A pre-discharge control circuit applied to a battery management system and a control method thereof

Abstract

The application relates to the technical field of two-wheel vehicle BMS, in particular to a pre-discharge control circuit applied to a battery management system, which comprises a pre-discharge control input unit, an input end of which is connected with a microcontroller; a level conversion and drive control unit, an input end of which is connected with the microcontroller; a pre-discharge power switch unit, which is connected in series between a power battery and a load bus, and whose control end is connected with an output end of the level conversion and drive control unit; an anti-backflow and energy clamping structure, which is arranged in a pre-discharge path; a current detection protection unit, which is connected in series with the pre-discharge circuit; and a voltage detection feedback unit, an input end of which is connected with a bus voltage, and an output end of which is connected with a voltage detection end of the microcontroller, and which is used for judging a pre-discharge completion state. The pre-discharge control circuit applied to the battery management system and the control method thereof adopt a multi-stage level conversion structure, improve driving reliability, and avoid damage of MOS linear area through a gate protection network.

Description

Technical Field

[0001] This invention relates to the field of pre-discharge control circuit technology for battery management systems, specifically to a pre-discharge control circuit and control method applied to a battery management system. Background Technology

[0002] With the development of new energy vehicles, lithium-ion batteries are widely used as energy sources in two-wheeled electric vehicles, electric motorcycles, and light electric vehicles. To ensure the safe operation of the power battery, the battery system is usually equipped with a Battery Management System (BMS) to realize functions such as battery status monitoring, protection control, and high-voltage power management.

[0003] In existing technologies, the power system of a two-wheeled electric vehicle generally includes a power battery pack, a battery management system (BMS), a motor controller, and load devices such as a DC bus capacitor. The motor controller input typically has a large-capacity filter capacitor or energy storage capacitor connected in parallel. When the vehicle is powered on or the key is turned on, if the power battery is directly connected to the controller through a main power switching device (such as a MOSFET or relay), the bus capacitor will charge from zero voltage to the battery voltage in a very short time, generating a large transient surge current.

[0004] To suppress the aforementioned surge current, existing technologies typically incorporate a pre-charge circuit in the BMS. This pre-charge circuit generally uses a pre-charge resistor and a control switch to perform current-limited charging of the bus capacitors before the main power path is switched on, thereby reducing power-on impact and improving system reliability.

[0005] However, in practical applications, especially in the field of two-wheeled electric vehicles, existing pre-discharge technologies still have many problems due to system cost constraints, compact structure, and complex user environments. These problems mainly include:

[0006] 1. Problem of excessive surge current at power-on:

[0007] In some existing BMS designs, unreasonable pre-discharge control timing or insufficient pre-discharge parameter matching leads to premature turn-on of the main power MOSFETs or insufficient pre-charge time, causing a large charging inrush current to be generated in the motor controller bus capacitor, which can easily cause MOSFET damage, connector burn-out, or even system failure.

[0008] 2. Problem with BMS and load device startup timing mismatch:

[0009] In two-wheeled electric vehicles, the motor controller and BMS are usually started by different power systems, and there are situations where the controller stabilizes before the BMS. When the load side enters the working state prematurely, it will generate reverse inrush current or voltage oscillation, causing the power devices to operate in the linear region, resulting in severe overheating or even breakdown damage.

[0010] 3. Issues related to the limited safe operating area of ​​power switching devices:

[0011] In existing pre-discharge control schemes, improper control of MOSFET drive rise speed or insufficient current sharing design of parallel devices may cause power devices to bear large currents in an incompletely enhanced state, causing them to remain in the linear operating region for a long time, leading to overheating and avalanche failure.

[0012] 4. Transient impact issues caused by user operations:

[0013] Two-wheeled electric vehicles are commonly used in scenarios such as plugging and unplugging while powered on, rapid battery replacement, or uncontrollable connection sequence, which can easily generate electric arcs, voltage spikes, and reverse impacts, causing additional stress to the BMS pre-discharge circuit and sampling circuit.

[0014] 5. Insufficient stability during the BMS power supply setup phase:

[0015] In the early stages of system startup, the internal power supply of the BMS is not yet stable. If the power circuit is turned on prematurely, it may cause repeated resets of the control logic, repeated switching of power devices, and abnormal inrush currents, further increasing the risk of system failure.

