Charging system, charging method, and power adapter

A charging system, comprising:

• a battery;
• a first rectifier, configured to rectify an input 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 and a secondary winding, and configured to output a second voltage with a second ripple waveform according to the modulated first voltage;
• a second rectifier, coupled to the secondary winding, and configured to rectify the second voltage to output a third voltage with a third ripple waveform, wherein the third voltage is configured to charge the battery;
• a sampling unit, arranged at a primary side of the transformer, and configured to sample voltage and/or current at the primary winding;
• a control unit, arranged at a secondary side of the transformer, coupled to the sampling unit and the switch unit respectively, and configured to output the control signal to the switch unit, wherein the control unit is further configured to change an output of the second rectifier by adjusting a duty ratio of the control signal according to the current sampling value and/or the voltage sampling value such that the third voltage meets a charging requirement of the battery;
• and
• a first isolation unit, arranged between the control unit and the sampling unit, and configured to prevent high voltages from affecting the control unit at the secondary side of the transformer receiving signals sent by the sampling unit at the primary side of the transformer.

A charging method, comprising:

• performing a first rectification on an input alternating current to output a first voltage with a first ripple waveform;
• modulating the first voltage by controlling a switch unit, and outputting a second voltage with a second ripple waveform by a conversion of a transformer;
• performing a second rectification on the second voltage to output a third voltage with a third ripple waveform, and applying the third voltage to a battery;
• sampling voltage and/or current at a primary winding of the transformer;
• and
• adjusting a duty ratio of a control signal for controlling the switch unit according to the current sampling value and/or the voltage sampling value such that the third voltage meets a charging requirement of the battery.