Patent Publication Number: US-7221334-B2

Title: Energy recovery circuit of plasma display panel and driving apparatus of plasma display panel including energy recovery circuit

Description:
BACKGROUND OF THE INVENTION 
   This application claims the priority of Korean Patent Application No. 2003-26392, filed on Apr. 25, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   1. Field of the Invention 
   The present invention relates to an energy recovery circuit of a plasma display panel and a plasma display panel driving apparatus including the same, and more particularly, to an energy recovery circuit of a plasma display panel, which recovers and supplies charging/discharging energies by operating controlling switches according to charging/discharging operations of a panel capacitor to reduce stress on the controlling switches using a transformer, and a plasma display panel driving apparatus including the energy recovery circuit. 
   2. Description of the Related Art 
     FIG. 1  is an inner perspective view of a structure of a plasma display panel in a conventional three-electrodes surface discharging type. 
   Referring to  FIG. 1 , address electrode lines A R1 , A G1 , . . . , A Gm , A Bm , dielectric layers  11  and  15 , Y electrode lines Y 1 , . . . , Y n , X electrode lines X 1 , . . . , X n , a phosphor layer  16 , a barrier rib  17 , and a magnesium monoxide layer  12  as a passivation layer are disposed between front and rear glass substrates  10  and  13  of a surface discharging plasma display panel  1 . 
   U.S. Pat. No. 5,541,618 discloses an address-display separated driving method which is mainly used as a driving method of the plasma display panel having above structure. 
     FIG. 2  is a block diagram of a driving apparatus for the plasma display panel shown in  FIG. 1 . 
   Referring to  FIG. 2 , the driving apparatus of the plasma display panel  1  includes an image processing unit  26 , a controlling unit  22 , an address driving unit  23 , X-driving unit  24 , and Y-driving unit  25 . The image processing unit  26  converts an external analog image signal into a digital signal to generate internal image signals such as image data of red (R), green (G), and blue (B) colors respectively having 8 bits, a clock signal, and vertical and horizontal synchronizing signals. The controlling unit  22  generates driving control signals (S A , S Y , S X ) according to the internal image signals from the image processing unit  26 . The address driving unit  23  processes the address signal S A  among the driving control signals S A , S Y , S X  from the controlling unit  22  to generate a display data signal, and applies the generated display data signal to address electrode lines. The X-driving unit  24  processes X-driving signal S X  among the driving control signals S A , S Y , S X  from the controlling unit  22 , and applies the X-driving signal to X-electrode lines. The Y-driving unit  25  processes Y-driving control signal S Y  among the driving control signals S A , S Y , S X  from the controlling unit  22 , and applies the Y-driving control signal S Y  to Y-electrode lines. 
     FIG. 3  is a timing view showing driving signals applied to the panel shown in  FIG. 1  on unit sub-field by the address-display separated driving method. 
   In  FIG. 3 , reference numerals S AR1 , . . . , A Bm  denote driving signals applied to respective address electrode lines (A R1 , A G1 , . . . , A Gm , A Bm  in  FIG. 1 ), S X1 , . . . , x n  denote driving signals applied to the X-electrode lines (X 1 , . . . , X n  in  FIG. 1 ), and S Y1 , . . . , Y n  denote driving signals applied to the Y-electrode lines (Y 1 , . . . , Y n  in  FIG. 1 ). 
   Referring to  FIG. 3 , in a reset period (PR) of the unit sub-field (SF), voltages applied to the X-electrode lines X 1 , . . . , X n , rise continuously from ground voltage to second voltage (V S ), for example, to 155 V. Here, ground voltages VG are applied to the Y-electrode lines Y 1 , . . . , Y n  and the address electrode lines A R1 , . . . , A Bm . 
   Then, voltages applied to the Y-electrode lines Y 1 , . . . ,Y n  rise continuously from the second voltage V S , for example, 155V to the highest voltage (V SET +V S ) which is higher than the second voltage V S  as much as third voltage (V SET ), for example, to 355V. Here, the ground voltages V G  are applied to the X-electrode lines X 1 , . . . , X n  and the address electrode lines A R1 , . . . , A Bm . 
