3 is connected to the drain terminal of the fourth MOSFET circuit 4. The source terminal of the fourth MOSFET circuit 4 is connected to the negative output terminal of the load. The discharge control terminal of the first control chip circuit 5 is connected to the gate terminal of the first MOSFET circuit 1. The charging control terminal of the first control chip circuit 5 is connected to the gate terminal of the third MOSFET circuit 3. The charging control terminal of the second control chip circuit 6 is connected to the gate terminal of the fourth MOSFET circuit 4.

[0036] An isolation circuit 7 for protecting the second control chip circuit 6 is connected between the discharge control terminal of the second control chip circuit 6 and the gate terminal of the second MOS transistor circuit 2. The discharge control terminal of the second control chip circuit 6 is connected to a control signal sampling circuit 8 for sampling the discharge control signal of the second control chip circuit 6 and a step-down circuit 9 for reducing the output voltage of the discharge control terminal of the second control chip circuit 6. The control signal sampling circuit 8 is connected to a drive control circuit 10 for controlling the rapid switching on and off of the second MOS transistor circuit 2. The step-down circuit 9 is connected to a power storage circuit 11 for storing energy and supplying power to the drive control circuit 10. A MOS energy discharge circuit 12 for protecting the second MOS transistor circuit 2 is connected between the gate terminal and the source terminal of the second MOS transistor circuit 2. A voltage regulation control circuit 13 for protecting the fourth MOS transistor circuit 4 is connected between the gate terminal and the source terminal of the fourth MOS transistor circuit 4.

[0037] In the first control chip circuit 5 and the second control chip circuit 6 of this invention, two identical control chips are used, namely control chip U2 and control chip U1; in the first MOS transistor circuit 1, the second MOS transistor circuit 2, the third MOS transistor circuit 3, and the fourth MOS transistor circuit 4, four identical N-type MOS transistors are used, namely MOS transistor Q5, MOS transistor Q6, MOS transistor Q7, and MOS transistor Q8, which is easy to purchase in large quantities and reduce costs; at the same time, considering the system's greater safety and reliability, protection IC1 and IC2 can also be selected from different models, and different models of MOS transistors can also be selected.

[0038] In this case, control chip U1 and control chip U2 perform the same function; therefore, all protection and monitoring of the battery cell are dual, including monitoring of various information such as temperature, voltage, and current. Figure 3 As shown, temperature sensor R13 in the second control chip circuit 6 and temperature sensor R17 in the first control chip circuit 5 are both used to detect the temperature of the lithium battery; connection terminal J2 in the second control chip circuit 6 is connected to the positive terminal of the lithium battery, and connection terminal J6 is connected to the negative terminal of the lithium battery, used to supply power to control chip U1 and control chip U2; connection terminals J3-J5 are respectively used to connect to individual battery cells, used by control chip U1 and control chip U2 to detect the voltage information of each individual battery cell; Is connection terminal in the second control chip circuit 6 and Is connection terminal in the first control chip circuit 5 are respectively connected to the negative terminal of the lithium battery, used to detect the lithium battery current information.

[0039] The control chip U2 in the first control chip circuit 5 controls the discharge MOSFET Q5 in the first MOSFET circuit 1 and the charging MOSFET Q7 in the third MOSFET circuit 3; the control chip U1 in the second control chip circuit 6 controls the discharge MOSFET Q6 in the second MOSFET circuit 2 and the charging MOSFET Q8 in the fourth MOSFET circuit 4.

[0040] When the cell temperature is abnormal, both control chip U1 and control chip U2 monitor the cell, and either or both of the two control chips will control the corresponding MOSFET to shut down for protection.

[0041] When an abnormal voltage occurs, both control chips monitor the battery cell, and either or both of the two control chips will control the corresponding MOSFET to shut down for protection.

[0042] When a large current is discharged, both control chips monitor the battery cell, and either or both of the two control chips will control the corresponding MOS to shut down for protection.

[0043] When the discharge MOSFET Q6 in the second MOSFET circuit 2 is activated first, the system operates normally. If the discharge MOSFET Q5 in the first MOSFET circuit 1 is activated first, the circuit operates as follows:

[0044] When the discharge MOSFET Q5 in the first MOSFET circuit 1 is turned off, a very high induced voltage will be generated across the drain (D) and source (S) of the discharge MOSFET Q5 due to the parasitic inductance of the circuit board and components. The theoretical formula for calculating this voltage is U = L * DI / DT. From this formula, it can be seen that the value of U is affected by the magnitude of the parasitic inductance, the magnitude of DI, and the magnitude of DT. Generally, the circuit drive resistance remains unchanged, and the parasitic inductance will not change much with the design of the circuit, that is, DT does not change much. Therefore, the only one with a large change in the circuit is DI. If the load is too heavy, the value of DI will be very large, resulting in a very high value of U.

