A BMS protection circuit

Abstract

The utility model provides a kind of BMS protection circuit, including single-chip microcontroller control unit, current detection unit;Current detection unit adopts the structure of external sampling resistance RS1+ single-chip microcontroller internal operational amplifier;Using the operational amplifier in the single-chip microcontroller control unit;The output signal of single-chip microcontroller internal operational amplifier is accessed single-chip microcontroller ADC channel, program subtracts bias voltage, and calculates actual current.The utility model adopts the structure of external sampling resistance RS1+ single-chip microcontroller internal operational amplifier, and cost is reduced.

Description

Technical Field

[0001] This utility model relates to the field of battery management systems, specifically to a BMS protection circuit, which is used in electronic devices that require power estimation, charge and discharge management, and current protection for lithium batteries. Background Technology

[0002] BMS, or Battery Management System, is the "brain" connecting the battery pack and the electrical device. It intelligently manages the battery to prevent overcharging / over-discharging, extend battery life, and monitor its status. Its core functions include: Status monitoring: Collect key data such as individual cell voltage, temperature, and total current.

[0003] Safety protection: Provides overcharge, over-discharge, overcurrent and short circuit protection to avoid safety hazards.

[0004] State of Charge (SOC): Accurately calculating the remaining battery power directly affects the accuracy of the electric vehicle's range display.

[0005] Balance control: Through passive / active balancing technology, ensure that the voltage of each cell in the battery pack is consistent.

[0006] With the popularization of new energy devices, users have significantly increased their requirements for device range stability and battery life. Accurate estimation of the remaining battery charge (SOC) directly determines the assessment of range and the selection of charging time. Large deviations in SOC estimation can lead to overcharging and discharging, severely impacting user experience and battery life. For current mainstream power supply solutions using 4-cell lithium batteries, the SOC estimation on the BMS protection board generally adopts the "current integration method" (coulomb counter method). The core of this method is to accurately detect the charging and discharging current and integrate it to calculate the remaining charge, making current accuracy particularly important. Current BMS current detection often uses a "sampling resistor + operational amplifier" architecture—the sampling resistor converts the current into a voltage signal, and the general-purpose operational amplifier amplifies the signal before transmitting it to the microcontroller. However, general-purpose operational amplifiers (such as LM324 and TL084) have offset voltages (typically 1mV~5mV) due to manufacturing process variations. The superposition of these offset voltages severely damages the authenticity of the sampling signal, directly leading to SOC estimation errors.

[0007] Currently, the mainstream solution for operational amplifier offset voltage is to select a high-precision, low-offset voltage dedicated operational amplifier (such as AD8221 or INA128), connect its input terminal in series across the sampling resistor, and directly connect its output terminal to the current detection port of the microcontroller. The low offset characteristics (typical value <100μV) of the dedicated operational amplifier can be used to cancel the sampling signal interference.

[0008] However, the unit price of high-precision dedicated op-amps is usually 10 to 20 times that of general-purpose op-amps, far exceeding the cost budget of consumer products.

[0009] Poor environmental adaptability: The offset voltage of some low-cost dedicated operational amplifiers is greatly affected by temperature (temperature drift coefficient >1μV / ℃). In wide temperature scenarios (such as outdoor equipment) of -20℃ to 60℃, the accuracy will decrease with the ambient temperature, resulting in an increase in the SOC estimation deviation.

[0010] Compatibility limitations: Dedicated operational amplifiers are usually designed for batteries with a fixed number of strings (such as 4 strings). If you need to adapt to 2-string or 3-string battery packs, you need to change the operational amplifier model or adjust the peripheral circuit, which increases the complexity of adapting to multiple scenarios. Utility Model Content

[0011] This invention addresses the shortcomings of current BMS circuits, which use high-precision, low-offset voltage dedicated operational amplifiers, with their input terminals connected in series across the sampling resistor and their output terminals directly connected to the microcontroller's current detection port, resulting in high costs. It provides a BMS protection circuit that utilizes the microcontroller's built-in operational amplifier.

