Patent Publication Number: US-7915832-B2

Title: Plasma display panel drive circuit and plasma display apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a plasma display panel drive circuit, as well as plasma display apparatus, used for wall-mounted TV sets and large-size monitors. 
     BACKGROUND ART 
     An AC surface discharge type plasma display panel (hereinafter called “PDP”) which is typical as the AC type is constituted by arranging a front plate containing a glass substrate formed by disposing a scan electrode and a sustain electrode which carry out surface discharge and a back plate containing a glass substrate formed by disposing data electrodes oppositely in parallel so that both electrodes set up a matrix and a discharge space is formed in a gap, and by sealing the perimeter portion with sealing materials such as glass frit, etc. Between both substrates of the front plate and the back plate, discharge cells divided by bulkheads are provided, and in a cell space between these bulkheads, a phosphor layer is formed. In PDP of such configuration, ultraviolet rays are generated by gas discharge, and with this ultraviolet ray, phosphors of each color of red (R), green (G) and blue (B) are excited to emit light, thereby achieving color display. 
     In this kind of plasma display apparatus, various electric power reduction techniques are proposed to reduce the electric power consumption. 
     As one of the techniques to reduce electric power consumption, there disclosed is a so-called power recovery circuit, in consideration to the fact that PDP is a capacitive load. By the power recovery circuit, the inductor and PDP capacitive load are LC-resonated by a resonance circuit in which an inductor is included as a component element, the electric power accumulated in the PDP capacitive load is recovered to a capacitor for electric power recovery, and the recovered electric power is reused for driving PDP (see, for example, patent document 1). 
     In this technique, for example, the electric power recovered from PDP is reused for applying sustain pulse voltage to the scan electrode and the sustain electrode in a sustain period to reduce the electric power consumed during the sustain period, and thereby reduction of electric power consumption can be achieved. 
     That is, in the sustain pulse generation circuit, a resonance circuit equipped with an inductor, that is, an electric recovery circuit is installed. By this, electric power accumulated in the PDP capacitive load (capacitive load generated in the scan electrode) is recovered, the recovered electric power is reused as driving electric power of the scan electrode, and electric power consumption is reduced. In addition, in the sustain pulse generation circuit, a power recovery circuit is installed. By this, electric power accumulated in PDP capacitive load (capacitive load generated in the sustain electrode) is recovered, and the recovered electric power is reused as driving power of the sustain electrode and electric power consumption is reduced. 
       FIG. 25  is a circuit diagram of a scan electrode drive circuit and sustain electrode drive circuit equipped with such a power recovery circuit. In the figure, a scan electrode drive circuit  5  includes a sustain pulse generation circuit  51 , a reset waveform generation circuit  52 , and a scan pulse generation circuit  53 . 
     The sustain pulse generation circuit  51  includes a power recovery circuit which has a coil L 1 , a recovery capacitor C 1 , switching elements S 1 , S 2 , and reverse blocking diodes D 1 , D 2 , and a voltage clamp circuit which has switching elements S 5 , S 6  and a constant voltage power supply V 1  of a voltage Vsus. The power recovery circuit causes LC-resonance between the capacitive load of PDP  10  and the coil L 1  by using the coil L 1  as an inductance element, and recovers and supplies electric power. During recovery of electric power, electric power accumulated in capacitive load generated in the scan electrode is transferred to the recovery capacitor C 1  via the current reverse blocking diode D 2  and switching element S 2 . During supply of electric power, electric power accumulated in recovery capacitor C 1  is transferred to PDP  10  via the switching element S 1  and reverse blocking diode D 1 . In this way, the scan electrode of PDP is driven during the sustain period. Consequently, because in the power recovery circuit, in the sustain period, the scan electrode is driven by LC resonance without supplying electric power from the power supply, theoretically, electric power consumption becomes zero. 
     In  FIG. 25 , in order to electrically separate the sustain pulse generation circuit  51  from the reset waveform generation circuit  52 , switching elements S 9  and S 10  are inserted in a main discharge pah X between the sustain pulse generation circuit  51  and the reset waveform generation circuit  52  in series and in such a manner that body diodes of each of them are directed in opposite directions. Hereinafter this kind of connection with diodes directed in opposite directions is called “back-to-back connection.” By achieving this kind of configuration, simultaneously turning off switching elements S 9  and S 10  can shut off both currents including current that flows from the sustain pulse generation circuit  51  to the reset waveform generation circuit  52  and current that flows from the reset waveform generation circuit  52  to the sustain pulse generation circuit  51 . Thus, it becomes possible to electrically separate the sustain pulse generation circuit  51  from the reset waveform generation circuit  52 . 
     This is intended to prevent influence of the constant-voltage power supply V 1  of the sustain pulse generation circuit  51  with lower potential from being exerted when electric power is supplied from the constant-voltage power supply V 2  of the reset waveform generation circuit  52 , and to prevent influence of potential higher than that, that is, grounding potential (hereinafter simply written “GND”) of a clamp section of the sustain pulse generation circuit  51  when electric power is supplied from constant-voltage power supply V 3  of negative potential in the reset waveform generation circuit  52 . 
     In addition, since large current as large as several hundreds of ampere may flow instantaneously when PDP  10  is driven, in a drive circuit of PDP  10 , a large number of MOSFETs are installed in parallel to form switching elements to proof such large current. In switching elements S 9  and S 10  inserted in series between the sustain pulse generation circuit  51  and the reset waveform generation circuit  52  in order to electrically separate the sustain pulse generation circuit  51  from the main discharge path, a large number of MOSFETs are installed to form switching elements in the same manner. 
     Impedance generated on the main discharge path by the switching elements S 9  and S 10  consumes ineffective electric power which does not contribute to light emission by the current that flows when the sustain pulse generation circuit  51  drives a scan electrode and generates unrequired joule heat associated with the electric power consumption. In particular, in a power recovery circuit, electric power consumption is cut down by recovering electric power accumulated in capacitive load of PDP  10  and reusing it, and thus in the event electric power is ineffectively consumed by such impedance, the electric power recovery ratio is degraded and electric power consumption reduction effect is lowered. 
     In order to solve this problem, a technique to install switching elements in a voltage clamp circuit of the sustain pulse generation circuit  51  in place of switching elements S 9  and S 10  is proposed (see, for example, patent document 2). 
       FIG. 26  is a circuit diagram of a scan electrode drive circuit  521  with switching elements S 101  and S 102  installed in a voltage clamp circuit of sustain pulse generation circuit  51  and a sustain electrode drive circuit  6 . 
     In  FIG. 26 , in place of switching elements S 9  and S 10  in  FIG. 25 , switching elements S 101  and S 102  are installed to a voltage clamp circuit of the sustain pulse generation circuit  5121 . And switching element S 101  is disposed to achieve back-to-back connection with the switching element S 5  and the switching element  102  is disposed to achieve back-to-back connection with the switching element S 6 . 
     Under this configuration, turning off switching element S 5  and switching element S 101  simultaneously can electrically separate the constant-voltage power supply V 1  from the main discharge path, and turning off switching element S 6  and switching element S 102  simultaneously can electrically separate GND of the voltage clamp circuit from the main discharge path. 
     Patent document 1: JP 07-109542, A 
     Patent document 2: JP 2005-70787, A 
     DISCLOSURE OF INVENTION 
     However, in the configuration shown in  FIG. 26 , the point is not changed in that a large number of MOSFETs are used to configure switching elements S 101  and S 102  to proof large current of several hundreds of ampere which instantaneously flows when PDP  10  is driven, and consequently, the problem of increasing the number of elements which compose the PDP drive circuit and increasing the circuit installation area is not solved. 
     In general, there are diodes which have larger maximum rated values as compared to switching elements such as MOSFETs, and By using such diodes with large rated values, circuits which can proof large current with smaller number of elements can be configured as compared to the case in which MOSFET is used. Therefore, in order to reduce an installation area of PDP drive circuit, it is possible to think of a configuration in which switching elements S 101  and S 102  are replaced with such diodes (referred to as “replacing diode”) with large rated values. By adopting such configuration, as compared to the case of  FIG. 26 , the installation area of drive circuit can be reduced. 
     However, under such configuration, for example, when the potential of the main discharge path becomes Vset by the electric power supply from the constant-voltage power supply V 2 , the potential on the cathode side of the replacing diode becomes Vset which is higher than Vsus while the potential on the anode side of the replacing diode is Vsus by the constant-voltage power supply V 1 . Thus no current flows from anode side to the cathode side of the replacing diode. If such thing occurs, it is unable to supply electric power from the constant-voltage power supply V 1  to the main discharge path and it is unable to generate normal drive waveforms. In order to supply electric power from the constant-voltage power supply V 1  to the main discharge path, potential of the main discharge path must be lowered from Vset to Vsus or lower so that current can flow from the anode side to the cathode side of the replacing diode. However, in the event that switch S 6  and switch S 22  are turned off, the path to transfer electric charge accumulated in the main discharge path is shut off, the potential of the main discharge path is kept at Vset. 
     As described above, in conventional technologies, by having a configuration with switching elements installed in a voltage clamp circuit of a sustain pulse generation circuit, it is possible to reduce impedance when a scan electrode is driven from a power recovery circuit of a sustain pulse generation circuit and to reduce electric power consumption by increasing the electric power recovery ratio. However switching elements must be configured by use of a large number of MOSFETs, etc. to proof large current of hundreds of ampere which flow instantaneously when PDP  10  is driven. This causes problems in that the number of elements that configures the PDP drive circuit increases and the installation area increases. 
     In addition, even if the number of elements that configure the PDP drive circuit is reduced by replacing switching elements consisting of MOSFETs, etc. with diodes with large maximum rated value in order to reduce the installation area of the PDP drive circuit, there still remains a problem in that switching control to normally generate drive waveform is extremely difficult or strain to the drive waveform is generated. 
     The present invention has been made in view of these problems, and it is an object of the present invention to provide a PDP drive circuit and a plasma display apparatus, which has a power recovery circuit, reduces impedance when a scan electrode is driven from the power recovery circuit, and improves the electric power recovery ratio. Particularly the PDP drive circuit and plasma display apparatus can reduce the number of elements which make up a drive circuit to reduce the installation area and which can generate drive waveforms with little strain. 
     The present invention provides the following drive circuits for driving a plasma display panel (PDP) with a plurality of scan electrodes and sustain electrodes to solve the above problems. 
     In the first aspect of the present invention, a plasma display panel (PDP) drive circuit includes: a pulse voltage generation circuit that includes main switching elements disposed on the high voltage side and main switching elements disposed on the low voltage side, and is operable to generate a pulse voltage by operating the main switching elements in accordance with an output voltage from a first power supply, and apply the pulse voltage to the scan electrodes and/or sustain electrodes of the plasma display panel; and a reset voltage generation circuit operable to generate a reset voltage in accordance with an output voltage from a second power supply that outputs a voltage higher than the output voltage of the first power supply and apply the reset voltage to the plasma display panel. The pulse voltage generator circuit includes a first diode operable to prevent the voltage outputted by the reset voltage generation circuit from being applied in reverse direction to the first power supply and a first switching element connected to the first diode in parallel. 
     In the second aspect of the present invention, a PDP drive circuit includes: a pulse voltage generation circuit that includes main switching elements disposed on the high voltage side and main switching elements disposed on the low voltage side, and is operable to generate a pulse voltage by operating the main switching elements in accordance with an output voltage from a first power supply, and apply the pulse voltage to the scan electrodes and/or sustain electrodes of the plasma display panel; a second reset voltage generation circuit operable to generate a second reset voltage in accordance with an output voltage from a third power supply that outputs a voltage lower than the output voltage of the first power supply and apply the second reset voltage to the plasma display panel; a second diode operable to prevent the voltage output by the second reset voltage generation circuit from being applied in reverse direction to the first power supply; and a second switching element connected to the second diode in parallel. 
