How to understand the double fuse design of mobile phone batteries? What is the purpose of the double fuse design?

Mobile phone battery double fuses refer to two different types of fuses used in mobile phone battery circuits, usually including current fuses and thermal fuses, which work together to ensure the safe operation of the battery.

The role and principle of the double fuse

Current fuse: Mainly used for short-circuit protection. When a short circuit occurs in the battery, the high current will quickly break the thermal balance during normal operation, causing the melt temperature to rise to the melting point of the material, thereby disconnecting the circuit and achieving safety protection. The advantage of a current fuse is that it cuts off the circuit quickly and completely, but does not react to external temperatures.

Thermal cut-off: Mainly used for overtemperature protection. When the ambient temperature inside or outside the battery exceeds the allowable range, the melt of the thermal fuse melts, cutting off the circuit to prevent overheating. Thermal cut-offs are sensitive to both internal and external temperatures, but have a slower response to overtemperature caused by overcurrent and are less reliable.

Application scenarios and importance of double fuses

The use of double fuses is to enhance the safety performance of mobile phone batteries. Lithium batteries may explode at high temperatures, so battery manufacturers will adopt a variety of protection measures, including structural design, IC over-current protection, MOS tube protection, etc. 

The double fuse is used as a secondary protection element to provide more comprehensive protection in different situations. 

Current fuse: Quickly cuts off the circuit in the event of a short circuit in the battery to prevent fire or explosion caused by a short circuit.

Thermal fuse: Cuts off the circuit when the battery overheats to prevent potential safety hazards caused by high temperatures. 

Through the synergistic effect of these two fuses, the safety and reliability of mobile phone batteries can be effectively improved, and safety accidents caused by overcurrent and overheating can be reduced.