Abstract:
An energy recovery apparatus including a sustaining voltage source for applying a sustaining voltage to a first electrode and a second electrode formed on an upper substrate; a equivalent capacitive load formed between the first electrode and the second electrode; and a power source capacitor disposed between the sustaining voltage source and a ground voltage source, for being charged with a voltage charged in the equivalent capacitive load and preventing a voltage drop phenomenon when a voltage of the sustaining voltage source is applied to the equivalent capacitive load.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an energy recovery apparatus, and more particularly to an apparatus and a method for energy recovery without a source capacitor. 
   2. Description of the Related Art 
   Recently, there has been developed various flat panel display devices reduced in weight and bulk that are capable of eliminating disadvantages associated with cathode ray tubes CRT. Such flat panel display devices include a liquid crystal display LCD, a field emission display FED, a plasma display panel PDP and an electro-luminescence EL panel, etc. 
   The PDP among these flat panel display devices is a display device using gas discharge and has an advantage that it is easy to be made on a large scale. A typical PDP is a three-electrode AC surface discharge PDP that has three electrodes, as shown in  FIG. 1 , and is driven by AC voltage. 
   Referring to  FIG. 1 , a discharge cell of the three-electrode AC surface-discharge PDP includes a first electrode  12 Y and a second electrode  12 Z formed on an upper substrate  10 , and an address electrode  20 X formed on a lower substrate  18 . 
   On the upper substrate  10  provided with the first electrode  12 Y and the second electrode  12 Z in parallel, an upper dielectric layer  14  and a passivation film  16  are disposed. Wall charges generated upon plasma discharge are accumulated in the upper dielectric layer  14 . The passivation film  16  prevents a damage of the upper dielectric layer  14  caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This passivation film  16  is usually made from magnesium oxide (MgO). 
   A lower dielectric layer  22  and barrier ribs  24  are formed on the lower substrate  18  provided with the address electrode  20 X. The surfaces of the lower dielectric layer  22  and the barrier ribs  24  are coated with a phosphorus  26 . The address electrode  20 X is formed in a direction crossing the first electrode  12 Y and the second electrode  12 Z. The barrier ribs  24  are formed in parallel to the address electrode  20 X to prevent an ultraviolet ray and a visible light generated by a discharge from being leaked to the adjacent discharge cells. The phosphorus  26  is excited by the ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. There is an inactive gas for a gas discharge injected into a discharge space defined between the upper and lower substrate  10  and  18  and the barrier ribs  24 . 
   Such a three-electrodes AC surface discharge PDP is divided into a plurality of sub-fields to be driven and there are lights emitted as frequent as the number of times proportional to a weight of video data in each sub-field period so as there to be a gray level display carried out. The sub-field SF 1  to SF 8  is divided again into a reset period, an address period, a sustaining period and an erasure period and is driven. 
   Herein, there are uniform wall charges formed in a discharge cell during the reset period. There is an address discharge generated in accordance with a logical value of video data during the address period. There is a discharge sustained in the discharge cell, in which the address discharge has been generated, during the sustaining period. There is a sustaining discharge, which was generated during the sustaining period, eliminated during the erasure period. 
   There is a high voltage of hundreds volt or more needed in the address discharge and the sustaining discharge of the AC surface discharge PDP, which is driven in this way. Accordingly, there is an energy recovery apparatus used for minimizing a driving power necessary for the address discharge and the sustaining discharge. The energy recovery apparatus recovers the voltage between the first electrode  12 Y and the second electrode  12 Z and makes use of the recovered voltage as the driving voltage for the next discharge. 
     FIG. 2  illustrates a circuit diagram of an energy recovery apparatus formed in a first electrode in order to recover a sustaining discharge voltage. 
   Referring to  FIG. 2 , an energy recovery apparatus according to the related art includes an inductor L connected between a panel capacitor Cp and a source capacitor Cs; a first switch S 1  and a third switch S 3  connected between the source capacitor Cs and the inductor L in parallel; a second switch S 2  and a fourth switch S 4  connected between the panel capacitor Cp and the inductor L in parallel; and a power source capacitor Cv connected between a reference voltage source Vs and a ground GND. 
