a2) United States Patent
`US 6,510,995 B2
`(10) Patent No.:
`Muthuetal.
`(45) Date of Patent:
`Jan. 28, 2003
`
`
`US006510995B2
`
`(54) RGB LED BASED LIGHT DRIVER USING
`MICROPROCESSOR CONTROLLED AC
`DISTRIBUTED POWER SYSTEM
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`(75)
`
`(*) Notice:
`
`Inventors: Subramanian Muthu, Ossining, NY
`(US), Chin Chang, Yorktown, NY (US)
`a
`;
`(73) Assignee: Koninklijke Philips Electronics N.V.,
`Eindhoven (NL)
`Subject to anydisclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C, 154(b) by 0 days.
`(21) Appl. No.: 09/810,142
`(22)
`Filed:
`Mar. 16, 2001
`(65)
`Prior Publication Data
`
`US 2002/0145041 A1 Oct. 10, 2002
`(SL) Unt, C17 ci
`ceeccceeccccseesccsseeeesesveesessseveesesnes G06K 7/14
`
`(52) US. Ch. cess
`.. 235/454; 235/462.25
`
`(58) Field of Search ......ccccccccssseeeen 235/462.25, 454,
`235/455, 462.01-462.49, 472.01, 472.03;
`358/509, 505, 475, 506, 501, 487
`
`4,859,832 A *
`5,508,825 A *
`5,808,286 A *
`6,084,692 A *
`
`8/1989 Uchara etal. cece 219/411
`4/1996 Kataoka ...eeeeecees 358/474
`9/1998 Nukuiet al.
`eee 235/472
`7/2000 Ohtaniet al. cece 358/509
`
`
`
`* cited by examiner
`
`Primary Examiner—Thien M. Le
`(57)
`ABSTRACT
`A device for controlling and adjusting a display light for a
`retail display system comprising a computer associated with
`plural light sources for adjusting the light sources to opti-
`mally display particular products. The light sources are
`adjusted based upon a prestored table specifying optimal
`lighting conditions for each of plural products, and a feed-
`back loopthat feeds back actuallighting conditions.
`
`16 Claims, 4 Drawing Sheets
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`1
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 1 of 4
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`US 6,510,995 B2
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 2 of 4
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`US 6,510,995 B2
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 3 of 4
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`US 6,510,995 B2
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`U.S. Patent
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`Jan. 28, 2003
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`Sheet 4 of 4
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`US 6,510,995 B2
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`FIG. 4
`
`401
`
`402
`
`ON/OFF
`
`‘m’ switches —
`for color
`selection
`
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`selection
`
`5
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`

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`US 6,510,995 B2
`
`1
`RGB LED BASED LIGHT DRIVER USING
`MICROPROCESSOR CONTROLLED AC
`DISTRIBUTED POWER SYSTEM
`
`TECHNICAL FIELD
`
`This invention relates to commercial display systems and
`the like, and more particularly, to an improved method and
`apparatus for lighting such commercial display systems and
`the like. The invention has particular applications in com-
`mercial refrigeration systems used in a retail environment,
`such as retail display freezers.
`
`BACKGROUNDOF THE INVENTION
`
`Red-Green-Blue (RGB) based white Light Emitting
`Diode (“LED”) illumination is known in the art and is
`finding applications in backlighting for LCD panels,lighting
`for commercial freezers, signage etc. For these applications,
`linear power supplies or switch-mode power supplies are
`used to drive the LEDs. Theefficiency of the overall system
`with the use of linear power supply is low and the switch-
`mode power supply overcomesthis problem. Since there are
`three LED light sources, three independent power supplies
`are used to drive the LEDs with a proper current control
`scheme.
`In this configuration, each power supply may
`contain independent AC/DC converter, a power factor cor-
`rection unit, an isolation transformer, and a DC/AC con-
`verter system. There exists a redundancyin this scheme due
`to the three independent AC/DC converters, power factor
`correction unit, and the isolation transformer. In addition, it
`requires independent control of the converters in the power
`supplies. This schemeresults in increase in cost, complexity
`in control and poor performance.
