Patent Publication Number: US-10764977-B2

Title: LED light temperature control

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 62/653,941 filed on Apr. 6, 2018 and entitled LED LIGHT TEMPERATURE CONTROL, which is hereby incorporated by reference 
    
    
     FIELD OF INVENTION 
     The present invention generally relates to a system and method for adjusting the color temperature of an LED light. 
     BACKGROUND 
     Light emitting diodes (LEDs) have many advantages over traditional lighting sources, such as tubular fluorescent lights, incandescent lights, or high intensity discharge lights. These advantages include high light-electricity conversion rate, small volume, long life, adopting DC current, fixed wavelength low heat generation, and complying with environmental protection requirements. For these reasons, LEDs have become a popular illumination device. 
     In some applications, it may be desirable to vary the color temperature of the LED lighting, such as varying the light from a cooler temperature (i.e. blue and purple hues) to warmer temperature (i.e. orange and red hues). This may be done by providing two or more banks of LEDs having distinct light frequencies, one that emits warmer light and one that emits cooler light. By dimming one bank of LEDs and brightening the other (or vice versa) the overall light emitted may be faded between warm and cool temperatures. 
     In systems that employ three or more wires to power and control an LED light this fading may be accomplished with ease by providing a dedicated power wire to the LEDs and providing power intensity signals to dim and brighten the lights. However, when a dedicated power wire is unavailable, such as is the case in certain RV and Marine applications, controlling variation in color temperature is more difficult. 
     Accordingly, an improved LED light temperature control circuit and method for making and employing the same is needed. 
     SUMMARY 
     An LED light temperature control system is generally presented. The LED light temperature control system includes a dimmer switch comprising a single power input, an output signal, and an control device configured to vary the duty cycle of the output signal. The LED light temperature control system further includes a light controller configured to receive the output signal from the dimmer switch. The light controller has a first light output signal configured to power a first group of LEDs and a second light output signal configured to power a second group of LEDs. The light controller is configured to vary the duty cycle of the first light output signal proportionate to the duty cycle of the dimmer switch output signal. The light controller is further configured to vary the duty cycle of the second light output signal inversely to the duty cycle of the dimmer switch output signal. 
     In an embodiment, the two groups of LEDs have distinct color temperatures, such as 1800 Kelvin and 3000 Kelvin. 
     In an embodiment the dimmer switch may include an on/off switch to control the dimmer output signal. The dimmer switch may further include a linear slide to act as the control device. The dimmer switch may be configured to vary the duty cycle of the output signal between 10 percent and 100 percent. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The operation of the invention may be better understood by reference to the detailed description taken in connection with the following illustrations, wherein: 
         FIG. 1  illustrates an LED light temperature control circuit; 
         FIG. 2  illustrates a light source having two LED banks configured to emit light at two unique frequencies; 
         FIG. 3  illustrates a two wire dimmer switch used in an LED light temperature control circuit. 
         FIG. 4  illustrates a circuit diagram for a LED light temperature control circuit; and 
         FIG. 5  illustrates a circuit diagram for an LED light source in an LED light temperature control circuit. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It is to be understood that other embodiments may be utilized and structural and functional changes may be made without departing from the respective scope of the invention. Moreover, features of the various embodiments may be combined or altered without departing from the scope of the invention. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments and still be within the spirit and scope of the invention. 
     An LED light temperature control circuit  10  is generally presented, as shown in  FIG. 1 . The control circuit  10  may be generally configured to adjust the output of a light source  12  between a first color frequency and a second color frequency, such as between a cooler color temperature and a warmer color temperature, while also dimming the brightness or intensity of the light. 
     The control circuit  10  may include a dimmer  14 . The dimmer  14  may be a two wire dimmer, such as is commonly used in RV and marine applications. As shown in  FIG. 3 , the dimmer  14  may include an ON/OFF switch  16  to turn output power off and a dimmer control  18  to provide adjustability of the output signal. The dimmer control  18  may comprise a linear slide, as shown in  FIG. 3 , to vary the duty cycle or pulse width modulation (“PWM”) of the output signal. It will be appreciated that the dimmer control may be any analog device, such as a dial or the like, or digital device that varies the PWM of the output signal. 
     The two-wire dimmer  14  may be generally configured to vary the duty cycle of the output to the light source  12  to vary the brightness or intensity of the light. As described below, the dimmer  14  and other system components may be configured to simultaneously vary the color temperature of the light source  12  from cooler to warmer light temperature as the light source  12  is dimmed, as described in further detail below. 
