Abstract:
A plasma display panel apparatus includes a pair of discharge sustaining electrodes, a panel capacitor to supply charged voltage alternately to each electrode of the pair of discharge sustaining electrodes, a switching device for discharge that is turned on when the panel capacitor is discharged, to thereby pass through discharged current of the panel capacitor, a current sensing part to sense the current passed through by the switching device for discharge, and an over-current controlling part that turns off the switching device for discharge when the current sensed in the current sensing part is at or above a predetermined reference value. With this configuration, the plasma display panel apparatus protects the switching device from over-current generated during an abnormal driving of the discharge sustaining electrode driving circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Application No. 2002-3386, filed Jan. 21, 2002, 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 in general to plasma display apparatuses, and more particularly, to a plasma display apparatus having an over-current protection circuit that protects a switching device from an over-current generated during an abnormal driving of a driving circuit of a discharge sustaining electrode and a method of protecting over-current thereof. 
     2. Description of the Related Art 
     A plasma display panel (PDP) is a display apparatus using a discharge of gas. The PDP is generally classified into a direct current (DC) type that applies a facing discharge, and an alternating current (AC) type that applies a surface discharge, depending upon its driving type. The AC type PDP has attracted more attention because it has a lower power consumption and a longer lifetime in comparison with the DC type. 
     The PDP using the AC driving type applies an alternating current (AC) voltage between electrodes insulated with a dielectric layer, and performs a discharge every half-cycle of the AC voltage, which is used to display a picture mainly in a sub-field method. In the sub-field method, since the power consumption used for a charge and the discharge of the PDP panel during the sustain of the discharge is very large, a circuit is used to collect reactive power in a driving device of the PDP. 
     As illustrated in FIG. 2, a circuit to drive the discharge sustaining electrode generally includes a unit driving cell of a discharge sustaining electrode connected to a Y-electrode (hereinafter referred to as ‘Y-electrode unit driving cell’) and a unit driving cell of a common electrode connected in common to a plurality of X-electrodes (hereinafter referred to as ‘X-electrode unit driving cell’). The Y-electrode and the X-electrode perform a surface discharge with supplied sustain pulses generated in the X-electrode unit driving cell and the Y-electrode unit driving cell as sustaining electrode pairs. By this, brightness of the picture displayed on a screen is sustained. Here, a panel capacitor  41  indicates equivalently electrostatic capacity formed between the Y-electrode and the X-electrode in the panel. 
     Referring to FIG. 2, the Y-electrode unit driving cell includes a capacitor  43   a  to collect energy, first and third switches  35   a ,  37   a  connected in parallel with the energy collecting capacitor  43   a , second and fourth switches  31   a ,  33   a  connected in series between a voltage supply source Vcc 1  and a ground, and a coil  39   a  connected between a first node n 1  and a second node n 2 . The X-electrode unit driving cell is positioned symmetrically relative to the Y-electrode unit driving cell through the panel capacitor  41 . 
     To the branch point of the first node n 1  and the second switch  31   a  are connected a reset resistance  45 , a reset capacitor  47  and a reset switch  48  to reset a voltage of the panel capacitor  41 . If the reset switch  48  is turned on, the voltages charged in the panel capacitor  41 , the X-electrode unit driving cell, and the Y-electrode unit driving cell become uniform. 
     An operation of the discharge sustaining electrode driving circuit will be described below with reference to FIGS. 3A to  3 E. The second switch  31   a  and a switch  49  to connect to the panel capacitor  41  (hereinafter, “panel capacitor connecting switch”) are turned on during the reset, and the electric current then flows. If the panel capacitor connecting switch  49  is turned off during the flow of the electric current, the reset switch  48  is turned on. Thus, a bypass current is formed by the reset capacitor  47  and the reset switch  48 . At this time, the electric current flowing in the panel capacitor  41  constitutes a reset pulse. 
