Switching Power Supply and Control Method Thereof

A method, comprising:

• receiving, at a secondary control circuit of a switching power supply, a power request signal of a load device of the switching power supply, the switching power supply comprising the secondary control circuit and a primary control circuit that are coupled, respectively, to a secondary side and a primary side of a transformer of the switching power supply;
• encoding, at the secondary control circuit, the power request signal to generate encoded information;
• receiving, at the primary control circuit using the transformer, a feedback signal that reflects an output voltage of the switching power supply;
• decoding, at the primary control circuit, the encoded information based on a change of the feedback signal;
• and
• supplying, by the switching power supply, power to the load device based on the decoding.

A switching power supply, comprising:

• a secondary control circuit coupled to a secondary winding of a transformer of the switching power supply, the secondary control circuit comprising a synchronous rectifier switch connected to the secondary winding, and the secondary control circuit being configured to:
• receive a power request signal from a load device, and encode the power request signal to generate encoded information by controlling an on-time of the synchronous rectifier switch;
• and
• a primary control circuit coupled to a primary winding and an auxiliary winding of the transformer, the primary control circuit being configured to:
• receive, by use of the transformer, a feedback signal related to an output voltage of the switching power supply, decode the encoded information based on a parameter of the feedback signal and a threshold to obtain decoded information, and determine to supply power to the load device based on the decoded information.