Light emitting device for AC power operation

• US 8,188,687 B2
• Filed: 05/09/2006
• Issued: 05/29/2012
• 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, Chung Hoon, Speck, James S., Kim, Hong San, Kim, Jae Jo, Kim, Sung Han, Lee, Jae Ho
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): Chen, Jianzi
• Application Number:
  US11/994,308
• Publication Number:
  US 20080211421A1
• Time in Patent Office: 2,212 Days
• Field of Search: 315/185.R, 315/186, 315/192, 315/193, 315/185.S, 315/200.R, 315/201, 315/203, 315/200.A, 315/209.R, 315/210, 315/226, 315/294, 315/295, 315/312, 315/313, 315/317, 315/320, 315/323, 315/360, 315/362, 362/217, 362/219, 362/221, 362/222, 362/223, 362/227, 362/249, 362/251, 362/252, 362/362, 362/363, 362/375, 362/800, 362/806, 362/812
• US Class Current: 315/323
• 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 comprising a substrate, an array of light emitting cells connected in series on the substrate, another array of light emitting cells connected in series on the substrate, the other array being connected in reverse parallel to the array of the light emitting cells, a source terminal, and a ground terminal; and

switching blocks that are each electrically connected to the source terminal, the ground terminal, and a respective one of a plurality of nodes between each of the light emitting cells, to sequentially turn on and off the light emitting cells, when an AC voltage is applied to the array,

wherein an n-th switching block (n being a positive integer) shorts the ground terminal and a node to which the n-th switching block is connected, when a voltage difference (Vac) 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 (Vac) is greater than (Predetermined Voltage×

(n+1)), and

wherein nodes between the light emitting cells of the other array of light emitting cells are respectively connected to the switching blocks.

2. The light emitting device as claimed in claim 1, wherein the predetermined voltage is a forward voltage of the light emitting cells at a reference current.

3. The light emitting device as claimed in claim 2, wherein the value of the reference current is 15 to 25 mA.

4. 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.

5. A light-emitting device for an AC power operation, the device comprising a light emitting diode chip comprising:

a substrate;

first arrays positioned on the substrate, the first arrays each having a different number of light emitting cells that are all connected to one another in series, the first arrays being connected in parallel to one another;

second arrays positioned on the substrate, the second arrays each having a different numbers of light emitting cells that are all connected to one another in series, the light emitting cells of the second arrays being connected in reverse parallel to the light emitting cells of the first arrays; and

a switching block connected to end portions of each of the arrays and directly connected an AC power source, to individually and sequentially operate to each of the first arrays and the second arrays, depending on a voltage level of the AC power source, such that when one of the arrays is turned on, the other arrays are electrically bypassed by the switching block.

6. The light-emitting device for an AC power operation as claimed in claim 5, 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.

7. The light-emitting device for an AC power operation as claimed in claim 5, wherein corresponding ones of the first and second arrays have the same number of light emitting cells.

8. The light-emitting device for an AC power operation as claimed in claim 7, wherein an array having the greater number of the light emitting cells in the first and second arrays has larger light emitting cells.

9. The light-emitting device for an AC power operation as claimed in claim 5, further comprising a common resistor serially connected in common to the first and second arrays.

10. The light-emitting device for an AC power operation as claimed in claim 5, 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.

11. The light-emitting device for an AC power operation as claimed in claim 10, 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.

12. The light-emitting device for an AC power operation as claimed in claim 10, 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.

13. A light emitting device, comprising:

a plurality of light emitting diode (LED) chips, each LED chip comprising;

a substrate,

an array of light emitting cells connected in series through metal wires on the substrate, each light emitting cell comprising a first conductive type semiconductor layer, a second conductive type semiconductor layer and an active layer interposed between the first conductive type semiconductor layer and the second conductive type layer, the light emitting cells being isolated from each other, and

an electrode formed on the second conductive type semiconductor layer, the electrode being a transparent electrode through which light is transmittable,

wherein the substrate has a partial region exposed by removing the second conductive type semiconductor layer, the active layer and the first conductive type semiconductor layer;

a source terminal;

a ground terminal; and

switching blocks that are each electrically connected to the source terminal, the ground terminal, and a respective one of a plurality of nodes between the LED chips, to sequentially turn on and off the LED chips, when an AC voltage is applied to the array,

wherein an n-th switching block (n being a positive integer) shorts the ground terminal and a node to which the n-th switching block is connected, when a voltage difference (Vac) 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 (Vac) is greater than (Predetermined Voltage×

(n+1)), and

wherein nodes between the LED chips are respectively connected to the switching blocks.