A THREE-DIMENSIONAL LATTICE STRUCTURE BASED LED ARRAY FOR ILLUMINATION

Abstract: A lighting system comprising a plurality of light-emitting diodes and a power supply source for driving current through a plurality of parallel disposed, electrically conductive branches, wherein the branches comprise at least one cell. The branches are configured to display the light-emitting diodes according to a three-dimensional arrangement. In each cell, each branch has a light-emitting diode with an anode terminal and a cathode terminal. The anode terminal of each light-emitting diode is coupled to the cathode terminal of a light-emitting diode of an adjacent branch via a shunt. The shunt further comprises a light-emitting diode. In each cell, each light-emitting diode may have a different forward voltage characteristic, while still insuring that all of the light-emitting diodes in the arrangement have the same brightness. Upon failure of one light-emitting diode in a cell, the remaining light-emitting diodes in the same cell are not extinguished and, in a multiple cell embodiment, the light-emitting diodes in the successive cells are not extinguished.

Description: A three-dimensional lattice structure based led array for illumination This invention relates generally to lighting systems, and more particularly to an improved three-dimensional array structure for light-emitting diodes used as illumination sources A light-emitting diode (LED) is a type of semiconductor device, specifically a p-n junction, which emits electromagnetic radiation upon the introduction of current thereto Typically, a light-emitting diode compπses a semiconducting mateπal that is a suitably chosen gallium-arsenic-phosphorus compound By varying the ratio of phosphorus to arsenic, the wavelength of the light emitted by a light-emitting diode can be adjusted With the advancement of semiconductor matenals and optics technology, light-emittmg diodes are increasingly being used for illumination purposes For instance, high bnghtness light-emitting diodes are currently being used in automotive signals, traffics lights and signs, large area displays, etc In most of these applications, multiple light-emittmg diodes are connected in an array structure so as to produce a high amount of lumens Figure 1 illustrates a typical arrangement of light-emittmg diodes 1 through m connected in senes Power supply source 4 delivers a high voltage signal to the light-emitting diodes via resistor R j , which controls the flow of current signal in the diodes Light-emitting diodes which are connected in this fashion usually lead to a power supply source with a high level of efficiency and a low amount of thermal stresses Occasionally, a light-emitting diode may fail The failure of a light-emittmg diode may be either an open-circuit failure or a short-circuit failure For instance, in short- circuit failure mode, light-emitting diode 2 acts as a short-circuit, allowing current to travel from light-emitting diode 1 to 3 through light-emitt g diode 2 without generating a light On the other hand, in open-circuit failure mode, light-emittmg diode 2 acts as an open circuit, and as such causes the entire array illustrated in Figure 1 to extinguish In order to address this situation, other arrangements of light-emitting diodes have been proposed For instance, Figure 2(a) illustrates another typical arrangement of ght- emitting diodes which consists of multiple branches of light-emitting diodes such as 10, 20, 30 and 40 connected in parallel. Each branch compπses light-emittmg diodes connected in seπes. For instance, branch 10 compπses light-emitting diodes 11 through n j connected in seπes. Power supply source 14 provides a cuπent signal to the light-emitting diodes via resistor R ?. Light-emittmg diodes which are connected in this fashion have a higher level of reliability than light-emittmg diodes which are connected according to the arrangement shown m Figure 1. In open-circuit failure mode, the failure of a light-emitting diode in one branch causes all of the light-emittmg diodes in that branch to extinguish, without significantly effecting the light-emitting diodes in the remaining branches. However, the fact that all of the light-emitting diodes in a particular branch are extinguished by an open-circuit failure of a single light-emitting diode is still an undesirable result. In short-circuit failure mode, the failure of a light-emittmg diode in a first branch may cause that branch to have a higher current flow, as compared to the other branches. The increased current flow through a single branch may cause it to be illuminated at a different level than the light-emitting diodes in the remaining branches, which is also an undesirable result. Still other arrangements of light-emittmg diodes have been proposed in