Patent Publication Number: US-8525422-B2

Title: Backlight apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 99105200, filed on Feb. 23, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a backlight apparatus. More particularly, the invention relates to a light emitting diode (LED) backlight apparatus. 
     2. Description of Related Art 
     At present, a liquid crystal display (LCD) panel is often comprised of an LED which serves as a backlight apparatus. The LED backlight apparatus is designed based on different requirements. For instance, a multi-loop LED backlight apparatus is frequently required when favorable display needs to be achieved. That is to say, a plurality of LED strings are applied in such a design. 
     After the number of the LED strings is increased, one issue derived therefrom lies in how to evenly emit light from each of the LED strings. In the existing design of the LED backlight apparatus, each of the LED strings is driven by individual driving circuit. Luminance variation in each of the LED strings driven by the corresponding driving circuit is adjusted, such that the luminance of each of the LED strings is similar, and brightness uniformity of the backlight apparatus can be improved. 
     Nonetheless, a plurality of driving circuits are required in said conventional LED backlight apparatus, and therefore circuit costs are relatively high. Moreover, complicated and costly technology should be applied in order to uniformize the luminance of the LED strings by accurately adjusting the corresponding driving circuits. As such, costs of the conventional LED backlight apparatus are significantly increased. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a backlight apparatus of which brightness uniformity can be effectively improved. 
     The invention provides a backlight apparatus including a plurality of LED modules. Each of the LED modules includes a first connection pin set, a second connection pin set, a driving circuit, a first LED string, and a second LED string. Each of the connection pin sets has a first power connection pin, a second power connection pin, a first ground connection pin, and a second ground connection pin. The first and second power connection pins are coupled to each other, and the first and second ground connection pins are coupled to each other. The first ground connection pin of the first connection pin set is coupled to the first power connection pin of the second connection pin set. The driving circuit is coupled to the first power connection pin of the first connection pin set and the first ground connection pin of the second connection pin set for providing a driving signal. Each of the LED strings is coupled between the second power connection pin and the second ground connection pin of each of the connection pin sets and receives the driving signal. 
     According to an embodiment of the invention, each of the LED modules further includes at least one third connection pin set and at least one third LED string. The third connection pin set has a first power connection pin, a second power connection pin, a first ground connection pin, and a second ground connection pin. The third connection pin set is coupled to a coupling path where the driving circuit is coupled to the first ground connection pin of the second connection pin set. The first power connection pin of the third connection pin set is coupled to the first ground connection pin of the second connection pin set. The first ground connection pin of the third connection pin set is coupled to the driving circuit. The third LED string is serially connected between the second power connection pin and the second ground connection pin of the third connection pin set to receive the driving signal. 
     According to an embodiment of the invention, the driving signal is a driving current. 
     According to an embodiment of the invention, the driving circuit is a direct current to direct current (DC-DC) power converter. 
     According to an embodiment of the invention, the DC-DC power converter includes an inductor, a semiconductor pseudo switch, a first diode, a voltage detecting circuit, and a controller. The inductor has an end that receives an input voltage. The semiconductor pseudo switch is serially connected between the other end of the inductor and a base voltage, and the semiconductor pseudo switch is controlled by a pulse width modulation (PWM) signal. An anode of the first diode is commonly coupled to the inductor and the semiconductor pseudo switch, and a cathode of the first diode generates the driving signal. The voltage detecting circuit receives the driving signal and generates an over voltage protecting signal by dividing a voltage of the driving signal. The controller receives an operating voltage, a feedback signal, the over voltage protecting signal, an enabling signal, and a dimming signal. The PWM signal is generated based on the feedback signal and the dimming signal when the enabling signal is enabled. The semiconductor pseudo switch can include a transistor switch and a MOS switch. Here, the MOS switch is applied to exemplify the invention. 
     According to an embodiment of the invention, the controller further stops generating the PWM signal based on the over voltage protecting signal when an over voltage effect arises in the driving circuit. 
