Patent Publication Number: US-8981669-B2

Title: Lamps and control circuit

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 100137648, filed Oct. 18, 2011, which is herein incorporated by reference. 
     BACKGROUND 
     1. Field of Invention 
     The invention relates to a lamp. More particularly the invention relates to a lamp having color temperature adjustment. 
     2. Description of Related Art 
     Light emitting diodes used in electronic components in the past have been widely used in lighting products currently. Since the light emitting diodes have excellent electrical property and structural feature, a demand for the light emitting diodes has been increased gradually. Compared to fluorescent lamps and incandescent lamps, white LEDs have attracted great attention. However, corresponding to different demands of users, a lamp which can meet the demand for generating lights with different color temperatures is generated consequently. However, the color temperatures of conventional LEDs have been determined before leaving the factory and can not be changed. If users have a demand for lights with different color temperatures, the demand can only be solved by replacing LEDs having different color temperatures. This is inconvenient for users. 
     SUMMARY 
     The invention provides a lamp or lighting system capable of controlling a color temperature. 
     The invention provides a control circuit, which can control emitting devices with different color temperatures in a lamp, and the color temperature of the whole lamp is adjusted through a control signal outputted by the control circuit. 
     The control circuit provided by the invention only requires a single control signal generator, and then at least two different control signals are generated by other circuits, to decrease the layout area and cost of the control circuit. 
     Other purposes and advantages of the invention may be further understood from the technical characteristics disclosed by the invention. 
     For realizing one purpose or a part of or all of the purposes described above or other purposes, an embodiment of the invention provides a lamp, including a first emitting device, a second emitting device and a control signal generation device. The control signal generation device generates a first control signal and a second control signal to control the first emitting device and the second emitting device, so that a first light flux generated by the first emitting device is equivalent to a second light flux generated by the second emitting device, wherein the second control signal is generated according to the first control signal. 
     A further embodiment of the invention provides a control circuit for controlling a color temperature of a lamp, which includes a pulse signal generation device, a buffer device, an inverter and a compensation device. The pulse signal generation device generates a first control signal. The buffer device receives and buffers the first control signal. The inverter receives the first control signal to generate an inverted first control signal. The compensation device receives a compensation signal and the inverted first control signal to generate the second control signal. The first control signal controls a first emitting device in the lamp. The second control signal controls a second emitting device in the lamp. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a lamp according to an embodiment of the invention; 
         FIG. 2  is a schematic view of an emitting module; 
         FIG. 3  is a schematic view of a control circuit according to an embodiment of the invention; 
         FIG. 4  is a schematic view of a control circuit according to a further embodiment of the invention; 
         FIG. 5  is a schematic view of a control signal generated according to an embodiment of the invention; 
         FIG. 6  is a schematic view of a control signal generated according to a further embodiment of the invention; and 
         FIG. 7  is a schematic view of a lamp according to a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The foregoing and other technical contents, features and functions of the invention may be clearly shown in the following detailed description of a preferred embodiment with reference to the drawings. Directional terms mentioned in the following embodiments, such as up, down, left, right, front or back, only refer to the directions of the accompany drawings. Therefore, the directional terms used herein are only used to illustrate the invention and are not limitative. 
       FIG. 1  is a schematic view of a lamp according to an embodiment of the invention. The lamp includes a control circuit  11  and an emitting module  12 . The emitting module  12  includes a first emitting device  14  and a second emitting device  15 . The first emitting device  14  is a cold white emitting device. The second emitting device  15  is a warm white emitting device. In the embodiment, the first emitting device  14  and the second emitting device  15  may include one LED or a plurality of LEDs. In the embodiment, the emitting module  12  only takes two emitting devices with different color temperatures for examples for illustration, but the invention is not limited to this. The emitting module  12  may include more than two emitting devices. Each emitting device has a different color temperature. Then, the control circuit  11  controls different emitting devices to change the color temperature of the lamp. The arrangement of the first emitting device  14  and the second emitting device  15  in the emitting module  12  may have some variations according to a demand of a designer. Referring to  FIG. 2 ,  FIG. 2  is a schematic view of an emitting module. The emitting module shown in  FIG. 2  is a flat emitting module with chip on board (COB). The emitting devices  21   a ,  21   b ,  21   c  and  21   d  are cold white emitting devices. The emitting device  22  is a warm white emitting device. The cold white emitting devices  21   a ,  21   b ,  21   c  and  21   d  are distributed around the warm white emitting device  22 . Then, the control circuit controls the turn-on and turn-off of the cold white emitting devices and the warm white emitting device for changing the color temperatures. 
