Abstract:
A lighting system having control architecture is disclosed for avoiding redundant lighting. The lighting system includes a switch, a pulse filter, a driving circuit, a lighting module, a light feedback module, a compensator, and a pulse width modulation (PWM) signal generator. The switch controls the transmission of a PWM signal to the driving circuit based on an enable control signal. The driving circuit generates a driving voltage for driving the lighting module to emit a light output based on the PWM signal. The light feedback module detects the light output for generating a feedback signal. The compensator provides a compensation signal to the PWM signal generator for generating the PWM signal based on the feedback signal and a reference signal. When the switch is turned off by the enable control signal, the pulse filter is utilized for filtering out periodical pulses caused by the equivalent capacitor of the switch.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a lighting system, and more particularly, to a lighting system having control architecture for avoiding redundant lighting. 
         [0003]    2. Description of the Prior Art 
         [0004]    Because light emitting diodes (LEDs) are characterized by long lifetime, small size, low power consumption and high-bright lighting capability, LEDs have been widely applied in a variety of indication applications, indoor or outdoor lighting applications, traffic lights, vehicle auxiliary lighting applications, camera flashlights, and so forth. Besides, due to the successful commercialization of the white light-emitting diode (WLED), the backlight sources of liquid crystal displays (LCDs) are switched from traditional cold cathode fluorescent lamps (CCFLs) or external electrode fluorescent lamps (EEFLs) to LED lighting modules. While an LED lighting module is put in use as the backlight source of an LCD, a light-output control mechanism of the LED lighting module is required to provide an accurate light output so that the LCD is capable of achieving a high-quality image display. 
         [0005]    Please refer to  FIG. 1 , which is a schematic diagram showing a prior-art lighting system  100  having control architecture. As shown in  FIG. 1 , the lighting system  100  comprises a plurality of resistors  110 - 115 , a plurality of capacitors  120 - 121 , a driving circuit  150 , a lighting module  160 , an operational amplifier  130 , and a transistor  135 . The resistors  110 - 114  in conjunction with the capacitors  120 - 121  are utilized for performing low-pass filtering and voltage dividing operations so as to generate a driving current control voltage Vx based on a pulse width modulation (PWM) signal S PWM  and an enable control signal S EN . The resistor  110  and the resistor  111  are further utilized for performing a voltage dividing operation on the pulse width modulation signal S PWM  and the enable control signal S EN  for generating a driving control signal Sdrc. In general, the driving circuit  150  comprises a voltage boost unit  155  for generating a driving voltage Vdr by boosting a supply voltage Vcc based on the driving control signal Sdrc. The operational amplifier  130 , the transistor  135  and the resistor  115  are coupled to form a current control circuit for generating a driving current Id based on the driving current control voltage Vx and the driving voltage Vdr. The lighting module  160  is then able to generate a light output based on the driving current Id. 
         [0006]    Please refer to  FIG. 2 , which presents a truth table  200  of the enable control signal, the PWM signal and the driving control signal regarding the operation of the lighting system in  FIG. 1 , wherein H represents a high-level signal and L represents a low-level signal. As illustrated in the truth table  200 , when both the enable control signal S EN  and the PWM signal S PWM  are high-level signals H, the driving control signal Sdrc is set to be a high-level signal H. When both the enable control signal S EN  and the PWM signal S PWM  are low-level signals L, the driving control signal Sdrc is set to be a low-level signal L. When the enable control signal S EN  is floated, the driving control signal Sdrc is conformed to the PWM signal S PWM . When the driving control signal Sdrc is a high-level signal H, the voltage boost unit  155  is enabled for boosting the supply voltage Vcc so as to generate the driving voltage Vdr having high voltage for driving the lighting module  160  to emit light. When the driving control signal Sdrc is a low-level signal L, the voltage boost unit  155  is disabled, and the lighting module  160  quits lighting due to the driving voltage Vdr having low voltage. That is, the average intensity of the light output generated by the lighting module  160  can be adjusted based on the duty cycle of the PWM signal S PWM . 
