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1. (WO2007003006) A MULTICOLOUR LED LIGHTING CIRCUIT
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A MULTICOLOUR LED LIGHTING CIRCUIT

Technical Field
The present invention relates to a multicolour light emitting diode (LED) lighting circuit, for eg. for illumination, display or signalling purposes. It also relates to a lighting system which comprises a plurality of the LED lighting circuits.

Background
The present invention makes use of the effect that when light of different colours is mixed, light of a third colour is produced. In fact, any colour in the visible spectrum can be produced by combining the three additive primary colours - red, green and blue - in different proportions. Thus the invention may utilize LED's of at least two, and preferably all three of the additive primary colours. By varying the intensity of light output from the different coloured LED's, it is possible to provide various different coloured outputs (an output in this sense being what the human eye will perceive as a particular colour from the different intensity outputs of the differently coloured LED's in combination).

Known multicolour LED lighting or display circuits generally provide for illumination of their LED's in a pulsed mode (eg. US 6150774 to Mueller et al) or provide for discrete stepped intensity output levels of the LED's (eg. US 5420482 to Phares). However illumination via a pulsed supply can produce flicker in the output and circuits providing discrete stepped intensity output levels are limited in the range of output colours that can be produced.

The present invention seeks to provide an alternative to the above known types of circuit which avoids the flicker problem whilst allowing for a continuously variable intensity adjustment for the LED's between a minimum value and a maximum value.

Disclosure of the Invention
According to the invention there is provided a lighting circuit including:
a plurality of voltage reference sources;

a plurality of power supply controllers, each of which is connected to a respective voltage reference source;
a plurality of LED loads, each of which is supplied with power from a respective one of the power supply controllers;
wherein each LED load is for emitting a different colour selected from at least two different colours, the LED loads being arranged together such that their respective outputs are additive to give a colour output from the plurality of LED loads;
wherein each voltage reference source operates its power supply controller independently of the others to control the supply of a substantially constant direct current to its LED load to provide a preselected light intensity output such that the plurality of LED loads together provide a particular colour output, each voltage reference source also being variable for the power supply controllers to vary, respectively, the direct current to each LED load to thereby independently vary the light intensity output from each LED load and thus change the colour output from the plurality of LED loads.

Illumination of the LED loads via a substantially constant but variable direct current avoids the flicker problem and each power supply controller is such that that direct current is continuously variable between the maximum and minimum intensity illumination limits for each LED load. Each power supply controller is uniquely operable by its voltage reference source and thus all are independently controllable to thereby allow independent control over the light intensity output of each LED load and thus a very large range of colour outputs is possible from the LED loads taken together.

Preferably the voltage reference sources are provided via a microprocessor and each power supply controller is uniquely addressable by the microprocessor. Alternatively the voltage reference sources can be provided via potentiometers, or a single potentiometer which is switchable to each power supply controller. Other arrangements are also possible which can supply a reference voltage which is variable.

Each LED load may be a single LED or more usually, a set or cluster of

LED's which may be connected in series, in parallel, or in a series/parallel array.

Preferably the lighting circuit includes a load of red LED's, a load of green

LED's and a load of blue LED's (that is, each of the three additive primary colours) so that any colour in the visible spectrum can be produced.

Preferably each power supply controller includes a feedback circuit in which a signal representative of the direct current is fed back for the power supply controller to maintain the direct current substantially at a level which is set via its reference voltage.

Where the reference voltages are provided via a microprocessor, preferably the microprocessor also includes, for each LED load, data that represents the minimum direct current that provides a light output from the LED load and the maximum direct current that the LED load can draw, and wherein the microprocessor operates each power supply controller such that the direct current supplied to its LED load does not exceed said maximum. The feedback circuitry together with the microprocessor "knowing" the minimum and maximum direct currents for a particular LED load means that the direct current to each LED load is dynamically managed by the power supply controller for that load. Effectively there is regulation of a steady but variable current flow to each LED load.