     In the third embodiment of the present invention, a PDP drive circuit includes: a pulse voltage generation circuit that includes main switching elements disposed on the high voltage side and main switching elements disposed on the low voltage side, and is operable to generate a pulse voltage by operating the main switching elements in accordance with an output voltage from a first power supply, and apply the pulse voltage to the scan electrodes and/or sustain electrodes of the plasma display panel; a reset voltage generation circuit operable to generate a reset voltage in accordance with an output voltage from a second power supply that outputs a voltage higher than the output voltage of the first power supply and apply the reset voltage to the plasma display panel; a first diode operable to prevent the voltage outputted by the reset voltage generation circuit from being applied in reverse direction to the first power supply; a first power recovery circuit operable to resonate with a capacitive load of the plasma display panel and recover electric power accumulated in the plasma display panel; a second power recovery circuit operable to supply the recovered electric power to the plasma display panel; a third diode (D 110 ) that allows a current to flow into the first power supply while shutting off a current flowing from the first power supply to the scan electrode; and a switching element that is connected to the third diode in series and is operable to control flowing and shutoff of a current to the first power supply. 
     In the fourth aspect of the present invention, a PDP drive circuit includes: a pulse voltage generation circuit that contains main switching elements disposed on the high voltage side and main switching elements disposed on the low voltage side, and is operable to generate a pulse voltage by operating the main switching elements in accordance with an output voltage from a first power supply, and apply the pulse voltage to the scan electrodes and/or sustain electrodes of the plasma display panel; a second reset voltage generation circuit operable to generate a second reset voltage in accordance with an output voltage from a third power supply that outputs a voltage lower than the output voltage of the first power supply, and apply to the plasma display panel; a second diode operable to prevent the voltage outputted by the second reset voltage generation circuit from being applied in reverse direction to the first power supply; a first power recovery circuit operable to resonate with a capacitive load of the plasma display panel and recover electric power accumulated in the plasma display panel; a second power recovery operable to supply the recovered electric power to the plasma display panel; a fourth diode operable to shut off a current flowing from the first power supply to a ground; and a fourth switching element connected to the fourth diode in series, and operable to control flowing/shutoff of a current from the ground via the fourth diode. 
     In the fifth aspect of the present invention, a PDP drive circuit includes: a pulse voltage generation circuit that contains a high-side main switching element (S 5 ) disposed on the high-voltage side and a low-side main switching element (S 6 ) disposed on the low-voltage side, generates a pulse voltage by operating the main switching elements in accordance with an output voltage from a first power supply (V 1 ), and applies the pulse voltage to the scan electrodes and/or sustain electrodes on the plasma display panel; 
     a first reset voltage generation circuit (V 2 , S 21 ) that generates a first reset voltage in accordance with an output voltage (Vset) from a second power supply (V 2 ) which outputs the voltage higher than the output voltage of the first power supply, and applies the first reset voltage to the plasma display panel; 
     a second reset voltage generation circuit (V 3 , S 22 ) operable to generate a second reset voltage in accordance with an output voltage (Vad) from a third power supply (V 3 ) which outputs the voltage lower than the output voltage of the first power supply, and apply the second reset voltage to the plasma display panel; 
     a diode (D 11 ) that is connected on the lower voltage side of the high-side main switching element (S 5 ) and is operable to prevent a voltage outputted by the reset voltage generation circuit from being applied backward to the first power supply; 
     a switching element (S 11 ) connected to the diode in parallel; 
     a switching element (S 9 ) inserted in a main discharge path, and operable to prevent a voltage outputted by the second reset voltage generation circuit from being applied backward to a reference potential of the first power supply; 
     a first power recovery circuit (C 1 , S 2 , D 2 , L 1 B) operable to recover electric power accumulated in a capacitive load of the plasma display panel; 
     a second power recovery circuit (C 1 , S 1 , D 1 , L 1 A) operable to supply the recovered electric power to the plasma display panel; and 
     a scan IC (IC 31 ) that is a circuit operable to select a scanning electrode for applying a voltage for address discharge, and has input terminals on the high-voltage side and low-voltage side. 
     The second power recovery circuit is connected to an node connecting the high-side main switching element and the diode. The first power recovery circuit is connected to a terminal of the diode which is not connected to the high-side main switching element. The first reset voltage generation circuit is connected to the high voltage side of the scan IC, and the second reset voltage generation circuit is connected to the low voltage side of the scan IC. 
     In the sixth aspect of the present invention, a plasma display apparatus is provided. The plasma display apparatus contains a plasma display panel that has a plurality of scan electrodes and sustain electrodes, and the PDP drive circuit described above which drives the plasma display panel. 
     According to the present invention, it is possible to provide a PDP drive circuit and plasma display apparatus which have a power recovery circuit utilizing a resonance circuit, and have electric power recovery ratio improved by reducing impedance when scan electrodes are driven from the electric recovery circuit. They can reduce the installation area by reducing the number of elements which compose the drive circuit and at the same time can generate drive waveforms with little strain. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an illustration of a PDP drive circuit configuration in embodiment 1 of the present invention; 
         FIG. 2  is a perspective view of the PDP structure; 
         FIG. 3  is an illustration of PDP electrode arrangement; 
         FIG. 4  is an illustration of drive voltage waveforms applied to electrodes of the PDP; 
         FIG. 5  is an illustration that indicates another example of the configuration of the PDP drive circuit; 
         FIG. 6  is an illustration that indicates still another example of the configuration of the PDP drive circuit; 
         FIG. 7  is an illustration that indicates still another example of the configuration of the PDP drive circuit; 
         FIG. 8  is an illustration that indicates still another example of the configuration of the PDP drive circuit; 
         FIG. 9  is an illustration that indicates still another example of the configuration of the PDP drive circuit; 
         FIG. 10  is an illustration that indicates still another example of the configuration of the PDP drive circuit; 
         FIGS. 11A and 11B  are illustrations that indicate other configuration examples of a power recovery circuit; 
         FIG. 12  is a block diagram that indicates electrical configuration of a plasma display apparatus with the PDP; 
         FIG. 13  is an illustration which indicates a PDP drive circuit configuration in embodiment 2 of the present invention; 
         FIG. 14  is an illustration that indicates another example of the PDP drive circuit configuration: 
         FIG. 15  is an illustration that indicates still another example of the PDP drive circuit configuration: 
         FIG. 16  is an illustration that indicates still another example of the PDP drive circuit configuration: 
         FIG. 17  is an illustration that indicates still another example of the PDP drive circuit configuration: 
         FIG. 18  is an illustration that indicates still another example of the PDP drive circuit configuration: 
         FIG. 19  is an illustration that indicates still another example of the PDP drive circuit configuration: 
         FIGS. 20A and 20B  are illustrations that indicate other configuration examples of the power recovery circuit; 
         FIG. 21A  is an illustration that indicates one example of circuit topology in the PDP drive circuit in embodiment 3 of the present invention; 
         FIG. 21B  is an illustration that indicates a configuration of scan IC; 
         FIG. 22  is an illustration that indicates one example of circuit topology in the PDP drive circuit in embodiment 4 of the present invention; 
         FIG. 23  is an illustration that indicates one example of circuit topology in the PDP drive circuit in embodiment 5 of the present invention; 
         FIG. 24  is an illustration that indicates one example of circuit topology in the PDP drive circuit in embodiment 6 of the present invention; 
         FIG. 25  is a circuit diagram of a scan drive circuit and a sustain electrode drive circuit equipped with a power recovery circuit; and 
         FIG. 26  is a circuit diagram of a scan electrode drive circuit with switching elements equipped to a voltage clamp circuit of a sustain pulse generation circuit, and a sustain electrode drive circuit. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  AD converter 
           2  Video signal processing circuit 
           3  Subfield processing circuit 
           4  Data electrode drive circuit 
           5 ,  501 ,  502 ,  503 ,  504 ,  505 ,  506 ,  507 ,  508 ,  509 ,  510 ,  511 ,  512 ,  513 ,  514 ,  521 ,  522  Scan electrode drive circuit 
           6  Sustain electrode drive circuit 
           10  Plasma display panel (PDP) 
           22  Scan electrode 
           23  Sustain electrode 
           32  Data electrode 
           51 ,  61 ,  5101 ,  5102 ,  5103 ,  5104 ,  5105 ,  5106 ,  5107 ,  5108 ,  5109 ,  5110 ,  5111 ,  5112 ,  5113 ,  5114 ,  5121 ,  5122  Sustain pulse generation circuit 
           52  Reset waveform generation circuit 
           53  Scan pulse generation circuit 
         C 1 , C 2  Recovery capacitor 
         C 31  Capacitor 
         L 1 , L 2 , L 1 A, L 1 B Coil 
         D 1 , D 2 , D 3 , D 4 , D 11 , D 12 , D 31 , D 101 , D 102 , D 110 , D 120  Diode 
         S 1 , S 2 , S 3 , S 4 , s 5 , S 6 , S 7 , S 8 , S 9 , S 10 , S 11 , S 12 , S 21 , S 22 , S 31 , S 32 , S 101 , S 102 , S 110 , S 120  Switching elements 
         V 1 , V 2 , V 3 , V 4 , V 5  Constant-voltage power supply 
         IC 31  Scan IC 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring now to the drawings, preferred embodiments of the invention are described specifically below. 
     Embodiment 1 
     1-1 Configuration 
       FIG. 1  is an illustration that shows a configuration of a PDP drive circuit in embodiment 1 of the present invention. The PDP drive circuit shown in  FIG. 1  is a circuit which applies drive voltage to electrodes of a plasma display panel (PDP) to drive the PDP. Before explaining the configuration and operation of the PDP drive circuit in detail, description is made on the PDP configuration and operation. 
     1-1-1 PDP Structure 
       FIG. 2  is a perspective view that indicates PDP structure. On a front plane  20  made of glass, which is the first substrate, a plurality of display electrodes forming a pair with stripe-form scan electrode  22  and sustain electrode  23  are formed. A dielectric layer  24  is formed to cover the scan electrode  22  and sustain electrode  23 , and a protective layer  25  is formed on the dielectric layer  24 . 
     On a back plane  30  which is the second substrate, a plurality of stripe-form data electrodes  32  covered with dielectric layer  33  are formed in such a manner that a plurality of data electrodes  32  make overhead crossing with scan electrodes  22  and sustain electrodes  23 . On the dielectric layer  33 , a plurality of bulkheads  34  are disposed in parallel with data electrodes  32 , and a phosphor layer  35  is formed on the dielectric layer  33  between these bulkheads  34 . In addition, the data electrode  32  is located at the position between adjacent bulkheads  34 . 
     These front plate  20  and back plate- 30  are disposed facing each other with a microscopic discharge space between in such a manner that a plurality of data electrodes  32  make overhead crossing with scan electrodes  22  and sustain electrodes  23  and the perimeter portion is sealed with sealing material such as glass frit, etc. In the discharge space, mixture gas of, for example, neon (Ne) and xenon (Xe) is sealed as discharge gas. The discharge space is partitioned into a plurality of compartments by bulkheads  34 . To each compartment, phosphor layers  35  that emit light of each color of red (R), green (G) and blue (B) are successively disposed. At portions where the scan electrode  22 , sustain electrode  23  and data electrode  32  intersect, discharge cells are formed and by adjacent three discharge cells with phosphor layers  35  formed, which emit light in each color, one pixel is composed. The region in which a discharge cell that composes this pixel is formed becomes an image display region and the perimeter of the image display region becomes a non-display region where no image is displayed, such as regions, etc. where glass frit is formed. 
     1-1-1-1 PDP Electrode Arrangement 
       FIG. 3  is an electrode arrangement diagram of PDP  10 . In a row direction, n rows of scan electrodes SC 1  through SCn (scan electrode  22  of  FIG. 2 ) and n rows of sustain electrodes SU 1  through SUn (sustain electrode  23  of  FIG. 2 ) are alternately arranged, and in the column direction, m columns of data electrodes D 1  through Dm (data electrode  32  of  FIG. 2 ) are arranged. A discharge cell Ci,j containing one pair of scan electrode SCi and sustain electrode SUi (i=1 through n) and one data electrode Dj (j=1 through m) are formed in the discharge space, and the total of discharge cells C amounts to (m×n) pieces. 