`A still further problem with the present state of the art is
`accurately controlling the amount of each type of light
`emitted. More specifically, the color of the light resulting
`from the combination of the light emitted by the red, green,
`and bluelights is determined largely by the relative amounts
`of each type of light that gets mixed together. The light
`source associated with each type of light has a different
`sensitivity to age and temperature, as well as other factors.
`As a result, maintaining the appropriate amount of each
`color of light such that the resultant total light amount is
`correct is a difficult if not impossible task.
`Another issue not addressed by prior systems is the fact
`that in a display case or retail display refrigeration device,
`the type and amount of light used to display particular
`products mayinfluence a consumer’s purchasing decisions.
`There exists no technique of uniformly assuring that each
`specific product is displayed using the optimum lighting
`conditions.
`
`
`
`SUMMARYOF THE INVENTION
`
`The above and other problem ofthe prior art are overcome
`in accordance with the present invention whichrelates to an
`LED current driver for a lighting system applicable in
`commercial displays.
`In accordance with the invention,
`drivers are utilized to drive red, green, and blue LEDs in a
`specified proportion with one another. A feedback loop
`transmits color and intensity information to a
`microprocessor, which adjusts the values of each of the red,
`green, and blue lights to achieve a prescribed lighting
`intensity and color.
`In an enhanced embodiment, a computer and storage are
`provided for determining the intensity and color of light
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`used based upon specific products being displayed, or spe-
`cific times of day. Specifically, a computer may adjust the
`light color and/or intensity to optimize display at particular
`times or
`for particular products.
`In one exemplary
`embodiment, a microprocessor controlled AC distributed
`powersupply system is used to provide LED drive currents
`to a white LED luminaryfor lighting commercial freezers.
`The AC distributed system contains a front-end AC/DC
`converter with power factor correction, a high frequency
`inverter, an isolation transformer and three DC/AC convert-
`ers with RGB drive current control system. A single, front-
`end AC/DC converter system converts the AC supply and
`maintains a constant DC link voltage as the input to the high
`frequency DC/AC inverter. The AC/DC converter also per-
`forms the powerfactor correction at the AC mains. The high
`frequency converter converts the DC voltage to AC and
`supplies powers to three AC/DC converters with LED drive
`current control.
`
`The power converter system is controlled by a micropro-
`cessor system. ‘he microprocessor system providesaninte-
`grated closed loop control and the PWM generation for the
`converter systems, in addition to the control of the white
`hight generated by the LED luminary. This approach pro-
`vides an integral solution for the control of the LED driver
`system. The control algorithm for the microprocessor sys-
`tem is developed for modularity and with multi-processing
`features, to provide the effective controlling capabilities for
`the microprocessor system.
`The microprocessor system is also optionally connected
`to a user computer, which is programmed with the food that
`will be displayed in the freezers. The computer in the shop
`selects the suitable white color point and the lighting level
`that should be generated by the system whena specified food
`is being displayed in the freezers, based upon programmed
`user priorities. The computer supplies this information to the
`microprocessor system at the appropriate times, which con-
`trols the driver system to produce the required color and
`lighting level. ‘Therefore,
`the selection of the color and
`lighting level for the displayed food is automated. The
`computer can also start and stop the freezer driver such that
`the freezer lights are switched off automatically when it is
`not needed, and therefore, the power saving is achieved.
`In another enhanced embodiment, the system is arranged
`to accept data from an input device, such as a hand held
`keyboard or bar code scanner.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 represents a block diagram overview of the exem-
`plary embodiment of the present invention;
`FIG. 2 depicts a representation of a distributed power
`supply for use in connection with the present invention;
`FIG. 3 shows a second embodiment ofa distributed power
`system for use in driving the lights in accordance with an
`exemplary embodiment of the present invention; and
`FIG. 4 showsthe user interface for selecting a particular
`color for the lighting system.
`
`DETAILED DESCRIPTION OF THE
`PREFFERED EMBODIMENT
`
`FIG. 1 presents the overview of the microprocessor con-
`trolled AC power supply system for RGB LEDbasedfreezer
`driver in accordance with an exemplary embodimentof the
`invention. The power is supplied by front-end AC/DC
`converter 10, high frequency DC/AC converter 20, and three
`load-end AC/DC converters 30, 31 and 32 for providing
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`US 6,510,995 B2
`
`3
`RGB LEDdrive currents. The system includes Red, Green
`and Blue LED light sources 120, 130 and 140 respectively.
