Driving apparatus of light emitting diode and driving method thereof

• US 8,288,969 B2
• Filed: 02/10/2012
• Issued: 10/16/2012
• Est. Priority Date: 09/16/2009
• 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, Liao, Ting-Wei
• Primary Examiner(s): Philogene, Haiss
• Application Number:
  US13/370,310
• Publication Number:
  US 20120139434A1
• Time in Patent Office: 249 Days
• Field of Search: 315/291, 315/294, 315/297, 315/169.1, 315/185.R, 315/307, 315/360, 315/312, 315/287, 345/46, 345/82, 345/63, 345/204, 345/211, 345/212, 345/207, 345/690, 345/691
• US Class Current: 315/360
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

A driving method of a light-emitting diode (LED) adapted to a driving apparatus is provided. The driving method includes receiving a dimming signal, detecting whether the driving apparatus performs dimming, and if the driving apparatus performs dimming, determining whether a duty cycle of the dimming signal is smaller than a predetermined value. When the duty cycle of the dimming signal is not smaller than the predetermined value, respective current magnitudes of a plurality of driving currents are regulated according to the dimming signal, and each of the driving currents is output for a full time of a period. Conversely, when the duty cycle of the dimming signal is smaller than the predetermined value, each of the driving currents is output for a partial time of a period. A driving apparatus employing the driving method is also provided.

Claims

1. A driving method of a light-emitting diode (LED), adapted to a driving apparatus, the driving method comprising:

receiving a dimming signal;

detecting whether the driving apparatus performs dimming;

if the driving apparatus performs dimming, determining whether a duty cycle of the dimming signal is smaller than a predetermined value;

when the duty cycle of the dimming signal is not smaller than the predetermined value, regulating respective current magnitudes of a plurality of driving currents according to the dimming signal, and outputting each of the driving currents for a full time of a period; and

when the duty cycle of the dimming signal is smaller than the predetermined value, outputting each of the driving currents for a partial time of a period.

2. The driving method of the LED as claimed in claim 1, wherein the step of regulating respective current magnitudes of the plurality of driving currents according to the dimming signal comprises:

determining the respective current magnitudes of the plurality of driving currents according to the duty cycle of the dimming signal.

3. The driving method of the LED as claimed in claim 2, wherein the respective current magnitude of each of the plurality of driving currents is determined to be a product of the duty cycle of the dimming signal and a current upper limit of the driving current.

4. The driving method of the LED as claimed in claim 3, further comprising:

in a situation where the duty cycle of the dimming signal is smaller than the predetermined value, arranging a respective current magnitude and a respective outputting time of each of the driving currents in a period according to the duty cycle of the dimming signal.

5. The driving method of the LED as claimed in claim 4, wherein:

in the situation where the duty cycle of the dimming signal is smaller than the predetermined value, the respective current magnitude and the respective outputting time of each of the driving currents in the period are arranged, such that a sum of the driving currents calculated for the period is determined according to the duty cycle of the dimming signal and a current upper limit.

6. The driving method of the LED as claimed in claim 1, further comprising:

in a situation where the duty cycle of the dimming signal is smaller than the predetermined value, arranging a respective current magnitude and a respective outputting time of each of the driving currents in a period according to the duty cycle of the dimming signal.

7. The driving method of the LED as claimed in claim 6, wherein in the situation where the duty cycle of the dimming signal is smaller than the predetermined value, the respective current magnitude and the respective outputting time of each of the driving currents in the period are arranged, such that a sum of the driving currents calculated for the period is determined according to the duty cycle of the dimming signal and a current upper limit.

8. The driving method of the LED as claimed in claim 1, regardless of whether each of the driving currents is output for a full time or a partial time of a period, maintaining a sum of the driving currents calculated for each period approximately to a fixed value for the same duty cycle of the dimming signal.

9. The driving method of the LED as claimed in claim 1, wherein the driving currents are output in turn according to a random sequence in a situation where the duty cycle of the dimming signal is smaller than the predetermined value.