   The panel capacitor Cp is equivalent to a capacitance formed between the first electrode Y and the second electrode Z. The second switch is connected to the reference voltage source Vs, and the fourth switch is connected to the ground GND. The source capacitor Cs recovers the voltage charged in the panel capacitor Cp upon the sustaining discharge to be charged with and applies the charged voltage to the panel capacitor Cp. 
   The power source capacitor Cv prevents the reference voltage source Vs from being dropped when the reference voltage source Vs is applied. In other words, the capacitor Cv prevents a swing of the reference voltage source Vs when the reference voltage source Vs is applied, thereby always applying a uniform voltage of the reference voltage source Vs. 
   The source capacitor Cs has a capacitance capable of charging a voltage of Vs/2 corresponding to a half value of the reference voltage source Vs. The inductor L forms a resonance circuit together with the panel capacitor Cp. The first to fourth switches S 1  to S 4  control the flow of current. The energy recovery apparatus formed in the second electrode Z and the energy recovery apparatus formed in the first electrode Y are symmetrically formed with respect to the panel capacitor Cp. 
   On the other hand, a fifth diode D 5  and a sixth diode D 6  disposed between the first switch S 1  and the inductor L and between the third switch S 3  and the inductor L respectively prevent electric current from flowing in a reverse direction. Also, the first to fourth switches S 1  to S 4  have internal diodes D 1  to D 4  additionally installed to be connected to each of switches S 1  to S 4  in parallel. 
     FIG. 3  illustrates a diagram representing on/off timing of the switches and an output waveform of a panel capacitor, shown in  FIG. 2 . 
   There will be an operation process described in detail assuming that there are the panel capacitor Cp charged with a voltage of 0V and the source capacitor Cs charged with a voltage of Vs/2 before a period T 1  of time. 
   During the period T 1  of time, the first switch S 1  is turned on, so that there is a current path formed linking the source capacitor Cs, the first switch S 1 , the inductor L and the panel capacitor Cp. If the current path is formed, the voltage of Vs/2 charged in the source capacitor Cs is applied to the panel capacitor Cp. At this moment, because the inductor L and the panel capacitor Cp form a serial resonance circuit, the panel capacitor Cp is charged with the voltage Vs twice as much voltage as the source capacitor Cs. 
   During a period T 2  of time, the second switch S 2  is turned on. If the second switch S 2  is turned on, the voltage of the reference voltage source Vs is applied to the first electrode Y. The voltage of the reference voltage source Vs applied to the first electrode Y prevents the voltage of the panel capacitor Cp from dropping below the reference voltage source Vs to make the sustaining discharge generated in a normal manner. On the other hand, because the voltage of the panel capacitor Cp rose to Vs during the period T 1 , the driving power that is applied from the outside for generating the sustaining discharge may be minimized. 
   During a period T 3  of time, the first switch S 1  is turned off. At this moment, the first electrode Y sustains the voltage of the reference voltage source Vs during the period T 3 . 
   During a period T 4  of time, the second switch S 2  is turned off and the third switch S 3  is turned on at the same time. When the third switch S 3  is turned on, there is a current path formed linking the panel capacitor Cp, the inductor L, the third switch S 3  and the source capacitor Cs, so that the voltage charged in the panel capacitor Cp is recovered to the source capacitor Cs. At this moment, the source capacitor Cs is charged with the voltage of Vs/2. 
   During a period T 5  of time, the third switch S 3  is turned off and the fourth switch S 4  is turned on at the same time. When the fourth switch S 4  is turned on, there is a current path formed between the panel capacitor Cp and the ground GND, so that the voltage of the panel capacitor Cp drops to 0V. 
   During a period T 6  of time, the state of the period T 5  is sustained for a specified period of time. Actually, the AC driving pulse applied to the first electrode Y and the second electrode Z is obtained as the periods T 1  to T 6  are periodically repeated. 
   However, because the source capacitor has been installed to have high capacitance in the energy recovery apparatus according to the related art, there is a big space required for it. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an energy recovery apparatus without a source capacitor. 
   In order to achieve these and other objects of the invention, an energy recovery apparatus according to an aspect of the present invention includes a sustaining voltage source for applying a sustaining voltage to a first electrode and a second electrode formed on an upper substrate; a equivalent capacitive load formed between the first electrode and the second electrode; and a power source capacitor disposed between the sustaining voltage source and a ground, for being charged with a voltage charged in the equivalent capacitive load and preventing a voltage drop phenomenon when a voltage of the sustaining voltage source is applied to the equivalent capacitive load. 