         [0007]    However, when the enable control signal S EN  is a high-level signal H and the PWM signal S PWM  is a low-level signal L, due to the voltage dividing operation of the resistors  110  and  111 , the driving control signal Sdrc is set to be a quasi low-level signal Lx 1  instead of an ideal low-level signal L. Similarly, when the enable control signal S EN  is a low-level signal L and the PWM signal S PWM  is a high-level signal H, due to the voltage dividing operation of the resistors  110  and  111 , the driving control signal Sdrc is set to be a quasi low-level signal Lx 2  instead of an ideal low-level signal L. The quasi low-level signals Lx 1  and Lx 2  cannot completely disable the voltage boosting operation of the voltage boost unit  155 , which results in unwanted redundant lighting of the lighting module  160 . Accordingly, the lighting system  100  is not able to provide an accurate control of the light output for an LCD to achieve a high-quality image display. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with an embodiment of the present invention, a lighting system having control architecture is disclosed for providing an accurate light-output control by avoiding redundant lighting. The lighting system comprises a switch, a first resistor, a second resistor, a pulse filter, a driving circuit, and a lighting module. 
         [0009]    The switch comprises a first end for receiving a pulse width modulation (PWM) signal, a control end for receiving an enable control signal, and a second end for outputting a driving control signal. The first resistor comprises a first end for receiving a supply voltage and a second end coupled to the control end of the switch. The pulse filter comprises a first end coupled to the second end of the switch and a second end coupled to a ground. The second resistor comprises a first end coupled to the lighting module and a second end coupled to the ground. The driving circuit is utilized for generating a driving voltage based on the supply voltage and the driving control signal. Furthermore, the driving circuit functions to generate a driving current control voltage based on the driving control signal. The driving circuit comprises a power end for receiving the supply voltage, an input end coupled to the second end of the switch for receiving the driving control signal, a first output end coupled to the lighting module for outputting the driving voltage, and a second output end coupled to the first end of the second resistor for outputting the driving current control voltage. The lighting module is coupled to both the driving circuit and the second resistor and functions to generate a light output based on the driving voltage and the driving current control voltage. 
         [0010]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram showing a prior-art lighting system having control architecture. 
           [0012]      FIG. 2  presents a truth table of the enable control signal, the PWM signal and the driving control signal regarding the operation of the lighting system in  FIG. 1 . 
           [0013]      FIG. 3  is a schematic diagram showing a lighting system having control architecture in accordance with a first embodiment of the present invention. 
           [0014]      FIG. 4  presents a truth table of the enable control signal, the PWM signal and the driving control signal regarding the operation of the lighting system in  FIG. 3 . 
           [0015]      FIG. 5  is a schematic diagram showing a lighting system having control architecture in accordance with a second embodiment of the present invention. 
           [0016]      FIG. 6  is a schematic diagram showing a lighting system having control architecture in accordance with a third embodiment of the present invention. 
           [0017]      FIG. 7  is a schematic diagram showing a lighting system having control architecture in accordance with a fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, it is to be noted that the present invention is not limited thereto. 
         [0019]    Please refer to  FIG. 3 , which is a schematic diagram showing a lighting system  300  having control architecture in accordance with a first embodiment of the present invention. As shown in  FIG. 3 , the lighting system  300  comprises a switch  330 , a first resistor  310 , a pulse filter  320 , a driving circuit  350 , a lighting module  360 , and a second resistor  311 . The switch  330  is a metal oxide semiconductor (MOS) field effect transistor or a junction field effect transistor (OFET). The lighting module  360  comprises an LED unit or a plurality of parallel-connected LED units. Each LED unit comprises an LED or a plurality of series-connected LEDs. The pulse filter  320  is a varistor, a transient voltage suppressor (TVS), or a high-pass filter. In an embodiment, the pulse filter  320  is a high-pass filter having only one capacitor. 
