Control Method Capable of Preventing Flicker Effect and Light Emitting Device Therefore

• US 20110037410A1
• Filed: 11/25/2009
• Published: 02/17/2011
• Est. Priority Date: 08/17/2009
• Status: Active Grant

• Current Assignee: Novatek Microelectronics Corporation (Novatek Microelectronics Corp Limited)
• Original Assignee: Novatek Microelectronics Corporation (Novatek Microelectronics Corp Limited)
• Inventors: Hsu, Kuo-Ching, Hsu, Chin-Hsun, Chang, Tsung-Hau
• Granted Patent: US 8,169,156 B2
• Time in Patent Office: Days
• US Class Current: 315/294
• CPC Class Codes: H05B 31/50 specially adapted for ac
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

A control method capable of preventing flicker effect for a light source module includes detecting variation situations of a driving current passing through the light source module to generate a current detection signal, adjusting a variable reference voltage according to the current detection signal, obtaining a feedback voltage from the light source module, generating a voltage control signal according to the feedback voltage and the variable reference voltage, and generating an output voltage according to the voltage control signal to drive the light source module.

Claims

1. A control method capable of preventing flicker effect in a light source module, the control method comprising:

detecting variation situations of a driving current passing through the light source module to generate a current detection signal;

adjusting a variable reference voltage according to the current detection signal;

obtaining a feedback voltage from the light source module;

generating a voltage control signal according to the feedback voltage and the variable reference voltage; and

generating an output voltage according to the voltage control signal to drive the light source module.

2. The control method of claim 1, wherein the light source module comprises a plurality of light-emitting diode (LED) groups and the driving current comprises a plurality of load currents passing through each LED group respectively.

3. The control method of claim 2, wherein the step of detecting variation situations of the driving current passing through the light source module to generate the current detection signal comprises:

generating the current detection signal according to the variation situations of at least one load current of the plurality of load currents having current variation when current variation of the at least one load current is detected.

4. The control method of claim 2, wherein the step of obtaining the feedback voltage from the light source module comprises:

selecting the lowest headroom voltage from a plurality of headroom voltages corresponding to the plurality of LED groups as the feedback voltage.

5. The control method of claim 1, wherein the feedback voltage is selected from headroom voltages corresponding to the light source module.

6. The control method of claim 1, wherein the step of adjusting the variable reference voltage according to the current detection signal comprises:

increasing the variable reference voltage when the current detection signal indicates the driving current becomes greater.

7. The control method of claim 1, wherein the step of adjusting the variable reference voltage according to the current detection signal comprises:

decreasing the variable reference voltage when the current detection signal indicates the driving current becomes smaller.

8. The control method of claim 1, wherein the step of adjusting the variable reference voltage according to the current detection signal comprises:

generating a reference voltage converting signal according to the current detection signal; and

generating the variable reference voltage according to the reference voltage converting signal.

9. A light-emitting diode (LED) device, comprising:

a voltage converter, for converting an input voltage into an output voltage according to a voltage control signal;

a light source module, coupled to the voltage converter;

a variable current source, coupled to the light source module, for providing a driving current to drive the light source module; and

a control unit, coupled to the light source module and the voltage converter, for obtaining a feedback voltage from the light source module and detecting variation situations of the driving current passing through the light source module to generate a current detection signal;

wherein the control unit adjusts a variable reference voltage according to the current detection signal and generates the voltage control signal sent to the voltage converter according to the feedback voltage and the variable reference voltage.

10. The LED device of claim 9, wherein the light source module comprises a plurality of LED groups and the driving current is composed of a plurality of load currents passing through each LED group respectively.

11. The LED device of claim 10, wherein each LED group of the plurality of LED groups comprises a plurality of LEDs in series.

12. The LED device of claim 10, wherein the control unit generates the current detection signal according to the variation situations of at least one load current of the plurality of load currents having current variation when the current variation of the at least one load current is detected.

13. The LED device of claim 10, wherein the control unit selects the lowest headroom voltage from a plurality of headroom voltages corresponding to the plurality of LED groups as the feedback voltage.

14. The LED device of claim 9, wherein the control unit comprises:

a voltage selector, coupled to the light source module, for selecting the feedback voltage from a plurality of headroom voltages corresponding to the light source module;

a current detector, coupled to the light source module, for detecting variation situations of the driving current passing through the light source module to generate the current detection signal;

a processing unit, coupled to the current detector, for generating a reference voltage converting signal according to the current detection signal;

a reference voltage converter, coupled to the processing unit, for generating the variable reference voltage according to the reference voltage converting signal;

an error amplifier, coupled to the voltage selector and the reference voltage generator, for generating an error voltage signal according to the feedback voltage and the variable reference voltage; and

a conversion controller, coupled to the error amplifier and the voltage converter, for generating the voltage control signal according to the error voltage signal for the voltage converter.

15. The LED device of claim 14, wherein the voltage selector selects the lowest headroom voltage from the plurality of headroom voltages as the feedback voltage.

