KR20100023400A - Light emitting diode for ac operation - Google Patents

Abstract

PURPOSE: A light emitting diode for an ac operation is provided to improve the photonic efficiency by increasing the number of light emitting cell driven by an AC power. CONSTITUTION: A light emitting diode for the AC comprises a plurality of bridge rectifiers and series arrays(31,32,33). A plurality of bridge rectifiers are serially connected with each other. The series arrays are connected to the bridge rectifiers. Each bridge rectifier is comprised of four bridges(21,22,23,24). A first bridge and a second bridge are connected to an input terminal(41). A third bridge and a fourth bridge are connected to an output terminal(43). The first bridge and the fourth bridge are connected to a first node(45). The second bridge and the third bridge are connected to a second node(47). Each series array is electrically connected to the first node and the second node. The Bridge units comprises at least one light emitting cells.

Description

Light emitting diode for AC {LIGHT EMITTING DIODE FOR AC OPERATION}

The present invention relates to a light emitting diode, and more particularly, to a light emitting diode for alternating current that can be connected and driven without using an external AC-DC converter.

A light emitting diode is an electroluminescent semiconductor device having a structure in which an N-type semiconductor and a P-type semiconductor are bonded to each other, and emit light by recombination of electrons and holes. Such light emitting diodes are widely used as display devices and backlights. In addition, the light emitting diode consumes less power and has a longer lifespan than existing light bulbs or fluorescent lamps, thereby replacing its incandescent lamps and fluorescent lamps, thereby expanding its use area for general lighting.

In general, since the light emitting diode is driven when a forward current flows, the light emitting diode is repeatedly turned on and off according to the direction of the current under an AC power supply. Therefore, when the light emitting diode is directly connected to an AC power source, the light emitting diode may not emit light continuously and may be easily damaged by a reverse voltage.

In order to solve the problem of the light emitting diode, a light emitting diode that can be directly connected to a high voltage AC power source is disclosed in International Publication No. WO 2004/023568 (Al) "Light-Emitting Device Having Light-Emitting Components". EMITTING ELEMENTS, which was disclosed by SAKAI et. Al.

1 is a schematic diagram illustrating a conventional AC light emitting diode.

Referring to FIG. 1, a conventional AC LED includes arrays of light emitting cells 13 connected in series to each other on a substrate 11. The light emitting cells are electrically connected to each other through metal wires. These series arrays are connected in anti-parallel to each other between the pads 15 formed on the substrate 11. Here, the light emitting cells 13 arranged in six columns are shown, and the light emitting cells of the first column 17, the third column, and the fifth column are connected in series to form an array, and the second column. (19), the light emitting cells of the fourth row and the sixth row are connected in series to each other to form another array, and these arrays are connected in anti-parallel between the pads 15.

When an external AC power source is connected to the pads 15, the array of first, third and fifth rows is driven for half a cycle, and the array of second, fourth and sixth rows is driven for the other half cycle. . Accordingly, the light emitting diode emits light by repeatedly turning on and off the arrays under an alternating current power source.

However, since the light emitting diodes are usually AC driven using anti-parallel arrays, only less than half of the light emitting cells emit light on average. Therefore, the conventional AC LED has a low driving efficiency of the light emitting cells formed on the substrate and consequently has a low light efficiency.

Meanwhile, a series array of light emitting cells may be connected to a bridge rectifier to drive a larger number of light emitting cells. However, since the voltage applied to the series array of light emitting cells is applied as a reverse voltage to the diode constituting the bridge rectifier, generally using a plurality of light emitting cells of the AC light emitting diode which is driven under high voltage, for example at 110V or 220V In this case, the bridge diode is likely to be destroyed.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an AC light emitting diode capable of improving light efficiency by increasing the number of light emitting cells driven under an AC power source and achieving stability against reverse voltage.

In order to solve the above problems, the AC LED according to the embodiments of the present invention includes a plurality of bridge rectifiers connected in series with each other and a series array of light emitting cells connected to each bridge rectifier. Meanwhile, each of the bridge rectifiers includes first to fourth bridge parts, and the first and second bridge parts and the third and fourth bridge parts are connected to an input terminal and an output terminal, respectively, and the first and fourth bridge rectifiers. Bridge portions are connected to the first node and the second and third brid portions are coupled to the second node. In addition, each series array is electrically connected to the first node and the second node.