[0045] When the value of U is very high, the isolation circuit 7 takes effect, isolating the high voltage U from the charging control terminal of the control chip U1 in the second control chip circuit 6, so the control chip U1 will not be damaged.

[0046] However, due to the isolation circuit 7, the discharge MOSFET Q6 controlled by the control chip U1 can only be turned on quickly but not turned off quickly. If the turn-off speed is too slow, the turn-off loss of the discharge MOSFET Q6 will be too high, which will lead to the damage of the discharge MOSFET Q6. Therefore, on the basis of setting the isolation circuit 7, a control signal sampling circuit 8, a step-down circuit 9, a drive control circuit 10, and a power supply energy storage circuit 11 are set to realize the rapid turn-off of M2.

[0047] The above solutions address the high-voltage isolation between control chips U1 and U, and the rapid turn-on and turn-off of discharge MOSFET Q6. However, there is still a problem where excessively high U causes the voltage VGS between the gate and source of discharge MOSFET Q6 to exceed the ±20 upper and lower limits. Therefore, a MOSFET energy discharge circuit 12 is set between the gate G and source S of discharge MOSFET Q6 to ensure that the VGS of MOSFET Q6 does not exceed the specified value.

[0048] On the other hand, when charging with abnormally high current and voltage, both control chips U1 and U2 monitor the battery cell. Either or both of these control chips will control the corresponding MOS transistor to shut down for protection. When the charging MOS transistor Q8 in the fourth MOS transistor circuit 4 is protected first, the system is protected normally. If the charging MOS transistor Q7 in the third MOS transistor circuit 3 is protected first, the charging MOS transistor Q8 is not yet turned off. At this time, an extremely high negative voltage appears between P- and GND. This negative voltage will cause the voltage VGS between the gate and source of the charging MOS transistor Q8 to exceed the ±20V upper and lower limits. Therefore, a voltage regulation control circuit 13 is set between the gate G and source S of the charging MOS transistor Q8. That is, even when the charging MOS transistor Q7 is turned off first, it can still be ensured that the VGS of the charging MOS transistor Q8 will not exceed the ±20V upper and lower limits, thus ensuring the reliability of the system.

[0049] like Figure 3-4As shown, specifically, the second MOS transistor circuit 2 includes a MOS transistor Q6. The source terminal of the MOS transistor Q6 is connected to the drain terminal of the first MOS transistor circuit 1 and one end of the resistor R37, respectively. The drain terminal of the MOS transistor Q6 is connected to the drain terminal of the third MOS transistor circuit 3, and the gate terminal of the MOS transistor Q6 is connected to the other end of the resistor R37 and one end of the resistor R40, respectively. The other end of the resistor R40 is connected to the discharge control terminal of the second control chip circuit 6 through the resistor R35.

[0050] Specifically, the isolation circuit 7 is diode D2, the positive terminal of diode D2 is connected to the discharge control terminal of the second control chip circuit 6, and the negative terminal of diode D2 is connected to resistor R35.

[0051] Specifically, the drive control circuit 10 includes MOSFET Q9 and MOSFET Q10. The drain of MOSFET Q9 is connected between resistor R40 and resistor R35, and the source of MOSFET Q9 is grounded. The gate of MOSFET Q9 is connected to one end of resistor R41 and one end of resistor R49, respectively. The other end of resistor R41 is grounded, and the other end of resistor R49 is connected to the drain of MOSFET Q10. The source of MOSFET Q10 is connected to one end of resistor R50 and the power supply energy storage circuit 11, respectively. The gate of MOSFET Q10 is connected to the other end of resistor R50 and the control signal sampling circuit 8.

[0052] Specifically, the control signal sampling circuit 8 includes a diode D8. The negative terminal of the diode D8 is connected to the discharge control terminal of the second control chip circuit 6, and the positive terminal of the diode D8 is connected to the gate terminal of the MOSFET Q10 through a resistor R52.