     In the PDP  10  with this configuration, ultraviolet ray is generated by gas discharge, to excite phosphors of each color of R, G, and B to emit light, thereby carrying out color display. In addition, in the PDP  10  one field period is divided into a plurality of subfields, and the PDP  10  is driven by combinations of subfields to carry out grey-scale display. Each subfield consists of a reset period, an address period, and a sustain period. In order to display image data, a signal waveform that varies in accord with a reset period, an address period, and a sustain period, respectively, is applied to each electrode. 
     1-1-1-2 Drive Voltage Waveform of PDP 
       FIG. 4  is an illustration that indicates each drive voltage waveform applied to each electrode of the PDP  10 . As shown in  FIG. 4 , each subfield has a reset period, an address period, and a sustain period. In addition, since relevant subfields carry out nearly same operations except varying number of sustain pulses during the sustain period in order to vary weights of the light-emitting period, and operating principle in each subfield is nearly same, in this part of the section, operation is explained for one subfield only. 
     First of all, during the reset period, for example, the positive pulse voltage is applied to all the scan electrodes SC 1  through SCn to accumulate necessary wall charges on protective layer  25  and phosphor layer  35  on dielectric layer  24  that covers scan electrodes SC 1  through SCn and sustain electrodes SU 1  through SUn. In addition, it generates priming (detonator for discharge=exciting particles) which reduces delay in discharge and stably generates address discharge. 
     Specifically, in the first half of the reset period, data electrodes D 1  through Dm and sustain electrodes SU 1  through SUn are held to 0 (V), respectively, and for scan electrodes SC 1  through SCn, a slope waveform voltage which slowly rises from voltage Vi 1  lower than the discharge start voltage to a voltage Vi 2  higher than a discharge start voltage is applied to data electrodes D 1  through Dm. While this slope waveform voltage is rising, the first faint reset discharge occurs between scan electrodes SC 1  through SCn and sustain electrodes SU 1  through SUn, and data electrodes D 1  through Dm, respectively. Negative wall voltage is accumulated on the top of scan electrodes SC 1  through SCn, and at the same time, positive wall voltage is accumulated on tops of data electrodes D 1  through Dm and sustain electrodes SU 1  through SUn. Wall voltage of the top of an electrode means voltage generated by wall charges accumulated on the dielectric layer that covers the electrode. 
     In the second half of the reset period, sustain electrodes SU 1  through SUn are kept at positive voltage Ve, and scan electrodes SC 1  through SCn are applied with slope waveform voltage which slowly lowers from voltage Vi 3  lower than the discharge start voltage for sustain electrodes SU 1  through SUn to voltage Vi 4  that exceeds the discharge start voltage is applied. During this period, the second faint reset discharge occurs between scan electrodes SC 1  through SCn and sustain electrodes SU 1  through SUn, and data electrodes D 1  through Dm, respectively. Negative wall voltage on top of scan electrodes SC 1  through SCn and positive wall voltage on top of sustain electrodes SU 1  through SUn are attenuated, and the positive wall voltage on the top of data electrodes D 1  through Dm is adjusted to a value suited for writing operation. This concludes the reset operation (hereinafter the drive voltage waveform applied to each electrode during the reset period is called the “reset waveform.”). 
     Then, in the address period, scan is carried out by applying a negative scan pulse successively to all the scan electrodes SC 1  through SCn. While scan electrodes SC 1  through SCn are scanned, based on the display data, positive write pulse voltage is applied to data electrodes D 1  through Dm. In this way, the address discharge is generated between scan electrodes SC 1  through SCn and data electrodes D 1  through Dm, and a wall charge is formed on the surface of the protective layer  25  on scan electrodes SC 1  through SCn. 
     Specifically, in the address period, scan electrodes SC 1  through SCn are temporarily kept at voltage Vscn. Then, in address operation of discharge cells Cp, 1  through Cp,m (p is integer of 1 through n), the scan pulse voltage Vad is applied to the scan electrode SCp, and at the same time, the positive write pulse voltage Vd is applied to the data electrode Dq (Dq is the data electrode to be selected from D 1  through Dm on the basis of video signals) which corresponds to video signals to be displayed on p-th row of data electrodes. In this way, address discharge is generated at the discharge cell Cp,q which corresponds to the intersecting portion between the data electrode Dq with the write pulse voltage applied and the scan electrode SCP with the scan pulse voltage applied. By this address discharge, positive voltage is accumulated on the top of the scan electrode SCp of the discharge cell Cp,q, negative voltage is accumulated on the top of the sustain electrode SUp, and the address operation is finished. Thereafter, the same address operation is carried out up to the discharge cells Cn,q on the n-th rows and thus address operation is finished. 
     In the following sustain period, a voltage sufficient to maintain discharge is applied between scan electrodes SC 1  through SCn and sustain electrodes SU 1  through SUn for a specified period. By this, discharge plasma is generated between scan electrodes SC 1  through SCn and sustain electrodes SU 1  through SUn, to excite the phosphor layer to emit light for a specified period. In such event, in the discharge space to which no write pulse voltage is applied during the address period, no discharge is generated and the phosphor layer  35  is not excited to emit light. 
     Specifically, in the sustain period, after scan electrodes SC 1  through SCn are temporarily returned to 0 (V), sustain electrodes SU 1  through SUn are returned to 0 (V). Thereafter, positive sustain pulse voltage Vsus is applied to scan electrodes SC 1  through SCn. In such event, the voltage between the top of the scan electrode SCp and the top of sustain electrode SUp at the discharge cell Cp,q which gives rise to address discharge is added with the wall voltage accumulated on the top of the scan electrode SCp and on the top of the sustain electrode SUp, in addition to the positive sustain pulse voltage Vsus during the address period, and becomes bigger than the discharge start voltage. Thus the first sustain discharge occurs. At the discharge cell Cp,q which caused sustain discharge, negative voltage is accumulated on the top of the scan electrode SCp and positive voltage is accumulated on the top of the sustain electrode SUp, so that the potential difference between the scan electrode SCP and the sustain electrode SUp at the time of occurrence of sustain discharge is cancelled. In this way, the first sustain discharge ends. After the first sustain discharge, scan electrodes SC 1  through SCn are returned to 0 (V), and thereafter Vsus is applied to sustain electrodes SU 1  through SUn. In such event, the voltage between the top of the scan electrode SCp and the top of the sustain electrode SUp at the discharge cell Cp,q which brought on the first sustain discharge is added with the wall voltage accumulated on the top of the scan electrode SCp and on the top of the sustain electrode SUp during the first sustain discharge added in addition to the positive sustain pulse voltage Vsus and becomes bigger than the discharge start voltage. Thus, the second sustain discharge occurs. Thereafter, in the same manner, by alternately applying sustain pulses to scan electrodes SC 1  through SCn and sustain electrodes SU 1  through SUn, sustain discharge is continuously carried out, by the number of times of sustain pulses, to the discharge cell Cp,q which has brought on the address discharge. 
     1-1-2 Configuration of PDP Drive Circuit 
     Going back to  FIG. 1 , operation of the PDP drive circuit will be described. The PDP drive circuit in the present embodiment is equipped with a scan electrode drive circuit  501  and sustain electrode drive circuit  6 . The scan electrode drive circuit  501  and the sustain electrode drive circuit  6  include power recovery circuits, respectively. The scan electrode drive circuit  501  has a sustain pulse generation circuit  5101  and the reset waveform generation circuit  52 , and the scan pulse generation circuit  53 . 
     The sustain pulse generation circuit  5101  includes a power recovery circuit  80  and a voltage clamp circuit  90 . The power recovery circuit  80  is equipped with a coil L 1 , a recovery capacitor C 1 , switching elements S 1  and S 2 , and reverse blocking diodes D 1  and D 2 . 
     In addition, the voltage clamp circuit  90  has a constant-voltage power supply V 1  which supplies sustain voltage Vsus, the first power supply, a switching element S 5  which is a power supply clamp switch, and a switching element S 6  which is a ground clamp switch. The voltage clamp circuit  90  is further equipped with a diode D 11  which is a first diode connected to the switching element S 5  in series and shutting off the current flowing into the constant-voltage power supply V 1 , a switching element S 11  which is a first switch, connected to the diode D 11  in parallel and capable of changing over whether to shut off or to pass the current flowing into the constant-voltage power supply V 1 , a diode D 12  which is a second diode connected to the switching element S 6  in series and shutting off the current flowing from GND of the voltage clamp circuit  90  into the main discharge path X via the switching element S 6 , and a switching element S 12  which is a second switch connected to the diode D 12  in parallel and capable of changing over whether to shut off or to pass the current flowing from GND of the voltage clamp circuit  90  into the main discharge path X via the switching element S 6 . The switching element S 11  is disposed in such a direction that its body diode shuts off the current flowing from the main discharge path X to the constant-voltage power supply V 1 . The switching element  12  is disposed in such a direction that its body diode shuts off the current flowing from GND of the voltage clamp circuit  90  to the main discharge path X. 
     Hereinafter, a diode which shuts off a current flowing into the constant-voltage power supply V 1  as the diode D 11  and a switch S 11  connected to the diode D 11  in parallel are called a “Vset separation switch.” In addition, a switch as the diode D 12  that shuts off a current flowing from GND to the main discharge path via the switching element S 6  is called a “Vad separation switch.” 
     In the sustain pulse generation circuit  5101 , by changing over switching elements S 1 , S 2 , S 5 , and S 6 , the power recovery circuit  80  and the voltage clamp circuit  90  are changed over to generate the sustain pulse to be applied to scan electrodes SC 1  through SCn. In the power recovery circuit  80 , by using a coil L 1  which is an inductance element, a capacitive load (capacitive load generated in scan electrodes SC 1  through SCn of  FIG. 3 ) of the PDP  10  and an inductance of the coil L 1  are LC-resonated to recover and supply the electric power. In the voltage clamp circuit  90 , electric power is supplied from the constant-voltage power supply V 1  of the voltage Vsus to scan electrodes SC 1  through SCn via the switching element S 5  and diode D 11  to clamp scan electrodes SC 1  through SCn to the voltage Vsus. In addition, by clamping scan electrodes SC 1  through SCn to the ground potential via diode D 12  and switching element S 6 , scan electrodes SC 1  through SCn are driven. 
     When the PDP  10  is driven, a large current of several hundreds ampere may flow instantaneously. In addition, there are diodes which have larger maximum rated value as compared to switching elements such as MOSFETs. By the use of diodes with a large rated value, a circuit that can proof large current can be configured with a number of elements less than that in the case of forming a switching element by the use of MOSFET, etc. 
     Therefore, in this embodiment, the diode D 11  with a large rated value is used to shut off the current flowing into the constant-voltage power supply V 1  and the diode  12  which has large rated value is used to shut off the current flowing from GND of the voltage clamp circuit  90  to the main discharge path X. Thus, it becomes possible to form a drive circuit with a smaller number of elements as compared to the case where a drive circuit is formed by the use of switching elements such as MOSFETs. It is also possible to configure switching elements S 11  and S 12  with a smaller number of elements. The reason will be discussed later. Consequently in the present embodiment, it becomes possible to configure the PDP drive circuit with the number of elements reduced from conventional cases. The detail of operations of these switching elements S 11  and S 12  will be discussed later. 
     In addition, switching elements S 11  and S 12  are configured by generally known elements, such as MOSFETs, which carry out switching operations. For the portion in which switching operation is carried out, a body diode is formed in anti-parallel. Thus, it is possible to allow the current which is to flow in the forward direction to the body diode even when the switching operation is in the shut-off state. In addition, switching elements S 1 , S 2 , S 5 , and S 6  are composed of generally known insulated gate bipolar transistors (IGBT) which have characteristics of low loss and simple control even during high-voltage operation. This is adopted in view of a large current of several hundreds of ampere that flows when PDP  10  is driven. In addition, with respect to switching elements S 5  and S 6 , since no parasitic diode is generated in IGBT, diodes which are equivalent to the body diode parasitically generated in MOSFET are installed in anti-parallel with switching elements S 5  and S 6 . In such event, a diode which is installed in anti-parallel with the switching element S 5  is disposed in the direction to shut off the current flowing from the constant-voltage power supply V 1  to the main discharge patch X and a diode which is installed in anti-parallel with the switching element S 6  is disposed in the direction to shut off the current flowing from the main discharge patch X to GND. 