         [0020]    The switch  330  comprises a first end for receiving a PWM signal S PWM , a control end for receiving an enable control signal S EN , and a second end for outputting a driving control signal Sdrc. The first resistor  310  comprises a first end for receiving a supply voltage Vcc and a second end coupled to the control end of the switch  330 . The pulse filter  320  comprises a first end coupled to the second end of the switch  330  and a second end coupled to a ground GND. The driving circuit  350  comprises an input end  356 , a power end  357 , a first output end  358 , a second output end  359 , a voltage boost unit  355 , a control circuit  351 , and a low-pass filter  353 . The power end  357  is utilized for receiving the supply voltage Vcc. The input end  356  is coupled to the second end of the switch  330  for receiving the driving control signal Sdrc. The first output end  358  is utilized for outputting a driving voltage Vdr. The second output end  359  is utilized for outputting a driving current control voltage Vx. The driving circuit  350  is utilized for generating the driving voltage Vdr based on the supply voltage Vcc and the driving control signal Sdrc. Furthermore, the driving circuit  350  functions to generate the driving current control voltage Vx based on the driving control signal Sdrc. The second resistor  311  comprises a first end coupled to the second output end  359  of the driving circuit  350  for receiving the driving current control voltage Vx and a second end coupled to the ground GND. The first end of the second resistor  311  is further coupled to the lighting module  360 . The lighting module  360  in conjunction with the second resistor  311  generates a driving current Id based on the driving voltage Vdr and the driving current control voltage Vx, and therefore the lighting module  360  can be driven to emit a light output by the driving current Id. 
         [0021]    The control circuit  351  is coupled between the input end  356  and the voltage boost unit  355  of the driving circuit  350 . The control circuit  351  is utilized to generate a control signal Sct by compensating the driving control signal Sdrc with the turn-on voltage drop of the switch  330 . In one embodiment, if the switch  330  is an N-type MOS field effect transistor, the turn-on voltage drop of the switch  330  is the drain-source voltage drop of the N-type MOS field effect transistor turned on. The voltage boost unit  355  is coupled to the power end  357 , the control circuit  351  and the first output end  358  of the driving circuit  350 . The voltage boost unit  355  functions to generate the driving voltage Vdr by boosting the supply voltage Vcc based on the control signal Sct. The low-pass filter  353  is coupled between the input end  356  and the second output end  359  of the driving circuit  350 . The low-pass filter  353  performs a low-pass filtering operation on the driving control signal Sdrc for generating the driving current control voltage Vx. In another embodiment, the control circuit  351  can be omitted, and the voltage boost unit  355  is directly coupled to the input end  356  of the driving circuit  350  for receiving the driving control signal Sdrc. That is, the voltage boost unit  355  generates the driving voltage Vdr by boosting the supply voltage Vcc directly based on the driving control signal Sdrc. 
         [0022]    Please refer to  FIG. 4 , which presents a truth table  400  of the enable control signal, the PWM signal and the driving control signal regarding the operation of the lighting system in  FIG. 3 , wherein H represents a high-level signal and L represents a low-level signal. As illustrated in the truth table  400 , when the enable control signal S EN  is a high-level signal H, the switch  330  is turned on for outputting the PWM signal S PWM  to become the driving control signal Sdrc. In view of that, the driving control signal Sdrc is conformed to the PWM signal S PWM . That is, the driving control signal Sdrc is a high-level signal H when the PWM signal S PWM  is a high-level signal H, or alternatively the driving control signal Sdrc is a low-level signal L when the PWM signal S PWM  is a low-level signal L. Because of the turn-on voltage drop of the switch  330 , the high-level voltage of the driving control signal Sdrc is less than that of the PWM signal S PWM  by the turn-on voltage drop of the switch  330 . However, in general, the high-level voltage of the driving control signal Sdrc is still high enough to enable the voltage boost unit  355  for boosting the supply voltage Vcc, and the control circuit  351  may be omitted without degrading the performance of the lighting system  300 . When the enable control signal S EN  is floated, the supply voltage Vcc can be furnished to the control end of the switch  330  via the first resistor, and therefore the switch  330  is turned on so that the driving control signal Sdrc is also conformed to the PWM signal S PWM . Similarly, the high-level voltage of the driving control signal Sdrc is still less than that of the PWM signal S PWM  by the turn-on voltage drop of the switch  330 . 
