Abstract:
Provided is a display apparatus that includes a light source, that further includes a current generator for outputting a predetermined driving current. Further provided is a first path for supplying the driving current output by the current generator to the light source and a second path for intercepting the driving current supplied to the light source. In addition, a switch is provided for supplying the driving current output by the current generator either to the first path or to the second path and a controller is provided for controlling the switch to supply the driving current output by the current generator to the first path while the light source is turned on, and to supply the driving current to the second path while the light source is turned off. Thus, the present invention provides a display apparatus which improves a response time of electrical current when a light source is turned on and off, and thereby improves display quality.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2005-0059378, filed on Jul. 1, 2005, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a display apparatus comprising a light source. More particularly, the present invention relates to a display apparatus, which improves a response time of electrical current while a light source is turned on and off, and thereby improves display quality.  
         [0004]     2. Description of the Related Art  
         [0005]     A display apparatus employs a light emitting diode (LED) instead of a conventional cold cathode fluorescent lamp (CCFL) as a light source in order to improve color performance. A display apparatus utilizing an LED light source produces more realistic colors.  
         [0006]     The LED light source in a conventional display apparatus uses either a linear type of control or a switching type of control. A method of controlling an LED light source using the conventional linear type of control and switching type of control will be described with reference to  FIGS. 1A and 1B .  
         [0007]     In the conventional linear type of control, the display apparatus comprises a constant voltage source in order to generate a voltage to be supplied to the LED light source. Further provided is a switch to be switched on and off in order to supply an electrical current to the LED light source that corresponds to the voltage supplied by the constant voltage source. Additionally provided is a pulse width modulation (PWM) generator for turning the switch on and off. In the linear type control of an LED light source, a current “ia” of a linear region “a” corresponding to an initial stage of supply current flowing through the LED elements is supplied to the LED light source as shown in  FIG. 1A . The current “ia” in the linear region “a” is always supplied to the LED light source, thereby causing a large voltage loss in the switch that continuously supplies the current “ia” in the linear region “a”, if the amount of the load current of the LED light source is large.  
         [0008]     In the conventional switching type of control, the display apparatus comprises a constant current source to generate a current to be supplied to the LED light source. Further provided is a switch to be switched on and off to supply the current supplied by the constant current source to the LED light source. Additionally provided is a pulse width modulation (PWM) generator to turn the switch on and off. In the switching type of control of the LED light source, the current “ia” flows through the LED light source in intervals (t 1 ˜t 3  and t 5 ˜) when the PWM generator is turned on to thereby turn on the LED light source as shown in  FIG. 1B . Also, a current of “0” flows through the LED light source during the interval (t 3 ˜t 5 ) which is when the PWM generator is turned off, so as to turn off the LED light source. The switch is turned on and off depending on the amount of the current flowing through the LED during the intervals (t 1 ˜t 3 , and t 5 ˜) which is when the PWM generator is turned on, so that the current flowing in the LED light source fluctuates during the interval of t 2 ˜t 3  and the average current “ia” flows therein.  
         [0009]     In the conventional switching type of control, the display apparatus is not affected by the amount of the LED light source&#39;s current load. However, in the conventional switching type of control, T 2  and T 1  become longer as shown in  FIG. 1B . T 2  refers to the amount of time taken to make the current flowing through the LED light source become “0” at “t 3 ”, which is when the PWM generator is turned off. T 1  refers to the amount of time taken to make the current flowing through the LED light source become the average current “ia” at t 1  and t 5 , which is when the PWM generator is turned on. Thus, the conventional display apparatus controlling the LED light source through the switching type of control may not have a quick response time when the LED light source is turned on and off.  
         [0010]     Accordingly, there is a need for an improved display apparatus which improves a response time of electrical current flowing through a light source that is turned on and off.  
       SUMMARY OF THE INVENTION  
       [0011]     Exemplary embodiments of the present invention address at least the above problems and/or disadvantages and provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a display apparatus which improves a response time of electrical current flowing through a light source that is turned on and off.  
         [0012]     The foregoing and/or other aspects of an exemplary embodiment of the present invention are also achieved by providing a display apparatus comprising a light source, further comprising a current generator for outputting a predetermined driving current. Further provided is a first path for supplying the driving current output by the current generator to the light source and a second path for intercepting the driving current supplied to the light source. In addition, a switch is provided for supplying the driving current output by the current generator either to the first path or to the second path and a controller is provided for controlling the switch to supply the driving current output by the current generator to the first path while the light source is turned on, and to supply the driving current to the second path while the light source is turned off.  
         [0013]     According to an aspect of an exemplary embodiment of the present invention, the light source comprises a light emitting diode (LED).  