In addition, each of the first to fourth bridge parts may include at least one light emitting cell. The light emitting cells in the first to fourth bridge parts may have the same structure as the light emitting cells in the serial array connected to the first node and the second node. That is, the light emitting cells in the bridge rectifier may be formed together by the same process while forming the light emitting cells in the series array.

In addition, the bridge rectifiers and the series arrays may be formed in a single light emitting diode chip.

New interconnected bridge rectifiers can be connected in parallel to the interconnected bridge rectifiers. Accordingly, a larger number of light emitting cells can be driven under the same AC voltage.

According to embodiments of the present invention, the light efficiency of the AC LED may be increased by increasing the number of light emitting cells driven while securing stability against reverse voltage.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; The following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, widths, lengths, thicknesses, and the like of components may be exaggerated for convenience. Like numbers refer to like elements throughout.

2 is a schematic circuit diagram illustrating an AC LED according to an embodiment of the present invention.

Referring to FIG. 2, the AC LED includes a plurality of bridge rectifiers and series arrays 31, 32, and 33 of light emitting cells connected to each bridge rectifier.

Each bridge rectifier consists of first to fourth bridge portions 21, 22, 23, 24. The first bridge portion 21 and the second bridge portion 22 are connected to the input terminal 41, and the third bridge portion 23 and the fourth bridge portion 24 are connected to the output terminal 43. Here, the input terminal 41 and the output terminal 43 are set for convenience of description and may be inverted depending on the direction of the current input to the AC power source.

The first bridge portion 21 and the second bridge portion 22 are connected to the input terminal 41 so as to be opposite polarities with respect to the voltage applied between the input terminal 41 and the output terminal 43, and the third bridge The unit 23 and the fourth bridge unit 24 are also connected to the output terminal 43 so as to be opposite polarities with respect to the voltage applied between the input terminal 41 and the output terminal 43.

Meanwhile, the first bridge portion 21 and the fourth bridge portion 24 are connected to the first node 45, and the second bridge portion 22 and the third bridge portion 23 are connected to the second node ( 47). The first bridge portion 21 and the fourth bridge portion 24 are connected to the first node 45 so as to be opposite polarities with respect to the voltage applied between the input terminal 41 and the output terminal 43, and the second The bridge portion 22 and the third bridge portion 23 are also connected to the second node 47 so as to be opposite polarities with respect to the voltage applied between the input terminal 41 and the output terminal 43.

The plurality of bridge rectifiers are connected in series by electrically connecting the input terminal 41 and the output terminal 43 of neighboring bridge rectifiers with each other. Thus, the current flowing through the output terminal 43 of one bridge rectifier flows into the input terminal 41 of the bridge rectifier connected thereto.

Meanwhile, the arrays 31, 32, and 33 in which the plurality of light emitting cells are connected in series are electrically connected to the first node 45 and the second node 47 of the bridge rectifier, respectively. The arrays 31, 32, 33 are electrically connected to the first node 45 and the second node 47 so as to be forward with respect to the current input from the AC power source 50, and thus the arrays 31. , 32, 33 are connected in series with each other via bridge portions of the bridge rectifier.

The first to second bridge parts 21 to 24 and the serial arrays 31, 32, and 33 may be formed on a single substrate 51 and disposed in a single light emitting diode chip.

Meanwhile, each of the first to second bridge parts 21 to 24 may include at least one light emitting cell, and may include only light emitting cells. The light emitting cells in the bridge portions may have the same structure as the light emitting cells in the serial arrays 31, 32, and 33, and may be formed by the same process.

In the present embodiment, the bridge rectifiers connected in series with each other are described as being connected to an AC power supply in an array, but the present invention is not limited thereto. That is, as shown in FIG. 3, new series connected bridge rectifiers may be connected in parallel to the array. That is, a new array of serially connected bridge rectifiers can be connected in parallel to the array of bridge rectifiers. A plurality of such new arrays can be connected in parallel to the array of bridge rectifiers. Accordingly, a larger number of light emitting cells can be driven under the same voltage of the AC power supply 50.