     According to an embodiment of the invention, the backlight apparatus further includes a voltage generator. The voltage generator is coupled to the driving circuit for generating the operating voltage based on the input voltage. 
     According to an embodiment of the invention, the voltage generator includes a first current limiting resistor, a second current limiting resistor, a transistor, a voltage stabilizing capacitor, and a second diode. An end of the first current limiting resistor and an end of the second current limiting resistor commonly receive the input voltage. A control end of the transistor is coupled to the other end of the first current limiting resistor. A first end of the transistor is coupled to the other end of the second current limiting resistor. The voltage stabilizing capacitor is serially connected between a second end of the transistor and the base voltage. An anode of the second diode receives the base voltage, and a cathode of the second diode is commonly coupled to the transistor and the first current limiting resistor. 
     Based on the above, the connection between the driving circuit and the LED strings of the backlight apparatus is changed, such that more of the LED strings are serially connected. Thereby, the required number of the driving circuits can be reduced, and the brightness uniformity of the backlight apparatus is improved. 
     In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanying figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view illustrating a backlight apparatus  100  according to an embodiment of the invention. 
         FIG. 2  is a schematic view illustrating a backlight apparatus  200  according to another embodiment of the invention. 
         FIG. 3  illustrates implementation of a driving circuit  211  according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Please refer to  FIG. 1 , which is a schematic view illustrating a backlight apparatus  100  according to an embodiment of the invention. The backlight apparatus  100  includes a plurality of LED modules  110  and  120 . The LED module  110 , which is taken for example, includes connection pin sets  112  and  113 , a driving circuit  111 , and LED strings  114  and  115 . The connection pin set  112  has a first power connection pin PI 1 , a second power connection pin PI 2 , a first ground connection pin GI 1 , and a second ground connection pin GI 2 . In the connection pin set  112 , the first power connection pin PI 1  and the second power connection pin PI 2  are connected (short circuit), and the first ground connection pin GI 1  and the second ground connection pin GI 2  are connected (short circuit). Similarly, the connection pin set  113  has a first power connection pin PI 3 , a second power connection pin PI 4 , a first ground connection pin GI 3 , and a second ground connection pin GI 4 . In the connection pin set  113 , the first power connection pin PI 3  and the second power connection pin PI 4  are connected (short circuit), and the first ground connection pin GI 3  and the second ground connection pin GI 4  are connected (short circuit). On the other hand, in this embodiment, the first ground connection pin GI 1  of the connection pin set  112  is directly connected to the first power connection pin PI 3  of the connection pin set  113 . 
     The driving circuit  111  is coupled to the first power connection pin PI 1  of the connection pin set  112  and the first ground connection pin GI 3  of the connection pin set  113 . The driving circuit  111  transmits the driving signal to the LED strings  114  and  115  through the connection pin sets  112  and  113 . The LED string  114  is comprised of a plurality of serially connected LEDs D 11 ˜D 1 N. Here, N is the number of the LEDs, and N is a positive integer. The LED string  115  is comprised of N serially connected LEDs D 21 ˜D 2 N. An anode of the first LED D 11  in the LED string  114  is coupled to the second power connection pin PI 2  of the connection pin set  112 , and a cathode of the last LED D 1 N in the LED string  114  is coupled to the second ground connection pin GI 2  of the connection pin set  112 . Similarly, an anode of the first LED D 21  in the LED string  115  is coupled to the second power connection pin PI 4  of the connection pin set  113 , and a cathode of the last LED D 2 N in the LED string  115  is coupled to the second ground connection pin GI 4  of the connection pin set  113 . 