Preferably the lighting circuit includes a white light balance circuit for sensing the colour output from the plurality of LED loads and which provides signals to the microprocessor for determining the direct current supplied to each

LED load for the LED loads to provide a white light output at their minimum output intensities and the direct current supplied to each LED load for the LED loads to provide a white light output at their maximum output intensities. This feature assists in determining reference voltage limits for the microprocessor to know the maximum and minimum currents for each LED load between which any colour can be produced. By knowing the reference voltages needed to produce white, the reference voltages for any other colour can be computed and used by the power supply controllers to produce the appropriate output for each LED load so generating that colour.

Each power supply controller may include a switching section operated via the reference voltage signal, for example from a microprocessor, for switching a supply of dc power through a smoothing filter section. That is, effectively a switched mode power supply, which is operated at a high frequency, may be provided for each LED load. Such a power supply effectively allows for a continuously variable adjustment of the smoothed direct current.

Alternatively each power supply controller may include a control section for providing a control signal in dependence upon the reference voltage signal, for example from a microprocessor, and a current regulation section for receiving the control signal to thereby regulate a direct current drawn from a dc power source. This alternative for the power supply controller allows for the control section and the current regulation section to be spatially separated whereby each current regulation section may be located in proximity to the LED loads.

The invention also provides a lighting system that includes:
a system controller;
a plurality of lighting circuits as described above;
wherein the system controller is connected to control the reference voltage sources of each lighting circuit.

Preferably the reference voltage sources are provided via a microprocessor.

With such a lighting system having a system controller, which is preferably a digital computer, it is possible to provide a master program to variously address, individually, the reference voltage sources, or the microprocessors, of the individual lighting circuits for them to operate their associated LED loads to provide a vastly increased range of lighting options, for example different lighting patterns and/or different lighting sequences can be provided. Also, such a lighting system because of its versatility, could be adapted for use in many different environments.

Such a lighting system also facilitates modularisation of componentry of the lighting circuits, thereby further enhancing the versatility of the invention. For example the voltage reference sources or microprocessor and plurality of power supply controllers of each lighting circuit may be provided as a module which is interchangeable with other such modules. This allows differently sized and/or differently configured LED loads to be connectable to each interchangeable module. Different current ratings for different sized LED loads can be input into a microprocessor of a particular module to suit the LED loads to be connected to that module.

Alternatively, the lighting system could be one where the power supply controller of each lighting circuit includes a separated control section and a current regulation section for each LED load, wherein the current regulation section of each power supply controller and the plurality of LED loads are provided as a module which is interchangeable with other such modules.

For a better understanding of the invention and to show how it may be performed, embodiments thereof will now be described, the way of non-limiting example only, with reference to the accompanying drawings.

Brief Description of Drawings
Fig. 1 is a schematic of a functional block diagram of a lighting circuit according to an embodiment of the invention.

Fig. 2 is a schematic of a functional block diagram of a lighting system which comprises a plurality of the lighting circuits of Fig. 1 .

Fig. 3 is a schematic of a block diagram of an embodiment for a lighting system which is an alternative to that of Fig. 2.

Fig. 4 is a circuit diagram for a controller of the embodiment of Fig. 3.

Fig. 5 is a circuit diagram for portions of the embodiment of Fig. 3.

Figs. 6A, 6B and 6C are circuit diagrams for further portions of the embodiment of Fig. 3.