[0012] The technical solution adopted by this utility model to achieve its technical objective is: a BMS protection circuit, including a microcontroller control unit and a current detection unit; the current detection unit adopts an external sampling resistor RS1 + microcontroller internal operational amplifier structure; and uses the operational amplifier in the microcontroller control unit; The sampling resistor RS1 is connected in series between the negative terminal of the battery pack and the protective ground, and includes a voltage divider resistor R26, a resistor R1, a resistor R25 and a resistor R27 connected in series between the protective ground and the negative terminal of the battery pack. The protective ground is connected to the inverting input terminal of the first operational amplifier inside the microcontroller through resistor R26, and the negative terminal of the battery pack is connected to the inverting input terminal of the first operational amplifier inside the microcontroller through resistor R18. Resistor R17 is set between the inverting input terminal and the output terminal of the first operational amplifier. The protective ground is connected to the inverting input of the second operational amplifier inside the microcontroller through resistor R32, and the negative terminal of the battery pack is connected to the non-inverting input of the second operational amplifier inside the microcontroller through resistor R27. Resistor R31 is set between the inverting input and output of the second operational amplifier. The output signals from the first and second operational amplifiers inside the microcontroller are connected to the microcontroller's ADC channel. After subtracting the bias voltage, the program calculates the actual current.

[0013] Furthermore, in the aforementioned BMS protection circuit: the microcontroller control unit uses an N32G031 microcontroller U3 with a built-in 12-bit ADC, internal comparator, internal operational amplifier, and I / O ports.

[0014] Furthermore, the BMS protection circuit described above also includes a temperature detection unit; the temperature detection unit includes a voltage divider resistor R29 and a thermistor RT1; the voltage divider resistor R29 and the thermistor RT1 are connected in series between pin 18 (VEN) of the microcontroller U3 and the negative terminal (BGND) of the battery pack, and a signal indicating the temperature is led out from the common terminal connected to the voltage divider resistor R29 and the thermistor RT1 and connected to pin 10 of the microcontroller U3.

[0015] Furthermore, the BMS protection circuit described above also includes a charge / discharge MOS drive circuit; the charge / discharge MOS drive circuit includes a discharge MOS transistor Q1 and a charge MOS transistor Q2. The source (S) of the discharge MOSFET Q1 is connected to the anode of the battery, and the gate (G) is driven by the I / O port of the microcontroller U3. The source (S) of the charging MOSFET Q2 is connected to the load anode, and the gate (G) is driven by the I / O port of the microcontroller U3. The drains of the discharge MOSFET Q1 and the charging MOSFET Q2 are connected.

[0016] Furthermore, in the above-mentioned BMS protection circuit: a discharge drive circuit is also provided between the IO port of the microcontroller U3 and the discharge MOSFET Q1, and a charging drive circuit is also provided between the IO port of the microcontroller U3 and the charging MOSFET Q2. The discharge drive circuit includes PNP transistor Q3 and PNP transistor Q5. The base of transistor Q5 is connected to an I / O port of microcontroller U3, the emitter is connected to the negative terminal of the battery pack, and the collector is connected to the base of transistor Q3. The base of transistor Q3 is also connected to the anode of the battery through resistor R11, the collector is connected to the anode of the battery through resistor R0, and the emitter is connected to the gate of the discharge MOSFET. The emitter of transistor Q3 is also connected to the anode of the battery through resistor R2, and resistor R6 is connected to the collector of transistor Q5 through diode D3. The charging drive circuit includes a PNP transistor Q6; The base of transistor Q6 is connected to another I / O port of microcontroller U3, the emitter is connected to the negative terminal of the battery pack, and the collector is connected to the gate of charging MOSFET Q2 through resistor R7. The collector is connected to the load anode through resistor R3 in series with resistor R7.

[0017] Furthermore, in the BMS protection circuit described above, both the discharge MOSFET Q1 and the charging MOSFET Q2 are ES3347 MOSFETs.