order to remedy this problem. For instance, Figure 2(b) illustrates another typical arrangement of light-emitting diodes, as employed by a lighting system of the pπor art. As in the aπangement shown in Figure 2(a), Figure 2(b) illustrates four branches of light-emitting diodes such as 50, 60, 70 and 80 connected m parallel. Each branch further compπses hght- emitting diodes connected in seπes. For instance, branch 50 compπses light-emitt g diodes 51 through n^ connected seπes. Power supply source 54 provides current signals to the light-emittmg diodes via resistor R3. The arrangement shown in Figure 2(b) further compπses shunts between adjacent branches of light-emitting diodes. For instance, shunt 55 is connected between hght- emitting diodes 51 and 52 of branch 50 and between light-emitting diodes 61 and 62 of branch 60. Similarly, shunt 75 is connected between light-emittmg diodes 71 and 72 of branch 70 and between light-emitting diodes 81 and 82 of branch 80 Light-emittmg diodes which are connected in this fashion have a still higher level of reliability than light-emittmg diodes which are connected according to the arrangements shown in either Figures 1 or 2(a). This follows because, in an open-circuit failure mode, an entire branch does not extinguish because of the failure of a single light- emitting diode in that branch. Instead, cuπent flows via the shunts to bypass a failed hght- emitting diode. In the short-circuit failure mode, a light-emittmg diode which fails has no voltage across it, thereby causing all of the current to flow through the branch having the failed light-emittmg diode For example, if light-emitting diode 51 short circuits, cuπent will flow through the upper branch. Thus, in the arrangement shown in Figure 2(b), when a single light-emittmg diode short circuits, the corresponding light-emittmg diodes 61, 71 and 81 m each of the other branches are also extinguished The arrangement shown in Figure 2(b) also expeπences other problems. For instance, in order to insure that all of the light-emittmg diodes in the arrangement have the same bπghtness, the arrangement requires that parallel connected light-emitting diodes have matched forward voltage characteπ sties. For instance, light-emittmg diodes 51, 61, 71 and 81, which are parallel connected, must have tightly matched forward voltage characteπstics Otherwise, the cuπent signal flow through the light-emitting diodes will vary, resulting in the light-emitting diodes having dissimilar bπghtness. In order to avoid this problem of varying bπghtness, the forward voltage characteπstics of each light-emitting diode must be tested pπor to its usage. In addition, sets of light-emittmg diodes with similar voltage characteπstics must be bmned into tightly grouped sets (i.e.- sets of light-emitting diodes for which the forward voltage characteπstics are nearly identical). The tightly grouped sets of light-emitting diodes must then be installed in a light-emittmg diode arrangement parallel to each other. This binning process is costly, time-consuming and inefficient. A light-emitting diode aπangement was proposed in Applicant's co-pending application, designated as Attorney Docket Number 755-003, which is incorporated herein b\ reference as fully as if set forth in its entirety. However, there exists a further need for an improved three-dimensional light-emittmg diode arrangement which does not suffer from the problems of the pπor art In accordance with one embodiment of the present invention, a lighting system compπses a plurality of light-emitting diodes. The lighting system further compπses a cuπent dπver for dπving a cuπent signal through a plurality of parallel disposed, electrically conductive branches, wherein the branches are configured to form a three-dimensional aπangement Each light-emittmg diode in one branch together with corresponding light- emitting diodes in the remaining branches define a cell unit. In each cell, the anode terminal of each light-emitting diode in one branch is coupled to the cathode terminal of a coπesponding light-emitting diode of an adjacent branch via a shunt. According to one embodiment, each shunt further comprises a light-emitting diode. The three-dimensional arrangement enables the lighting system to be viewed from various different directions, thus rendering the system particularly well-suited for applications such as desk lamps, traffic signals, safety lights, advertising signs, etc. In another embodiment, the three-dimensional arrangement is configured such that each of the light- emitting diodes is arranged on a panel for display. In one embodiment of the invention, the lighting system comprises three branches and has a triangular cross-section. In another embodiment, the lighting system comprises six branches and has a hexagonal