     Based on the above, the driving circuit  111  is serially connected to the LED string  114  through the connection pin set  112  and further serially connected to the LED string  115  from the connection pin set  112  to the connection pin set  113 , so as to form an electrical loop (the driving circuit  111 —the LED string  114 —the LED string  115 ). That is to say, the driving signal (e.g., the driving current) provided by the driving circuit  111  is transmitted to the LED string  114  through the first and second power connection pin sets PI 1  and PI 2  of the connection pin set  112 , and the driving signal is transmitted to the LED string  115  through the first and second ground connection pins GI 1  and GI 2  of the connection pin set  112  and the first and second power connection pins PI 3  and PI 4  of the connection pin set  113 . Finally, the driving signal is transmitted back to the driving circuit  111  through the first and second ground connection pins GI 3  and GI 4  of the connection pin set  113 . 
     As such, the LED strings  114  and  115  receive the same driving signal that is not attenuated. Namely, the luminance of the LED strings  114  and  115  is the same. 
     Note that each set of driving circuits  111  can drive two LED strings  114  and  115  in this embodiment. That is to say, in the backlight apparatus  100 , the number of the driving circuits is half the number of the LED strings, such that the required number of the driving circuits can be effectively reduced. 
     Please refer to  FIG. 2 , which is a schematic view illustrating a backlight apparatus  200  according to another embodiment of the invention. The backlight apparatus  200  includes a plurality of LED modules  210  and  220 . The LED module  210 , which is taken for example, includes connection pin sets  212 ,  213 , and  214 , a driving circuit  211 , and LED strings  215 ,  216 , and  217 . The connection pin set  212  has a first power connection pin PI 1 , a second power connection pin PI 2 , a first ground connection pin GI 1 , and a second ground connection pin GI 2 . In the connection pin set  212 , the first power connection pin PI 1  and the second power connection pin PI 2  are connected (short circuit), and the first ground connection pin GI 1  and the second ground connection pin GI 2  are connected (short circuit). Similarly, the connection pin set  213  has a first power connection pin PI 3 , a second power connection pin PI 4 , a first ground connection pin GI 3 , and a second ground connection pin GI 4 . In the connection pin set  213 , the first power connection pin PI 3  and the second power connection pin PI 4  are connected (short circuit), and the first ground connection pin GI 3  and the second ground connection pin GI 4  are connected (short circuit). The connection pin set  214  has a first power connection pin PI 5 , a second power connection pin PI 6 , a first ground connection pin GI 5 , and a second ground connection pin GI 6 . In the connection pin set  214 , the first power connection pin PI 5  and the second power connection pin PI 6  are connected (short circuit), and the first ground connection pin GI 5  and the second ground connection pin GI 6  are connected (short circuit). 
     Besides, in this embodiment, the first ground connection pin GI 1  of the connection pin set  212  is directly connected to the first power connection pin PI 3  of the connection pin set  213 , and the first ground connection pin GI 3  of the connection pin set  213  is directly connected to the first power connection pin PI 5  of the connection pin set  214 . 
     The driving circuit  211  is coupled to the first power connection pin PH of the connection pin set  212  and the first ground connection pin GI 5  of the connection pin set  214 , and the driving circuit  211  provides the driving signal. 
     The LED strings  215 ˜ 217  respectively include a plurality of serially connected LEDs D 11 ˜D 1 N, D 21 ˜D 2 N, and D 31 ˜D 3 N. The LED strings  215 ˜ 217  are respectively connected to the second power connection pins PI 2 , PI 4 , and PI 6  and the second ground connection pins GI 2 , GI 4 , and GI 6  of the connection pin sets  212 ,  213 , and  214 . 
     Different from the previous embodiment, this embodiment provides one more connection pin set  214  that is coupled to a coupling path where the driving circuit  211  is coupled to the first ground connection pin GI 3  of the connection pin set  213 . Besides, in this embodiment, the LED string  217  is connected between the second power connection pin PI 6  and the second ground connection pin GI 6  of the connection pin set  214 . Namely, the driving signal provided by the driving circuit  211  is transmitted to the LED string  215  through the connection pin set  212 , to the LED string  216  through the connection pin set  213 , to the LED string  217  through the connection pin set  214 , and back to the driving circuit  211  through the second and first ground connection pins GI 6  and GI 5  of the connection pin set  214 . 