`Each Red, Green and Blue LED light source is made of a
`plurality of LEDs connected in a suitable series and/or
`parallel configuration.
`The light source also houses light sensors such as photo-
`diodes and heat-sink temperature sensors (not shown) for
`closed-loop fecdback control of the white light. The light
`output of the light source may be supplied to mixing optics
`and an optical fiber system (not shown)for transmission of
`the light into the freezer or similar environment. However,
`any suitable means of conveying the light is acceptable.
`The system is controlled by a Microprocessor system 50.
`The Microprocessor system uses feedback system 62 to
`convey variables to the Microprocessor 50. Control signals
`are provided to PWM generation and isolation 61 as shown
`for use in controlling DC/AC converter 20. By adjusting the
`amplitude and/or duty cycle of the PWM signal produced,
`the power to each driver 30-32 is adjusted.
`The microprocessor system is connected to a user inter-
`face and a messaging display system 64. The microprocessor
`system is also interfaced to an optional computer 51, or to
`the computer network 53 either via infrared communications
`or though series/parallel ports 52.
`The primary function of the front-end AC/DC converter
`10 is to convert the AC supply voltage to a DC voltage. In
`addition, the AC/DC converter 10 is made to perform the
`power factor correction alt
`the AC mains, possibly with
`universal voltage range input. The front-end AC/DC con-
`verter 10 can be based on Flyback or Boost topologies.
`The feedback control system for the output voltage and
`the powerfactor correction at the AC mainsis carried out by
`the microprocessor 50 which outputs the necessary control
`signals via the PWM generation and the isolation block 61.
`The PWMgating signals are also generated by the micro-
`processor 50. For this, the line current is also one of the
`feedback variables in addition to the DC link voltage. This
`is shown at 62.
`
`The microprocessor 50 then directly provides the PWM
`gating signals to the AC/DC converter 10. Alternatively, the
`power factor correction and the PWM function can be
`carried out externally. In this case, the AC/DC converter
`contains the necessary function blocks for the PFC and the
`PWM generation.
`The output of the AC/DC converter system is connected
`to the input section of the high frequency DC/AC inverter
`system 20. The DC/AC converter system converts the DC
`voltage to a high frequency AC voltage. The DC/AC con-
`verter is realized either by resonant converter or a square
`wave converter topology. As an example, the DC/AC con-
`verter system based on a resonant converter topology is
`shownin FIG. 2. In FIG. 2, the resonant converter system is
`based on the half bridge converter system 202 connected to
`a resonant tank 201. Alternatively, a full bridge configura-
`tion can also be used. The output of the converter is fed to
`a suitable resonant tank, whose output is connected to a high
`frequency isolation transformer 203. The transformers then
`drive converters 30-32 as shown.
`
`Certain simplifications are possible for particular appli-
`cations. For example, whenthe light output level is not high,
`some single stage circuils could be utilized. FIG. 3 showsan
`additional embodimentof the power supply system of FIG.
`2. The arrangement of FIG. 3 includes three Flyback con-
`verters operated with unity power factor correction, con-
`nected in parallel. In this case, the AC distributed system is
`realized at the line frequency of the input voltage. Such
`system is also controlled by microprocessor 50.
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`Returning to FIG. 1, the outputs of the AC/DC converters
`30-32 are connected to the RGB LED light sources, and
`provide regulated drive currents to the LED light sources
`120, 130 and 140. The RGB LED light sources may be
`supplied either with the constant DC current or by PWM
`current pulse. The magnitude of the DC current or the duty
`ratio of the PWM current pulses is determined by a white
`light control system in order to control the color and the
`lighting level of the white light in accordance with known
`techniques. The control system is also executed by the
`microprocessor.
`A suitable light sensor 40 and a heat sink temperature
`sensor 41, as shown in FIG.1, are used to sense the light
`output and the heat sink temperature of the LEDs. These
`parameters are fed into the microprocessor 50,
`through
`feedback circuit 62. The microprocessor 50 calculates the
`color and the lighting level of the white luminary. Then, the
`microprocessor 50 obtains the required LED drive currents
`or the PWM gating pulse widths. The AC/DC converter is
`then controlled to provide the required LED drive currents.