cross-section, irrespective of the number of branches, the lighting system may also comprise at least one central branch having additional branches disposed therearound. In one embodiment of the invention, at least one of the branches are coupled to the central branch, while in another embodiment, each of the branches are coupled to the central branch. In still another embodiment, each branch of a cell is coupled to two or more other branches in the cell. Thus, in each cell, the anode terminal of a light-emitting diode in one branch may be coupled to the cathode terminal of coπesponding light-emitting diodes of a plurality of adjacent branches via shunts. According to this embodiment, each of the shunts may further comprise a light-emitting diode. The aπangement of light-emitting diodes according to the present invention enables the use of light-emitting diodes having different forward voltage characteristics, while still insuring that all of the light-emitting diodes in the aπangement have substantially the same brightness. Advantageously, the lighting system of the present invention is configured such that, upon failure of one light-emitting diode in a branch, the remaining light-emitting diodes in that branch are not extinguished. In another embodiment, the lighting system comprises at least two cells which are cascading, wherein the cascading cells are successively coupled such that the cathode terminal of each light-emitting diode in a branch is coupled to an anode terminal of a light-emitting diode of the same branch in a next successive cell. In a prefeπed embodiment, each branch of the lighting system includes a cuπent-regulating element, such as a resistor, coupled for example, as the first and the last element in each branch. The present invention will be further understood from the following descnption with reference to the accompanying drawings, in which Figure 1 illustrates a typical aπangement of light-emitting diodes, as employed by a lighting system of the pπor art, Figure 2(a) illustrates another typical aπangement of light-emitting diodes, as employed by a lighting system of the pπor art, Figure 2(b) illustrates another typical arrangement of light-emitting diodes, as employed by a lighting system of the pπor art, Figure 3(a) illustrates a three-dimensional arrangement of ght- emitting diodes, in accordance with one embodiment of the present invention, Figure 3(b) illustrates a cross-section of the three-dimensional aπangement, in accordance with one embodiment of the present invention, Figure 3(c) illustrates an extended cross-section of the three- dimensional arrangement of light-emitting diodes, in accordance with another embodiment of the present invention, Figure 4(a) illustrates another three-dimensional aπangement of light- emittmg diodes, in accordance with one embodiment of the present invention, Figure 4(b) illustrates a cross-section of the three-dimensional arrangement, m accordance with one embodiment of the present invention, Figure 4(c) illustrates an extended cross-section of the three- dimensional aπangement of light-emitting diodes, in accordance with another embodiment of the present invention, Figure 5(a) illustrates still another three-dimensional arrangement of light-emittmg diodes, in accordance with one embodiment of the present invention, Figure 5(b) illustrates a cross-section of the three-dimensional aπangement, in accordance with one embodiment of the present invention, and Figure 5(c) illustrates an extended cross-section of the three- dimensional aπangement of light-emitting diodes, m accordance with another embodiment of the present invention Figure 3(a) illustrates an arrangement 100 of light-emitting diodes, as employed by a lighting system, according to one embodiment of the present invention The lighting system compπses a plurality of electπcally-conductive branches, wherein the branches are configured to form a three-dimensional arrangement. It is noted that, in accordance with vaπous embodiments of the present invention, the aπangement may be configured such that each of the light-emitting diodes is arranged on a panel for displa} In the embodiment shown, the lighting system compπses three branches and has a tπangular cross-section. The tπangular cross-section is also illustrated in Figure 3(b). although the present invention is not limited in scope in this regard. Each of the branches 102(a), 102(b) and 102(c) of Figure 3(a) is designated as br -ch end nodes 102(a), 102(b) and 103(c) in Figure 3(b) Figure 3(c) illustrates another emoodiment, in which the tπangular cross-section is repeated, on each of its sides, so as to form three additional tnangular cross- sections, with a total of six branches, wherein the end of each branch is designated by branch end nodes 102(a) through 102(f) The present