A system for maintaining light characteristics from a multi-chip led package

Description of equivalent WO 2004002198 A1

A SYSTEM FOR MAINTAINING LIGHT CHARACTERISTICS FROM A MULTI-CHIP LED PACKAGE

0002This invention relates generally to a LED powered lighting system. Specifically, it relates to a system for maintaining light characteristics from a multi-chip LED package.

0003Light emitting diodes (LEDs) are being used more frequently in general illumination applications where they will have to provide high-intensity, constant user-specified color. In order to provide high-intensity light, packages containing multiple LED chips (of the same or different colors) must be used to avoid bulky lamps. We will refer to these below as "multi- chip LED packages".

0004Light intensity and other properties vary among LED chips. This can cause color variations in light output from multi-chip LED packages. Light intensity and color of a multi-chip LED package can be measured and kept constant with the use of optical sensors and supporting electronics and control systems which are positioned in packages separate from the LED chips. To obtain LED lamps that are compact, consistent in light output, and that require minimal design work from the lamp designer using multi-chip LED packages, integration of the sensors (and possibly other electronics) in the LED package is desirable. Placement of the sensors so that they provide useful signals for control of light output, then would be critical.

0005It would be desirable, therefore, to provide a system for maintaining light characteristics of multi-chip LED packages that overcomes these and other disadvantages.

0006One aspect of the present invention provides a system for maintaining light characteristics from a multi-chip LED package. The system may include means for restricting transmitted light to at least one light sensor to produce a restricted light signal and means for measuring the restricted light signal by the at least one light sensor to produce a sensed light signal. The system also includes means for comparing the sensed light signal to a desired light signal and means for adjusting current to at least one light emitting diode on the multi-chip LED package based on the comparison. Another aspect of the present invention provides a structure for maintaining light characteristics from a multi-chip LED package. The structure includes a plurality of LEDs; at least one enclosure positioned to receive an amount of light output from the plurality of LEDs; at least one light sensor positioned in the enclosure to measure the light output from the plurality of LEDs; and a controller operably connected to the LED chips to control current to the LED chips based on the measured light.

0007The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.

0008FIG. 1 is a schematic diagram of one embodiment of a system for maintaining light characteristics from a multi-chip LED package in accordance with the present invention; FIG. 2 is flow diagram of one embodiment of a system for maintaining light characteristics from a multi-chip LED package in accordance with the present invention; and

0009FIG.3 to FIG.6 are schematic diagrams of various embodiments of a system for maintaining light characteristics within a multi-chip LED package in accordance with the present invention. FIG. 1 shows one embodiment of a system for maintaining light characteristics from a multi-chip LED package in accordance with the present invention at 100. In one embodiment, the system 100 may include a multi-chip LED package 102 and input device 140.

0010Multi-chip LED package 102 may include control system 130, temperature sensing device 120, light emitting diode (LED) 150 and light sensing device 110.

0011Multi-chip LED package 102 includes at least one Light Emitting Diode chip 150 with connecting electronics 135. The LED may be, for example, Red, Green or Blue in color, and in another example, a plurality of LEDs may be all one color or may be a combination of colors. Other embodiments of system 100 may include white LED chips, other colors of LED chips or combinations of colored and white LED chips.

0012The multi-chip LED package 102 also includes control system 130. In one embodiment, the control system may be any suitable hardware or software, or combination of hardware and software that performs logic processing such as a computer chip with RAM. This control system 130 may be operably connected to system components 110, 120, 140, 150 with control system electronics wiring 115, 125, 135 or any other suitable connection known in the art. The control system 130 may alter the current flow to the various system components via the wiring 115, 125, 135. For example, the control system electronics 130 may alter the current flowing into the LED chips 150 via electronics wiring 135. The computer software in the control system 130 may include instructions to control current flow to various system components by any suitable means known in the art.