     If the panel capacitor connecting switch  49  and the third switch  37   a  are turned on after the circuit is in the reset state and the current charged in the panel capacitor  41  is discharged, electric charge is transmitted to the energy collecting capacitor  43   a  and charging is performed. The first switch  35   a  and the panel capacitor connecting switch  49  are turned on during a voltage rising time t 0  of the discharge sustaining pulse. An electric current due to the energy charged in the energy collecting capacitor  43   a  is transmitted to the panel capacitor  41 , through the first switch  35   a , the coil  39   a  and the panel capacitor connecting switch  49 . On an end of the voltage rising time t 0  of the discharge sustaining pulse, the second switch  31   a  and the panel capacitor connecting switch  49  are turned on, thereby allowing the discharge sustaining pulse to remain in a “high” state t 1 . On an end terminal point of the discharge sustaining pulse in the t 1 , the third switch  37   a  and the panel capacitor connecting switch  49  are turned on, the voltage of the discharge sustaining pulse reduces to a “low” state. The electric current due to the energy charged in the panel capacitor  41  is stored in the energy collecting capacitor  43   a  through the panel capacitor connecting switch  49  and the third switch  37   a , and the discharge sustaining pulse is in the “suspension” state. On an end point of a falling time t 2  of the discharge sustaining pulse, the fourth switch  33   a  and the panel capacitor connecting switch  49  are turned on and the panel capacitor  41  is completely discharged, so the discharge sustaining pulse remains in the “low” state t 3 . The discharge is sustained through a repetition of the above-described processes. 
     If a sub-field ends, each switch  31   a ,  33   a ,  35   a ,  37   a ,  48 ,  49  is turned on or off so as to return back to the “reset” state to maintain the discharge sustaining pulse, and the discharge process is progressed, thereby allowing a plasma display panel to emit light. Also, like the Y-electrode unit driving cell, the X-electrode unit driving cell operates alternately with the Y-electrode unit driving cell through the above-described processes. 
     However, if any of the switches  31   a ,  33   a ,  35   a ,  37   a ,  48 ,  49  are abnormally turned on at the same time during the process of applying an on/off control signal to each of the switches  31   a ,  33   a ,  35   a ,  37   a ,  48 ,  49  while a conventional discharge sustaining electrode driving circuit has been driven, over-current flows into the switches  31   a ,  33   a ,  35   a ,  37   a ,  48 ,  49  by which they may be damaged. 
     SUMMARY OF THE INVENTION 
     The present invention has been made keeping in mind the above-described and other shortcomings, and an object of the present invention is to provide a plasma display apparatus having an over-current protection circuit that protects a switching device from the over-current generated during an abnormal driving of the driving circuit of discharge sustaining electrode. 
     Additional objects and 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. 
     This and other objects of the present invention may be achieved by providing a plasma display panel apparatus according to an embodiment of the invention that includes a pair of discharge sustaining electrodes, a panel capacitor to supply charged voltage alternately to each electrode of the pair of discharge sustaining electrodes, at least one discharge switching device to perform a discharge, the switching device being turned on when the panel capacitor is discharged to thereby pass through discharged current of the panel capacitor, a current sensing part to sense the current passing through the discharge switching device, and an over-current controlling part to turn off the discharge switching device when the current sensed in the current sensing part is at or higher than a predetermined reference value. 
     According to an aspect of the invention, the current sensing part comprises a current sensing resistance connected in series to the discharge switching device, and the over-current controlling part comprises a comparator to compare the sensed voltage detected in the current sensing resistance with a predetermined internal reference value and to output a break signal, and switching device to break the current to control the discharge switching device to be turned on or off according to a “high” or “low” signal of the break signal. 
     According to another aspect of the invention, the over-current controlling part further includes a direct current (DC) converting part positioned between the current sensing resistance and the comparator. 
     According to a further aspect of the invention, the over-current controlling part further includes an OR gate disposed between the comparator and the break switching device. 
     According to yet another aspect of the invention, the discharge switching device comprises a field effect transistor. 
     According to a still further aspect of the invention, the over-current controlling part further includes a microcomputer to turn off the discharge switching device when the sensed current of the current sensing part is at or higher than the predetermined value. 
     According to another embodiment of the invention, a method of protecting over-current of a plasma display panel apparatus that includes a pair of discharge sustaining electrodes, a panel capacitor to alternately supply a charged voltage to each electrode of the pair of the discharge sustaining electrodes, and a plurality of switching devices to control the charged voltage to be alternately supplied from the panel capacitor to each electrode of the pair of discharge sustaining electrodes, the method comprising sensing current passing through the discharge switching device, and turning off the discharge switching device when the sensed current is at or higher than a predetermined reference value. 
