Method and apparatus of providing synchronous regulation for offline power converter

• US 20090141521A1
• Filed: 12/03/2007
• Published: 06/04/2009
• Est. Priority Date: 12/03/2007
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: System General Corporation (ON Semiconductor Corporation)
• Inventors: Yang, Ta-Yung
• Granted Patent: US 7,796,407 B2
• Time in Patent Office: Days
• US Class Current: 363/49
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A synchronous regulation circuit is provided to improve the efficiency for an offline power converter. A secondary-side switching circuit is coupled to the output of the power converter to generate a synchronous signal and a pulse signal in response to an oscillation signal and a feedback signal. An isolation device transfers the synchronous signal from the secondary side to the primary side of the power converter. A primary-side switching circuit further receives the synchronous signal to generate a switching signal for soft switching a transformer. The pulse signal is utilized to control a synchronous switch for rectifying and regulating the power converter. The synchronous switch includes a power switch and a control circuit. The control circuit receives the pulse signal for turning on/off the power switch. The power switch is connected in between the transformer and the output of the power converter. In addition, a flyback switch is operated as a synchronous rectifier to freewheel the inductor current of the power converter. The flyback switch is turned on in response to the off of the power switch. The on time of flyback switch is correlated to the on time of the power switch.

Claims

1. An offline synchronous regulation power converter, comprising:

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

an isolation device coupled to the secondary-side switching circuit for transferring the synchronous signal from the secondary side of the power converter to the primary side of the power converter;

a primary-side switching circuit generating a switching signal to switch a primary winding of a transformer in response to the synchronous signal; and

a synchronous switch having a power switch and a control circuit, the power switch coupled from a secondary winding of the transformer to 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 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 power converter as claimed in claim 1, wherein the pulse signal is coupled from the secondary-side switching circuit to the synchronous switch through capacitors.

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

switching-transistors coupled to switch the transformer in accordance with the switching signal;

wherein the switching signal includes phase shifts to achieve soft switching of switching-transistors, the phase shifts of the switching signal are generated in accordance with the synchronous signal.

4. The synchronous regulation power converter as claimed in claim 1, wherein the primary-side switching circuit further comprises:

a timer generating an enable signal in response to the synchronous signal;

wherein the enable signal is coupled to control the on/off of a PFC circuit of the power converter.

5. The synchronous regulation power converter as claimed in claim 1, wherein the primary-side switching circuit further comprises:

a maximum-duty circuit coupled to limit the maximum duty of the switching signal in response to the synchronous signal.

6. The synchronous regulation power converter as claimed in claim 1, further comprising:

a current-sense device generating a current-sense signal in response to the switching current of the transformer;

wherein the current-sense signal is coupled to the primary-side switching circuit to disable the switching signal once the current-sense signal is over an over-current threshold.

7. The synchronous regulation power converter 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.

8. The synchronous regulation power converter as claimed in claim 7, 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.

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

10. The synchronous regulation power converter as claimed in claim 1, further comprising:

a flyback switch coupled to the power switch to freewheel an inductor current of the power converter;

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

11. The synchronous regulation power converter 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 pulse signal;

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

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

an oscillation circuit generating oscillation signals for generating the synchronous signal;

a PWM circuit generating a PWM signal in response to the oscillation signals;

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 synchronous signal is a differential signal, the polarity of the synchronous signal determines the on/off of switching-transistors to switch the transformer, the PWM signal is enabled in response to the oscillation signals, the PWM signal is disabled in response to the oscillation signals and a clear signal, the clear signal is generated by the PWM circuit in response to the error signal and the ramp signal, the pulse signal is a differential signal, the polarity of the pulse signal determines the on/off of the power switch.

13. The synchronous regulation power converter as claimed in claim 12, 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.

14. The synchronous regulation power converter as claimed in claim 12, 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 on/off the switching signal during the light load of the power converter.

15. The synchronous regulation power converter as claimed in claim 1, wherein the synchronous switch comprises:

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

a regulated 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 regulated terminal, the first input terminal and the second input terminal are coupled to receive the pulse signal for turning on/off the power switch.

16. The synchronous regulation power converter 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.

17. A synchronous regulation circuit for offline power converter, comprising:

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

a primary-side switching circuit generating a switching signal to switch a transformer in response to the synchronous signal;

a power switch coupled from the transformer to the output of the power converter; and

a control circuit coupled to receives 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 that is coupled to control the power switch for rectifying and regulating of the power converter, the synchronous signal is also a differential signal that is coupled from the secondary-side switching circuit to the primary-side switching circuit to generate the switching signal.

18. The synchronous regulation circuit as claimed in claim 17, wherein the synchronous signal is coupled from the secondary-side switching circuit to the primary-side switching circuit through an isolation device to generate the switching signal.

19. The synchronous regulation circuit as claimed in claim 17, wherein the pulse signal is coupled from the secondary-side switching circuit to the control circuit through capacitors.

20. The synchronous regulation circuit as claimed in claim 17, further comprising:

switching-transistors coupled to switch the transformer in accordance with the switching signal;

wherein the switching signal includes phase shifts to achieve soft switching of switching-transistors, the phase shifts of the switching signal are generated in accordance with the synchronous signal.

21. The synchronous regulation circuit as claimed in claim 17, wherein the secondary-side switching circuit generates the synchronous signal and the pulse signal in response to a power-on signal, switching-transistors and the power switch are turned off once the power-on signal is disabled.

22. The synchronous regulation circuit as claimed in claim 17, wherein the primary-side switching circuit further generates an enable signal in response to the synchronous signal, the enable signal shows output load conditions of the power converter.

23. The synchronous regulation circuit as claimed in claim 17, 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.

24. The synchronous regulation power converter as claimed in claim 23, 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.

25. The synchronous regulation circuit as claimed in claim 17, further comprising:

a flyback switch coupled to the power switch;

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

26. The synchronous regulation circuit as claimed in claim 17, 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 pulse signal;

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

27. The synchronous regulation circuit as claimed in claim 17, wherein the secondary-side switching circuit further comprises:

an oscillation circuit generating oscillation signals for generating the synchronous signal;

a PWM circuit generating a PWM signal in response to the oscillation signals;

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 polarity of the synchronous signal determines the on/off of switching-transistors to switch the transformer, the PWM signal is enabled in response to the oscillation signals, the PWM signal is disabled in response to the oscillation signals and a clear signal, the clear signal is generated by the PWM circuit in response to the error signal and the ramp signal, the polarity of the pulse signal determines the on/off of the power switch.

28. The synchronous regulation circuit as claimed in claim 27, 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.

29. The synchronous regulation circuit as claimed in claim 27, 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 on/off the switching signal during the light load of the power converter.

30. The synchronous regulation circuit as claimed in claim 17, 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.

31. A method for providing synchronous regulation, comprising:

generating a synchronous signal and a pulse signal in response to a feedback signal and an oscillation signal;

transferring the synchronous signal through an isolation device;

generating a switching signal to switch a transformer in response to the synchronous 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 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.

32. The method as claimed in claim 31, further comprising:

receiving a program signal; and

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

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

33. The method as claimed in claim 31, further comprising:

generating an error signal in accordance with the feedback signal;

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 and the power switch.

34. The method as claimed in claim 31, wherein a maximum on time of the power switch is limited by a maximum-on-time circuit.