invention contemplates that any number of branches and any shape of cross-section may be employed Returning to Figure 3(a), each branch has light-emittmg diodes which are connected in seπes. A set of coπespondmg light-emitting diodes of all branches defines a cell. The aπangement shown in Figure 3(a) illustrates cascading cells 101(a), 101(b) through 101(n) of light-emitting diodes. It is noted that, in accordance with vaπous embodiments of the present invention, any number of cells may be formed Each cell 101 of arrangement 100 compnses a first light-emittmg diode (such as light-emittmg diode 110) of branch 102(a), a first hght-emitting diode (such as light- emittmg diode 111) of branch 102(b), and a first light-emitting diode (such as light-emittmg diode 116) of branch 102(c). Each of the branches having the light-emitting diodes are initially (i.e - before the first cell) coupled in parallel via resistors (such as resistors 103, 104 and 105) The resistors preferably have the same resistive values, to insure that an equal amount of cuπent is received via each branch The anode terminal of the light-emittmg diode m each branch is coupled to the cathode terminal of coπesponding light-emitting diodes in adjacent branches For example, the anode terminal of light-emittmg diode 110 is connected to the cathode terminal of light- emittmg diode 111 by a shunt (such as shunt 114) having a light-emittmg diode (such as light-emittmg diode 112) connected therein. Furthermore, the anode terminal of light- emittmg diode 110 is connected to the cathode terminal of light-emitting diode 116 by a shunt (such as shunt 124) having a light-emitting diode (such as light-emitting diode 121) connected therein. Similarly, the anode terminal of light-emitting diode 111 is connected to the cathode terminal of light-emitting diode 110 by a shunt (such as shunt 115) having a light- emitting diode (such as light-emitting diode 113) connected therein. The anode terminal of light-emitting diode 111 is also connected to the cathode terminal of light-emitting diode 116 by a shunt (such as shunt 120) having a light-emitting diode (such as light-emitting diode 118) connected therein. Power supply source 199 provides a cuπent signal to the light- emitting diodes via resistors 103, 104 and 105. Additional resistors 106, 107 and 108 are employed in arrangement 100 at the cathode terminals of the last light-emitting diodes in each branch. Light-emitting diodes which are connected according to the aπangement shown in Figure 3(a) have a level of reliability which is comparable to light-emitting diodes which are connected according to the arrangement shown in Figure 2(b). This follows because, in open-circuit failure mode, an entire branch does not extinguish because of the failure of a light-emitting diode in that branch. Instead, cuπent flows via shunts 114, 115, etc. to bypass a failed light-emitting diode. For instance, if light-emitting diode 110 of Figure 3(a) fails, cuπent still flows to (and thereby illuminates) light-emitting diode 140 via branch 102(b) and light-emitting diode 113, and via branch 102(c) and light-emitting diode 122. In addition, cuπent from branch 102(a) still flows to adjacent branches 102(b) and 102(c) via shunts 114 and 124, respectively. Furthermore, in short-circuit failure mode, light-emitting diodes in other branches and shunts do not extinguish because of the failure of a light-emitting diode in one branch. This follows because the light-emitting diodes are not connected in parallel. For example, if light-emitting diode 110 short circuits, current will flow through upper branch 102(a), which has no voltage drop, and will also flow through light-emitting diodes 112 and 121 in shunts 114 and 124, respectively. Light-emitting diodes 112 and 121 remain illuminated because the current flowing through them drops only a small amount, unlike that which occurs in the aπangement of Figure 2(b). Light-emitting diodes 111 and 116, and the shunts which are coupled to their input terminals, also remain illuminated because a cuπent flow is maintained through them via branches 102(b) and 102(c). In addition, arrangement 100 of light-emitting diodes also alleviates other problems experienced by the light-emitting diode arrangements of the prior art. For instance, light-emitting diode aπangement 100 of the present invention, according to one embodiment. insures that all of the light-emitting diodes in the arrangement have the same bπghtness without the requirement that the light-emitting diodes have tightly matched forward voltage characteπstics. For instance, hght-emitting diodes 110, 111, 112, 113, 116, 117, 118. 