Isolated power supply control circuit and isolated power supply

An isolated power supply comprising a control circuit, wherein the isolated power supply comprises:

• a transformer comprising a primary-side winding and a secondary-side winding;
• a primary-side switching transistor coupled to the primary-side winding;
• and a synchronous rectification transistor coupled to the secondary-side winding, and wherein the control circuit comprises:
• a secondary-side control signal generation circuit, comprising:
• an input terminal that is electrically connected to the secondary-side winding and is for detecting a voltage signal across the secondary-side winding;
• and an output terminal that is electrically connected to a control terminal of the synchronous rectification transistor and is for outputting a control signal for the synchronous rectification transistor;
• and
• a primary-side control signal generation circuit, comprising:
• an input terminal for receiving a signal indicating that the synchronous rectification transistor is turned off;
• and an output terminal that is electrically connected to a control terminal of the primary-side switching transistor and is for outputting a control signal for the primary-side switching transistor,
• wherein in a present switching period, the secondary-side control signal generation circuit provides an indication for turning on the synchronous rectification transistor when detecting that the voltage signal across the secondary-side winding reaches a first predetermined voltage;
• and provides an indication for turning off the synchronous rectification transistor when a period of time over which the synchronous rectification transistor has been conducted reaches a first conduction time, wherein the first conduction time is adjustable based on a first instant at which an indication for turning off the synchronous rectification transistor is provided in a previous switching period, a second instant at which an indication for turning on the primary-side switching transistor is provided in the previous switching period and a predetermined reference period,
• wherein the secondary-side control signal generation circuit comprises:
• a first signal generation unit, comprising an input terminal electrically connected to the secondary-side winding and an output terminal electrically connected to the synchronous rectification transistor, wherein the first signal generation unit is configured to determine an instant at which the voltage signal across the secondary-side winding reaches the first predetermined voltage as a turn-on instant for the synchronous rectification transistor, and to generate and output a rising edge of the control signal for the synchronous rectification transistor based on the turn-on instant for the synchronous rectification transistor;
• and
• a second signal generation unit, comprising an input terminal electrically connected to the secondary-side winding and an output terminal electrically connected to the synchronous rectification transistor, wherein the second signal generation unit is configured to:
• i) determine a pulse width of a reference signal in the previous switching period;
• ii) adjust the first conduction time for the synchronous rectification transistor in the present switching period based on a relationship of the pulse width of the reference signal in the previous switching period and the predetermined reference period;
• iii) determine a turn-off instant for the synchronous rectification transistor based on an instant when the period of time over which the synchronous rectification transistor has been conducted reaches the first conduction time;
• iv) and generate and output a falling edge of the control signal for the synchronous rectification transistor based on the turn-off instant for the synchronous rectification transistor,
• wherein the reference signal is generated based on the first instant and the second instant, and wherein the pulse width of the reference signal is a time difference between the first and second instants in a same period.