[0016] To address the problems of large surge current impact, unstable pre-discharge control timing, easy damage to power devices, and insufficient transient resistance of analog front-end circuits in the existing battery management system for two-wheeled electric vehicles during power-on, this invention provides a pre-discharge control circuit and control method for a battery management system, so as to achieve a safe power-on connection between the power battery and the load device, and improve system reliability and device lifespan. Summary of the Invention

[0017] To address the shortcomings of existing technologies, this invention provides a pre-discharge control circuit and its control method for a battery management system, used to suppress the safe power-on impact of the load during the connection process between the power battery and the load device.

[0018] To achieve the above objectives, the present invention provides the following technical solution: a pre-discharge control circuit applied to a battery management system, comprising:

[0019] The pre-discharge control input unit, whose input terminal PRE_DIS_MOS_EN is connected to the microcontroller, is used to output the pre-discharge enable signal;

[0020] The level conversion and drive control unit, whose input terminal is connected to the microcontroller, is used to convert low-voltage control signals into high-voltage drive signals and amplify the drive current;

[0021] A pre-discharge power switch unit is connected in series between the power battery and the load bus, and its control terminal is connected to the output terminal of the level conversion and drive control unit to form a current-limited charging path.

[0022] An anti-backflow and energy clamping structure is installed in the pre-discharge path to protect the pre-discharge power switching unit;

[0023] The current detection and protection unit is connected in series with the pre-discharge circuit to detect the pre-discharge current;

[0024] The voltage detection feedback unit has its input connected to the bus voltage and its output connected to the voltage detection terminal MCU_PRE_V of the microcontroller, which is used to determine the pre-discharge completion status.

[0025] Furthermore, the pre-discharge control input unit includes:

[0026] Protection circuit, used to protect input signals;

[0027] An input-level switch is connected to the output terminal of the protection circuit to form a primary control switch.

[0028] Resistor networks are used to construct bias stabilization circuits, enabling control signals to resist interference.

[0029] Furthermore, the protection circuit includes a current-limiting resistor R340 and a transient suppressor D71. The transient suppressor D71 is used to suppress electrostatic discharge and prevent external abnormal voltage from entering the control circuit. The input stage switch is a transistor Q104. The resistor network includes a pull-up resistor R252, a base current-limiting resistor R342, and a pull-down resistor R258.

[0030] Furthermore, the level conversion and drive control unit includes a multi-stage cascaded level conversion MOSFET Q101, a power enable switch Q93, a level conversion switch Q35, and a gate drive switch Q8, with the output terminal of the gate drive switch Q8 connected to the pre-discharge power switch unit.

[0031] Furthermore, the pre-discharge power switching unit includes a pre-discharge main switch Q97 and an inductor L5, wherein the pre-discharge main switch Q97 is connected in series between the power battery and the load bus.

[0032] Furthermore, the gate side of the pre-discharge main switch Q97 is provided with:

[0033] Gate drive resistor R247 is connected in series between the drive signal output terminal and the gate of the pre-discharge main switch Q97 to limit the turn-on speed.

[0034] A gate pull-down resistor R249 is connected between the gate and source of the pre-discharge main switch Q97 to prevent false turn-on.

[0035] A gate-source voltage clamping diode Dm9 is connected in parallel between the gate and source of the pre-discharge main switch Q97 to limit the gate-source voltage.

[0036] Furthermore, the anti-reverse current and energy clamping structure includes a clamping diode Dm23 and an anti-reverse current diode Dm27, which are used to keep the current of inductor L5 flowing back to the pack, suppress the inductive flyback voltage on the load side, and reduce the avalanche risk of the pre-discharge main switch Q97.

[0037] Furthermore, the current detection and protection unit includes a sampling resistor RN13 connected in series with the pre-discharge circuit, and a filter resistor R253, a clamping diode D35, a TVS protection device D69, and a filter capacitor C193 connected in sequence. Its output terminal is connected to the MCU comparator terminal MCU_COMP2+.

[0038] A control method for a pre-discharge control circuit applied to a battery management system includes the following steps:

[0039] The microcontroller outputs a pre-discharge enable signal, which first passes through the transient suppressor D71 and the current-limiting resistor R340.

