WO2012140634A1

WO2012140634A1 - Apparatus, system and method for pulse width modulated lighting control

Info

Publication number: WO2012140634A1
Application number: PCT/IB2012/051919
Authority: WO
Inventors: Henricus Marius Joseph Maria Kahlman
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-04-12
Filing date: 2012-04-17
Publication date: 2012-10-18
Also published as: CN103493590A; TW201247016A

Abstract

Systems and methods of illumination are provided. A plurality of solid state light sources is operable to emit light. The operation of an illumination system is controlled to determine a first duty cycle of a pulse width modulated signal for each of the plurality of solid state light sources, respectively, to provide a desired color point and a desired luminous flux of the plurality of solid state light sources. The controller is further configured to phase-shift the respective pulse width modulated signals to reduce a combined peak current provided for operation of each of the plurality of solid state light sources at the respective duty cycle.

Description

APPARATUS, SYSTEM AND METHOD FOR PULSE WIDTH MODULATED

LIGHTING CONTROL

Technical Field

[0001] The present invention is directed generally to systems and methods for controlling a plurality of light sources. More particularly, various inventive methods and apparatus disclosed herein relate to the control of multiple solid state light sources to provide light with a decreased flicker ratio .

Background

[0002] Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Patent Nos. 6,016,038 and 6,211,626, incorporated herein by reference.

[0003] The brightness and color point of LEDs can vary based on a number of conditions. For example, brightness level and spectral distribution of the LED will change as the LED's temperature changes. Further, the LED's flux and peak wavelength will change as the LED ages. Generally, LED operation is controlled using a pulse width modulated (PWM) signal. Known approaches employ control loops that use the LED temperature and flux measurements that are provided to the PWM controller to maintain the desired color point and brightness level of the LED. In addition, some light modules allow the user to set the color point and dimming levels for the module. [0004] However, the use of PWM control can result in the rapid switching of the LEDs based on the calculated duty cycle. These switching cycles can produce a high flicker ratio and cause high peak loads for the associated power supply unit. The variable loading of the power supply unit also results in electro-mechanical stress, the generation of audible noise and additional electromagnetic interference. In specialized lighting applications, the high flicker ratio can degrade the quality of the light and can result in unwanted visual artifacts. For example, if the light source is used in a camera, the noise and electromagnetic interference can result in undesired image flutter.

[0005] Known approaches sequence PWM control signals for LED strings by dividing the PWM period by the number of LED strings in the system. These systems are static and do not address changes in LED output. These systems also do not adjust the PWM control signals based on the duty cycles of the signals relative to one another.

[0006] Thus, there is a need in the art to provide an illumination system and method that provides dynamically adjustable pulse width modulated current signals to light sources to lower the combined peak current resulting in decreased flicker ratio, noise and electromagnetic interference.

Summary

[0007] The present disclosure is directed to inventive methods and apparatus for providing illumination from a lighting source. For example, a plurality of solid state light sources to emit light. Pulse width modulated signals having a duty cycle are controlled to emit light of a desired color point and a desired luminous flux. The pulse width modulated signals are phase-shifted to reduce a combined peak current provided to the plurality of solid state light sources.

[0008] Generally, in one aspect, an illumination system to generate light is provided. The illumination system includes a plurality of solid state light sources and a plurality of drivers, each of the plurality of drivers electrically coupled to each of the plurality of solid state light sources, respectively. The illumination system also includes a controller configured to generate a pulse width modulated signal having a duty cycle for each of the plurality of drivers, respectively, where each driver is configured to supply current to an associated one of the plurality of solid state light sources based on the respective pulse width modulated signal. The controller is further configured to determine a first duty cycle of the pulse width modulated signal for each of the plurality of solid state light sources, respectively, to provide a desired color point and a desired luminous flux of the plurality of solid state light sources. The controller is further configured to phase-shift the respective pulse width modulated signals to reduce a combined peak current provided to the plurality of drivers for operation of each of the plurality of solid state light sources at the respective duty cycle.

[0009] In some embodiments, the controller includes an input configured to receive a temperature feedback and a luminous flux feedback from the plurality of solid state light sources. In at least one embodiment, the illumination system also includes a power supply unit configured to provide current to the plurality of drivers.

[0010] In at least one embodiment, the controller further includes a duty cycle module configured to respond to changes in at least one of temperature and luminous flux by

determining a second duty cycle of the pulse width modulated signal for each of the plurality of solid state light sources. The controller further includes a phase-shifting module configured to automatically phase-shift the respective pulse width modulated signals with the second duty cycle to reduce the combined peak current. In some embodiments, the duty cycle module is configured to automatically respond to changes in at least one of the desired color point and the desired luminous flux to determine a second duty cycle.

[0011] In various embodiments, the controller includes a phase-shifting module configured to phase-shift the respective pulse width modulated signals and to determine the combined peak current as an average of a sum of the respective pulse width modulated signals. In at least one embodiment, the phase-shifting module is configured to minimize the combined peak current. In some embodiments, the phase-shifting module is configured to minimize a flicker ratio of the illumination system. In the embodiments that include a power supply coupled to each of the plurality of solid state light sources, the phase-shifting module is configured to minimize electromagnetic interference generated by operation of the power supply unit.

[0012] In one aspect, a method of providing illumination with a lighting source including a plurality of solid state light sources is provided. The method includes an act of generating a pulse width modulated signal having a duty cycle for each of the plurality of solid state light sources, respectively. The method also includes the act of determining a first duty cycle of the pulse width modulated signal for each of the plurality of solid state light sources, respectively, to operate the plurality of solid state light sources at a desired color point and a desired luminous flux. The method further includes the act of phase-shifting the respective pulse width modulated signals to reduce a combined peak current provided to the plurality of solid state light sources when operated at the respective duty cycle.