16. The LED device of claim 14, wherein the processing unit increases the variable reference voltage when the current detection signal indicates the driving current becomes greater.

17. The LED device of claim 14, wherein the processing unit decreases the variable reference voltage when the current detection signal indicates the driving current becomes smaller.

18. A control method capable of preventing flicker effect in a light source module, the control method comprising:

detecting variation situations of a driving current provided by a variable current source to generate a current detection signal;

adjusting a variable reference voltage according to the current detection signal;

obtaining a feedback voltage from the light source module;

generating a voltage control signal according to the feedback voltage and the variable reference voltage; and

generating an output voltage according to the voltage control signal to drive the light source module.

19. The control method of claim 18, wherein the light source module comprises a plurality of light-emitting diode (LED) groups and the driving current is composed of a plurality of load currents passing through each LED group respectively.

20. The control method of claim 19, wherein the step of detecting variation situations of the driving current provided by the variable current source to generate the current detection signal comprises:

generating the current detection signal according to the variation situations of at least one load current of the plurality of load currents having current variation when the current variation of the at least one load current is detected.

21. The control method of claim 19, wherein the step of obtaining the feedback voltage from the light source module comprises:

selecting the lowest headroom voltage from a plurality of headroom voltages corresponding to the plurality of LED groups as the feedback voltage.

22. The control method of claim 18, wherein the feedback voltage is selected from headroom voltages corresponding to the light source module.

23. The control method of claim 18, wherein the step of adjusting the variable reference voltage according to the current detection signal comprises:

increasing the variable reference voltage when the current detection signal indicates the driving current becomes greater.

24. The control method of claim 18, wherein the step of adjusting the variable reference voltage according to the current detection signal comprises:

decreasing the variable reference voltage when the current detection signal indicates the driving current becomes smaller.

25. The control method of claim 18, wherein the step of adjusting the variable reference voltage according to the current detection signal comprises:

generating a reference voltage converting signal according to the current detection signal; and

generating the variable reference voltage according to the reference voltage converting signal.

26. A light-emitting diode (LED) device, comprising:

a voltage converter, for converting an input voltage into an output voltage according to a voltage control signal;

a light source module, coupled to the voltage converter;

a variable current source, coupled to the light source module, for generating a driving current to drive the light source module; and

a control unit, coupled to the variable current source and the voltage converter, for obtaining a feedback voltage from the light source module and detecting variation situations of the driving current provided by the variable current source to generate a current detection signal;

wherein the control unit adjusts a variable reference voltage according to the current detection signal and generates the voltage control signal according to the feedback voltage and the variable reference voltage to the voltage converter.

27. The LED device of claim 26, wherein the light source module comprises a plurality of LED groups and the driving current comprises a plurality of load currents passing through each LED groups respectively.

28. The LED device of claim 27, wherein each LED group of the plurality of LED groups comprises a plurality of LEDs in series.

29. The LED device of claim 27, wherein the control unit generates the current detection signal according to the variation situations of at least one load current of the plurality of load currents having current variation when the current variation of the at least one load current is detected.

30. The LED device of claim 27, wherein the control unit selects the lowest headroom voltage from a plurality of headroom voltages corresponding to the plurality of LED groups as the feedback voltage.

31. The LED device of claim 26, wherein the variable current source generates the driving current according to requirements of the light source module.

32. The LED device of claim 26, wherein the variable current source generates the driving current according to a dimming signal.

33. The LED device of claim 26, wherein the variable current source comprises:

a variable current mirror, coupled to the control unit, for generating the driving current; and

a current driving element, coupled to the variable current mirror and the light source module, for controlling the driving current to the light source module.

34. The LED device of claim 33, wherein the control unit detects variation situations of the current provided by the variable current mirror to generate the current detection signal.

35. The LED device of claim 26, wherein the control unit comprises:

a voltage selector, coupled to the light source module, for selecting the feedback voltage from a plurality of headroom voltages corresponding to the light source module;

a current detector, coupled to the variable current source, for detecting variation situations of the driving current generated by the variable current source to generate the current detection signal;

a processing unit, coupled to the current detector, for generating a reference voltage converting signal according to the current detection signal;

a reference voltage converter, coupled to the processing unit, for generating the variable reference voltage according to the reference voltage converting signal;

an error amplifier, coupled to the voltage selector and the reference voltage generator, for generating an error voltage signal according to the feedback voltage and the variable reference voltage; and

a conversion controller, coupled to the error amplifier and the voltage converter, for generating the voltage control signal according to the error voltage signal for the voltage converter.

36. The LED device of claim 35, wherein the voltage selector selects the lowest headroom voltage from the plurality of headroom voltages as the feedback voltage.

37. The LED device of claim 35, wherein the processing unit increases the variable reference voltage when the current detection signal indicates the driving current becomes greater.

38. The LED device of claim 35, wherein the processing unit decreases the variable reference voltage when the current detection signal indicates the driving current becomes smaller.