     In the present embodiment, there is no intention to limit these switching elements to any specific kind but switching elements S 11  and S 12  may be configured with IGBT or switching elements S 1 , S 2 , S 5 , and s 6  may be configured with MOSFET, or a configuration to use other generally known elements which carry out switching operation may be adopted. 
     The reset waveform generation circuit  52  has switching elements S 21  and S 22  composed of generally known elements such as MOSFETs which carry out switching operation, a constant-voltage power supply V 2  of voltage Vset, which is the second power supply with higher potential than the constant-voltage power supply V 1 , and a constant-voltage power supply V 3  of negative voltage Vad, the third power supply. The electric power is supplied from the constant-voltage power supply V 2  to scan electrodes SC 1  through SC 2  via a switching element S 21 , and the electric power which is a negative potential is supplied from the constant-voltage power supply V 3  to scan electrodes SC 1  through SCn via a switching element S 22 , and reset waveform is generated. In addition, the switching element S 21  is disposed in such a direction that its body diode shuts off the current which flows from the constant-voltage power supply V 2  to the main discharge path. The switching element  22  is disposed in such a manner that its body diode shuts off the current flowing from the main discharge path X to the constant-voltage power supply V 3 . 
     In the first half of the reset period, the reset waveform generation circuit  52  generates slope waveform which slowly rises from the voltage Vi 1  lower than the discharge start voltage towards voltage Vi 2 , that is, Vset which exceeds the discharge start voltage, for data electrodes D 1  through Dm. In the second half of the reset period, it generates slope waveform which slowly lowers from the voltage Vi 3  lower than the discharge start voltage towards voltage Vi 4 , that is, Vad which exceeds the discharge start voltage, for sustain electrodes SU 1  through SUn. Hence the waveform is applied to scan electrodes SC 1  through SCn. 
     The scan pulse generation circuit  53  has switching elements S 31 , S 32  composed of generally known elements which carry out switching operation such as MOSFETs, a constant-voltage power supply V 4  of voltage Vscn, a reverse blocking diode D 31  that prevents the current from flowing into the constant-voltage power supply V 4 , a capacitor C 31 , and a scan IC (IC 31 ) which carries out switching operation. The scan pulse generation circuit  53  generates negative scan pulses during the address period and successively applies to scan electrodes SC 1  through SCn. The scan IC (IC 31 ) is a circuit to select scan electrodes SC 1  through SCn to which the voltage for address discharge shall be applied. 
     These switching elements S 1 , S 2 , S 5 , S 6 , S 21 , S 22 , S 31 , and S 32  as well as scan IC (IC 31 ) are controlled for change-over in accordance with subfield control signals generated in the subfield processing circuit  3 . 
     1-2 Operation of PDP Drive Circuit 
     The PDP drive circuit operation will be discussed with particular emphasis on the operation of switching elements S 11  and S 12 . The drive voltage waveforms applied during the reset period, address period, and sustain period are as per shown in  FIG. 4 . 
     1-2-1 Reset Period 
     First of all, description will be made on the operation of switching elements S 11  and S 12  during the reset period, that is, the period when scan electrodes SC 1  through SCn are driven by the reset waveform generation circuit  52 . 
     In the voltage clamp circuit  90  of the sustain pulse generation circuit  5101 , a diode D 11  is disposed in the direction to shut off the current flowing into the constant-voltage power supply V 1 , and the switching element S 11  is disposed in the direction in such a manner as for its body diode to shut off the current flowing into the constant-voltage power supply V 1 . 
     By having this kind of configuration, turning off the switching element S 11  can shut off both the current that flows from the constant-voltage power supply V 1  to the main discharge path X and the current that flows from the main discharge path X to the constant-voltage power supply V 1  because switching element S 5  is off. Thus it can electrically separate the constant-voltage power supply V 1  from the reset waveform generation circuit  52 . When only current flowing from the main discharge path X to the constant voltage supply V 1  is shut off, the switching element S 5  can be on, which causes no problem. By such a configuration, when scan electrodes SC 1  through SCn are driven by the constant-voltage power supply V 2  with higher potential than the constant-voltage power supply V 1 , the current flowing from the constant-voltage power supply V 2  to the constant-voltage power supply V 1  can be shut off and voltage drop of the main discharge path X and strain of drive waveform generated as a result of it can be prevented. 
     In addition, in the voltage clamp circuit of the sustain pulse generation circuit  5101 , the diode D 12  is disposed in the direction to shut off the current flowing from GND of the voltage clamp circuit into the main discharge path X, and the switching element S 12  is disposed in the direction in such a manner as for its body diode to shut off the current flowing from GND of the voltage clamp circuit  90  into the main discharge path X. 
     By having this configuration, turning off the switching element S 12  can shut off both the current that flows from the main discharge path X to GND of the voltage clamp circuit  90  and the current that flows from GND of the voltage clamp circuit  90  to the main discharge path because switching element S 6  is turned off, and can electrically separate GND of the voltage clamp circuit  90  from the reset waveform generation circuit  52 . When only current flowing from GND of the voltage clamp circuit  90  to the constant main discharge path is shut OFF, the switching element S 6  can be ON, which causes no problem. By this, when scan electrodes SC 1  through SCn are driven by the constant-voltage power supply V 3  with negative potential, the current flowing from GND of the voltage clamp circuit  90  to the constant-voltage power supply V 3  can be shut off and voltage increase of the main discharge path and strain of drive waveform generated as a result of it can be prevented. 
     Consequently, in the first half portion of the reset period, the switching element S 11  is off, the constant-voltage power supply V 1  and GND of the voltage clamp circuit  90  can be electrically separated from the main discharge path and the reset waveform generation circuit  52  is allowed to stably generate slope waveforms which slowly increase voltage Vi 1  to voltage Vi 2 , that is, voltage Vset. 
     On the other hand, when the potential of the main discharge path X reaches the voltage Vset by electric power supply from the constant-voltage power supply V 2 , the cathode-side potential of the diode D 11  becomes the voltage Vset which is higher than the voltage Vsus, whereas the anode-side potential of the diode D 11  is the voltage Vsus by the constant-voltage power supply V 1 , resulting in the electrically blocked-out condition where the current is prevented from flowing from the anode to the cathode of the diode D 11 . As described above, in the reset waveform in the present embodiment, voltage must be quickly lowered from voltage Vi 2  to voltage Vi 3  as soon as the first half portion of the reset period is finished. For example, when the voltage Vi 3  is equal to the voltage Vsus, it is possible to quickly bring the main discharge path at the potential same as the constant-voltage power supply V 1  by electrically connecting the constant-voltage power supply V 1  to electrically conduct to the main discharge path to lower the reset waveform from voltage Vi 2  to voltage Vi 3 . However, once the diode D 11  is brought into the electrically disconnected condition, it is no longer possible to quickly bring the main discharge path to the potential same as that of constant-voltage power supply V 1 , and it becomes difficult to generate normal drive waveform. 
     Therefore, in the present embodiment, as soon as the first half of the reset period is finished, the switching element S 11  is turned on. Hence, the constant-voltage power supply V 1  is allowed to electrically connected to the main discharge path, and electric charges accumulated in the main discharge path are able to be transferred to the constant-voltage power supply V 1  via the switching element S 11  and the diode connected to the switching element S 5  in antiparallel, and thus the potential of the main discharge path can be quickly brought to the potential same as that of the constant-voltage power supply V 1 . By the way, in such event, the current that flows in the switching element S 11  is primarily attributed to charges accumulated in the main discharge path and forms a comparatively small current. Consequently, the switching element S 11  may be of the size that enables this current to flow and is able to be configured with reduced number of elements such as MOSFETs with comparatively small rated value. In addition, because in such event, this current flows to the diode connected to the switching element S 5  in antiparallel, the switching element S 5  may be either on or off. 
     In this way, in the second half of the reset period, first of all, the switching element S 11  is turned on and the potential of reset waveform is quickly lowered to the voltage Vi 3 . Thereafter, the switching element S 11  or S 5  is turned off, and further the switching element S 12  is turned off, thus the constant-voltage power supply V 1  is electrically separated from the main discharge path, thereby allowing the reset waveform generation circuit  52  to stably generate slope waveforms which gradually lowers from the voltage Vi 3  to the voltage Vi 4 , that is, to the negative voltage Vad. 
     1-2-2 Address Period 
     Next description will be made on the operation of switching elements S 11  and S 12  during the address period, that is, the period for which scan electrodes SC 1  through SCn are driven by the scan pulse generation circuit  53 . 
     As described above, in the drive waveforms of scan electrodes SC 1  through SCn in the present embodiment, the voltage must be raised from the voltage Vi 4  to the voltage Vscn as soon as the second half of the reset period is finished (see  FIG. 4 ). Therefore, the switching element S 31  of the scan pulse generation circuit  53  is turned on, the electric power of the voltage value Vscn supplied from the constant-voltage power supply V 4  via the reverse blocking diode D 31  and switching element S 31  is fed to one of the input ports of IC 31  which carries out switching operation, and IC 31  carries out switching operation to supply the electric power to scan electrodes SC 1  through SCn. By a series of these operations, the drive waveform applied to scan electrodes SC 1  through SCn quickly rises from voltage Vi 4  to the voltage Vscn as soon as the second half of the reset period is finished. 
     In addition, as shown in  FIG. 4 , in the address period, scanning is carried out by successively applying negative scan pulses to all the scan electrodes SC 1  through SCn. Consequently, in the address period, the switching element S 22  of the reset waveform generation circuit  52  is kept turned on and the constant-voltage power supply V 3  and the main discharge path X are kept electrically connected to each other. In addition, the switching element S 32  of the scan pulse generation circuit  53  is turned off and the switching element S 5  of the sustain pulse generation circuit  5101  is turned off. Thus the constant-voltage power supply V 1  and GND of the voltage clamp circuit  90  are electrically separated from the main discharge path. Further, the constant-voltage power supply V 2  is electrically separated from the main discharge path X by turning off the switching element S 21  of the reset waveform generation circuit  52 . Thus, the potential of the main discharge path X is kept at negative voltage Vad. In this way, to the other input port of IC 31 , electric power of the negative voltage Vad is entered from the constant-voltage power supply V 3  supplied via the switching element S 22 . IC 31  carries out switching operations in such a manner as to supply the electric power from the constant-voltage power supply V 3  to scan electrodes SC 1  through SCn in a timing of applying negative scan pulse, and in other occasions, in such a manner as to supply the electric power from the constant-voltage power supply V 4  to scan electrodes SC 1  through SCn. 
     1-2-3 Sustain Period 
     Next description will be made on the operations of switching elements S 11  and S 12  during the sustain period, that is, the period in which scan electrodes SC 1  through SCn are driven by the sustain pulse generation circuit  5101 . 
     As shown in  FIG. 4 , in drive waveforms of scan electrodes SC 1  through SCn in the present embodiment, the drive voltage is brought temporarily to 0 (V) when the address period is finished. 
     However, when the potential of the main discharge path X becomes the negative voltage Vad by electric power supply from the constant-voltage power supply V 3 , the potential on the cathode side of diode D 12  is made 0 (V) by GND of the voltage clamp circuit  90 , whereas the anode-side potential becomes the negative voltage Vad lower than that 0 (V) and the electrically disconnected condition results in which no current is allowed to flow from anode side to cathode side of the diode D 12 . In order to make the main discharge path be 0 (V), GND of the voltage clamp circuit should be brought to be electrically connected to the main discharge path X. However when the diode D 12  comes into the electrically blocked out condition, the main discharge path X is unable to be quickly brought to 0 (V) and it becomes difficult to generate normal drive waveforms. 