[0018] Furthermore, in the aforementioned BMS protection circuit: the battery consists of four lithium batteries connected in series, including a voltage detection circuit that detects the voltage of the first lithium battery, the voltage of the first lithium battery connected in series with the second lithium battery, the voltage of the first lithium battery connected in series with the second lithium battery, the voltage of the first lithium battery connected in series with the third lithium battery, and the total voltage of the four lithium batteries connected in series; the voltage detection circuit uses a high-precision low-temperature drift resistor-capacitor array to achieve voltage acquisition, and two voltage divider resistors are connected in series with the positive and negative terminals of each battery string, and a filter capacitor is connected in parallel at the voltage divider node; the voltage divider signals are respectively connected to the V1-V4 pins of the microcontroller U3.

[0019] Furthermore, the BMS protection circuit mentioned above also includes a short-circuit protection circuit; the short-circuit protection circuit includes resistors R51 and R52 connected in series between the positive terminal of the working power supply (VDD) and the negative terminal of the battery (BGND), and a filter capacitor C51 is connected in parallel across resistor R52 to filter the signal before it is sent to the negative terminal of the low-power comparator inside the microcontroller.

[0020] Furthermore, the aforementioned BMS protection circuit also includes a power display circuit, which is driven by a microcontroller and includes a current-limiting resistor and an LED. The positive terminal of the power supply is connected to the current-limiting resistor and the LED in sequence and then connected to the I / O port of the microcontroller. The anode of the LED is connected to the I / O port of the microcontroller.

[0021] Furthermore, the aforementioned BMS protection circuit also includes an SMBus communication circuit; the SMBus communication circuit includes a current-limiting resistor on each data transmission line and a Zener diode between each wire and the negative terminal of the battery.

[0022] This invention reduces costs by using an external sampling resistor RS1 and an internal operational amplifier of a microcontroller.

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0024] Appendix Figure 1 This is a block diagram of the BMS protection circuit in Embodiment 1 of this utility model; Appendix Figure 2 This is a schematic diagram of the microcontroller and peripheral circuit of Embodiment 1 of this utility model; Appendix Figure 3 This is a schematic diagram of the current detection unit circuit in Embodiment 1 of this utility model; Appendix Figure 4 This is a schematic diagram of the temperature detection unit circuit in Embodiment 1 of this utility model; Appendix Figure 5 This is a schematic diagram of the charging and discharging MOS driving circuit of Embodiment 1 of this utility model; Appendix Figure 6 This is a schematic diagram of the voltage detection circuit in Embodiment 1 of this utility model; Appendix Figure 7 This is a schematic diagram of the short-circuit protection circuit in Embodiment 1 of this utility model; Appendix Figure 8 This is a schematic diagram of the power display circuit in Embodiment 1 of this utility model; Appendix Figure 9 This is a schematic diagram of the SMBus communication circuit in Embodiment 1 of this utility model; Appendix Figure 10 This is a schematic diagram of the power supply circuit for Embodiment 1 of this utility model. Detailed Implementation

[0025] This embodiment is a BMS protection circuit, specifically a BMS protection circuit for 2-4 series lithium batteries. Its core is a microcontroller control unit, externally connected to a 2-4 series battery pack (CELL1-CELL4), and includes voltage detection, current detection, temperature detection, short-circuit protection, power display, MOS input / output drive circuits, and an external SMBus communication circuit. The overall circuit block diagram is shown below. Figure 1 As shown.

[0026] like Figure 2 As shown: The microcontroller control unit uses the N32G031 microcontroller U3, which has a built-in 12-bit ADC, internal comparator, internal operational amplifier, and I / O ports. It is the control core of the entire system. Using the N32G031 microcontroller, with its built-in 12-bit ADC, internal comparator, internal operational amplifier, and multiple I / O ports, it performs logic control and data processing for all functions, including voltage acquisition, current detection, short-circuit protection, MOSFET driving, power display, SMBus communication, and SOC power calculation.

[0027] The current detection unit adopts an external sampling resistor RS1 + microcontroller internal operational amplifier structure; it uses the operational amplifier in the microcontroller control unit; such as Figure 3 As shown: The sampling resistor RS1 is connected in series between the negative terminal BGND of the battery pack and the protective ground PGND. It includes the voltage divider resistors R26, R1, R25 and R27 connected in series between the protective ground PGND and the negative terminal BGND of the battery pack.