[0013] In one embodiment, the method includes an act of determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of temperature and luminous flux of the plurality of solid state light sources. In further embodiments, the method also includes an act of phase-shifting the respective pulse width modulated signals with the second duty cycle to reduce the combined peak current.

[0014] In some embodiments, the method includes an act of determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of the desired color point and the desired luminous flux. In further embodiments, the method also includes an act of phase-shifting the respective pulse width modulated signals with the second duty cycle to reduce the combined peak current.

[0015] In further embodiments, the method includes an act of reducing the combined peak current by reducing an average value of a sum of the respective pulse width modulated signals. In various embodiments, the method can also include an act of phase-shifting the pulse width modulated signal to minimize the combined peak current. In some embodiments, the method may further include an act of phase-shifting the pulse width modulated signal to minimize a flicker ratio of the lighting source. In various embodiments, the method can phase-shift the pulse width modulated signal to minimize electromagnetic interference generated by the lighting source.

[0016] In some embodiments, the method includes an act of organizing an array of the respective duty cycles by maximizing a difference in duty cycle value between neighboring duty cycles included in the array. The method can also include an act of determining a plurality of timeslots based on a number of members in the array. The method can further include an act of locating each of the respective pulse width modulating signals within an overall pulse width modulating period by matching a mid point of the respective pulse width modulating signals with a start of a timeslot included in the plurality of timeslots. [0017] In at least one embodiment, the method includes an act of determining whether two or more of the respective pulse width modulating signals begin at a common time within the overall pulse width modulating signal period.

[0018] In one aspect, a computer readable medium is provided. The computer readable medium is encoded with a program for execution on a processor. The program, when executed on the processor performs a method of providing illumination from a lighting source having a plurality of solid state light sources. The method includes an act or acts of generating a pulse width modulated signal having a duty cycle for each of the plurality of solid state light sources, respectively. The method also includes an act of determining a first duty cycle of the pulse width modulated signal for each of the plurality of solid state light sources, respectively, to operate the plurality of solid state light sources at a desired color point and a desired luminous flux. The method further includes an act of phase-shifting the respective pulse width modulated signals to reduce a combined peak current provided to the plurality of solid state light sources when operated at the respective duty cycle.

[0019] In some embodiments, the program performs a method that includes an act of phase- shifting the pulse width modulated signal to minimize the combined peak current. In at least one embodiment, the program performs a method that includes acts of determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of temperature and luminous flux of the plurality of solid state light sources, and phase-shifting the respective pulse width modulated signals with the second duty cycle to reduce the combined peak current.

[0020] In various embodiments, the program performs a method that includes acts of determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of the desired color point and the desired luminous flux, and phase-shifting the respective pulse width modulated signals with the second duty cycle to reduce the combined peak current.

[0021] In at least one embodiment, the program performs a method that includes an act of organizing an array of the respective duty cycles by maximizing a difference in duty cycle value between neighboring duty cycles included in the array. The program can perform a method that includes acts of determining a plurality of timeslots based on a number of members in the array, and locating each of the respective pulse width modulating signals within an overall pulse width modulating period by matching a mid point of the respective pulse width modulating signals with a start of a timeslot included in the plurality of timeslots.

[0022] As used herein for purposes of the present disclosure, the term "LED" should be understood to include any electroluminescent diode or other type of carrier injection/junction- based system that is capable of generating radiation in response to an electric signal. Thus, the term LED includes, but is not limited to, various semiconductor-based structures that emit light in response to current, light emitting polymers, organic light emitting diodes (OLEDs), electroluminescent strips, and the like. In particular, the term LED refers to light emitting diodes of all types (including semi-conductor and organic light emitting diodes) that may be configured to generate radiation in one or more of the infrared spectrum, ultraviolet spectrum, and various portions of the visible spectrum (generally including radiation wavelengths from approximately 400 nanometers to approximately 700 nanometers). Some examples of LEDs include, but are not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs, green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed further below). It also should be appreciated that LEDs may be configured and/or controlled to generate radiation having various bandwidths (e.g., full widths at half maximum, or FWHM) for a given spectrum (e.g., narrow bandwidth, broad bandwidth), and a variety of dominant wavelengths within a given general color categorization.

[0023] For example, one implementation of an LED configured to generate essentially white light (e.g., a white LED) may include a number of dies which respectively emit different spectra of electroluminescence that, in combination, mix to form essentially white light. In another implementation, a white light LED may be associated with a phosphor material that converts electroluminescence having a first spectrum to a different second spectrum. In one example of this implementation, electroluminescence having a relatively short wavelength and narrow bandwidth spectrum "pumps" the phosphor material, which in turn radiates longer wavelength radiation having a somewhat broader spectrum.

[0024] It should also be understood that the term LED does not limit the physical and/or electrical package type of an LED. For example, as discussed above, an LED may refer to a single light emitting device having multiple dies that are configured to respectively emit different spectra of radiation (e.g., that may or may not be individually controllable). Also, an LED may be associated with a phosphor that is considered as an integral part of the LED (e.g., some types of white LEDs). In general, the term LED may refer to packaged LEDs, non-packaged LEDs, surface mount LEDs, chip-on-board LEDs, T-package mount LEDs, radial package LEDs, power package LEDs, LEDs including some type of encasement and/or optical element (e.g., a diffusing lens), etc.