0013The multi-chip LED package 102 may also include an enclosure 105, surrounding a light sensing device 110. Referring now to FIG. 1 and FIG. 3, which illustrates an exemplary embodiment of an enclosure 105, enclosure 310 includes at least one aperture 320, opening towards an LED, that channels light emitted from a light source (LED) to the light sensing device 110. The aperture 320 may be of various sizes and shapes depending on the placement and number of LEDs associated with each enclosure, this is discussed in greater detail below in relation to FIGS. 4-6. The size of these apertures may determine the amount of light that reaches the light sensors. In one embodiment, the enclosure interior 315 is a white interior, which provides a more efficient combining of light from different desired light sources. The apertures determine how much light from which LEDs enters the enclosure. Once it is in the enclosure, the white interior surface mixes the admitted light. The purpose of this internal mixing is to make the photodiode less sensitive to variations among the LEDs that it is measuring.

0014The multi-chip LED package 102 also includes at least one light sensing device 110 located within enclosure 105. The light sensing device may be a photodiode, a photoconductor or any other suitable light sensing device known in the art. The light sensing device may be positioned such that the light transmitted from adjacent LEDs passes through the aperture and to the light sensor. The light sensor 110 converts the transmitted light to a sensed light signal. The light sensing device 110 may be operably connected 115 to the control system 130 by electronics wiring, fiber optics or any other suitable connecting means known in the art. The transmitted light from the LEDs may be restricted from or allowed to impinge upon the light sensors. This may be accomplished by the placement of the sensors beneath the enclosure 105, the placement of the LED chips, by the shape of the enclosure, or combinations thereof.

0015The multi-chip LED package 102 may include a temperature sensing device 120 operably connected to the control system 130. This temperature sensing device may be a thermocouple or any other suitable means known in the art used to measure the temperature of a component. The temperature sensing device may be used to measure the temperature of the LEDs used in this multi-chip LED package 102. The temperature sensing device 120 may be configured to measure LED temperature continuously or at specified intervals of time, for example, every two seconds. In one embodiment, the temperature sensing device may be included within the multi-chip LED package 102. In another embodiment, the temperature sensing device may be connected to and monitor the temperature of a heat sink upon which the multi-chip LED package system 100 is mounted.

0016The system may also include an input device 140, wherein the user may predetermine the color and intensity of the desired light output. In one embodiment, this input device 140 is a handheld keypad with an electronic selection menu. The input device may also be a keypad mounted on the wall or a personal computer operably connected to the control system 130. In practice, the user may simply push buttons on the keypad to select the corresponding profile of the light desired. For example, the user may select an off white color and a high- intensity bright light. The input device 140 may be any suitable hardware or software, or combination of hardware and software that allows the user to select a preferred profile of light.

0017Referring now to FIG. 2, a method for maintaining light characteristics of a multi- chip LED package is shown generally at 200. In practice, the user selects a desired light profile (Block 210) using input device 140. The desired light profile includes the color and intensity of the transmitted light.

0018Once the multi-chip LED package 102 begins to transmit light, a sensor 110 associated with each of the LEDs measures the transmitted light for both color and intensity (Block 215). The sensor 110 converts the measured transmitted light to a sensed light signal (Block 220). In one embodiment, the overall light color and intensity may be determined by the summation of all the individual light intensities of the individual LEDs. In another embodiment, the individual values of each separate color are summed to obtain a sensed light signal value for that specific color. For example, the sensed light signal for each red LED is summed for a total sensed signal value. The determined sensed light signal is then compared to the desired light signal value that is associated with the desired light profile the user selected (Block 225). The results of the comparison will determine whether an adjustment of the current to one or more LED is required (Block 230). If the sensed light value is within a predetermined acceptable range of the desired light signal value the method returns to Block 215. However, if the sensed light signal is not within that predetermined range, the current to one or more LED will be adjusted (Block 235) and the method will return to Block 215 for continued monitoring of the multi- chip LED package. Altering the current flow to the LEDs alters the color and intensity of the light emitted from the multi-chip package. Based on the selected desired light profile, the control system determines the amount of current to be released to the various components in the multi-chip LED package. The profile of the desired light characteristics may be used to evaluate the light measured by the light sensor. Current flowing to the components of the system may then be adjusted by the control system 130 to alter the light emitted from the LEDs. This process may be continued until the desired light is no longer demanded.

