Charging system and charging method, and power adapter

A charging system, comprising:

• a battery;
• a first rectifier, configured to rectify a first alternating current and output a first voltage with a first ripple waveform;
• a switch circuit, configured to modulate the first voltage according to a control signal and output a modulated first voltage;
• a transformer, configured to output a plurality of voltages with ripple waveforms according to the modulated first voltage;
• a compositing circuit, configured to composite the plurality of voltages to output a second alternating current, wherein, for each cycle of the second alternating current, a peak voltage of a positive half is greater than an absolute value of a valley voltage of a negative half;
• a sampling circuit, configured to sample voltage and/or current at a primary winding of the transformer to obtain a voltage sampling value and/or a current sampling value;
• and
• a control circuit, coupled to the sampling circuit and the switch circuit respectively, and configured to output the control signal to the switch circuit, to adjust a duty ratio of the control signal according to the current sampling value and/or the voltage sampling value, such that the second alternating current meets a charging requirement of the battery.

A charging method, comprising:

• performing a rectification on a first alternating current to output a first voltage with a first ripple waveform;
• modulating the first voltage by controlling a switch circuit, and outputting a plurality of voltages with ripple waveforms by a conversion of a transformer;
• compositing the plurality of voltages to output a second alternating current, wherein, for each cycle of the second alternating current, a peak voltage of a positive half is greater than an absolute value of a valley voltage of a negative half;
• applying the second alternating current to a battery;
• sampling voltage and/or current at a primary winding of the transformer to obtain a voltage sampling value and/or a current sampling value;
• and
• adjusting a duty ratio of a control signal for controlling the switch circuit according to the voltage sampling value and/or the current sampling value, such that the second alternating voltage meets a charging requirement of the battery.