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

1. A controller for a quasi-resonant switching power supply, the controller comprising:

a valley detector configured to receive a voltage signal, detect one or more voltage valleys of the voltage signal in magnitude, and generate a detection signal representing the detected one or more voltage valleys;

a valley-locking controller configured to receive one or more signals, generate a mode control signal that indicates a selected valley-locking mode based at least in part on the one or more signals, select from the detected one or more voltage valleys, one or more valleys that correspond to the selected valley-locking mode, and generate a valley control signal indicating the one or more selected valleys; and

a gate driver configured to generate a drive signal based on at least information associated with the valley control signal and change 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 valley-locking controller is further configured to select one or more n th 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; and

the gate driver is further configured to:

start one or more first switching cycles of the multiple switching cycles at the one or more n th valleys of the voltage signal respectively; and

start 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.

2. The controller of claim 1 wherein one first switching cycle of the one or more first switching cycles that starts at an n th valley of the voltage signal is followed immediately by one second switching cycle of the one or more second switching cycles that starts at an (n+1) th valley of the voltage signal.

3. The controller of claim 2 wherein the one second switching cycle of the one or more second switching cycles that starts at the (n+1) th valley of the voltage signal is followed immediately by another first switching cycle of the one or more first switching cycles that starts at another n th valley of the voltage signal.

4. The controller of claim 3 wherein the another first switching cycle of the one or more first switching cycles that starts at the another n th valley of the voltage signal is followed immediately by another second switching cycle of the one or more second switching cycles that starts at another (n+1) th valley of the voltage signal.

5. The controller of claim 1 wherein one second switching cycle of the one or more second switching cycles that starts at an (n+1) th valley of the voltage signal is followed immediately by one first switching cycle of the one or more first switching cycles that starts at an n th valley of the voltage signal.

6. The controller of claim 5 wherein the one first switching cycle of the one or more first switching cycles that starts at the n th valley of the voltage signal is followed immediately by another second switching cycle of the one or more second switching cycles that starts at another (n+1) th valley of the voltage signal.

7. The controller of claim 6 wherein the another second switching cycle of the one or more second switching cycles that starts at the another (n+1) th valley of the voltage signal is followed immediately by another first switching cycle of the one or more first switching cycles that starts at another n th valley of the voltage signal.

8. The controller of claim 1 wherein:

the valley-locking controller is further configured to change the mode control signal from indicating a first valley-locking mode to indicating the selected valley-locking mode, based at least in part on the one or more signals; and

in the first valley-locking mode, the gate driver is further configured to start all multiple switching cycles at multiple n th valleys of the voltage signal respectively.

9. The controller of claim 8 wherein:

the valley-locking controller is further configured to change the mode control signal from indicating the selected valley-locking mode to indicating a second valley-locking mode, based at least in part on the one or more signals; and

in the second valley-locking mode, the gate driver is further configured to start all switching cycles at multiple (n+1) th valleys of the voltage signal respectively.

10. The controller of claim 1 wherein:

the valley-locking controller is further configured to change the mode control signal from indicating a first valley-locking mode to indicating the selected valley-locking mode, based at least in part on the one or more signals; and

in the first valley-locking mode, the gate driver is further configured to start all multiple switching cycles at multiple (n+1) th valleys of the voltage signal respectively.

11. The controller of claim 10 wherein:

the valley-locking controller is further configured to change the mode control signal from indicating the selected valley-locking mode to indicating a second valley-locking mode, based at least in part on the one or more signals; and

in the second valley-locking mode, the gate driver is further configured to start all switching cycles at multiple n th valleys of the voltage signal respectively.

12. The controller of claim 1 wherein:

the valley-locking controller is further configured to not to allow the mode control signal to change directly from indicating a first valley-locking mode to indicating a second valley-locking mode;

in the first valley-locking mode, the gate driver is further configured to start all multiple switching cycles at multiple n th valleys of the voltage signal respectively; and

in the second valley-locking mode, the gate driver is further configured to start all multiple switching cycles at multiple (n+1) th valleys of the voltage signal respectively.

13. The controller of claim 1 wherein:

the valley-locking controller is further configured to not to allow the mode control signal to change directly from indicating a first valley-locking mode to indicating a second valley-locking mode;

in the first valley-locking mode, the gate driver is further configured to start all multiple switching cycles at multiple (n+1) th valleys of the voltage signal respectively; and

in the second valley-locking mode, the gate driver is further configured to start all multiple switching cycles at multiple n th valleys of the voltage signal respectively.

14. The controller of claim 1 wherein the valley detector is further configured to receive the voltage signal from a voltage divider connected to an auxiliary winding coupled to a primary winding and a secondary winding.

15. The controller of claim 14 wherein the gate driver is further configured to output the drive signal to a transistor connected to the primary winding.

16. The controller of claim 15 wherein the gate driver is further configured to change the drive signal from the first logic level to the second logic level to turn on the transistor.

17. The controller of claim 16 wherein:

the first logic level is a logic low level; and

the second logic level is a logic high level.

18. The controller of claim 1 wherein the one or more signals include a feedback signal representing an output voltage of the quasi-resonant switching power supply.

19. The controller of claim 1 wherein the one or more signals include the drive signal.

20. The controller of claim 19 wherein the one or more signals further include a feedback signal representing an output voltage of the quasi-resonant switching power supply.

21. The controller of claim 1 wherein the mode control signal represents an m-digit binary number that indicates the selected valley-locking mode.

22. 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 n th 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 n th 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.