Abstract:
A light emitting diode (LED) driver drives a plurality of LEDs, and includes a plurality of LED drivers with inherent addresses thereof respectively driving the plurality of LEDs; a serial bus connected to the plurality of LED drivers; and a sequence controller serially transmitting a control signal for driving the plurality of LEDs and the inherent addresses, allowing the plurality of LED drivers to be sequentially driven, in the form of digital data through the serial bus. Thus, the LED driver accomplishes appropriate response speed corresponding to a human eye&#39;s recognition limit. Further, the LED driver provides easy fabrication, small size and lower production cost. The LED driver generates less noise while large current and high voltage fluctuate. Also, the LED driver automatically detects malfunction and automates initial current setting for production.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from Korean Patent Application No. 2005-0013575, filed on Feb. 18, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a light emitting diode (LED) driver device, and more particularly, to an LED driver device providing appropriate response speed, small size, easy fabrication, lower production costs and less noise. 
   2. Description of the Related Art 
   LEDs form a plurality of arrays with respect to three colors of red, green and blue, respectively, to be used as a back light of a liquid crystal display (LCD) apparatus. 
   As shown in  FIG. 1 , a conventional driver  200  for driving such an LED includes a dimming amount calculator  202  receiving the average luminance (Y) value of a video signal and calculating the dimming controlling amount of respective RGB colors; a modulation controller  206  receiving the dimming controlling amount, receiving information about the RGB colors inputted from a light sensor  204  and outputting a pulse width modulation signal; a signal shifting part  208  generating a reference timing signal having a phase shifted in sequence to sequentially shift the phase of the pulse width modulation signal with respect to each of the RGB LEDs  250 ; an AND gate  210  receiving the pulse width modulation signal of the modulation controller  206  and the reference timing signal of the signal shifting part  208  and outputting a signal by a logical AND operation thereof; and a plurality of LED drivers  212  receiving an output signal of the AND gate  210  and driving the LED  250 . 
   If the pulse width modulation signal of the modulation controller  206  is simultaneously applied to the plurality of LED drivers  212  in parallel, large current stress is applied to a power source unit. Hence, the LED driver  200  sequentially applies the pulse width modulation signal to each of LED lines or the drivers. 
   Then, the signal shifting part  208  generates the reference timing signal having phase difference, as much as the number of the drivers, by using a counter  214  and a shift register  216 . When the reference timing signal of the signal shifting part  208  and the pulse width modulation signal of the modulation controller  206  are performed with an AND operation by the AND gate  210 , the phase of the pulse width modulation signal is sequentially shifted and the drivers  212  are sequentially driven. 
   The conventional LED driver  200  employs a field-programmable gate array (FPGA) or a complex programmable logic device (CPLD) in the signal shifting part  208  to achieve fast response of high brightness LED, thereby sequentially dimming at high speed. 
   However, it is required to slow down the response speed of the light sensor  204  and the modulation controller  206  to the range of 100 ms to 500 ms to prevent drastic color change recognized by human&#39;s eye. That is, the response speed of the whole system should be slowed down to maintain stable white balance. Further, the high speed response of the LED may cause adverse effects on the LCD back light. Thus, the dimming control at appropriate speed corresponding to a human eye&#39;s recognition limit is more effective than the dimming control using high speed digital logic. 
   Meanwhile, the conventional LED driver  200  utilizes the signal shifting part  208  as a complex additional logic number to supply information on analog dimming, PWM dimming, etc. to each of the drivers in parallel through an analog signal line, thereby requiring many circuit wires. 
   Also, in the analog signal line corresponding to a low voltage, much noise may be introduced into the circuit when a large current and a high voltage repeatedly fluctuate, thereby leading to malfunction and abnormal oscillation. 
   Further, as a main controller of the conventional LED driver  200  does not have a function for determining a current value of the LEDs, the malfunction thereof is not automatically detected, and initial current setting for production cannot be automated. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide an LED driver device comprising appropriate response speed corresponding to a human eye&#39;s recognition limit. 
   It is another aspect of the present invention to provide an LED driver device providing easy fabrication, small size and lower production cost. 
   It is another aspect of the present invention to provide an LED driver device generating less noise while large current and high voltage fluctuate. 
   It is another aspect of the present invention to provide an LED driver device automatically detecting malfunction and automating initial current setting for production. 
   According to an aspect of the present invention, there is provided an LED driver device driving a plurality of LEDs, comprising a plurality of LED drivers, each having corresponding addresses and driving the plurality of LEDs; a serial bus connected to the plurality of LED drivers; and a sequence controller serially transmitting a control signal for driving the plurality of LEDs and the addresses allowing the plurality of LED drivers to be sequentially driven in the form of digital data through the serial bus. 