     Therefore, in the present embodiment, as soon as the address period is finished, the switching element S 12  is turned on. By doing so, GND of the voltage clamp circuit is connected to the main discharge path, electric charges from GND of the voltage clamp circuit are supplied to the main discharge path X via the diode connected to the switching element S 6  in antiparallel and the switching element S 12  as to cancel negative electric charges accumulated in the main discharge path X, and the potential of the main discharge path X quickly becomes 0 (V). The current that flows the switching element S 12  in such event becomes a comparatively small current that is enough to cancel negative electric charges accumulated in the main discharge path X. Consequently, the switching element S 12  may be of a size that can allow this current to flow, and can be configured with reduced number of elements, such as MOSFETs, with comparatively small rated value. In addition, in such event, the current flows in a diode connected to the switching element S 6  in antiparallel, and thus it does not need to turn on the switching element S 6 . 
     After the potential of the main discharge path becomes 0 (V), by controlling switching elements S 1 , S 2 , S 5 , and S 6  in the way of the prior art, when the electric power is recovered, the electric power accumulated in the capacitive load generated in scan electrodes SC 1  through SCn is transferred to a recovery capacitor C 1  via the reverse blocking diode D 2  and switching element S 2 . When the electric power is supplied, the electric power accumulated in the recovery capacitor C 1  can be transferred to scan electrodes SC 1  through SCn via the switching element S 1  and reverse blocking diode D 1 . In addition, at the time of clamping, the constant-voltage power supply V 1  of the voltage Vsus allows voltages of scan electrodes SC 1  through SCn to be kept at V 1  via the switching element S 5  and diode D 11 , and also kept at GND via the diode D 12  and switching element S 6 . 
     In such event, when the rise of sustain pulse by the sustain pulse generation circuit  5101  is configured to take place after the fall of the sustain pulse by the sustain electrode drive circuit  6 , the switching element S 12  is kept on during the sustain pulse down period. Thus, electric charge of grounding potential is supplied from GND to PDP  10  via the switching element S 12 . Accordingly it is possible to allow sustain pulses by the sustain electrode drive circuit  6  to have down-waveforms free of strain. 
     When it is configured to simultaneously carry out fall of sustain pulses by the sustain electrode drive circuit  6  and rise of sustain pulses by the sustain pulse generation circuit  5101 , the switching element S 12  does not always have to be turned on during the period of fall of sustain pulses by the sustain electrode drive circuit  6 . This is because electric charges are supplied from the recovery capacitor C 1  to PDP  10  via the switching element S 1 , and thereby the sustain pulses by the sustain electrode drive circuit  6  become down-waveforms free of strain. 
     1-3 Effects 
     As described above, according to the present embodiment, a configuration with diodes D 11  and D 12  provided to the voltage clamp circuit of the sustain pulse generation circuit  5101  can electrically separate the constant-voltage power supply V 1  and GND of the voltage clamp circuit from the main discharge path without disposing a switching element between the sustain pulse generation circuit  5101  and the reset waveform generation circuit  52 . Consequently, it is possible to reduce impedance in the main discharge path X from the coil L 1  of the power recovery circuit  80  to scan electrodes SC 1  through SCn, to improve the recovery ratio of electric power accumulated in the capacitive load of PDP  10 , and to achieve reduction of power consumption. 
     Furthermore, since a drive circuit can be configured by the use of diodes with large rated values, as compared to the case in which MOSFETs and other switching elements are used, the number of elements that compose the drive circuit can be reduced. 
     Furthermore, since a configuration with the switching element S 11  which is connected to the diode D 11  in parallel and can switch from shutting off or passing or vice versa the current that flows from the main discharge path X to the constant-voltage power supply V 1  is adopted. Thus even if the diode D 11  comes into an electrically disconnected state, by turning on the switching element S 11 , it is possible to allow the current to pass from the main discharge path X to the constant-voltage power supply V 1  via the switching element S 11  and the diode connected to the switching element S 5  in antiparallel. For example, it is possible to quickly transfer electric charges of the voltage Vset accumulated in the main discharge path X to the constant-voltage power supply V 1  and to bring the potential of the main discharge path X to the potential equal to that of the constant-voltage power supply V 1 . 
     Furthermore, since a configuration with the switching element S 12  which is connected to the diode D 12  in parallel and can switch from shutting off or passing or vice versa the current that flows from GND of the voltage clamp circuit  90  to the main discharge path X is adopted. Thus even if the diode D 12  comes into an electrically disconnected state, by turning on the switching element S 12 , it is possible to allow the current to pass from GND of the voltage clamp circuit  90  to the main discharge path X via the diode connected to the switching element  6  in antiparallel and the switching element  12 . For example, it is possible to quickly supply electric charges that cancels the negative voltage Vad accumulated in the main discharge path X from GND of the voltage clamp circuit  90  to the main discharge path X and to bring the potential of the main discharge path X to the potential equal to that of GND. Hence, it becomes possible to generate voltage waveforms for driving scan electrodes SC 1  through SCn stably free of strain. 
     When the constant-voltage power supply V 3  of negative voltage is not used for the reset waveform generation circuit  52 , it is possible to configure a voltage clamp circuit without using the diode D 12  and the switching element S 12 . 
     1-4 Modification Examples 
     1-4-1 Modification Example 1 
       FIG. 5  is an illustration that indicates another example of the configuration of PDP drive circuit in embodiment 1 of the present invention. The PDP drive circuit shown in  FIG. 5  has a scan electrode drive circuit  502  and a sustain electrode drive circuit  6 , and the scan electrode drive circuit  502  has a sustain pulse generation circuit  5102 , a reset waveform generation circuit  52 , and a scanning pulse generation circuit  53 . 
     For example, as shown in  FIG. 5 , when there is no need to have negative voltage for generating the reset waveform and no constant-voltage power supply of negative potential is used for the reset waveform generation circuit  52 , a voltage clamp circuit  91  of the sustain pulse generation circuit  5102  may be configured without using the diode D 12  and the switching element S 12  of  FIG. 1 . In this configuration, the same effects as described above can be obtained. 
     1-4-2 Modification Example 2 
       FIG. 6  is an illustration that indicates still another example of the configuration of the PDP drive circuit in embodiment 1. The PDP drive circuit shown in  FIG. 6  is equipped with a scan electrode drive circuit  503  and the sustain electrode drive circuit, and the scan electrode drive circuit  503  has a sustain pulse generation circuit  5103 , the reset waveform generation circuit  52 , and the scan pulse generation circuit  53 . 
     As shown in  FIG. 6 , it is possible to have a configuration using a switching element S 102  by MOSFET, etc. same as prior art for the voltage clamp circuit  92  of the sustain pulse generation circuit  5103  in place of the diode D 12  and switching element S 12  of  FIG. 1 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 102 , it is possible to switch whether to shut off or pass the current flowing from GND of the voltage clamp circuit  92  to the main discharge path. 
     1-4-3 Modification Example 3 
       FIG. 7  is an illustration that indicates still another example of the configuration of PDP drive circuit in embodiment 1 of the present invention. The PDP drive circuit shown in  FIG. 7  is equipped with a scan electrode drive circuit  504  and the sustain electrode drive circuit  6 , and the scan electrode drive circuit  504  has a sustain pulse generation circuit  5104 , the reset waveform generation circuit  52  and the scan pulse generation circuit  53 . 
     As shown in  FIG. 7 , it is possible to have a configuration using a switching element S 101  by MOSFET, etc. same as prior art for the voltage clamp circuit  93  of the sustain pulse generation circuit  5104  in place of the diode D 11  and switching element S 11  of  FIG. 1 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 101 , it is possible to switch whether to shut off or pass the current that flows from the main discharge path to the constant-voltage power supply V 1 . 
     As shown in modification examples 2 and 3, in place of either set of diode D 11  and switching element S 11  or set of diode D 12  and switching element S 12 , the switching element S 101  or S 102  by MOSFET, etc. may be used, and under such configuration, the same effects as described above can be obtained. 
     1-4-4 Modification Example 4 
       FIG. 8  is an illustration that shows still another example of the configuration of the PDP drive circuit in embodiment 1 of the present invention. The PDP drive circuit shown in  FIG. 8  is equipped with a scan electrode drive circuit  505  and the sustain electrode drive circuit  6 , and the scan electrode drive circuit  505  has a sustain pulse generation circuit  5105 , the reset waveform generation circuit  52 , and the scan pulse generation circuit  53 . 
     As shown in  FIG. 8 , it is possible to have a configuration in which a switching element S 9  by MOSFET, etc. same as prior art is installed on the main discharge path between the sustain pulse generation circuit  5105  and the reset waveform generation circuit  52  in place of the diode D 12  and switching element S 12  of  FIG. 1 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 9 , it is possible to switch whether to shut off or pass the current flowing from GND of the voltage clamp circuit  94  to the main discharge path. 
     1-4-5 Modification Example 5 
       FIG. 9  is an illustration that indicates still another example of the configuration of the PDP drive circuit in embodiment 1 of the present invention. The PDP drive circuit shown in  FIG. 9  is equipped with a scan electrode drive circuit  506  and the sustain electrode drive circuit  6 , and the scan electrode drive circuit  506  has a sustain pulse generation circuit  5106 , the reset waveform generation circuit  52  and the scan pulse generation circuit  53 . 
     As shown in  FIG. 9 , it is possible to have a configuration in which a switching element S 10  by MOSFET, etc. same as prior art is installed on the main discharge path between the sustain pulse generation circuit  5106  and the reset waveform generation circuit  52  in place of the diode D 11  and switching element S 11  of  FIG. 1 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 10 , it is possible to switch whether to shut off or pass the current that flows from the main discharge path to the constant-voltage power supply V 1 . In this way, in place of either set of diode D 11  and switching element S 11  or set of diode D 12  and switching element S 12 , a switching element using MOSFET, etc. may be installed on the main discharge path between the sustain pulse generation circuit  5105  or  5106  and the reset waveform generation circuit  52 . 
     1-4-6 Modification Example 6 
     In the present embodiment, an example in which a coil for LC-resonance in the power recovery circuit is configured by the coil L 1  only as shown in  FIG. 1  and  FIG. 5  through  FIG. 9 . However the present invention shall not be limited to this configuration. For example, in order to change resonance frequency, etc. at the time of electric power recovery and at the reuse, two coils may be used for the power recovery circuit, under which the same effects can be obtained.  FIG. 10  is an illustration that indicates still another example of the configuration of the PDP drive circuit in embodiment 1. What differs in configuration shown in  FIG. 10  from the configuration shown in  FIG. 1  is that two coils, coil L 1 A and coil L 1 B, are used for the coil for LC-resonance in the power recovery circuit of the sustain pulse generation circuit  5107  in the scan electrode drive circuit  507 . The coil L 1 B is used at the time of electric power recovery, and the coil L 1 A is used at the time of reusing electric power. For example, even when the power recovery circuit is configured in this way, the same effects as described above can be obtained. By the way, in  FIG. 10 , a configuration in which the coil L 1 A of the power recovery circuit  81  is connected to the cathode side of the diode D 11  and the coil L 1 B is connected to the anode side of the diode D 12  is shown. However, for example, a configuration in which the coil L 1 A is connected to the anode side of the diode D 11  or coil L 1 B is connected to the cathode side of the diode D 12  may be adopted. In addition, in configurations shown in  FIG. 5  through  FIG. 9 , same as the configuration shown in  FIG. 10 , the configuration in which two coils are used for the power recovery circuit may be adopted. 
     1-4-7 Modification Example 7 
       FIGS. 11A and 11B  are figures that show another configuration examples of the power recovery circuit. The power recovery circuit shown in  FIG. 11A  has switching circuits Q 1  and Q 2  used in place of switching elements S 1  and S 2  in configurations of power recovery circuits of  FIG. 1  and  FIG. 5  through  FIG. 9 . The switching circuit Q 1  is a parallel circuit of the switching element Q 11  and the diode Q 12 . The switching circuit Q 2  is a parallel circuit of the switching element Q 21  and the diode Q 22 . The diode D 1  and diode Q 12  as well as the diode D 2  and diode Q 22  are back-to-back connected, respectively. Switching elements Q 11  and Q 21  are configured with MOSFET, IGBT, etc., and are properly selected in accord with specifications such as withstand voltage. 
