Abstract:
A multi-lamp driver t disclosed, comprising a power driver coupled to a plurality of lamps to supply power thereto, a feedback circuit coupled to at least one of the lamps to generate a feedback signal, a control circuit coupled between the feedback circuit and the power driver to control the power driver according to an illumination control signal and the feedback signal for total illumination adjustment of the lamps, and at least one switch controlled by the control circuit to turn at least one of the lamps on or off In a total illumination adjustment of the lamps, the switch turns on or off timely. The difference between the maximum and minimum value of the total illumination of the lamps is thus increased.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a multi-lamp driver and more particularly to a multi-lamp driver used in a LCD backlight module.  
         [0003]     2. Description of the Related Art  
         [0004]     Illumination control of a backlight module in a LCD panel is typically realized by adjusting current in each lamp simultaneously. However, due to lamp nature, maximum and minimum values of current in each lamp are limited, resulting in insufficient difference between maximum and minimum value of total lamp illumination. This leads to poor performance, or even failure to comply with TCO03 standards.  
         [0005]      FIG. 1  is a schematic diagram of a conventional multi-lamp driver  100  driving a first lamp Lp 1  and second lamp Lp 2 . The multi-lamp driver  100  comprises a power driver  102 , a feedback circuit  106 , and a control circuit  108 . The power driver  102  comprises a driving circuit  104  and a transformer T 1 . The driving circuit  104  converts DC voltage Vin to AC voltage, provided to a primary coil of the transformer T 1 . A secondary coil of the transformer T 1  is coupled to high voltage ends of the first lamp T 1  and second lamp T 2  to provide power to the first lamp T 1  and second lamp T 2 . The feedback circuit  106  is coupled to low voltage ends of the two lamps to generate a feedback signal Sf to the control circuit  108 . The control circuit  108  then controls the driving circuit  104  based on an illumination control signal Sb and the feedback signal S f , such that the AC voltage produced by the driving circuit  104  provides the two lamps Lp 1  and Lp 2  with stable illumination.  
         [0006]      FIG. 2  is a schematic diagram of another conventional multi-lamp driver  200 , comprising a power driver  202 , a controlling circuit  104 , a feedback circuit  106 , and a control circuit  108 . Here, multi-lamp driver  200  comprises two transformers T 1  and T 2  with secondary coils coupled respectively to high voltage ends of lamps Lp 1  and Lp 2  through capacitors C 1  and C 2 . Further, the feedback circuit  106  is coupled to the secondary coil of the transformer T 2  rather than to the low voltage ends of lamps Lp 1  and Lp 2 . All other aspects of multi-lamp driver  100  and  200  are the same. Similarly, the control circuit  108  controls the driving circuit  104  based on an illumination control signal S b  and a feedback signal S f  received from the feedback circuit  104 , such that the AC voltage produced by the driving circuit  104  provides the two lamps Lp 1  and Lp 2  with stable illumination.  
         [0007]     As shown in  FIGS. 1 and 2 , illumination in both the multi-lamp drivers  100  and  200  is controlled by changing the AC voltage generated by the control circuit  108  to control currents of the lamps Lp 1  and Lp 2 . During illumination adjustment, current in lamps Lp 1  and Lp 2  varies in the same manner and lamps Lp 1  and Lp 2  are turned on and off simultaneously. However, maximum and minimum current in the lamps Lp 1  and Lp 2  is limited, resulting in unobvious difference between maximum and minimum total lamp illumination of a panel. In view of such a problem, a multi-lamp driver with increased illumination range is called for.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The invention discloses a multi-lamp driver with decreased minimum value of total lamp illumination. The multi-lamp driver comprises at least one switch turning off lamp(s) at a desired time, decreasing minimum value and thereby increasing range of total lamp illumination.  