     According to an additional aspect of the invention, the turning off the discharge switching device comprises converting the voltage according to the sensed current into direct current voltage, and turning off the discharge switching device where the converted direct current voltage is at or higher than a predetermined reference value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood and its various objects and advantages will be more fully appreciated from the following description of the embodiments taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a schematic showing an over-current protected circuit of a discharge sustaining electrode driving circuit of a plasma display panel apparatus according to an embodiment of the present invention; 
     FIG. 2 is a schematic view showing a discharge sustaining electrode driving circuit of a conventional plasma display panel apparatus; 
     FIGS. 3A to  3 E show a relation between switching states and a discharge sustaining pulse of the discharge sustaining electrode driving circuit of FIG. 2; and 
     FIG. 4 is a perspective view of a plasma display panel according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinbelow, the present invention will be described in more detail, 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. 
     FIG. 1 is a schematic view showing a discharge sustaining electrode driving circuit of a PDP shown in FIG. 4 according to an embodiment of the present invention. A circuit to drive a discharge sustaining electrode includes a unit driving cell of the discharge sustaining electrode connected to Y-electrode  114  (hereinafter referred to as “Y-electrode unit driving cell”), a unit driving cell of common electrodes connected commonly to a plurality of X-electrodes  113  (hereinafter referred to as “X-electrode unit driving cell”), and a panel capacitor  11  to supply voltages to the X-electrodes  113  and the Y-electrodes  114 . Here, the panel capacitor  11  indicates an equivalent capacitance formed between the Y-electrodes  114  and the X-electrodes  113 . The Y-electrodes  114  and the X-electrode  113  perform a surface discharge by sustain pulses generated in the Y-electrode unit driving cell and the X-electrode unit driving cell, thereby sustaining brightness of a picture displayed. 
     The Y-electrode driving cell comprises an energy collecting capacitor  13 , first and third switches  5 ,  7  connected in parallel to the energy collecting capacitor  13 , second and fourth switches  1 ,  3  connected in series between a discharge sustaining voltage supply source Vcc 1  and a ground, and a coil  9  connected between a first node n 1  and a second node n 2 . Here, the first through fourth switches  1 ,  3 ,  5 ,  7  are field effect transistors (FETs). 
     To the branch point of the first node n 1  and the second switch  1  are connected a reset resistance  15  and a reset capacitor  17  to reset a voltage of the panel capacitor  11 . To the branch point of the reset resistance  15  and the reset capacitor  17  is connected a reset switch  18 . When the reset switch  18  is turned on, the voltages charged in the panel capacitor  11 , the X-electrode  113  and the Y-electrode  114  are reset to be uniform. The structure of the X-electrode unit driving cell is symmetrical relative to the Y-electrode unit driving cell, in the center of which the panel capacitor  11  is placed. Herein, description of an operation of driving the discharge sustaining electrode driving circuit will be omitted because it is otherwise generally the same as that of a conventional discharge sustaining electrode driving circuit. 
     According to the present invention, the Y-electrode unit driving cell includes an over-current protection circuit  20  to protect the driving cell from the over-current. The over-current protected circuit  20  comprises an over-current sensing resistance  21  connected in series to a source terminal of the fourth switch  3 , which is an FET according to an embodiment of the invention. A direct current (DC) converting circuit  27  converts the voltage sensed in the over-current sensing resistance  21  into a direct current. A comparator  23  compares the sensed voltage converted into the direct current in the DC converting circuit  27  with a predetermined reference value and to output a “high” signal when the sensed voltage is at or higher than the predetermined reference value. An OR gate  25  adds the output signal of the comparator  23  and a ground voltage (“low”) by an OR operation thereof, and an over-current breaking switch  22  positioned between an output terminal of the OR gate  25  and a gate terminal of the fourth switch  3 . The over-current breaking switch  22  is turned on in response to the “high” signal outputted from the OR gate  25  when there is over-current, to thereby turn off the fourth switch  3 . 
