Systems and methods for valley locking related to quasi-resonant switching power supplies

A method for a quasi-resonant switching power supply, the method comprising:

• receiving a voltage signal;
• detecting one or more voltage valleys of the voltage signal in magnitude;
• generating a detection signal representing the detected one or more voltage valleys;
• receiving one or more signals;
• generating a mode control signal that indicates a selected valley-locking mode based at least in part on the one or more signals;
• selecting from the detected one or more voltage valleys, one or more valleys that correspond to the selected valley-locking mode;
• generating a valley control signal indicating the one or more selected valleys;
• processing information associated with the valley control signal;
• generating a drive signal based on at least information associated with the valley control signal;
• and
• changing the drive signal from a first logic level to a second logic level to start multiple switching cycles in response to the one or more selected valleys;
• wherein, in the selected valley-locking mode, the selecting from the detected one or more voltage valleys, one or more valleys that correspond to the selected valley-locking mode includes:
• selecting one or more nth valleys of the voltage signal and one or more (n+1)th valleys of the voltage signal as the one or more selected valleys, n being a positive integer;
• wherein, in the selected valley-locking mode, the changing the drive signal from a first logic level to a second logic level to start multiple switching cycles in response to the one or more selected valleys includes:
• starting one or more first switching cycles of the multiple switching cycles at the one or more nth valleys of the voltage signal respectively;
• and
• starting one or more second switching cycles of the multiple switching cycles at the one or more (n+1)th valleys of the voltage signal respectively.