Charging system and method, and power adapter

A charging system, comprising:

• a battery;
• a first rectifier, configured to rectify an input first alternating current and output a first voltage with a first ripple waveform;
• a switch unit, configured to modulate the first voltage according to a control signal and output a modulated first voltage;
• a transformer, having a primary winding, a plurality of secondary windings, and an auxiliary winding, wherein the transformer is configured to output a plurality of voltages with ripple waveforms via the plurality of secondary windings according to the modulated first voltage, and to couple the modulated first voltage via the auxiliary winding;
• a compositing unit, configured to composite the plurality of voltages to output a second alternating current, wherein for each cycle of the second alternating current, an absolute value of a peak voltage of a positive half of the second alternating current is greater than that of a trough voltage of a negative half of the second alternating current, wherein the second alternating current is configured to charge the battery;
• a sampling unit, configured to sample voltage and/or current at the auxiliary winding to obtain a voltage sampling value and/or a current sampling value;
• and
• a control unit, coupled to the sampling unit and the switch unit respectively, and configured to output the control signal to the switch unit, 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 first rectification on an input first alternating current to output a first voltage with a first ripple waveform;
• modulating the first voltage by controlling a switch unit, 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, an absolute value of a peak voltage of a positive half of the second alternating current is greater than that of a trough voltage of a negative half of the second alternating current;
• applying the second alternating current to a battery;
• coupling a primary output of the transformer via an auxiliary winding of the transformer, and sampling voltage and/or current at the auxiliary winding 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 unit according to the voltage sampling value and/or the current sampling value, such that the second alternating current meets a charging requirement.