Abstract:
A color temperature adjusting system includes a processing unit, a constant-current drive unit, and an light emitting unit (LED) unit including two unmatched LED modules with different basic color temperatures. A table records a relationship between coefficient values and current values for the current(s) flowing through the two LED modules. The processing unit selects one of a number of predetermined formulas to calculate the coefficient value by comparing a desired value with a threshold value, and further determines the current values according to the calculated coefficient value listed in a table. The constant-current drive unit includes two drive module generating modulating signals to adjust the respective values of the current flowing through the two LED modules to match the determined current values, thereby adjusting the color temperature value of the LED unit to the desired level. A related method is also provided.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a system and method for adjusting color temperature. 
         [0003]    2. Description of the Related Art 
         [0004]    Many LED lamps includes a number of LED modules each with a different color temperature, and the luminance of the LED modules can be adjusted by pulse width modulation (PWM) signals provided by constant-current drive circuit of each LED module, thus the color temperature of the LED lamps can be adjusted to a desired value. Integrated circuits (ICs) may be employed in the LED lamp to adjust the color temperature values of the LED lamp over a wide range. However, these ICs have complicated structures and are expensive. 
         [0005]    Therefore, there is room for improvement within the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0007]      FIG. 1  is a block diagram of a system for adjusting color temperatures of an LED unit in accordance with an exemplary embodiment. 
           [0008]      FIG. 2  is a flow diagram that describes steps in a method for adjusting color temperature of the LED unit in accordance with an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Referring to  FIG. 1 , a system for adjusting color temperatures is provided. The system  1  includes a processing unit  2 , a constant-current drive unit  3 , a light emitting diode (LED) unit  4  and a setting unit  5 . The LED unit  4  includes a first LED module  41  and a second LED module  42  which has color temperature different from that of the first LED module  41 . In the embodiment, the first LED module  41  is a white LED module with a relatively low value of color temperature, such as 2700K (Kelvin). The second LED module  42  is a white LED module with a relatively high value of color temperature, such as 6500K. When only the first LED module  41  is working, the color temperature value of the LED unit  4  is the lowest, for example, at 2700K. When only the second LED module  42  is working, the color temperature value of the LED unit  4  is the highest, for example, at 6500K. 
         [0010]    When a user inputs a desired value for a correlated color temperature (CCT) via the setting unit  5 , the setting unit  5  generates signals for adjusting the color temperature of the LED unit  4  to the desired value CCT in response to the user&#39;s input. In the embodiment, the setting unit  5  may be a touch panel with a display screen, a keyboard, a remote control or the like. 
         [0011]    The processing unit  2  includes a storage module  21 , a calculating module  22 , and an executing module  23 . The storage module  21  is configured to store a table, as shown below, the table includes a coefficient X column which records a coefficient for each desired value, a I 1  column, and a I 2  column which respectively record first current values I 1  of the current flowing through the first LED module  41 , and second current values I 2  of the current flowing through the second LED module  42 , to achieve the desired values. 
         [0012]    The table stored in the storage module  21   
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 X 
                 I1 (mA) 
                 I2 (mA) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1.0000 
                 60.00 
                 0.00 
               
