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　　How to protect lithium-ion batteries in mobile phone fast charging technology

　　Lithium-ion batteries are now high-energy-density and very light batteries, but due to their very active chemical properties, they need to be protected for safety, and a charge-discharge protection circuit has been added. Mosfet, the key component of the charge and discharge protection circuit, also has a certain short-circuit failure rate. If the output value of the lithium-ion battery is not large, then this effect will not be reflected. However, the demand for lithium-ion batteries is huge. In 2014 alone, 5.6 billion small lithium-ion batteries were sold globally. With such a large amount of transportation, even with a probability risk of 1ppm, there are an average of 5,600 dangerous incidents per year. Therefore, in addition to the main protection circuit, a secondary protection is added to further reduce the risk. Among the secondary protection components, there is generally only one component, such as a primary fuse, a PTC, and a temperature fuse. You don't fuse with PTC, you don't fuse with PTC, the guards compete with each other like different alleles compete for the same position on a chromosome. However, since various protection components are not the overall winner, the combination of multiple components can meet various usage requirements.

　　However, with the rapid popularization of smart phones and the continuous increase of mobile phone battery capacity, fast charging is required. At present, there are multiple specifications such as OPPOVooc specification, qualcomm's QC2.0 specification, and MTK's PumpExpressPlus specification. In the case of fast charging, the current will be very large in the first 30 minutes, generally reaching about 3A.

　　Under the high current impact of fast charging in the first 30 minutes, accompanied by high temperature and temperature rise, the competitive situation of lithium-ion battery secondary protection components will be changed, and a cooperative form will be replaced: PTC+fuse to form a protection combination.

　　First, PTC+ fuses can be used as a supplement to temperature protection and overcurrent protection. PTC has a temperature protection function, but due to the relatively high temperature drop, the specification selection is relatively large, the relative overcurrent protection capability is relatively weak, and the PTC action speed is slow. The fuse (Fuse) is not sensitive to temperature and cannot provide temperature protection, but the temperature drop rate is also very low, so a relatively small current specification can be selected, and the overcurrent protection ability is relatively strong, and the operating speed is much faster.

　　Second, PTC+fuse will be processed by a low-cost solution of UL2054. In the case of high current charging, since each component of UL2054 has its own advantages and disadvantages, it is difficult for a single component to pass all the tests of UL2054. One is the commonly used PTC. Since the charging current is very large, in order to ensure that no action occurs in the case of fast charging and high temperature rise, the selected specification must reach 12066A/7A. With such a large specification, it is difficult for Li-ion batteries to pass the LPS test of UL2054, because it is difficult to limit the current to less than 8A for 60 seconds. Second, common fuses. The biggest advantage is that it is not sensitive to temperature, and you can choose a fuse with a specification of 5A. A fuse with a specification of ≤5A is very helpful for lithium-ion batteries to pass the LPS test of UL2054; Temperature insensitive, no over-temperature protection. The third is the three-terminal fuse. Although it can handle over-temperature protection, it cannot pass the LPS test due to its large specifications, up to 10A/12A; and the cost is very high. Fourth, some manufacturers adopt the dual-IC method, although the effect is better, but the cost is higher. Assume that PTC and fuse are combined. First of all, the 5A type fuse that is not sensitive to temperature is easy to pass the detection items such as LPS and short circuit. Then, relying on the PTC of 12066A/7A, it passes the inspection items such as 6V/1C, 6V2C overcharge, etc. The cost of the whole project is very low.

　　Ultimately, the PTC+fuse protection method will be safer than individual components. Combining these two components is equivalent to adding a new protection on the basis of the secondary protection, adding a heavy insurance for the safety of lithium-ion batteries, thereby greatly reducing the risk factor.