[0053] Specifically, the power storage circuit 11 includes a storage capacitor C5. One end of the storage capacitor C5 is connected to one end of the resistor R48 and the source terminal of the MOSFET Q10. The other end of the resistor R48 is connected to the step-down circuit 9, and the other end of the storage capacitor C5 is grounded.

[0054] Specifically, the step-down circuit 9 is diode D7. The positive terminal of diode D7 is connected to the discharge control terminal of the second control chip circuit 6, and the negative terminal of diode D7 is connected to resistor R48.

[0055] Specifically, the MOS energy discharge circuit 12 is diode D6, with the positive terminal of diode D6 connected to the source terminal of MOS transistor Q6 and the negative terminal of diode D6 connected to the gate terminal of MOS transistor Q6.

[0056] Specifically, the fourth MOSFET circuit 4 includes a MOSFET Q8. The drain terminal of the MOSFET Q8 is connected to the source terminal of the third MOSFET circuit 3. The source terminal of the MOSFET Q8 is connected to the negative output terminal of the load. The gate terminal of the MOSFET Q8 is connected to the collector terminal of the transistor Q12. The base of the transistor Q12 is grounded through resistor R39. The emitter of the transistor Q12 is connected to the charging control terminal of the second control chip circuit 6 through resistor R32.

[0057] Specifically, the voltage regulation control circuit 13 is a Zener diode D5, with the positive terminal of Zener diode D5 connected to the source terminal of MOSFET Q8 and the negative terminal of Zener diode D5 connected to the gate terminal of MOSFET Q8.

[0058] like Figure 3-4 As shown, the protective functions of each circuit in this case are as follows:

[0059] like Figure 4 As shown, the isolation circuit 7 provides protection when the lithium battery pack is short-circuited. If the discharge MOSFET Q5 in the first MOSFET circuit 1 is turned off first, the presence of parasitic inductance in the circuit board and components will cause an extremely high voltage U to be generated between the drain D and B- of the discharge MOSFET Q5. At this time, the isolation circuit 7 takes effect. Diode D2 has unidirectional conductivity, and the current can only flow from the anode to the cathode of diode D2. Since the high voltage U will not exceed the diode's withstand voltage, the current cannot flow from the cathode to the anode of the diode, thus isolating the high voltage U from the discharge control terminal of the control chip U1 in the second control chip circuit 6 and realizing the function of protecting the control chip U1.

[0060] like Figure 4 As shown, the MOS energy discharge circuit 12 has the following protection function: when the lithium battery pack is short-circuited, if the discharge MOS transistor Q5 in the first MOS transistor circuit 1 is turned off first, due to the presence of parasitic inductance of the circuit board and components, the drain D of the discharge MOS transistor Q5 will generate an extremely high voltage U with respect to B-. At this time, the MOS energy discharge circuit 12 plays its corresponding role in discharging the energy of the MOS transistor.

[0061] When the battery pack is short-circuited, in the second MOSFET circuit 2, between the gate and source (GS) and between the gate and drain (GD) of the discharge MOSFET Q6, due to the presence of parasitic capacitance, if a very large voltage value occurs for a short period of time, the voltages of GS and GD of the discharge MOSFET Q6 will be divided according to the equivalent impedance. In actual testing, this value often exceeds the limit voltage of GS by ±20V. In the MOSFET energy discharge circuit 12, the GS of the discharge MOSFET Q6 is short-circuited by diode D6. The energy of the high voltage U is directly released through the GD terminal. The voltage across GS is clamped at the conduction of diode D6 and the voltage drop is about -0.6V, thus protecting the GS of the discharge MOSFET Q6 from damage. The conventional method is to add a Zener diode and a TVS at the GS terminal of the discharge MOSFET Q6, but in actual testing, neither can achieve good voltage clamping. Therefore, although the MOSFET energy discharge circuit 12 is simple, the implementation idea and protection effect are excellent, and the cost is low.

[0062] like Figure 3-4 As shown, the protection function of isolation circuit 7, control signal sampling circuit 8, step-down circuit 9, drive control circuit 10, and power storage circuit 11 on the discharge MOSFET Q6 in the second MOSFET circuit 2 is as follows:

[0063] When the DO1 output of the control chip U1 in the second control chip circuit 6 is high, the drive current of DO1 will flow through the diode D2 to the gate and gate terminals of the discharge MOSFET Q6 in the second MOSFET circuit 2, and the discharge MOSFET Q6 will be turned on normally.

