Switching controller having synchronous input for the synchronization of power converters

1. A switching controller of a power converter, comprising:

a synchronous input circuit generating a first signal in response to a synchronous input signal;

a soft start circuit generating a soft start signal;

an enable circuit coupled to generate a second signal in response to the first signal and the soft start signal; and

an oscillation circuit coupled to the synchronous input circuit and the enable circuit for generating an oscillation signal in response to the first signal and the second signal, wherein the oscillation signal is coupled to generate the switching signal of the power converter and determine the maximum duty cycle of the switching signal; the maximum duty cycle of the switching signal is changed in response to the synchronous input signal; the switching signal is synchronized with the synchronous input signal when the second signal is enabled; the switching signal is running free once the second signal is disabled.

2. The switching controller as claimed in claim 1 , further comprising a signal converter coupled to the oscillation circuit, wherein the signal converter receives a feedback signal of the power convener to generate a modulation signal coupled to the oscillation circuit, and the oscillation signal is modulated in response to the modulation signal.

3. The switching controller as claimed in claim 1 , wherein the second signal is enabled upon when the voltage of the soft start signal is higher than a threshold voltage.

4. The switching controller as claimed in claim 1 , wherein the oscillation signal is synchronized with the synchronous input signal after the generation of the first signal when the second signal is enabled.

5. The switching controller as claimed in claim 1 , wherein the synchronous input circuit comprises:

a debounce circuit for receiving the synchronous input signal and generating an input signal corresponding to the synchronous input signal; and

a one-shot circuit coupled ,to the debounce circuit for generating the first signal in response to the rising edge of the input signal, wherein the pulse width of the first signal is shorter than the pulse width of the input signal.

6. The switching controller as claimed in claim 1 , wherein the oscillation circuit comprises:

a capacitor for generating a ramp signal;

a first charge current coupled to the capacitor;

a first discharge current coupled to the capacitor;

a second charge current coupled to the capacitor;

a second discharge current coupled to the capacitor; and

an oscillation control circuit coupled to the capacitor and the synchronous input circuit for generating the oscillation signal, a sync-charge signal, and a sync-discharge signal in response to the ramp signal and the first signal, wherein the oscillation signal is used to enable the first charge current; the first discharge current is enabled when the oscillation signal and the second signal are disabled; the second charge current is enabled in response to the enabling of the sync-charge signal and of the second signal; the second discharge current is enabled in response to the enabling of the sync-discharge signal, the enabling of the second signal, and the disabling of the sync-charge signal.

7. The switching controller as claimed in claim 6 , wherein the oscillation control circuit comprises:

a first flip-flop for generating the oscillation signal, wherein the oscillation signal is enabled when the ramp signal is lower than a first trip-point voltage, and the oscillation signal is disabled when the ramp signal is higher than a second trip-point voltage;

a second flip-flop for generating the sync-discharge signal, wherein the sync-discharge signal is enabled in response to the enable of the first signal, and the sync-discharge signal is disabled when the ramp signal is lower than the first trip-point voltage; and

a third flip-flop for generating the sync-charge signal, wherein the sync-charge signal is enabled in response to the enable of the first signal, and the sync-charge signal is disabled when the ramp signal is higher than a third trip-point voltage, wherein the third trip-point voltage is higher than the second trip-point voltage, and the second trip-point voltage is higher than the first trip-point voltage.

8. A switching control circuit of a power converter, comprising:

a synchronous input circuit for generating a first signal in response to a synchronous input signal;

an oscillation circuit coupled to the synchronous input circuit for receiving the first signal and generating an oscillation signal response to the first signal, wherein the oscillation signal is utilized to generate a switching signal of the power converter and determine a maximum duty cycle of the switching signal; the maximum duty cycle of the switching signal is changed in response to the synchronous input signal; the switching signal is synchronized with the synchronous input signal; and the switching signal is running free once the synchronous signal is not inputted.

9. The switching control circuit as claimed in claim 8 , further comprising a signal converter coupled to the oscillation circuit, wherein the signal converter receive a feedback signal of the power converter, and the feedback signal modulates the frequency of the oscillation signal.

10. The switching control circuit as claimed in claim 8 , wherein the synchronous input signal is coupled from the output of another switching control circuit.

11. The switching control circuit as claimed in claim 8 , wherein the oscillation signal is. synchronized with the synchronous input signal once the first signal is generated.

12. The switching control circuit as claimed in claim 8 , wherein the synchronous input circuit comprises:

a debounce circuit for receiving the synchronous input signal and generating an input signal in accordance with synchronous input signal; and

a one-shot circuit coupled to the debounce circuit for generating the first signal in response to the rising edge of the input signal, wherein the pulse width of the first signal is shorter than the pulse width of the input signal.

13. The switching control circuit as claimed in claim 8 , wherein the oscillation circuit comprises:

a capacitor for generating a ramp signal;

a first charge current coupled to the capacitor;

a first discharge current coupled to the capacitor;

a second charge current coupled to the capacitor;

a second discharge current coupled to the capacitor; and

an oscillation control circuit coupled to the capacitor and the synchronous input circuit for generating the oscillation signal, a sync-charge signal, and a sync-discharge signal in response to the ramp signal and the first signal.

