Abstract:
A high-efficiency power supply apparatus used with a driving system of a display panel and a method of designing the same to improve an electrical power efficiency by providing a non-isolated direct current (DC) power directly to a display panel driving circuit comprise: a DC power supplying circuit to improve a power factor by rectifying an alternating current (AC) power and generating the non-isolated DC power, which is not isolated from the AC power, and an isolated DC power; a display panel driving circuit to generate various driving signals for driving the display panel with the non-isolated DC power; and a video signal processing circuit to perform a predetermined video signal processing for generating data to drive the display panel with the isolated DC power.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the priority of Korean Patent Application No. 2003-40098, filed on Jun. 20, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
         BACKGROUND OF THE INVENTION 1. Field of the Invention  
         [0002]    The present invention relates to a power supply apparatus used with a display system and a method of designing the same, and more particularly, to a high-efficiency power supply apparatus used with a driving system of a display panel and a method of designing the same to improve a power efficiency by supplying a non-isolated direct current (DC) power from an input alternating current (AC) power directly to a display driving circuit. 2. Description of the Related Art  
           [0003]    Generally, display panels, such as plasma display panels (PDPs) or ferro electric liquid crystal (FLC) panels, are driven in a digital way.  
           [0004]    An alternating current plasma display panel (AC PDP) is a next-generation flat panel display for displaying texts or images using plasma formed by a discharging gas. Tens to hundreds of millions of pixels are arranged in a matrix form according to a size of the AC PDP.  
           [0005]    The AC PDP has the following advantages: wide view angle, large size, long lifespan, high contrast ratio, and super-thin shape. Common disadvantages of the AC PDP are high cost and high power consumption.  
           [0006]    [0006]FIG. 1 shows a conventional power supply apparatus used for an AC PDP.  
           [0007]    Referring to FIG. 1, the power supply apparatus includes an AC power source  110 , a rectifier circuit  120 , a power factor correction circuit  130 , first and second DC-DC conversion circuits  104 - 1  and  140 - 2 , and a display panel driving circuit  150 .  
           [0008]    An output voltage of the second DC-DC converting circuit  140 - 2  is supplied to a signal and data processing circuit, such as a video signal processing circuit, and a microprocessor.  
           [0009]    The circuit of the power supply apparatus in the conventional AC PDP is configured in a serially connected 2-stage configuration (hereinafter, referred to as a two-stage configuration) such that a DC output voltage of the power factor correction circuit  130  is supplied as an input voltage to the first and second DC-DC conversion circuits  140 - 1  and  140 - 2 , and output voltages of the first and second DC-DC conversion circuits  140 - 1  and  140 - 2  are supplied to various loads.  
           [0010]    The power supplied to the display panel driving circuit  150  is configured in the two-stage serial connection to improve the power factor and to regulate an output voltage. However, an independent DC-DC conversion circuit of a 2-TR forward or a half-bridge type should be used for the display panel driving circuit  150 . The display panel driving circuit  150  uses 75% of an entire output power of the system.  
           [0011]    However, when the power for the display panel driving circuit  150  is configured in the two-stage serial connection, the size of a plasma display panel (PDP) increases, and power efficiency is lowered since power conversion is performed twice. For example, if the efficiency of the power factor correction circuit  130  is 95% and the efficiency of the first DC-DC conversion circuit  140 - 1  is 95%, the efficiency of the display panel driving circuit  150  is lowered to 90%.  
         SUMMARY OF THE INVENTION  
         [0012]    Accordingly, it is an aspect of the present invention to provide a power supply apparatus used with a driving system of a display panel and a method of designing the same to minimize lost of power by supplying a non-isolated direct current (DC) power from an alternating current (AC) power directly to a display panel driving circuit without passing through a DC-DC converting circuit.  
