Cross-Reference to Related Applications

This application claims the benefit of U.S. Provisional Application No.

61/271.954 filed July 29, 2009. Technical Field

The present invention relates generally to light emitting diodes (LBDs). and more particularly, some embodiments relate driving systems for LED lighting systems.

Description of the Related Art

Some LED-based luminaires provide white light by mixing from a plurality of monochromatic LEDs. Such multi-color LEDs may utilize two, three, four, or more different colors of monochromatic LHDs. White light, and even other colors of light, is provided by modifying the relative outputs of the various monochromatic LEDs. Typically, these multi-color LED-based color luminaires often utilize three color LED modules which have red, green, and blue LEDs. Figure 1 illustrates such a system. Λ three color LED module 100 comprises a red LED 103. a green LED 102, and a blue LED 10 L Three separate drivers, a blue LED driver 104, a green LED driver 105, and a red LED driver 106 control the relative outputs of LEDs 101. 102, and 103, respectively.

In the illustrated system, each driver utilizes a pair of wires 108 and 109, 1 10 and 1 10, or 1 12 and 1 13. to control its respective LED. Accordingly, the wire 107 used to connect the drivers to the module 100 requires a total of six wires. In some systems, a common anode or common cathode wire is used to reduce this total to four wires.

Brief Summary of Embodiments of the Invention

According to various embodiments of the invention, a multicolored LED luminaire module is provided that can be controlled using a single driver and only two wires. The LED luminaire module comprises a plurality of LEDs and a sequencer. The sequencer connects each LED to the circuit in a predetermined order. Synchronously with the sequencer, the driver transmits a control signal comprising a time division multiplexed (TDM) signal that combines the driving currents for each LED into one TDM signal. The sequencer and TDM rate are sufficiently fast such that the light emitted by the LKD luminaire appears to be the combined light from all the I-KDs.

According to an embodiment of the invention, a multicolor Sight emitting diode (LFJ)) lighting system, comprises an LHD module comprising a plurality of LBDs. and a sequencer electrically coupled to the plurality of LFJDs configured to connect LKDs of the plurality to a circuit and isolate other LHDs of the plurality from the circuit in a predetermined sequence; and a driver electrically coupled to the circuit and configured to provide a driving signal to the plurality of LKDs according to the predetermined sequence and in synchronization with the sequencer. Other features and aspects of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features in accordance with embodiments of the invention. The summary is not intended to limit the scope of the invention, which is defined solely by the claims attached hereto. Brief Description of the Drawings

The present invention, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the invention. These drawings are provided to facilitate the reader's understanding of the invention and shall not be considered limiting of the breadth, scope, or applicability of the invention. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.

Figure 1 illustrates a prior art multicolor LED that requires separate drivers for each color LKD. figure 2 illustrates an LK D module implemented in accordance with an embodiment of the invention

Figure 3 illustrates a variety of driving currents implemented in accordance with an embodiment of the invention.

Figure 4 illustrates driving signals having embedded control signals implemented in accordance with an embodiment of the invention.

-9- Figure 5 illustrates a driver signal with embedded control signals implemented in accordance with an embodiment of the invention.

Figure 6 illustrates a multicolor LKD lighting system according to an embodiment of the invention. Figure 7 illustrates a plurality of LKD modules by a single driver in aecordanee with an embodiment of the invention.

Figure 8 illustrates an LED module comprising a shunting circuit implemented in accordance with an embodiment of the invention.

Figure 9 illustrates a circuit having repeating LED drivers implemented in accordance with an embodiment of the invention.

Figure 10 illustrates a shunting system for a redundant repeating driver circuit implemented in accordance with an embodiment of the invention.

Figure i 1 illustrates a parallel circuit configuration for a plurality of LED modules implemented in accordance with an embodiment of the invention. The figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the invention be limited only by the claims and the equivalents thereof.

Detailed Description of the Embodiments of the Invention The present invention is directed toward an LED-based illumination system. Use of time division multiplexing allows a multi-color LHD luminaϊre to be operated using a single driver and a single pair of wires.