   Next, in a status where the voltages applied to the X-electrode lines X 1 , . . . , X n  are maintained to be the second voltages V S , the voltages applied to the Y-electrode lines Y 1 , . . . , Y n  are descended from the second voltage V S  to the ground voltage V G  continuously. Here, the ground voltage V G  are applied to the address electrode lines A R1 , . . . , A Bm . 
   Accordingly, in a next address period (PA), the display data signals are applied to the address electrode lines and scan signals of ground voltages are sequentially applied to the Y-electrode lines Y 1 , . . . , Y n  which are biased to be fourth voltages (V SCAN ) lower than the second voltage V S , and thereby performing smooth addressing operations. The display data signals applied to respective address electrode lines A R1 , . . . , A Bm  are applied with address voltage (V A ) of straight polarity in a case where a discharge cell is selected, or applied with ground voltages (V G ). Here, the second voltages V S  are applied to the X-electrode lines X 1 , . . . , X n  for performing the addressing operation more accurately and effectively. 
   In a next sustain period (PS), display sustain pulses of second voltages V S  are alternatively applied to all Y-electrode lines Y 1 , . . . , Y n  and to the X-electrode lines X 1 , . . . , X n  to generate a discharge for maintaining the display on the discharging cells in which wall charges are formed in the corresponding address period (PA). 
   In the plasma display panel, a voltage higher than discharge starting voltage of the discharged gas should be alternately applied between the sustain electrodes (X electrode and Y electrode) in the discharged cell in driving. 
   Therefore, in order to apply a positive (+) high voltage and a ground voltage (V G ) alternately between the sustain electrodes when the plasma display panel is operating, the panel capacitor should be changed and discharged. Here, the panel capacitor consumes a lot of reactive power in the charging/discharging operations, and a size of the panel capacitor increases in proportion to that of the display panel, thus increasing the power consumption. 
   To solve the above problem, U.S. Pat. No. 4,866,349 discloses an energy is recovery apparatus for reducing power loss in the charging/discharging operations of the panel capacitor. 
     FIG. 4  is a circuit diagram of a typical energy recovery apparatus using an external capacitor. 
   Referring to  FIG. 4 , the general energy recovery circuit  30  includes an inductor (L 1 ) forming an LC resonance circuit with the panel capacitor (Cp) of the display panel. The energy recovery circuit  30  recovers the energy lost when the panel capacitor Cp is discharged through the inductor L 1  and temporarily stores the energy, and uses the stored electric current energy in next charging operation of the panel capacitor Cp. This reduces the reactive power in driving the plasma display panel. 
   The above circuit is included in the conventional energy recovery apparatus using an external capacitor. The energy recovery apparatus further includes a first energy recovery unit  30  and a second energy recovery unit  40  for maintaining the plasma display panel with the sustain voltage Vs, and for recovering the energy lost in the discharging operation of the panel capacitor Cp to provide the panel capacitor Cp with the retrieved energy in the next charging operation. The first and second energy recovery units  30  and  40  are symmetrically configured as interposing the panel capacitor Cp therebetween. 
   Also, the first and second energy recovery units  30  and  40  are alternately operated so that the voltages (Vp) on both ends of the panel capacitor Cp change respectively to the anode (+) and the cathode (−) in the charging/discharging operations of the panel capacitor Cp. 
   In  FIG. 4 , the first energy recovery unit  30  includes a controlling switch S 1  for supplying the sustain voltage V S  to the panel capacitor Cp in the sustain operation of the display panel, the inductor L 1  resonated in the charging/discharging operations of the panel capacitor Cp, one-way diodes D 15  and D 16  to prevent reversal of the resonance current, an external capacitor C 1  for storing the energy recovered when the inductor L 1  and the panel capacitor Cp are resonated, and controlling switches S 11  and S 12  connected between the panel capacitor Cp and the external capacitor C 1  for switching the energy recovery path. 
     FIG. 5  is a waveform diagram showing waveforms according to switching operations of respective controlling switches in the energy recovery apparatus shown in  FIG. 4 . 
   Referring to  FIG. 5 , waveforms of voltages on the both ends of the panel capacitor Cp and waveforms of the current flowing on the inductor L 1  according to the switching operation of the respective controlling switches in the general energy recovery apparatus are shown as I and II in  FIG. 5 . 