121 and 122 of the aπangement shown in Figure 3(a) may have forward voltage characteπstics which are not as tightly matched as the forward voltage characteπstics of light-emitting diodes 51 , 61, 71 and 81 of the arrangement shown in Figure 2(b) This follows because, unlike the arrangements of the pπor art, the light-emitting diodes in cell 101 of arrangement 100 are not parallel-connected to each other. Because light-emitting diodes in each cell are not parallel-connected, the voltage drop across the diodes does not need to be the same Therefore, forward voltage characteπstics of each light-emitting diode need not be equal to others in order to provide similar amounts of illumination. In other words, the cuπent flow through a light-emitt g diode having a lower forward voltage will not increase in order to equalize the forward voltage of the light-emitting diode with the higher forward voltage of another light-emitting diode. Because it is not necessary to have light-emitting diodes with tightly matched forward voltage characteπstics, the present invention alleviates the need for binning hght- emitting diodes with tightly matched voltage characteπstics. Therefore, the present invention reduces the additional manufactuπng costs and time which is necessitated by the binning operation of pπor art light-emitting diode arrangements. Figure 4(a) illustrates a three-dimensional arrangement 200 of hght-emitting diodes, as employed by a lighting system, according to another embodiment of the present invention. The aπangement shown in Figure 4(a) again illustrates a three-dimensional lattice structure having cascading cells 201(a), 201(b) through 201(n) of hght-emitting diodes. In accordance with vaπous embodiments of the present invention, any number of cells 201 may be connected in cascading fashion. It is noted that, in accordance with other embodiments of the present invention and as previously mentioned, the aπangement may be configured such that each of the light-emittmg diodes is arranged on a panel for display In the embodiment shown in Figure 4(a), the lighting system compπses six branches and has a hexagonal cross-section. The hexagonal cross-section is also illustrated m Figure 4(b), although the present invention is not limited in scope in this regard. Each of the branches 202(a) through 202(f) of Figure 4(a) is designated as branch end nodes 202(a) through 202(f) m Figure 4(b) Figure 4(c) illustrates another embodiment, in which the hexagonal cross-section is repeated, on each of its sides, so as to form six additional hexagonal cross-sections with a total of twenty-four branches, wherein the end of each branch is designated by branch end nodes 202(a) through 202(x) The present invention contemplates that any number of branches and any shape of cross-section may be employed Returning to Figure 4(a), each cell 201 of arrangement 200 compπses coπesponding light-emitting diodes from six branches 202(a) through 202(f) Branches 202(a) through 202(f) are initially (I e - before the first cell) coupled in parallel via resistors 203 through 208, respectively The resistors preferably have the same resistive values, to insure that an equal amount of current is received via each branch Power supply source 299 provides cuπent to the light-emitting diodes via resistors 203 through 208 Additional resistors (such as those shown as resistors 209 through 212) are employed in arrangement 200 at the cathode terminals of the last light-emitting diodes in the arrangement shown In each cell, the anode terminal of the light-emitting diode in a branch is coupled to the cathode terminal of the light-emitting diode an adjacent branch by a shunt having a light-emitting diode connected therein Thus, between adjacent branches 202(a) and 202(b), the anode terminal of light-emitting diode 210 is coupled to the cathode terminal of light-emittmg diode 211 by shunt 214 having light-emitting diode 212 connected therein. In addition, the anode terminal of light-emittmg diode 211 is coupled to the cathode terminal of light-emitting diode 210 by shunt 215 having light-emittmg diode 213 connected therein Similarly, between adjacent branches 202(b) and 202(c), the anode terminal of light-emitting diode 211 is connected to the cathode terminal of light-emitting diode 216 by shunt 220 Shunt 220 has light-emitting diode 218 connected therein. The anode terminal of light-emittmg diode 216 is connected to the cathode terminal of light-emittmg diode 211 by shunt 219 Shunt 219 has light-emittmg diode 217 connected therein. In addition, between adjacent branches 202(f) and 202(a), the anode terminal of light-emitting diode 225 is connected to the cathode terminal of light-emittmg diode 210 by shunt 223. Shunt 223 has light-emitting diode 222 connected therein. The anode terminal of light-emitting diode 210 is connected to the cathode terminal of light-emitting diode 225 by shunt 224 Shunt 224 has light-emitting diode 221 connected