`Forinputting the feedback signals into the microprocessor
`system, the feed back circuit 62, is used. The feed back
`circuit 62 includes sensing and conditioning circuits for
`inputting the feed back signals directly to the analog-to-
`digital converter 161 in the microprocessor system 50. The
`feed back variables may comprise the LED light source
`output from LEDs 120, 130 and 140, heat sink temperature
`from sensor 41, LED drive currents, DC link voltages,
`and/or line currents.
`The feed back circuit also contains fault-sensing circuits,
`which generate interrupts upon a fault. The outputs of the
`fault sensing circuits are directly connected to non-maskable
`interrupts in the microprocessor system.
`The microprocessor 50 directly provides the PWM gating
`signals, which are first passed through an isolation circuit
`61. The outputs of this isolation circuit are fed into indi-
`vidual MOSTETdrivers in AC/DC converter 10, DC/AC
`converter 20, and LED drivers 30,31, and 32.
`The microprocessor 50 is also connected to a user inter-
`face system 63, for manually selecting the color and the
`lighting level for the white light. An exemplary embodiment
`of the user interface system 63 is shown in FIG. 4, which
`comprises switches 401-403 and switch decoding logic 404.
`Whena switch is closed, the decoding logic 404 detects the
`switch closure and outputs the data in digital form. The
`output of the decoding logic can be interfaced to the micro-
`processor 50 using either infrared communications or via
`cables or other means. Theuserinterface 64 also contains on
`ON/OFF switch 401 for starting and stopping the system,
`and switches 402 and 403 for selecting color and lightlevel.
`The microprocessor 50 is also connected to a message
`display system 64, which is used to display the status of the
`microprocessor system such as the selected color, system
`condition, and the lighting levels.
`The microprocessor 50 mayinclude at least one CPU or
`a DSP 160, analog interface devices 161 such as analog-to-
`digital converter and digital-to-analog converter system,
`digital interfaces 162 such as serial input/output, infrared
`port, JIAG interface, digital ports, and other devices 163
`such as memory,
`timers and a clock. A multi-processor
`system with more than one microprocessor can be usedif all
`the control functions and the PWM generation are imple-
`mented in the microprocessor system.
`The output of the feed back circuit 62 for sensing light,
`LEDdrive currents, and the DC link voltage are input to the
`analog-to-digital converters 161, which converts the analog
`signals to digital for the use by the control algorithms.
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`US 6,510,995 B2
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`5
`The microprocessor system is also connected to a com-
`puter 51, which contains the information about the food, and
`the time and the date of the food that will be displayedin the
`freezer. The computeris also programmedto select a proper
`white color point and the lighting level based on the food
`that will be displayed. The microprocessor system can be
`interfaced to this computer cither via an infrared port, or
`through a serial port or parallel port or a JTAG connector.
`The microprocessor system is properly equipped with a
`suitable interfacing system to handle such connectivity. The
`computer then supplies the information for the color and the
`lighting level of the white light depending on the food that
`is being displayed. Therefore, the selection of the color and
`dimming level for the white light is automated and the
`appropriate white light is automatically generated based on
`the food.
`
`the
`The computer also contains the information about
`operational hours for the shop. Therefore, it can start the
`LED freezer light source when the shop is opened and shut
`down the driver when the shop is closed. This arrangement
`results in automatic power savings.
`the computer may
`Altematively, rather than use time,
`either locally store or access a database of all products.
`Whenthe user puts product into a freezer, he/she scansit
`ioto the computer using, an optional bar code reader, hand
`held keyboard, or other similar device. The computer then
`sets the light levels and colors in accordance with the stored
`information for that product by performing a table look up.
`While the above describes the preferred embodiment of
`the invention, various other modifications and additions will
`be apparent to those of skill in the art. These modifications
`are intendedto fall within the scope of the following claims.