[0025] The term "light source" should be understood to refer to any one or more of a variety of radiation sources, including, but not limited to, LED-based sources (including one or more LEDs as defined above), incandescent sources (e.g., filament lamps, halogen lamps), fluorescent sources, phosphorescent sources, high-intensity discharge sources (e.g., sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of electroluminescent sources, pyro- luminescent sources (e.g., flames), candle-luminescent sources (e.g., gas mantles, carbon arc radiation sources), photo -luminescent sources (e.g., gaseous discharge sources), cathode luminescent sources using electronic satiation, galvano -luminescent sources, crystallo- luminescent sources, kine-luminescent sources, thermo -luminescent sources, triboluminescent sources, sonoluminescent sources, radioluminescent sources, and luminescent polymers.

[0026] A given light source may be configured to generate electromagnetic radiation within the visible spectrum, outside the visible spectrum, or a combination of both. Hence, the terms "light" and "radiation" are used interchangeably herein. Additionally, a light source may include as an integral component one or more filters (e.g., color filters), lenses, or other optical components. Also, it should be understood that light sources may be configured for a variety of applications, including, but not limited to, indication, display, and/or illumination. An

"illumination source" is a light source that is particularly configured to generate radiation having a sufficient intensity to effectively illuminate an interior or exterior space. In this context, "sufficient intensity" refers to sufficient radiant power in the visible spectrum generated in the space or environment (the unit "lumens" often is employed to represent the total light output from a light source in all directions, in terms of radiant power or "luminous flux") to provide ambient illumination (i.e., light that may be perceived indirectly and that may be, for example, reflected off of one or more of a variety of intervening surfaces before being perceived in whole or in part). [0027] The term "spectrum" should be understood to refer to any one or more frequencies (or wavelengths) of radiation produced by one or more light sources. Accordingly, the term

"spectrum" refers to frequencies (or wavelengths) not only in the visible range, but also frequencies (or wavelengths) in the infrared, ultraviolet, and other areas of the overall electromagnetic spectrum. Also, a given spectrum may have a relatively narrow bandwidth (e.g., a FWHM having essentially few frequency or wavelength components) or a relatively wide bandwidth (several frequency or wavelength components having various relative strengths). It should also be appreciated that a given spectrum may be the result of a mixing of two or more other spectra (e.g., mixing radiation respectively emitted from multiple light sources).

[0028] For purposes of this disclosure, the term "color" is used interchangeably with the term "spectrum." However, the term "color" generally is used to refer primarily to a property of radiation that is perceivable by an observer (although this usage is not intended to limit the scope of this term). Accordingly, the terms "different colors" implicitly refer to multiple spectra having different wavelength components and/or bandwidths. It also should be appreciated that the term "color" may be used in connection with both white and non-white light.

[0029] The term "color temperature" generally is used herein in connection with white light, although this usage is not intended to limit the scope of this term. Color temperature essentially refers to a particular color content or shade (e.g., reddish, bluish) of white light. The color temperature of a given radiation sample conventionally is characterized according to the temperature in degrees Kelvin (K) of a black body radiator that radiates essentially the same spectrum as the radiation sample in question. Black body radiator color temperatures generally fall within a range of from approximately 700 degrees K (typically considered the first visible to the human eye) to over 10,000 degrees K; white light generally is perceived at color

temperatures above 1500-2000 degrees K.

[0030] The term "lighting fixture" is used herein to refer to an implementation or arrangement of one or more lighting units in a particular form factor, assembly, or package. The term

"lighting unit" is used herein to refer to an apparatus including one or more light sources of same or different types. A given lighting unit may have any one of a variety of mounting

arrangements for the light source(s), enclosure/housing arrangements and shapes, and/or electrical and mechanical connection configurations. Additionally, a given lighting unit optionally may be associated with (e.g., include, be coupled to and/or packaged together with) various other components (e.g., control circuitry) relating to the operation of the light source(s). An "LED-based lighting unit" refers to a lighting unit that includes one or more LED-based light sources as discussed above, alone or in combination with other non LED-based light sources. A "multi-channel" lighting unit refers to an LED-based or non LED-based lighting unit that includes at least two light sources configured to respectively generate different spectrums of radiation, wherein each different source spectrum may be referred to as a "channel" of the multichannel lighting unit.

[0031] The term "controller" is used herein generally to describe various apparatus relating to the operation of one or more light sources. A controller can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein. A "processor" is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein. A controller may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0032] In various implementations, a processor or controller may be associated with one or more storage media (generically referred to herein as "memory," e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM, floppy disks, compact disks, optical disks, magnetic tape, etc.). In some implementations, the storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at least some of the functions discussed herein. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement various aspects of the present invention discussed herein. The terms "program" or "computer program" are used herein in a generic sense to refer to any type of computer code (e.g., software or microcode) that can be employed to program one or more processors or controllers. [0033] The term "network" as used herein refers to any interconnection of two or more devices (including controllers or processors) that facilitates the transport of information (e.g. for device control, data storage, data exchange, etc.) between any two or more devices and/or among multiple devices coupled to the network. As should be readily appreciated, various

implementations of networks suitable for interconnecting multiple devices may include any of a variety of network topologies and employ any of a variety of communication protocols.

Additionally, in various networks according to the present disclosure, any one connection between two devices may represent a dedicated connection between the two systems, or alternatively a non-dedicated connection. In addition to carrying information intended for the two devices, such a non-dedicated connection may carry information not necessarily intended for either of the two devices (e.g., an open network connection). Furthermore, it should be readily appreciated that various networks of devices as discussed herein may employ one or more wireless, wire/cable, and/or fiber optic links to facilitate information transport throughout the network.