               
                 0.9522 
                 60.00 
                 2.7 
               
               
                 0.9043 
                 60.00 
                 5.71 
               
               
                 0.8565 
                 60.00 
                 9.04 
               
               
                 0.8086 
                 60.00 
                 12.76 
               
               
                 0.7608 
                 60.00 
                 16.96 
               
               
                 0.7129 
                 60.00 
                 21.72 
               
               
                 0.6651 
                 60.00 
                 27.16 
               
               
                 0.6172 
                 60.00 
                 33.44 
               
               
                 0.5694 
                 56.31 
                 38.28 
               
               
                 0.5215 
                 51.84 
                 42.74 
               
               
                 0.4737 
                 47.32 
                 47.26 
               
               
                 0.4258 
                 42.76 
                 51.82 
               
               
                 0.3780 
                 38.15 
                 56.43 
               
               
                 0.4075 
                 41.00 
                 53.58 
               
               
                 0.3905 
                 39.36 
                 55.22 
               
               
                 0.3735 
                 37.72 
                 56.86 
               
               
                 0.3565 
                 36.07 
                 58.51 
               
               
                 0.3396 
                 34.32 
                 60.00 
               
               
                 0.3226 
                 31.79 
                 60.00 
               
               
                 0.3056 
                 29.38 
                 60.00 
               
               
                 0.2886 
                 27.09 
                 60.00 
               
               
                 0.2716 
                 24.90 
                 60.00 
               
               
                 0.2547 
                 22.81 
                 60.00 
               
               
                 0.2377 
                 20.82 
                 60.00 
               
               
                 0.2207 
                 18.91 
                 60.00 
               
               
                 0.2037 
                 17.08 
                 60.00 
               
               
                 0.1868 
                 15.33 
                 60.00 
               
               
                 0.1698 
                 13.65 
                 60.00 
               
               
                 0.1528 
                 12.04 
                 60.00 
               
               
                 0.1358 
                 10.49 
                 60.00 
               
               
                 0.1188 
                 9.00 
                 60.00 
               
               
                 0.1019 
                 7.57 
                 60.00 
               
               
                 0.0849 
                 6.19 
                 60.00 
               
               
                 0.0679 
                 4.86 
                 60.00 
               
               
                 0.0509 
                 3.58 
                 60.00 
               
               
                 0.0340 
                 2.35 
                 60.00 
               
               
                 0.0170 
                 1.15 
                 60.00 
               
               
                 0.0000 
                 0.00 
                 60.00 
               
               
                   
               
             
          
         
       
     
         [0013]    The first current values I 1  are inversely proportional to the desired value of CCT, and the second current values I 2  are directly proportional to the desired value CCT. For example, if 3600K is input, via the setting unit  5 , as the desired value CCT, the corresponding first current value I 1  and the corresponding second current value I 2  are found to be 56.31 mA and 38.28 mA respectively from the table, as show above. If the desired value CCT input via the setting unit  5  is 3800K, the corresponding first current value I 1  and the corresponding second current value I 2  of the coefficient X are obtained from the table and found to be 47.32 mA and 47.26 mA respectively, as shown above. 
         [0014]    The calculating module  22  is configured to apply one or more formulas for calculating the coefficient X by comparing the desired value CCT with a threshold value CCT(0) in response to the signals generated by the setting unit  5 . 
         [0015]    In the embodiment, there are three predetermined formulas used to calculate the coefficient X, the three predetermined formulas are: 
         [0000]        CCT (0)= CCT (1)+Δ CCT*A   0 ;  First formula:
 
         [0000]      when  CCT&lt;=CCT (0), CCT=CCT (1)+Δ CCT *(1 −X )* A   1 ; and  Second formula:
 
         [0000]      when  CCT&gt;CCT (0),  CCT=CCT (2)−Δ CCT*X*A   2 .  Third formula:
 