[0064] At this time, the driving current of DO1 will also charge the energy storage capacitor C5 through diode D7 and resistor R48. Due to the voltage drop of diode D7, the voltage value of energy storage capacitor C5 after it is fully charged is about 0.3-0.5V lower than that of DO1. Therefore, when the MOSFET Q10 is turned on normally, the current at the source of the MOSFET Q10 cannot flow back to DO1 through the gate. It has good anti-interference capability when turned on and will not cause the MOSFET Q10 to be mis-turned on, resulting in the discharge MOSFET Q6 being turned off.

[0065] When DO1 outputs a low level, due to the presence of diode D2, the voltage across the gate (GS) terminals of the discharge MOSFET Q6 cannot be quickly discharged directly through DO1; DO1 is 0V at this time. Meanwhile, due to the presence of energy storage capacitor C5 and diode D7, the energy of energy storage capacitor C5 at the source (S) of MOSFET Q10 will not be released by DO1. At this time, the voltage at the source (S) of MOSFET Q10 is higher than the voltage at the gate (G) of MOSFET Q10, causing MOSFET Q10 to conduct. This releases the energy of energy storage capacitor C5 to the gate (GS) terminals of MOSFET Q9, enabling MOSFET Q9 to conduct quickly. This, in turn, quickly releases the voltage across the gate (GS) of the discharge MOSFET Q6, achieving rapid turn-off. Once the energy of energy storage capacitor C5 and the energy of MOSFET Q9 are consumed, the voltage across the gate (GS) terminals of the discharge MOSFET Q6 is pulled down by resistor R37, achieving long-term turn-off without floating voltage.

[0066] like Figure 4 As shown, the protection function of the voltage regulation control circuit 13 is that when abnormal charging occurs with high voltage and high current, if CO2 of the control chip U2 in the first control chip circuit 5 is turned off first, and CO1 of the control chip U1 in the second control chip circuit 6 is not turned off, the voltage across the GS of the charging MOSFET Q8 in the fourth MOSFET circuit 4 will exceed ±20V. By adding a Zener diode D5 and clamping the voltage value of the Zener diode D5, the protection of the MOSFET GS can be achieved.

[0067] Therefore, the circuit in this case realizes the normal fast turn-on and turn-off function of the discharge MOSFET Q6 in the second MOSFET circuit 2; when the discharge MOSFET Q5 in the first MOSFET circuit 1 is turned off, it realizes the protection of the control chip and the MOSFET; and it realizes the protection of the charging MOSFET Q8 in the fourth MOSFET circuit 4 when the charging MOSFET Q7 in the third MOSFET circuit 3 is turned off first.

[0068] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct or indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A dual protection circuit for a lithium battery, comprising a first MOSFET circuit (1) and a second MOSFET circuit (2) for controlling discharge, a third MOSFET circuit (3) and a fourth MOSFET circuit (4) for controlling charging, a first control chip circuit (5) and a second control chip circuit (6), wherein the first control chip circuit (5) and the second control chip circuit (6) can detect lithium battery temperature information, voltage and current information, and control lithium battery charging and discharging; the negative terminal of the lithium battery is connected to the source terminal of the first MOSFET circuit (1) through a resistor R1, and the drain terminal of the first MOSFET circuit (1) is connected to the drain terminal of the second MOSFET circuit (2). The source terminal is connected, the drain terminal of the second MOS transistor circuit (2) is connected to the drain terminal of the third MOS transistor circuit (3), the source terminal of the third MOS transistor circuit (3) is connected to the drain terminal of the fourth MOS transistor circuit (4), the source terminal of the fourth MOS transistor circuit (4) is connected to the negative output terminal of the load, the discharge control terminal of the first control chip circuit (5) is connected to the gate terminal of the first MOS transistor circuit (1), the charging control terminal of the first control chip circuit (5) is connected to the gate terminal of the third MOS transistor circuit (3), and the charging control terminal of the second control chip circuit (6) is connected to the gate terminal of the fourth MOS transistor circuit (4). The characteristic feature is that: An isolation circuit (7) for protecting the second control chip circuit (6) is connected between the discharge control terminal of the second control chip circuit (6) and the gate terminal of the second MOS transistor circuit (2). The discharge control terminal of the second control chip circuit (6) is connected to a control signal sampling circuit (8) for sampling the discharge control signal of the second control chip circuit (6) and a step-down circuit (9) for reducing the output voltage of the discharge control terminal of the second control chip circuit (6). The control signal sampling circuit (8) is connected to a drive control circuit (10) for controlling the rapid switching of the second MOS transistor circuit (2). The step-down circuit (9) is connected to a power storage circuit (11) for storing energy and supplying power to the drive control circuit (10). A MOS energy discharge circuit (12) for protecting the second MOS transistor circuit (2) is connected between the gate terminal and the source terminal of the second MOS transistor circuit (2). A voltage regulation control circuit (13) for protecting the fourth MOS transistor circuit (4) is connected between the gate terminal and the source terminal of the fourth MOS transistor circuit (4).

