Lithium battery protection circuit method

Among the various types of batteries currently in use, lithium batteries (also known as lithium ion secondary batteries or lithium ion batteries) are a new type of power source that has only been developed in the past ten years. Lithium batteries are different from general chemical power sources. The charging and discharging process of lithium batteries is realized by the insertion and extraction of lithium ions in the positive and negative electrodes of the battery. The negative electrode of a lithium battery is a carbon material, such as graphite; the positive electrode is a lithium-containing transition metal oxide, such as lithium cobalt oxide (LiC002). In addition, the positive and negative electrode materials of the lithium battery all adopt the lithium ion intercalation compound with a layered structure in which lithium ions can be freely inserted and extracted. The lithium ions between the layers will undergo electrochemical reactions in an appropriate electrolyte. During charging, lithium ions are extracted from the positive electrode lattice under the drive of an external electric field, pass through the electrolyte, and are inserted into the negative electrode lattice. The process of discharging is just the opposite. Lithium ions return to the positive electrode, and electrons pass through the external circuit to the positive electrode to recombine with lithium ions. Compared with the commonly used nickel-cadmium and nickel-metal hydride batteries, lithium batteries have many superior characteristics, which are mainly shown in the following aspects: (1) The power supply voltage of lithium batteries is high, generally 3.6V, which is about nickel-cadmium batteries and nickel-hydrogen batteries. 3 times the battery voltage. Regarding electronic equipment with higher power supply voltage requirements, the number of batteries in series required for the battery pack can also be greatly reduced. Therefore, the combined use of lithium batteries is easy to obtain a higher voltage. (2) The specific energy is higher, that is, the energy supplied by the lithium battery of the same weight is higher than that of other batteries. The specific energy of lithium batteries is generally 2 to 3 times that of nickel-cadmium batteries and nickel-hydrogen batteries. Therefore, it is conducive to the miniaturization and weight reduction of portable electronic equipment. (3) No memory effect. Nickel-cadmium batteries and nickel-metal hydride batteries have a memory effect and must be discharged regularly, otherwise the battery will fail due to the memory effect. The lithium battery has no memory effect and can be charged straight without worrying about the amount of residual power. In this way, the performance of the lithium battery can be fully utilized. (4) Long service life. Lithium batteries use carbon anodes, which do not generate metal lithium during charging and discharging, so that the battery can be warned of damage due to internal metal lithium short-circuits. At present, the cycle life of lithium batteries can reach more than 5000 times, which is much higher than other types of batteries. (5) The working environment has a wide temperature range. Generally, it can work between 30℃ and 0℃, and it has excellent high and low temperature discharge performance. (6) Low self-discharge rate. Self-discharge rate, also known as charge retention rate, refers to how much the battery automatically discharges when it is not in use. The self-discharge rate of lithium batteries is between 2% and 5%, nickel-cadmium batteries are between 25% and 30%, and nickel-hydrogen batteries are between 30% and 35%. Therefore, the lithium battery maintains the longest charge in the same environment. (7) Lithium batteries do not contain any toxic elements such as mercury and cadmium, and are truly environmentally friendly batteries. Based on the above advantages, lithium batteries are widely used in portable electronic devices. On the other hand, because of its high energy density, lithium batteries make it difficult to ensure battery safety. In detail, in the overcharged state, the electrolyte will be analyzed, causing the temperature and pressure inside the battery to rise; in the overdischarged state, the electrolytic material copper in the negative electrode will melt, causing an internal short circuit and increasing the temperature: externally When the circuit is short-circuited or the discharge current is too large, due to the high internal resistance, the internal power consumption of the battery will increase, and the temperature will rise, which may cause the oxidation or analysis of the electrolyte and shorten the life of the lithium battery. In addition, if the lithium battery is excessively discharged, the electrolyte in the battery will change, and the number of cycles that can be charged will therefore be reduced, thereby affecting the service life of the lithium battery. Because lithium batteries have the above-mentioned decomposing shortcomings, a protection circuit must be added to the use of lithium batteries. The basic functions of the protection circuit should also correspond to the above shortcomings, so we require the lithium battery power protection chip to achieve the following most basic functions: overcharge protection, overdischarge protection, overcurrent protection, and short circuit protection. From the above requirements for the use of lithium batteries, in order to improve the service life of the lithium battery and ensure the safe use of the battery, the lithium battery protection circuit must have the following functions: (1) If the charging voltage exceeds the maximum allowed by the battery, it can supply the battery discharge circuit . (2) If the discharge voltage is lower than the minimum allowed by the battery, the battery charging circuit can be supplied. The connection between the battery and the external circuit is cut off, and the connection between the battery and the external circuit is cut off, and (3) if the charging and discharging current of the battery is greater than the limit value, the connection between the battery and the external circuit is cut off. (4) When the battery returns to the normal state, the protection circuit should be able to release the protection state accordingly, so that the battery can continue to work normally. 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