         [0016]    In the three formulas, A 0 , A 1 , A 2  are constant values preset according to an illumination device employing the system  1 . CCT(1) is the color temperature value of the first LED module  41 . CCT(2) is the color temperature value of the second LED module  42 . ΔCCT is a fixed value difference between the color temperature value of the second LED module  42  CCT(2) and the color temperature value of the first LED module  41  CCT(1). In the embodiment, ΔCCT is 3800K (solving 6500-2700). CCT(0) is the fixed threshold value calculated according to the first formula. The executing module  23  determines the choice of formula from between the second formula and the third formula to calculate the coefficient X by comparing the desired value CCT with the threshold value CCT(0). If the desired value CCT is equal to or less than the threshold value CCT(0), the second formula is used to calculate the coefficient X. If the desired value CCT is greater than the threshold value CCT(0), the first formula is used to calculate the coefficient X. 
         [0017]    The executing module  23  is configured to determine the first current value I 1  and the second current value I 2  according to the coefficient value X produced by the calculating module  22 . 
         [0018]    The constant-current drive unit  3  includes a first drive module  31  connected to the first LED module  41 , and a second drive module  32  connected to the second LED module  42 . The first drive module  31  and the second drive module  32  are both connected to the executing module  23 . The first drive module  31  is configured to generate a first modulated signal to adjust the current flowing through the first LED module  41  to equal the first current value I 1  as determined by the executing module  23 . The second drive module  32  is configured to generate a second modulated signal to adjust the current flowing through the second LED module  42  to equal the second current value I 2  as determined by the executing module  23 . Thereby, the color temperature value of the overall LED unit  4  may be adjusted to be the desired value for CCT. 
         [0019]    For example, if the desired value CCT set by the setting unit  5  is 2800K which is less than the threshold value CCT(0), the second formula is selected to calculate the coefficient X and the calculating module  22  functions accordingly to establish 0.9522 as the coefficient X. Thus, the corresponding first current value I 1  (60 mA) and the corresponding second current value I 2  (2.7 mA) of the coefficient X can be obtained from the table as shown above. The first drive module  31  generates the first modulated signal to adjust the current flowing through the first LED module  41  to be 60.00 mA, and the second drive module  32  generates the second modulated signal to adjust the current flowing through the second LED module  42  to be 2.7 mA. In this way, the color temperature color value of the LED unit  4  is adjusted to the desired value (2800K). 
         [0020]      FIG. 2  is a flow diagram that describes the steps in a method in accordance with an exemplary embodiment. 
         [0021]    In step S 60 , the setting unit  5  generates adjusting signals to achieve the desired value for CCT in response to user&#39;s operation. 
         [0022]    The setting unit  5  may be a touch panel with a display screen, a keyboard, or a remote control. 
         [0023]    In step S 61 , the calculating module  22  determines the formula to be applied in calculating the coefficient X by comparing the desired value CCT with the threshold value CCT(0) when receiving the adjusting signals generated by the setting unit  5 . 
         [0024]    In the embodiment, there are three predetermined formulas available for calculating the coefficient value X, the three predetermined formulas are: 
         [0000]        CCT (0)= CCT (1)+Δ CCT*A   0 ;  First formula:
 
         [0000]      when  CCT&lt;=CCT (0), CCT=CCT (1)+Δ CCT *(1 −X )* A   1 ; and  Second formula:
 
         [0000]      when  CCT&gt;CCT (0),  CCT=CCT (2)−Δ CCT*X*A   2 .  Third formula:
 
         [0025]    In the three formulas, A 0 , A 1 , A 2  are constant values. CCT(1) is the lowest color temperature value of the LED unit  4 , namely, the color temperature value of the first LED module  41 . CCT(2) is the highest color temperature value of the LED unit  4 , namely, the color temperature value of the second LED module  42 . ΔCCT is a fixed value difference between the highest color temperature value CCT(2) and the lowest color temperature value CCT(1) of the LED unit  4 . In the embodiment, ΔCCT is 3800K (solving 6500-2700). CCT(0) is a fixed threshold value calculated according to the first formula. If the desired value CCT is equal to or less than the threshold value CCT(0), the second formula is used to calculate the coefficient X. If the desired value CCT is greater than the threshold value CCT(0), the third formula is used to calculate the coefficient X. 
         [0026]    In step S 62 , the calculating module  22  selects the formula to be applied in calculating the coefficient value X. The coefficient value X is a ratio of the color temperature value of the first LED module  41  over the desired value CCT. 
         [0027]    In step S 63 , the executing module  23  establishes the first current value I 1  and the second current value I 2  according to the coefficient value X as calculated by the calculating module  22 . 
         [0028]    In step S 64 , the first drive module  31  generates the first modulated signal to adjust the amount of current flowing through the first LED module  41  to equal the established first current value I 1 , and the second drive module  32  generates the second modulated signal to adjust the amount of current flowing through the second LED module  42  to equal the established second current value I 2 , thereby adjusting the color temperature value of the LED unit  4  to match the desired color temperature value. 
         [0029]    It is understood that the present disclosure may be embodied in other forms without departing from the spirit thereof. The present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the disclosure is not to be limited to the details given herein.