Detailed Description
Fig. 1 schematically illustrates a lighting circuit 10 that includes a microprocessor 12, which provides a plurality of reference voltage sources, and a plurality of LED loads, respectively 14 for red LED's, 16 for green LED's and 18 for blue LED's. Each LED load 14, 16, 18 is supplied with power from a power supply controller, respectively 20, 22, 24. The LED loads 14, 16 and 18 are arranged together such that their additive primary colour outputs, to a viewer, are perceived as providing a particular colour output. Each power supply controller 20, 22, 24 is uniquely addressable by the microprocessor 12 such that the microprocessor 12, suitably programmed, independently provides a reference voltage to each power supply controller 20, 22, 24 as indicated by the control connections labelled 26 from a bus 28, to control the supply of a substantially constant direct current to each LED load along current supply connections labelled 30. Such substantially constant direct currents to each LED load 14, 16, 18 provide a preselected light intensity output for each LED load 14, 16, 18 and thus a particular colour output from the LED loads together. The preselection of the desired colour output and thus of the direct currents to be supplied to each LED load 14, 16, 18 is from information inputted into the microprocessor 12.

The microprocessor 12 is also operable, via appropriate programming or specific inputs (which may be from a digital computer system controller as will be described below with reference to Fig. 2), to vary the direct current supply 30 to each LED load 14, 16 18 to thereby vary, independently of each other, the light intensity output from each LED load 14, 16, 18 and thus change the colour output of the LED load 14, 16, 18.

Each power supply controller 20, 22, 24 includes a feedback circuit, respectively 32, 34, 36 which, under control signals from the microprocessor 12 as indicated by control connections 38, feeds back a signal derived from the direct currents on supply connections 30 to its power supply controller 20, 22 or 24, as indicated by feedback connections labelled 40. This feedback can maintain or regulate the direct current supplies 30 substantially at a level which is set via a reference voltage from the microprocessor 12.

The lighting circuit 10 may also include a white balance circuit 42. This is for sensing the colour output from the plurality of LED loads and it provides signals, as indicated by reference 43, to the microprocessor 12 for determining the direct currents supplied to each LED load 14, 16, 18 for the LED loads to provide a white light output at their minimum output intensities. It also determines the direct current supplied to each LED load 14, 16, 18 for the LED loads to provide a white light output at their maximum output intensities. Thus an operating range for each LED load is established.

Before start up of the lighting circuit 10, data is inputted to the microprocessor 12 of the maximum direct current for each of the LED loads 14, 16 and 18. On start up, the microprocessor 12 initiates operation of each power supply controller 20, 22 and then 24 and from the respective feed back circuit 32, 34 and then 36, which each sense when current begins to flow into its respective LED load 14, 16, 18, determines the minimum operating direct current for each LED load 14, 16, 18 (in operation, the feedback circuits 32, 34, 36 manage the maximum current for their respective LED loads 14, 16, 18). The microprocessor 12 then utilizes information from the white balance circuit 42 to determine the direct current settings for each of the power supply controllers 32, 34, 36 for the LED loads 14, 16 and 18 together to provide a maximum intensity white output and a minimum intensity white output. The microprocessor 12 is thus loaded with information that gives maximum and minimum operating currents for each LED load 14, 16, 18 and, within or at those limits, the maximum and minimum currents that give a white light output of, respectively, maximum intensity and minimum intensity. With this information in the microprocessor 12 of a full operating range for each LED load, 14, 16, 18, the lighting circuit 10 can be operated via suitable inputs to the microprocessor 12 to produce any colour in the visible spectrum by variation of the direct current to each LED load and thus of the intensity of the red, green and/or blue light output.

Each power supply controller 20, 22, 24 may comprise a high frequency switched mode power supply which will be described in detail below. With such power supplies, the microprocessor 12, the power supply controllers 20, 22, 24, feedback circuits 32, 34, 36 and white balance circuit 42 may be provided in the form of a module, as indicated by the dashed outline 44 in Fig. 1 . With such a module 44, differently sized or configured LED loads 14, 16, 18 may be connected to the module 44 via suitable connectors, as indicated by references 46, which may be plug and socket connectors. Such modularisation allows for a lighting system 50 (see Fig. 2) to be formed using a plurality of the modules 44 controlled by a system controller 52, which may be a digital computer and which provides control data for each microprocessor 12 in each power supply controller module 44. Data exchange between a computer controller 52 and the microprocessor 12 in each module 44 is indicated by the data connections 54 between the computer 52 and module 44 via a data bus 56. Persons skilled in the art will know of appropriate cabling and input/output connectors between the computer controller 52 and modules 44 that will need to be used. Such a lighting system 50, due to the modularisation of the lighting circuity 10, can be readily expanded to provide various lighting configurations, for example a binary tree network of modules 44 could be formed. Also by appropriate programming of the computer controller 52, the microprocessors 12 of each module 44 can be variously sequenced for operation and instructed to generate various colours to provide many different lighting patterns, either for illumination, display, signalling or other applications.