     The two-wire dimmer  14  may be configured to receive a single power input  22  and provide a single output signal  20 . The input, shown as wire  22  in  FIG. 1 , may comprise a DC voltage such as a 12 volt DC signal. The common or ground wire  24  may also connected to the dimmer  14  and may also connect to each component in the control circuit  10 . The output signal  20  may be controlled by the ON/OFF switch  16  and dimmer switch  18  on the dimmer  14 . Specifically, duty cycle of the dimmer output  20  may be varied by adjusting the dimmer slider switch  18 . For example, the dimmer  14  may output a 12 volt DC signal between a 10% and 100% duty cycle on the output wire  20  based on movement of the slider between its range of travel. In traditional systems the varied duty cycle may be used vary only the intensity of one or more LEDs by changing the amount of time that the LED is on and thus dimming or brightening the connected lights. At lower duty cycles the LEDs may be dimmer and at higher duty cycles the LEDs may be brighter. Here, LED light temperature control circuit  10  may adjust both the brightness or intensity of the light source  12  as well as the color temperature when the duty cycle is varied. 
     The light source  12  in the control circuit may comprise two or more distinct LEDs or two or more distinct groups of LEDs. For example, the light source  12  may include a first group of LEDs  26  that operate at a first light temperature, such as 1800 Kelvin to emit warmer light, and a second group of LEDs  28  that operate at a second light temperature, such as 3000 Kelvin. However, it will be appreciated that the two or more distinct LED&#39;s or groups of LEDs may operate at any two distinct light temperatures to provide a cooler light temperature and a warmer light temperature. Each group of LEDs  26 ,  28  may be configured to receive a DC signal to power the LEDs and may be varied in brightness by varying the duty cycle of the input power signal. 
     The control circuit  10  may further include a controller  30 , as illustrated in  FIG. 4 . The controller  30  may be powered by the dimmer output  20  and may provide separate power and control signals to each bank of LEDs  26 ,  28  on the light source  12 . The first controller output  32  may be tied to the first bank of LEDs  26  and the second controller output  34  may be tied to the second back of LEDs  28 . 
     In operation, dimming the two-wire dimmer  14  will decrease the duty cycle of the power input to the controller  30 , thus causing the controller  30  to lose power sporadically. In order to maintain consistent power to the controller, a voltage buffer circuit  40  comprising a plurality of capacitors  42  may be used to buffer the input power to the controller  30 . The voltage buffer circuit  40  maintains the voltage at a high condition, even during low duty cycles, thus providing consistent power to the controller  30  even while the duty cycle of the output  20  is varied. When the voltage is too low the light will default to using the warm LEDs only. 
     The controller  30  may use the output  20  of the dimmer  14  as both input power and as an input signal to the controller  30  to monitor the duty cycle of the output signal  20 . The controller  30  may be configured to vary the duty cycle of the first controller output  32  in an opposite manner to the second controller output  34 , based on the duty cycle of the dimmer output  20 . For example, the controller  30  may read the duty cycle of the dimmer output  20  to determine the desired light temperature for the light source  12 . When the dimmer output  20  is at a high duty cycle the controller  30  will output a high duty cycle signal to the first controller output  32  and a low duty cycle signal to the second controller output  34 , yielding a bright output from the first bank of LEDs  26  and dimmed output from the second bank of LEDs  28  to provide a cooler light temperature of the light source  12 . As the dimmer output  20  is adjusted and the duty cycle is lowered, the controller  30  will lower the duty cycle of the first controller output  32  and raise the duty cycle of the second controller output  34 , thus dimming the first bank of LEDs and brightening the second bank of LEDs  28  to adjust the light source output from cool light temperature to a warmer light temperature. 
     In operation, the control circuit  10  may be connected as illustrated in  FIG. 1 . The controller  30  may be stored in the assembly of the light source  12  to allow for a simple two-wire connection between the dimmer  14  and the light source. When the ON/OFF switch  16  is initially turned on, the controller  30  may be configured to first provide a high duty cycle to the first bank of LEDs  26  and a low duty cycle to the second bank of LEDs  28  (yielding an initial warmer light temperature) then may automatically vary the light output to cool by varying the duty cycles of the first and second banks of LEDs  26 ,  28  in opposite directions. Once this initial boot up sequence is complete, a user may adjust the color temperature of the light source  12  by varying the dimmer slider switch  18  along its path of travel. 
     Although the embodiments of the present invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it is to be understood that the present invention is not to be limited to just the embodiments disclosed, but that the invention described herein is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the claims hereafter. The claims as follows are intended to include all modifications and alterations insofar as they come within the scope of the claims or the equivalent thereof.