     In addition, the power recovery circuit shown in  FIG. 11B  is a configuration in which two coils are used as is the case of  FIG. 10 . In the power recovery circuit shown in  FIG. 11B , in the configuration of  FIG. 10 , switching circuits Q 1  and Q 2  composed of a parallel circuit of a switching element and a diode are used, respectively, in place of switching elements S 1  and S 2 . 
     1-5 Plasma Display Apparatus 
       FIG. 12  is a block diagram that indicates a configuration of a plasma display apparatus with the PDP drive circuit according to the present embodiment incorporated. 
     The plasma display apparatus shown in  FIG. 12  includes an AD converter  1 , a video signal processing circuit  2 , a subfield processing circuit  3 , a data electrode drive circuit  4 , a scan electrode drive circuit  5 , a sustain electrode drive circuit  6 , and a PDP  10 . 
     The scan electrode drive circuit  5  and sustain electrode drive circuit  6  have the configuration and operation shown in  FIG. 1  and  FIG. 5  through  FIG. 10 . 
     The AD converter  1  converts the entered analog video signals into digital video signals. The video signal processing circuit  2  converts entered digital video signals into subfield data which carries out control of each subfield from 1-field video signal, in order to emit light and display entered digital video signals to the PDP  10  by combinations of a plurality of subfields with varying weights of light-emitting period. 
     The subfield processing circuit  3  generates a control signal for the data electrode drive circuit, a control signal for the scan electrode drive circuit, and a control signal for the sustain electrode drive circuit from subfield data prepared by the video signal processing circuit  2  and outputs them to the data electrode drive circuit  4 , scan electrode drive circuit  5 , and sustain electrode drive circuit  6 , respectively. 
     The PDP  10  has n-rows of scan electrodes SC 1  through SCn (scan electrode  22  of  FIG. 2 ) and n-rows of sustain electrodes SU 1  through SUn (sustain electrode  23  of  FIG. 2 ) arranged alternately in the row direction and m-columns of data electrodes D 1  through Dm (data electrode  32  in  FIG. 2 ) arranged in the row direction as described above. (m×n) pieces of discharge cell Ci,j containing a pair of scan electrode SCi and sustain electrode SUi (i=1 through n) and one data electrode Dj (j=1 through m) are formed in the discharge space, and one pixel is configured by three discharge cells which emit light in each color of red, green, and blue. 
     The data electrode drive circuit  4  drives each data electrode Dj independently in accordance with the data electrode drive circuit control signals. 
     The scan electrode drive circuit  5  is equipped inside with a sustain pulse generation circuit  51  to emit sustain pulses applied to scan electrodes SC 1  through SCn during the sustain period and can independently drive each scan electrode SC 1  through SCn, respectively. In accordance with the scan electrode drive circuit control signals, the scan electrode drive circuit  5  independently drives each of scan electrodes SC 1  through SCn. 
     The sustain electrode drive circuit  6  is equipped inside with a sustain pulse generation circuit  61  to generate sustain pulses applied to sustain electrodes SU 1  through SUn during the sustain period, and can drive all the sustain electrodes SU 1  through SUn of PDP  10  in bulk. In accordance with the sustain electrode drive circuit control signal, the sustain electrode drive circuit  6  drives sustain electrodes SU 1  through SUn. 
     The PDP drive circuits shown in the following embodiments can be applied to the plasma display apparatus shown in  FIG. 12 , too. 
     Embodiment 2 
     2-1 Configuration of PDP Drive Circuit 
       FIG. 13  is an illustration that indicates a configuration of PDP drive circuit in embodiment 2 of the present invention. Structure and electrode arrangement of PDP which the PDP drive circuit in the present embodiment is subject to drive, each drive voltage waveform which the PDP drive circuit in the present embodiment applies to each electrode of PDP  10 , and electrical configuration of a plasma display apparatus in which the PDP drive circuit and PDP  10  of the present embodiment are same as those of embodiment 1. Thus descriptions on the relevant configuration and operation will be omitted. 
     As shown in  FIG. 13 , the PDP drive circuit in embodiment 2 of the present invention is equipped with a scan electrode drive circuit  508  and the sustain electrode drive circuit  6  which have power recovery circuits. The scan electrode drive circuit  508  has a sustain pulse generation circuit  5108 , reset waveform generation circuit  52 , and scan pulse generation circuit  53 . Because the reset waveform generation circuit  52  and scan pulse generation circuit  53  are the same as the reset waveform generation circuit  52  of the scan electrode drive circuit  501  and the scan pulse generation circuit  53  shown in  FIG. 1 , description of the relevant configurations and operations will be omitted. 
     The sustain pulse generation circuit  5108  shown in  FIG. 13  includes a power recovery circuit  80   b  and a voltage clamp circuit  90   b , and the power recovery circuit  80   b  contains a coil L 1 , a recovery capacitor C 1 , switching elements S 1  and S 2  and reverse blocking diodes D 1  and D 2 . The power recovery circuit  80   b  includes a diode D 110  which is a third diode that shuts off current flowing from the constant-voltage power supply V 1  to the main discharge path, a switching element S 110  as a third switch which can be changed over between shutting off or passing the current which flows into the constant-voltage power supply V 1  connected to the diode D 110  in series, a diode D 120  as a fourth diode which shuts off the current backflowing from the main discharge path to GND of the voltage clamp circuit  90   b , and a switching element S 120  as a forth switch that can change over between shutting off or passing the current flowing from GND of the voltage clamp circuit connected to the diode D 120  in series to the main discharge path via the diode D 120 . 
     In addition, the voltage clamp circuit  90   b  includes a switching element S 5  which is a power supply clamp switch, a switching element S 6  which is a ground clamp switch, a constant-voltage power supply V 1  of the voltage Vsus which is a first power supply, a diode D 11  as a first diode that is connected to the switching element S 5  in series and shuts off current flowing into the constant-voltage power supply V 1 , and a diode D 12  which is a second diode that is connected to the switching element S 6  in series and shuts off current flowing from GND of the voltage clamp circuit to the main discharge path via the switching element S 6 . 
     In the sustain pulse generation circuit  5108 , the power recovery circuit  80   b  has a configuration in which a diode D 110  and a switching element S 110  connected in series are connected in parallel to the switching element S 5  and the diode D 11  in series with the coil L 1  interposed between them, a diode D 120  and a switching element S 120  connected in series are connected in parallel to the switching element S 6  and the diode D 12  connected in series with the coil L 1  interposed between them. 
     The point that the sustain pulse generation circuit  5108  shown in  FIG. 13  differs from the sustain pulse generation circuit  5101  shown in  FIG. 1  is that in place of the switching element S 11  connected to the diode D 11  in parallel and the switching element S 12  connected to the diode D 12  in parallel, the diode D 110  and the switching element S 110  as well as the diode D 120  and the switching elements S 110  and S 120  are included, respectively. 
     In addition, the sustain pulse generation circuit  5108  shown in  FIG. 13  and the sustain pulse generation circuit  5101  shown in  FIG. 1  carry out practically same operations. That is, in the sustain pulse generation circuit  5108 , by changing over switching elements S 1 , S 2 , S 5 , S 6 , S 110 , and S 120 , the power recovery circuit  80   b  and the voltage clamp circuit  90   b  are changed over, and thus sustain pulses to apply to scan electrodes SC 1  through SCn are generated. In the power recovery circuit  80   b , by use of the coil L 1  which is an inductance element, the capacitive load of PDP  10  (capacitive load generated in scan electrodes SC 1  through SCn of  FIG. 3 ) and inductance of the coil L 1  are LC-resonated to recover and supply the electric power. In the voltage clamp circuit  90   b , the electric power is supplied from the constant-voltage power supply V 1  of the voltage Vsus to scan electrodes SC 1  through SCn via the switching element S 5  and the diode D 11  to clamp scan electrodes SC 1  through SCn to the voltage Vsus, and by clamping scan electrodes SC 1  through SCn to the grounding potential via the diode D 12  and the switching element S 6 , scan electrodes SC 1  through SCn are driven. 
     2-2 Operation of the PDP Drive Circuit 
     The PDP drive circuit operation will be discussed with particular emphasis on the operation of switching elements S 110  and S 120 . The drive voltage waveforms applied during the reset period, address period, and sustain period are as per shown in  FIG. 4 . 
     2-2-1 Reset Period 
     First of all, description will be made on the operation of switching elements S 110  and S 120  during the reset period, that is, a period when scan electrodes SC 1  through SCn are driven by the reset waveform generation circuit  52 . 
     In the voltage clamp circuit  90   b  of the sustain pulse generation circuit  5108 , the diode D 11  is disposed in the direction to shut off the current flowing into the constant-voltage power supply V 1 , and the switching element S 110  is disposed in the direction in such a manner as for its body diode to shut off the current flowing into the constant-voltage power supply V 1 . 
     By having this configuration, turning off the switching element S 110  can electrically separate the constant-voltage power supply V 1  from the reset waveform generation circuit  52 . By this, when scan electrodes SC 1  through SCn are driven by the constant-voltage power supply V 2  with higher potential than the constant-voltage power supply V 1 , the current flowing from the constant-voltage power supply V 2  to the constant-voltage power supply V 1  can be shut off and voltage drop of the main discharge path and strain of drive waveform generated as a result of it can be prevented. 
     In addition, in the voltage clamp circuit  90   b  of the sustain pulse generation circuit  5108 , the diode D 12  is disposed in the direction to shut off the current flowing from GND of the voltage clamp circuit  90   b  to the main discharge path and the switching element S 120  is disposed in the direction in such a manner as for its body diode to shut off the current flowing from GND to the main discharge path. 
     By having this configuration, turning off the switching element S 120  can electrically separate GND of the voltage clamp circuit  90   b  from the reset waveform generation circuit  52 . Thus, when scan electrodes SC 1  through SCn are driven by the constant-voltage power supply V 3  with negative potential, the current flowing from GND of the voltage clamp circuit  90   b  to the constant-voltage power supply V 3  can be shut off, and voltage increase of the main discharge path and strain of drive waveform generated as a result of it can be prevented. 
     Consequently, in the first half portion of the reset period, switching elements S 110  is off to separate electrically the constant-voltage power supply V 1  from the main discharge path so that the reset waveform generation circuit  52  is allowed to stably generate slope waveforms which slowly increase voltage Vi 1  to voltage Vi 2 , that is, voltage Vset. 
     On the other hand, when the potential of the main discharge path reaches the voltage Vset by electric power supply from the constant-voltage power supply V 2 , while the anode-side potential of the diode D 11  is equal to the voltage Vsus by the constant-voltage power supply V 1 , the cathode-side potential of the diode  11  becomes the voltage Vset which is higher than the voltage Vsus. This results in the electrically disconnected condition where the current is prevented from flowing from the anode side to the cathode side of the diode D 11 . As described above, in the reset waveform in the present embodiment, voltage must be quickly lowered from voltage Vi 2  to voltage Vi 3  as soon as the first half portion of the reset period is finished. For example, when voltage Vi 3  is equal to the voltage Vsus, it is possible to quickly bring the main discharge path to the potential same as the constant-voltage power supply V 1  by connecting the constant-voltage power supply V 1  to electrically to the main discharge path and to lower the reset waveform from voltage Vi 2  to voltage Vi 3 . However, once the diode D 11  is brought into the electrically disconnected condition, it is no longer possible to quickly bring the main discharge path to the potential same as that of constant-voltage power supply V 1 , and it becomes difficult to generate normal drive waveform. 
