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| 16 | Protecting Li-Ion Batteries and Packs To ensure long life and reliability, individual battery cells and battery packs must be electrically protected. Bourns has been doing just that for decades, while it also continually innovates and expands its portfolio. Bourns' broad portfolio allows designers to select the right circuit protection component to meet their increasingly complex, demanding, and compact battery pack requirements. Managing Li-Ion Battery Packs High Voltage Li-Ion battery packs offer significant advantages such as low weight and high energy density. However, they require Battery Management Systems (BMS) to operate within safe limits. BMS connects to the Li-Ion battery packs and performs four major functions: • Monitor voltage, current, temperature, state of charge (SoC), state of health (SoH) • Balance individual cell voltages for maximum battery pack efficiency • Protect against overcurrent, overvoltage and over- temperature events • Communicate via CANbus and/or wireless communication protocols Bourns offers a broad portfolio of components suitable for Battery Management Systems (Figure 4). These components include isolation transformers, signal transformers, power inductors, common mode chokes, TVS diodes, fuses, current sensing resistors, and TBU® HSPs (Transient Blocking Unit High-Speed Protectors). Battery Packs Mobile devices, including smartphones, tablets, and single-lens digital cameras, primarily employ Li-ion battery packs. Larger physical items such as electric vehicles (EV) along with industrial machinery and robotics also use battery packs. Battery cells have inherent electrical, environmental, and mechanical challenges. When overcharged or overheated, a battery cell can rupture, combust, or explode. Even if overcharging or overheating does not result in a fire, the battery can still be compromised and can be more susceptible to further damage from physical factors, including vibration, impact, and exposure to heat. Charge and Temperature During charging and discharging cycles, battery cells can face overcurrent, overvoltage, and overtemperature conditions. The charging process for Li-ion batteries consists of two phases: constant current and constant voltage. In the constant current charging phase, the charge current is applied to the battery until the voltage limit per cell is reached. Li-ion batteries cannot accept a higher voltage charge than specified without being damaged. The constant voltage phase then begins as the applied current declines to a few percent of the constant charge current. During this time, the maximal cell voltage is applied to the battery. For multi-cell battery packs, a balancing phase occurs between the constant current and constant voltage phases to ensure a consistent charge among cells. In such packs, the voltage applied in the constant voltage stage is the product of the number of cells and the maximal voltage per cell. Figure 4 Bourns offers a broad portfolio of components suitable for Battery Management Systems (Source: Bourns)