         [0023]    When the enable control signal S EN  is a low-level signal L, the switch  330  is turned off so that the PWM signal S PWM  cannot be forwarded to the second end of the switch  330 , and the driving control signal Sdrc is retained to be a low-level signal L. However, due to the effect of an equivalent capacitor between the first and second ends of the switch  330  on the PWM signal S PWM , a periodical pulse noise will occur to the second end of the switch  330 , and the periodical pulse noise is likely to result in redundant lighting of the lighting module  360 . In other words, an unwanted light output may be generated by the periodical pulse noise. For solving the problem of redundant lighting caused by the periodical pulse noise, the pulse filter  320  is installed to get rid of the periodical pulse noise. That is, in the operation of the lighting system  300 , the driving control signal Sdrc is generated without the quasi low-level signal and the periodical pulse noise so that the problem of redundant lighting can be solved completely, and therefore the lighting system  300  is able to provide an accurate control of the light output. 
         [0024]    Please refer to  FIG. 5 , which is a schematic diagram showing a lighting system  500  having control architecture in accordance with a second embodiment of the present invention. As shown in  FIG. 5 , the lighting system  500  comprises a switch  330 , a first resistor  310 , a pulse filter  320 , a driving circuit  350 , a lighting module  360 , a second resistor  311 , a light feedback module  370 , a compensator  375 , and a PWM signal generator  380 . The coupling relationships and related functionalities regarding the switch  330 , the first resistor  310 , the pulse filter  320 , the driving circuit  350 , the lighting module  360  and the second resistor  311  are similar to the above description on the lighting system  300 . Consequently, in the operation of the lighting system  500 , the truth table of the enable control signal S EN , the PWM signal S PWM  and the driving control signal Sdrc is the same as the truth table  400  in  FIG. 4 . The light feedback module  370  is utilized for generating a feedback signal Sf based on the light output of the lighting module  360 . The light feedback module  370  comprises a light sensor  371  and a feedback signal processing unit  373 . The light sensor  371  senses the light output of the lighting module  360  for generating a light sensing signal Ss, and the feedback signal processing unit  373  performs a signal processing operation on the light sensing signal Ss for generating the feedback signal Sf. 
         [0025]    The compensator  375  is coupled between the light feedback module  370  and the PWM signal generator  380  and functions to generate a compensation signal Scm based on the feedback signal Sf and a reference signal Sref. The compensator  375  comprises a first input end  376  coupled to the light feedback module  370  for receiving the feedback signal Sf, a second input end  377  for receiving the reference signal Sref, and an output end  378  for outputting the compensation signal Scm. The PWM signal generator  380  is coupled between the compensator  375  and the switch  330  and functions to generate the PWM signal S PWM  based on the compensation signal Scm. The PWM signal generator  380  comprises a comparator  381  and a ramp-wave signal generator  383 . The ramp-wave signal generator  383  is used for generating a ramp-wave signal Sramp. The ramp-wave signal Sramp is a triangular-wave signal or a sawtooth-wave signal. The comparator  381  can be an operational amplifier for generating the PWM signal S PWM  by comparing the ramp-wave signal Sramp with the compensation signal Scm. The comparator  381  comprises a first input end coupled to the output end  378  of the compensator  375  for receiving the compensation signal Scm, a second input end coupled to the ramp-wave signal generator  383  for receiving the ramp-wave signal Sramp, and an output end for outputting the PWM signal S PWM  to the first end of the switch  330 . In the embodiment shown in  FIG. 5 , the first and second input ends of the comparator  381  are the positive and negative input ends respectively. 