[0034] The term "user interface" as used herein refers to an interface between a human user or operator and one or more devices that enables communication between the user and the device(s). Examples of user interfaces that may be employed in various implementations of the present disclosure include, but are not limited to, switches, potentiometers, buttons, dials, sliders, a mouse, keyboard, keypad, various types of game controllers (e.g., joysticks), track balls, display screens, various types of graphical user interfaces (GUIs), touch screens, microphones and other types of sensors that may receive some form of human-generated stimulus and generate a signal in response thereto.

[0035] The term "primary color" should be understood to refer to any color provided by a discrete light source, whether provided by a color LED, a phosphor alone or in combination with a filter, lens or other optical component. A primary color includes any color that can be combined with at least one other primary color to create a secondary color. It should be appreciated that the term "primary color" may be used in connection with a discrete light source that emits radiation at any frequency.

[0036] The term "pulse width modulation" or PWM should be understood to refer to a commonly used technique for controlling power to LEDs. A PWM signal is produced by the controller turning input power "on" or "off and generating an output signal of fixed amplitude and frequency. The average of the output pulse width modulated power is the same as that of the input signal.

[0037] The term "duty cycle" should be understood to refer to the period of "on" time in proportion to the regular interval or full cycle of the input power. Duty cycle is expressed in percent.

[0038] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

Brief Description of the Drawings

[0039] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

[0040] FIG. 1 illustrates a block diagram of an illumination system in accordance with an embodiment;

[0041] FIG. 2 illustrates a graph comparing the combined peak current output for pulse width modulated signals with a duty cycle of 30 percent, in accordance with an embodiment;

[0042] FIG. 3 illustrates a graph comparing the combined peak current output for pulse width modulated signals with different duty cycles, in accordance with an embodiment;

[0043] FIG. 4 illustrates a graph comparing the combined peak current output for pulse width modulated signals with a duty cycle of 25 percent, in accordance with an embodiment;

[0044] FIG. 5 illustrates a flow chart of a method of providing illumination from an illumination system in accordance with an embodiment; [0045] FIG. 6 illustrates a flow chart of a method of providing illumination from an illumination system in accordance with an embodiment; and

[0046] FIG. 7 illustrates a graph of pulse width modulated signals for an illumination system, in accordance with an embodiment.

Detailed Description

[0047] In illumination systems controlled by pulse width modulated (PWM) signals, high flicker ratio and unwanted high peak load for the associated power supply unit remain a problem. Applicants have recognized and appreciated that it would be beneficial to reduce the combined current of the pulse width modulated signals to the light sources. In view of the foregoing, various embodiments and implementations of the present invention are directed to illumination systems and methods that dynamically phase-shift PWM control signals in a way that reduces the combined peak current, thus reducing the high flicker ratio of the light sources and the unwanted high peak load on the power supply unit.

[0048] Referring to FIG. 1 , in one embodiment, an illumination system 100 includes a controller 102, a plurality of solid state light sources 104, a plurality of current drivers 106, and a power supply unit 108. The controller 102, the light sources 104, the current drivers 106 are shown separately, however, as should be appreciated, these elements can be incorporated into one lighting unit. The controller 102, each of the light sources 104, and each of the current drivers 106 and the power supply unit 108 include one or more inputs and outputs.

[0049] In accordance with the embodiment illustrated in FIG. 1, the output of the power supply unit 108 is electrically coupled to the input of each of the current drivers 106,

respectively. Each of the outputs of the current drivers 106 is electrically coupled to a corresponding input of the light source 104. Each current driver 106 has an input to receive the output of the controller 102. The controller 102 includes inputs to receive feedback from the light sources 104, as well as, inputs to receive user-defined settings. As shown, the illumination system 100 includes a quantity (n) of PWM control signals generated for (n) current drivers 106, where each current driver 106 (1 -n) corresponds to a respective light source 104 (1-n). [0050] The power supply unit 108 provides power to drive the components of the illumination system 100. Each of the inputs of the current drivers 106 receives power from the power supply unit 108. The current drivers 106 provide current to the inputs of the corresponding light sources 104 based on a respective PWM control signal received from the controller 102. The controller 102 generates the PWM control signals for the light sources 104 based on the received feedback and user-defined settings to produce light of a desired color point and desired luminous flux. The resulting operation of the light sources 104 provides light of the desired color point and luminous flux.

[0051] Each light source 104 may include one or more LEDs that emit light of a primary color, such as red, green, blue, cyan, amber, royal, deep red, or white, among others. The LEDs may be encapsulated with domes, or may be free of encapsulation. In one embodiment, each light source 104 includes a string with a plurality of LEDs. In a further embodiment, the LEDs included in a string are all of the same color. In one embodiment, the LEDs includes in the string include a plurality of primary colors of light that can be mixed to provide mixed white light having a desired color point and color temperature. In another embodiment, the LEDs are used as a backlight, such that light from red, green and blue LEDs is mixed to provide homogenous light to the back surface of a display.

[0052] In some embodiments, a plurality of light sources 104 are included in the illumination system 100, where each of the plurality of light sources 104 is configured to emit light of a different primary color. In one embodiment, eighteen light sources 104 (n=18) are included, where the light sources 104 include three strings of red LEDs, five strings of amber LEDs, six strings of blue LEDs and four strings of white LEDs. As should be apparent, other

configurations of a plurality of light sources can be employed.