10. The driving method of the LED as claimed in claim 1, further comprising dispersing the outputting time of the driving currents in a period in a situation where the duty cycle of the dimming signal is smaller than the predetermined value.

11. The driving method of the LED as claimed in claim 10, wherein the step of dispersing the outputting time of the driving currents comprises equally allocating the outputting time of the driving currents in the period.

12. The driving method of the LED as claimed in claim 10, wherein the step of dispersing the outputting time of the driving currents comprises arranging the outputting time of the driving currents in the period to be equal in length.

13. The driving method of the LED as claimed in claim 12, wherein the outputting time of each of the driving currents is substantially equal to a period divided by a number of the driving currents.

14. The driving method of the LED as claimed in claim 10, wherein the step of dispersing the outputting time of the driving currents comprises arranging the outputting time of the driving currents not to overlap each other in the period.

15. The driving method of the LED as claimed in claim 1, wherein the predetermined value is a ratio between the period and a number of the driving currents.

16. The driving method of the LED as claimed in claim 1, wherein the driving currents are sequentially output in turn in a situation where the duty cycle of the dimming signal is smaller than the predetermined value.

17. A driving apparatus of an LED, comprising:

a current driving unit, outputting a plurality of driving currents to respectively drive a plurality of LEDs;

a plurality of switches, respectively coupled between the current driving unit and the LEDs for controlling whether or not to output the driving currents to the LEDs;

a dimming detector, receiving a dimming signal, and detecting whether the driving apparatus performs dimming according to the dimming signal and detecting whether a duty cycle of the dimming signal is smaller than a predetermined value, so as to output a dimming mode signal; and

a current control unit, coupled to the dimming detector and the switches, and controlling conducting time of the switches, wherein

when the driving apparatus performs dimming and the duty cycle of the dimming signal is not smaller than the predetermined value, the current control unit controls each of the switches to be conducted for a full time of a period, and controls the current driving unit to regulate respective current magnitudes of the driving currents according to the dimming signal, and

when the driving apparatus performs dimming and the duty cycle of the dimming signal is smaller than the predetermined value, the current control unit controls each of the switches to be conducted for a partial time of a period.

18. The driving apparatus of the LED as claimed in claim 17, wherein the current driving unit comprises:

a plurality of voltage-controlled current sources, commonly coupled to the current control unit.

19. The driving apparatus of the LED as claimed in claim 18, wherein the current driving unit controls the current driving unit to regulate the respective current magnitudes of the plurality of driving currents according to the duty cycle of the dimming signal when the duty cycle of the dimming signal is not smaller than the predetermined value.

20. The driving apparatus of the LED as claimed in claim 19, wherein controls the current driving unit to regulate the respective current magnitude of each of the plurality of driving currents to be a product of the duty cycle of the dimming signal and a current upper limit of the driving current.

21. The driving apparatus of the LED as claimed in claim 20, wherein in a situation where the duty cycle of the dimming signal is smaller than the predetermined value, the current control unit controls the current driving unit to regulate a respective current magnitude of each of the driving currents and the current control unit arranges a respective conducting time of each of the switches in a period according to the duty cycle of the dimming signal.

22. The driving apparatus of the LED as claimed in claim 21, wherein in the situation where the duty cycle of the dimming signal is smaller than the predetermined value, the current control unit controls the current driving unit to regulate the respective current magnitude of each of the driving currents and the current control unit arranges the respective conducting time of each of the switches in a period, such that a sum of the driving currents calculated for the period is determined according to the duty cycle of the dimming signal and a current upper limit.

23. The driving apparatus of the LED as claimed in claim 18, wherein in a situation where the duty cycle of the dimming signal is smaller than the predetermined value, the current control unit controls the current driving unit to regulate a respective current magnitude of each of the driving current and the current control unit arranges a respective conducting time of each of the switches in a period, according to the duty cycle of the dimming signal.