Figure 2 illustrates an LED module implemented in accordance with an embodiment of the invention. LED module 200 comprises a plurality of LEDs 203, sufficient to span a predetermined color space. In the illustrated embodiment, a red LED 204, a green LED 205, and a blue LED 206 allow color mixing to form white light or other colored light, such as purple, yellow, etc... In other embodiments, dichromatic, tetrachromatic. or larger numbers of colors maj be employed. Λ sequencer module 202 sequentially connects and disconnects individual LFJDs of the plurality 203 to the circuit. In the illustrated embodiment, the sequence module 202 comprises a sequencer control module 201 that controls 207 a plurality of switches 208, 209. 210. Each switch is electrically coupled to an individual LED. By connecting and disconnecting the switches, the sequencer connects and disconnects LEDs to the leads 21 1 and 212. For example, by connecting switch 208 and disconnecting switches 209 and 210 the red LED 204 is coupled to the leads 23 1 and 212, and the green LED 205 and the blue LED 206 are isolated from the circuit.

In some embodiments, the sequencer operates on a predetermined switching sequence to sequentially isolate and connect individual LK-Ds to the circuit. Λ driving signal provided on the leads may then control each of the LEDs in the order determined by the sequencer. In some embodiments, when the sequencer advances to the next element of the predetermined sequence is determined by the driver. In a particular embodiment, a

synchronization signal is embedded in the driving signal. When the synchronization signal is received, the sequencer advances to the next element of the sequence. In other embodiments, the sequence module 202 operates independently and the driver synchronizes to the sequence module without transmitting control information. For example, each LBD may be coupled in series with a resistor, with each resistor having a different resistance. In this example, a driver operating in a constant current mode can determine the sequence and sequence timing of the sequencer 201 and synchronize by monitoring the continuous voltage on the line.

In other embodiments, the sequence module 202 is coupled to a control line 213 to allow control signals to be transmitted to the sequencer 201. For example, a stop/start or restart control signal may comprise a low current signal at a predetermined current level. When the sequencer 201 receives this signal it restarts the sequence, allowing the external driver to synchronize. For example, the low current signal may comprise a current that is insufficient to produce a noticeable illumination level in the LEDs 203. For example, the current level may only produce a luminance between 0 and K) ^"2 cd/m ² in the LEDs 203. Accordingly, the control signals embedded in the driving signals may be imperceptible to those viewing the luminaire.

Figure 3 illustrates a variety of driving currents implemented in accordance with an embodiment of the invention. Figure 3Λ illustrates a constant current driving current 303. Λs described above, an LhD module includes a sequencer that sequentially connects a plurality of LLDs to a circuit. In the illustrated embodiment, the sequencer connects a red LItD to the circuit during period 300, a green LED during period 301, and a blue LED during 302, after which the pattern repeats. Λ constant current signal 303 results in each LLD receiving the same amount of current during its respective operating period. Given a sufficiently rapid switching rate, this will appear to a system viewer as a mixed illumination. Of course, to the human eye a mixed sequence of equal intensity red. green, and blue light may not appear as a white light, or may appear as an non- preferred shade of white. In such embodiments, individual current adjusters or other circuit elements may be coupled to the individual LEDs within the IJiD lυmϊnaire module to modify the respective contributions of the red, green, and blue light. Although this would result in a static light source, it may serve to generate a desired frequency or color of light.

Figure 3B illustrates a TDM current signal that is configured to provide different current levels to different LEDs. For purposes of illustration, the sequence is again red, green blue, etc. In the illustrated embodiment, the driving signal comprises a red current level 304 transmitted during red period 300, a green current level 305 transmitted during green period 301 and a blue current level 306 transmitted during blue period 302. Accordingly, by individually varying each color's current level, the relative proportion of the red, green, and blue LEDs to the ϊuminaire's illumination may be modified. This allows dynamic generation of different colors and shades of colors. In further embodiments, luminal re dimming may be implemented by reducing total system current while maintaining the relative ratios of each LED's current.