[0053] In one embodiment, the power supply unit 108 is electrically coupled to the current drivers 106 and supplies power to the light sources 104. The power supply unit 108 can be configured to receive AC line voltage and can supply a filtered, scaled, and regulated DC voltage to the current drivers 106. The power supply unit 108 can include a rectifier, a low pass filter and/or other circuitry configured to provide conditioned output power to the current drivers 106. In other embodiments, the power supply unit 108 can be configured for use with other types of input power sources (e.g, D.C. power sources). [0054] The current drivers 106 may be implemented as DC/DC converters and regulate voltage from the power supply unit 108 to provide current to drive the light sources 104. The DC/DC converters can include integrated circuits, transistors, and any other combination of active and/or passive components. The DC/DC converters can be arranged with the LED-based light sources 104 in buck configuration, boost configuration, buck-boost configurations or in other circuit topologies that can be employed to supply current to drive the light sources 104, for example, by providing a PWM current signal. The current drivers 106 can further employ driver circuitry including one or more voltage-to -current converters. The drive circuitry can be configured such that each light source 104 is associated with a voltage-to-current converter that provides a corresponding current to the light source 104.

[0055] According to one embodiment, the controller 102 controls the operation of light sources 104, based on operation of a phase-shifting module 112, a duty cycle module 1 10 and using the PWM control signals generated by a PWM module 114. In one embodiment, the duty cycle module 110, the phase-shifting module 1 12, and the PWM module 1 14 include one or more inputs and outputs. The output(s) of the duty cycle module 110 are connected to the input(s) of the phase-shifting module 112. The output(s) of the phase-shifting module 112 are connected to the input(s) of the PWM module 114. In another embodiment, the input(s) of the PWM module 114 are connected to both the output(s) of the duty cycle module 110 and the output(s) of the phase-shifting module 1 12.

[0056] In various embodiments, the illumination system 100 can also include one or more detectors or sensors that provide information about the light sources 104. As shown in FIG. 1 , the illumination system 100 includes a luminous flux detector 116, a temperature sensor 118 and a user-defined settings input 120. The outputs from the luminous flux detector 116, the temperature sensor 118 and the user-defined settings input 120 are connected to the inputs of the duty cycle module 110. The information received from the luminous flux detector 116, the temperature sensor 118 and the user-defined settings input 120 can be used to control the operation of the light souses 104.

[0057] In one embodiment, the duty cycle module 1 10 determines the duty cycle value of PWM control signals that for the light sources 104 to operate the illumination system 100 and the individual light sources to generate light of the desired color point and flux (i.e. dimming level). In some embodiments, the duty cycle module 1 10 includes inputs to receive information about the light sources 104 from the detectors and sensors coupled to them. In further embodiments, the duty cycle module 110 also has inputs to receive user-defined settings provided for the illumination system 100. According to one embodiment, the duty cycle values calculated by the duty cycle module 1 10 can also be determined using the predefined system settings, which may be set by the manufacturer of the illumination system 100. The duty cycle module 1 10 can calculate the duty cycle value using one, or any combination of the predefined system settings, the user-defined settings and/or feedback information from the detectors or sensors.

[0058] In one embodiment, the duty cycle module 1 10 provides duty cycle values determined for the light sources 104 to the phase-shifting module 112. The phase-shifting module 112 receives the duty cycle values, as described in further detail below, and provides phase-shifted duty cycle values to the PWM module 1 14. The PWM module 1 14 generates PWM control signals based on the phase-shifted duty cycle values. In some embodiments, the PWM module 1 14 can receive signals from both the duty cycle module 110 and the phase-shifting module 1 12 and generate PWM control signals based on each of these signals. In accordance with one embodiment, each of the duty cycle module 110, the phase-shifting module 1 12 and the PWM module 1 14 are included in a single module.

[0059] In one embodiment, the PWM control signals generated by the PWM module 114 are high frequency periodic signals at constant current and varying duty cycle. The PWM control signals control the operation of the current drivers 106 to regulate the current to the light sources 104. For example, the PWM signal can be an oscillating square waveform, oscillating between 0 and 12 V with a frequency of 1 kHz. PWM signals with different amplitudes and frequencies can be employed depending on the embodiment. Each PWM signal has a duty cycle, which is the percentage of "on" time of the oscillating square wave within one period.

[0060] In the illustrated embodiments, the phase-shifting module 1 12, receives the calculated values of the duty cycles from the duty cycle module 1 10 and generates phase-shifted duty cycle values for the light sources 104. In some embodiments, the duty cycles are phase-shifted by amounts that are calculated to optimize the output of the power supply unit 108 while achieving the desired output of the light sources 104. For example, approaches described herein can optimize the power supply output by reducing or minimizing the combined peak current provided to the light sources 104. In some embodiments, the combined peak current is calculated as an average value of a sum of duty cycle values of PWM controlled current signals provided to the light sources 104.

[0061] As described above, in some embodiments, the duty cycle module 1 10 can calculate the duty cycle values based at least in part on predefined system settings. Predefined system settings can include a lower output threshold and an upper output threshold. The lower and upper threshold values can be based on preset limits by the manufacturer that assure reliable or energy efficient operation of the illumination system. In one embodiment, the threshold values limit the duty cycle module 110 to producing duty cycle values that result in a limited range of luminous flux levels and limited range of desired color point values emitted by the light sources 104. In alternative embodiment, predefined system settings are not employed.