`Whatis claimedis:
`
`1. An apparatus for controlling multiple light sources to be
`mixed to form light of a predeterminedcolor, said apparatus
`comprising:
`plural color sensors, for detecting an amount of light
`emitted from each light source;
`storage means, for storing predetermined values indica-
`tive of a desired amount of light to be emitted from
`each light source; and
`a processor, for comparing the amount of light detected
`from each light sources with a desired amountof light
`to be emitted from each light source and for adjusting
`a Pulse Width Modulated (PWM)signal inputted to a
`powersource supplying the lights sources in response
`thereto.
`2. The apparatus of claim 1, wherein a duty cycle of the
`PWMsignalis adjusted.
`3. The apparatus of claim 1, wherein the PWMsignal is
`adjusted to control both the predetermined color and an
`intensity of light emitted at the predetermined color.
`4. An apparatusfor controlling multiple light sources to be
`mixed to form light of a predeterminedcolor, said apparatus
`comprising:
`plural color sensors, for detecting an amount of light
`emitted from each light source;
`storage means, for storing predetermined values indica-
`tive of a desired amount of light to be emitted from
`each light source; and
`a processor, for comparing the amount of light detected
`from each light sources with a desired amountof light
`to be emitted from each light source and for adjusting
`a Pulse Width Modulated (PWM)signal inputted to a
`power source supplying the lights sources in response
`thereto,
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`wherein said processor is connected to a separate
`computer, the computer including data and software tor
`controlling the amountof light emitted from each light
`source based upon measured conditions and predeter-
`mined inputs.
`5. The apparatus of claim 4, wherein the measured con-
`ditions are obtained by inputting a product to be displayed
`with the light of the predetermined color, and the predeter-
`mined inputs are stored values indicating the predetermined
`color.
`
`6. The apparatus of claim 4, wherein the measured con-
`ditions includes time.
`7. A computer apparatus for adjusting at least one of a
`color and an intensity of light emitted to display products for
`sale, said computer apparatus comprising:
`a table of stored values indicative of desired relative
`values of each of plural light sources for each type of
`product to be displayed;
`an external interface for accepting from an input device
`information indicative of a product to be displayed with
`the light; and
`control logic for performing a table lookup and adjusting
`a Pulse Width Modulated signal to cause said light
`sources to emit said stored desired values.
`
`8. The computer apparatus of claim 7, wherein the input
`device is a bar code scanner.
`
`9. The computer apparatus of claim 7, wherein the input
`device is permanently connected to a refrigeration appara-
`tus.
`
`10. A method of adjusting light used in a commercial
`refrigeration device to display particular products, said
`method comprising:
`storing a table indicative of a color and an intensity of
`light desired to be utilized for display of each of a
`plurality of products;
`accepting information indicative of a product to be dis-
`played;
`performing a table lookup to adjust the color and the
`intensity of the light in a manner such that the product
`is displayed with the light desired; and
`adjusting at least one of an amplitude or a duty cycle of
`a Pulse Width Modulated (PWM)signal in a manncr
`such that the color and the intensity of the light is
`properly adjusted.
`11. The method of claim 10, further comprising:
`utilizing a DC/AC converter to adjust the output current
`of each of a plural of Light Emitting Diode (LED)
`drivers to thereby separately adjusting current deliv-
`ered to each of LED drivers.
`12. The method of claim 10, wherein said accepting of
`information is implemented by accepting the information
`from a keyboard attached permanently to the refrigeration
`device.
`
`13. A display device for a product to be sold in a retail
`environmentor the like, said display device comprising:
`a shelf for holing the product;
`a lighting device attached to the shelf; and
`storage and input meansfor storing values indicative of a
`color and an intensity of a light to be usedto display the
`product and for adjusting a Pulse Width Modulated
`(PWM)signalto alter the color and the intensity of the
`light being displayed in response to an input of infor-
`mation specifying the product being displayed.
`14. The display device of claim 13, wherein said shelf is
`included within a refrigeration device.
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`US 6,510,995 B2
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`7
`15. A device for controlling a light, said device compris-
`ing:
`a stored table of products and desired lighting conditions
`for each product;
`means for inputting a specific product;
`means for adjusting the light to optimally display the
`product; and
`
`8
`a pulse width modulation circuit for adjusting power
`delivered to each of a plural of light emitting diodes in
`response to the information stored in the table and
`information fed back from light sensors.
`16. The device of claim 15, whercin said means for
`inputting a specific products is a bar code scanner.
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