[0028] The protective ground PGND is connected to the non-inverting input CIN of the first operational amplifier inside the microcontroller through resistor R26, and the negative terminal BGND of the battery pack is connected to the inverting input DIP of the first operational amplifier inside the microcontroller through resistor R18. Resistor R17 is set between the inverting input DIP and the output COUT of the first operational amplifier.

[0029] Protective ground PGND is connected to the inverting input terminal DIN of the second operational amplifier inside the microcontroller through resistor R32. The negative terminal BGND of the battery pack is connected to the non-inverting input terminal CIP of the second operational amplifier inside the microcontroller through resistor R27. Resistor R31 is set between the inverting input terminal DIN and the output terminal COUT of the second operational amplifier.

[0030] The output signals from the first and second operational amplifiers inside the microcontroller are connected to the microcontroller's ADC channel. After subtracting the bias voltage, the program calculates the actual current.

[0031] In this embodiment, the current detection adopts an "external sampling resistor + microcontroller internal operational amplifier" structure. The sampling resistor RS1 is connected in series between the negative terminals BGND and PGND of the battery pack, and the voltage across its terminals is the current sampling signal. A bias voltage is generated by voltage divider resistors R1, R26, R25, and R27, which is connected to the operational amplifier to counteract the offset voltage. When detecting the discharge current, DIN is connected to the non-inverting input of the operational amplifier, DIP is connected to the inverting input of the operational amplifier, and COUT is connected to the output of the operational amplifier. R17 and R18 control the amplification factor. When detecting the charging current, CIP is connected to the non-inverting input of the operational amplifier, CIN is connected to the inverting input of the operational amplifier, and COUT is connected to the output of the operational amplifier. R31 and R32 control the amplification factor. The amplified operational amplifier output signal is connected to the microcontroller's ADC channel. After subtracting the bias voltage, the program calculates the actual current.

[0032] In this embodiment, a temperature detection unit is also included; such as Figure 4 As shown, the temperature detection unit includes a voltage divider resistor R29 and a thermistor RT1. The voltage divider resistor R29 and the thermistor RT1 are connected in series between pin 18 (VEN) of the microcontroller U3 and the negative terminal (BGND) of the battery pack. A signal representing the temperature is led out from the common terminal connected to the voltage divider resistor R29 and the thermistor RT1 and connected to pin 10 (NTC) of the microcontroller U3. In this embodiment, the temperature is determined by a voltage divider between the fixed resistor and the thermistor. The voltage generated by the voltage divider is sent to the microcontroller's ADC, and the program calculates the current temperature and current based on the collected values.

[0033] It also includes charge / discharge MOS drive circuits; such as Figure 5 The charging and discharging MOS driving circuit shown includes a discharging MOS transistor Q1 and a charging MOS transistor Q2.

[0034] The source (S) of the discharge MOSFET Q1 is connected to the anode (B+) of the battery, and the gate (G) is driven by the I / O port of the microcontroller U3.

[0035] The source (S) of the charging MOSFET Q2 is connected to the load anode VP+, and the gate (G) is driven by the I / O port of the microcontroller U3.

[0036] The drains of the discharge MOSFET Q1 and the charging MOSFET Q2 are connected.

[0037] A discharge drive circuit is provided between the I / O port of the microcontroller U3 and the discharge MOSFET Q1, and a charging drive circuit is provided between the I / O port of the microcontroller U3 and the charging MOSFET Q2. The discharge drive circuit includes PNP transistors Q3 and Q5; The base of transistor Q5 is connected to an I / O port of microcontroller U3, the emitter is connected to the negative terminal BGND of the battery pack, and the collector is connected to the base of transistor Q3. The base of transistor Q3 is also connected to the anode B+ of the battery through resistor R11, the collector is connected to the anode B+ of the battery through resistor R0, and the emitter is connected to the gate of the discharge MOSFET. The emitter of transistor Q3 is also connected to the anode B+ of the battery through resistor R2, and resistor R6 is connected to the collector of transistor Q5 through diode D3.