     Therefore, in the present embodiment, as soon as the first half of the reset period is finished, the switching elements S 110  and S 5  are turned on. By doing this, the constant-voltage power supply V 1  is connected electrically to the main discharge path, and electric charges accumulated in the main discharge path are able to be transferred to the constant-voltage power supply V 1  via the coil L 1 , the switching element S 110  and the diode D 110 . Thus the potential of the main discharge path can be quickly brought to the potential same as that of the constant-voltage power supply V 1 . In such event, the current that flows in the switching element S 110  is primarily attributed to charges accumulated in the main discharge path and forms a comparatively small current. Consequently, the switching element S 110  may be of the size that enables this current to flow and is able to be configured with reduced number of elements such as MOSFET with comparatively small rated value. 
     In this way, in the second half of the reset period, first of all, the switching element S 110  is turned on and the potential of reset waveform is quickly lowered to voltage Vi 3 . Thereafter, the switching elements S 5 , S 120  are turned off and the constant-voltage power supply V 1  and GND are electrically separated from the main discharge path, thereby allowing the reset waveform generation circuit  52  to stably generate slope waveforms which gradually lowers from voltage Vi 3  to voltage Vi 4 , that is, to the negative voltage Vad. 
     2-2-2 Address Period 
     Next description will be made on the operation of switching elements S 110  and S 120  during the address period, that is, the period for which scan electrodes SC 1  through SCn are driven by the scan pulse generation circuit  53 . 
     As described above, in the drive waveforms of scan electrodes SC 1  through SCn in the present embodiment, as soon as the second half of the reset period is finished, the switching element S 31  of the scan pulse generation circuit  53  is turned on, and the electric power of the voltage Vscn is supplied to SC 1  through SCn via IC 31  which carries out switching operation. Thus, the drive waveforms applied to scan electrodes SC 1  through SCn quickly rise from the voltage Vi 4  to the voltage Vscn as soon as the second half of the reset period is finished. 
     On the other hand, in the address period, in order to successively apply negative scan pulses to all the scan electrodes SC 1  through SCn, the switching element S 22  of the reset waveform generation circuit  52  is turned on to connect electrically the constant-voltage power supply V 3  to the main discharge path. In addition, the constant-voltage power supply V 1  and GND of voltage clamp circuit  90   b  is electrically separated from the main discharge path by turning off the switching element S 32  of the scan pulse generation circuit  53  and turning off the switching elements S 110  and S 120  of the sustain pulse generation circuit  5108 . Further, the constant-voltage power supply V 2  is electrically separated from the main discharge path by turning off the switching element S 21  of the reset waveform generation circuit  52 . Hence the potential of the main discharge path is kept at negative voltage Vad. In this way, IC 31  supplies the electric power from the constant-voltage power supply V 3  to scan electrodes SC 1  through SCn in a timing of applying negative scan pulses, or supplies the electric power from the constant-voltage power supply V 4  to scan electrodes SC 1  through SCn in other occasions. 
     2-2-3 Sustain Period 
     Next description will be made on the operations of switching elements S 110  and S 120  during the sustain period, that is, the period for which scan electrodes SC 1  through SCn are driven by the sustain pulse generation circuit  5108 . 
     As described above, in drive waveforms of scan electrodes SC 1  through SCn in the present embodiment, the drive voltage is brought temporarily to 0 (V) when the address period is finished. 
     However, when the potential of the main discharge path becomes the negative voltage Vad by electric power supply from the constant-voltage power supply V 3 , the potential on the cathode side of the diode D 12  is made 0 (V) by GND of the voltage clamp circuit  90   b , whereas the anode-side potential becomes the negative voltage Vad lower than 0(V) and the electrically blocked-out condition results in which no current is allowed to flow from anode side to cathode side of diode D 12 . In order to make the main discharge path be 0 (V), GND of the voltage clamp circuit should be connected electrically to the main discharge path, but when the diode D 12  comes into the electrically blocked out condition, the main discharge path is unable to be quickly brought to 0 (V) and it becomes difficult to generate normal drive waveforms. 
     Therefore, in the present embodiment, as soon as the address period is finished, the switching element S 120  and the switching element S 6  are turned on. By doing so, GND of the voltage clamp circuit  90   b  is connected electrically to the main discharge path, electric charges from GND of the voltage clamp circuit are supplied to the main discharge path via the diode D 120 , the switching element S 120 , and the coil L 1  in such a manner as to cancel negative electric charges accumulated in the main discharge path, and the potential of the main discharge path quickly becomes 0 (V). The current that flows the switching element S 120  in such event becomes a comparatively small current that is enough to cancel negative electric charges accumulated in the main discharge path. Consequently, the switching element S 120  may be of a size that can allow this current to flow, and can be configured by reduced number of elements, such as MOSFET, with comparatively small rated value. 
     After the potential of the main discharge path becomes 0 (V), by controlling switching elements S 1 , S 2 ,  5 , and S 6  in the way as prior art, when the electric power is recovered, the electric power accumulated in the capacitive load generated in scan electrodes SC 1  through SCn is transferred to a recovery capacitor C 1  via the reverse blocking diode D 2  and switching element S 2 . When the electric power is supplied, the electric power accumulated in the recovery capacitor C 1  can be transferred to scan electrodes SC 1  through SCn via the switching element S 1  and reverse blocking diode D 1 . In addition, at the time of clamping, the electric power is supplied from the constant-voltage power supply V 1  of a voltage Vsus to scan electrodes SC 1  through SCn via the switching element S 5  and diode D 11 , and the electric power accumulated in the capacitive load generated in scan electrodes SC 1  through SCn is discharged to GND via the diode D 12  and switching element S 6 . 
     In such event, when it is configured that the rise of sustain pulse by the sustain pulse generation circuit  5108  takes place after the fall of the sustain pulse by the sustain electrode drive circuit  6 , at least the switching element S 120  is kept on during the sustain pulse down period. In addition, during the sustain period for which the switching element S 5  is on, the switching element S 110  is kept on. In addition, it is configured that the fall of the sustain pulse by the sustain pulse generation circuit  5108  takes place before the rise of the sustain pulse by the sustain electrode drive circuit  6 , at least the switching elements S 120  is kept on during the sustain pulse up period. During other sustain periods, switching elements S 110  and S 120  may be on or off, whichever is acceptable. Thus, it is possible to have down-waveforms free of strain. When it is configured to simultaneously carry out fall of sustain pulses by the sustain electrode drive circuit  6  and rise of sustain pulses by the sustain pulse generation circuit  5108 , the switching element S 120  is turned off during the period of fall of sustain pulses by the sustain electrode drive circuit  6 . In addition, when it is configured to simultaneously carry out rise of sustain pulses by the sustain electrode drive circuit  6  and fall of sustain pulses by the sustain pulse generation circuit  5108 , similarly the switching element S 120  is turned off during the down period of sustain pulse of the sustain electrode drive circuit  6 . Other operations during other sustain period take place as described above. 
     2-3 Effects 
     As described above, according to the present embodiment, having a configuration to provide diodes D 11  and D 12  to the voltage clamp circuit  90   b  of the sustain pulse generation circuit  5108  can electrically separate the constant-voltage power supply V 1  and GND of the voltage clamp circuit  90   b  from the main discharge path without disposing a switching element between the sustain pulse generation circuit  5108  and the reset waveform generation circuit  52 . Consequently, it is possible to reduce impedance in the main discharge path from the coil L 1  of the power recovery circuit to scan electrodes SC 1  through SCn, to improve the recovery ratio of electric power accumulated in the capacitive load of PDP  10 , thereby achieving reduction of power consumption. 
     Furthermore, since a drive circuit can be configured by the use of diodes with large rated values. Thus, as compared to the case in which MOSFETs and other switching elements are used, the number of elements that compose the drive circuit can be reduced. 
     Furthermore, since a configuration with the switching element S 110  and diode D 110  which are able to switch from shutting off or passing or vice versa the current that flows from the main discharge path to the constant-voltage power supply V 1  and diode D 110  are connected in series, and the switching element  5  and diode D 11  which are connected in series are disposed in parallel to the switching element S 110  and diode D 120  via the coil L 1  is adopted, it is possible to allow the current from the main discharge path to the constant voltage power supply V 1  via the switching element S 110  and diode D 110 , even if the diode D 11  is disconnected electrically. For example electric charge of the voltage Vset accumulated in the main discharge path can be quickly transferred to the constant-voltage power supply V 1  to bring the potential of the main discharge path to the potential equal to that of the constant-voltage power supply V 1 . 
     In addition, it is configured that the switching element S 120  and a diode D 120  which can switch from shutting off or passing the current that flows from GND of the voltage clamp circuit  90   b  to the main discharge path are connected in series and a switching element S 6  and diode D 12  which are connected in series are connected to the switching element S 120  and diode D 120  in parallel via the coil L 1 . Thus, even if the diode D 12  comes into an electrically shut off state, it is possible to allow the current to pass from GND to the main discharge path via the switching element S 120  and the diode D 120 . For example, it is possible to quickly supply electric charges that cancels the negative voltage Vad accumulated in the main discharge path from GND of the voltage clamp circuit  90   b  to the main discharge path and to bring the potential of the main discharge path to the potential equal to that of GND. Accordingly, it becomes possible to generate voltage waveforms for driving scan electrodes SC 1  through SCn stably free of strain. 
     When the constant-voltage power supply V 3  of negative voltage is not used for the reset waveform generation circuit  52 , it is possible to configure a voltage clamp circuit without using the diode D 120  and the switching element S 120 . 
     2-4 Modification Examples 
     2-4-1 Modification Example 1 
       FIG. 14  is an illustration that indicates another example of the configuration of PDP drive circuit in embodiment 2 of the present invention. The PDP drive circuit shown in  FIG. 14  has a scan electrode drive circuit  509  and a sustain electrode drive circuit  6 , and the scan electrode drive circuit  509  has a sustain pulse generation circuit  5109 , a reset waveform generation circuit  52 , and a scanning pulse generation circuit  53 . 
     When there is no need to apply negative voltage at the time of generating the reset waveform and no constant-voltage power supply with negative potential is used for the reset waveform generation circuit  52 , as shown in  FIG. 14 , a voltage clamp circuit  91   b  of the sustain pulse generation circuit  5109  may be configured without using the diode D 120  and the switching element S 120  of  FIG. 13 . Even in this configuration, the same effects as described above can be obtained. 
     2-4-2 Modification Example 2 
       FIG. 15  is an illustration that indicates still another example of the configuration of the PDP drive circuit in embodiment 2. The PDP drive circuit shown in  FIG. 15  is equipped with a scan electrode drive circuit  510  and the sustain electrode drive circuit  6 , and the scan electrode drive circuit  510  has a sustain pulse generation circuit  5110 , the reset waveform generation circuit  52 , and the scan pulse generation circuit  53 . 
     As shown in  FIG. 15 , it is possible to have a configuration using a switching element S 102  by MOSFET, etc. same as prior art for the voltage clamp circuit  92   b  of the sustain pulse generation circuit  5110  in place of the diode D 120  and switching element S 120  of  FIG. 13 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 102 , it is possible to switch whether to shut off or pass the current flowing from GND of the voltage clamp circuit  92   b  to the main discharge path. 
     2-4-3 Modification Example 3 
       FIG. 16  is an illustration that indicates still another example of the configuration of the PDP drive circuit in embodiment 2 of the present invention. The PDP drive circuit shown in  FIG. 16  is equipped with a scan electrode drive circuit  511  and the sustain electrode drive circuit  6 , and the scan electrode drive circuit  511  has a sustain pulse generation circuit  5111 , the reset waveform generation circuit  52  and the scan pulse generation circuit  53 . 
     As shown in  FIG. 16 , it is possible to have a configuration using a switching element S 101  by MOSFET, etc. same as prior art for the voltage clamp circuit  93   b  of the sustain pulse generation circuit  5111  in place of the diode D 110  and switching element S 110  of  FIG. 13 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 101 , it is possible to switch whether to shut off or pass the current that flows from the main discharge path to the constant-voltage power supply V 1 . 
     As shown in modification examples 2 and 3, in place of either set of diode D 110  and switching element S 110  or set of diode D 120  and switching element S 120 , the switching element S 101  or S 102 , such as MOSFET, may be used. Even under such configuration, the same effects as described above can be obtained. 