Figure 3C illustrates a TDM and pulse width modulated (PWM) current signal implemented in accordance with an embodiment of the invention. In addition to modifying the current levels of the driving signal, modification of the pulse widths allows further control of luminaire light output. In the illustrated driving current, the current level 307 drives the red LED for a portion 310 of the red period 300, the current level 308 drives the green LED for a portion 31 1 of the green period 301. and the current level 309 drives the blue LtTJ for a portion 312 of the blue period 302. The human eye tends to integrate a short light burst over a longer period, making the light appear less bright. Accordingly, the pulse width of each specific LED current provides a second dimension for modulation in addition to amplification modulation. In some embodiments, PWM may be employed such that each current pulse has an equal width. These equal widths may be modified to dim and brighten the luminare, as discussed with respect to Figure 3d. In further embodiments, different LKDH may be provided with different pulse widths. This allows modification of the relative contributions of each color LED to the final luminaire light output, allowing for a second level of luminaire color control.

Figure 3D illustrates a constant current PWM signal implemented in accordance with an embodiment of the invention, in this embodiment, each current pulse has an equal current level 316. Luminaire shade and illumination level is controlled through PWM. In this embodiment, pulse 313 drives the red LIiD during period 300. pulse 314 drives the green LEI) during period 301 , and pulse 315 drives the blue LED during period 302. As discussed above, modifying the relative lengths of the pulses modifies the contribution of each LED to the mixed color perceived by the viewer, while modifying the absolute pulse lengths while maintaining the relative pulse length ratios controls dimming.

Figure 4 illustrates driving signals having embedded control signals implemented in accordance with an embodiment of the invention. In some embodiments, synchronization between the driving system and the f ,ED luminaire is achieved through synchronization control signals that are embedded in the driving signal, In particular embodiments, the sequencer advances to the next switch in the sequence when it receives a signal transmitted at a control level 400. Accordingly, synchronization between the driver and the sequencer is achieved through the driver's control of the sequencer. In the embodiment illustrated in Figure 4A, the driving signal drives the red LFiD during period 401 using driving current 404. Then, the driving signal transmits control current 407, causing the sequencer to advance the switching system to the green LED. During the green LED period 402, the driving current drives the green LED using driving current 405, and then transmits control signal 408 to cause the sequencer to

ance the switching system to the blue LED. During the blue LED period 403, the driving signal drives the blue LED with driving current 406. and then transmits control signal 409 to cause the sequencer to advance to the red LED. In the embodiment illustrated in Figure 4A, different current levels for each of the different LFiDs allows color mixing or dimming to be implemented. In further embodiments, PWM may also be implemented to achieve mixing or dimming, as described above.

Additionally, in further embodiments, different periods for different LEDs may be different time lengths. Figure 4 B illustrates one such embodiment. In the embodiment in Figure 4B, red period 401 , green period 402, and blue period 403 have different lengths because the timing of the control signals 413, 414. and 415 determines when the sequencer advances to the next LED. Accordingly, the relative lengths of the driving periods 410, 41 1. and 412 may be modified to allow for modify ing the shade of the lnminaire. Additionally, PWM may be further implemented to increase the total deactivation time, for dimming purposes.

Additionally, embedded control signals may be used to initially activate the sequencer or LHD luminairc. Figure 5 illustrates a driver signal with such control signals.

During period 500 the iuminairc is deactivated, and no current is transmitted. To activate the !uminaire, a control signal is transmitted at the limited control voltage during period 501 . In some embodiments, the luminaire module may be configured to respond to a control signal that meets a predetermined duration. In other embodiments, the luminaire module may be configured to respond to an increase in current from the control current. In which case, the luminaire module may stay in a ready state while current is transmitted at control level during activation period 501. After the luminaire module is activated, operation proceeds as described above. When the driver signal current increases, the luminaire begins the predetermined sequence, and connects the red LED to the circuit. Driver current during period 502 drives the red LHD. A transition to the control current level 503 triggers the luminaire to connect the green LED.