     When the discharge sustaining electrode driving circuit is in an abnormal operation, if the over-current is applied to the reset switch  18  and the fourth switch  3 , an over-voltage is applied to the over-current sensing resistance  21 . The over-voltage sensed by the over-current sensing resistance  21  is converted into a DC voltage through a resistance R 3  and a capacitor C 5  of the DC converting circuit  27 , and then the sensed DC voltage is applied to a non-inverting “+” terminal of the comparator  23 . When the sensed DC voltage is higher than a reference voltage (0V) of the comparator  23 , the comparator  23  amplifies a difference between the sensed voltage and the reference voltage, and outputs a “high” signal. The “high” signal outputted from the comparator  23  is transmitted to the OR gate  25 . The OR gate  25  adds the “high” signal and the ground voltage (a “low” signal) by the OR operation and outputs the “high” signal. The “high” signal outputted from the OR gate  25  is inputted to the gate terminal of the over-current breaking switch  22 , which is an FET according to an aspect of the invention. As such, the over-current breaking switch  22  is turned on and the fourth switch  3  the turned off. The fourth switch  3  is turned off by decreasing a gate voltage of the fourth switch  3  connected to a drain terminal of the over-current breaking switch  22 . Accordingly, as the fourth switch  3  is turned off, a current loop flowing between the reset switch  18  and the fourth switch  3  is broken off, and thereby, the reset switch  18  and the fourth switch  3  are protected from the over-current. 
     When the discharge sustaining electrode driving circuit is in a normal operation, a “low” signal is outputted from the comparator  23 . According to this state, the “low” signal is also outputted from the OR gate  25  and inputted into the over-current breaking switch  22 , thereby allowing an operation of the over-current breaking switch  22  to be maintained in a turned off state. 
     The over-current protected circuit  20  described above can also be applied to the X-electrode unit driving cell. 
     In the above-described embodiment, protection of the switching devices of the discharge sustaining electrode is performed by a device that senses the overcurrent. However, the sensed voltage detected by the over-current sensing resistance  21  can be supplied to a microcomputer controlling the on or off state of each switching device S 1  through S 4  (i.e., switches  5 ,  1 ,  7 ,  3 ). According to this embodiment, the microcomputer directly turns off the switching devices S 1  through S 4  (i.e., switches  5 ,  1 ,  7 ,  3 ) when the over-current is sensed. 
     According to an aspect of the invention, any or all of the resistances including resistances  15 ,  21 , R 3  are resistors. However, it is understood that other devices can be utilized to provide resistance. 
     FIG. 4 shows an AC type plasma display panel  100  using the over-current protected circuit  20  according to an embodiment of the invention. The plasma display panel  100  has a front substrate  111  and a rear substrate  112  opposed to and facing each other. Strip-shaped common electrodes  113  and strip-shaped scan electrodes  114  (X and Y electrodes  113 ,  114 ) are alternately formed on a bottom surface of the front substrate  111 . A bus electrode  115 , which reduces the line resistance, is formed on a bottom surface of each of the common and scan electrodes  113  and  114 . A first dielectric layer  116  is formed on a bottom surface of the front substrate  111  to cover the common electrodes  113 , the scan electrodes  114 , and the bus electrodes  115 . A protective layer  117 , such as a magnesium oxide (MgO), is formed on a bottom surface of the first dielectric layer  116 . 
     Strip-shaped address electrodes  118  are formed on a top surface of the rear substrate  112  to be perpendicular with the common and scan electrodes  113  and  114 . The address electrodes  118  are covered by a second dielectric layer  119 . Strip-shaped partitions  200  are formed on the second dielectric layer  119  parallel with the address electrodes  118 . Red (R), green (G) and blue (B) phosphor layers  210  are formed on the inner walls of the partitions  200 . 
     According to the present invention, where a plurality of switching devices provided in the discharge sustaining electrode driving circuit is abnormally turned on and the over-current flows, such over-current can be broken off. 
     As described above, according to the present invention, there is provided a plasma display panel device having an over-current protected circuit with which switching devices can be protected from over-current generated by an abnormal driving of the discharge sustaining electrode driving circuit. 
     Although the embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims and equivalents thereof.