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Mobile phone battery circuit protection components: current fuse, thermal fuse and positive temperature coefficient thermistor

Article Source:Thermal protectorAuthor:YaxunPopularity:Published time:2019-07-13 10:07

Three mobile phone battery circuit protection commonly used components The batteries used in mobile phones are all lithium batteries, which may explode at high temperatures, and in fact have occurred and have serious consequences. Therefore, most battery manufacturers will adopt protective measures. In addition to structural design, IC overcurrent protection and MOS tube protection, secondary protection elements will be used to strengthen protection measures.
There are three types of circuit protection components commonly used on mobile phone batteries: Current fuses, thermal fuses and PTC thermistors with different components reflect different protection requirements and different design concepts.

Mobile phone battery circuit protection component design
Current fuses are primarily used for short circuit protection:
The principle of protection is that once the battery is short-circuited, large overcurrent quickly breaks the thermal balance of normal operation. If the melt temperature is raised to the melting point of the material in an instant, the circuit will be disconnected to achieve the function of safety protection. The advantage of using current fuse protection is that the circuit is cut quickly and thoroughly, and the accuracy of the fuse characteristics is high. Whether it is charging, when using or during standby, any short circuit in any part will act quickly. However, it is only sensitive to current and does not respond to external temperatures.

The thermal fuse is mainly used for overheat protection:
The principle of protection is that the melt composed of low-melt electric alloy material will melt once it meets the allowable temperature, thus cutting off the circuit to achieve the function of safety protection. The advantage of using temperature fuse protection is that the melt is sensitive to both internal and external temperatures of components, especially when the mobile phone is placed in high temperature environment or for other reasons, too high temperature will act. However, the over-temperature caused by over-current seems to be relatively slow, low-precision, and the reliability is not as high as that of the current fuse.

Positive temperature coefficient thermistors are mainly used for overcharge protection:

The protection principle is to use the positive temperature coefficient characteristics of the resistance of the PTC material and the characteristics of the Curie point mutation. That is, the temperature rise caused by any cause (including over current and environment) will cause the material resistance to rise. Once raised to the Curie point, the resistance will become large enough to turn off the charging current for safe protection. The advantage of using thermistor protection is that it reacts to both current and temperature. When the battery is overcharged, it can limit the current in time. The disadvantage is that the response time is slow, there is still a small leakage current when the circuit is turned off, and the reliability is not high enough.

Positive temperature coefficient thermistors are also called self-recovery fuses. However, the self-recovery function in the protection of the mobile phone battery is not necessary, especially the overcurrent caused by the circuit failure. If the fault is not eliminated and the PTC is self-healing, it does not make sense for the actual application.

There are also some low-end mobile phone batteries. In order to save costs, no protection components are used, or using zero-ohm resistors as protection components to fool the supporting factories or customers is irresponsible and has considerable safety risks.