[0038] The charging drive circuit includes a PNP transistor Q6; the base of transistor Q6 is connected to another IO port of microcontroller U3, the emitter is connected to the negative terminal BGND of the battery pack, and the collector is connected to the gate of charging MOSFET Q2 through resistor R7, and connected to the load anode VP+ through resistor R3 in series with resistor R7.

[0039] Both the discharge MOSFET Q1 and the charge MOSFET Q2 are ES3347 MOSFETs.

[0040] like Figure 5 As shown, the gate of the discharge MOSFET Q1 is connected to the microcontroller's I / O port via a transistor drive circuit with transistors Q3 and Q5. When the microcontroller outputs a high level, transistor Q5 conducts, creating a voltage difference between the gate and source terminals of the discharge MOSFET Q1, which then conducts and begins discharging. The gate of the charging MOSFET Q2 is connected to the microcontroller's I / O port via a drive circuit with transistor Q6 as its core. When the microcontroller outputs a high level, transistor Q6 conducts, creating a voltage difference between the gate and source terminals of the charging MOSFET Q2, which then conducts and begins charging. When any protection threshold is reached during charging or discharging, the MOSFETs will be turned off.

[0041] The battery consists of four lithium batteries connected in series. It includes a voltage detection circuit that measures the voltage of the first lithium battery (CELL1), the voltage of the first battery connected in series with the second battery (CELL2), the voltage of the first, second, and third batteries connected in series (CELL3), and the total voltage (CELL4) of the four batteries connected in series. The voltage detection circuit uses a high-precision, low-temperature drift resistor-capacitor array for voltage acquisition. Two voltage-dividing resistors are connected in series with the positive and negative terminals of each battery string, and a filter capacitor is connected in parallel at the voltage-dividing nodes. The voltage divider signals are connected to pins V1-V4 of the microcontroller U3. The schematic diagram of the voltage detection circuit is shown below. Figure 6As shown: a high-precision, low-temperature drift resistor-capacitor array is used to acquire voltage. Two voltage divider resistors are connected in series at the positive and negative terminals of each battery string, and a filter capacitor is connected in parallel at the voltage divider node to suppress external interference. The voltage divider signals are connected to the V1-V4 pins of the microcontroller. The microcontroller periodically acquires the signals and calculates the actual single-cell voltage. For example, if the acquired value of V1 is 1.85V, the actual voltage of the first cell is 3.7V.

[0042] This embodiment also includes a short-circuit protection circuit; such as Figure 7 As shown, the short-circuit protection circuit includes resistors R51 and R52 connected in series between the positive terminal of the power supply (VDD) and the negative terminal of the battery (BGND). A filter capacitor C51 is connected in parallel across resistor R52, and the filtered signal is sent to the negative terminal of the low-power comparator inside the microcontroller. In this embodiment, the short-circuit protection circuit uses a resistor divider and a capacitor filter to send the filtered signal to the negative terminal of the low-power comparator inside the microcontroller. When a short circuit occurs in the battery, the comparator triggers a microcontroller interrupt, and the program controls the MOSFET to quickly turn off, protecting the battery.

[0043] This embodiment also includes a power display circuit, such as... Figure 8 As shown: The power display circuit is driven by a microcontroller and includes a current-limiting resistor and an LED. The positive terminal of the power supply, VDD, is connected sequentially to the current-limiting resistor and the LED, and then connected to the microcontroller's I / O port. The anode of the LED is also connected to the microcontroller's I / O port. Figure 8 As shown in this embodiment, the microcontroller accurately calculates the remaining battery power by detecting voltage and current, and drives the LED1-LED5 to turn on and off in combination to realize the power display; pressing the SW1 switch can wake up the dormant LED display, and the LED will automatically go into sleep mode after no operation; the user can quickly judge the remaining battery power by the number of LEDs on and off.

