Synchronous rectification control apparatus and method, and flyback switching power supply

A flyback switching power supply, comprising the synchronous rectification control apparatus which comprises a primary Metal-Oxide-Semiconductor (MOS) transistor, a transformer, a secondary MOS transistor, a primary control chip, and a secondary control circuit;

• wherein the primary control chip is configured to control the primary MOS transistor to turn on at a valley position to excite a primary inductor of the transformer to increase a primary current, and then control the primary MOS transistor to turn off to terminate the excitation of the primary inductor;
• and
• the secondary control circuit is configured to control the secondary MOS transistor to turn on for a first time during a secondary side demagnetization process of the transformer after the excitation of the primary inductor ends, and to control the secondary MOS transistor to turn on for a second time during a resonance stage after the secondary side demagnetization process of the transformer ends, to reduce a drain voltage of the primary MOS transistor before being turned on again.