14. The switching control circuit as claimed in claim 13 , wherein the oscillation control circuit comprises:

a first flip-flop for generating the oscillation signal, wherein the oscillation signal is enabled when the ramp signal is lower than a first trip-point voltage, and the oscillation signal is disabled when the ramp signal is higher than a second trip-point voltage;

a second flip-flop for generating the sync-discharge signal, wherein the sync-discharge signal is enabled in response to the enable of the first signal, and the sync-discharge signal is disabled when the ramp signal is lower than the first trip-point voltage; and

a third flip-flop for generating the sync-charge signal, wherein the sync-charge signal is enabled in response to the enabling of the first signal, and the sync-charge signal is disabled when the ramp signal is higher than a third trip-point voltage, wherein the third trip-point voltage is higher than the second trip-point voltage, and the second trip-point voltage is higher than the first trip-point voltage.

15. A control circuit of a power converter, comprising:

an oscillation circuit coupled to a synchronous input circuit for receiving an output from the synchronous input circuit and generating an oscillation signal in response to a synchronous input signal;

a signal converter receiving a feedback signal of the power converter for modulating the frequency of the oscillation signal in response to the feedback signal, wherein the oscillation signal is utilized to generate the switching signal of the power converter, and the switching signal is synchronized with the synchronous input signal.

16. The control circuit as claimed in claim 15 , wherein the synchronous input signal is coupled from the output of another control circuit.

17. The control circuit as claimed in claim 15 , wherein the synchronous input circuit comprises:

a debounce circuit for receiving the synchronous input signal and generating an input signal in accordance with the synchronous input signal; and

a one-shot circuit coupled to the debounce circuit for generating a first signal in response to the rising edge of the input signal, wherein the pulse width of the first signal is shorter than the pulse width of the input signal.

18. The control circuit as claimed in claim 15 , wherein the oscillation circuit comprises:

a capacitor for generating a ramp signal;

a first charge current coupled to the capacitor;

a first discharge current coupled to the capacitor;

a second charge current coupled to the capacitor;

a second discharge current coupled to the capacitor; and

an oscillation control circuit coupled to the capacitor and the synchronous input circuit for generating the oscillation signal, a sync-charge signal, and a sync-discharge signal in response to the ramp signal and the synchronous input signal.

19. The control circuit as claimed in claim 18 , wherein the oscillation control circuit comprises:

a first flip-flop for generating the oscillation signal, wherein the oscillation signal is enabled when the ramp signal is lower than a first trip-point voltage, and the oscillation signal is disabled when the ramp signal is higher than a second trip-point voltage;

a second flip-flop for generating the sync-discharge signal, wherein the sync-discharge signal is enabled in response to the synchronous input signal when the ramp signal is lower than the first trip-point voltage; and

a third flip-flop for generating the sync-charge signal, wherein the sync-charge signal is enabled in response to the synchronous input signal when the ramp signal is higher than a third trip-point voltage, wherein the third trip-point voltage is higher than the second trip-point voltage, and the second trip-point voltage is higher than the first trip-point voltage.

20. A controller of a power converter, comprising:

a synchronous input circuit for receiving a synchronous input signal; and

an oscillation circuit coupled to the synchronous input circuit for receiving an output from the synchronous input circuit and generating an oscillation signal in response to the synchronous input signal, wherein the oscillation signal is utilized to generate the switching signal of the power converter, and the switching signal is synchronized with the synchronous input signal immediately after the synchronous input signal is inputted.

21. The controller as claimed in claim 20 , wherein the switching signal is synchronized with the synchronous input signal within one switching cycle of the switching signal once the synchronous input signal is inputted.

22. The controller as claimed in claim 20 , further comprising a signal converter coupled to the oscillation circuit, wherein the signal converter receives a feedback signal of the power converter for modulating the frequency of the oscillation signal.

23. The controller as claimed in claim 20 , wherein the synchronous input signal is coupled from the output of another controller.

24. The controller as claimed in claim 20 , wherein the synchronous input circuit comprises:

a debounce circuit for receiving the synchronous input signal and generating an input signal in accordance with synchronous input signal; and

a one-shot circuit coupled to the debounce circuit for generating the first signal in response to the rising edge of the input signal, wherein the pulse width of the first signal is shorter than the pulse width of the input signal.

25. The controller as claimed in claim 20 , wherein the oscillation circuit comprises:

a capacitor for generating a ramp signal;

a first charge current coupled to the capacitor;

a first discharge current coupled to the capacitor;

a second charge current coupled to the capacitor;

a second discharge current coupled to the capacitor; and

an oscillation control circuit coupled to the capacitor and the synchronous input circuit for generating the oscillation signal, a sync-charge signal, and a sync-discharge signal in response to the ramp signal and the synchronous input signal.

26. The controller as claimed in claim 25 , wherein the oscillation control circuit comprises:

a first flip-flop for generating the oscillation signal, wherein the oscillation signal is enabled when the ramp signal is lower than a first trip-point voltage, and the oscillation signal is disabled when the ramp signal is higher than a second trip-point voltage;

a second flip-flop for. generating the sync-discharge signal, wherein the sync-discharge signal is enabled in response to the synchronous input signal when the ramp signal is lower than the first trip-point voltage; and

a third flip-flop for generating the sync-charge signal, wherein the sync-charge signal is enabled in response to the synchronous input signal when the ramp signal is higher than a third trip-point voltage, wherein the third trip-point voltage is higher than the second trip-point voltage, and the second trip-point voltage is higher than the first trip-point voltage.