         [0009]     The multi-lamp driver of the invention comprises a power driver coupled to a plurality of lamps to supply power to the lamps, a feedback circuit coupled to at least one of the lamps to generate a feedback signal, a control circuit coupled between the feedback circuit and the power driver to control the power driver according to an illumination control signal for adjustment of lamp illumination, and at least one switch controlled by the control circuit to turn at least one of the lamps on and off. Since the invention adjusts not only current in each lamp but also incidents of turning on lamps, minimum value of total lamp illumination can be lower than conventional drivers. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a schematic diagram of a conventional multi-lamp driver;  
         [0012]      FIG. 2  is a schematic diagram of another conventional multi-lamp driver;  
         [0013]      FIG. 3  is a schematic diagram of a multi-lamp driver in accordance with an embodiment of the invention;  
         [0014]      FIG. 4  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention;  
         [0015]      FIG. 5  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention;  
         [0016]      FIG. 6  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention;  
         [0017]      FIG. 7  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention;  
         [0018]      FIG. 8  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention;  
         [0019]      FIG. 9  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention;  
         [0020]      FIG. 10  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention; and  
         [0021]      FIG. 11  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 3  is a schematic diagram of a multi-lamp driver in accordance with an embodiment of the invention. The multi-lamp driver  100 ′ also drives the first and second lamps Lp 1  and Lp 2  like the multi-lamp driver  100 ′ shown in  FIG. 1 . The only difference between the multi-lamp drivers  100 ′ and  100  is that an additional switch SW 1  is inserted between the feedback circuit  106  and a low voltage end of the first lamp Lp 1 , controlled by a switch control signal S SW1  generated by the control circuit  108 . When the switch SW 1  is turned off, the only lamp conducting is the second lamp Lp 2 , and the feedback circuit  106  coupled to the second lamp Lp 2  continues outputting the feedback signal S f  to the control circuit  108  such that illumination of the second lamp Lp 2  is controlled. Since only the second lamp Lp 2  is conducting, the total lamp illumination is lower than in  FIG. 1  in which both the lamps Lp 1  and Lp 2  are conducting.  
         [0023]     The time for the switch control signal S SW1  to turn on the first lamp Lp 1  is set according to design requirements. In an embodiment, a predetermined illumination value is established. When the illumination control signal S b  sets the total lamp illumination lower than the predetermined value, the switch control signal S SW1  turns off the switch SW 1 . When the illumination control signal S b  sets the total lamp illumination higher than the predetermined value, the switch control signal S SW1  turns on the switch SW 1 . Total lamp illumination, when below the predetermined value, is provided by the second lamp Lp 2  and can be lowered until the current of the second lamp Lp 2  reaches a minimum value. Resultingly, the multi-lamp driver  100 ′ has a lower minimum value of total lamp illumination than the multi-lamp driver  100 .  
         [0024]     Moreover, when the switch SW 1  is turned off/on, the total lamp illumination may descend/ascend suddenly. To solve this problem, the control circuit  108  can control the driving circuit  104  to increase/decrease AC voltage when the switch SW 1  is turned off/on to stabilize total lamp illumination.  
         [0025]      FIG. 4  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention. Multi-lamp driver  200 ′ also drives the first and second lamps Lp 1  and Lp 2  like the multi-lamp driver  200 . The only difference between the multi-lamp drivers  200 ′ and  1200  is that here an additional switch SW 1  is inserted between the ground and the low voltage end of the first lamp Lp 1 , wherein the switch SW 1  is controlled by a switch control signal S SW1  generated by the control circuit  108 . When the switch SW 1  is turned off, the only lamp conducting is the second lamp Lp 2 , and the feedback circuit  106  coupled to the second lamp Lp 2  continues outputting the feedback signal S f  to the control circuit  108  such that illumination of the second lamp Lp 2  is controlled. Since only the second lamp Lp 2  is conducting, total lamp illumination is lower than in  FIG. 2  in which both the lamps Lp 1  and Lp 2  are conducting.  
         [0026]     Similarly, the time for the switch control signal S SW1  to turn on the first lamp Lp 1  is set according to design requirements. In an embodiment, a predetermined illumination values is established. When the illumination control signal S b  sets the total lamp illumination lower than the predetermined value, the switch control signal S SW1  turns off the switch SW 1 . When the illumination control signal S b  sets the total lamp illumination higher than the predetermined value, the switch control signal S SW1  turns on the switch SW 1 . Total lamp illumination, when below the predetermined value, is provided by the second lamp Lp 2  and can be lowered until the current of the second lamp Lp 2  reaches a minimum value. Resultingly, the multi-lamp driver  200 ′ has a lower minimum value of total lamp illumination than the multi-lamp driver  200 .  