   The energy recovery apparatus further includes a first switch and a third switch disposed between the sustaining voltage source and the ground in parallel to the power source capacitor; a second switch and a fourth switch disposed between the sustaining voltage source and the ground in parallel to the first and third switches; and an inductor with its first end connected to the first and third switches and its second end connected to the second and fourth switches. 
   The second end of the inductor is connected to the equivalent capacitive load. 
   The first and second switches are connected to the sustaining voltage source and the third and fourth switches are connected to the ground. 
   The energy recovery apparatus further includes a first internal diode connected in parallel to the first switch, having its cathode connected to the sustaining voltage source and its anode connected to the inductor; a second internal diode connected in parallel to the second switch, having its cathode connected to the sustaining voltage source and its anode connected to the inductor; a third internal diode connected in parallel to the third switch, having its cathode connected to the inductor and its anode connected to the ground; and a fourth internal diode connected in parallel to the fourth switch, having its cathode connected to the inductor and its anode connected to the ground voltage source. 
   The energy recovery apparatus further includes a first diode disposed between the first switch and the power source capacitor; a second diode disposed between the third switch and the first end of the inductor; a third diode disposed between the sustaining voltage source and the second end of the inductor; and a fourth diode disposed between the ground and the second end of the inductor. 
   Herein, there is a designated current applied to the ground voltage source via the inductor by a voltage charged in the power source capacitor when the first and fourth switches are turned on, and there is a designated current applied from the ground to the equivalent capacitive load via the third internal diode when the first and fourth switches are turned off. 
   Herein, there is a designated current applied to the ground via the inductor by a voltage charged in the power source capacitor when the first and fourth switches are turned on, and there is a designated current applied from the ground to the equivalent capacitive load via the fourth diode when the first and fourth switches are turned off. 
   Herein, a voltage charged in the equivalent capacitive load and a charging gradient are determined by turn-on times of the first and fourth switches. 
   Herein, a first voltage with a first gradient is charged in the equivalent capacitive load when the first and fourth switches are turned on for a first period of time, and a voltage higher than the first voltage with a second gradient higher than the first gradient is charged in the equivalent capacitive load when the first and fourth switches are turned on for longer than the first period of time. 
   Herein, there is a designated current applied to the ground via the inductor by a voltage charged in the equivalent capacitive load when the third switch is turned on, and there is a designated current applied from the ground to the power source capacitor via the first internal diode when the third switch is turned off and the fourth switch is turned on at the same time. 
   Herein, there is a designated current applied to the ground via the inductor by a voltage charged in the equivalent capacitive load when the third switch is turned on, and there is a designated current applied from the ground to the power source capacitor via the third diode when the third switch is turned off and the fourth switch is turned on at the same time. 
   Herein, a voltage charged in the power source capacitor and a charging gradient are determined by a turn-on time of the third switch. 
   The energy recovery apparatus further includes at least one or more other inductors connected in parallel to the inductor. 
   Herein, an inductance of said other inductor connected in parallel to the inductor is set different from an inductance of the inductor. 
   Herein, the energy recovery apparatus also includes an inductor with a low inductance among the inductors provides a path for a current charged in the equivalent capacitive load, and an inductor with a high inductance among the inductors provides a path for a current discharged from the equivalent capacitive load. 
   A method for energy recovery with a equivalent capacitive load formed between a first electrode and a second electrode formed on an upper substrate, a sustaining voltage source applying a sustaining voltage to the first electrode and the second electrode, and a power source capacitor disposed between the sustaining voltage source and a ground according to another aspect of the present invention includes charging the equivalent capacitive load with a first current applied from the power source capacitor to the ground via the inductor; and charging the power source capacitor with a second current applied from the equivalent capacitive load to the ground via the inductor. 
   In the method, a third current corresponding to the first current is applied from the ground to the equivalent capacitive load via the inductor when the first current is stopped. 