   First, the conventional energy recovery apparatus is to reduce the loss of electric power due to the reactive power generated when the charged panel capacitor Cp is discharged after the system power is applied and the plasma display panel is sustained. Also, the energy transfer in the charging/discharging operations of the panel capacitor Cp is made through the resonance operation between the panel capacitor Cp and the inductor L 1 . 
   Also, the energy recovery apparatus operates in four sections (T 1 ˜T 4 ) as shown in  FIG. 5 . The second energy recovery unit  40  operates in the same manner as the first energy recovery unit  30 . Following is described how the energy recovery unit operates. 
   The charged energy of the panel capacitor Cp is stored in the external capacitor C 1  through the resonance between the inductor L 1  and the panel capacitor Cp. 
   The resonance current i 1  of the inductor L 1  and the panel capacitor Cp is formed from the external capacitor C 1  included in the first energy recovery unit  30 , and voltages Vp on both ends of the panel capacitor Cp rise to the sustain voltage V S  by the resonance current i 1 . Here, the controlling switch S 11  is turned on so as to provide the current path (section T 1 ). 
   Next, the controlling switch S 1  is turned on to sustain the plasma display panel, and the sustain voltages are continually applied as the voltages Vp on both ends of the panel capacitor Cp (section T 2 ). 
   After sustaining the display panel, the inductor L 1  and the panel capacitor Cp are resonated in the discharging operation of the panel capacitor Cp so that the charged energy of the panel capacitor Cp is recovered in the outer capacitor C 1  of the first energy recovery unit  30 . Here, the controlling switch S 12  is turned on so as to provide the current path (section T 3 ). 
   Next, the controlling switch S 2  is turned on, and the voltages Vp on both ends of the panel capacitor Cp are maintained at zero electric potential (section T 4 ). 
   Here, the both ends voltages Vp of the panel capacitor Cp rises from the external capacitor C 1  that is charged with the voltage corresponding to half of the sustain voltage Vs to the sustain voltage Vs by the resonance operation of the inductor L 1  and the panel capacitor Cp. However, a voltage is actually lost as much as Δ due to a line resistance and other parasitic resistance of devices in the circuit. This lowers energy recovery efficiency and panel driving features due to the discharge before sustaining the display panel. 
   Therefore, the sustain voltage cannot rise to the desired voltage Vs or cannot be lowered to the ground voltage 0V. When the sustaining operation is performed in this status, the switches for applying and discharging the sustain voltage perform hard-switching operations, creating problems of electromagnetic interference (EMI). 
   Also, in the conventional energy recovery apparatus, the rising or descending time of the panel voltage is long, thus generating the panel discharge in the energy recovery section. Here, the dropped panel voltage causes a hard-switching operation in applying the sustain voltage at the voltage much less than the sustain voltage. This increases a surge current and stresses the switch. 
   SUMMARY OF THE INVENTION 
   The present invention provides an energy recovery circuit of a plasma display panel, which recovers and supplies charging/discharging energies by operating controlling switches according to charging/discharging operations of a panel capacitor and reduces stresses of controlling switches using a transformer, and a driving apparatus of a plasma display panel including the above energy recovery circuit. 
   According to an aspect of the present invention, there is provided an energy recovery circuit of a plasma display panel, which recovers charging/discharging energies of a panel capacitor to a power source supplying unit using a transformer according to charging/discharging operations of the panel capacitor on a plasma display panel including X-electrode lines and Y-electrode lines formed alternately side by side, discharging cells formed on areas where X and Y-electrode lines and address electrode lines cross each other, and panel capacitors formed between the electrode lines, including a second controlling switch, a first controlling switch, and a transformer. 
   The second controlling switch may be connected between the panel capacitor and the power source supplying unit and switched according to a controlling signal input from outside to control the energy recovery from the panel capacitor to the power source supplying unit. The first controlling switch may be connected between the panel capacitor and the power source supplying unit and switched according to a controlling signal input from outside to control the energy recovered in the power source supplying unit to be supplied to the panel capacitor. The transformer may be connected between the first and second controlling switches and the panel capacitor so that resonance current flows on a primary inductor by the switching operations of the first and second controlling switches, and induced current induced by the resonance current flowing on a secondary inductor flows to a direction compensating the resonance current through the first and second controlling switches. 