[0040] When the microcontroller outputs a high-level pre-discharge enable signal, transistor Q104 turns on and generates a low-level control signal. When transistor Q104 turns on, the gate of power enable switch Q93 goes low, and power enable switch Q93 meets the turn-on condition and turns on, thus completing the 3.3V to 12V level conversion.

[0041] The connection between the gate drive switch Q8 and the level shifting switch Q35 constitutes a push-pull drive structure. In this structure, the gate drive switch Q8 provides switching current to the gate of the pre-discharge main switch Q97, and the level shifting switch Q35 controls the discharge capability of the gate of the pre-discharge main switch Q97, thereby driving the pre-discharge main switch Q97.

[0042] The purpose of setting the gate drive resistor R247 on the gate side of the pre-discharge main switch Q97 is to limit the gate charging current, prevent ringing, and control the turn-on speed.

[0043] Furthermore, by pulling down the gate of the pre-discharge main switch Q97 to ground using the gate pull-down resistor R249 and the gate-source voltage clamping diode Dm9, the gate of the pre-discharge main switch Q97 is pulled down to ground to prevent false turn-on caused by the Miller effect, avoid the pre-discharge main switch Q97 from breaking down due to excessive voltage change rate, and protect its gate oxide layer.

[0044] Finally, the gate voltage of the pre-discharge main switch Q97 rises to the turn-on threshold, the pre-discharge main switch Q97 turns on, and the pre-discharge current begins to flow.

[0045] During the shutdown process, when the microcontroller turns off the pre-discharge enable signal, the transistor Q104 shutdown control node returns to a high level.

[0046] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0047] 1. The pre-discharge control circuit and its control method applied to the battery management system adopt a multi-level level conversion structure to improve drive reliability;

[0048] 2. The pre-discharge control circuit and its control method applied to the battery management system prevent damage to the linear region of the MOS through a gate protection network;

[0049] 3. The pre-discharge control circuit and its control method applied to the battery management system realize the pre-discharge judgment of both voltage and current closed loop;

[0050] 4. The pre-discharge control circuit and its control method applied to the battery management system effectively suppress power-on surges and reverse impacts;

[0051] 5. The pre-discharge control circuit and its control method applied to the battery management system improve the transient resistance of the BMS analog front-end and power devices;

[0052] 6. The pre-discharge control circuit and its control method applied to the battery management system change the energy loss problem caused by the current resistor pre-discharge and realize the recovery of energy loss. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the structure of the present invention;

[0054] Figure 2 This is a circuit diagram of the present invention. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Please see Figure 1-2 A pre-discharge control circuit for a battery management system in this embodiment includes:

[0057] The pre-discharge control input unit, whose input terminal PRE_DIS_MOS_EN is connected to the microcontroller, is used to output the pre-discharge enable signal;

[0058] The level conversion and drive control unit, whose input terminal is connected to the microcontroller, is used to convert low-voltage control signals into high-voltage drive signals and amplify the drive current;

[0059] A pre-discharge power switch unit is connected in series between the power battery and the load bus, and its control terminal is connected to the output terminal of the level conversion and drive control unit to form a current-limited charging path.

[0060] An anti-backflow and energy clamping structure is installed in the pre-discharge path to protect the pre-discharge power switching unit;

[0061] The current detection and protection unit is connected in series with the pre-discharge circuit to detect the pre-discharge current;

[0062] The voltage detection feedback unit has its input connected to the bus voltage and its output connected to the voltage detection terminal MCU_PRE_V of the microcontroller, which is used to determine the pre-discharge completion status.

[0063] The above-mentioned units work together to achieve controlled power-on of the power system.

[0064] The pre-discharge control input unit includes:

[0065] Protection circuit, used to protect input signals;

[0066] An input-level switch is connected to the output terminal of the protection circuit to form a primary control switch.

[0067] Resistor networks are used to construct bias stabilization circuits, enabling control signals to resist interference.

[0068] In a preferred embodiment, the protection circuit includes a current-limiting resistor R340 and a transient suppressor D71. The transient suppressor D71 is used to suppress electrostatic discharge and prevent external abnormal voltage from entering the control circuit. The input stage switch is a transistor Q104. The resistor network includes a pull-up resistor R252, a base current-limiting resistor R342, and a pull-down resistor R258. One end of the pull-up resistor R252 is connected to the power supply, and the other end is connected to the control terminal of the transistor Q104. The base current-limiting resistor R342 is connected in series between the control terminal and the input terminal of the transistor Q104. The pull-down resistor R258 is connected between the control terminal and ground of the transistor Q104.