therein. Though not shown in Figure 4(a), additional light-emittmg diodes are coupled to branches 202(d) and 202(e), each of which are also coupled to adjacent branches so as to have shunts with light-emittmg diodes therebetween. In addition, it is noted that, in accordance with vaπous other embodiments of the present invention, each of the branches m a cell may be coupled via shunts to any or all of the other branches in the cell, not merely those that are closest in proximity thereto Thus, for example, branch 202(a) may be coupled via shunts to 202(c), 202(d) or 202(e) in addition to be coupled to branches 202(b) and 202(f) as shown in Figure 4(a). Light-emitting diodes which are connected according to the three-dimensional aπangement shown in Figure 4(a) have a high level of reliability because, in open-circuit failure mode, an entire branch does not extinguish because of the failure of a light-emitt g diode in that branch. Instead, cuπent flows via the shunts (e.g.- shunts 214 or 215, etc.), to bypass a failed light-emittmg diode. For instance, if light-emitting diode 211 of Figure 4(a) fails and is an open circuit, cuπent still flows to (and thereby illuminates) light-emitting diode 241 via branch 202(a) and light-emitting diode 212, and via branch 202(c) and ght- emitting diode 218 In addition, current from branch 202(b) still flows to the adjacent branches 215 and 219. Furthermore, in short-circuit failure mode, light-emittmg diodes in other branches and shunts do not extinguish because of the failure of a light-emitting diode in one branch. This follows because the light-emitting diodes are not connected in parallel. For example, if light-emitting diode 210 short circuits, cuπent will flow through upper branch 202(a), which has no voltage drop, and will also flow through light-emitting diodes 212 and 221 in shunts 214 and 224, respectively. Light-emitt g diodes 212 and 221 remain illuminated because the current flowing through them drops only a small amount, unlike that which occurs in the arrangement of Figure 2(b). Light-emitting diodes 211, 216, etc. and the shunts which are coupled to their input terminals, also remain illuminated because a cuπent flow is maintained through them via branches 202(b) through 202(f). As in the previously descπbed embodiments, the light-emittmg diode aπangement shown in Figure 4(a) also alleviates the problem expeπenced by the aπangements of the pπor art, which require that the light-emittmg diodes in a cell have tightly matched forward voltage characteπstics. For instance, the light-emitting diodes in cell 201 of arrangement 200, specifically light-emitting diodes 210 through 225, are not parallel- connected to each other such as to cause the cuπent flow through an light-emittmg diode having a lower forward voltage to increase in order to equalize the forward voltage of the light-emittmg diode with the higher forward voltage of another light-emitting diode Thus, the present invention reduces the additional manufactuπng costs and time which is necessitated by the binning operation of pπor art light-emittmg diode aπangements. Figure 5(a) illustrates a three-dimensional arrangement 300 of light-emitt g diodes, as employed by a lighting system, according to still another embodiment of the present invention. The aπangement shown in Figure 5(a) again illustrates a three-dimensional lattice structure having cascading cells 301 of light-emitting diodes It is noted that, in accordance with vaπous embodiments of the present invention, any number of cells 301 may be connected m cascading fashion. In the embodiment shown in Figure 5(a), the lighting system compπses seven branches (six outer branches and one central branch) and has a hexagonal cross-section. The hexagonal cross-section is also illustrated in Figure 5(b), although the present invention is not limited in scope in this regard. Each of the branches 302(a) through 302(g) of Figure 5(a) is designated as branch end nodes 302(a) through 302(g) in Figure 5(b). Figure 5(c) illustrates another embodiment, in which the hexagonal cross-section is repeated, on each of its sides, so as to form six additional hexagonal cross-sections with a total of thirty-one branches, wherein the end of each branch is designated by branch end nodes 302(a) through 302(ee). The present invention contemplates that any number of outer branches and central branches may be employed. It is also noted that the terms "outer" and "central" merely descπbe one possible proximity, and that the arrangement may be configured differently from that shown in Figure 5(a). Returning to Figure 5(a), aπangement 300 compπses branches 302(a) through 302(g), each branch having a plurality of light-emitting diodes coupled in seπes A set of coπesponding light-emitting diodes of each branch (together with