   According to another aspect of the present invention, there is provided a driving apparatus of a plasma display panel, which recovers charging/discharging energies of a panel capacitor to a power source supplying unit using a transformer according to charging/discharging operations of the panel capacitor for a plasma display panel including X-electrode lines and Y-electrode lines formed alternately side by side, discharging cells formed on areas where X and Y-electrode lines and address electrode lines cross each other, and panel capacitors formed between the electrode lines, including a sustain driving unit and an energy recovery circuit. 
   The sustain driving unit, of which one end is connected to a power source supplying end of the power source supplying unit, may be switched by an external controlling signal to supply sustain voltage to the panel capacitor so as to sustain the display panel and to discharge the charged power periodically. 
   The energy recovery circuit may include a second controlling switch, a first controlling switch, and a transformer. The second controlling switch may be connected between the panel capacitor and the power source supplying unit and switched according to a controlling signal input from outside to control the energy recovery from the panel capacitor to the power source supplying unit. The first controlling switch may be connected between the panel capacitor and the power source supplying unit and switched according to a controlling signal input from outside to control the energy recovered in the power source supplying unit to be supplied to the panel capacitor. The transformer may be connected between the first and second controlling switches and the panel capacitor so that resonance current flows on a primary inductor by the switching operations of the first and second controlling switches, and induced current induced by the resonance current flowing on a secondary inductor flows to a direction compensating the resonance current through the first and second controlling switches. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings. 
       FIG. 1  is an inner perspective view of a structure of a plasma display panel of a conventional three-electrode surface discharging type. 
       FIG. 2  is a block diagram of a general driving apparatus of the plasma display panel shown in  FIG. 1 . 
       FIG. 3  is a timing view showing driving signals applied to the panel of  FIG. 1  on a unit sub-field by an address-display separated driving method. 
       FIG. 4  is a schematic circuit diagram of a typical energy recovery apparatus using an external capacitor. 
       FIG. 5  is a diagram showing waveforms according to switching operations of respective controlling switches in the energy recovery apparatus in  FIG. 4 . 
       FIG. 6  is a schematic circuit diagram of an energy recovery circuit of a plasma display panel according to an embodiment of the present invention. 
       FIG. 7  is a schematic circuit diagram of a driving apparatus of the plasma display panel including the energy recovery apparatus of  FIG. 6 . 
       FIG. 8  is a view showing waveforms according to switching operations of respective controlling switches in the driving apparatus of the plasma display panel of  FIG. 7 . 
       FIGS. 9A ,  9 B,  9 C,  9 D,  9 E and  9 F are circuit diagrams showing current flowing on respective sections when operating the driving apparatus of the plasma display panel of  FIG. 8 . 
       FIG. 10  is a circuit diagram of a driving apparatus of a plasma display panel including the energy recovery circuit according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, the most preferred embodiments of the present invention will be described with reference to accompanying figures in detail. 
     FIG. 6  is a circuit diagram schematically showing an energy recovery circuit of a plasma display panel according to an embodiment of the present invention. 
   Referring to  FIG. 6 , the energy recovery circuit  50  of the plasma display panel, which recovers charging/discharging energies of a panel capacitor into a power source supplying unit using a transformer T 0  according to charging/discharging operations of the panel capacitor Cp, includes a first controlling switch Yr, a second controlling switch Yf, and a transformer T 0 . The plasma display panel includes X-electrode lines and Y-electrode lines that are alternately formed side by side, discharging cells formed on areas where X and Y-electrode lines and address electrode lines cross each other, and panel capacitors Cp formed between the electrode lines. 
   The second controlling switch Yf is switched according to an external controlling signal input to control the energy recovery from the panel capacitor Cp to the power source supplying unit, and connected between the panel capacitor Cp and a ground end of the power source supplying unit. 
   The first controlling switch Yr is switched according to an external controlling signal input to control the recovered energy in the power source supplying unit to the panel capacitor Cp, and connected between the panel capacitor Cp and a power source supplying end (A) of the power source supplying unit. 