   In the method, a third current corresponding to the second current is applied from the ground to the equivalent capacitive load via the inductor when the second current is stopped. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
       FIG. 1  illustrates a perspective view of a discharge cell structure of a three-electrodes AC surface discharge PDP according to the related art; 
       FIG. 2  illustrates a circuit diagram of an energy recovery apparatus according to the related art; 
       FIG. 3  is a diagram representing on/off timings of switches and an output waveform of a panel capacitor shown in  FIG. 2 ; 
       FIG. 4  illustrates a circuit diagram of an energy recovery apparatus according to an embodiment of the present invention; 
       FIG. 5  is a diagram representing on/off timings of switches and an output waveform of a panel capacitor shown in  FIG. 4 ; 
       FIGS. 6 and 7  are diagrams representing currents that flow in an inductor in accordance with on/off timings of a first and a third switching device shown in  FIG. 4 ; 
       FIG. 8  illustrates a circuit diagram of an energy recovery apparatus according to another embodiment of the present invention; 
       FIGS. 9 and 10  illustrate circuit diagrams of energy recovery apparatuses according to still another embodiment of the present invention; and 
       FIG. 11  illustrates a circuit diagram of an energy recovery apparatus according to still another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 4  illustrates a circuit diagram of an energy recovery apparatus according to an embodiment of the present invention. 
   Referring to  FIG. 4 , the energy recovery apparatus includes a power source capacitor Cv disposed between a reference voltage source Vs and a ground voltage source GND; a first switch S 1  and a third switch S 3  disposed between the reference voltage source Vs and the ground GND in parallel to the power source capacitor Cv; a second switch S 2  and a fourth switch S 4  disposed between the reference voltage source Vs and the ground GND in parallel to the power source capacitor Cv; an inductor L disposed between a first node N 1  and a second node N 2 ; and a panel capacitor Cp connected to the inductor L. Also illustrated is a controller  40  for controlling the switches. 
   The panel capacitor Cp is equivalent to a capacitance formed between the first electrode and the second electrode. Such a panel capacitor Cp has a low capacitance, e.g., about 300 nF. The first and second switches S 1  and S 2  are connected to the reference voltage source Vs, and the third and fourth switches S 3  and S 4  are connected to the ground GND. 
   The power source capacitor Cv recovers the voltage charged in the panel capacitor Cp upon a sustaining discharge, and then applies the charged voltage to the panel capacitor Cp again. Further, when the voltage of the reference voltage source Vs is applied to the panel capacitor Cp, the power capacitor Cv prevents a swing of the voltage to always make a uniform voltage applied to the panel capacitor Cp. 
   The first to fourth switches S 1  to S 4  control the flow of current. There are internal diodes D 1  to D 4  installed, which are connected in parallel to the switches S 1  to S 4  respectively. 
   Cathodes of the first and second diodes D 1  and D 2  are connected to the reference voltage source Vs, and anodes thereof are connected to the inductor L. Cathodes of the third and fourth diodes D 3  and D 4  are connected to the inductor, and anodes thereof are connected to the ground GND. When these are compared with the conventional energy recovery circuit shown in  FIG. 2 , it can be seen that the source capacitor Cs is eliminated in the energy recovery apparatus of the present invention. 
     FIG. 5  is a diagram representing on/off timings of switches and an output waveform of a panel capacitor shown in  FIG. 4 . 
   There will be an operation process described in detail assuming that there are the panel capacitor Cp charged with a voltage of 0V and the power source capacitor Cv charged with a designated voltage before a period T 1  of time. 
   During the period T 1  of time, the fourth switch S 4  is turned on. During a period T 2  of time, the first switch is turned on, so that there is a current path formed linking the first switch S 1 , the inductor L, the fourth switch S 4  and the ground GND. If the current path is formed, the voltage charged in the power source capacitor Cv is applied to the ground GND. At this moment, there flows a current proportional to a turn-on timing of the first switch S 1  in the inductor L as shown in  FIG. 5 . 
   During a period T 3  of time, the first and fourth switches S 1  and S 4  are turned off. If the first and fourth switches are turned off in this way, there is a designated current applied to the inductor L via the ground GND and the third diode D 3  by the flow of the current which has flowed during the period T 2 . The current applied to the inductor L is applied to the panel capacitor Cp via the inductor L. 
   If a designated current is applied to the panel capacitor Cp, the panel capacitor Cp is charged with a designated voltage. At this moment, the amplitude of the voltage charged in the panel capacitor Cp is determined by a turn-on time of the first and fourth switches S 1  and S 4 . In the same manner, the gradient of the voltage charged in the panel capacitor Cp, i.e., the gradient of a sustaining pulse, is determined by the turn-on time of the first and fourth switches S 1  and S 4 . 
