APPARATUS AND METHOD FOR CONSTANT POWER OFFLINE LED DRIVER

• US 20100308733A1
• Filed: 01/06/2010
• Published: 12/09/2010
• Est. Priority Date: 06/09/2009
• Status: Active Grant

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Shao, Jianwen
• Granted Patent: US 8,305,004 B2
• Time in Patent Office: Days
• US Class Current: 315/119
• 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 my 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 an input voltage waveform from a waveform distribution circuit, and generate a drive signal;

a switch coupled to the power factor corrector controller, and operable, in response to the drive signal, to generate an inductor current;

an inductor operable to receive the inductor current and distribute power throughout 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 to provide a constant voltage to the current-sensing node of the power factor corrector controller;

wherein said waveform distribution circuit receives a rectified input AC signal.

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 current across the inductor.

3. The integrated circuit as set forth in claim 2, 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 2, wherein the integrated circuit operates in a substantially constant power mode having a substantially constant peak current.

5. The integrated circuit as set forth in claim 2, wherein the integrated circuit operates in a power factor-improving mode when the input AC signal is near line zero crossing.

6. The integrated circuit as set forth in claim 2, wherein the integrated circuit is a buck-boost circuit.

7. The integrated circuit as set forth in claim 2, wherein the power factor corrector controller operates in transition mode.

8. The integrated circuit as set forth in claim 2, wherein the power factor corrector controller is a partial soft-switched converter.

9. The integrated circuit as set forth in claim 2, wherein said waveform distribution circuit comprises a voltage divider.

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 inductor 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 2, wherein the peak current setting of the inductor is approximately 1 A when the input AC signal is at peak line voltage.

13. The integrated circuit as set forth in claim 2, wherein the peak current setting of the inductor is less than 1 A when the input AC signal is near line zero crossing.

14. The integrated circuit as set forth in claim 2, 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 2, 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 an input voltage waveform from a waveform distribution circuit, and generate a drive signal;

a switch coupled to the power factor corrector controller, and operable, in response to the drive signal, to generate a transformer current;

a transformer operable to receive the transformer current and distribute power throughout 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 to provide a constant voltage to the current-sensing node of the power factor corrector controller;

wherein said waveform distribution circuit receives a rectified input AC signal.

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 transformer.

17. The integrated circuit as set forth in claim 16, 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 16, wherein the integrated circuit operates in a substantially constant power mode having a substantially constant peak current.

19. The integrated circuit as set forth in claim 16, 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 16, wherein the integrated circuit is an isolated flyback circuit.

21. The integrated circuit as set forth in claim 16, wherein the integrated circuit is a non-isolated flyback circuit.

22. The integrated circuit as set forth in claim 16, wherein the power factor corrector controller operates in transition mode.

23. The integrated circuit according to claim 16, wherein the power factor corrector controller is a partial soft-switched converter.

24. The integrated circuit as set forth in claim 16, wherein said waveform distribution circuit comprises a voltage divider.

25. The integrated circuit as set forth in claim 16, wherein said transformer 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 16, wherein the peak current setting of the transformer is approximately 1 A when the input AC signal is at peak line voltage.

27. The integrated circuit as set forth in claim 16, wherein the peak current setting of the transformer is less than 1 A when the input AC signal is near line zero crossing.

28. The integrated circuit as set forth in claim 16, 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 16, wherein the integrated circuit is a buck-boost circuit.

40. The integrated circuit as set forth in claim 16, wherein the integrated circuit is a buck circuit.

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

receiving an input voltage waveform;

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

shaping the waveform of said current across said power distribution circuit to be in phase with said input voltage waveform.

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 an input voltage waveform;

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

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 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.