The light emitting cells in the bridge parts 21 to 24 and the serial arrays are electrically connected to each other through wires. Such wires may be formed by an air bridge or step cover process.

4 and 5 are partial cross-sectional views illustrating the series arrays 31, 32, and 33 of light emitting cells. 4 is a partial cross-sectional view for describing light emitting cells connected in series by wires formed by an air bridge process, and FIG. 5 is a view for explaining that light emitting cells are connected in series by wires formed by a step cover process. It is a partial cross section.

Referring to FIG. 4, a plurality of light emitting cells 58 are spaced apart from each other on the substrate 51. Each of the light emitting cells includes a first conductive lower semiconductor layer 55, an active layer 57, and a second conductive upper semiconductor layer 59. The active layer 57 may be a single quantum well structure or a multi quantum well structure, and its material and composition are selected according to the emission wavelength required. For example, the active layer may be formed of a gallium nitride-based compound semiconductor. The lower and upper semiconductor layers 55 and 59 may be formed of a material having a larger band gap than the active layer 57, and may be formed of a gallium nitride-based compound semiconductor.

Meanwhile, a buffer layer 53 may be interposed between the lower semiconductor layer 55 and the substrate 51. The buffer layer 53 is employed to mitigate lattice mismatch between the substrate 51 and the lower semiconductor layer 55. The buffer layer 53 may be spaced apart from each other as shown, but is not limited thereto. When the buffer layer 53 is formed of an insulating material or a high resistance material, the buffer layer 53 may be continuous to each other.

As illustrated, the upper semiconductor layer 59 is positioned above a portion of the lower semiconductor layer 55, and the active layer is interposed between the upper semiconductor layer 59 and the lower semiconductor layer 55. In addition, the transparent electrode layer 61 may be positioned on the upper semiconductor layer 59. The transparent electrode layer 61 may be formed of an indium tin oxide film (ITO) or a material such as Ni / Au.

Meanwhile, wirings 67 electrically connect the light emitting cells 58. The wirings 67 connect the lower semiconductor layer 55 of one light emitting cell and the transparent electrode layer 61 of the light emitting cell adjacent thereto. As shown in the drawings, the electrode pad 64 formed on the transparent electrode layer 61 and the electrode pad 65 formed on the exposed region of the lower semiconductor layer 55 may be connected to each other. Here, the wirings 67 are formed by an air bridge process, and portions except for the contact portion are physically separated from the substrate 51 and the light emitting cells 58. The wirings 67 form a series array 31, 32, 33 in which light emitting cells are connected in series on a single substrate 51.

Referring to FIG. 5, the wirings connecting the light emitting cells 58 may be formed by a step cover process. That is, except for portions for contacting the wirings 87, all the layers of the light emitting cells and the substrate 51 are covered with the insulating layer 85. The wirings 87 electrically connect the light emitting cells on the insulating layer 85.

For example, the insulating layer 85 has openings exposing the electrode pads 64 and 65, and the wires 87 open the electrode pads 64 and 65 of adjacent light emitting cells through the openings. Connect the light emitting cells in series with each other.

Meanwhile, the light emitting cells in the bridge parts 21 to 24 may also have the same structure as the light emitting cells in the serial arrays 31, 32, and 33, and may be electrically connected to each other by the same wires as the wires. have.

Hereinafter, the operation of the AC LED according to the embodiments of the present invention under an AC voltage will be described again with reference to FIG. 2.

First, when a positive voltage is applied to the input terminal 41 of the first bridge rectifier among the bridge rectifiers connected in series by an AC power source and a negative voltage is applied to the output terminal 43 of the last (third) bridge rectifier, the current is zero. It is input through the input terminal 41 of the first bridge rectifier, and via the output terminal 43 of the first bridge rectifier via the second bridge portion 22, the first series array 31, and the fourth bridge portion 24. I'm going.

On the other hand, the current flows back into the input terminal 41 of the second bridge rectifier, and again, the second bridge rectifier via the second bridge portion 22, the second series array 32, and the fourth bridge portion 24. Exit through the output terminal 43 of.

