Light Emitting Device For Ac Power Operation

• US 20080211421A1
• Filed: 05/09/2006
• Published: 09/04/2008
• Est. Priority Date: 06/28/2005
• Status: Active Grant

• Current Assignee: Seoul Viosys Co., Ltd. (Seoul Semiconductor Co., Ltd.)
• Original Assignee: Seoul Optodevice Company Limited (Seoul Semiconductor Co., Ltd.)
• Inventors: Lee, Jae Ho, Speck, James S., Kim, Hong San, Lee, Chung Hoon, Kim, Sung Han, Kim, Jae Jo
• Granted Patent: US 8,188,687 B2
• Time in Patent Office: Days
• US Class Current: 315/250
• CPC Class Codes: H01L 2224/48137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 2224/49107 on the semiconductor or solid-state body
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 27/153 in a repetitive configuration, e.g. LED bars
• CPC Class Codes: H01L 27/156 two-dimensional arrays
• CPC Class Codes: H05B 33/02 Details
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/40 Details of LED load circuits
• CPC Class Codes: H05B 45/42 Antiparallel configurations
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: H05B 47/155 Coordinated control of two or more light sources

Abstract

Disclosed is an improved light-emitting device for an AC power operation. A conventional light emitting device employs an AC light-emitting diode having arrays of light emitting cells connected in reverse parallel. The arrays in the prior art alternately repeat on/off in response to a phase change of an AC power source, resulting in short light emission time during a ½ cycle and the occurrence of a flicker effect. An AC light-emitting device according to the present invention employs a variety of means by which light emission time is prolonged during a ½ cycle in response to a phase change of an AC power source and a flicker effect can be reduced. For example, the means may be switching blocks respectively connected to nodes between the light emitting cells, switching blocks connected to a plurality of arrays, or a delay phosphor. Further, there is provided an AC light-emitting device, wherein a plurality of arrays having the different numbers of light emitting cells are employed to increase light emission time and to reduce a flicker effect.

Claims

1. A light emitting device, comprising:

a light emitting diode (LED) chip having an array of light emitting cells connected in series; and

switching blocks connected to nodes between the light emitting cells, respectively,

wherein the light emitting cells are sequentially turned on and off by the switching blocks when the array is connected to and driven by an AC voltage power source.

2. The light emitting device as claimed in claim 1, wherein the switching blocks are connected to source and ground terminals of the array;

and

an n-th switching block shorts the ground terminal and a node to which the n-th switching block is connected when a voltage difference (V_ac) between the source and ground terminals is in a range of (Predetermined Voltage×

n) to (Predetermined Voltage×

(n+1)), and opens the node from the ground terminal if the voltage difference (V_ac) is greater than (Predetermined Voltage×

(n+1)).

3. The light emitting device as claimed in claim 2, wherein the predetermined voltage is a forward voltage of the light emitting cells at a reference current.

4. The light emitting device as claimed in claim 3, wherein the value of the reference current is 15 to 25 mA.

5. The light emitting device as claimed in claim 1, wherein the light emitting cells are turned off in an order reverse to the order in which the light emitting cells are turned on.

6. The light emitting device as claimed in claim 1, further comprising another array of light emitting cells connected in series, the another array being connected in reverse parallel to the array of the light emitting cells connected in series.

7. The light emitting device as claimed in claim 6, wherein nodes between the light emitting cells within the another array of the light emitting cells connected in series are connected to the switching blocks, respectively.

8. A light-emitting device for an AC power operation, the device comprising:

a substrate;

a plurality of first arrays positioned on the substrate and having different numbers of light emitting cells connected in series, the first arrays being connected in parallel to one another; and

a plurality of second arrays positioned on the substrate and having different numbers of light emitting cells connected in series, the second arrays being connected in reverse parallel to the first arrays.

9. The light-emitting device for an AC power operation as claimed in claim 8, further comprising a switching block for controlling light emission of each of the plurality of first and second arrays depending on a voltage level of an AC power source.

10. The light-emitting device for an AC power operation as claimed in claim 9, wherein one terminal of each of the first and second arrays is connected in common to a first power source connection terminal, and the other terminals thereof are connected to second power source connection terminals, respectively.

11. The light-emitting device for an AC power operation as claimed in claim 10, wherein the switching block is connected between the second power source connection terminals and the AC power source to form a current path depending on the voltage level of the AC power source.