         [0014]     According to an aspect of an exemplary embodiment of the present invention, the controller outputs a pulse width modulation (PWM) control signal to the switch to turn off the switch so as to supply the driving current output by the current generator to the first path while the light source is turned on, and to turn on the switch so as to supply the driving current to the second path while the light source is turned off.  
         [0015]     According to an aspect of an exemplary embodiment of the present invention, the controller turns off the switch so as to supply the driving current supplied to the second path, to the light source through the first path when the light source is turned on again while the light source is turned off.  
         [0016]     According to an aspect of an exemplary embodiment of the present invention, the first path and the second path are provided in parallel with each other, and the switch comprises a transistor which is provided in the second path and controlled to turn on and off by the controller.  
         [0017]     According to an aspect of an exemplary embodiment of the present invention, the controller controls the current generator to be disabled when the display apparatus is turned off.  
         [0018]     Other objects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The above and other objects, features, and advantages of certain embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:  
         [0020]      FIGS. 1A and 1B  illustrate waveforms of an LED driving current of a conventional driving control method;  
         [0021]      FIG. 2  is a control block diagram according to a display apparatus of an exemplary embodiment of the present invention; and  
         [0022]      FIG. 3  illustrates a pulse width modulation (PWM) control signal, a current waveform of an inductor and a waveform of a light emitting diode (LED) driving current according to a control method of the display apparatus of an exemplary embodiment of the present invention. 
     
    
       [0023]     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.  
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0024]     The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention and are merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.  
         [0025]     As shown in  FIG. 2 , a display apparatus according to an exemplary embodiment of the present invention comprises a light source  20 ; a current generator  10  to output a predetermined driving current; a first path  2   a  to supply the driving current output by the current generator  10  to the light source  20 ; a second path  2   b  to intercept the driving current supplied to the light source  20 ; a switch  30  to supply the driving current output by the current generator  10  either to the first path  2   a  or to the second path  2   b ; a controller  40  to control the switch  30  to supply the driving current output by the current generator  10  to the first path  2   b  when the light source  20  is turned on and to supply the driving current to the second path  2   b  when the light source  20  is turned off; and a user input part  50 .  
         [0026]     The light source  20  supplies light to a display part (not shown) which displays an image thereon. Preferably, the light source  20  according to an exemplary embodiment of the present invention comprises a light emitting diode (LED) which is provided in the first path  2   a . The LED light source  20  may comprise a plurality of LED elements.  
         [0027]     The current generator  10  provides a predetermined driving current to the LED light source  20 . The current generator  10  comprises a power source V S  to generate power V F  that is used by the LED light source  20  A pulse width modulation (PWM) generator  14  is provided to control a current flow so as to control the luminance of the LED light source  20  according to a predetermined order value. A current maintaining switch  12  is provided to control a current supplied from the power source V S  to the LED light source  20 . An inductor L is provided between an area where the first path  2   a  and the second path  2   b  are branched, and the current maintaining switch  12 . A current detecting resistor R S  is provided between an area where the first path  2   a  and the second path  2   b  are combined, and the power V S . A diode D is provided wherein an anode terminal is connected between the current detecting resistor R S  and the power source V S , and a cathode terminal is connected between the current maintaining switch  12  and the inductor L.  
         [0028]     The current maintaining switch  12  controls the current supplied from the power source V S  to the LED light source  20 . Preferably, the current maintaining switch  12  is provided as a metal-oxide semiconductor field effect transistor (MOSFET). However, other types of switches may be used.  
         [0029]     The PWM generator  14  PWM-controls the current maintaining switch  12  and allows the current generator  10  to output a constant driving current to maintain the luminance of the LED light source  20  according to the predetermined order value. The PWM generator  14  receives a turn-on control signal (the predetermined order value) of the LED light source  20  from the controller  40  at an initial stage of driving the display apparatus, and turns on the current maintaining switch  12 . Also, the PWM generator  14  detects a comparison voltage supplied to the current detecting resistor R S , and determines whether the current flowing to either the first path  2   a  or to the second path  2   b  is larger than the predetermined current value by comparing the detected comparison voltage and the predetermined order value. The PWM generator  14  turns off the current maintaining switch  12  if the detected comparison voltage is larger than the predetermined order value. After a predetermined period of time, the PWM generator  14  again turns on the current maintaining switch  12 . As described above, the PWM generator  12  turns on the current maintaining switch  12  according to the control of the controller  40  at the initial stage of driving the display apparatus. The PWM generator  12  repeatedly turns on and off the current maintaining switch  12  based on the result of the comparison of the comparison voltage supplied to the current detecting resistor R S  and the predetermined order value, and the predetermined period of time. Thus, the current generator  10  may output the constant driving current while the display apparatus is driven, regardless of turning on and off of the LED light source  20 .  
