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  Intelligent drive circuit for a light emitting diode (led) light engineUSPTO Application #: 20070040518Title: Intelligent drive circuit for a light emitting diode (led) light engine Abstract: A controller for controlling a light emitting diode (LED) light engine. The controller includes a temperature sensor configured to sensor temperature at the LED light engine. A current sensor senses a drive current of the LED light engine. A voltage differential sensor senses a voltage differential across LEDs of the LED light engine. A timer monitors a time of operation of the LED light engine. Further, a control device controls the drive current to the LED light engine based on the sensed temperature, the sensed drive current, the sensed voltage differential, and the monitored time of operation. Further, the control device outputs an indication of intensity degradation of an LED, and if the intensity degradation exceeds a predetermined threshold the control can output an indication of such to a user, so that the user can be apprised that the LED needs to be changed. (end of abstract)
Agent: Oblon, Spivak, Mcclelland, Maier & Neustadt, P.C. - Alexandria, VA, US Inventor: Garrett Young USPTO Applicaton #: 20070040518 - Class: 315309000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070040518. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention is directed to a control device for a light emitting diode (LED) light engine, and more particularly to a control device that can efficiently control a drive current provided to the LED light engine. [0003] 2. Description of the Background Art [0004] Light engines including LEDs as light sources are well known. An LED as a light source degrades over time, in contrast to an incandescent lamp that operates at a given light output and then at a specific time burns out and ceases to operate at all. [0005] One manner to compensate for the long term degradation of light output by an LED is to initially drive the LED with a much higher driving current than is necessary for a desired light output. For example, an LED can be initially driven with a drive current at, for example, 30% higher than required for a desired light output. In that manner when the LED slowly degrades over time, the light output from the LED will decrease, but the light output can decrease 30% and still output the desired amount of light. For example in this instance if a LED degrades to output 30% less light over five years, then by initially driving the LED with 30% greater drive current than necessary to have a 30% greater light output, the LED will properly operate for five years before its light output falls below a desired level. [0006] Further, in such a background system when the LED finally outputs less light than desired, i.e. in this example when the light output is degraded by greater than 30%, no clear indication is provided that the light output from the LED has significantly decreased or fallen below a determined threshold. SUMMARY OF THE INVENTION [0007] The applicant of the present invention recognized that such a background way of driving an LED has significant drawbacks in that it requires the LED to be driven harder than necessary and to consume significantly more energy than needed to provide a desired light output. That is, when the LED initially is driven with a drive current 30% higher than that necessary to achieve a desired light output, the LED will consume significantly more energy than needed. As one of the benefits of using LEDs is that they are more energy efficient than an incandescent bulb, driving an LED with more power than needed for a desired light output mitigates one of the benefits of using an LED. Also, driving LEDs with more power accelerates degradation of the LEDs and shortens their operating life, thereby mitigating another benefit of using LEDs. [0008] Accordingly, one object of the present invention is to provide a novel device and method for driving an LED light engine that addresses and reduces the above-noted drawbacks in the background art. [0009] A more specific object of the present invention is to provide a novel control for driving an LED light engine that is more energy efficient and leads to a longer operating life for an LED, by not initially driving an LED with a higher drive current than needed for a desired light output. The novel control of the present invention intelligently varies a drive current supplied to an LED light engine to drive an LED light engine to output a constant desired light output throughout its life. [0010] Further, another object of the present invention is to provide a novel system and method for providing an indication when an LED light output has degraded below a certain point. BRIEF DESCRIPTION OF THE DRAWINGS [0011] A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: [0012] FIG. 1 shows an overview of a control system of the present invention; [0013] FIG. 2 shows a control operation performed in the control system of FIG. 1 of the present invention; [0014] FIG. 3 shows a further control operation performed in the control system of FIG. 1 of the present invention; [0015] FIG. 4 shows another control operation performed in the control system of FIG. 1 of the present invention; and [0016] FIGS. 5A and 5B show another control operation performed in the control system of FIG. 1 of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS [0017] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, an overview of a control system for driving an LED light engine 5 that contains LEDs, or at least one LED, for illumination is shown. [0018] In FIG. 1, a temperature sensor 7 senses a temperature at the LED light engine 5, and outputs a sensed temperature signal T(s) based on the sensed temperature. A current waveform sensor 8 senses a drive current of the LED light engine 5 and outputs a corresponding sensed current waveform signal I(s). A voltage differential sensor 9 senses a voltage differential across the LEDs of the LED light engine 5 and outputs a corresponding voltage differential signal V(s). [0019] A controller/driver 10 receives the sensed temperature signal T(s), the sensed current waveform signal I(s), and the sensed voltage differential signal V(s). The controller/driver 10 also includes a timer 11 that monitors a time that the LED light engine 5 operates. That is, the timer 11 starts a time count when the LED light engine initially starts to operate and continues to count the time that the LED light engine 5 operates. The controller/driver 10 further outputs a drive signal D(s) that drives the LED light engine 5. The controller/driver 10 is also connected to or includes an optional indication control 12, which can provide an indication when the LED light engine 5 has been calculated to have its light output degrade below a certain value. [0020] FIG. 2 shows control operations performed by the controller/driver 10 of FIG. 1; that is, the operation blocks shown in FIG. 2 are performed by the controller/driver 10. Continue reading... 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