     Certainly, the driving signal (e.g., the driving current) transmitted by the driving circuit  211  can be sent to the serially connected LED strings  215 ,  216 , and  217  without being attenuated. In other words, the luminance of the LED strings  215 ,  216 , and  217  remains consistent. Thereby, brightness uniformity of the backlight apparatus  200  can be improved. Moreover, the number of the driving circuits can be ⅓ of the number of the LED strings, which is conducive to reduction of the driving circuits and the circuit costs. 
     It should be mentioned that one more connection pin set can be further disposed between the connection pin set  214  and the driving circuit  211 , and the driving signal provided by the driving circuit  211  is expanded to pass through the four-stage serially connected LED strings. As such, the brightness uniformity of the backlight apparatus  200  is further enhanced, while the circuit costs can be further lowered down. 
     Please refer to  FIG. 3 , which illustrates implementation of the driving circuit  211  according to an embodiment of the invention. Here, the driving circuit  211  includes an inductor L 1 , a semiconductor pseudo switch Q 2 , a diode D 1 , an over voltage protecting circuit  312 , a feedback circuit  313 , and a controller  311 . The inductor L 1  has an end that receives an input voltage VIN 1 . The semiconductor pseudo switch Q 2  is serially connected between the other end of the inductor L 1  and a base voltage GND, and the semiconductor pseudo switch Q 2  is controlled by a PWM signal from the controller  311 . An anode of the diode D 1  is commonly coupled to the inductor L 1  and the semiconductor pseudo switch Q 2 , and a cathode of the diode D 1  generates the driving signal. The over voltage protecting circuit  312  receives the driving signal and generates an over voltage protecting signal OVP by dividing a voltage of the driving signal. Here, the feedback circuit  313  includes feedback detecting resistors R 3  and R 4 . The controller  311  receives an operating voltage VCC, the over voltage protecting signal OVP, a feedback signal FB, a dimming signal Dimming, and an enabling signal EA. When the enabling signal EA is enabled, the controller  311  generates the PWM signal based on the feedback signal FB and the dimming signal Dimming. Besides, the controller  311  stops generating the PWM signal based on the over voltage protecting signal OVP when an over voltage effect arises in the driving circuit  211 . 
     In this embodiment, the operating voltage VCC is generated by the voltage generator  320  according to the input voltage VIN 1 . The voltage generator  320  is coupled to the driving circuit  211 , and the voltage generator  320  includes current limiting resistors R 1  and R 2 , a transistor Q 1 , a voltage stabilizing capacitor C 3 , and a diode D 2 . An end of the current limiting resistor R 1  and an end of the current limiting resistor R 2  commonly receive the input voltage VIN 1 . A control end of the transistor Q 1  is coupled to the other end of the current limiting resistor R 1 . A first end of the transistor Q 1  is coupled to the other end of the current limiting resistor R 2 . The voltage stabilizing capacitor C 3  is serially connected between a second end of the transistor Q 1  and the base voltage GND. An anode of the diode D 2  receives the base voltage GND, and a cathode of the diode D 2  is commonly coupled to the transistor Q 1  and the current limiting resistor R 1 . A voltage VIN is serially connected to a fuse Fuse to generate the input voltage VIN 1  at the other end of the fuse Fuse. 
     Note that the driving circuits  360  and  380  and the driving circuit  211  are implemented in the same manner to generate the driving signal with favorable uniformity, and the implementation details are not described hereinafter. 
     In light of the foregoing, the connection of connection pins in the connection sets is modified in this invention, so as to change the number of the LED strings which are serially connected to the driving circuit. Thereby, the driving signal provided by a single driving circuit can be continuously and serially connected to the LED strings, so as to improve the brightness uniformity of the backlight apparatus. Moreover, the required number of the driving circuits and the circuit costs can be effectively reduced. 
     Although the invention has been described with reference to the above embodiments, it will be apparent to one of the ordinary skill in the art that modifications to the described embodiment may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed descriptions.