This current flows back into the input terminal 41 of the third bridge rectifier, and again through the second bridge portion 22, the third series array 32, and the fourth bridge portion 24. Exit through 43.

Therefore, forward current may flow through the first to third series arrays 31, 32, and 33, and light emitting cells in the arrays may be driven to emit light.

Now, the case where the voltage application direction of the AC power supply is changed will be described.

A current flows through the output terminal 43 of the third bridge rectifier, and the current flows through the third bridge portion 23, the third series array 33, and the first bridge portion 21 of the third bridge rectifier. Exit through input 41 of the third bridge rectifier.

On the other hand, the current from the input terminal 41 of the third bridge rectifier flows into the output terminal 43 of the second bridge rectifier, the third bridge portion 23, the second series array 33, the first bridge portion Exit 21 via input terminal 41 of the second bridge rectifier via 21.

In addition, the current from the input terminal 41 of the second bridge rectifier flows into the output terminal 43 of the first bridge rectifier, and again, the third bridge unit 23, the first series array 33, and the first bridge unit Exit 21 via input terminal 41 of the first bridge rectifier via 21.

Accordingly, even in this case, forward current may flow through the first to third series arrays 31, 32, and 33, and light emitting cells in the arrays may be driven to emit light.

As a result, the light emitting cells in the series arrays 31, 32, and 33 are driven regardless of the direction in which the AC power is applied, so that the number of driven light emitting cells can be increased.

On the other hand, when a current flows through the first bridge portion 21, the first series array 31, and the fourth bridge portion 24, the voltage drop between the input terminal 41 and the first node 45 decreases. The reverse voltage acts on the first bridge portion 21 and the voltage drop between the second node 47 and the output terminal 43 acts on the reverse voltage of the third bridge portion 23.

In the case of connecting a series array of light emitting cells to a single bridge rectifier in an alternating light emitting diode driven at a high voltage, such as 110V or 220V, a large number of light emitting cells are included in the series array, thus the first bridge portion 21 Alternatively, the reverse voltage applied to the third bridge portion 23 also increases considerably. Therefore, there is a high possibility that diodes, particularly light emitting cells, in the first bridge portion 21 or the third bridge portion 23 are destroyed by a high reverse voltage.

This problem appears equally in the second bridge portion 22 and the fourth bridge portion 24 when the polarity of the AC power source is changed.

In contrast, embodiments of the present invention can disperse light emitting cells in first to third series arrays 31, 32, 33 by connecting a plurality of bridge rectifiers in series, thus providing bridge portions 21 and 23, or It is possible to lower the reverse voltage applied to 22 and 24), thereby making it possible to stabilize the light emitting diode for alternating current with respect to the reverse voltage.

1 is a schematic diagram illustrating a light emitting diode for alternating current according to the prior art.

2 is a schematic diagram illustrating an AC LED according to an embodiment of the present invention.

3 is a schematic diagram illustrating an AC LED according to another embodiment of the present invention.

4 is a partial cross-sectional view for describing light emitting cells in an AC LED according to embodiments of the present invention.

5 is a partial cross-sectional view illustrating another example of light emitting cells in an AC LED according to embodiments of the present invention.

Claims (5)

A plurality of bridge rectifiers connected in series with each other; And A series array of light emitting cells coupled to each bridge rectifier, Each bridge rectifier is composed of first to fourth bridge portions, The first and second bridge portions and the third and fourth bridge portions are respectively connected to an input terminal and an output terminal, the first and fourth bridge portions are connected to a first node, and the second and third bridging portions are connected. Is connected to this second node, Wherein each series array is electrically connected to the first node and the second node. The light emitting diode of claim 1, wherein the first to fourth bridge portions each include at least one light emitting cell. The light emitting diode of claim 2, wherein the light emitting cells in the first to fourth bridge parts have the same structure as the light emitting cells in the series array connected to the first node and the second node. The light emitting diode of claim 1, wherein the bridge rectifiers and the series arrays are formed in a single light emitting diode chip. The light emitting diode of claim 1, further comprising new mutually connected bridge rectifiers connected in parallel to the mutually connected bridge rectifiers.

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