   To described this more particularly, if the turn-on times of the first and fourth switches S 1  and S 4  are set at below a designated time, as in  FIG. 6 , a current below a designated amount flows in the inductor L. For example, it is assumed that a current of 4 mA flows in the inductor L when the first and fourth switches S 1  and S 4  are turned on. There flows a current gradually lowered from 4 mA when the first and fourth switches S 1  and S 4  are turned off. At this moment, the current gradually lowered from 4 mA is applied to the panel capacitor Cp, and the panel capacitor Cp is charged with a voltage having a low gradient by a current value applied to itself.  FIG. 7  illustrates the turn-on times being longer than in  FIG. 6 . 
   On the other hand, turn-on times of the first and fourth switches S 1  and S 4  are set at over a designated time, as in  FIG. 7 , more than a designated current flow in the inductor L. For instance, it is assumed that a current of 10 mA flows in the inductor L when the first and fourth switches S 1  and S 4  are tuned on for a designated time. Accordingly, when the first and fourth switches S 1  and S 4  are turned off, there is a current gradually lowered from 10 mA flows in the inductor L. At this moment, a current gradually lowered from 10 mA is applied to the panel capacitor Cp, the panel capacitor Cp is charged with a voltage having a high gradient by the current value applied to itself. 
   In other words, when the turn-on time of the first and fourth switches S 1  and S 4  are set long, a lot of current is applied. Accordingly, the panel capacitor Cp is charged with a voltage in a rapid time, i.e., high gradient. Further, if the turn-on time of the first and fourth switches S 1  and S 4  are set long, a lot of current is applied to the panel capacitor Cp and a high voltage is charged in it. 
   During a period T 4  of time, the second switch S 2  is turned on. If the second switch S 2  is turned on, the voltage of the reference voltage source Vs is applied to the panel capacitor Cp. The voltage of the reference voltage source Vs applied to the panel capacitor Cp prevents the voltage of the panel capacitor Cp from dropping to below the reference voltage source Vs, so that a sustaining discharge is made to be generated in a normal manner. 
   As shown in  FIG. 5 , during a period T 4  of time, the second switch is turned on such that a voltage from voltage source Vs is applied to the panel capacitor Cp. During a period T 5  of time, the second switch S 2  is turned-off, and the third switch S 3  is turned on. If the third switch S 3  is turned on, the voltage charged in the panel capacitor Cp is discharged to the ground GND via the inductor L and the third switch S 3 . At this moment, there flows a designated current in the inductor L. 
   During the period T 1  after the period T 5 , the third switch S 3  is turned off and the fourth switch S 4  is turned on at the same time. If the fourth switch S 4  is turned on, there is a designated current applied from the ground GND to the power source capacitor Cv via the first diode D 1  by the flow of a current that flowed during the period T 5 . At this moment, the power source capacitor Cv is charged with a designated voltage. 
   On the other hand, in the same way as the period T 3 , the voltage charged in the power source capacitor Cv is proportional to the turn-on time of the third switch S 3 . In other words, if the turn-on time of the third switch S 3  is set long, there is a high voltage is applied to the power source capacitor Cv. Further, if the turn-on time of the third switch S 3  is set short, there is a low voltage applied to the power source capacitor Cv. 
   On the other hand, the energy recovery apparatus of the present invention further includes a fifth diode D 5 , a sixth diode D 6 , a seventh diode D 7  and an eighth diode D 8 , as in  FIG. 8 . 
   The fifth diode D 5  is disposed between the first switch S 1  and the power capacitor Cv. The sixth diode D 6  is disposed between the inductor and the third switch S 3 . The seventh diode D 7  is disposed between the reference voltage source Vs and the inductor L. The eighth diode D 8  is disposed between the inductor L and the ground GND. 
   The fifth and sixth diodes D 5  and D 6  prevent a reverse current from flowing in the first and third switches S 1  and S 3 . The eighth diode D 8  applies a designated current from the ground GND to the inductor L via itself during the period T 3  shown in  FIG. 5 . At this moment, there flows no current in the third switch S 3  by the sixth diode D 6 . 
   The seventh diode D 7  applies a designated current from the ground GND to the power source capacitor Cv via itself during the period T 5  shown in  FIG. 5 . At this moment, there flows no current in the first switch S 1  by the fifth diode D 5 . 