   The transformer T 0  is connected between the first controlling switch Yr and the second controlling switch Yf and the panel capacitor Cp so that resonance currents I L1  and I L2  flow on a primary inductor L 01 , and induced currents I a  and I b  induced by the resonance currents and flowing on secondary inductors L 12  and L 22  can flow toward a direction compensating the resonance currents. 
   It is desirable that a first transformer and a second transformer are disposed as the transformer T 0 . The first transformer is connected between the first controlling switch Yr and the panel capacitor Cp to reduce the current flowing on the first controlling switch Yr. The second transformer is connected between the second controlling switch Yf and the panel capacitor Cp to reduce the current I yr  and I yf  flowing on the second controlling switch Yf. 
   The resonance current I L1  flows on the primary inductor L 01  according to the switching of the first controlling switch Yr to supply the energy recovered in the power source supplying unit into the panel capacitor Cp, and the induced current I a  induced by the resonance current I L1  flows on the secondary inductor L 12 . Here, the induced current I a  flows toward the direction compensating the resonance current I L1  through the first controlling switch Yr, and a differential current (I yr ) between the resonance current I L1  and of the induced current I a  flows on the first controlling switch Yr. Therefore, the induced current I a  is formed to flow toward the opposite direction of the resonance current I L1  on the first controlling switch Yr using the transformer, thus reducing current stress due to the current I yr  flowing on the first controlling switch Yr. 
   The resonance current I L2  flows on the primary inductor L 01  due to the switching operation of the second controlling switch Yf to recover the energy of the panel capacitor Cp to the power source supplying unit, and the induced current I b  which is induced by the resonance current I L2  flows on the secondary inductor L 22 . Here, the induced current I b  flows toward a direction compensating the resonance current I L2  through the second controlling switch Yf, thus the differential current I yf  between the resonance current I L2  and the induced current I b  flows on the second controlling switch Yf. Therefore, the current stress due to the current I yf  flowing on the second controlling switch Yf can be reduced by making the induced current I b  flow to the opposite direction of the resonance current I L2  on the second controlling switch Yf using the transformer. 
   Here, the primary inductor of the first transformer and the primary inductor of the second transformer are used commonly as the primary inductor L 0 . The common primary inductor L 0 , the secondary inductor L 12  of the first transformer, and the secondary inductor L 22  of the second transformer can form one transformer T 0 . Therefore, one transformer including three inductors can be used instead of using two transformers including two inductors, thus reducing the number of required devices and simplifying the circuit. 
   It is desirable that a resonance inductor L 0  is connected between the panel capacitor Cp and the transformer T 0  to form paths of recovering and supplying the charging/discharging energies of the panel capacitor Cp. That is, an additional resonance inductor L 0  is connected between the primary inductor L 01  of the transformer T 0  and the panel capacitor Cp, and the resonance inductor L 0  is disposed as separated from the transformer to store the current energy recovered from the panel capacitor and the current energy supplied to the panel capacitor primarily. 
   One end of the first controlling switch Yr is connected to a power source supplying end A of the power source supplying unit, and the other end of the first controlling switch Yr is connected to one end of the primary inductor L 01  of the transformer T 0  through the diode Dyr. The other end of the primary inductor L 01  of the transformer T 0  is connected to one end of the resonance inductor L 0 , and the other end of the resonance inductor L 0  is connected to the panel capacitor Cp. 
   Therefore, when the first controlling switch Yr is turned on, the resonance current I L1  flows on the current path formed by the power source supplying end A, the first controlling switch Yr, a diode Dyr, the primary inductor L 01  of the transformer T 0 , the resonance inductor L 0 , and the panel capacitor Cp to supply the energy recovered in the power source supplying unit to the panel capacitor Cp. Here, the diode Dyr is for restraining the current from flowing reverse direction of the resonance current I L1 . 
   One end of the secondary inductor L 12  of the transformer T 0  is connected to the other end of the first controlling switch Yr, and the other end of the secondary inductor L 12  is grounded to a reference potential through a diode D 1 . Therefore, the induced current I a  flowing on the secondary inductor L 12  by the inducement of the resonance current I L1  flowing on the primary inductor L 01  of the transformer T 0  can be flowed on a current path formed by the ground end, the diode D 1 , the secondary inductor L 12 , the first controlling switch Yr, and the power source supplying end A. 
