HK1155314B - Led light output linearization - Google Patents

Description

LED light output linearization

Technical Field

The present invention relates generally to LED lighting schemes, and more particularly to linearizing the output of LED light to produce a more consistent output over the life of the LED.

Background

Product dispensers can have many different shapes and sizes. Each dispenser typically requires some product illumination and/or sign illumination. Light emitting diode ("LED") lighting has become popular in many lighting applications due to increased service life and decreased power usage. Typical LEDs used for illumination in a product dispenser setting may range from 0.5 to 3 watts and 25 to 70 lumens per watt. Such LEDs may typically be rated to run for 40,000 to 50,000 hours before failing. Unlike many light sources, where failure is defined as the point in time when no output is produced, LED failure is typically defined as the point in time when the light output is less than 70% of the LED's initial output.

Although the failure mode in LEDs is more satisfactory than that of other light sources, problems still exist. For example, many product vending machines use LEDs to illuminate product selections available for purchase. When a vending machine containing a "new" LED array is located in the vicinity of a vending machine with an "old" LED array (an LED array that has not failed, but has aged and produced less output than originally desired), the apparent difference in light output is apparent to potential consumers as dimming of the light occurs in the "old" LED array.

Dimly lit dispensers or dispensers with dimmed lighting sources may at least give the consumer the perception that the product therein is not adequately maintained. As a result, potential consumers will tend to purchase from vending machines with "newer" LED arrays because of their visually appealing appearance and appeal to the consumer's eyes. These LED problems often need to be addressed with sufficient product marketing, i.e., the dispenser and the product therein should be properly illuminated to be visually appealing and to attract the eyes of the consumer.

Therefore, an improved LED power scheme that maintains consistent light output of the LED over its rated lifetime is desired. This improved LED power scheme should ensure a uniform appearance of the LED over its actual lifetime.

Summary of The Invention

The present invention thus describes a system for producing a smooth characteristic for LED light output. The system may include: an array comprising one or more light emitting diodes; a power supply connected to the LED array for providing a driving current to the LED array; a timer connected to the controller, wherein the timer records the on-time of the LED array and communicates the LED array on-time to the controller; and a controller connected to the power supply, wherein the controller adjusts the intensity of the drive current provided to the LED array based on the on-time data received from the timer such that the resulting relative light output is approximately equal to the initial relative light output.

The LED array may simply be any number of LEDs operating in conjunction with each other and powered by the same power source. Notably, the array may contain only a single LED. Typical LEDs for illumination in a product dispenser setting may range from 0.5 to 3 watts and 25 to 70 lumens per watt. Such LEDs may typically be rated to run for 40,000 to 50,000 hours before failing. While the present invention discusses LEDs generally in the context of product dispensers, it should be recognized that the present invention is operable with LEDs used in any context and is not limited to any particular implementation.

The power supply providing the drive current may be any suitable power supply for powering the LED array. In a preferred embodiment of the invention, the power supply may provide alternating current power from a pulse width modulated power supply. While the present application discusses the use of ac power, it should be recognized that the present invention may be operated using dc power. However, the drawings provided herein are in the context of an ac power source. The power supply provides a variable drive current to power the LED array. The controller is used for controlling the intensity of the power output according to a preset instruction, wherein the intensity corresponds to the relative power output intensity of the LED array on time indicated by the timer.

The timer connected to the controller may be any timer suitable for monitoring the "on time" of the LED array. The controller can be programmed to trigger adjustments to the drive current based on the current timing usage data transmitted by the timer to help ensure that the proper drive current intensity is provided to maintain the light output of the array at a consistent level.

These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the appended claims and drawings.

Brief Description of Drawings

FIG. 1 is an illustration of one embodiment according to an aspect of the present invention.

Fig. 2 is a graphical representation of the general dimming of LED light output.

Fig. 3 is a graphical representation of the relative power output required in accordance with aspects of the present invention.

Detailed Description

The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

Fig. 1 illustrates an exemplary embodiment of the present invention used in a product dispenser 100. The dispenser 100 is typically a dispenser in the vending industry. However, it should be noted that the present invention is not so limited and may be used in any setting where a consistent light output is desired. Generally, the dispenser 100 includes at least one power bus 110. Any type of power supply 120 may be used in accordance with the present invention. The power bus 110 may be in electrical communication from the power source 120 to one or more LEDs 130 via electrical wiring. The power bus 110 carries the drive current required to illuminate the LED130 at the desired intensity.

The power supply 120 can affect the current, voltage, and duty cycle to achieve different amperage levels. Generally, a single power supply 120 may be sufficient to efficiently power multiple LEDs 130.