24. The driving apparatus of the LED as claimed in claim 23, wherein in the situation where the duty cycle of the dimming signal is smaller than the predetermined value, the current control unit controls the current driving unit to regulate the respective current magnitude of each of the driving currents and the current control unit arranges the respective conducting time of each of the switches in the period, such that a sum of the driving currents calculated for the period is determined according to the duty cycle of the dimming signal and a current upper limit.

25. The driving apparatus of the LED as claimed in claim 18, regardless of whether each of the driving currents is output for a full time or a partial time of a period, a sum of the driving currents calculated for each period is maintained approximately to a fixed value for the same duty cycle of the dimming signal.

26. The driving apparatus of the LED as claimed in claim 17, wherein the current driving unit outputs the driving currents in turn according to a random sequence in a situation where the duty cycle of the dimming signal is smaller than the predetermined value.

27. The driving apparatus of the LED as claimed in claim 18, wherein the current control unit further disperses the conducting time of the switches in a period in a situation where the duty cycle of the dimming signal is smaller than the predetermined value.

28. The driving apparatus of the LED as claimed in claim 27, wherein when the current control unit disperses the conducting time of the switches, it equally allocates the conducting time of the switches in the period.

29. The driving apparatus of the LED as claimed in claim 27, wherein when the current control unit disperses the conducting time of the switches, it arranges the conducting time of the switches in the period to be equal in length.

30. The driving apparatus of the LED as claimed in claim 29, wherein the outputting time of each of the driving currents is substantially equal to a period divided by a number of the driving currents.

31. The driving apparatus of the LED as claimed in claim 27, when the current control unit disperses the conducting time of the switches, it arranges the outputting time of the driving currents not to overlap each other in the period.

32. The driving apparatus of the LED as claimed in claim 17, wherein the predetermined value is a ratio between the period and a number of the driving currents.

33. The driving apparatus of the LED as claimed in claim 17, wherein the current driving unit sequentially outputs the driving currents in turn in a situation where the duty cycle of the dimming signal is smaller than the predetermined value.

34. The driving apparatus of the LED as claimed in claim 17, wherein the current control unit comprises:

a multiplexer, coupled to the dimming detector for receiving the dimming mode signal, wherein an input terminal of the multiplexer receives the dimming signal, and whether a first output terminal or a second output terminal thereof outputs the dimming signal is determined according to the dimming mode signal;

a disperse delay unit, coupled to the first output terminal of the multiplexer and the switches, and controlling a conducting state of each of the switches according to the dimming signal received from the first output terminal of the multiplexer; and

a duty cycle to voltage converter, coupled to the second output terminal of the multiplexer, the disperse delay unit and the current driving unit, and generating a control voltage for controlling the current driving unit to regulate the current magnitudes of driving currents under control of the multiplexer and the disperse delay unit.

35. The driving apparatus of the LED as claimed in claim 34, wherein when the disperse delay unit receives the dimming signal, it controls each of the switches to be conducted for a partial time of a period, and outputs the dimming signal and a gain signal, and when it does not receive the dimming signal, it controls each of the switches to be conducted for a full time of a period.

36. The driving apparatus of the LED as claimed in claim 35, wherein when the duty cycle to voltage converter receives the dimming signal from the multiplexer, it controls the current driving unit to regulate the current magnitudes of the driving currents according to the dimming signal, and when the duty cycle to voltage converter receives the dimming signal and the gain signal from the disperse delay unit, it controls the current driving unit to regulate the current magnitudes of the driving currents according to the dimming signal and the gain signal.

37. The driving apparatus of the LED as claimed in claim 36, wherein the duty cycle to voltage converter comprises:

a low pass filter, coupled to the multiplexer and the disperse delay unit; and

an analog multiplier, coupled to the low pass filter, the disperse delay unit and the current driving unit, and regulating an output voltage of the low pass filter according to the gain signal so as to control the current driving unit.