[0062] According to some embodiments, a user of the illumination system 100 can select the user-defined settings for the illumination system 100 by adjusting the color point and diming level of the light sources through a user interface. In one embodiment, the duty cycle module 1 10 receives the user inputs of desired color point and desired luminous flux (e.g. color and dimming level) and calculates duty cycle values that produce light of the desired color point and desired luminous flux.

[0063] According to some embodiments, the duty cycle module 110 can also calculate the duty cycle values to compensate for changes to luminous flux and wavelength of light sources 104 that result from the temperature of the light source and/or aging of the light source. For example, LED drive currents can affect the temperature of light sources 104, which in turn affects the peak output wavelength of light sources 104. In one embodiment, a photosensitive detector such as a photodiode senses luminous flux of each light source 104. Based on the sensed flux information and manufacturer established flux values of light sources 104, the duty cycle module 1 10 can adjust the duty cycles of the PWM control signal provided to current driver 106 to maintain the established flux levels and correct for flux variations that would otherwise occur.

[0064] In one embodiment, a temperature sensor measures the temperature of at least one light source 104 and provides temperature feedback to the controller 102. For example, temperature sensor may measure LED junction temperature indirectly through temperature measurements taken at a heat sink of the LED. Based on the sensed temperature feedback, controller 102 can determine the peak wavelength of the light source 104 and adjust the duty cycles provided to the light sources 104 to maintain the desired color point. In another embodiment, both photosensitive detector measurements and temperature detector measurements are combined, allowing the controller 102 to maintain desired luminous flux levels and desired color point and compensate for changes that would otherwise result from temperature and aging.

[0065] In various embodiments, temperature and flux measurements can include any of temperature feed forward measurements and flux feedback alone or in combination. Further, color coordinates feedback can be employed alone or in combination with the preceding.

[0066] As described above, PWM control of a plurality of lighting sources can produce undesirable effects, such as, a high flicker ratio and can place high peak loads on the power supply unit 108. In one embodiment, the phase-shifting module 1 12 is configured to reduce or eliminate such unwanted side effects, by dynamically adjusting the phase of the PWM control signals provided to current drivers 106.

[0067] In some embodiments, dynamic phase-shifting of the PWM control signals is desired because duty cycle values calculated by the duty cycle module 1 10 are dynamic. For example, the duty cycle values can vary over time as a result of changes to the wavelength and the luminous flux levels of the light sources 104 due to age and temperature, as well as, changes to the user-defined color point and brightness levels of the illumination system 100. According to one embodiment, the phase-shift module 112 calculates a new phase-shift to reduce the combined peak current supplied to the light sources 104 in response to changed in the duty cycles determined by the duty cycle module 1 10. According to some embodiments, the phase- shifting process occurs for every period of the PWM control signals to continuously adjust the phase of individual PWM control signals. The resulting phase-shifted duty cycles PWM 1 ... (n) provided by the controller 102 can continuously minimize the ripple of the combined peak current despite changes to the duty cycle values determined by the duty cycle module 1 10. In addition, minimizing the ripple of the combined peak current also minimizes the flicker ratio of the light sources 104 and reduces the electromagnetic interference generated by operation of the power supply unit 108. Thus, in some embodiments, the flicker ratio and/or electromagnetic interference are also continuously minimized. [0068] The controller 102 may be a current-mode or a voltage-mode pulse-width modulation controller implemented using software, hardware components, or a combination of software and hardware. The hardware components may be implemented using hardware devices such as field- programmable gate arrays (FPGA's), application-specific integrated circuits (ASIC's), microcontrollers, programmable logic devices (PLD's) or other such devices known in the art.

[0069] FIGs. 2-4 graphically illustrate a comparison of the combined peak current output for PWM controlled current signals with different combinations of duty cycles, with and without embodiments of the present invention. For each of the FIGs. 2-4, the x-axis represents time expressed in seconds. The y-axis for the PWM controlled current signals represents amplitude of the duty cycles, expressed in amperes. The y-axis for the combined peak current (shown in FIG. 2 as I-PSU), represents amplitude of the power supply output, expressed in amperes.

[0070] In the example of FIG. 2, graph 200 shows PWM control signals for three light sources 104 (shown in FIG. 2 as PWM 1, PWM 2 and PWM 3), with each PWM control signal having a duty cycle of approximately 30 percent. In addition, the resulting combined current output of the power supply is shown (I PSU). The graph 202 represents the PWM control and the power supply output signals without processing by the phase-shifting module 1 12. The graph 204 represents PWM control signals and the power supply output after processing by the phase-shifting module 112. As shown in FIG. 2, the resulting combined peak current is substantially reduced following the phase-shifting of the original PWM signals. For this example, the combined peak current of the original signals is approximately 980 milliamps and the combined peak current of the phase shifted signals is approximately 160 milliamps, a reduction of approximately 84 percent.

[0071] In the example of FIG. 3, graph 300 shows the PWM signals (shown in FIG. 3 as PWM 1, PWM 2 and PWM 3) with different duty cycles. For example, the duty cycles illustrated in plot 302 may have been generated by duty cycle module 110 to compensate for changes in luminous flux and wavelength due to temperature and/or user-settings of a new desired color point value or a new luminous flux value. In graph 302, PWM 1 has a duty cycle of approximately 50 percent, PWM 2 has a duty cycle of approximately 30 percent and PWM 3 has a duty cycle of approximately 50 percent. Here too, the combined peak current produced as the result of phase-shifting the PWM control signals, shown in graph 304, is substantially reduced relative to the original PWM signals illustrated in graph 302. For this example, the combined peak current of the original PWM signals is approximately 830 milliamps and the combined peak current of the phase-shifted PWM signals is approximately 300 milliamps, a reduction of approximately 63 percent.

