What is the internal structure of a charger? What is its working principle?

Internal structure: is a rectifier, filtering, voltage regulator, the role of the protection of the transformer and a display of whether the charging and whether fully charged indicator! Working principle: the charger is just a power supply to provide a cell phone cell phone has a voltage detection circuit if the charge is full to stop charging, if it is a universal punch output 4.2, there are detection circuits inside the battery voltage is low that flow through the battery current in the current-limiting resistor at the ends of the drop in voltage to take out the voltage to control the red light on, with the battery voltage increases current drops current-limiting resistor at the ends of the drop in voltage is insufficient to maintain the control of the red diode! Conductivity on the red light out of the green light, reminding the completion of the charge, but there is still a weak current charge, will not damage the battery, there are some universal flush output voltage is very high even if the battery with a protection circuit will also damage the battery, so to measure, the above is my understanding.