           [0013]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
           [0014]    In order to achieve the foregoing and/or other aspects of the present invention, there is provided a high-efficiency power supply apparatus used with a display panel driving system, comprising: a direct current (DC) power supplying circuit to improve a power factor by rectifying alternating current power and generating a DC power, which is not isolated from the alternating current power, and an isolated DC power, which is isolated from the alternating current power; a display panel driving circuit to generate various driving signals to drive the display panel with the non-isolated DC power; and a video signal processing circuit to perform a predetermined video signal processing to generate data used to drive the display panel with the isolated DC power.  
           [0015]    In order to achieve the foregoing and/or other aspects of the present invention, there is also provided a method of designing a high-efficiency power supply apparatus in a display panel driving system, the method comprising: providing a non-isolated DC power, which is not isolated from an input alternating current (AC) power, directly to a display panel driving circuit; providing an isolated DC power, which is isolated from the input AC power, to a video signal processing circuit which performs a predetermined video signal process to generate data used to drive a display panel; and isolating the display panel driving circuit and the video signal processing circuit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The above and/or other aspects, features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0017]    [0017]FIG. 1 is a block diagram showing a conventional power supply apparatus used for an alternating current plasma display panel (AC PDP);  
         [0018]    [0018]FIG. 2 is a block diagram showing a high-efficiency power supply apparatus used with a display panel driving system, according to an embodiment of the present invention;  
         [0019]    [0019]FIG. 3 is a detailed block diagram showing a rectifier circuit and a power factor correction circuit of the power supply apparatus shown in FIG. 2;  
         [0020]    [0020]FIG. 4 is a detailed block diagram showing the rectifier circuit of the power supply apparatus shown in FIG. 2;  
         [0021]    [0021]FIG. 5 is a detailed block diagram showing a ripple filter of the power supply apparatus shown in FIG. 2; and  
         [0022]    [0022]FIG. 6 is a view showing a ground system of a plasma display panel driving system according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
         [0024]    A high-efficiency power supply apparatus used with a driving system of a display panel uses a non-isolated output voltage of a power factor correction circuit as a power supplied to the display panel driving circuit. That is, the non-isolated output voltage of the power factor correction circuit is directly supplied to the display panel driving circuit without passing through a direction current (DC)-DC conversion circuit to improve power efficiency.  
         [0025]    Especially, a sustain driving circuit consumes about 75% of an entire power in the plasma display panel driving system. Therefore, when the present invention is applied to thesustain driving circuit, the power efficiency can increase.  
         [0026]    However, in order to supply the output voltage of the non-isolated power factor correction circuit directly to the display panel driving circuit without passing through the DC-DC conversion circuit, the following items should be considered.  
         [0027]    First, the voltage outputted from the power factor correction circuit and the voltage used in the display panel driving circuit should have the same value.  
         [0028]    Second, since the output voltage of the power factor correction circuit includes lower frequency ripple voltage twice as much as the alternating current (AC) power frequency, the power factor correction circuit does not have good regulation features.  
         [0029]    Third, since the output voltage of the power factor correction circuit, that is, the DC-DC converter is not isolated from the used AC power, an electrical isolation between the display panel and the driving circuit should be properly solved to satisfy an electricity safety standard.  
         [0030]    The present invention that solves the above problems will be described with reference to the accompanying figures.  
         [0031]    As shown in FIG. 2, the power supply apparatus for the display panel driving system, according to the present invention, includes an AC power  210 , a rectifier circuit  220 , a power factor correction circuit  230 , a ripple filter  240 , a DC-DC conversion circuit  250 , a display panel driving circuit  260 , and a video signal processing circuit  270 .  
         [0032]    The rectifier circuit  220 , the power factor correction circuit  230 , the ripple filter  240 , and the DC-DC conversion circuit  250  are referred to as a DC power supplying circuit  1000 .  
         [0033]    The video signal processing circuit  270  processes an input broadcasting signal or a video signal to generate data used to drive the display panel, and an isolated DC power output from the DC-DC conversion circuit  250  is used as a driving power of the video signal processing circuit  270 .  
         [0034]    Detailed circuit configurations of the rectifier circuit  220  and the power factor correction circuit  230  are shown in FIG. 3.  
