Apparatus and method for constant power offline LED driver

• US 8,305,004 B2
• Filed: 01/06/2010
• Issued: 11/06/2012
• Est. Priority Date: 06/09/2009
• Status: Active Grant

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Shao, Jianwen
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): PHAM, THAI N
• Application Number:
  US12/683,230
• Publication Number:
  US 20100308733A1
• Time in Patent Office: 1,035 Days
• Field of Search: 315/119, 315/209.R, 315/219, 315/224, 315/247, 315/307, 363/21.04, 363/21.12, 363/21.16, 363/53, 363/84
• US Class Current: 315/247
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• CPC Class Codes: H02M 1/4258 using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage H02M1/4241 takes precedence
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/385 using flyback topology
• 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 single-stage integrated circuit drives LED sources in a constant power mode to eliminate the need for LED current sensing, while reshaping the waveform of the inductor current near line zero crossing to achieve high power factor. The integrated circuit achieves substantially constant input power by maintaining a constant voltage at a power factor corrector controller through an input voltage feedforward system. Accordingly, the disclosed circuit provides a high power factor, high efficiency, simple, and cost-effective solution with substantially consistent input power for both isolated and non-isolated offline LED applications.

Claims

1. An integrated circuit, comprising:

a power factor corrector controller operable to receive, at a first input node, a rectified input voltage waveform of an input AC signal, and operable to generate a drive signal;

a switch coupled to the power factor corrector controller, and operable, in response to the drive signal, to generate an output current across a power distribution circuit, wherein the output current varies in phase with the rectified input voltage waveform during a first mode, and is substantially constant during a second mode,

wherein the power distribution circuit is operable during the second mode to distribute a substantially constant power throughout at least a portion of the integrated circuit; and

an input voltage feedforward system coupled to the first input node and a current-sensing node of the power factor corrector controller, and operable, in the first and second modes, to provide a constant voltage to the current-sensing node of the power factor corrector controller,

wherein the first mode is when the input AC signal is near line zero crossing, and the second mode is when the input AC signal is near peak line voltage.

2. The integrated circuit as set forth in claim 1, further comprising:

a current-sensing voltage located at a node disposed between the switch and input voltage feedforward system;

a zero current detection circuit operable to detect a low current at the power factor corrector controller; and

an open load protection circuit operable to detect an open load and turn off the integrated circuit;

wherein the current-sensing voltage varies in response to a variation of the output current.

3. The integrated circuit as set forth in claim 1, wherein said input voltage feedforward system comprises a diode and capacitor in series with at least two current-sensing resistors.

4. The integrated circuit as set forth in claim 1, wherein the output current is clamped at a substantially constant peak current value during the second mode.

5. The integrated circuit as set forth in claim 1, wherein the integrated circuit operates in a power factor-improving mode during the first mode.

6. The integrated circuit as set forth in claim 1, wherein the integrated circuit is a buck-boost circuit.

7. The integrated circuit as set forth in claim 1, wherein the power factor corrector controller operates in a transition mode.

8. The integrated circuit as set forth in claim 1, wherein the power factor corrector controller is a partial soft-switched converter.

9. The integrated circuit as set forth in claim 1, wherein said power distribution circuit comprises one of an inductor or transformer.

10. The integrated circuit as set forth in claim 2, wherein said open load protection circuit comprises a voltage divider.

11. The integrated circuit as set forth in claim 2, wherein said power distribution circuit comprises a primary winding and secondary winding, the primary winding operable to distribute power to at least said input voltage feedforward system, and the secondary winding operable to distribute power to at least one of said power factor corrector controller, zero current detection circuit, and open load protection circuit.

12. The integrated circuit as set forth in claim 1, wherein a peak current setting of the power distribution circuit is approximately 1 A during the second mode.

13. The integrated circuit as set forth in claim 1, wherein a peak current setting of the power distribution circuit is less than 1 A during the first mode.

14. The integrated circuit as set forth in claim 1, wherein the integrated circuit is operable to drive Light Emitting Diode sources in an offline LED application.

38. The integrated circuit as set forth in claim 1, wherein the integrated circuit is a buck circuit.

15. An integrated circuit, comprising:

a power factor corrector controller operable to receive, at a first input node, a rectified input voltage waveform of an input AC signal, and operable to generate a drive signal;

a switch coupled to the power factor corrector controller, and operable, in response to the drive signal, to generate an output current across a power distribution circuit, wherein the output current has a shape in phase with the rectified input voltage waveform when the input AC signal is near line zero crossing, and is substantially constant when the input AC signal is not near line zero crossing,

wherein the power distribution circuit is operable to distribute a substantially constant power throughout the integrated circuit when the input AC signal is near peak line voltage; and

an input voltage feedforward system coupled to the first input node and a current-sensing node of the power factor corrector controller, and operable to provide a constant voltage at the current-sensing node of the power factor corrector controller in response to changes in the output current across the power distribution circuit.