[0069] The pre-discharge control input terminal PRE_DIS_MOS_EN is connected to the microcontroller (MCU) and is used to output a pre-discharge enable signal. The input signal is first protected by a current-limiting resistor R340 and a transient suppressor D71. The transient suppressor D71 is used to suppress electrostatic discharge and prevent external abnormal voltage from entering the control circuit. The input signal drives the transistor Q104 to form a first-level control switch. The bias stabilization circuit is formed by the pull-up resistor R252, the base current-limiting resistor R342, and the pull-down resistor R258 in the resistor network, so that the control signal has anti-interference capability.

[0070] In a preferred embodiment, in order to achieve low-voltage control of high-voltage, the present invention provides a level conversion and drive control unit, which includes a multi-stage cascaded level conversion MOSFET Q101, a power enable switch Q93, a level conversion switch Q35, and a gate drive switch Q8. The output terminal of the gate drive switch Q8 is connected to a pre-discharge power switch unit.

[0071] Its working process is as follows:

[0072] When the microcontroller (MCU) outputs a pre-discharge enable signal, the gate drive switch Q8 outputs a drive current to the pre-discharge MOS gate. Through the above cascaded structure, the low-voltage logic is converted into high-voltage drive isolation and the gate drive current is amplified, and the microcontroller (MCU) is prevented from directly being subjected to high-voltage impact.

[0073] In a preferred embodiment, the pre-discharge power switching unit includes a pre-discharge main switch Q97 and an inductor L5. The pre-discharge main switch Q97 is connected in series between the power battery and the load bus, and a current-limiting charging path is formed through the pre-discharge inductor and the bus capacitor.

[0074] Furthermore, to improve system reliability, the gate side of the pre-discharge main switch Q97 is also provided with:

[0075] Gate drive resistor R247 is connected in series between the drive signal output terminal and the gate of the pre-discharge main switch Q97 to limit the turn-on speed.

[0076] A gate pull-down resistor R249 is connected between the gate and source of the pre-discharge main switch Q97 to prevent false turn-on.

[0077] A gate-source voltage clamping diode Dm9 is connected in parallel between the gate and source of the pre-discharge main switch Q97 to limit the gate-source voltage.

[0078] This structure enables soft-start conduction of the MOSFET, avoiding the high-power state in the linear region.

[0079] In a preferred embodiment, the anti-reverse current and energy clamping structure includes a clamping diode Dm23 and an anti-reverse current diode Dm27, the functions of which are:

[0080] Inductor L5 keeps the current flowing back to the pack;

[0081] Suppress inductive flyback voltage on the load side;

[0082] And reduce the risk of avalanche in the pre-discharge main switch Q97.

[0083] In a preferred embodiment, the current detection and protection unit includes a sampling resistor RN13 connected in series with the pre-discharge circuit for detecting the pre-discharge current, and a filter resistor R253, a clamping diode D35, a TVS protection device D69, and a filter capacitor C193 connected in sequence, with its output terminal connected to the MCU comparator terminal MCU_COMP2+.

[0084] The two ends of the sampling resistor RN13 are respectively connected to the pre-discharge circuit and one end of the filter resistor R253. The other end of the filter resistor R253 is connected to the common node of the clamping diode D35 and the TVS protection device D69. The filter capacitor C193 is connected in parallel between the input terminal of the MCU comparator and ground.

[0085] Specifically, the pre-discharge circuit is connected in series with a sampling resistor RN13 to detect the pre-discharge current.

[0086] The sampling signal passes through: filter resistor R253, clamping diode D35, TVS protection device D69, and filter capacitor C193;

[0087] The current is fed into the MCU comparator terminal MCU_COMP2+, and the MCU determines the following based on the detected current information:

[0088] ① Is there any abnormal surge? Has a short circuit occurred?

[0089] ② Whether the main power path is allowed to conduct.

[0090] In a preferred embodiment, the bus voltage signal in the voltage detection feedback unit is fed back to the MCU terminal MCU_PRE_V through a detection network.

[0091] The controller determines the pre-discharge completion status by comparing the bus voltage with the battery voltage.

