Systems and methods for regulating power conversion systems with output detection and synchronized rectifying mechanisms

1. A system controller for a power converter, the system controller comprising:

a first terminal; and

a second terminal;

wherein the system controller is configured to:

receive an input signal at the first terminal; and

generate a drive signal at the second terminal;

wherein the system controller is further configured to:

determine whether a time interval from a first time when the input signal becomes larger than a first threshold to a second time when the input signal becomes smaller than a second threshold is longer than a predetermined duration;

in response to the time interval being determined to be longer than the predetermined duration,

determine whether the input signal is smaller than a third threshold at a time following the time interval; and

in response to the input signal being determined to be smaller than the third threshold at the time, change the drive signal at the second terminal from a first logic level to a second logic level.

2. The system controller of claim 1 is further configured to, in response to the time interval not being determined to be longer than the predetermined duration, keep the drive signal at the first logic level regardless of whether the input signal is smaller than the second threshold at the time.

3. The system controller of claim 1 wherein the second threshold is smaller than the first threshold.

4. The system controller of claim 3 wherein the third threshold is smaller than the second threshold.

5. The system controller of claim 4 wherein the first threshold and the second threshold each are larger than zero.

6. The system controller of claim 5 wherein the third threshold is smaller than zero.

7. The system controller of claim 1 is further configured to, in response to the input signal being determined to be smaller than the third threshold at the time, change the drive signal, after a delay, from the first logic level to the second logic level to turn on a transistor.

8. The system controller of claim 1 is further configured to, in response to the input signal being determined to be smaller than the second threshold at the time, change the drive signal, without a delay, from the first logic level to the second logic level to turn on a transistor.

9. The system controller of claim 1 wherein:

the first logic level is a logic low level; and

the second logic level is a logic high level.

10. The system controller of claim 1 , and further comprising:

a first comparator configured to generate a first comparison signal based on at least information associated with the input signal, the first comparison signal indicating whether the input signal is larger than the first threshold;

a second comparator configured to generate a second comparison signal based on at least information associated with the input signal, the second comparison signal indicating whether the input signal is smaller than the second threshold;

a timer configured to receive the first comparison signal and the second comparison signal and generate a timer signal, the timer signal indicating whether the time interval from the first time when the input signal becomes larger than the first threshold to the second time when the input signal becomes smaller than the second threshold is longer than the predetermined duration;

a third comparator configured to, in response to the time interval being longer than the predetermined duration, generate a third comparison signal based on at least information associated with the input signal, the third comparison signal indicating whether the input signal is smaller than the third threshold at the time; and

a driver configured to output the drive signal at the second terminal based at least in part on the third comparison signal.

11. The system controller of claim 10 wherein the driver includes:

a timing controller configured to receive the third comparison signal and output a first timing signal based at least in part on the third comparison signal;

a logic controller configured to receive the first timing signal and generate a logic signal based at least in part on the first timing signal; and

a gate driver configured to receive the logic signal and output the drive signal based at least in part on the logic signal.

12. The system controller of claim 11 , and further comprising:

a fourth comparator configured to receive a voltage signal associated with an output voltage of the power conversion system and generate a fourth comparison signal based at least in part on the voltage signal;

a load detector configured to receive a second timing signal from the timing controller and a clock signal, and to generate a detection signal based at least in part on the second timing signal and the clock signal; and

a pulse signal generator configured to receive the fourth comparison signal and the detection signal and output a pulse signal to the logic controller based at least in part on the fourth comparison signal and the detection signal.

13. The system controller of claim 1 wherein the system controller is located on a first chip.

14. The system controller of claim 13 wherein a transistor is also located on the first chip.

15. The system controller of claim 13 wherein the system controller is at least a part of a multi-chip package, the multi-chip package further including a transistor on a second chip, the second chip being different from the first chip.

16. A method for regulating a power converter, the method comprising:

receiving an input signal;

processing the input signal; and

generating a drive signal;

wherein the processing the input signal includes determining whether the input signal remains larger than a first threshold for a time period that is longer than a predetermined duration;

wherein the generating a drive signal includes, in response to the input signal being determined to have remained larger than the first threshold for the time period that is longer than the predetermined duration,

determining whether the input signal is smaller than a second threshold at a time following the time period; and

in response to the input signal being determined to be smaller than the second threshold at the time, changing the drive signal from a first logic level to a second logic level.

17. A method for regulating a power converter, the method comprising:

receiving an input signal;

processing the input signal; and

generating a drive signal;

wherein the processing the input signal includes determining whether a time interval from a first time when the input signal becomes larger than a first threshold to a second time when the input signal becomes smaller than a second threshold is longer than a predetermined duration;

wherein the generating a drive signal includes, in response to the time interval being determined to be longer than the predetermined duration,

determining whether the input signal is smaller than a third threshold at a time following the time interval; and

in response to the input signal being determined to be smaller than the third threshold at the time, change the drive signal from a first logic level to a second logic level.