         [0030]     If the display apparatus is not driven, the PWM generator  14  is controlled to be disabled by the controller  40 . Preferably, the current generator  10  may not output the driving current.  
         [0031]     The switch  30  supplies the driving current output by the current generator  10  to either the first path  2   a  or to the second path  2   b . The switch  30  is provided in the second path  2   b  and is turned on and off by the PWM control signal of the controller  40 . Preferably, a MOSFET is provided as the switch  30  to intercept the driving current supplied from the current generator  10  to the LED light source  20 .  
         [0032]     The controller  40  controls respective circuits (not shown) of the display apparatus to drive the display apparatus, and at the same time outputs the turn-on control signal (the predetermined order value) of the LED light source  20  to the PWM generator  14  when a power key of the user input part  50  of the display apparatus is manipulated via. Of course, a turn-on control signal can also be outputted when a wired or wireless control signal is received by the display apparatus.  
         [0033]     The controller  40  outputs the PWM control signal to control the switch  30  so as to supply the driving current output by the current generator  10  to the first path  2   a  when the LED light source  20  is turned on, and to supply the driving current to the second path  2   b  when the LED light source  20  is turned off. That is, the controller  40  turns off the switch  30  to supply the driving current output by the current generator  10  to the LED light source  20  when the LED light source  20  is turned on, and turns on the switch  30  to supply the driving current supplied to the LED light source  20  to the second path  2   b  when the LED light source  20  is turned off.  
         [0034]     Here, a process of turning on and off the LED light source  20  will be described as an exemplary embodiment of the present invention. If a blue color B is not required to display a desired image, the light sources red R and green G among the lights sources R, G and B are turned on to receive the driving current while the LED light source B is turned off so as not to receive the driving current.  
         [0035]     The display apparatus according to an exemplary embodiment of the present invention may comprise a digital light processing (DLP) display, a liquid crystal display (LCD), a plasma display panel (PDP), a Liquid Crystal on Silicon (LCoS) display, or any other variant or display types that can display an image using an LED light source  20 . Preferably, the display apparatus according to an exemplary embodiment of the present invention is a DLP display.  
         [0036]     The method of controlling the LED light source  20  according to the display apparatus of an exemplary embodiment of the present invention will be described with reference to  FIG. 3 .  
         [0037]     First, when the power key (not shown) of the display apparatus is manipulated so as to drive the display apparatus at a time t 1 , the controller  40  controls the current generator  10  to output the driving current according to the predetermined order value. As the PWM generator  14  receives the turn-on control signal (the predetermined order value) from the controller  40  and turns on the current maintaining switch  12 , the driving current is output. At this time, the controller  40  outputs the PWM control signal to turn off the switch  30  as shown in (A) of  FIG. 3 . The driving current output from the power V S  is charged in the inductor L through the current maintaining switch  12 , so as to be supplied to the LED light source  20  provided in the first path  2   a . Then, the driving current output from the LED light source  20  flows to a third path  3   a  through the current detecting resistor R S . The flow path of the driving current output from the power source V s  is as follows: V S →L→LED light source  20 →R S →V S . Thus, at an initial stage of t 1 ˜t 2  when the LED light source  20  receives the driving current, the LED light source  20  is turned on and the current (refer to ‘B’ of  FIG. 3 ) flowing through the inductor L and the current (refer to ‘C’ of  FIG. 3 ) flowing in the LED light source  20  become larger. At the initial stage of driving the display apparatus, the response time T 1  of the LED light source  20  is similar to that of the conventional art.  
         [0038]     The PWM generator  14  detects the comparison voltage supplied to the current detecting resistor R S , and compares the detected comparison voltage and the predetermined order value. If the detected comparison voltage is larger than the predetermined order value at time t 2 , the PWM generator  14  determines that the driving current flowing through the LED light source  20  is larger than a predetermined current value “ic” and turns off the current maintaining switch  12 . Then, the current charged in the inductor L is supplied to the LED light source  20  through the first path  2   a , and then flows to the diode D through the current detecting resistor R S  and the a fourth path  3   b . The flow path of the current flowing through the inductor L is as follows: L→LED light source  20 →R S →D→L. Thus, the current (refer to ‘B’ of  FIG. 3 ) flowing in the inductor L and the current (refer to ‘C’ of  FIG. 3 ) flowing in the LED light source  20  becomes smaller from the time t 2 .  
         [0039]     After turning off the current maintaining switch  12 , the PWM generator  14  again turns on the current maintaining switch  12  after a predetermined period of time (t 3 −t 2 ). From a time t 3 , the flow path of the driving current output from the power source V S  is as follows: V S →L→LED light source  20 →R S →V S . Thus, the current (refer to ‘B’ of  FIG. 3 ) flowing through the inductor L and the current (refer to ‘C’ of  FIG. 3 ) flowing through the LED light source  20  becomes larger again.  