   According to an aspect of the present invention, each of the plurality of LED drivers comprises a first serial bus interface performing data communication with the sequence controller through the serial bus to receive the digital data corresponding to the control signal and the address; a DA converter performing DA conversion of the digital data to restore the control signal; a switch turned on or off to electrically connect or cut off a predetermined power source unit and the corresponding LEDs; and a switch driver outputting a signal turning on or off the switch according to the control signal. 
   According to an aspect of the present invention, the control signal comprises a level signal indicating a level of current flowing in the LEDs and a pulse width modulation signal controlling operation of the switch driver, and the respective drivers further comprise a first register and a second register respectively storing the level signal and the pulse width modulation signal. 
   According to an aspect of the present invention, the control signal further comprises an offset current signal indicating a level of offset current flowing in the LEDs, and the respective drivers further comprise a third register respectively storing the offset current signal. 
   According to an aspect of the present invention, the drivers further comprise a current detector detecting the current flowing in the LEDs; an AD converter performing AD conversion of the detected current signal; and a fourth register storing the current signal performed with the AD conversion, and the first serial bus interface transmits data of the current signal stored in the fourth register through the serial bus. 
   According to an aspect of the present invention, the serial bus comprises an inter-integrated circuit (I2C) bus, and the first serial bus interface and the second serial bus interface perform the data communication according to an I2C bus protocol. 
   According to an aspect of the present invention, the sequence controller comprises a second serial bus interface performing the data communication with the plurality of LED drivers through the serial bus to transmit the control signal and the address in the form of digital data; and an interface controller sequentially changing the address of the plurality of LED drivers and providing the second serial bus interface with the control signal and the address in the form of digital data. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a block diagram of a configuration of a conventional LED driver; 
       FIG. 2  is a block diagram of a configuration of an LED driver device according to an exemplary embodiment of the present invention; 
       FIG. 3  is a block diagram of an internal configuration of a sequence controller of the LED driver device in  FIG. 2  according to an exemplary embodiment of the present invention; and 
       FIG. 4  is a block diagram of an internal configuration of a driver of the LED driver device in  FIG. 2  according to an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. Exemplary embodiments are described below in order to explain the present invention by referring to the figures. 
     FIG. 2  is a block diagram schematically illustrating a configuration of an LED driver device  10  according to an exemplary embodiment of the present invention. 
   The LED driver device  10  according to an exemplary embodiment of the present invention drives a plurality of LEDs  30  used as a back light of an LCD apparatus. The plurality of LEDs  30  are provided with respect to each of RGB (red, green and blue) colors in the present exemplary embodiment. 
   The LED driver device  10  of the present exemplary embodiment serially transmits a control signal in the form of digital data through a serial bus to control current flowing in the plurality of LEDs  30 . Also, the LED driver device  10  of the present exemplary embodiment sequentially changes an address of a driver corresponding to the plurality of LEDs  30  to sequentially drive the plurality of LEDs  30 . 
   As shown in  FIG. 2 , the LED driver device  10  of the present exemplary embodiment comprises a plurality of LED drivers  14 , a serial bus  40  and a sequence controller  12 . The plurality of LED drivers  14  and the sequence controller  12  perform data communication with each other through the serial bus  40 . 
   Each of the plurality of LED drivers  14  has a corresponding address, and corresponds to each of the plurality of LEDs  30 . The respective drivers  14  receive the control signal and the address from the serial bus  40  to control the current flowing in the plurality of LEDs  30 . If the received address conforms to their corresponding addresses, the drivers  14  drive the LEDs  30  corresponding to the control signal. The respective drivers  14  are connected to the serial bus  40  in parallel. Also, the respective drivers  14  are provided with a first serial bus interface  142  (to be described later with reference to  FIG. 4 ) performing the data communication with the sequence controller  12  through the serial bus  40 . 
   The sequence controller  12  serially transmits the control signal and the address in the form of the digital data to the serial bus  40 , and sequentially changes the addresses of the plurality of LED drivers  14  to allow the control signal to be sequentially transmitted to the plurality of LED drivers  14 . 
     FIG. 3  is a block diagram illustrating an internal configuration of the sequence controller  12  of the present embodiment. As shown therein, the sequence controller  12  of the present exemplary embodiment comprises a second serial bus interface  122  and an interface controller  124 . 
   The second serial bus interface  122  performs the data communication with the plurality of LED drivers  14  through the serial bus  40  to transmit the control signal and the address in the form of the digital data. The serial bus of the present exemplary embodiment comprises an inter-integrated circuit (I2C) bus. It is preferable but not necessary that the second serial bus interface  122  performs the data communication according to an I2C bus protocol. 