         [0026]    It is noted that the lighting system  500  is a feedback control system, the enable control signal S EN  is utilized for enabling/disabling the light output of the lighting module  360 , and the reference signal Sref is utilized for controlling the intensity of the light output. When the enable control signal S EN  enables the light output of the lighting module  360 , the light feedback module  370  senses the light output for generating the feedback signal Sf. If the feedback signal Sf is less than the reference signal Sref, the compensator  375  raises the compensation signal Scm so that the intensity of the light output can be increased through increasing the duty cycle of the PWM signal S PWM  by the PWM signal generator  380 . On the other hand, if the feedback signal Sf is greater than the reference signal Sref, the compensator  375  reduces the compensation signal Scm so that the intensity of the light output can be decreased through decreasing the duty cycle of the PWM signal S PWM  by the PWM signal generator  380 . 
         [0027]    In another embodiment, the first and second input ends of the comparator  381  are the negative and positive input ends, and the duty cycle of the PWM signal S PWM  is increasing following the decrease of the compensation signal Scm. That is, if the feedback signal is less than the reference signal Sref, the compensator  375  decreases the compensation signal Scm so that the intensity of the light output can be increased through increasing the duty cycle of the PWM signal S PWM  by the PWM signal generator  380 . Alternatively, if the feedback signal is greater than the reference signal Sref, the compensator  375  increases the compensation signal Scm so that the intensity of the light output can be decreased through decreasing the duty cycle of the PWM signal S PWM  by the PWM signal generator  380 . 
         [0028]    Please refer to  FIG. 6 , which is a schematic diagram showing a lighting system  600  having control architecture in accordance with a third embodiment of the present invention. As shown in  FIG. 6 , the lighting system  600  comprises a switch  330 , a first resistor  310 , a pulse filter  320 , a driving circuit  350 , a lighting module  360 , a second resistor  311 , a light feedback module  370 , a compensator  375 , an analog-to-digital converter  385  and a PWM signal generator  380 . The coupling relationships and related functionalities regarding the switch  330 , the first resistor  310 , the pulse filter  320 , the driving circuit  350 , the lighting module  360 , the second resistor  311 , the light feedback module  370 , and the compensator  375  are similar to the above description on the lighting systems  300  and  500 . Consequently, in the operation of the lighting system  600 , the truth table of the enable control signal S EN , the PWM signal S PWM  and the driving control signal Sdrc is still the same as the truth table  400  in  FIG. 4 . The analog-to-digital converter  385  is coupled between the compensator  375  and the PWM signal generator  390  and functions to convert the compensation signal Scm into a digital compensation signal Sdcm. 
         [0029]    The PWM signal generator  390  is substantially a digital signal processor for generating the PWM signal S PWM  based on the digital compensation signal Sdcm. The PWM signal generator  390  comprises a duty cycle modulation unit  391  and a memory  395 . The memory  395  is utilized for storing a default duty cycle  397 . The memory  395  can be an electrically erasable programmable read only memory or a flash memory. The duty cycle modulation unit  391  regulates the duty cycle of the PWM signal S PWM  based on the digital compensation signal Sdcm. When the lighting system  600  is initially powered, the duty cycle modulation unit  391  may set the initial duty cycle of the PWM signal S PWM  to be the default duty cycle  397  stored in the memory  395 . 