coupling shunts which are further explained below), compπses a cell unit. Each cell 301 of arrangement 300 compπses a set of coπesponding light-emitting diodes from the six outer branches 302(a) through 302(f). In addition, cells 301 compπses a central branch 302(g), to which, according to one embodiment, each of the outer branches are connected. According to vaπous other embodiments of the invention, central branch 302(g) is coupled to one or more of outer branches 302(a) through 302(f). Though only a single central branch is shown in Figure 5(a), the present invention contemplates that more than one centrally-disposed branches may be employed. As previously mentioned, each cell 301 of aπangement 300 compπses a first light-emitting diode (such as light-emitting diode 310) of branch 302(a), a first light-emittmg diode (such as light-emittmg diode 311) of branch 302(b), and a first light-emitting diode (such as light-emittmg diode 316) of central branch 302(g). Each of the branches having the light-emittmg diodes are initially (i.e.- before the first cell) coupled in parallel via resistors (such as resistors 303, 304 and 305). The resistors preferably have predetermined resistive values, to insure that an equal amount of cuπent is received via each branch. The anode terminal of the light-emitting diode in each branch is coupled to the cathode terminal of corresponding light-emitting diodes in other branches. For example, the anode terminal of light-emitting diode 310 is connected to the cathode terminal of hght- emittmg diode 311 by a shunt (such as shunt 314) having a light-emittmg diode (such as light-emitting diode 312) connected therein. Furthermore, the anode terminal of ght- emitting diode 310 is connected to the cathode terminal of light-emitting diode 316 by a shunt (such as shunt 324) having a light-emitting diode (such as light-emittmg diode 321 ) connected therein. Similarly, the anode terminal of light-emittmg diode 311 is connected to the cathode terminal of light-emittmg diode 310 by a shunt (such as shunt 315) having a hght- emitting diode (such as light-emittmg diode 313) connected therein. The anode terminal of light-emitting diode 311 is also connected to the cathode terminal of light-emittmg diode 316 by a shunt (such as shunt 320) having a light-emitting diode (such as light-emitting diode 318) connected therein. Power supply source 399 provides a cuπent signal to the light- emitting diodes via resistors 303 through 308. Additional resistors 391, 392, etc. are employed in arrangement 300 at the cathode terminals of the last light-emittmg diodes in each branch Light-emitting diodes which are connected according to the arrangement shown in Figure 5(a) have a high level of reliability. This follows because, m open-circuit failure mode, an entire branch does not extinguish because of the failure of a light-emitting diode in that branch. Instead, cuπent flows via shunts 314, 315, etc. to bypass a failed light- emittmg diode For instance, if light-emitting diode 310 of Figure 5(a) fails, cuπent still flows to (and thereby illuminates) other light-emittmg diodes in branch 302(a) via branch 302(b) and light-emittmg diode 313, and via branch 302(g) and hght-emittmg diode 322 In addition, cuπent from branch 302(a) still flows to adjacent branches 302(b) and 302(c) via shunts 314 and 324, respectively Furthermore, in short-circuit failure mode, light-emittmg diodes in other branches and shunts do not extinguish because of the failure of a hght-emittmg diode m one branch. This follows because the ght-emittmg diodes are not connected in parallel For example, if hght-emittmg diode 310 short circuits, cuπent will flow through upper branch 302(a), which has no voltage drop, and will also flow through hght-emittmg diodes 312 and 321 in shunts 314 and 324, respectively. Light-emittmg diodes 312 and 321 remain illuminated because the cuπent flowing through them drops only a small amount, unlike that which occurs in the aπangement of Figure 2(b) Light-emitting diodes 311 and 316, and the shunts which are coupled to their input terminals, also remain illuminated because a cuπent flow is maintained through them via branches 302(b) through 302(g). In addition, aπangement 300 of light-emitting diodes also alleviates other problems experienced by the light-emitting diode arrangements of the prior art. For instance, light-emitting diode aπangement 300 of the present invention, according to one embodiment, insures that all of the light-emitting diodes in the aπangement have the same brightness without the requirement that the light-emitting diodes have tightly matched forward voltage characteristics. For instance, light-emitting diodes 310, 311, 312, 313, 316, 317, 318, 321 and 322 of the aπangement shown in Figure 5(a) may have forward voltage