Patent Application
20050273237
1. Field of the Invention
This invention relates to the field of electroluminescent devices, and more particularly to a control scheme implemented in a lighting system to control the light outputs at a color temperature.
2. Description of the Related Art
The rapid progress made in the field of display technology has particularly driven the development of electroluminescent devices, also commonly called light-emitting devices (LEDs). LEDs can be implemented in a wide range of applications including backlight modules of liquid crystal displays, direct light sources of display in electroluminescent displays, lighting systems, etc.
In operation, a forward electric current flows through the LED to produce light. Depending on the specific active material incorporated therein, the LED can be configured to irradiate light of a particular color. The color emission is usually determined according to the requirement of the particular application of the LED.
U.S. Pat. No. 6,411,046, which is incorporated herein by reference, describes a lighting system that incorporates LEDs of different color emissions additively mixing with one another to produce white light. To prevent undesirable chromatic deviation of the white light, this patent reference discloses a control method that incorporates LED chromaticity coordinates and LED temperature as factor of adjustment of the LED light outputs. Such a control scheme is accomplished by automatic regulation and requires the implementation of a complex structure, including micro-controllers to compute the control rules, to be effective.
Therefore, there is presently a need for a control structure and control method that can simplify the manufacture of the lighting system and reduce the manufacture cost.
The application describes a lighting system and a method of controlling the operation of a lighting system that can overcome the prior problems.
In one embodiment, the lighting system comprises a plurality of light-emitting devices of different color emissions, a plurality of current drivers delivering electric currents to the light-emitting devices in response to drive signals, and a control circuit operable to configure the drive signals in response to a difference between the light outputs from the light-emitting devices and preset light intensity references.
In another embodiment, the method of controlling the lighting system includes generating electric currents flowing through the light-emitting devices to produce light outputs of different colors, wherein the level of the electric currents respectively varies in response to a plurality drive signals, and configuring the drive signals in response to a difference between the light outputs from the light-emitting devices and preset light intensity references.
In an embodiment, one light intensity reference reflects a target average of light output for one color emission. In a variant embodiment, configuring the drive signals further includes configuring the drive signals to adjust the respective light outputs of specific color emissions to the light intensity references. In a variation, the drive signals include pulse width modulated signals the duty cycles of which are set according to the difference between the light intensity references and the light outputs of specific colors.
The foregoing is a summary and shall not be construed to limit the scope of the claims. The operations and structures disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the invention, as defined solely by the claims, are described in the non-limiting detailed description set forth below.
Current drivers 212 are operable to generate electric currents flowing through the LEDs 214R, 214G, 214B. Upon the input of current levels from the current drivers 212, the LEDs 214R, 214G, 214B irradiate diverse light outputs of basic light colors R, G, B that mix with one another to achieve a full spectrum of colors.
Color photosensors 220 are installed to determine the brightness of specific colors emitted by the LEDs 214R, 214G, 214B, respectively. Red color photosensor 220R is configured to sense the brightness of red color irradiated from the red LEDs 214R, green color photosensor 220G is configured to sense the brightness of green color irradiated from the green LEDs 214G, and blue color photosensor 220B is configured to sense the brightness of blue color irradiated from the blue LEDs 214B. The photosensors 220 can be photodiodes equipped with color filters configured selectively pass red, green and blue lights, respectively.
The analog signals issued from the color photosensors 220 according to the amount of light sensed for each color R, G, B are scaled via amplifiers 230 before they are inputted to comparators 240. The comparators 240 output feedback signals reflecting the differences between the sensed color outputs R, G, B and references Ri, Gi, Bi, which characterize the error between the target light outputs and the actual light outputs of red, green and blue, respectively.
In response to the feedback signals, controllers 250 deliver respective drive signals to the current drivers 212 to control and adjust the level of electric current supplied to the LEDs 214. In an embodiment, the controllers 250 can be implemented as pulse width modulated (PWM) control integrated circuits. In PWM control, the drive signals are configured in the form of PWM duty cycles delivered to the current drivers 212 to adjust the LED driving electric current.
It understood that the foregoing PWM control implementation is only an example provided for the purpose of illustration, and other variant control schemes such as amplitude modulated control or the like can be also suitable.
Initially, reference values Ri, Gi, Bi are set in accordance with the desired intensity of the light outputs R, G, B from LEDs of different colors (302). In an embodiment, the references Ri, Gi, Bi can be set corresponding to target averages of light outputs of red, green and blue color for a desired color temperature. Drive signals are outputted to illuminate the LEDs (304). In an embodiment, the drive signals can be pulse width modulated signals the duty cycles of which determine the levels of light outputs from the LEDs.
The lights of different colors irradiated from the LEDs are sensed (306), and corresponding sensing signals Rf, Gf, Bf are generated and respectively compared with the references Ri, Gi, Bi (308). If one or more of the target references Ri, Gi, Bi is not met the drive signals are accordingly configured to correct the respective light outputs of the LEDs to the levels defined by the references Ri, Gi, Bi (310). The steps 306˜310 form an infinite loop in which the light outputs Rf, Gf, Bf from the LEDs are continuously sensed so as to determine and correct any light output variations relative to the references Ri, Gi, Bi.
The lighting system and control method as described herein can be implemented in a wide range of LED applications, and more particularly in white lighting systems used as backlights of liquid crystal displays. The feedback control scheme allows to simply maintain a constant color temperature of the emitted white light based upon the detection of the LED light outputs.
Realizations in accordance with the present invention have been described in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Additionally, structures and functionality presented as discrete components in the exemplary configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of the invention as defined in the claims that follow.