         [0027]     Moreover, when the switch SW 1  is turned off/on, the total lamp illumination may descend/ascend suddenly. To solve this problem, the control circuit  108  can control the driving circuit  104  to increase/decrease AC voltage when the switch SW 1  is turned off/on to stabilize total lamp illumination.  
         [0028]      FIG. 5  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention. Multi-lamp driver  200 ″ differs from the multi-lamp driver  200 ′ of  FIG. 4  only in that the low voltage ends of the lamps Lp 1  and Lp 2  are coupled to the feedback circuit  106  rather than the ground. Similarly, when the switch SW 1  is turned off, the lamp conducting is the second lamp Lp 2 , and the feedback circuit  106  coupled to the second lamp Lp 2  continues outputting the feedback signal S f  to the control circuit  108  such that illumination of the second lamp Lp 2  is controlled. Since only the second lamp Lp 2  is conducting, total lamp illumination is lower than in  FIG. 2  in which both the lamps Lp 1  and Lp 2  are conducting. Operating details are the same as for multi-lamp driver  200 ′, and not described here for brevity.  
         [0029]     The multi-lamp drivers  100 ′,  200 ′ and  200 ″ described above all drive two lamps Lp 1  and Lp 2 . However, this is only for purposes of illustration. It should be obvious to those skilled in the art that the multi-lamp driver of the invention can be extended to drive more than two lamps, as described below.  
         [0030]      FIG. 6  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention. The multi-lamp driver  600 , driving a plurality of lamps Lp 1  to Lpn, has an extended structure of the multi-lamp driver  100 ′ in  FIG. 3 . In the multi-lamp driver  600 , a transformer T 1  is coupled to lamps Lp 1  to Lp n  through capacitors C 1  to C n , respectively. Switches SW 1  to SWN n−1  are coupled between a feedback circuit  106  and low voltage ends of the lamps Lp 1  to Lp n−1  respectively, and turned on or off according to switch control signals S SW1  to S SWn−1  generated by a control circuit  108 . When any of the switches is turned off, the lamp coupled to the turned-off switch is turned off responsively, while the feedback circuit  106  remains coupled to the lamps still conducting and outputting a feedback signal S f  to the control circuit  108  such that the total illumination of the lamps t still conducting is controlled. Since not all of the lamps are conducting, the lamps Lp 1  to Lp n  driven by the multi-lamp driver  600  can have a lower illumination minimum than conventional drivers in which all the lamps Lp 1  to Lp n  are conducting.  
         [0031]     Similarly, the respective time for the switch control signal S SW1  to S SWn−1  to turn on the corresponding lamp Lp 1  to Lpn n-1  is set according to design requirements. For example, a plurality of predetermined illumination values can be established, including a first predetermined value, a second predetermined value, and so on, until the n−1 predetermined value. When the illumination control signal S b  sets the total lamp illumination lower than the first predetermined value, the switch control signal S SW1  turns off the switch SW 1 , and the other switch control signals S SW1  to S SWn−1  turn on the switches SW 2  to SWn−1, respectively. Resutlingly, lamps remaining conducting are the lamps Lp 2  to Lp n . Similarly, when the illumination control signal S b  sets the total lamp illumination lower than the second predetermined value, the switch control signal S SW1  turns off the switch SW 1 , the switch control signal S SW2  turns off the switch SW 2 , and the other switch control signals S SW3  to S SWn−1  turn on the switches SW 3  to SW n−1 , respectively. Resutlingly, lamps left conducting are the lamps Lp 3  to Lp n . And so proceed, until only one lamp Lp n  is left conducting.  
