A control method for controlling a battery charging circuit having at least one switch, includes: generating a first difference signal based on a charging current feedback signal and a charging current reference signal; generating a second difference signal based on a battery voltage feedback signal and a battery voltage reference signal; based on a battery voltage, selecting one of the first and second difference signals, and a ground voltage as a third difference signal; generating a bias signal by proportionally integrating the third difference signal; comparing the sum of a system voltage feedback signal and a ramp signal with the sum of the bias signal and a system voltage reference signal and generating a comparison signal; generating a control signal to control the at least one switch of based on the comparison signal and a constant time period control signal.