         [0030]    Please refer to  FIG. 7 , which is a schematic diagram showing a lighting system  700  having control architecture in accordance with a fourth embodiment of the present invention. As shown in  FIG. 7 , the lighting system  700  comprises a switch  330 , a first resistor  310 , a pulse filter  320 , a driving circuit  350 , a lighting module  360 , a second resistor  311 , a light feedback module  370 , a comparator  386 , a counter  387 , and a PWM signal generator  790 . The coupling relationships and related functionalities regarding the switch  330 , the first resistor  310 , the pulse filter  320 , the driving circuit  350 , the lighting module  360 , the second resistor  311 , and the light feedback module  370  are similar to the above description on the lighting systems  300  and  500 . Consequently, in the operation of the lighting system  700 , the truth table of the enable control signal S EN , the PWM signal S PWM  and the driving control signal Sdrc is also the same as the truth table  400  in  FIG. 4 . 
         [0031]    The comparator  386  can be an operational amplifier  386  for generating a compare signal Scmp by comparing the feedback signal Sf with the reference signal Sref. The comparator  386  comprises a first input end coupled to the light feedback module  370  for receiving the feedback signal Sf, a second input end for receiving the reference signal Sref, and an output end for outputting the compare signal Scmp. In the embodiment shown in  FIG. 7 , the first and second input ends of the comparator  386  are the negative and positive input ends. If the reference signal Sref is greater than the feedback signal Sf, the comparator  386  outputs the compare signal Scmp with high voltage level. On the contrary, if the reference signal Sref is less than the feedback signal Sf, the comparator  386  outputs the compare signal Scmp with low voltage level. 
         [0032]    The counter  387  is coupled between the comparator  386  and the PWM signal generator  790 . The counter  387  functions to generate a count signal Scount by performing an up-counting process or a down-counting process based on the compare signal Scmp. The counter  387  comprises a memory unit  388  for storing a default count value  389 . The memory unit  388  can be an electrically erasable programmable read only memory or a flash memory. When the lighting system  700  is initially powered, the counter  387  may set the initial count value of the count signal Scount to be the default count value  389  stored in the memory unit  388 . The PWM signal generator  790  comprises a duty cycle modulation unit  791  and a memory  795 . The memory  795  is utilized for storing a default duty cycle  797 . The memory  795  can be an electrically erasable programmable read only memory or a flash memory. The duty cycle modulation unit  791  regulates the duty cycle of the PWM signal S PWM  based on the count signal Scount. When the lighting system  700  is initially powered, the duty cycle modulation unit  791  may set the initial duty cycle of the PWM signal S PWM  to be the default duty cycle  797  stored in the memory  795 . In another embodiment, the memory  795  can be omitted, and the duty cycle modulation unit  791  may set the initial duty cycle of the PWM signal SPWM based on the count signal Scount having the default count value  389  when the lighting system  700  is initially powered. 
         [0033]    In the feedback operation of the lighting system  700 , if the intensity of the light output is lower than a desired intensity, then the feedback signal Sf is less than the reference signal Sref, and the comparator  386  outputs the compare signal Scmp with high voltage level so that the counter  387  is driven to perform an up-counting process for raising the count signal Scount. Accordingly, the duty cycle of the PWM signal S PWM  is increased for enhancing the light output of the lighting module  360  following the increase of the count signal Scount. Alternatively, if the intensity of the light output is higher than the desired intensity, then the feedback signal Sf is greater than the reference signal Sref, and the comparator  386  outputs the compare signal Scmp with low voltage level so that the counter  387  is driven to perform a down-counting process for lowering the count signal Scount. Accordingly, the duty cycle of the PWM signal S PWM  is decreased for reducing the light output of the lighting module  360  following the decrease of the count signal Scount. 
         [0034]    To sum up, in the operation of the lighting system of the present invention, regardless of an open-loop control or a feedback control, the quasi low-level signal will not occur to the driving control signal, and furthermore the periodical pulse noise regarding the driving control signal is filtered out. Accordingly, the lighting system of the present is capable of providing an accurate control of the light output by completely solving the problem of redundant lighting. 
         [0035]    The present invention is by no means limited to the embodiments as described above by referring to the accompanying drawings, which may be modified and altered in a variety of different ways without departing from the scope of the present invention. Thus, it should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations might occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.