     FIG. 9  illustrates a circuit diagram of an energy recovery apparatus according to another embodiment of the present invention. 
   Referring to  FIG. 9 , the energy recovery apparatus includes a first inductor L 1  providing a discharge path of a voltage charged in the power source capacitor Cv and a charging path of a current applied to the panel capacitor Cp; and a second inductor L 2  providing a discharge path of a voltage charged in the panel capacitor Cp and a charging path of a current applied to the power source capacitor Cv. 
   The fifth diode D 5  is disposed between the first inductor L 1  and a first node N 1  in order to prevent a reverse current. The sixth diode D 6  is disposed between the second inductor L 2  and a third node N 3  in order to prevent a reverse current. There are a ninth diode D 9  and a tenth diode D 10  disposed to apply currents in different directions. Herein, the inductance of the second inductor L 2  is set higher than the inductance of the first inductor L 1 . 
   The current discharged from the power source capacitor Cv is applied to the ground GND via the first switch S 1 , the fifth diode D 5 , the first inductor L 1  and the fourth switch S 4 . At this moment, the current is applied from the ground GND to the panel capacitor Cp via the third internal diode D 3 , the fifth diode D 5  and the first inductor L 1 . 
   The current discharged from the panel capacitor Cp is applied to the ground GND via the second inductor L 2 , the sixth diode D 6  and the third switch S 3 . At this moment, the current charged in the power source capacitor Cv is applied from the ground GND to the power source capacitor Cv via the fourth internal diode D 4 , the second inductor L 2 , the sixth diode D 6  and the first internal diode D 1 . 
   On the other hand, the fifth diode D 5  may be disposed between the first inductor L 1  and the second node N 2 . Further, the sixth diode D 6  may be disposed between the second inductor L 2  and the fourth node N 4 . For instance, the fifth and sixth diodes D 5  and D 6 , as in  FIG. 10 , may be disposed between the first inductor L 1  and the second node N 2  and between the second inductor L 2  and the fourth node N 4  respectively. 
     FIG. 11  illustrates a circuit diagram of an energy recovery apparatus according to still another embodiment of the present invention. 
   Referring to  FIG. 11 , the energy recovery apparatus includes a first inductor L 1  providing a discharge path of a voltage charged in the power source capacitor Cv and a charging path of a current applied to the panel capacitor Cp; and a second inductor L 2  providing a discharge path of a voltage charged in the panel capacitor Cp and a charging path of a current applied to the power source capacitor Cv. 
   There is a ninth diode D 9  disposed between the first inductor L 1  and a first node N 1  in order to prevent a reverse current. There is a tenth diode D 10  disposed between the second inductor L 2  and a fourth node N 4  in order to prevent a reverse current. The ninth and tenth diodes D 9  and D 10  are disposed to apply currents in different directions. Herein, the inductance of the second inductor L 2  is set higher than the inductance of the first inductor L 1 . 
   The current discharged from the power source capacitor Cv is applied to the ground GND via the fifth diode, the first switch S 1 , the ninth diode D 9 , the first inductor L 1  and the fourth switch S 4 . At this moment, the current is applied from the ground GND to the panel capacitor Cp via the eight diode D 8 , the ninth diode D 9  and the first inductor L 1 . 
   The current discharged from the panel capacitor Cp is applied to the ground GND via the tenth diode D 10 , the second inductor L 2 , the sixth diode D 6  and the third switch S 3 . At this moment, the current charged in the power source capacitor Cv is applied from the ground GND to the power source capacitor Cv via the fourth internal diode D 4 , the tenth diode D 10 , the second inductor L 2  and the seventh diode D 7 . 
   On the other hand, the ninth diode D 9  may be disposed between the first inductor L 1  and the second node N 2 . In the same manner, the tenth diode  10  may be disposed between the second inductor L 2  and the third node N 3 . 
   As described above, the power source capacitor is used as the source capacitor according to the energy recovery apparatus of the present invention. Further, it may be possible to control the level of the voltage charged in the power source capacitor and the panel capacitor by controlling the switching timing. Further, it may be possible to control the gradient of the voltage charged in the panel capacitor, i.e., the gradient of the sustaining pulse, by controlling the switching timing. 
   Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.