         [0040]     The PWM generator  12  repeatedly turns on and off the current maintaining switch  12  based on the comparison result of the comparison voltage supplied to the current detecting resistor R S  and the predetermined order value, and the predetermined period of time. The current flowing in the inductor L and the LED light source  20  maintains “ia”, which is an average value of current “ic” and “ib”.  
         [0041]     If the LED light source  20  is turned on at a time t 4 , the controller  40  outputs the PWM control signal to turn on the switch  30  as shown in ‘A’ of  FIG. 3 . As the current flowing in the LED light source  20  at the time t 4  reaches the predetermined current value “ic”, the PWM generator  14  turns off the current maintaining switch  12 . From the time t 4 , the current charged in the inductor L flows through the diode D through the switch  30  provided in the second path  2   b , the current detecting resistor R S  and the fourth path  3   b . The flow path of the current charged in the inductor L is as follows: L→switch  30 →R S →D→L. Thus, the current (refer to ‘Bb’ of  FIG. 3 ) flowing through the inductor L becomes smaller from the time t 4 . The current (refer to ‘C’ of  FIG. 3 ) flowing through the LED light source  20  is cut off at the time t 4 , and becomes “0”. When the LED light source  20  is turned off, the turn-off response time T 3  of the LED light source  20  becomes shorter and the current (refer to ‘b’ of  FIG. 3 ) flowing in the inductor L becomes smaller regardless of turning on and off the LED light source  20 .  
         [0042]     After turning off the current maintaining switch  12 , the PWM generator  14  again turns on the current maintaining switch  12  after a predetermined period of time. The driving current output from the power source V S  is charged in the inductor L through the current maintaining switch  12  to flow to the third path  3   a  through the switch  30  of the second path  2   b  and the current detecting resistor R S . The flow path of the driving current output from the power source V S  is as follows: V S →L→switch  30 →R S →V S . Thus, the current (refer to ‘B’ of  FIG. 3 ) flowing in the inductor L again becomes larger regardless of turning on and off the LED light source  20 .  
         [0043]     When the LED light source  20  is turned off, the PWM generator  12  repeatedly turns on and off the current maintaining switch  12  based on the comparison result of the comparison voltage supplied to the current detecting resistor R S  and the predetermined order value, and the predetermined period of time. The current flowing in the inductor L maintains “ia”, which is an average value of current “ic” and “ib”, regardless of turning on and off the LED light source  20 .  
         [0044]     If the LED light source  20  is turned on again at a time t 6 , the controller  40  outputs the PWM control signal to turn off the switch  30  as shown in (A) of  FIG. 3 .  
         [0045]     As the time t 6  refers to predetermined time after the switch  12  is turned off, the PWM generator  14  turns on the current maintaining switch  12 . The current flowing to the inductor L through the path (L→switch  30 →R S →D→L) before the time t 6 , flows to the LED light source  20  through the path (V S →L→LED light source  20 →R S →V S ) from the time t 6 . As the LED light source  20  receives the current flowing in the inductor L directly at the time t 6 , the turn-on response time T 4  of the LED light source  20  becomes shorter when the LED light source  20  is turned on, and the current (refer to ‘b’ of  FIG. 3 ) flowing in the inductor L becomes larger regardless of turning on and off the LED light source  20 .  
         [0046]     When the LED light source  20  is turned on, the current flowing in the inductor L and the LED light source  20  maintains “ia” through the current maintaining switch  12  turned on and off by the PWM generator  12 .  
         [0047]     When the display apparatus is turned off by a manipulation of the power key (not shown) of the display apparatus at a time t 8 , the controller  40  disables the PWM generator  14  so that the current generator  10  does not output the driving current. Then, the current flowing through the inductor L and the LED light source  20  becomes smaller so as to be “0” at a time t 9 .  
         [0048]     As described above, the display apparatus according to an exemplary embodiment of the present invention makes the driving current supplied to the LED light source  20  flow through the path (L→switch  30 →R S →D→L) or through the path (V S →L→switch  30 →R S →V S ) when the LED light source  20  is turned off, thereby quickly changing the current supplied to the LED light source  20  into “0” and improving the turn-off response time of the LED light source  20 .  
         [0049]     Also, the display apparatus according to an exemplary embodiment of the present invention maintains the driving current through the path (L→switch  30 →R S →D→L) or through the path (V S →L→switch  30 →R S →V S ) when the LED light source  20  is turned off. When the LED light source  20  is turned on, the driving current maintained through the path (L→switch  30 →R S →D→L) or through the path (V S →L→switch  30 →R S →V S ) is supplied to the LED light source  20 , thereby quickly changing the current supplied to the LED light source  20  into the current “ia” and improving the turn-on response time of the LED light source  20 .  
         [0050]     While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.