12. The light-emitting device for an AC power operation as claimed in claim 8, wherein each of the second arrays has the same number of light emitting cells as each of the corresponding arrays in the first arrays.

13. The light-emitting device for an AC power operation as claimed in claim 12, wherein an array having the greater number of the light emitting cells in the first and second arrays has larger light emitting cells.

14. The light-emitting device for an AC power operation as claimed in claim 8, further comprising:

first resistors connected in series to the first arrays, respectively; and

second resistors connected in series to the second arrays, respectively.

15. The light-emitting device for an AC power operation as claimed in claim 14,

wherein the first resistors have different resistance values;

the second resistors have different resistance values; and

the first and second resistors are respectively connected in series to the first and second arrays in such a manner that a resistor with a larger resistance value is connected to an array having the smaller number of the light emitting cells.

16. The light-emitting device for an AC power operation as claimed in claim 15, wherein the second resistors have resistance values corresponding to those of the first resistors, respectively.

17. The light-emitting device for an AC power operation as claimed in claim 14, wherein the first and second resistors are positioned on the substrate.

18. The light-emitting device for an AC power operation as claimed in claim 8, further comprising a common resistor serially connected in common to the first and second arrays.

19. The light-emitting device for an AC power operation as claimed in claim 8, wherein in each of the first and second arrays, light emitting cells within an array having the smallest number of the light emitting cells have luminous intensity larger than that of light emitting cells within an array having the greatest number of the light emitting cells.

20. The light-emitting device for an AC power operation as claimed in claim 19, wherein the light emitting cells within the array having the smallest number of the light emitting cells have roughened surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells.

21. The light-emitting device for an AC power operation as claimed in claim 19, wherein the light emitting cells within the array having the smallest number of the light emitting cells have inclined side surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells.

22. A light-emitting device for an AC power operation, the device comprising:

a substrate;

a plurality of arrays positioned on the substrate and having different numbers of light emitting cells connected in series, the arrays being connected in parallel to one another; and

a bridge rectifier two nodes of which are electrically connected to both end portions of the arrays, respectively.

23. The light-emitting device for an AC power operation as claimed in claim 22, wherein the bridge rectifier is positioned on the substrate.

24. The light-emitting device for an AC power operation as claimed in claim 22, further comprising a switching block connected between one end portions of the arrays and one of the nodes of the bridge rectifier to control light emission of each of the plurality of the arrays depending on a voltage level of an AC power source.

25. The light-emitting device for an AC power operation as claimed in claim 22, further comprising resistors positioned between the bridge rectifier and the plurality of the arrays and connected in series to the plurality of the arrays, respectively.

26. The light-emitting device for an AC power operation as claimed in claim 25, wherein the resistors have different resistance values and are respectively connected in series to the plurality of arrays in such a manner that a resistor with a larger resistance value is connected to an array having the smaller number of the light emitting cells.

27. The light-emitting device for an AC power operation as claimed in claim 22, further comprising a common resistor serially connected in common to the plurality of arrays.

28. The light-emitting device for an AC power operation as claimed in claim 22, wherein an array having the greater number of the light emitting cells in the plurality of arrays has larger light emitting cells.

29. The light-emitting device for an AC power operation as claimed in claim 22, wherein in the plurality of arrays, light emitting cells within an array having the smallest number of the light emitting cells have luminous intensity larger than that of light emitting cells within an array having the greatest number of the light emitting cells.

30. The light-emitting device for an AC power operation as claimed in claim 29, wherein the light emitting cells within the array having the smallest number of the light emitting cells have roughened surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells.

31. The light-emitting device for an AC power operation as claimed in claim 29, wherein the light emitting cells within the array having the smallest number of the light emitting cells have inclined side surfaces so that they can have luminous intensity larger than that of the light emitting cells within the array having the greatest number of the light emitting cells.

32. A light-emitting device for an AC power operation, the device comprising:

an LED chip having a plurality of light emitting cells;

a transparent member for covering the LED chip; and

a delay phosphor excited by light emitted from the light emitting cells to emit light in a visible light range.

33. The light-emitting device for an AC power operation as claimed in claim 32, wherein the delay phosphor is positioned between the LED chip and the transparent member, or dispersed within the transparent member.

34. The light-emitting device for an AC power operation as claimed in claim 32, wherein the delay phosphor has a decay time of 1 msec to 10 hours.

35. The light-emitting device for an AC power operation as claimed in claim 32, further comprising another phosphor excited by light emitted from the LED chip to emit light in a visible light range.