1. temperature protection: there is a temperature sensor inside the cell phone battery. When the temperature exceeds a certain threshold, the protection circuit will stop charging to prevent the battery from overheating. An overheated battery may damage or cause a safety accident.

2. Voltage protection: The protection circuit will monitor the battery voltage. When the battery voltage exceeds a certain threshold, charging will stop. This is to prevent the battery from being overcharged, resulting in battery damage or danger.

3. Abnormal protection of the charger: The protection circuit will also detect the state of the charger. If the charger is abnormal, such as unstable voltage and excessive current, the protection circuit will stop charging to prevent the battery and mobile phone from being damaged.

4. Protection after charging: When the battery is full, the protection circuit will stop charging, so as to avoid overcharging the battery, prolong the battery life and reduce the safety risk.