         [0032]     Moreover, when the switch SW 1  is turned off/on, the total lamp illumination may descend/ascend suddenly. To solve this problem, the control circuit  108  can control the driving circuit  104  to increase/decrease AC voltage when any one of the switches SW 1 -SW n−1  is turned off/on to stabilize the total lamp illumination  
         [0033]      FIG. 7  is a schematic diagram of a multi-lamp driver in accordance with another embodiment of the invention. The multi-lamp driver  700 , driving a plurality of lamps Lp 1  to Lp n , has an extension structure of the multi-lamp driver  200 ′ in  FIG. 4 . In the multi-lamp driver  700 , transformers T 1  to Tn are coupled to lamps Lp 1  to Lp n  through capacitors C 1  to C n , respectively. Switches SW 1  to SW n−1  are coupled between the ground and low voltage ends of the lamps Lp 1  to Lp n−1 , respectively, and turned on or off according to switch control signals S SW1  to S SWn−1  generated by a control circuit  108 . When any of the switches is turned off, the lamp coupled to the turned-off switch is turned off responsively, while the feedback circuit  106  remains coupled to the lamps that are still conducting through the transformer T n  and outputting a feedback signal S f  to the control circuit  108  such that total illumination of the lamps still conducting is controlled. Since not all of the lamps are conducting, the lamps Lp 1  to Lp n  driven by the multi-lamp driver  700  can have a lower illumination minimum than the prior art in which all the lamps Lp 1  to Lp n  are conducting.  
         [0034]     Similarly, the respective time for the switch control signal S SW1  to S SWn−1  to turn on the corresponding lamp Lp 1  to Lp n−1  is set according to design requirements. For example, a plurality of predetermined illumination values can be designed to correspond to one of the switches SW 1  to SW n−1 , with details the same as for multi-lamp driver  600 , and not described here for brevity.  
         [0035]      FIG. 8  is a schematic diagram of a multi-lamp driver  800  in accordance with another embodiment of the invention, differing from the multi-lamp  700  shown in  FIG. 8  in that the switches SW 1  to SW n−1  in the multi-lamp driver  800  are coupled between the feedback circuit  106  and the low voltage ends of the lamps Lp 1  to Lp n−1 , rather than between the ground and the low voltage ends of the lamps. Similar to multi-lamp  700 , the number of conducting lamps and hence the minimum value of total lamp illumination minimum of lamps driven by the multi-lamp driver  800  is decreased. Detailed operation is quite similar to the multi-lamp driver  700 , and is thus not descried here for brevity.  
         [0036]     However, switches can also be coupled to high voltage ends of lamps, as is obvious to those skilled in the art. Further, switches can control the lamps without being directly coupled to lamps. For example, when each of the lamps has a respective transformer, switch(es) can be coupled to a respective primary coil of a corresponding transformer, as described in the following.  
         [0037]      FIG. 9  is a schematic diagram of a multi-lamp driver  900  in accordance with another embodiment of the invention. The multi-lamp  900  has an extension structure of the multi-lamp driver  200 ′ in  FIG. 4  with the only difference therebetween being the switch SW 1  is coupled to primary coil in the transformer T 1  rather than the first lamp Lp 1 . Similar to the multi-lamp driver  200 ′, the first lamp Lp 1  is turned off and on responsively when the switch SW 1  is turned on and off. The minimum value of total lamp illumination minimum is thus decreased. Moreover, it is noted that the low voltage ends of the lamps Lp 1  and Lp 2  can be coupled to the feedback circuit  106  (not shown e), similar to the modification from the multi-lamp driver  200 ′ to  200 ″.  
         [0038]     Similarly,  FIGS. 10 and 11  respectively show multi-lamp drivers  1000  and  1100  having extension structures of  FIG. 9  to illustrate no restriction to only two lamps. The multi-lamp drivers  1000  and  1100  are extended from the multi-lamp drivers  700  in  FIG. 7  and  800  in  FIG. 8 , respectively. The only difference is that the switches SW 1  to SW n−1  are coupled to the primary coils in transformers T 1  to T n−1  rather than lamps Lp 1  to Lp n−1 . When one of the switches SW 1  to SW n−1  is turned on or off, the corresponding lamp is turned on or off responsively. The minimum values of total lamp illumination minimum of lamps driven by the multi-lamp driver  1000  and  1100  are decreased. Detailed operations of the multi-lamp drivers  1000  and  1100  are similar to those of the multi-lamp drivers  700  and  800 , and are thus not descried here for brevity.  
         [0039]     It should be noted that in all the above multi-lamp drivers, the number of switches is equal to the number of lamps less one, such that one lamp is left turned on eventually and the total lamp illumination is controlled through the feedback circuit. However, in the invention, even with only one switch, the minimum value of total lamp illumination is still lower than the prior art. The number of switches varies with requirement. Moreover, each switch can be coupled to more than one lamp, and accordingly, when any switch is turned on or off, more than one lamp is turned on or off responsively.  
         [0040]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.