2. The lithium battery dual protection circuit according to claim 1, characterized in that: The second MOS transistor circuit (2) includes a MOS transistor Q6. The source terminal of the MOS transistor Q6 is connected to the drain terminal of the first MOS transistor circuit (1) and one end of the resistor R37. The drain terminal of the MOS transistor Q6 is connected to the drain terminal of the third MOS transistor circuit (3). The gate terminal of the MOS transistor Q6 is connected to the other end of the resistor R37 and one end of the resistor R40. The other end of the resistor R40 is connected to the discharge control terminal of the second control chip circuit (6) through the resistor R35.

3. The lithium battery dual protection circuit according to claim 2, characterized in that: The isolation circuit (7) is diode D2. The positive terminal of diode D2 is connected to the discharge control terminal of the second control chip circuit (6), and the negative terminal of diode D2 is connected to resistor R35.

4. The lithium battery dual protection circuit according to claim 2, characterized in that: The drive control circuit (10) includes a MOSFET Q9 and a MOSFET Q10. The drain of the MOSFET Q9 is connected between resistors R40 and R35. The source of the MOSFET Q9 is grounded. The gate of the MOSFET Q9 is connected to one end of resistor R41 and one end of resistor R49. The other end of resistor R41 is grounded. The other end of resistor R49 is connected to the drain of the MOSFET Q10. The source of the MOSFET Q10 is connected to one end of resistor R50 and the power supply energy storage circuit (11). The gate of the MOSFET Q10 is connected to the other end of resistor R50 and the control signal sampling circuit (8).

5. A dual protection circuit for a lithium battery according to claim 4, characterized in that: The control signal sampling circuit (8) includes a diode D8. The negative terminal of the diode D8 is connected to the discharge control terminal of the second control chip circuit (6), and the positive terminal of the diode D8 is connected to the gate terminal of the MOS transistor Q10 through a resistor R52.

6. The lithium battery dual protection circuit according to claim 4, characterized in that: The power supply energy storage circuit (11) includes an energy storage capacitor C5. One end of the energy storage capacitor C5 is connected to one end of the resistor R48 and the source end of the MOS transistor Q10. The other end of the resistor R48 is connected to the step-down circuit (9). The other end of the energy storage capacitor C5 is grounded.

7. A dual protection circuit for a lithium battery according to claim 6, characterized in that: The step-down circuit (9) is diode D7. The positive terminal of diode D7 is connected to the discharge control terminal of the second control chip circuit (6), and the negative terminal of diode D7 is connected to resistor R48.

8. A dual protection circuit for a lithium battery according to claim 2, characterized in that: The MOS energy discharge circuit (12) is diode D6. The positive terminal of diode D6 is connected to the source terminal of MOS transistor Q6, and the negative terminal of diode D6 is connected to the gate terminal of MOS transistor Q6.

9. A dual protection circuit for a lithium battery according to claim 1, characterized in that: The fourth MOS transistor circuit (4) includes a MOS transistor Q8. The drain terminal of the MOS transistor Q8 is connected to the source terminal of the third MOS transistor circuit (3). The source terminal of the MOS transistor Q8 is connected to the negative output terminal of the load. The gate terminal of the MOS transistor Q8 is connected to the collector terminal of the transistor Q12. The base of the transistor Q12 is grounded through resistor R39. The emitter of the transistor Q12 is connected to the charging control terminal of the second control chip circuit (6) through resistor R32.

10. A dual protection circuit for a lithium battery according to claim 9, characterized in that: The voltage regulation control circuit (13) is a Zener diode D5. The positive terminal of the Zener diode D5 is connected to the source terminal of the MOSFET Q8, and the negative terminal of the Zener diode D5 is connected to the gate terminal of the MOSFET Q8.

Images