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

0001This 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.

0002Light 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 "multichip LED packages".

0003Light 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.

0004In Unites States Patent Application <patcit id="pcit0001" dnum="US2001032985A"><text>US 2001/032985</text></patcit> a light-emitting device that may include several LEDs, mounted on a shared sub mount, and coupled to circuitry formed on the sub mount is described. A photosensitive diode is positioned on the sub mount, or under the LED, such that it receives a portion of the light emitted by the LED. In the situation where there is a group of LEDs on the sub mount, the diodes are placed individually underneath each LED. In this way the photosensitive diodes monitors the light emitted by corresponding LEDs, and separately adjusts the current received by the LEDs via a control unit.

0005Further, <patcit id="pcit0002" dnum="US2002047624A1"><text>US2002/047624 A1</text></patcit> discloses an illuminator assembly that is capable of utilizing a plurality of LEDs to produce a desired resultant hue. Light from LEDs is radiated onto a diffuser. While most of the light from LEDs passes through the diffuser and onto the illuminated scene, some of the light is scattered from the diffuser back towards a detector and allows detector to measure the relative output of the LEDs. The detector sends information to a processor that adjusts the intensity of each of the light sources to provide the resultant hue. When multiple detectors are utilized they are typically configured to view different LEDs. A detector may be configured with a filter, which allows a single colour of light from LEDs to be detected.

0006It would be desirable, therefore, to provide a system for maintaining light characteristics of multi-chip LED packages that overcomes these and other disadvantages.

0007One 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.

0008Another 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.

0009The 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.

0010<figref idref="f0001"><b>FIG. 1</b></figref> 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;

0011<figref idref="f0002"><b>FIG. 2</b></figref> 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

0012<figref idref="f0002 f0003 f0004 f0005"><b>FIG. 3</b> to <b>FIG. 6</b></figref> 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.

0013<figref idref="f0001"><b>FIG. 1</b></figref> shows one embodiment of a system for maintaining light characteristics from a multi-chip LED package in accordance with the present invention at <b>100.</b> In one embodiment, the system <b>100</b> may include a multi-chip LED package <b>102</b> and input device <b>140.</b>

0014Multi-chip LED package <b>102</b> may include control system <b>130,</b> temperature sensing device 120, light emitting diode (LED) <b>150</b> and light sensing device <b>110.</b>

0015Multi-chip LED package <b>102</b> includes at least one Light Emitting Diode chip <b>150</b> with connecting electronics <b>135.</b> 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 <b>100</b> may include white LED chips, other colors of LED chips or combinations of colored and white LED chips.

0016The multi-chip LED package <b>102</b> also includes control system <b>130.</b> 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 <b>130</b> may be operably connected to system components <b>110,120,140, 150</b> with control system electronics wiring <b>115,125,135</b> or any other suitable connection known in the art. The control system <b>130</b> may alter the current flow to the various system components via the wiring <b>115, 125, 135.</b> For example, the control system electronics <b>130</b> may alter the current flowing into the LED chips <b>150</b> via electronics wiring <b>135.</b> The computer software in the control system <b>130</b> may include instructions to control current flow to various system components by any suitable means known in the art.

0017The multi-chip LED package <b>102</b> may also include an enclosure <b>105,</b> surrounding a light sensing device <b>110.</b> Referring now to <figref idref="f0001"><b>FIG.1</b></figref> and <figref idref="f0002"><b>FIG. 3</b></figref><b>,</b> which illustrates an exemplary embodiment of an enclosure <b>105,</b> enclosure <b>310</b> includes at least one aperture <b>320,</b> opening towards an LED, that channels light emitted from a light source (LED) to the light sensing device <b>110.</b> The aperture <b>320</b> 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 <figref idref="f0003 f0004 f0005"><b>FIGS. 4-6</b></figref><b>.</b> The size of these apertures may determine the amount of light that reaches the light sensors. In one embodiment, the enclosure interior <b>315</b> is a white interior, which provides a more efficient combining of light from different desired light source. 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.

0018The multi-chip LED package <b>102</b> also includes at least one light sensing device <b>110</b> located within enclosure <b>105.</b> 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 <b>110</b> converts the transmitted light to a sensed light signal. The light sensing device <b>110</b> may be operably connected <b>115</b> to the control system <b>130</b> 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 <b>105,</b> the placement of the LED chips, by the shape of the enclosure, or combinations thereof.

0019The multi-chip LED package <b>102</b> may include a temperature sensing device <b>120</b> operably connected to the control system <b>130.</b> 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 <b>102.</b> The temperature sensing device <b>120</b> 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 <b>102.</b> 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 <b>100</b> is mounted.

0020The system may also include an input device <b>140,</b> wherein the user may predetermine the color and intensity of the desired light output. In one embodiment, this input device <b>140</b> 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 <b>130.</b> 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 <b>140</b> may be any suitable hardware or software, or combination of hardware and software that allows the user to select a preferred profile of light.