   Here, the direction of the induced current I a  flowing on the first controlling switch Yr is opposite to the resonance current I L1 , and first switch current I yr  flowing on the first controlling switch Yr is the differential current between the resonance current I L1  and the induced current I a . Therefore, the current stress applied to the first controlling switch Yr is reduced. 
   One end of the second controlling switch Yf is connected to the ground end of the power source supplying unit, and the other end of the second controlling switch Yf is connected to one end of the primary inductor L 01  of the transformer through the diode Dyf. The other end of the primary inductor L 01  of the transformer T 0  is connected to one end of the resonance inductor L 0 , and the other end of the resonance inductor L 0  is connected to the panel capacitor Cp. 
   Therefore, when the second controlling switch Yf is turned on (ON), the resonance current I L2  flows on a current path formed by the panel capacitor Cp, the resonance inductor L 0 , the primary inductor L 01  of the transformer T 0 , the diode Dyf, the second controlling switch Yf, and the ground end to recover the energy of the panel capacitor Cp into the power source supplying unit. Here, the diode Dyf is for restraining the current from flowing reverse to the direction of the resonance current I L2 . 
   One end of the secondary inductor L 22  of the transformer T 0  is connected to the other end of the second controlling switch Yf, and the other end of the secondary inductor L 22  is connected to the power source supplying end through a diode D 2 . Therefore, the induced current I b  flowing on the secondary inductor L 22  by the inducement of the resonance current I L2  flowing on the primary inductor L 0  of the transformer T 0  can flow on a current path formed by the ground end, the second controlling switch Yf, the secondary inductor L 22 , the diode D 2 , and the power source supplying end A. 
   Here, the direction of the induced current I b  flowing on the second controlling switch Yf is opposite of the resonance current I L2 , and thus second switch current I yf  flowing on the second controlling switch Yf is the differential current between the resonance current I L2  and the induced current I b . Therefore, the current stress to the second controlling switch Yf can be reduced. 
     FIG. 7  is a circuit diagram of a driving apparatus of the plasma display panel including the energy recovery circuit of  FIG. 6 . 
   Referring to  FIG. 7 , the driving apparatus  5  of the plasma display panel includes a sustain driving unit  70  and energy recovery circuits  50  and  60 . The driving apparatus  5  according to the present embodiment includes the energy recovery circuit  50  of  FIG. 6 . The same reference numerals are used for the same components and detailed descriptions thereof will be omitted. 
   The sustain driving unit  70  having one end connected to the first power source supplying end A is switched according to an external controlling signal to supply sustain voltage to the panel capacitor Cp so as to sustain the display panel, and discharges the charged electric power periodically. 
   The sustain driving unit  70  includes a first switch Ys and a second switch Yg connected to each other and commonly connected to Y-electrode lines, and a third switch Xs and a fourth switch Xg connected to each other and commonly connected to the X-electrode lines. 
   The energy recovery circuits  50  and  60  are a first energy recovery circuit  50  and a second energy recovery circuit  60  which are connected to both ends of the panel capacitor symmetrically. In the present embodiment, these are connected to the sustain driving unit, the is first energy recovery circuit  50  is connected to the Y-electrode driving unit, and the second energy recovery circuit  60  is connected to the X-electrode driving unit. Hereinafter, the energy recovery circuit will be described based on the first energy recovery circuit driving the Y-electrode lines, since the second energy recovery circuit  60  functions same as the first energy recovery circuit  50 . 
     FIG. 8  is a view of waveforms according to switching operations of the respective controlling switches in the driving apparatus of the plasma display panel shown in  FIG. 7 .  FIGS. 9A ,  9 B,  9 C,  9 D,  9 E and  9 F are circuit diagrams of current flowing on respective steps when operating the driving apparatus of the plasma display panel. 
   Referring to  FIGS. 9A ,  9 B,  9 C,  9 D,  9 E and  9 F, a method for recovering the energy in the driving apparatus  5  of the plasma display panel includes step  1  through step  6  (M 1 , . . . ,M 6 ). Also, switching signals are applied to respective first switch Ys, the second switch Yg, the first controlling switch Yr, and the second controlling switch Yf in respective steps. Each of the figures show the step from M 1  through M 6  respectively. 
