Standby method for switching power supply, switching power supply, and primary and secondary control circuits

A switching power supply comprising:

• an optical coupler circuit coupled between a primary side and a secondary side;
• a mode signal generating circuit, configured to measure a load device power supply demand of the switching power supply, and generate a second mode control signal when the load device power supply demand is less than or equal to a preset value;
• an optical coupler control circuit, which controls, according to the second mode control signal, a bias current of the optical coupler circuit to be turned off;
• a switching power supply output control circuit, configured to generate a first mode control signal when the load device power supply demand is greater than the preset value, control, according to the first mode control signal, the switching power supply to enter a first mode, control a output voltage of the switching power supply by means of the optical coupler circuit, control, according to the second mode control signal, the switching power supply to enter a second mode, generate, according to the bias current of the optical coupler circuit, a notification signal indicating that the switching power supply has entered the second mode, controlling, according to the notification signal maintained for a first preset time length, a secondary side control chip to enter the second mode, and control the output voltage of the switching power supply by means of a driving pulse signal, so as to reduce bias currents of the primary side and the secondary side of the switching power supply, and reduce standby power consumption of the switching power supply;
• and
• when a primary side control chip acquires that a level signal of a voltage signal outputted by the optical coupler circuit has been inverted and a retention time length of the inverted level signal has reached a time threshold, controlling the primary side control chip to enter the second mode.

A secondary control circuit of a switching power supply comprising:

• an optical coupler circuit coupled between a primary side and a secondary side of the switching power supply;
• a mode signal generating circuit, configured to measure a load device power supply demand of the switching power supply, and generate a second mode control signal when the load device power supply demand is less than or equal to a preset value;
• an optical coupler control circuit, which controls, according to the second mode control signal, a bias current of the optical coupler circuit to be turned off;
• and
• a notification signal control circuit, which generates a notification signal upon receiving the second mode control signal, and is configured to notify a primary side control chip to enter or exit a second mode, so that the switching power supply controls output of the switching power supply by means of a driving pulse signal, so as to reduce bias currents of the primary side and the secondary side of the switching power supply, and reduce standby power consumption of the switching power supply, wherein the notification signal control circuit further comprises:
• a second-mode-entering control circuit, configured to control, when the primary side control chip acquires that a level signal of a voltage signal outputted by the optical coupler circuit has been inverted and a retention time length of the inverted level signal has reached a time threshold, the primary side control chip to enter the second mode,
• wherein the time threshold is greater than a maximum value of a duration of the level signal in a first mode, and a secondary side control chip controls a duration of the second mode control signal indicating that the load device power supply demand is less than or equal to the preset value to be greater than the time threshold.