0019In another embodiment, the temperature sensor 120 also may measure the temperature of the LEDs. As long as the temperature remains constant within acceptable limits for the particular multi-chip LED package, the current flow rate to the components will be maintained by the control system. However, if the measured temperature is not within acceptable limits, the control system 130 will alter the current flow to the LEDs as required.

0020Referring now to FIG. 4, an exemplary arrangement of the LED chips, enclosures and light sensors of a multi-chip LED package is shown generally at 400. Light sensors 412 may be positioned on the multi-chip package to measure the light intensity from the LED chips located on the package. The sensors 412 may be positioned where they may monitor a plurality of LEDs on the package. The sensors 412 may be partially covered by an enclosure 402 that channels incoming light to the sensor 412. In one embodiment, the enclosure may control the amount of light that impinges upon the sensors. The enclosure 402 may have various apertures that face adjacent LED chips 403, 405, 411. The total intensity and color of the multi-chip LED package 401 may be determined by summing the intensity of each LED chip.

0021The enclosure may have smaller apertures that face LED chip 411. In LED package 401, the control system may measure the intensity of the LED chips 403, 405, 411. LED chip 411 may be measured by four sensors 412 which may be covered by enclosures 402.

0022Because this measuring may result in an over-consideration of LED chip 411, the apertures of enclosures 402 that face LED chip 411 may be reduced to of the size of the other apertures that face the corner LED chips 403. This ratio is equal to the inverse of the number of times a specific LED chip is measured. For example, LED chip 405 may be measured by two sensors 412 so the aperture facing LED chips 405 may be reduced to ^lA of the size of the other apertures that face the corner LED chips 403. These ratios may not be exact and may depend on the distribution of light actually emitted by the LEDs. It may be assumed that the LED chips 403, 405, 411 may be of equal size and may be positioned equidistant from the sensors 412.

0023If filtered photodiodes are used in this system, the light emitted from various colors of

0024LED chips may be sampled simultaneously. If unfiltered photodiodes are used on the LED chips only one color may be measured at a time using a time multiplex sampling method. For example, in a package containing red, blue and green LED, the green and blue LEDs may be turned off, while the red LEDs light intensity is measured. Immediately following this step, the red and green LEDs may be turned off, while the blue LEDs light intensity is measured.

0025Immediately following this step, the red and blue LEDs may be turned off, while the green LEDs light intensity is measured. The results of these measurements may be sent to the control system 130 and used to determine whether the current to the various devices needs to be altered in order to achieve the desired light output.

0026Referring now to FIG. 5, another exemplary arrangement of the LED chips, enclosures and light sensors of a multi-chip LED package is shown generally at 500. Because each LED chip 503 in the array of multi-chip LED packages faces only one aperture of the enclosure 502 the LED may be measured once. Also, because each LED chip

0027503 may be the same size and may be equidistant from each enclosure 502, the apertures of enclosure 502 may be the same size.

0028Referring now to FIG. 6 yet another exemplary arrangement of the LED chips, enclosures and light sensors of a multi-chip LED package is shown generally at 600.

0029Similar to the multi-chip package shown generally at 400, the system may include

0030LED chips 603, 605, 609, 611 with connecting electronics, enclosures 612 and at least one optical sensor 602 all operably connected together and mounted on the multi-chip package

0031601. The system may operate as that of the system in FIG. 4, generally shown at 400; however two enclosures may be used instead of four. Similar to FIG. 4 the ratio of one LED to the number of times the LED is measured may be determined to calculate the relative size of the apertures facing each the LED chips 603, 605, 609, 611 on the LED multi-chip package 601.

0032While the embodiments of the present invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.