[0092] When the precharge percentage (1 - (DSV / total voltage)) reaches the set threshold, the MCU allows the main MOS to turn on and turns off the pre-discharge MOS.

[0093] In this embodiment, a control method for a pre-discharge control circuit applied to a battery management system includes the following steps:

[0094] The microcontroller (MCU) outputs a pre-discharge enable signal. This signal first passes through a transient suppressor (D71) and a current-limiting resistor (R340). The transient suppressor D71 absorbs ESD and prevents the microcontroller's I / O ports from being damaged by high-voltage coupling. The microcontroller outputs an 80kHz PWM wave to drive the transistor Q104. The pull-down resistor R342 pulls the gate stage of the transistor Q104 down to digital ground (DGND) to ensure a stable static operating point.

[0095] When the microcontroller outputs a high-level pre-discharge enable signal, transistor Q104 turns on and generates a low-level control signal (first logic flip). When transistor Q104 turns on, the gate of power enable switch Q93 goes low. At this time, power enable switch Q93 meets the conduction condition and turns on, completing the level conversion from 3.3V to 12V.

[0096] The connection between the gate drive switch Q8 and the level shifting switch Q35 constitutes a push-pull drive structure. In this structure, the gate drive switch Q8 provides switching current to the gate of the pre-discharge main switch Q97, and the level shifting switch Q35 controls the discharge capability of the gate of the pre-discharge main switch Q97, thereby driving the pre-discharge main switch Q97.

[0097] The purpose of setting the gate drive resistor R247 on the gate side of the pre-discharge main switch Q97 is to limit the gate charging current, prevent ringing, and control the turn-on speed.

[0098] Furthermore, the gate of the pre-discharge main switch Q97 is pulled down to ground through the gate pull-down resistor R249 and the gate-source voltage clamping diode Dm9 to prevent the Miller effect and avoid the pre-discharge main switch Q97 from breaking down due to excessive voltage change rate (dv / dt) and damage to its gate oxide layer.

[0099] Finally, the gate voltage of the pre-discharge main switch Q97 rises to the turn-on threshold, the pre-discharge main switch Q97 turns on, and the pre-discharge current begins to flow.

[0100] During the shutdown process, when the microcontroller (MCU) turns off the pre-discharge enable signal, the transistor Q104 shutdown control node returns to a high level.

[0101] It should be noted that before the main system power MOSFET is turned on, the relationship between the charger's C-terminal voltage and the battery's total voltage is checked first, and then the pre-discharge start-up method is decided, which includes the following three:

[0102] 1. Skip the pre-discharge phase;

[0103] When the ratio of the charger's C-terminal voltage to the battery's total voltage is less than 20%, it is determined that the external load capacitor is basically fully charged. At this point, skipping the pre-discharge process and directly turning on the discharge MOSFET will not result in a large current.

[0104] 2. Initiate the pre-discharge phase;

[0105] When the ratio of the charger's C-terminal voltage to the battery's total voltage is between 20% and 50%, it is determined that there is no external short circuit fault. If the discharge MOSFET is directly turned on, a large current surge will occur. Therefore, a formal pre-discharge process needs to be executed.

[0106] 3. Slow start pre-discharge stage;

[0107] When the ratio of the charger's C-terminal voltage to the battery's total voltage is greater than 50%, the microcontroller outputs a pre-discharge enable signal, the pre-discharge MOSFET is turned on under control, and the pre-discharge current and bus voltage are detected in real time. After the preset conditions are met, the main power circuit is turned on.

[0108] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0109] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pre-discharge control circuit applied to a battery management system, characterized in that, include: The pre-discharge control input unit, whose input terminal PRE_DIS_MOS_EN is connected to the microcontroller, is used to output the pre-discharge enable signal; The level conversion and drive control unit, whose input terminal is connected to the microcontroller, is used to convert low-voltage control signals into high-voltage drive signals and amplify the drive current; A pre-discharge power switch unit is connected in series between the power battery and the load bus, and its control terminal is connected to the output terminal of the level conversion and drive control unit to form a current-limited charging path. An anti-backflow and energy clamping structure is installed in the pre-discharge path to protect the pre-discharge power switching unit; The current detection and protection unit is connected in series with the pre-discharge circuit to detect the pre-discharge current; The voltage detection feedback unit has its input connected to the bus voltage and its output connected to the voltage detection terminal MCU_PRE_V of the microcontroller, which is used to determine the pre-discharge completion status.