         [0035]    Referring to FIGS. 2 and 3, the rectifier circuit  220  rectifies an input from an AC power  210  using a bridge diode circuit configuration having diodes D 1 -D 4 , and outputs a DC voltage according to the rectified input.  
         [0036]    Then, the power factor correction circuit  230  receives the DC voltage, improves a power factor using a pulse width modulation (PWM) controlling signal, and outputs an output voltage into a capacitor C 1  according to the improved power factor. After that, the voltage charged in the capacitor C 1  is discharged and supplied to a load (Z), such as the display panel driving circuit  260  or the video signal processing circuit  270 , as a stabilized DC voltage.  
         [0037]    That is, in a high state section of the PWM controlling signal (CTL), a switch S 1  is turned on, a magnetic energy is charged in an inductor L 1 , and the energy charged in the capacitor C 1  is transferred to the load (Z).  
         [0038]    In addition, in a low state section of the PWM controlling signal, the switch S 1  is turned off and the magnetic energy charged in the inductor L 1  is transferred to the capacitor Cl and charged therein.  
         [0039]    The power factor is improved through the above charging/discharging processes by the PWM controlling signal.  
         [0040]    The voltage output from the power factor correction circuit  230  and the voltage used in the display panel driving circuit should have the same value.  
         [0041]    Therefore, the voltage output from the power factor correction circuit  230  and the voltage used in the display panel driving circuit  260  are equalized by changing the display panel driving voltage.  
         [0042]    That is, as an example, the output voltage of the power factor correction circuit  230  applied to the plasma display system is designed to be about 360˜400V DC generally, and a sustain driving voltage of the sustain driving circuit is designed to be about 160V.  
         [0043]    Accordingly, in the present invention, the output voltage of the power factor correction circuit  230  should be lowered, or the sustain driving voltage should be increased.  
         [0044]    In order to lower the output voltage of the power factor correction circuit  230 , a single ended primary inductance converter (SEPIC) including a converter controlling a level of the output voltage shown in FIG. 4 can be applied. The SEPIC includes inductors L 41 , L 42 , and L 43 , a transistor S 41 , resistors R 41  and R 42 , capacitors C 41 , C 42 , and C 43 , and a diode D 41 . That is, the output voltage can be lowered using a secondary winding, such as the inductor L 42  or L 43 , in the power factor correction circuit  230 . Also, the sustain driving voltage can be increased by changing the sustain driving circuit.  
         [0045]    The low frequency ripple voltage and the regulation feature of the ripple filter  240  of the power supply apparatus can be improved in the following ways.  
         [0046]    The low frequency ripple and the regulation features can be improved by increasing the capacity of the output capacitor C 1  of the power factor correction circuit  230  shown in FIG. 3.  
         [0047]    Also, the ripple filter  240  is inserted between the power factor correction circuit  230  and the display panel driving circuit  260  for more improved functions. FIG. 5 shows an example of the ripple filter  240 .  
         [0048]    The output electrical power of the power factor correction circuit  230  shown in FIG. 5 is P 0 =v 0 i 0 , and it is divided into two parts. That is, P 01 =v 0 i 0  is converted into P 02 =v 0 i 02  with efficiency η c . Therefore, a final output electrical power of a serial type ripple filter is P oss=V   oss i 02 =V oc i o2 +V o i o2 . Here, if v 0C i 02 =V o i 01 ·η C , it is the output electrical power of the DC-DC converter used in the serial type switching ripple filter, and an actual change of the electrical power is only generated on the above DC-DC converter. When it is assumed that the serial type switching ripple filter circuit is in one electrical power conversion stage, an entire efficiency η SS  can be calculated using the following equation 1.  
               η   SS     =       1   +       v   oC       v   0           1   +         v     0      C         v   0         η   C                   (   1   )                               
 
         [0049]    Therefore, in order to obtain high efficiency, the efficiency η C  of the DC-DC converter should increase, and a ratio of the voltage converted into the electric power for the output voltage of the power factor correction circuit  230  should decrease.  