[0072] In the example of FIG. 4, graph 400 shows PWM control signals for three light sources 104, with each PWM control signal (PWM 1 , PWM 2 and PWM 3) having a duty cycle of approximately 25 percent. Again, the combined peak current produced as the result of phase- shifting the PWM control signal, shown in graph 404, is substantially reduced relative to the original PWM signals illustrated in the graph 402. For this example, the combined peak current in graph 402 is approximately 700 milliamps and the combined peak current in graph 404 is approximately 220 milliamps, a reduction of approximately 63 percent.

[0073] FIG. 5 illustrates a flow chart of a method 500 of providing illumination from an illumination system in accordance with one embodiment. In one embodiment, the method includes an act of receiving feedback regarding color point and/or luminous flux for n-light sources (ACT 502). For example, n represents all the light sources 104 in the illumination system 100. For each light source a duty cycle is calculated that will produce desired color point and desired luminous flux based on the feedback received (ACT 504). The desired color point and desired luminous flux may be based on any one of or any combination of predefined system settings, user-defined settings, temperature measurements and flux measurements, as described above or other information alone or in combination with any of the proceeding. The phase-shift is determined for the PWM control signals with the calculated duty cycles to reduce the combined peak current to the n-light sources (ACT 506). The calculated duty cycles (ACT 504) and the optimal phase-shift values are used to generate PWM control signals for each individual light source (ACT 508). Acts 504-508 may be repeated for each new calculation of duty cycle values, due to changes in received luminous flux and temperature feedback (ACT 502) or due to user changes to the desired luminous flux and/or color point.

[0074] FIG. 6 illustrates a flow chart of a method 600 for providing illumination from an illumination system in accordance with one embodiment. In one embodiment, the method 600 is included in the act of phase-shifting the PWM control signals (ACT 506). In one embodiment, the method 600 includes the acts of receiving calculated duty cycles from step 504 (ACT 602) for n-light sources representing the desired color point and the desired luminous flux. The calculated duty cycles are analyzed to remove duty cycles for the light sources that are equal to zero (i.e., a light source that if turned off) and to provide m-light sources (ACT 604), where m- light sources represents the number of the remaining light sources.

[0075] According to some embodiments, the remaining duty cycles are formed into an array of duty cycles, where each duty cycle for each light source is a member of the array. The array is arranged by maximizing a difference in duty cycle value between neighboring duty cycle members included in the array (ACT 606). According to one embodiment, first and last members in the array are considered neighboring. In one embodiment, Act 606 can be performed iteratively by finding the total difference for all the existing combinations of duty cycle members. The total difference represents the sum of all the differences between neighboring duty cycle members in the array. The total difference is found for every existing combination of neighboring duty cycle members and the array with the largest total difference is selected. The resulting set of combinations may contain more than one array of duty cycles that maximizes the difference in duty cycle value. According to another embodiment, the array is generated at Act 606 without giving consideration to maximizing the differences between neighbors in the array. Once an array is formed, a total of m-timeslots are created for m-light sources (ACT 608). The m-timeslots are created by dividing the overall period of the PWM control signals by the number of duty cycle members. The duty cycle members in the array (ACT 608) are located within the overall PWM period by matching the mid-point of each duty cycle member with the start of a respective timeslot (ACT 610).

[0076] In one embodiment, the phase-shifted duty cycles resulting from the method 600 are analyzed to determine whether two or more of the duty cycles begin at a common time within the overall PWM signal period. The common start time can be determined by comparing rise times of the duty cycles. Because the set of neighboring combinations (ACT 606) may contain more than one array that maximizes the difference in duty cycle value, a different array of duty cycle members may be generated as the result of finding a common start time within the PWM signal period. The remaining acts are performed accordingly (ACTs 608-610).

[0077] FIG. 7 shows graph 700 of PWM control signals illustrating one example of performing the method 600 for an illumination system, comprising six light sources. The phase- shifted duty cycles (shown in FIG. 7 as PWM l through PWM 6) are displayed for the duration of a PWM period of one millisecond. The calculated duty cycles for that period are received as PWM_1 = 20%, PWM_2=40%, PWM_3=0%, PWM_4=80%, PWM_5=60%, and PWM_6=10% (for example, at ACT 602). In this example, PWM 3 is removed as the light source with zero value to provide m=five light sources (for example, at ACT 604). The resulting duty cycles for five light sources are formed into an array of duty cycles by maximizing a difference in duty cycle value between neighboring duty cycle values included in the array (for example, at ACT 606). In this example, out of the total possible number of arrays, an array is selected that comprises: PWM_6, PWM_4, PWM_1 , PWM_5, and PWM_2. The total difference between the neighboring duty cycle values is 220%, where PWM_6 and PWM_2 are included as neighbors. A total of m=five timeslots are created for five light sources (for example, at ACT 608). Here, five timeslots of 200 microseconds are created by dividing the overall period of one millisecond by m (shown in FIG. 7 as slotl through slot5). The duty cycles in the array are located within the overall PWM period by matching the mid point of each PWM signal with the start of each timeslot (for example, at ACT 610). As shown, the mid point of the duty cycle PWM 6 is located in the first timeslot (slotl), followed by the midpoint of PWM_4 at the second time slot (slot2), followed by the midpoint of PWM l at the third time slot (slot3), followed by the midpoint of PWM 5 at the fourth time slot (slot4), and finally the midpoint of PWM 2 at the fifth time slot (slot5). The value for PWM 3 remains zero for the displayed period.