Fig. 3 illustrates an alternative lighting system 60 to that of Fig. 2, which involves different modularisation of the componentry. In this lighting system 60, the power supply controller for each LED load 14, 16, 18 of each lighting circuit is spatially divided between a control section in a controller 62 and a current regulation section 64, 66, 68. Thus there is a current regulator 64 for the red LED load 14, a current regulator 66 for the green LED load 16 and a current regulator 68 for the blue LED load 18. With this arrangement, the current regulators 64, 66, 68 and their associated LED loads 14, 16, 18 can be provided in the form of a module, as indicated by a reference 70, two of which are illustrated in Fig. 3. Each module 70 may, for example, be a lighting strip having "n" LED's of each colour 14, 16, 18 connected in series.

The controller 62 may include a microprocessor for each colour which operates a control circuit that includes an appropriate feedback section (similar to the arrangement of Fig. 1 ). Such control circuitry outputs a control reference voltage signal, respectively Vb, V9 or Vr, which is supplied to the current regulators 64, 66, 68 of the modules 70 via a control bus loom 72.

One or more dc power supplies 74 for operation of the lighting system 60 are provided which provide a supply voltage V+, V. via the control bus loom 72.

The control reference voltage signals Vb, V9 or Vn provide the reference voltage to their respective current regulators 64, 66, 68 causing them to regulate the direct current to each LED load 14, 16, 18 to a predetermined value thus producing the desired output colour.

Persons skilled in the art will know of appropriate cabling for the control bus loom 72 and input and output connectors for the connections between the loom 72 and the controller 62, dc power supply 74 and modules 70.

An overall system controller (such as 52 in Fig. 2), eg. a digital computer (not shown) may be provided to operate the microprocessors in the controller 62.

An advantage of a lighting system 60 (as in Fig. 3) over a lighting system

50 (as in Fig. 2) is that the direct current carrying connections between each current regulator 64, 66, 68 and their respective LED loads 14, 16, 18 can be much shorter than the equivalent connections 30 in the Figs. 1 and 2 embodiment because of the close proximity of the regulators 64, 66, 68 to the LED loads 14, 16, 18. Furthermore the dc power source 74 may also be located in close proximity to the current regulators. Thus the controller 62 can be spaced a reasonably long distance away from the modules 70.

Fig. 4 shows a circuit for the controller 62 of Fig. 3 which is based upon a microprocessor chip IC1 and provides the control reference voltage signals RC, GC and BC (respectively Vr, V9 and Vb as described above) via transistors respectively Q3, Q2 and Q1 . The control reference voltage signals are fed to their respective current regulators 64, 66, 68 (see circuit of Fig. 5) via an integrated circuit chip IC3. Figs. 6A to 6C show circuitry of the integrated circuit chip IC3 which provides feedback control sections for regulating the operation of output transistors respectively Q4, Q5 and Q6 (see circuit of Fig. 5) of the current regulators 64, 66 and 68. Each current regulator 64, 66, 68 connects to its respective LED load 14, 16, 18. Figures 4, 5 and 6 illustrate circuit structures and componentry which will equip a person who is skilled in the art with the requisite knowledge to be able to perform the embodiment of the invention as illustrated by Fig. 3. The embodiments of Figs 1 and 2 can be performed based on similar circuitry as disclosed for the Fig. 3 embodiment by Figs. 4 to 6.

The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the scope of the following claims.