   In step  1 (M 1 ), the first controlling switch Yr is turned on. Accordingly, when the first controlling switch Yr is continued, Vs is applied to the primary inductor L 01  of the transformer T 0  from the power source supplying end A. In addition, the resonance current I L1  flows on the current path formed by the power source supplying end A, the first controlling switch Yr, the diode Dyr, the primary inductor L 01  of the transformer T 0 , the resonance inductor L 0 , and the panel capacitor Cp to supply the energy recovered in the power source supplying unit to the panel capacitor Cp. Here, the panel voltage Vy rises from a reference potential (GND) to the potential Vs of the power source supplying unit ( FIG. 9A ). 
   Accordingly, voltage of n1*Vs is induced into the secondary inductor L 12  of the transformer T 0 , and the induced current I a  flowing on the secondary inductor L 12  flows on the current path formed by the ground end, the diode D 1 , the secondary inductor L 12 , the first controlling switch Yr, and the power source supplying end A. Here, since the differential current between the resonance current I L1  and the induced current I a  flows on the first controlling switch Yr, the current stress applied on the first controlling switch Yr can be reduced as much as the induced current I a . 
   In step  2  (M 2 ), the first switch Ys is turned on in a state that the first controlling switch Yr is maintained to be the turn-on status (ON). Accordingly, the current path is formed from the power source supplying end A to the panel capacitor Cp as passing through the first switch Ys, and the panel voltage Vy rises to the sustain voltage Vs ( FIG. 9B ). 
   Here, the resonance current I L1  flowing on the resonance inductor L 0  flows on the current path formed by the power source supplying end A, the first controlling switch Yr, the diode Dyr, the primary inductor L 01  of the transformer T 0 , the resonance inductor L 0 , and the first switch Ys. Therefore, a zero voltage switching condition is made on the first switch Ys, the current flowing on the first switch Ys reduces linearly with a slope of (n1*Vs−Vs)/L. 
   In step  3  (M 3 ), the first controlling switch Yr is turned off (OFF), and the first switch Ys maintains the turned-on (ON) status. Therefore, the transformer T 0  is totally reset, and the panel voltage Vy is maintained to be Vs ( FIG. 9C ). 
   In step  4  (M 4 ), the first switch Ys is turned off (OFF), the second controlling switch Yf is turned on (ON). Accordingly, when the second controlling switch Yf continues to be turned on, Vs voltage is applied to the primary inductor L 01  of the transformer T 0 , and the resonance current I L2  flows on the current path formed by the panel capacitor Cp, the resonance inductor L 0 , the primary inductor L 0  of the transformer T 0 , the diode Dyf, the second controlling switch Yf, and the ground end to recover the charging/discharging energies of the panel capacitor Cp into the power source supplying unit. Here, the panel voltage Vy is descended from Vs to the reference potential (GND) ( FIG. 9D ). 
   Accordingly, a voltage of n2*Vs is induced into the secondary inductor L 22  of the transformer T 0 , and the induced current I b  flowing on the secondary inductor L 22  flows on the current path formed by the ground end, the second controlling switch Yf, the secondary inductor L 22 , the diode D 2 , and the power source supplying end A. Here, since the differential current between the resonance current I L2  and the induced current I b  flows on the second controlling switch Yf, the current stress to the second controlling switch Yf is reduced as much as the induced current I b . 
   In step  5  (M 5 ), the second controlling switch Yf is maintained to be the turned-on (ON) status, and the second switch Yg is turned on. Accordingly, the current path is formed from the ground end to the panel capacitor Cp as passing through the second switch Yg, and the panel voltage Vy is descended to the reference potential (GND) ( FIG. 9E ). 
   Here, the resonance current I L2  flowing on the resonance inductor L 0  flows on the current path formed by the ground end, the resonance inductor L 0 , the primary inductor L 01  of the transformer T 0 , the diode Dyf, the second controlling switch Yf, and the ground end. Therefore, the zero voltage switching condition is made on the second switch Yg, the size of the current flowing on the second switch Yg reduces linearly with a slope of n2*Vs/L. 