         [0050]    The electric isolation between the display panel and the driving circuit can be solved in the following ways.  
         [0051]    [0051]FIG. 6 is a view showing a ground system to solve the isolation problem in the plasma display panel driving system applied by the present invention.  
         [0052]    The video signal processing circuit  270  processes the input broadcasting signal or the video signal to generate the data used to drive the display panel, and the isolated DC power output from the DC-DC conversion circuit is used as the driving power of the video signal processing circuit  270 .  
         [0053]    In addition, the power of the video signal processing circuit  270  is isolated by the DC-DC conversion circuit  620  from a scan and address driving circuit  640  using high voltage, and a data line is isolated by a photocoupler  630 .  
         [0054]    In the AC plasma display panel driving system, voltages larger than 160V are applied alternatively in the sustain driving operation and a lamp voltage is applied in a resetting operation, and therefore, it is similar to that the address and the scan driver IC is operated in an electrically floated status. Thus, the DC-DC conversion circuit  620  and the photocoupler  630  are used to isolate the circuit.  
         [0055]    Also, since a large current of nearly  100 A flows through the sustain driving circuit  260 - 1  with high frequency, the ground potential around the display panel changes a lot so that a mis-operation may be generated on a ground of the video signal processing circuit  270 .  
         [0056]    Therefore, it is required that the plasma display panel driving circuit and the video signal processing circuit  270  are isolated by the DC-DC conversion circuit  620  and the photocoupler  630  for a stabilized operation.  
         [0057]    Thus, a ground (first ground) of an output circuit of the non-isolated power factor correction circuit  230 , a ground (first ground) of the sustain driving circuit  260 - 1 , a ground (first ground) of an output circuit of the DC-DC conversion circuit  660 , and a ground (first ground) of the scan and address driving circuit  640  are electrically connected together. In addition, a ground (second ground) of the output circuit of the DC-DC conversion circuit  250  and a ground (second ground) of the video signal processing circuit  270  are electrically connected together.  
         [0058]    Next, the grounds are designed so that the first grounds and the second grounds are electrically blocked from each other.  
         [0059]    Accordingly, the ground of the video signal processing circuit  270  is isolated from the ground of the AC power by the DC-DC conversion circuit  250 , and isolated from the ground on the display panel driving circuit by the DC-DC conversion circuit  620  and the photocoupler  630 . Thus, if a user touches a metal portion which is connected to the ground on the video signal processing circuit  270  and exposed outward, the user is not electrocuted, and the international electricity safety standard IEC 60035  can be satisfied.  
         [0060]    In addition, the plasma display panel  610  itself is in non-isolated status, however, since a special glass, which is a superior insulating material, is generally used as the plasma display panel, there is no problem about the non-isolated plasma display panel. However, outer cases for an exposed electrode portion of the plasma display panel and printed circuit board (PCB) mounted portion should be prepared.  
         [0061]    Therefore, the above described three problems which may be generated according to the circuit configuration in which the output voltage of the non-isolated power factor correction circuit is transferred directly to the display panel driving circuit without passing through the DC-DC conversion circuit can be dealt with according to above method.  
         [0062]    In an aspect of the present invention, the ripple filter  240  is inserted between the power factor correction circuit  230  and the display panel driving circuit  260 , however, the ripple filter  240  may be omitted and the capacity of the output capacitor C 1  of the power factor correction circuit can be increased to improve the low frequency ripple and the regulation features.  
         [0063]    As described above, according to the present invention, the output voltage of the power factor correction circuit is directly applied to the display panel driving circuit or applied to the display panel driving circuit after being passed through the ripple filter without 2-stage serially configuring the power used in the display panel driving circuit. Thus, an electrical power efficiency can be improved, reliability of the circuit can be improved by simplifying the electrical circuits, and material costs can be lowered by reducing the number of semiconductor elements.  
         [0064]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.