Nokia 8210 mobile phone travel charger circuit

The random travel charger produced in Shanghai for the Nokia 8210 mobile phone is marked on the casing: input AC220V/50Hz (≤30mA), output 4.2V (≤200mA). During charging, for a nominal 3.6V lithium battery that needs to be charged, when it is charged to 3.98V, the red light of the charger circuit will turn off and the green light will turn on. The entire charging time is about four hours. The author analyzed this charger and drew a circuit diagram for readers' reference during use and maintenance. All operational amplifier ICs in the circuit are used as comparators.