Synchronous regulation circuit and method for providing synchronous regulation for power converters

1. A synchronous regulation circuit for a power converter, comprising:

a primary-side switching circuit generating a switching signal and a synchronous signal, the switching signal coupled to switch a transformer;

a secondary-side switching circuit coupled to the output of the power converter to generate a pulse signal in response to the synchronous signal and a feedback signal;

an isolation device coupled to the primary-side switching circuit for transferring the synchronous signal in the primary side of the transformer to the secondary-side switching circuit in the secondary side of the transformer; and

a synchronous switch having a power switch and a control circuit, the power switch coupled in between the secondary side of the transformer and the output of the power converter, the control circuit receiving the pulse signal for turning on/off the power switch;

wherein the feedback signal is correlated to the output of the power converter, the pulse signal is a differential signal generated for rectifying and regulating of the power converter, the polarity of the pulse signal determines the on/off of the power switch.

2. The synchronous regulation circuit as claimed in claim 1 , wherein the pulse signal is coupled from the secondary-side switching circuit to the synchronous switch through two transistors operated in differential mode.

3. The synchronous regulation circuit as claimed in claim 1 , further comprising:

a flyback switch coupled to the synchronous switch and the output of the power converter;

wherein the flyback switch is turned on in response to the off of the power switch, an on time of the flyback switch is correlated to an on time of the power switch.

4. The synchronous regulation circuit as claimed in claim 1 , wherein the power switch comprises a first transistor and a second transistor connected in series, the first transistor has a first diode connected in parallel, the second transistor has a second diode connected in parallel.

5. The synchronous regulation circuit as claimed in claim 4 , wherein the control circuit generates a first-control signal and a second-control signal to control the first transistor and the second transistor respectively, the first transistor can be turned on once the first diode is conducted.

6. The synchronous regulation circuit as claimed in claim 1 , wherein the isolation device is a pulse transformer or capacitors.

7. The synchronous regulation circuit as claimed in claim 1 , wherein the primary-side switching circuit generates the synchronous signal in response to the switching signal, a delay time is developed between the switching signal and the synchronous signal.

8. The synchronous regulation circuit as claimed in claim 1 , wherein the secondary-side switching circuit comprises:

a programming device generating a program signal; and

a linear-predict circuit generating a drive signal in response to the program signal and the synchronous signal;

wherein the drive signal is utilized to control a flyback switch.

9. The synchronous regulation circuit as claimed in claim 1 , wherein the secondary-side switching circuit comprises:

a PWM circuit generating a PWM signal in response to the synchronous signal;

an error amplifier coupled to the output of the power converter to receive the feedback signal and generate an error signal;

a ramp circuit generating a ramp signal in response to the PWM signal; and

a pulse signal generator generating the pulse signal in accordance with the PWM signal;

wherein the PWM signal is enabled in response to the synchronous signal, the PWM signal is disabled in response to the synchronous signal and a clear signal, the clear signal is generated by the PWM circuit in response to the error signal and the ramp signal.

10. The synchronous regulation circuit as claimed in claim 9 , wherein the secondary-side switching circuit further comprises:

a soft-start circuit generating a soft-start signal in response to a reset signal;

wherein the soft-start signal is coupled to control the pulse width of the PWM signal.

11. The synchronous regulation circuit as claimed in claim 9 , wherein the secondary-side switching circuit further comprises:

a power management circuit coupled to receive the error signal for generating a light-load signal;

wherein the light-load signal is coupled to the primary-side switching circuit to disable the switching signal during the light load of the power converter.

12. The synchronous regulation circuit as claimed in claim 1 , wherein the synchronous switch comprises:

a rectifying terminal coupled to the secondary side of the transformer;

a ground terminal coupled to the output of the power converter;

a first input terminal; and

a second input terminal;

wherein the power switch is connected in between the rectifying terminal and the ground terminal, the first input terminal and the second input terminal are coupled to receive the pulse signal for turning on/off the power switch.

13. The synchronous regulation circuit as claimed in claim 1 , wherein the control circuit comprises a latch circuit coupled to receive the pulse signal for set or reset the latch circuit, the latch circuit is coupled to turn on/off the power switch.

14. A method for providing synchronous regulation of a power converter, comprising:

generating a synchronous signal;

generating a switching signal to switch a transformer;

generating a pulse signal in response to the synchronous signal and a feedback signal;

transferring the pulse signal to a latch circuit;

setting or resetting the latch circuit in response to the polarity of the pulse signal; and

turning on/off a power switch in accordance with the status of the latch circuit;

wherein the pulse signal is a one-shot differential signal, the feedback signal is correlated to the output of the power converter, the power switch is coupled in between the transformer and the output of the power converter for the rectifying and the regulation.

15. The method as claimed in claim 14 , further comprising:

generating a program signal; and

generating a drive signal to turn on/off a flyback switch in response to the program signal and the synchronous signal;

wherein the flyback switch is coupled to the power switch and the output of the power converter.

16. The method as claimed in claim 14 , further comprising:

generating an error signal in accordance with the feedback signal; and

generating a light-load signal by comparing the error signal with a threshold signal;

wherein the light-load signal is coupled to turn off the switching signal.

17. The method as claimed in claim 14 , wherein a maximum on time of the power switch is limited by a maximum-on-time circuit.