Switching converter with quasi-resonant control and control method thereof

1. A controller used in a switching converter having a first switch and an energy storage component coupled to the first switch, the controller comprising:

a hysteresis feedback circuit configured to generate a hysteresis feedback signal based on an output feedback signal indicative of an output signal of the switching converter;

a first comparison circuit configured to compare the hysteresis feedback signal with a ramp signal and generate a first comparison signal;

a second comparison circuit configured to compare the output feedback signal with the ramp signal and generate a second comparison signal;

a valley detection circuit configured to provide a valley pulse signal in response to one or more valleys of a voltage drop across the first switch during an OFF state of the first switch; and

a turn-on control circuit configured to generate a target locked valley number based on the valley pulse signal, the first comparison signal, the second comparison signal and a current locked valley number, and further configured to generate a turning on control signal corresponding to the target locked valley number for turning ON the first switch.

2. The controller of claim 1 , further comprising:

a third comparison circuit configured to compare a current sensing signal indicative of a current flowing through the first switch and a first threshold voltage and generate a turning OFF control signal for turning off the first switch.

3. The controller of claim 1 , wherein the first hysteresis voltage varies with an input line voltage of the switching converter.

4. The controller of claim 1 , wherein the turn-on control circuit is configured to determine whether to increase the target locked valley number by comparing a first designated valley number when the ramp signal reaches the hysteresis feedback signal with the current locked valley number.

5. The controller of claim 4 , wherein the turn-on control circuit is further configured to determine whether to decrease the target locked valley number by comparing a difference between a second designated valley number and the current locked valley number with a predetermined value, and wherein the second designated valley number is the valley number when the ramp signal reaches the output feedback signal.

6. The controller of claim 1 , wherein:

the hysteresis feedback circuit is configured to provide a first hysteresis voltage based on the output feedback signal and provide the hysteresis feedback signal by adding the first hysteresis voltage onto the output feedback signal; and

wherein the ramp signal ramps down during the OFF state of the first switch.

7. The controller of claim 1 , wherein:

the hysteresis feedback circuit is configured to provide a second hysteresis voltage based on the output feedback signal and provide the hysteresis feedback signal by subtracting the second hysteresis voltage from the output feedback signal; and

wherein the ramp signal ramps up during the OFF state of the first switch.

8. The controller of claim 6 , wherein the first hysteresis voltage and the output feedback signal have the following relationships:

the first hysteresis voltage has a maximum value when the output feedback signal is greater than a first feedback voltage;

the first hysteresis voltage decreases as the output feedback signal decreases when the output feedback signal is between the first feedback voltage and a second feedback voltage; and

the first hysteresis voltage has a minimum value when the output feedback signal is less than the second feedback voltage.

9. A switching converter, comprising:

an energy storage component;

a first switch coupled to the energy storage component;

a hysteresis feedback circuit configured to generate a hysteresis feedback signal based on an output feedback signal indicative of an output signal of the switching converter;

a first comparison circuit configured to compare the hysteresis feedback signal with a ramp signal and generate a first comparison signal;

a second comparison circuit configured to compare the output feedback signal with the ramp signal and generate a second comparison signal;

a valley detection circuit configured to provide a valley pulse signal in response to one or more valleys of a voltage drop across the first switch during an OFF state of the first switch; and

a turn-on control circuit configured to generate a target locked valley number based on the valley pulse signal, the first comparison signal, the second comparison signal and a current locked valley number, and further configured to generate a turning on control signal corresponding to the target locked valley number for turning ON the first switch.

10. The switching converter of claim 9 , wherein the turn-on control circuit is configured to determine whether to increase the target locked valley number by comparing a first designated valley number when the ramp signal increases to reach the hysteresis feedback signal with the current locked valley number.

11. The switching converter of claim 9 , wherein the turn-on control circuit is further configured to determine whether to decrease the target locked valley number by comparing a difference between a second designated valley number and the current locked valley number with a predetermined value, and wherein the second designated valley number is the valley number when the ramp signal increases to reach the output feedback signal.

12. The switching converter of claim 9 , further comprising:

a third comparison circuit configured to compare a current sensing signal indicative of a current flowing through the first switch and a first threshold voltage and generate a turning OFF control signal for turning off the first switch.

13. The switching converter of claim 9 , wherein:

the hysteresis feedback circuit is configured to provide a first hysteresis voltage based on the output feedback signal and provide the hysteresis feedback signal by adding the first hysteresis voltage onto the output feedback signal; and

wherein the ramp signal ramps down during the OFF state of the first switch.

14. The switching converter of claim 13 , wherein the first hysteresis voltage and the output feedback signal have the following relationships:

the first hysteresis voltage has a maximum value when the output feedback signal is greater than a first feedback voltage;

the first hysteresis voltage decreases as the output feedback signal decreases when the output feedback signal is between the first feedback voltage and a second feedback voltage; and

the first hysteresis voltage has a minimum value when the output feedback signal is less than the second feedback voltage.

15. The switching converter of claim 9 , wherein:

the hysteresis feedback circuit is configured to provide a second hysteresis voltage based on the output feedback signal and provide the hysteresis feedback signal by subtracting the second hysteresis voltage from the output feedback signal; and

wherein the ramp signal ramps up during the OFF state of the first switch.

16. A control method of a switching converter having an energy storage component and a first switch coupled to the energy storage component, the control method comprising:

generating an output feedback signal by sensing an output signal of the switching converter;

generating a hysteresis feedback signal based on the output feedback signal;

comparing the hysteresis feedback signal with a ramp signal and generating a first comparison signal;

comparing the output feedback signal with the ramp signal and generating a second comparison signal;

detecting one or more valleys of a voltage drop across the first switch during an OFF state of the first switch and generating a valley pulse signal;

generating a target locked valley number based on the valley pulse signal, the first comparison signal, the second comparison signal and a current locked valley number; and

generating a turning on control signal corresponding to the target locked valley number for turning on the first switch.

17. The control method of claim 16 , wherein generating the hysteresis feedback signal comprising:

providing a second hysteresis voltage based on the output feedback signal; and

providing the hysteresis feedback signal by subtracting the second hysteresis voltage from the output feedback signal.

18. The control method of claim 16 , wherein generating the target locked valley number comprising:

determining whether to increase the target locked valley number by comparing a first designated valley number when the ramp signal reaches the hysteresis feedback signal with the current locked valley number; and

determining whether to decrease the target locked valley number by comparing a difference between a second designated valley number and the current locked valley number with a predetermined value, and wherein the second designated valley number is the valley number when the ramp signal reaches the output feedback signal.

19. The control method of claim 18 , wherein generating the hysteresis feedback signal comprising:

providing a first hysteresis voltage based on the output feedback signal; and

providing the hysteresis feedback signal by adding the first hysteresis voltage onto the output feedback signal.

20. The control method of claim 19 , wherein:

the first hysteresis voltage has a maximum value when the output feedback signal is greater than a first feedback voltage;

the first hysteresis voltage decreases as the output feedback signal decreases when the output feedback signal is between the first feedback voltage and a second feedback voltage; and

the first hysteresis voltage has a minimum value when the output feedback signal is less than the second feedback voltage.