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With the rapid development of electric vehicles (EVs), renewable energy storage systems, and portable semiconductor electronics, the role of Battery Management Systems (BMS) in ensuring battery safety, prolonging lifespan, and enhancing efficiency has become increasingly critical. As a vital semiconductor device, MOSFETs play an indispensable role in BMS, particularly in battery charge/discharge management, cell protection, and temperature regulation, among other functions.

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1. Fundamental Working Principle of MOSFETs
A MOSFET is a three-terminal device whose operation relies on using an electric field to modulate carrier concentration in the channel, thereby controlling current flow between the source and drain. Based on structure, MOSFETs are categorized into NMOS and PMOS. NMOS is typically used for low-side switching, while PMOS is employed in high-side switching applications. By regulating the gate voltage (VGS), MOSFETs achieve rapid switching operations, delivering significant advantages in high-frequency and high-efficiency applications such as power conversion systems.

2. Role of MOSFETs in BMS

In Battery Management Systems (BMS), MOSFETs primarily serve the following critical functions:

2.1 Battery Charge/Discharge Control

• As a core BMS function, MOSFETs regulate battery charging/discharging processes to maintain safe and efficient operation. Key implementations include:

• Charge Path Control: Precisely modulate charging current via gate voltage (VGS) switching (e.g., <1μs response in TI BQ76952), preventing overcharge.

• Discharge Path Protection: Block excessive discharge currents (e.g., <2.5V/cell cutoff) to avoid lithium plating.

• Dynamic Efficiency: Achieve >99% conduction efficiency with RDS(on) <0.5mΩ (Infineon OptiMOS™).

2.2 Battery Protection

MOSFETs enable real-time safety interventions through:

• Overcurrent Protection: Trigger <5μs cutoff at 150% rated current (STL325N4LF6AG).

• Overvoltage/Undervoltage Lockout: Isolate battery packs when voltage exceeds 4.35V/cell or falls below 2.7V/cell.

• Thermal Runaway Prevention: Integrate with NTC sensors to disconnect circuits at Tj >125°C.

2.3 Thermal Management

MOSFETs enhance thermal safety via:

• Active Current Throttling: Reduce current by 50% when battery temperature reaches 60°C.

• Dual-Level Protection:

Stage 1 (45°C): Activate cooling systems

Stage 2 (70°C): Hard disconnect (UL1973 certified)

2.4 Cell Balancing

In multi-cell configurations (e.g., 48V EV packs), MOSFETs enable:

• Passive Balancing: Bleed excess charge through resistors (≤100mA, 98% voltage synchronization accuracy).

• Active Balancing: Transfer energy between cells via inductors (efficiency >85%, using Renesas ISL94202).

• Voltage Tolerance: Maintain <±10mV cell-to-cell deviation after 500 cycles.

3. Key Considerations for MOSFETs in BMS Design

Although MOSFETs play a critical role in Battery Management Systems (BMS), multiple factors must be considered during the design process.

First, the selection of MOSFETs must account for the operating voltage and current range of the battery pack. Choosing MOSFETs with appropriate voltage and current ratings is essential to ensure system reliability.

Second, the switching speed and on-resistance (RDS(on)) of the MOSFET are also key parameters that require careful attention. To achieve efficient charge and discharge control, MOSFETs should exhibit low on-resistance and fast switching response, thereby reducing power losses and improving system efficiency.

Additionally, the thermal characteristics of the MOSFET must be fully considered in the design. In high-power applications, the power dissipation and heat generation of the MOSFET may affect its performance and lifespan. Therefore, proper thermal management mechanisms must be designed to ensure the MOSFET operates within safe temperature limits.

As a critical component in battery management systems (BMS), MOSFETs play a vital role in multiple functions including battery charge/discharge control, battery protection, temperature management, and voltage balancing, owing to their excellent switching performance, low on-resistance, and reliable protection features. With the continuous advancement of battery technology and the electric vehicle market, the application of MOSFETs in BMS will become increasingly widespread and important. Through continuous optimization of MOSFET performance and design, BMS systems will be better equipped to ensure the safe, reliable, and efficient operation of battery packs.