characteristics which are not as tightly matched as the forward voltage characteristics of light-emitting diodes 51, 61, 71 and 81 of the arrangement shown in Figure 2(b). This follows because, unlike the arrangements of the prior art, the light-emitting diodes in cells 301 of arrangement 300 are not parallel-connected to each other. As in the previously described embodiments, because light-emitting diodes in each cell of aπangement 300 are not parallel-connected, the voltage drop across the diodes does not need to be the same. Therefore, forward voltage characteristics of each light- emitting diode need not be equal to others in order to provide similar amounts of illumination, and the current flow through a light-emitting diode having a lower forward voltage will not increase in order to equalize the forward voltage of the light-emitting diode with the higher forward voltage of another light-emitting diode. By alleviating the need for binning light-emitting diodes with tightly matched voltage characteristics, the present invention reduces the additional manufacturing costs and time which is necessitated by the combining operation of prior art light-emitting diode aπangements. As previously mentioned, in accordance with various embodiments, the three- dimensional light-emitting diode aπangement of the present invention enables the lighting system to be viewed from various different directions. As a result, the lighting system of the present invention is particularly well-suited for applications such as desk lamps, traffic signals, safety lights, advertising signs, etc. By contrast, most of the light-emitting diode aπangements of the prior art are configured to be viewed from substantially a single direction. While there has been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications can be made therein without departing from the invention, and therefore, the appended claims shall be understood to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims: CLAIMS 1 A lighting system (100) compπsmg a power supply source. a plurality of electπcally-conductive branches (102) configured in a three- dimensional aπangement, said branches (102) coupled in parallel to said power supp source, each of said branches (102) compnsing at least one hght-emittmg diode (110), and a plurality of shunts (114), wherein each one of said shunts (114) couples an anode terminal of a light-emitting diode (110) in one of said branches to a cathode terminal of a coπesponding light-emitting diode (111) in a different branch, such that a coπesponding set of light-emitting diodes together with their coπesponding coupling shunts define a cell (101) 2 The lighting system (100) according to claim 1, wherein a cross-section of said plurality of branches (102) is tπangular 3 The lighting system (100) according to claim 2, wherein each side of said cross-section further compπses additional tπangular sections so as to form additional branches 4 The lighting system (100) according to claim 1, wherein a cross-section of saiα plurality of branches (102) is hexagonal 5 The lighting system (100) according to claim 4 wherein each side of said cross-section of said plurality of branches (102) further compπses additional hexagonal sections so as to form additional branches 6 The lighting system (100) according to claim 1, wherein each one of said shunts (114) couples an anode terminal of a hght-emittmg diode (110) in one of said branches to a cathode terminal of a coπesponding hght-emittmg diode (111) in an adjacent branch 7. The lighting system (100) according to claim 1, wherein, for each said light- emittmg diode (110), said anode terminal is coupled to the cathode terminal of at least two coπesponding light-emitting diodes (111), (116) 8 The lighting system (100) according to claim 1, wherein said plurality of branches further compπses at least one central branch (302(g)) 9. The lighting system (100) according to claim 8 wherein at least one of said plurality of branches is coupled via a shunt to said at least one central branch (302(g)) 10 The lighting system (100) according to claim 1, wherein each shunt (114) compπse a hght-emitting diode (112) 11. The lighting system (100) according to claim 1, wherein each said branch (102) further compπses a resistor 12. The lighting system (100) according to claim 1, wherein for each said branch (102), said resistor is a first element 13. The lighting system (100) according to claim 1, wherein for each said branch (102), said resistor is a last element 14. The lighting system (100) according to claim 1, wherein light-emitting diodes of each one of said cells have different forward voltage characteπstics.

Inventors: CHANG CHIN, CHANG, CHIN
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: H05B33
IPC codes: F21S8, F21Y101, G09F13, H05B33