[0044] This embodiment also includes an SMBus communication circuit; such as Figure 9 As shown: The SMBus communication circuit includes a current-limiting resistor on each data transmission line and a Zener diode between each wire and the battery's negative terminal (BGND). The SMBus external communication interface allows users to monitor the battery's current status in real time.

[0045] The power supply circuit used in this embodiment is as follows: Figure 10 As shown: The LDO is supplied with dual power through diodes. P+ is the external output interface of the BMS protection board, and B+ is the positive terminal of the battery pack. When a charger is connected, it automatically switches to charger power supply.

[0046] This embodiment has the following advantages: 1. It offers significant cost advantages and ensures SOC estimation accuracy. It eliminates the need for high-precision dedicated operational amplifiers and achieves bias voltage using only conventional surface-mount resistors, reducing hardware costs while meeting the needs of consumer devices.

[0047] 2. The SOC estimation accuracy is stable and unaffected by the environment and lifespan. The bias resistor adopts a ±1% accuracy, low temperature drift resistor, and the current detection fluctuation is small, which solves the pain point of accuracy decay due to environment and lifespan.

[0048] 3. The circuit is simple and easy to mass produce, with strong adaptability, small space occupation, and good batch consistency. It can be adapted to multiple battery packs by adjustment without modifying the core SOC estimation algorithm, reducing the difficulty of adapting to multiple scenarios.

[0049] In some other embodiments, the microcontroller model can be replaced: N32G031K8Q7 can be replaced with a similar microcontroller with internal op-amp + ADC (such as STM32G031K8U6, GD32G031K8U6, etc.), only requiring adjustment of the pin mapping.

[0050] Existing voltage divider resistors can be replaced with resistors of the same precision but different values. As long as the voltage division ratio remains unchanged and is compatible with the ADC input range, the same voltage detection function can be achieved. Alternatively, digital potentiometers, such as the MCP4131, can be used to replace fixed resistors. The voltage division ratio can be dynamically adjusted through a microcontroller program to adapt to battery packs with different total voltages. Current sampling resistors can be replaced with alloy resistors of other values. By adjusting the operational amplifier amplification factor, different discharge current requirements can be met.

Claims

1. A BMS protection circuit, comprising a microcontroller control unit and a current detection unit; characterized in that: The current detection unit adopts an external sampling resistor RS1 + microcontroller internal operational amplifier structure; it uses the operational amplifier in the microcontroller control unit; The sampling resistor RS1 is connected in series between the negative terminal (BGND) of the battery pack and the protective ground (PGND), and includes a voltage divider resistor R26, a resistor R1, a resistor R25 and a resistor R27 connected in series between the protective ground (PGND) and the negative terminal (BGND) of the battery pack. Protective ground (PGND) is connected to the inverting input terminal (DIN) of the first operational amplifier inside the microcontroller through resistor R26, and the negative terminal of the battery pack (BGND) is connected to the inverting input terminal (DIP) of the first operational amplifier inside the microcontroller through resistor R18. Resistor R17 is set between the inverting input terminal (DIP) and the output terminal (COUT) of the first operational amplifier. Protective ground (PGND) is connected to the inverting input (CIN) of the second operational amplifier inside the microcontroller through resistor R32, and the negative terminal of the battery pack (BGND) is connected to the non-inverting input (CIP) of the second operational amplifier inside the microcontroller through resistor R27. Resistor R31 is set between the inverting input (CIN) and the output (COUT) of the second operational amplifier. The output signals from the first and second operational amplifiers inside the microcontroller are connected to the microcontroller's ADC channel. After subtracting the bias voltage, the program calculates the actual current.

2. The BMS protection circuit according to claim 1, characterized in that: The microcontroller control unit uses the N32G031 microcontroller U3, which has a built-in 12-bit ADC, internal comparator, internal operational amplifier and I / O ports.

