Application of PPTC Thermistor in Batteries

　　Compared with NiMH or NICd batteries, lithium-ion batteries have a higher current density and are widely used in various portable devices.

　　Lithium ion batteries are usually very sensitive to overcharging. When the voltage at both ends of the battery is too high during charging, it will increase battery leakage

　　The danger of smoking, burning, and bursting (which is often quite severe). Overcharging may be caused by uncontrolled charging, electrode errors, or

　　Caused by using an incorrect charger. When the charging and discharging current of lithium-ion batteries is too high or there is an external short circuit, internal heating may damage the battery or burn other components, seriously shortening the battery's cycle life.

　　The task of protecting the circuit is to monitor the parameters of the battery's charging and discharging status in response to various possible faults, in order to ensure battery life and efficiency, and to prevent damage to the battery and external devices such as mobile phones, PDAs, laptops, etc.

　　Mobile phone batteries typically use a primary protection circuit consisting of a battery protection dedicated integrated IC and metal oxide field-effect transistors. The protection IC controls the conduction or shutdown of FET by monitoring the voltage at both ends of the battery and the discharge current, preventing faults such as overcharging, short circuit, and overdischarging.

　　Although one-time protection is generally considered reliable, the protection IC or MOS-FET may be damaged when the electrostatic discharge voltage is too high or overheated, and the integrated circuit may oscillate in the event of a short circuit. At the same time, most IC+MOS-FET circuits detect charging and discharging overcurrent indirectly, and cannot guarantee overcurrent protection in all working states of the battery, reducing the reliability of protection. After adding a dedicated PTC for battery protection from Kote Company to the protection circuit, even in the event of a protection circuit failure or high temperature rise, the PTC can still provide protection against overcharging, overcurrent, short circuit, overheating and other faults, ensuring that the battery does not have safety issues in case of misuse or abuse.

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