2. The pre-discharge control circuit for a battery management system according to claim 1, characterized in that: The pre-discharge control input unit includes: Protection circuit, used to protect input signals; An input-level switch is connected to the output terminal of the protection circuit to form a primary control switch. Resistor networks are used to construct bias stabilization circuits, enabling control signals to resist interference.

3. The pre-discharge control circuit for a battery management system according to claim 2, characterized in that: The protection circuit includes a current-limiting resistor R340 and a transient suppressor D71. The transient suppressor D71 is used to suppress electrostatic discharge and prevent external abnormal voltage from entering the control circuit. The input stage switch is a transistor Q104. The resistor network includes a pull-up resistor R252, a base current-limiting resistor R342, and a pull-down resistor R258.

4. The pre-discharge control circuit and control method for a battery management system according to claim 1, characterized in that: The level conversion and drive control unit includes a multi-stage cascaded level conversion MOSFET Q101, a power enable switch Q93, a level conversion switch Q35, and a gate drive switch Q8. The output terminal of the gate drive switch Q8 is connected to the pre-discharge power switch unit.

5. The pre-discharge control circuit and control method for a battery management system according to claim 1, characterized in that: The pre-discharge power switching unit includes a pre-discharge main switch Q97 and an inductor L5. The pre-discharge main switch Q97 is connected in series between the power battery and the load bus.

6. The pre-discharge control circuit and control method for a battery management system according to claim 5, characterized in that: The gate side of the pre-discharge main switch Q97 is provided with: Gate drive resistor R247 is used to limit the turn-on speed; The gate pull-down resistor R249 is used to prevent false turn-on. The gate-source voltage clamping diode Dm9 is used to limit the gate-source voltage.

7. The pre-discharge control circuit and control method for a battery management system according to claim 5, characterized in that: The anti-reverse current and energy clamping structure includes clamping diode Dm23 and anti-reverse current diode Dm27, which are used to keep the current of inductor L5 flowing back to the pack, suppress the inductive flyback voltage on the load side, and reduce the avalanche risk of the pre-discharge main switch Q97.

8. The pre-discharge control circuit and control method for a battery management system according to claim 1, characterized in that: The current detection and protection unit includes a sampling resistor RN13 connected in series with the pre-discharge circuit, and a filter resistor R253, a clamping diode D35, a TVS protection device D69, and a filter capacitor C193 connected in sequence. Its output terminal is connected to the MCU comparator terminal MCU_COMP2+.

9. A control method for a pre-discharge control circuit applied to a battery management system, characterized in that, Includes the following steps: The microcontroller outputs a pre-discharge enable signal, which first passes through the transient suppressor D71 and the current-limiting resistor R340. When the microcontroller outputs a high-level pre-discharge enable signal, transistor Q104 turns on and generates a low-level control signal. When transistor Q104 turns on, the gate of power enable switch Q93 goes low, and power enable switch Q93 meets the turn-on condition and turns on, thus completing the 3.3V to 12V level conversion. The connection between the gate drive switch Q8 and the level shifting switch Q35 constitutes a push-pull drive structure. In this structure, the gate drive switch Q8 provides switching current to the gate of the pre-discharge main switch Q97, and the level shifting switch Q35 controls the discharge capability of the gate of the pre-discharge main switch Q97, thereby driving the pre-discharge main switch Q97. The purpose of setting the gate drive resistor R247 on the gate side of the pre-discharge main switch Q97 is to limit the gate charging current, prevent ringing, and control the turn-on speed. Furthermore, by pulling down the gate of the pre-discharge main switch Q97 to ground using the gate pull-down resistor R249 and the gate-source voltage clamping diode Dm9, the gate of the pre-discharge main switch Q97 is pulled down to ground to prevent false turn-on caused by the Miller effect, avoid the pre-discharge main switch Q97 from breaking down due to excessive voltage change rate, and protect its gate oxide layer. Finally, the gate voltage of the pre-discharge main switch Q97 rises to the turn-on threshold, the pre-discharge main switch Q97 turns on, and the pre-discharge current begins to flow. During the shutdown process, when the microcontroller turns off the pre-discharge enable signal, the transistor Q104 shutdown control node returns to a high level.

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