18650 battery 3500mah.On the Self Protection Function of Lithium Batteries

　　Lithium ion batteries are widely used rechargeable batteries, which have advantages such as high operating voltage, small size, light weight, high energy density, long cycle life, fast and sufficient charging in a short period of time, and a wide range of discharge temperatures. In addition, lithium-ion batteries have advantages such as low self discharge current, no memory effect, and no environmental pollution. Its global supply and lithium battery suppliers are continuously increasing. According to a market research company report, the global supply of lithium rechargeable batteries increased by 17% in 2007 compared to the previous year. With the expansion of the usage of lithium-ion batteries, the charge and discharge protection of lithium-ion batteries has become increasingly important. The increase in lithium battery suppliers and the safety of lithium battery power supply equipment are currently the most concerned issues, so their protection is very important. The protection of lithium batteries mainly includes overcharging protection, over discharge protection, overcurrent and short circuit protection, etc.

　　1. Overcharge protection

　　When the charger overcharges the lithium battery, in order to prevent internal pressure rise caused by temperature rise, the charging state needs to be terminated. For this purpose, the protective device needs to monitor the battery voltage. When it reaches the overcharge voltage of the battery, the overcharge protection function is activated and charging is terminated.

　　2. Overdischarge protection

　　In order to prevent the over discharge state of lithium-ion batteries, when the voltage of the lithium-ion battery is lower than its over discharge voltage detection point, the over discharge protection is activated, the discharge is terminated, and the battery is kept in a low static current standby mode.

　　3. Overcurrent and short circuit protection

　　When the discharge current of a lithium-ion battery is too high or a short circuit occurs, the protective device will activate the overcurrent protection function.

　　4. Protection of multi section lithium circuits

　　The rated voltage of a single lithium-ion battery is 3.6V, which cannot meet the needs of high-voltage power supply scenarios. Therefore, multiple lithium-ion batteries need to be used in series. For this reason, various manufacturers of power management and control integrated circuits have launched their own multi section lithium battery (battery pack) protection integrated circuit chips. The characteristic of these products is to monitor the charging and discharging status of 3 or 4 lithium batteries, which can achieve overcharge, overdischarge, and overcurrent protection.

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