16. The integrated circuit as set forth in claim 15, further comprising:

a current-sensing voltage located at a node disposed between the switch and input voltage feedforward system; and

a zero current detection circuit operable to detect a low current at the power factor corrector controller;

wherein the current-sensing voltage varies in response to a variation of the current across the power distribution circuit.

17. The integrated circuit as set forth in claim 15, wherein said input voltage feedforward system comprises a diode and capacitor in series with at least two current-sensing resistors.

18. The integrated circuit as set forth in claim 15, wherein the power factor corrector controller is operable to clamp the output current at a substantially constant peak current when the input AC signal is near peak line voltage.

19. The integrated circuit as set forth in claim 15, wherein the integrated circuit operates in a power factor-improving mode when the input AC signal is near line zero crossing.

20. The integrated circuit as set forth in claim 15, wherein the integrated circuit is an isolated flyback circuit.

21. The integrated circuit as set forth in claim 15, wherein the integrated circuit is a non-isolated flyback circuit.

22. The integrated circuit as set forth in claim 15, wherein the power factor corrector controller operates in a transition mode.

23. The integrated circuit according to claim 15, wherein the power factor corrector controller is a partial soft-switched converter.

24. The integrated circuit as set forth in claim 15, wherein said power distribution circuit comprises one of an inductor or transformer.

25. The integrated circuit as set forth in claim 16, wherein said power distribution circuit comprises a primary winding and secondary winding, the primary winding operable to distribute power to at least said input voltage feedforward system, and the secondary winding operable to distribute power to at least said zero current detection circuit.

26. The integrated circuit as set forth in claim 15, wherein a peak current setting of the power distribution circuit is approximately 1 A when the input AC signal is at peak line voltage.

27. The integrated circuit as set forth in claim 15, wherein a peak current setting of the power distribution circuit is less than 1 A when the input AC signal is near line zero crossing.

28. The integrated circuit as set forth in claim 15, wherein the integrated circuit is operable to drive Light Emitting Diode sources in an offline LED application.

39. The integrated circuit as set forth in claim 15, wherein the integrated circuit is a buck-boost circuit.

40. The integrated circuit as set forth in claim 15, wherein the integrated circuit is a buck circuit.

29. A method for improving the power factor of an integrated circuit, said method comprising:

receiving a rectified input voltage waveform of an input AC signal;

activating a switch to generate a current across a power distribution circuit;

shaping the waveform of said current across said power distribution circuit to be in phase with said rectified input voltage waveform when the input AC signal is near line zero crossing; and

clamping the current across said power distribution circuit at a substantially constant peak current value when the input AC signal is near peak line voltage.

30. The method as set forth in claim 29, wherein shaping the waveform of the current across said power distribution circuit comprises:

generating a reference signal in response to the input voltage waveform;

generating a current-sensing voltage in response to the current across said power distribution circuit;

comparing the current-sensing voltage to the reference signal; and

deactivating said switch when the current-sensing voltage is equal to the voltage of the reference signal.

31. The method as set forth in claim 29, wherein said power distribution circuit is an inductor.

32. The method as set forth in claim 29, wherein said power distribution circuit is a transformer.

33. The method as set forth in claim 29, wherein the integrated circuit is operable to drive Light Emitting Diode sources in an offline LED application.

34. A method for maintaining constant power of an integrated circuit, said method comprising:

receiving a rectified input voltage waveform of an input AC signal;

activating a switch to generate a current across a power distribution circuit;

shaping the waveform of the current across the power distribution circuit to be in phase with the rectified input voltage waveform when the input AC signal is near line zero crossing;

generating a current-sensing voltage in response to the current across said power distribution circuit, wherein said current-sensing voltage is part of a feedback loop connecting said switch to a power factor corrector controller;

detecting a peak input voltage of the input AC signal at an input voltage feedforward system;

adding the current from the peak input voltage to said feedback loop; and

adjusting the current-sensing voltage in response to a variation in the peak input voltage to maintain a constant voltage at the power factor corrector controller.

35. The method as set forth in claim 34, wherein said power distribution circuit is an inductor.

36. The method as set forth in claim 34, wherein said power distribution circuit is a transformer.

37. The method as set forth in claim 34, wherein the integrated circuit is operable to drive Light Emitting Diode sources in an offline LED application.