How does the law enforcement recorder use lithium batteries to protect the circuit?

　　In order to actively adapt to the requirements of the standardization of law enforcement, in recent years, the Ministry of Public Security has taken the lead in deploying and using law enforcement recorders in political and legal institutions across the country.

　　In order to actively adapt to the requirements of the standardization of law enforcement, in recent years, the Ministry of Public Security has taken the lead in deploying and using law enforcement recorders in political and legal institutions across the country. At present, the law enforcement recorder has become a "weapon" for the grassroots front-line police to carry out law enforcement work on duty. The revised GA/T 947.2-2015 "Single Police Law Enforcement Video and Audio Recording System Part 2: Law Enforcement Recorder" standard adds requirements for battery safety protection performance, and the lithium battery pack used in law enforcement recorders should comply with GA/T The 18287-2013 "General Specification for Lithium Ion Batteries and Battery Packs for Mobile Phones" requires battery protection performance in Article 4.4, that is, lithium battery packs should have the functions of overcharge protection, overdischarge protection and short circuit protection.

　　From August to October 2016, there were more than 30 explosions and fire accidents caused by battery defects in Samsung NOTE7 mobile phones worldwide, which aroused widespread concern in the society. At present, lithium battery combustion and explosion incidents occur in various electronic products that use lithium batteries. Lithium battery explosion is mainly due to the battery temperature exceeding 100°C, overcharging or short circuit, etc., which causes a large amount of heat to be generated inside the battery, which eventually burns or even explodes. The unreasonable design of the lithium battery protection board may also cause the battery to overheat, causing it to explode or burn. Overheating has become an important issue affecting the life of the lithium battery. Lithium batteries are widely used in various police equipment, and their safety requirements have become more urgent. Police equipment manufacturers, supervisory departments, and standard setting departments should pay more attention to the safety of lithium batteries. Law enforcement recorder is an important equipment for the on-site video and audio collection of law enforcement. Its importance is self-evident. Standardizing the battery quality of law enforcement recorder not only ensures the integrity and reliability of the collected video and audio data, but also protects the law enforcement personnel. Safety.

　　In 1991, Sony Corporation of Japan launched the first commercial lithium-ion rechargeable battery, which became an important milestone in the field of energy technology. Lithium batteries have quickly replaced nickel-cadmium and nickel-metal hydride batteries because of their high discharge current, low internal resistance, no memory effect, high energy density, environmental protection, long service life, wide operating temperature range, low self-discharge rate, and high safety performance. , Become the mainstream power supply for portable electronic devices. Many well-known semiconductor companies at home and abroad, such as Ricoh, Seiko, Texas Instruments, Wuxi Risheng Microelectronics, Fuxiang Microelectronics, and Nanjing Tuowei, have carried out research and development work on lithium batteries and protection circuits, and launched a series of lithium battery chargers. The framework and solution of the discharge protection chip. Representative application chips are: Texas Instruments' BQ2057 series and bqTINY series, Seiko's S82 series, and Ricoh's R54 series. Domestic semiconductor companies have also launched a variety of lithium battery protection chips with different levels of complexity. Representative application chips include: Wuxi Risheng Microelectronics' SUN4000 series and SUN5000 series, Fuxiang Microelectronics DW01 series and Nanjing Tuowei's TP5000, TP4057 , TP4056, etc. At present, the actual specific energy of commercial lithium batteries is as high as 555wh/kg, and the cycle life can reach more than 2000 times.

　　Requirements for battery protection circuits

　　In the actual use of lithium batteries, there may be overcharge, overdischarge, and overcurrent conditions, which may seriously damage the performance of the lithium battery, and even cause spontaneous combustion or explosion. In the overcharged state, the heat accumulates after the temperature of the lithium battery rises, causing the electrolyte to decompose and produce gas, which is easy to increase the internal pressure and cause the lithium battery to spontaneously ignite or rupture; in the overdischarged state, the electrolyte decomposes to cause the battery characteristics and durability Therefore, it is necessary to limit the discharge voltage to ensure that some lithium ions can stay in the negative electrode to prevent all the lithium ions in the graphite layer of the negative electrode from falling back to the positive electrode during discharge, blocking the next charging circuit, and damaging the battery; short circuit or external circuit When the discharge current is too large, the internal power consumption of the battery increases, and the temperature rises, which may cause the oxidation or decomposition of the electrolyte, resulting in a decrease in cycle life, thereby affecting the service life of the lithium battery.

　　Temperature is also an important factor affecting the performance of lithium batteries. If the temperature is too high, the performance degradation and aging of the lithium battery will accelerate, and the internal thermal effect will increase accordingly, which may eventually cause an explosion; if the temperature is too low, the capacity of the lithium battery will rapidly decay, or even useless at all, even if the lithium battery returns to normal temperature , Part of its capacity cannot be restored.

　　In summary, the lithium battery protection circuit is very important and indispensable. Combined with the actual application, the lithium battery protection circuit needs to meet the following requirements:

　　(1) Ultra-low power consumption

　　The lithium battery protection circuit is powered by a lithium battery. The ultra-low power consumption protection circuit can reduce the extra loss of the lithium battery and increase the external output power.

　　(2) High-precision detection voltage

　　When the voltage of the lithium battery is lower than 1.2% of its full charge voltage, the capacity will be reduced by 9%[8]. Therefore, the deviation of the detection voltage directly affects the usable capacity of the lithium battery.

　　(3) Work correctly under a large voltage range

　　Since the power supply voltage of the lithium battery protection circuit is the lithium battery voltage, and the lithium battery voltage may fluctuate in a larger range, the lithium battery protection circuit is required to work correctly within a larger voltage range.

　　(4) Quick response

　　When protecting lithium batteries, precise and fast control actions are required. If an abnormal situation occurs and the protection circuit cannot take protective measures in time, it will also affect the service life and capacity of the lithium battery, and even cause an explosion.

　　(5) High-precision temperature detection

　　The temperature is too high or too low will accelerate the aging of the lithium battery, the lithium battery protection circuit should respond correctly and timely to the abnormal temperature, so the protection circuit must be able to accurately detect the temperature of the lithium battery pack.

　　(6) High integration

　　Design a circuit with a simple structure, avoid complex wiring, can complete the design on a smaller PCB, improve integration and reduce production costs.