     The control circuit  11  includes a control signal generation device  13 . The control signal generation device  13  generates a first control signal S 1  and a second control signal S 2  to control the first emitting device  14  and the second emitting device  15 , wherein the second control signal S 2  is generated according to the first control signal S 1  and a compensation signal  16 . The control circuit  11  may adjust the amplitude and duty cycle of the first control signal S 1  and the second control signal S 2  to control the brightness and turn-on time of the first emitting device  14  and the second emitting device  15 . In the embodiment, the emitting efficiency of the first emitting device  14  is different from the emitting efficiency of the second emitting device  15 ; for example, the first emitting efficiency is greater than the second emitting efficiency. Therefore, the compensation signal  16  may be generated according to a difference between a first emitting efficiency of the first emitting device  14  and a second emitting efficiency of the second emitting device  15 , and then the second control signal S 2  is generated through the compensation signal  16  and the first control signal S 1 . By means of the above-mentioned control signal generation mode, a first light flux generated by the first emitting device  14  may be equivalent to a second light flux generated by the second emitting device  15 . 
       FIG. 3  is a schematic view of a control circuit according to an embodiment of the invention. The control circuit includes a pulse signal generation device  31  (e.g., a pulse width modulation (PWM) circuit), a buffer  32 , an inverter  33  and a compensation device  34 . The control circuit outputs the first control signal S 1  and the second control signal S 2  at the same time to control a first emitting device and a second emitting device. The pulse signal generation device  31  generates the first control signal S 1 , wherein the duty cycle of the first control signal S 1  is determined according to a color temperature. The pulse signal generation device  31  comprises an oscillator  311 , and the duty cycle of the first control signal is predetermined. The first control signal S 1  is transferred to the buffer  32  and the inverter  33  respectively. The buffer  32  delays a predetermined time of the first control signal S 1 , so that the first control signal S 1  outputted by the buffer  32  is synchronized with the second control signal S 2  outputted by the compensation device  34 . The predetermined time may be determined according to the processing speed of the inverter  33  and the compensation device  34 . The inverter  33  makes an inverted processing to the first control signal S 1  to generate and transfer an inverted first control signal S 1 ′ to the compensation device  34 . The compensation device  34  outputs the second control signal S 2  after it receives the inverted first control signal S 1 ′ and a compensation signal  35 . In the embodiment, the emitting efficiency of the first emitting device is different from the emitting efficiency of the second emitting device. In order to make the light flux generated by the first emitting device equivalent to the light flux generated by the second emitting device, the compensation device  34  may modify the inverted first control signal S 1 ′ according to the compensation signal  35  for reaching the foregoing purpose. In the embodiment, the compensation signal  35  is generated according to a difference between the emitting efficiency of the first emitting device and the emitting efficiency of the second emitting device. In the embodiment, the first emitting device is the cold white emitting device, and the second emitting device is the warm white emitting device. Since the emitting efficiency of the warm white emitting device is poorer, the compensation device  34  compensates the insufficient part of the emitting efficiency of the warm white emitting device. However, those skilled in the art also may design the compensation device  34  for changing the first control signal S 1  transferred to the cold white emitting device so as to decrease the excessive part of the emitting efficiency of the cold white emitting device. In one embodiment, the compensation device  34  is a DC level adjustment circuit, the compensation signal is a DC bias compensation value, and the compensation device  34  adjusts a low voltage level of the inverted first control signal according to the DC bias compensation value. 
       FIG. 4  is a schematic view of a control circuit according to a further embodiment of the invention. The control circuit includes a pulse signal generation device  41  (e.g., a PWM circuit), a buffer  42 , an inverter  43  and an OR gate  44 . The control circuit outputs the first control signal S 1  and the second control signal S 2  at the same time to control a first emitting device and a second emitting device. The pulse signal generation device  41  generates the first control signal S 1 , wherein the duty cycle of the first control signal S 1  is determined according to a color temperature. The first control signal S 1  is transferred to the buffer  42  and the inverter  43  respectively. The buffer  42  delays a predetermined time of the first control signal S 1 , so that the first control signal S 1  outputted by the buffer  42  is synchronized with the second control signal S 2  outputted by the OR gate  44 . The predetermined time may be determined according to the processing speed of the inverter  43  and the OR gate  44 . The inverter  43  makes the inverted processing to the first control signal S 1  to generate and transfer an inverted first control signal S 1 ′ to the OR gate  44 . The OR gate  44  makes an OR operation after it receives the inverted first control signal S 1 ′ and a compensation signal  45  to output the second control signal S 2 . In the embodiment, the emitting efficiency of the first emitting device is different from the emitting efficiency of the second emitting device. In order to make the light flux generated by the first emitting device equivalent to the light flux generated by the second emitting device, the OR gate  44  may modify the inverted first control signal S 1 ′ according to the compensation signal  45  for reaching the foregoing purpose. In the embodiment, the compensation signal  45  is generated according to a difference between the emitting efficiency of the first emitting device and the emitting efficiency of the second emitting device. In the embodiment, the first emitting device is the cold white emitting device, and the second emitting device is the warm white emitting device. Since the emitting efficiency of the warm white emitting device is poorer, the OR gate  44  makes the OR operation to the inverted first control signal S 1 ′ and a compensation signal  45  for compensating the insufficient part of the emitting efficiency of the warm white emitting device. However, those skilled in the art also may design the OR gate  44  for changing the first control signal S 1  transferred to the cold white emitting device so as to decrease the excessive part of the emitting efficiency of the cold white emitting device. 
