ALTERNATING CURRENT LIGHT EMITTING DEVICE

• US 20090160370A1
• Filed: 12/18/2008
• Published: 06/25/2009
• Est. Priority Date: 12/19/2007
• Status: Active Grant

• Current Assignee: Epistar Corporation
• Original Assignee: Industrial Technology Research Institute
• Inventors: Yeh, Wen-Yung, Tai, Sheng-Chieh, Chan, Yi-Jen
• Granted Patent: US 8,598,799 B2
• Time in Patent Office: Days
• US Class Current: 315/312
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers
• CPC Class Codes: H05B 41/16 in which the lamp is fed by dc or by low-frequency ac, e.g. by 50 cycles/sec ac, or with network frequencies
• CPC Class Codes: H05B 45/00 Circuit arrangements for operating light-emitting diodes [LED]

Abstract

An alternating current (AC) light emitting device includes an AC light emitting diode (LED) module and a waveform modulation unit. The AC LED module includes at least two sets of micro-diodes. The waveform modulation unit coupled between the AC LED module and an AC voltage source modulates a waveform of the AC voltage source.

Claims

1. An alternating current (AC) light emitting device, comprising:

an AC light emitting diode (LED) module comprising at least two sets of micro-diodes; and

a waveform modulation unit, coupled between the AC LED module and an AC voltage source, for modulating a waveform of the AC voltage source.

2. The AC light emitting device according to claim 1, wherein the waveform modulation unit is for increasing a full width at half maximum (FWHM) of the AC voltage source.

3. The AC light emitting device according to claim 1, wherein the waveform modulation unit and the AC LED module are integrated within a chip.

4. The AC light emitting device according to claim 1, wherein the waveform modulation unit and the AC LED module are disposed in a package.

5. The AC light emitting device according to claim 1, wherein the micro-diodes are micro-light emitting diodes.

6. The AC light emitting device according to claim 1, wherein the waveform modulation unit adjusts the waveform of the AC voltage source into a square wave.

7. The AC light emitting device according to claim 1, wherein the AC voltage source modulated by the waveform modulation unit turns on one of the two sets of micro-diodes for a first time in a positive half cycle, and turns on the other one of the two sets of micro-diodes for a second time in a negative half cycle.

8. The AC light emitting device according to claim 7, wherein the first time is longer than the second time.

9. The AC light emitting device according to claim 7, wherein the first time is shorter than the second time.

10. An alternating current (AC) light emitting device, comprising:

an AC light emitting diode (LED) module comprising at least two sets of micro-diodes; and

a frequency modulation unit, coupled between the AC LED module and an AC voltage source, for adjusting a frequency of the AC voltage source.

11. The AC light emitting device according to claim 10, wherein the frequency modulation unit adjusts the frequency of the AC voltage source to be higher than or equal to 60 Hz.

12. The AC light emitting device according to claim 10, wherein the frequency modulation unit adjusts the frequency of the AC voltage source to fall between 100 Hz and 1 KHz.

13. The AC light emitting device according to claim 10, wherein the frequency modulation unit adjusts the frequency of the AC voltage source to fall between 100 Hz and 60 KHz.

14. The AC light emitting device according to claim 10, wherein the AC LED module is packaged in a package containing fluorescent powder.

15. The AC light emitting device according to claim 10, wherein one of the two sets of micro-diodes comprises micro-diodes for outputting a first color, the other one of the two sets of micro-diodes comprises the micro-diodes for outputting a second color.

16. An alternating current (AC) light emitting device, comprising:

a plurality of light emitting diodes (LEDs), wherein at least some of the LEDs have different micro diode areas; and

a control unit for respectively controlling the LEDs, wherein when the LEDs are driven by an AC voltage source, the control unit sequentially turns on the LEDs having the different micro diode areas according to a voltage of the AC voltage source.

17. The AC light emitting device according to claim 16, wherein the control unit controls a current direction of the AC voltage source such that the LEDs withstand forward voltages.

18. The AC light emitting device according to claim 16, wherein the control unit turns on the LEDs with the larger micro diode areas when the voltage of the AC voltage source is lower, and turns on the LEDs with the smaller micro diode areas when the voltage of the AC voltage source is higher.

19. The AC light emitting device according to claim 16, wherein the LEDs are connected in series, and an anode and a cathode of each of the LEDs are electrically connected to the control unit.

20. The AC light emitting device according to claim 19, wherein the LEDs connected in series are sequentially arranged according to sizes of the micro diode areas of the LEDs.

21. The AC light emitting device according to claim 19, wherein each of the LEDs connected in series is connected in parallel to the LED having the micro diode area different from that of the LED.

22. The AC light emitting device according to claim 19, wherein each of the LEDs connected in series is further connected in parallel to the LED having the micro diode area the same as that of the LED.

23. The AC light emitting device according to claim 22, wherein the LEDs connected in series are respectively connected in parallel to the same number of LED/LEDs.

24. The AC light emitting device according to claim 22, wherein the LEDs connected in series are respectively connected in parallel to different numbers of LEDs, the number of LEDs connected in parallel to the LED with the larger micro diode area is smaller, and the number of LEDs connected in parallel to the LED with the smaller micro diode area is greater.

25. The AC light emitting device according to claim 16, wherein the LEDs comprise a first LED string and a second LED string, the first LED string and the second LED string are connected in anti-parallel and controlled by the control unit, the first LED string is driven in a positive half cycle of the AC voltage source, and the second LED string is driven in a negative half cycle of the AC voltage source.

26. The AC light emitting device according to claim 16, further comprising:

a bridge rectifier, electrically connected between the LEDs and the AC voltage source, for rectifying the AC voltage source such that the LEDs withstand forward voltages.

27. The AC light emitting device according to claim 16, wherein the control unit and the LEDs are integrated within a chip or a package, or the control unit is disposed outside the package.

28. An alternating current (AC) light emitting device, comprising:

a control unit; and

a plurality of LEDs each having an anode and a cathode, which are electrically connected to the control unit,

wherein when the LEDs are driven by an AC voltage source, the control unit changes serial or parallel connection states of the LEDs according to a voltage of the AC voltage source so that currents flowing through the LEDs become uniform.

29. The AC light emitting device according to claim 28, wherein the control unit enables most of the LEDs to be connected in parallel when the voltage of the AC voltage source is lower, and enables most of the LEDs to be connected in series when the voltage of the AC voltage source is higher.

30. The AC light emitting device according to claim 28, wherein the control unit controls a current direction of the AC voltage source such that the LEDs withstand forward voltages.

31. The AC light emitting device according to claim 28, wherein the control unit and the LEDs are integrated within a chip or a package, or the control unit is disposed outside the package.