If multiple LEDs 13 are used in the LED array 130, they may be wired together and electrically connected to the power supply 120. Further, it should be noted that while the embodiments discussed herein refer to an LED array 130, it should be clear that the present invention can similarly be used with a single LED 130. In addition, other forms of LED arrays 130 may be used in accordance with the present invention. For example, the power supply 120 may supply either an alternating supply voltage or a direct supply voltage. Additionally, in some embodiments, the power supply 120 may be mounted on a flexible printed circuit board.

It is apparent that the LED array 130 may operate at direct or pulsed power and current. In this embodiment, the controller 140 implements pulse width modulation to cause the current intensity to change.

The timer 150 operates to record the operating time of the LED array 130. As the LED array 130 operation time is extended, the controller 140, interacting with the power supply 120, operates to increase the relative power output to a level corresponding to the amount of LED array 130 on time received from the timer 150. The controller 140 uses a stored algorithm, as discussed below, to determine the correct adjustment of the relative power output with respect to the received on-time to result in the maintenance of a constant light output intensity. The controller 140 may be a computer board, an embedded device, a digital signal processor, or any other suitable controller device known to those skilled in the art.

In a preferred embodiment of the present invention, pulse width modulation is implemented by the controller 140 to achieve the desired relative light output of the LED array 130. The timer 150 communicates the LED array 130 on-time to the controller 140. The controller 140 then calculates the required change, if any, in the relative power output to maintain a constant relative light output. To effect a change in relative power output, the controller 140 is operable to modulate the pulse width of the incoming power current to cause a longer or shorter LED on-time per cycle, thereby increasing or decreasing the relative light output accordingly.

Fig. 2 illustrates the general dimming of the light output of LEDs typically used in product containers 100. The x-axis 210 represents the operating time of the LED130 (or LED array 130) in hours. The y-axis 220 represents the relative light output of the LED 130. In this figure, the relative light output of the LED130 when it first enters operation has a value of 1.0. When the LED130 is in operation for an initial period of time (typically less than 100 hours), it reaches a peak 230 in its lifetime light output. Typically this so-called "burn-in" peak 230 reaches a relative light output level of about 1.05.

After reaching the initial "burn" peak 230, the relative light output decreases over time over the remaining life of the LED 130. The light output degrades approximately logarithmically as the operating time. As seen in the segment labeled 240, the relative light output is fairly constant from an operating time of about 100 hours to an operating time of about 2000 hours.

Point 250 shows a typical failure point for LED 130. As noted above, an LED130 failure point is generally defined where its relative light output is less than 0.7 times its initial relative light output. Typically, the LED130 reaches its failure point 250 after 40,000 to 50,000 hours of operation. Finally, point 260 shows the time at which a typical LED130 reaches a point where its relative light output reaches less than 0.5 times its initial relative light output. This typically occurs after about 100,000 hours of operation.

Similarly, the operating temperature may play a role when evaluating the dimming mode of the LED 130. In general, approximately one percent (1%) loss of intensity per degree celsius increase in temperature is observed in some commercially available LEDs. It will be appreciated that this is a general principle and is not meant to limit the application of the invention in any way.

Fig. 3 illustrates the power output required to power the LEDs 130 in a manner that creates a smooth relative light output over the general lifetime of the LEDs 130. The x-axis 310 represents the operating time of the LED130 (or LED array) in hours. The y-axis 320 represents the relative power output of the power supply 120. In this figure, the relative power output when the LED130 first enters operation is 1.0. The level of relative power output required at any given point in time can be calculated by a simple formula: [ 2.0-relative light output ]. Thus, at the "burn" peak 230, where the relative light output will be around 1.05, the controller 140 will adjust the relative power output to around 0.95 to achieve the proper current intensity increase in LED brightness. The aim of the invention is to always be at a sustained relative light output of 1.0 or about 1.0.

It should be apparent that the foregoing relates only to the preferred embodiments of the present invention and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.

Claims (6)

1. A method for powering an LED array, comprising:

powering an array comprising one or more light emitting diodes using a power supply connected to the LED array, wherein the power supply provides a drive current to the LED array;

recording the on-time of the LED array using a timer connected to a controller;

transmitting LED array on-time data to the controller,

based on the on-time data received from the timer, the controller automatically adjusts the intensity of the drive current provided to the LED array such that the resulting relative light output is approximately equal to the initial relative light output.

2. The method of claim 1, wherein the power supply powers the array of LEDs using a pulse width modulation scheme.

3. The method of claim 1, wherein the power supply supplies an alternating supply voltage or a direct supply voltage.

4. The method of claim 1, further comprising the step of mounting the power supply to a flexible printed circuit board.

5. The method of claim 1, wherein the array of light emitting diodes comprises one or more series-connected light emitting diodes.

6. The method of claim 1, wherein the light output is used to illuminate a product contained in a product dispenser.