     In order to illustrate the operation of the first control signal, the second control signal and the compensation signal more clearly,  FIGS. 5 and 6  are referred to.  FIG. 5  is a schematic view of a control signal generated according to an embodiment of the invention. After the control signal generation device outputs the first control signal S 1 , firstly an inverter makes the inverted processing to the first control signal S 1  for generating the inverted first control signal  S 1   . Then, a compensator may generate a DC voltage offset according to a difference between the emitting efficiency of two emitting devices. Afterwards, the compensator adjusts the low voltage level of the inverted first control signal  S 1    to a voltage V 1  according to the DC voltage offset for generating the second control signal S 2 . In such a way, the second emitting device with a lower emitting efficiency may generate a light flux equivalent to the light flux of the first emitting device. 
       FIG. 6  is a schematic view of a control signal generated according to a further embodiment of the invention. After the control signal generation device outputs the first control signal S 1 , firstly an inverter makes the inverted processing to the first control signal S 1  for generating the inverted first control signal  S 1   . Then, a compensation signal Sc is generated according to a difference between the emitting efficiency of the first emitting device and the emitting efficiency of the second emitting device. Afterwards, the compensator makes the OR operation to the inverted first control signal  S 1    and the compensation signal Sc for generating the second control signal S 2 . In such a way, the second emitting device with a lower emitting efficiency may generate a light flux equivalent to the light flux of the first emitting device. 
       FIG. 7  is a schematic view of a lamp according to a further embodiment of the invention. The lamp includes a control signal generation device  71 , a driving circuit  72  and an emitting module  73 . The emitting module  73  includes a first emitting device  74  and a second emitting device  75 . The first emitting device  74  is a cold white emitting device. The second emitting device  75  is a warm white emitting device. In the embodiment, the first emitting device  74  and the second emitting device  75  may include one LED or a plurality of LEDs. In the embodiment, the emitting module  73  only takes two emitting devices with different color temperatures for example, but the invention is not limited to this. The emitting module  73  may include more than two emitting devices. Each emitting device has a different color temperature. Then, the control circuit  71  controls the driving device  72  to drive different emitting devices for changing the color temperature of the lamp. 
     The control signal generation device  71  generates a first control signal S 1 , and a second control signal S 2  is generated according to the first control signal S 1  and a compensation signal  76 . The driving device  72  outputs a corresponding first driving signal SD 1  and a second driving signal SD 2  after it receives the first control signal S 1  and the second control signal S 2  so as to drive the first emitting device  74  and the second emitting device  75 . The control signal generation device  71  may adjust the amplitude and duty cycle of the first control signal S 1  and the second control signal S 2  to change the voltage, current or turn-on time of the first driving signal SD 1  and the second driving signal SD 2 , thereby controlling the brightness and turn-on time of the first emitting device  74  and the second emitting device  75 . In the embodiment, the emitting efficiency of the first emitting device  74  is different from the emitting efficiency of the second emitting device  75 . Therefore, the compensation signal  76  may be generated according to a difference between a first emitting efficiency of the first emitting device  74  and a second emitting efficiency of the second emitting device  75 , and then the second control signal S 2  is generated through the compensation signal  76  and the first control signal S 1 . The driving circuit  72  is controlled by means of the above-mentioned control signal generation mode, so that a first light flux generated by the first emitting device  74  is equivalent to a second light flux of the second emitting device  75 . 
     The above-mentioned descriptions are only preferred embodiments of the invention, and the implementation scope of the invention can not be limited to this. That is, all simple equivalent variations and modifications generally made according to the claims and the summary of the invention still fall within the scope of the invention. Additionally, any embodiment or the claims of the invention are not necessary to reach all purposes, advantages or features disclosed by the invention. Moreover, the abstract and the title are only used for assisting to search a patent document, and are not intended to limit the claims of the invention.