[0078] As shown in the example of FIG. 7, the light sources PWM l and PWM 5 begin at a common time within the overall PWM period (located by rises edges). In some embodiments, a different array of duty cycles may be generated as the result of the common start time (ACT 606). For example, an array comprising PWM_1 , PWM_2, PWM_6, PWM_5, and PWM_2, has the same total difference value of 220%, but does not include light sources with common start times within the PWM period.

[0079] While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0080] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

[0081] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[0082] The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0083] As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0084] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited. Any reference numerals or other characters, appearing between parentheses in the claims, are provided merely for convenience and are not intended to limit the claims in any way.

[0085] In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding,"

"composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively.

What is claimed is:

Claims

1. An illumination system (100) comprising:

a plurality of solid state light sources (104);

a plurality of drivers (106), each of the plurality of drivers electrically coupled to each of the plurality of solid state light sources, respectively; and

a controller (102) configured to:

generate a pulse width modulated signal having a duty cycle for each of the plurality of drivers, respectively, wherein each driver is configured to supply current to an associated one of the plurality of solid state light sources based on the respective pulse width modulated signal,

determine a first duty cycle of the pulse width modulated signal for each of the plurality of solid state light sources, respectively, to provide a desired color point and a desired luminous flux of the plurality of solid state light sources, and

phase-shift the respective pulse width modulated signals to reduce a combined peak current provided to the plurality of drivers for operation of each of the plurality of solid state light sources at the respective duty cycle.

2. The illumination system of claim 1, wherein the controller includes an input configured to receive a temperature feedback and a luminous flux feedback from the plurality of solid state light sources.

3. The illumination system of claim 1 , wherein the controller includes

a duty cycle module configured to respond to changes in at least one of temperature and luminous flux by determining a second duty cycle of the pulse width modulated signal for each of the plurality of solid state light sources; and

a phase-shifting module configured to automatically phase-shift the respective pulse width modulated signals with the second duty cycle to reduce the combined peak current.

4. The illumination system of claim 3, wherein the duty cycle module is configured to automatically respond to changes in at least one of the desired color point and the desired luminous flux to determine a second duty cycle.

5. The illumination system of claim 1 , further comprising a power supply unit configured to provide current to the plurality of drivers.

6. The illumination system of claim 1, wherein the controller includes a phase- shifting module configured to phase-shift the respective pulse width modulated signals and to determine the combined peak current as an average of a sum of the respective pulse width modulated signals.

7. The illumination system of claim 6, wherein the phase-shifting module is configured to minimize the combined peak current.

8. The illumination system of claim 6, wherein the phase-shifting module is configured to minimize a flicker ratio of the illumination system.

9. The illumination system of claim 6, further comprising a power supply unit coupled to each of the plurality of solid state light sources, wherein the phase-shifting module is configured to minimize electromagnetic interference generated by operation of the power supply unit.

10. A method of providing illumination with a lighting source including a plurality of solid state light sources, comprising:

generating a pulse width modulated signal having a duty cycle for each of the plurality of solid state light sources, respectively;

determining a first duty cycle of the pulse width modulated signal for each of the plurality of solid state light sources, respectively, to operate the plurality of solid state light sources at a desired color point and a desired luminous flux; and phase-shifting the respective pulse width modulated signals to reduce a combined peak current provided to the plurality of solid state light sources when operated at the respective duty cycle.

1 1. The method of claim 10, further comprising:

determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of temperature and luminous flux of the plurality of solid state light sources; and

phase-shifting the respective pulse width modulated signals with the second duty cycle to reduce the combined peak current.

12. The method of claim 10, further comprising:

determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of the desired color point and the desired luminous flux; and

13. The method of claim 10, wherein phase-shifting the pulse width modulated signal to reduce the combined peak current further comprises reducing the combined peak current by reducing an average value of a sum of the respective pulse width modulated signals.

14. The method of claim 10, further comprising:

phase-shifting the pulse width modulated signal to minimize the combined peak current.

15. The method of claim 10, further comprising:

phase-shifting the pulse width modulated signal to minimize a flicker ratio of the lighting source.

16. The method of claim 10, further comprising:

phase-shifting the pulse width modulated signal to minimize electromagnetic interference generated by the lighting source.

17. The method of claim 10, further comprising:

organizing an array of the respective duty cycles by maximizing a difference in duty cycle value between neighboring duty cycles included in the array.

18. The method of claim 17, further comprising:

determining a plurality of timeslots based on a number of members in the array; and

locating each of the respective pulse width modulating signals within an overall pulse width modulating period by matching a mid point of the respective pulse width modulating signals with a start of a timeslot included in the plurality of timeslots.

19. The method of claim 18, further comprising:

determining whether two or more of the respective pulse width modulating signals begin at a common time within the overall pulse width modulating signal period.

20. A computer readable medium encoded with a program for execution on a processor, the program, when executed on the processor performing a method of providing illumination from a lighting source having a plurality of solid state light sources, the method comprising acts of:

21. The computer readable medium of claim 20, the method further comprising: phase-shifting the pulse width modulated signal to minimize the combined peak current.

22. The computer readable medium of claim 20, the method further comprising: determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of temperature and luminous flux of the plurality of solid state light sources; and

23. The computer readable medium of claim 20, the method further comprising: determining a second duty cycle of the pulse width modulated signal in response to a change in at least one of the desired color point and the desired luminous flux; and

24. The computer readable medium of claim 20, the method farther comprising: organizing an array of the respective duty cycles by maximizing a difference in duty cycle value between neighboring duty cycles included in the array.