Lithium Battery Protection Components and Cell Phone Fast Charge Technology

Lithium batteries are currently batteries with high energy density and very light, but due to their very active chemical properties, they themselves have increased charge-discharge protection circuits because of the need for safety protection. Mosfet, the key component of the charging and discharging protection circuit, also has a certain percentage of short-circuit failure. If the lithium battery output is not large, then this effect will not be reflected. However, the demand for lithium batteries is very large. In 2014 alone, the global shipment of small lithium batteries reached 5.6 billion. In the face of such a huge shipment volume, even if the probability risk of 1 ppm, that is an average of 5,600 dangerous events may occur. Therefore, in addition to the main protection circuit, a secondary protection is added to further reduce the risk. In secondary protected components, there is generally only one component, one for primary breakage fuses, one for PTC, and one for temperature fuses. With PTC, there is no fuse, and with fuse, there is no PTC. The protective devices are in competition with each other, just as different alleles compete for the same position on the chromosome. However, due to the fact that various protection components are not fully won, a variety of components coexist and meet various application needs.

However, with the rapid popularity of smart phones, mobile phone battery capacity has become larger and larger, and there has been a need for rapid charging. There are already several standards such as OPPOVooc standard, Qualcomm QC 2.0 standard, and MTK's PumpExpress Plus standard. In the case of rapid charging, the current in the first 30 minutes will be large, generally reaching around 3A

Under the impact of a large current 30 minutes before the rapid charging, accompanied by heat and temperature rise, the competition for the secondary protection element of the lithium battery will be changed and replaced by a cooperative mode: PTC + fuse forms a protection combination.

First, PTC + fuse can complement temperature protection and overcurrent protection. The PTC has a temperature protection function, but due to the relatively high temperature reduction ratio, the selection specification is relatively large, the relative overcurrent protection capability is weak, and the PTC is slower. Fuse is not sensitive to temperature and can not provide temperature protection, but the temperature reduction ratio is also very low, so you can choose a relatively small current specification, which is relatively strong for overcurrent protection and is much faster.

Second, PTC + fuse will be a low-cost solution through UL2054. In the case of high current charging, it is difficult to pass the full test of UL2054 with only a single component because each component has some advantages and disadvantages. First, commonly used PTC. Because the charging current is large, in order to ensure that the temperature rise is high in the case of rapid charging, the selected specification must be 1206 A/7A. Choosing such a large specification, lithium batteries will encounter difficulties when passing the UL2054 LPS test because it is difficult to limit the current to below 8A within 60 seconds. Second, the common fuse. The biggest advantage is that it is not sensitive to temperature, you can choose the 5A specification, ≤ 5A specification fuse is very conducive to the lithium battery passing the UL2054 LPS test; However, because it is not sensitive to temperature and does not have an overtemperature protection function, it is difficult to pass UL2054's 6V/1C and 6V2C spamming test items. Third, the three-terminal fuse, although it can solve the temperature of overtemperature protection, but because the current specification is larger, up to 10A/12A, it can not pass the LPS test; And the cost is high. Fourth, some manufacturers use dual IC solutions, although the effect is relatively good, but the cost is relatively high. If the PTC and fuse are combined, the 5A fuse that is not sensitive to temperature is first easily passed through LPS, short circuit and other test items; Then relying on the 1206 A/7A PTC to pass the 6V/1C and 6V2C spamming test items, the entire program costs are very low.

Finally, the PTC + fuse protection scheme will be safer than a single component. Because the combination of the two components is equivalent to adding another protection in addition to the secondary protection, the safety of the lithium battery is added with a heavy insurance, further greatly reducing the risk coefficient.

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