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  • 2013-10-10
    How to set up a safe lithium battery protection circuit


According to statistics, the global demand for lithium-ion batteries has reached 1.3 billion , and with the ever-expanding field of application , the data on a yearly basis . For this reason , with the lithium-ion battery usage in various industries proliferated rapidly , the battery safety performance is increasingly prominent, not only requires the lithium-ion battery has excellent charge and discharge performance, but also requires a higher safety performance. That lithium battery fire or explosion in the end how it happened , and what measures can be avoided to prevent it ?

Laptop battery explosion, which not only with lithium batteries used in the production process , but also on the same battery packaged battery protection board, laptop charging and discharging management circuitry and notebook cooling design. Unreasonable laptop thermal design and management of charging and discharging , the batteries battery will overheat , thereby greatly increasing the electrical activity of the core , while increasing the explosion risk of burning .

Analysis of the composition and properties of lithium battery materials

First let us look at the material lithium batteries , lithium-ion batteries used in battery performance depends on the internal structure and properties of materials . These materials include internal battery anode material , electrolyte , separator and a positive electrode material . Wherein the positive and negative materials selection and directly determines the quality of lithium ion battery performance and price . So cheap , high-performance positive and negative materials research has been the development of lithium-ion battery industry focus .

Anode material generally used in the carbon material , the current development is more mature. The cathode material development has become a constraint to further improve the performance of lithium-ion batteries , an important factor in further price reduction . In the current commercial production of lithium- ion battery cathode material costs account for about 40% of the entire cost of the battery about lower prices cathode material of lithium ion battery directly determines the lower prices . The lithium -ion battery in particular. Such as a mobile phone with a compact lithium-ion batteries about only 5 grams of cathode material, while driving a bus with a lithium-ion battery may require up to 500 kg of cathode materials .

Although in theory it can be used as cathode material for lithium ion batteries many types of common cathode material mainly composed of LiCoO2, charging, added to the battery positive pole of the electric potential to force the release of lithium -ion compounds , embedded negative elements arranged in lamellar structure carbon neutral . Discharge , lithium ions from the lamellar structure of carbon precipitation and re-cathode combination of compounds . Movement of lithium ions generated current. This is the working principle of the lithium battery .

Lithium battery charge and discharge management design

Lithium battery charging, plus the battery positive pole of the electric potential to force the release of lithium -ion compounds , embedded negative elements arranged in lamellar structure of carbon . Discharge , lithium ions from the lamellar structure of carbon precipitation and re-cathode combination of compounds . Movement of lithium ions generated current. Although the principle is simple , but in actual industrial production, need to be considered to be much more practical problems : a positive electrode material additives required to maintain the activity of repeated charge- discharge , the negative electrode material needs to design the molecular structure to accommodate more level more lithium ions; filled in electrolyte between the positive and negative , in addition to maintaining stability , but also need to have good electrical conductivity , reducing the battery internal resistance .

Although the lithium -ion batteries have all the advantages mentioned above , but it requires the protection circuit is relatively high, in the course should strictly avoid overcharge, over -discharge phenomenon , the discharge current is not too large , in general, the discharge rate should not exceed 0.2C. Battery charging process shown in Fig. In a charge cycle , the lithium -ion batteries need charging before the battery voltage and temperature testing to determine whether rechargeable . If the battery voltage or temperature is outside the range allowed by the manufacturer is prohibited charging. Allows charging voltage range is : each battery 2.5V ~ 4.2V.

Deep discharge of the battery in the case , must require charger has a pre-filled process that allows for fast battery charging conditions ; Then, according to the battery manufacturer's recommended charging speed quickly , usually 1C, constant current charging the battery charger , battery voltage rises slowly ; Once the battery voltage reaches the set termination voltage ( typically 4.1V or 4.2V), constant current charge termination , the charging current fast decay , charging into the full charge process ; process in full charge , the charging current gradually attenuated until C/10 charge rate decreased to less time-out or fully charged when charging into the top end ; top off charge , the charger to the battery charging current minimal additional energy . Top off the charging period of time, turn off the charge .

Lithium battery protection circuit design

Since the chemical properties of lithium-ion batteries in the normal course of its internal energy and chemical energy is transformed into each other chemical reactions, but under certain conditions , such as its overcharge, over -discharge and over-current will cause the battery internal chemical side reactions , the side reaction intensified , it will seriously affect the battery performance and service life , and may produce a lot of gas , so that the battery internal pressure increases rapidly after the explosion caused by security problems, so all lithium-ion batteries are required a protection circuit for battery charging and discharging state effective monitoring and shutdown under certain conditions, charge and discharge circuit to prevent damage to the battery .

Lithium-ion battery protection circuit includes over- charge protection, over current / short circuit protection and over-discharge protection, overcharge protection requirements of high precision, protect the IC low power consumption, high-voltage and zero -volt rechargeable other characteristics. The following article will detail these three principles of the protection circuit , new features, and performance requirements for the design and development engineers, protection circuits have reference value .
Lithium battery protection circuit design Case Study

A lithium battery as the power supply circuit design , it is required to more complex mixed-signal system integrated into a small area of the chip , which is bound to the digital , analog circuits proposed voltage , low power consumption. Constraints in power and functionality , how to get the best design is the current power management technology (PowerManagement, PM) is a research hotspot. On the other hand , the application of lithium batteries also greatly promoted the appropriate battery management, battery protection circuit design and development . Lithium battery applications must have complex control circuit to prevent battery overcharge, over -discharge and over-current condition.

Energy from the electric bike trend of changes discussed using ultra-low power , high performance MSP430F20X3 design electric bicycle lithium battery charge and discharge protection circuit solution. The program from the system architecture , charge and discharge circuit , detection and protection circuit design in every detail discussed the design process , the designers of power for the electric bike provides a more comprehensive reference.