   The second serial bus interface  122  receives data corresponding to the control signal from the interface controller  124  and the address designating the driver  14  to which the control signal is to be transmitted, and transmits the data and the address to the serial bus  40  which comprises a SDA as a data line and a SCL as a clock line according to the I2C bus protocol. 
   The interface controller  124  sequentially changes the addresses of the plurality of LED drivers  14 , and provides the second serial bus interface  122  with the control signal and the sequentially changed address in the form of the digital data. The interface controller  124  stores the addresses of the plurality of LED drivers  14  in a predetermined memory (not shown) in advance, and sequentially changes the addresses of the plurality of LED drivers  14  with respect to a predetermined interval of the control signal and provides them to the second serial bus interface  122 . 
   That is, the interface controller  124  transmits the control signal with a predetermined interval as many times as the number of the drivers  14  while sequentially changing the driver  14  address. 
   The response speed of the light sensor  20  and the modulation controller  16  which is appropriate for the human eye&#39;s recognition limit is approximately 100 ms. In accordance with the response speed, the predetermined interval of the control signal may be fully transmitted to the plurality of LED drivers  14  in a single frame. 
   Meanwhile, the LED driver device  10  of the present invention may further comprise a dimming amount calculator  18 , the modulation controller  16  and the light sensor  20 , as shown in  FIG. 2 . 
   The dimming amount calculator  18  receives the average luminance (Y) value of a video signal and calculates the dimming amount of the respective RGB colors corresponding thereto. The light sensor  20  senses light emitted from the plurality of LEDs  30  and provides information on each of the RGB colors. 
   The modulation controller  16  receives the dimming amount of the RGB colors calculated by the dimming amount calculator  18  and the information of the respective RGB colors, and generates the pulse width modulation signal corresponding thereto. The pulse width modulation signal of the present exemplary embodiment is an example of the control signal of the present invention. 
   The sequence controller  12  of the present exemplary embodiment may be provided with the control signal, i.e. the pulse width modulation signal from the modulation controller  16 . 
     FIG. 4  is a block diagram illustrating an internal configuration of the respective LED drivers  14  according to an exemplary embodiment of the present invention. As shown therein, the respective drivers  14  comprise the first serial bus interface  142 , a digital-to-analog (DA) converter  144 ,  146  and  148 , a switch  150  and a switch driver  152 . 
   The first serial bus interface  142  performs the data communication with the sequence controller  12  through the serial bus  40  to receive the digital data corresponding to the control signal and the address. The serial bus  40  of the present exemplary embodiment comprises the I2C bus. It is preferable but not necessary that the first serial bus interface  142  performs the data communication according to the I2C bus protocol. 
   That is, the first serial bus interface  142  receives the digital data corresponding to the control signal and the address from the serial bus  40 , decodes them according to the I2C bus protocol and checks the received address. If the address received from the serial bus  40  conforms to its address, the first serial bus interface  142  continues receiving the data. 
   The DA converters  144 ,  146  and  148  perform DA conversion of the digital data and restore the control signal. The switch  150  is turned on or off to electrically connect or cut off a power source unit  50  and the corresponding LEDs  30 . 
   The switch driver  152  outputs a signal to turn on or off the switch  150  according to the control signal, to thereby drive the switch  150 . 
   The control signal of the present exemplary embodiment comprises a level signal indicating a level of the current flowing in the LEDs  30 ; and the pulse width modulation signal controlling operation of the switch driver  152 . Further, the control signal may comprise an offset current signal indicating a level of offset current flowing in the LEDs  30 . 
   The respective LED drivers  14  may further comprise a first register  156 , a second register  158  and a third register  160  storing data corresponding to the level signal, the pulse width modulation signal and the offset current signal. 
   Each of the first, second and third registers  156 ,  158  and  160  has a corresponding address. The first serial bus interface  142  checks the address about the received digital data according to the I2C bus protocol, and stores the data corresponding to the level signal, the pulse width modulation signal and the offset current signal to the register  156 ,  158  or  160  having the corresponding checked address. 
   Further, the respective LED drivers  14  may further comprise a current detector  162  detecting the current flowing in the LEDs  30 ; and an analog-to-digital (AD) converter  164  performing AD conversion of the detected current signal. At this time, it is preferable but not necessary that the respective drivers  14  further comprise a fourth register  166  storing data corresponding to the AD converted current signal. 
   If receiving request of transmitting the detected current signal through the serial bus  40 , the first serial bus interface  142  transmits the data corresponding to the stored current signal through the serial bus  40  referring to the fourth register  166 . 
   Accordingly, the LED driver device  10  of the present invention provides a detected value of the current flowing in the LEDs  30  to the main controller (not shown), thereby detecting where malfunction happens and automating initial current settings, comprising different current-light output characteristics, of the plurality of LED driving circuits, respectively, during initial production. 
   Although a few exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.