0021Referring now to <figref idref="f0002"><b>FIG. 2</b></figref><b>,</b> a method for maintaining light characteristics of a multi-chip LED package is shown generally at <b>200.</b> In practice, the user selects a desired light profile (Block <b>210</b>) using input device <b>140.</b> The desired light profile includes the color and intensity of the transmitted light

0022Once the multi-chip LED package <b>102</b> begins to transmit light, a sensor <b>110</b> associated with each of the LEDs measures the transmitted light for both color and intensity (Block <b>215</b>). The sensor <b>110</b> converts the measured transmitted light to a sensed light signal (Block <b>220</b>). 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.

0023The 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 <b>225</b>). The results of the comparison will determine whether an adjustment of the current to one or more LED is required (Block <b>230</b>). If the sensed light value is within a predetermined acceptable range of the desired light signal value the method returns to Block <b>215</b>. However, if the sensed light signal is not within that predetermined range, the current to one or more LED will be adjusted (Block <b>235</b>) and the method will return to Block <b>215</b> for continued monitoring of the multi-chip LED package.

0024Altering 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 <b>130</b> to alter the light emitted from the LEDs. This process may be continued until the desired light is no longer demanded.

0025In another embodiment, the temperature sensor <b>120</b> 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 <b>130</b> will alter the current flow to the LEDs as required.

0026Referring now to <figref idref="f0003"><b>FIG. 4</b></figref><b>,</b> an exemplary arrangement of the LED chips, enclosures and light sensors of a multi-chip LED package is shown generally at <b>400.</b> Light sensors <b>412</b> may be positioned on the multi-chip package to measure the light intensity from the LED chips located on the package. The sensors <b>412</b> may be positioned where they may monitor a plurality of LEDs on the package. The sensors <b>412</b> may be partially covered by an enclosure <b>402</b> that channels incoming light to the sensor <b>412.</b> In one embodiment, the enclosure may control the amount of light that impinges upon the sensors. The enclosure <b>402</b> may have various apertures that face adjacent LED chips <b>403, 405, 411.</b> The total intensity and color of the multi-chip LED package <b>401</b> may be determined by summing the intensity of each LED chip.

0027The enclosure may have smaller apertures that face LED chip <b>411.</b> In LED package <b>401,</b> the control system may measure the intensity of the LED chips <b>403, 405, 411.</b> LED chip <b>411</b> may be measured by four sensors <b>412</b> which may be covered by enclosures <b>402.</b> Because this measuring may result in an over-consideration of LED chip <b>411,</b> the apertures of enclosures <b>402</b> that face LED chip <b>411</b> may be reduced to ¼ of the size of the other apertures that face the corner LED chips <b>403.</b> This ratio is equal to the inverse of the number of times a specific LED chip is measured. For example, LED chip <b>405</b> may be measured by two sensors <b>412</b> so the aperture facing LED chips <b>405</b> may be reduced to ½ of the size of the other apertures that face the corner LED chips <b>403.</b> 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 <b>403, 405, 411</b> may be of equal size and may be positioned equidistant from the sensors <b>412.</b>

0028If filtered photodiodes are used in this system, the light emitted from various colors of LED 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. Immediately 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 <b>130</b> and used to determine whether the current to the various devices needs to be altered in order to achieve the desired light output.

0029Referring now to <figref idref="f0004"><b>FIG. 5</b></figref><b>,</b> another exemplary arrangement of the LED chips, enclosures and light sensors of a multi-chip LED package is shown generally at <b>500.</b>

0030Because each LED chip <b>503</b> in the array of multi-chip LED packages faces only one aperture of the enclosure <b>502</b> the LED may be measured once. Also, because each LED chip <b>503</b> may be the same size and may be equidistant from each enclosure <b>502,</b> the apertures of enclosure <b>502</b> may be the same size.

0031Referring now to <figref idref="f0005"><b>FIG. 6</b></figref> yet another exemplary arrangement of the LED chips, enclosures and light sensors of a multi-chip LED package is shown generally at <b>600.</b>

0032Similar to the multi-chip package shown generally at <b>400,</b> the system may include LED chips <b>603, 605, 609, 611</b> with connecting electronics, enclosures <b>612</b> and at least one optical sensor <b>602</b> all operably connected together and mounted on the multi-chip package <b>601.</b> The system may operate as that of the system in <figref idref="f0003"><b>FIG. 4</b></figref><b>,</b> generally shown at <b>400;</b> however two enclosures may be used instead of four. Similar to <figref idref="f0003"><b>FIG. 4</b></figref> 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 <b>603, 605, 609, 611</b> on the LED multi-chip package <b>601.</b>

0033While 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.