Lithium battery overcharge, overdischarge, short circuit protection circuit details and advantages and types
The circuit is primarily composed of a lithium battery protection ASIC, the DW01, along with charge and discharge control MOSFETs (including two N-channel MOSFETs). A single lithium cell is connected between B+ and B-, while the battery pack outputs from P+ to P-. During charging, the charger's output voltage is applied across P+ and P-, allowing current to flow from P+ through B+ and B- of the individual cell, and then through the charge control MOSFET back to P-. When the voltage of a single cell exceeds 4.35V, the OC pin of the DW01 triggers to turn off the charge control MOSFET, stopping the charging process immediately to prevent overcharging damage.
During discharge, if the voltage of a single cell drops below 2.30V, the OD pin of the DW01 activates the discharge control MOSFET to shut down the discharge, preventing overdischarge. The CS pin of the DW01 acts as a current detection point. If a short circuit occurs, the conduction voltage drop of the charge/discharge MOSFET increases rapidly, causing the CS pin voltage to rise quickly. This prompts the DW01 to turn off the MOSFET, providing overcurrent or short-circuit protection. An image illustrating the details and advantages of this protection circuit is included for reference.
Lithium batteries offer several advantages, including high energy density, high operating voltage, no memory effect, long cycle life, low pollution, light weight, and minimal self-discharge. Lithium polymer batteries, in particular, have unique benefits such as no leakage due to solid electrolytes, flexibility in design, thin form factors, and the ability to be bent or shaped into various forms. They can also achieve higher voltages without the need for multiple series connections.
The IEC standard for lithium battery cycle life testing involves charging at 1C to 4.2V with a cutoff current of 20mA, followed by discharging at 0.2C to 3.0V. After 500 cycles, the capacity should remain above 60% of the initial value. For charge retention tests, batteries are charged to 4.2V at 1C, stored at 20±5°C for 28 days, and then discharged at 0.2C to 0.25V to measure remaining capacity.
Self-discharge refers to the natural loss of charge when a battery is not in use. It is influenced by manufacturing quality, materials, and storage conditions. Lower temperatures generally reduce self-discharge but may affect performance if too extreme. Lithium batteries typically have lower self-discharge rates compared to other rechargeable types.
Internal resistance is an important parameter affecting battery performance. It includes AC and DC internal resistance, with AC resistance being more accurate for measuring true values. Internal pressure arises from gas generated during charge and discharge, which must be controlled to avoid damage. Internal pressure tests simulate high-altitude conditions to ensure safety.
Ambient temperature significantly affects battery performance. High temperatures increase reaction rates, boosting power output, while low temperatures reduce it. However, extreme temperatures can cause chemical imbalances and damage the battery.
Overcharge protection methods include peak voltage detection, temperature change rate monitoring, time-based control, and others. Overcharging can lead to increased internal pressure, deformation, and leakage, while overdischarge can damage active materials and reduce capacity. Using mismatched batteries can cause uneven charging and discharging, leading to failure or leakage.
Battery explosions occur when solid particles are expelled beyond 25 cm. Safety tests involve placing batteries under a mesh to detect such events. In lithium battery packs, inconsistent cells can cause overcharge or overdischarge, making individual cell monitoring essential.
Lithium-ion batteries operate at 3.6V or 3.7V, with termination voltages depending on anode material. Discharge below the specified voltage causes damage. Portable electronics rely heavily on battery advancements, with lithium-ion batteries offering high specific energy, stable voltage, and long life.
Non-rechargeable lithium batteries, like lithium-manganese dioxide and lithium-thionyl chloride, are used in cameras, clocks, and medical devices. They feature high voltage, long shelf life, and low self-discharge but are not suitable for recharging. Proper handling, including avoiding overheating and incorrect usage, is crucial to prevent damage or hazards.
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