Driver current during period 504 drives the green LED, and transition 505 triggers the precession to the blue LED. Driver current 506 drives the blue LEiD and transition 507 triggers the sequence to repeat. In the illustrated embodiment, color mixing is achieved through PWM, but as described above, other methods are possible. Figure 6 illustrates a multicolor LED lighting system according to an embodiment of the invention. LED module 200 comprises a device substantially as described with respect to Figure 2. Additionally, a driver 214 is electrically coupled to the LED module 200 using a cable 215. In some embodiments, driver 214 comprises a control module 216 and a driving signal module 217. In response to control signals from control module 216, the driving signal module 217 generates a driving signal to control the operation of the LED module 200. The driver 214 and the sequencer 202 operate in synchronization to allow the single pair of leads 21 1 and 212 to provide driving signals to all of the plurality of LEDs 203. As described above with respect to Figures 3-5, the driving signals may include control signals embedded with the driving signals. These control signals can control this synchronization and may also control the activation of the LED module.

As illustrated, a plurality of LEDs may driven in this manner through the use of only two wires. In addition to substantial materials savings in wires 215, this allows some embodiments to serve in otherwise unsuitable locations. For example, the illustrated system may be particularly suitable for situations involving long wire runs, or situations where only two conductors are available, such as track lighting or lighting upgrades in a vehicle with only two available conductors. figure 7 illustrates a plurality of LED modules driven by a single driver in accordance with an embodiment of the invention, ϊn the embodiment illustrated in Figure 7, a plurality of LHD modules 701 , 702. and 703 are connected in series and driven by a single driver 700. Such configurations may be used to provide a luminairc that covers a large area or a long span. For example, lighted bridge spans, escape lighting within an airplane, and sign back lighting. For these applications, multiple LED modules may be placed in a series circuit with cable runs between the LED modules.

When large numbers of LED modules are connected in series with a driver, the failure of any given LED module might prevent the entire chain from operating. Accordingly, in some embodiments, LKD modules are coupled to shunt circuits that shunt current around a failed LBD module. Figure 8 illustrates one example of such a shunting circuit. Shunting circuit 218 comprises a zener diode 219, resistor 221 , and silicon controlled rectifier 220 in the illustrated configuration. If the LED module 200 fails, current across the shunting circuit rises beyond a predetermined threshold, causing the silicon controlled rectifier to transition into an "on' ^" state, conducting and bypassing the failed LFID module 200. In general, the number of LED modules in series is limited by the available compliance voltage of the driver. In other words, the maximum voltage that the driver can output while maintaining current control. For typical laboratory drivers, this limit is 100-200V. With typical IJiDs and circuit components, this corresponds to 20-40 LED modules.

To allow for longer chains of LED modules, repeating drivers may be implemented. Because control signals are transmitted within the driving signals themselves, repeating drivers may be connected to the same circuits without the use of separate control or signaling cables. A repeating driver is configured to sense the driving signal and retransmit it to allow for an increased number of LED modules within the circuit. Figure 9 illustrates such a configuration. Driver 704 is configured to sense the driving signal originally transmitted by driver 700 and to retransmit it on the circuit to allow for an increased number of LED modules 705. In some embodiments, analog driving signals may be employed, and a repeating LED driver may be configured to retransmit the analog drh ing signal as it senses the signal. However, in some applications, imperfections in signal reproduction can degrade the quality of the signal, and consequently impact the quality of the light produced by the luminaire. In these embodiments, a TDM modulation scheme is employed that uses discrete current levels and discrete LED period durations. Λ downstream repeating driver then senses a transmitted driving signal and repeats the closest discrete signal to the received signal. Accordingly, normal signal degradation does not impact the quality of downstream light, because the retransmitted signal is equivalent to the original driving signal. In this configuration, the overall error for any arbitrary length chain of drivers is equal to the error of one driver.