   In step  6 (M 6 ), the second controlling switch Yf is turned off, and the second switch Yg maintains the turned-on (ON) status. Therefore, the transformer T 0  is totally reset, and the panel voltage Vy is maintained to the reference potential (GND) ( FIG. 9F ). 
   According to the present invention, in recovering and supplying the charging/discharging energies by operating the controlling switches depending on the charging/discharging operations of the panel capacitor, the charging/discharging currents for recovering and supplying the charging/discharging energies to the controlling switches are flowed by the operations of the controlling switches, and the induced current is flowed on the controlling switches to opposite directions of the charging/discharging currents using the transformer, thus reducing the current stress applied to the controlling switch. 
   Also, the current stress to the controlling switch for recovering and supplying the charging/discharging energies is reduced using the induced current of the transformer, and therefore, the number of used controlling switches can be reduced and the cost for the energy recovery circuit can be reduced. 
     FIG. 10  is a circuit diagram of a driving apparatus for the plasma display panel including the energy recovery circuit according to another embodiment of the present invention. 
   The driving apparatus  6  of the plasma display panel includes a sustain driving unit  70 , a first energy recovery circuit  80 , and a second energy recovery circuit  90 . The first energy recovery circuit  80  is connected to the Y-driving unit, and the second energy recovery circuit is connected to the X-driving unit. Also, the plasma display panel driving apparatus  6  is operated in the way shown in  FIGS. 8 , and  9 A,  9 B,  9 C,  9 D,  9 E and  9 F. 
   Referring to  FIG. 10 , it is desirable that the transformer includes a first transformer T 1  and a second transformer T 2 . The first transformer T 1  is connected between the first controlling switch Yr and the panel capacitor Cp to reduce the current I yr  flowing on the first controlling switch Yr. The second transformer T 2  is connected between the second controlling switch Yf and the panel capacitor Cp to reduce the current I yf  flowing on the second controlling switch Yf. 
   It is desirable that the resonance inductor includes a first resonance inductor L 1  and a second resonance inductor L 2 . The first resonance inductor L 1  is connected between the panel capacitor Cp and the first transformer T 1  to form a supplying path of the charging/discharging energies. The second resonance inductor L 2  is connected between the panel capacitor Cp and the second transformer T 2  to form a recovery path of the charging/discharging energies. 
   One end of the first controlling switch Yr is connected to the power source supplying end A of the power source supplying unit, and the other end of the first controlling switch Yr is connected to one end of the primary inductor L 11  of the first transformer T 1 . The other end of the primary inductor L  11  of the first transformer T 1  is connected to one end of the first resonance inductor L  1 , and the other end of the first resonance inductor L 1  is connected to the panel capacitor Cp. One end of the secondary inductor L 12  of the first transformer T 1  is connected to the other end of the first controlling switch Yr, and the other end of the secondary inductor L 12  is grounded to the reference potential through the diode D 1 . 
   One end of the second controlling switch Yf is connected to the ground end of the power source supplying unit, and the other end of the second controlling switch Yf is connected to one end of the primary inductor L 21  of the second transformer T 2 . The other end of the primary inductor L 21  of the second transformer T 2  is connected to one end of the second resonance inductor L 2 , and the other end of the second resonance inductor L 2  is connected to the panel capacitor Cp. One end of the secondary inductor L 22  of the second transformer T 2  is connected to the other end of the second controlling switch Yf, and the other end of the secondary inductor L 22  is connected to the power source supplying end through the diode D 2 . 
   According to the energy recovery circuit of the plasma display panel and the driving apparatus of the plasma display panel including the energy recovery circuit of the present invention, in recovering and supplying the charging/discharging energies by operating the controlling switches based on the charging/discharging operations of the panel capacitor, the charging/discharging currents for recovering and supplying the charging/discharging energies to the controlling switches flow by the operations of the controlling switches, and the induced current also flows on the controlling switches to opposite directions of the charging/discharging currents using the transformer. This reduces the current stress applied to the controlling switch. 
   Also, the current stress applied to the controlling switch for recovering and supplying the charging/discharging energies is reduced using the induced current of the transformer, and therefore, the number of used controlling switches can be reduced and the cost for the energy recovery circuit can be reduced. 
   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.