3. The BMS protection circuit according to claim 2, characterized in that: It also includes a temperature detection unit; the temperature detection unit includes a voltage divider resistor R29 and a thermistor RT1; the voltage divider resistor R29 and the thermistor RT1 are connected in series between pin 18 (VEN) of the microcontroller U3 and the negative terminal (BGND) of the battery pack, and a signal indicating the temperature is led out from the common terminal of the voltage divider resistor R29 and the thermistor RT1 and connected to pin 10 (NTC) of the microcontroller U3.

4. The BMS protection circuit according to claim 2, characterized in that: It also includes a charge / discharge MOS driving circuit; the charge / discharge MOS driving circuit includes a discharge MOS transistor Q1 and a charge MOS transistor Q2; The source (S) of the discharge MOSFET Q1 is connected to the anode (B+) of the battery, and the gate (G) is driven by the I / O port of the microcontroller U3. The source (S) of the charging MOSFET Q2 is connected to the load anode (VP+), and the gate (G) is driven by the I / O port of the microcontroller U3. The drains of the discharge MOSFET Q1 and the charging MOSFET Q2 are connected.

5. The BMS protection circuit according to claim 4, characterized in that: A discharge drive circuit is provided between the I / O port of the microcontroller U3 and the discharge MOSFET Q1, and a charging drive circuit is provided between the I / O port of the microcontroller U3 and the charging MOSFET Q2. The discharge drive circuit includes PNP transistor Q3 and PNP transistor Q5. The base of transistor Q5 is connected to an I / O port of microcontroller U3, the emitter is connected to the negative terminal (BGND) of the battery pack, and the collector is connected to the base of transistor Q3. The base of transistor Q3 is also connected to the anode (B+) of the battery through resistor R11, the collector is connected to the anode (B+) of the battery through resistor R0, and the emitter is connected to the gate of the discharge MOSFET. The emitter of transistor Q3 is also connected to the anode (B+) of the battery through resistor R2, and resistor R6 is connected to the collector of transistor Q5 through diode D3. The charging drive circuit includes a PNP transistor Q6; The base of transistor Q6 is connected to another I / O port of microcontroller U3, the emitter is connected to the negative terminal of the battery pack (BGND), the collector is connected to the gate of charging MOSFET Q2 through resistor R7, and the collector is connected to the load anode (VP+) through resistor R7 and series resistor R3.

6. The BMS protection circuit according to claim 5, characterized in that: Both the discharge MOSFET Q1 and the charge MOSFET Q2 are ES3347 MOSFETs.

7. The BMS protection circuit according to claim 2, characterized in that: The battery consists of four lithium batteries connected in series. It includes a voltage detection circuit that detects the voltage of the first lithium battery (CELL1), the voltage of the first battery connected in series with the second battery (CELL2), the voltage of the first, second, and third batteries connected in series (CELL3), and the total voltage of the four batteries connected in series (CELL4). The voltage detection circuit uses a high-precision, low-temperature drift resistor-capacitor array to acquire voltage. Two voltage-dividing resistors are connected in series with the positive and negative terminals of each battery string, and a filter capacitor is connected in parallel at the voltage-dividing nodes. The voltage-dividing signals are respectively connected to the V1-V4 pins of the microcontroller U3.

8. The BMS protection circuit according to claim 2, characterized in that: It also includes a short-circuit protection circuit; the short-circuit protection circuit includes resistors R51 and R52 connected in series between the positive terminal of the working power supply (VDD) and the negative terminal of the battery (BGND), and a filter capacitor C51 is connected in parallel across the two ends of resistor R52 to filter the signal before it is sent to the negative terminal of the low-power comparator inside the microcontroller.

9. The BMS protection circuit according to claim 2, characterized in that: It also includes a power display circuit, which is driven by a microcontroller and includes a current-limiting resistor and an LED. The positive terminal of the power supply (VDD) is connected to the current-limiting resistor and the LED in sequence and then connected to the I / O port of the microcontroller. The anode of the LED is connected to the I / O port of the microcontroller.

10. The BMS protection circuit according to claim 2, characterized in that: It also includes an SMBus communication circuit; the SMBus communication circuit includes a current-limiting resistor on each data transmission line and a Zener diode between each wire and the negative terminal (BGND) of the battery.

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