In some embodiments, repeating drivers may be provided with redundant fault protection. Figure 10 illustrates a shunting system that may be used to provide such protection in accordance with an embodiment of the invention, In this embodiment, a plurality of relays are coupled to the circuit to switch between a driver 252 and a bypass line 255. As illustrated, when a driver fails, the relays switch to the bypass line, allowing upstream drivers to provide the driving signal to LED modules previously driven by the failed driver. In a particular

embodiment, the relays are configured so that they are in their energized state when coupled to the driver and in their de-energized state when coupled to the bypass line 255. Accordingly, when the relays arc de-energized, for example through a local power failure that would also cause the driver 252 to fail, then the relays automatically enter the bypassed state. In some embodiments, each driver in a multi-driver system is able to power more than double the normal compliance voltage of the connected LED modules. In addition to improving long-term reliability this de-rated operating point allows any given driver of the plurality of drivers to fail without interrupting luminaire operation. In addition to series circuits of multiple LED modules, some embodiments of the invention may provide for multiple LED modules in parallel. Figure 1 1 illustrates such a configuration where a plurality of LED modules 750, 752, and 753 are connected in parallel to driver 751. In this mode of operation, the driver 751 is configured to operate in a constant voltage mode, rather than a constant current mode. To support this mode of operation, LED modules 750, 752, and 753 further comprise internal current control devices, such as positive temperature coefficient resistors (PTCs). However, because the current to the LED modules is fixed by the PTCs, the driver 751 cannot modify the current provided to the LED modules and PWM must be used for brightness control and color mixing. These parallel configurations have particular usefulness in applications such as overhead track or open conductor cable lighting that have only two conductors available,

As used herein, the term module might describe a given unit of functionality that can be performed in accordance with one or more embodiments of the present invention. Λs used herein, a module might be implemented utilizing any form of hardware, software, or a combination thereof. For example, one or more processors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs, logical components, software routines, circuit elements, or other mechanisms might be used in a module. In implementation, the various modules described herein might be implemented as discrete modules or the functions and features described can be shared in part or in total among one or more modules. In other words, as would be apparent to one of ordinary skill in the art after reading this description, the various features and functionality described herein may be implemented in any given application and can be implemented in one or more separate or shared modules in various combinations and permutations. Even though various features or elements of functionality may be individually described or claimed as separate modules, one of ordinary skill in the art will understand that these features and functionality can be shared among one or more common software and hardware elements, and such description shall not require or imply that separate hardware or software components are used to implement such features or functionality. While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. Likewise, the various diagrams may depict an example architectural or other configuration for the invention, which is done to aid in understanding the features and functionality that can be included in the invention. The invention is not restricted to the illustrated example architectures or configurations, but the desired features can be implemented using a variety of alternative architectures and configurations. Indeed, it will be apparent to one of skill in the art how alternative functional, logical or physical partitioning and configurations can be implemented to implement the desired features of the present invention. Also, a multitude of different constituent module names other than those depicted herein can be applied to the various partitions. Additionally, with regard to flow diagrams, operational descriptions and method claims, the order in which the steps are presented herein shall not mandate that various embodiments be implemented to perform the recited functionality in the same order unless the context dictates otherwise,

Although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the \arious features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, aione or in various combinations, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the present i mention should not be limited by any of the above-described exemplary embodiments.

Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term "including" should be read as meaning "including, without limitation" or the like; the term "example ^" ' is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms "a" or "an" should be read as meaning '"at least one. ^" "one or more ^" or the like: and adjectives such as "conventional." "traditional," "normal," "standard,' ^" "known ^' ' and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such

technologies encompass those apparent or known to the skilled artisan now or at any time in the future.

The presence of broadening words and phrases such as "one or more." "at least," "but not limited to ^" or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. The use of the term "module" does not imply that the components or functionality described or claimed as part of the module are all configured in a common package. Indeed, any or all of the various components of a module, whether control logic or other components, can be combined in a single package or separately maintained and can further be distributed in multiple groupings or packages or across multiple locations. Additionally, the various embodiments set forth herein arc described m terms of exemplar} block diagrams, flow charts and other illustrations. Λs will become apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives can be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular architecture or configuration.