     2-4-4 Modification Example 4 
       FIG. 17  is an illustration that shows still another example of the configuration of PDP drive circuit in embodiment 2 of the present invention. The PDP drive circuit shown in  FIG. 17  is equipped with a scan electrode drive circuit  512  and the sustain electrode drive circuit  6 , and the scan electrode drive circuit  512  has a sustain pulse generation circuit  5112 , the reset waveform generation circuit  52 , and the scan pulse generation circuit  53 . 
     As shown in  FIG. 17 , it is possible to have a configuration in which a switching element S 9 , such as MOSFET, same as prior art is installed on the main discharge path between the sustain pulse generation circuit  5112  and the reset waveform generation circuit  52  in place of the diode D 120  and switching element S 120  of  FIG. 13 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 9 , it is possible to switch whether to shut off or pass the current flowing from GND of the voltage clamp circuit to the main discharge path. 
     2-4-5 Modification Example 5 
       FIG. 18  is an illustration that indicates still another example of the configuration of PDP drive circuit in embodiment 2 of the present invention. The PDP drive circuit shown in  FIG. 18  is equipped with a scan electrode drive circuit  513  and the sustain electrode drive circuit  6 , and the scan electrode drive circuit  513  has a sustain pulse generation circuit  5113 , the reset waveform generation circuit  52  and the scan pulse generation circuit  53 . 
     As shown in  FIG. 18 , it is possible to have a configuration in which a switching element S 10 , such as MOSFET, same as prior art is installed on the main discharge path between the sustain pulse generation circuit  5113  and the reset waveform generation circuit  52  in place of the diode D 110  and switching element S 110  of  FIG. 13 . Under this configuration, by changing over OFF from ON and vice versa of the switching element S 10 , it is possible to switch whether to shut off or pass the current that flows from the main discharge path to the constant-voltage power supply V 1 . In this way, in place of either set of diode D 110  and switching element S 110  or set of diode D 120  and switching element S 120 , a switching element using MOSFET, etc. may be installed on the main discharge path between the sustain pulse generation circuit  5112  or  5113  and the reset waveform generation circuit  52 . 
     2-4-6 Modification Example 6 
     In the present embodiment, an example in which a coil for LC-resonance in the power recovery circuit is configured by the coil L 1  only as shown in  FIG. 13  through  FIG. 18 , but the present invention shall not be limited to this configuration only. For example, in order to change resonance frequency, etc. at the time of electric power recovery and at the reuse, two coils may be used for the power recovery circuit, under which the same effects can be obtained.  FIG. 19  is an illustration that indicates still another example of the configuration of the PDP drive circuit in embodiment 2. What differs in configuration shown in  FIG. 19  from the configuration shown in  FIG. 13  is that two coils including the coil L 1 A and coil LIB, are used for the coil for LC-resonance in the power recovery circuit of the sustain pulse generation circuit  5114  in the scan electrode drive circuit  514 , the coil L 1 B is used at the time of electric power recovery and the coil L 1 A is used at the time of reusing electric power. For example, even when the power recovery circuit is configured in this way, the same effects as described above can be obtained. In  FIG. 19 , a configuration in which the coil L 1 A of the power recovery circuit is connected to the cathode side of the diode D 11  and the coil L 1 B is connected to the anode side of the diode D 12  is shown. However, for example, a configuration in which the coil L 1 A is connected to the anode side of the diode D 11  or the coil LIB is connected to the cathode side of the diode D 12  may be adopted. In addition, in configurations shown in  FIG. 14  through  FIG. 18 , too, the configuration of the power recovery circuits shown in  FIG. 19  and  FIGS. 20A and 20B  may be adopted. 
     2-4-7 Modification Example 7 
       FIGS. 20A and 20B  are figures that show another configuration examples of the power recovery circuit. The power recovery circuit shown in  FIG. 20A  has switching circuits Q 1  and Q 2  used in place of switching elements S 1  and S 2  in configurations of power recovery circuits of  FIG. 13  through  FIG. 18 . The switching circuit Q 1  is a parallel circuit of the switching element Q 11  and diode Q 12 . The switching circuit Q 2  is a parallel circuit of the switching element Q 21  and diode Q 22 . The diode D 1  and diode Q 12  as well as the diode D 2  and diode Q 22  are back-to-back connected, respectively. Switching elements Q 11  and Q 21  are configured with MOSFET, IGBT, etc., and are properly selected in accord with specifications such as withstand voltage. 
     In addition, the power recovery circuit shown in  FIG. 20B  is a configuration in which two coils are used as is the case of  FIG. 19 . For the power recovery circuit shown in  FIG. 20B , in the configuration of  FIG. 19 , switching circuits Q 1  and Q 2  composed of a parallel circuit of a switching element and a diode are used, respectively, in place of switching elements S 1  and S 2 . 
     In  FIGS. 20A and 20B , both series circuit of diode D 110  and switching element S 110  and series circuit of diode D 120  and switching element S 120  are shown. However, the series circuit of diode D 110  and switching element S 110  is required when the Vset separation switch is formed with diodes, while the series circuit of diode D 120  and switching element S 120  is required only when the Vad separation switch is formed with diodes. That is, as shown in  FIG. 17 , where the diode D 12  is not provided as the Vad separation switch, in  FIGS. 20A and 20B , the series circuit of diode D 120  and switching element S 120  is no longer required. In addition, as in the case of  FIG. 18 , where the diode D 1  is not provided as the Vset separation switch, in  FIGS. 20A and 20B , the series circuit of diode D 110  and switching element S 110  is no longer required. 
     In the drive waveform desired by PDP  10  in embodiment 1 and embodiment 2 of the present invention, when the potential of the address period is equal to and less than 0 (V) and the first potential of the sustain period is 0 (V) is shown. But it is needless to say that the switching elements S 12  and S 120 , and diode D 12  will not be required when the drive waveform desired by the PDP  10  is equal to or higher than 0 (V) and the first potential in the sustain period is 0 (V). 
     Embodiment 3 
     In the present embodiment and the following embodiments, various variations will be described with respect to connection position of sustain switches, separation switches, and power recovery circuits. 
       FIG. 21A  is an illustration that indicates one example of circuit topology in a PDP drive circuit. In the figure, a sustain switch, a separation switch, and a power recovery circuit are suitably disposed at either of blocks A through L, respectively. A block to which nothing is disposed is regarded as a simple connection node. In  FIG. 21A , the circuit composed of the power supply V 4 , the diode D 31 , the capacitor  31 , and switching elements S 31  and S 32  in the scan pulse generation circuit  53  shown in  FIG. 1 , etc. is omitted for convenience of explanation, but the circuit should be connected to the scan IC (IC 31 ) in the connection relationship same as  FIG. 1 , etc. in  FIG. 21A , too. 
     The sustain switch contains a high-side sustain switch disposed on the high voltage side and a low-side sustain switch disposed on the low-voltage side. The high-side sustain switch is a switch to supply the sustain voltage Vsus and corresponds to the switch S 5  in the above-mentioned embodiments. The low-side sustain switch is a switch to supply ground potential and corresponds to the switch S 6  in the above-mentioned embodiments. 
     The separation switch includes a Vset separation switch and a Vad separation switch. The Vset separation switch corresponds to the diode D 11 , switching element S 10  or switching element S 101 . In particular, in the case of embodiment 1, a switching element  11  is connected to the diode D 11  in parallel. The Vad separation switch corresponds to the diode D 12 , switching element S 9  or switching element S 102 . In particular, in the case of embodiment 1, a switching element S 12  is connected to the diode D 12  in parallel. 
     The power recovery circuit includes a low-side power recovery circuit which recovers electric power from the PDP  10  to the recovery capacitor C 1  and a high-side power recovery circuit which supplies the recovered electric power from recovery capacitor C 1  to the PDP  10 . These specific configurations are shown as per  FIGS. 1 ,  10 ,  11 ,  13 ,  19 ,  20 , etc. 
     For example, the low-side power recovery circuit corresponds to a circuit that includes the recovery capacitor C 1 , diode D 2 , switching element S 2 , and coil L 1  in, for example,  FIG. 1 , etc. of embodiment 1. In  FIG. 10 , it corresponds to a circuit that includes the recovery capacitor C 1 , switch S 2 , diode D 2 , and coil L 1 B. In addition, in  FIG. 13 , etc. of embodiment 2, the low-side power recovery circuit corresponds to a circuit that includes the recovery capacitor C 1 , diode D 2 , switching element S 2 , and coil L 1 , as well as the diode D 120  and switching element S 120 . 
     The high-side power recovery circuit corresponds to a circuit that includes the recovery capacitor C 1 , diode D 1 , switching element S 1 , and coil L 1  in, for example,  FIG. 1 , etc. of embodiment 1. In addition, in  FIG. 10 , it corresponds to a circuit that includes the recovery capacitor C 1 , switch S 1 , diode D 1 , and coil L 1 A. In addition, in  FIG. 13 , etc. of embodiment 2, the high-side power recovery circuit corresponds to a circuit that includes the recovery capacitor C 1 , diode D 1 , switching element S 1 , and coil L 1 , as well as the diode D 110  and switching element S 110 . 
     In  FIG. 21A , a block  90  is a circuit block that supplies positive voltage Vsus in the reset period and corresponds to a circuit that includes the constant-voltage power supply V 2  and switching element S 21  in  FIG. 1 , etc. A block  91  is a circuit block that supplied negative voltage Vad in the reset period and corresponds to a circuit that includes the constant-voltage power supply V 3  and switching element S 22  in  FIG. 1 , etc. 
     A scan IC (IC 31 ) has a configuration as shown in  FIG. 21B , and is a circuit which has series circuits of high-voltage side switches and low-voltage side switches are connected in parallel in the number equivalent to that of scan electrodes. High-voltage side ends of high-voltage side switches are connected to the high-voltage side input terminal P 1  in common. Low-voltage side ends of each low-voltage side switch are all connected to low-voltage-side input terminal P 2  in common. 
     In the example of  FIG. 21A , the high-voltage side input terminal P 1  of the scan IC (IC 31 ) is connected to the block  90  which supplies voltage Vsus and the low-voltage side input terminal P 2  of the low-voltage side switch is connected to the block  91  that supplies voltage Vad. In addition, the output of the sustain pulse generation circuit is connected to the low-voltage side input terminal P 2  of the scan IC (IC 31 ). That is, during the sustain period, current is supplied to the PDP  10  via the low-voltage side input terminal P 2  of scan IC (IC 31 ) or current from the PDP  10  is drawn. 
     In the circuit topology as shown in  FIG. 21A , variations with the following arrangements could be considered. 
     3-1 Pattern  1   
     In this pattern, a high-side sustain switch is arranged in block A, a low-side sustain switch is arranged in block D, a Vset separation switch is arranged in block B, and a Vad separation switch is arranged in block C, respectively. The high-side power recovery circuit is arranged to either one of blocks G, H, I, and L, and the low-side power recovery circuit is arranged in either one of blocks G, H, I, and L, too. 
     In the present pattern, the Vset separation circuit and the Vad separation circuit can be configured with diodes thereby resulting in an effect that the mounting area can be reduced. 
     3-2 Pattern  2   
     In this pattern, the high-side sustain switch is arranged in block A, the low-side sustain switch in block C, the Vset separation switch in block B, and the Vad separation switch in block D, respectively. The high-side power recovery circuit is arranged in either one of blocks G, H, and L, and the low-side power recovery circuit is arranged in either one of blocks G, H, and L, too. 
     In the present pattern, the Vset separation circuit and the Vad separation circuit can be configured with diodes, thereby resulting in an effect that the mounting area can be reduced. 
     3-3 Pattern  3   
     In this pattern, the high-side sustain switch is arranged in block B, the low-side sustain switch in block D, the Vset separation switch in block A, and the Vad separation switch in block F, respectively. Since in such event, the Vad separation switch is inserted in the main discharge path, the Vad separation switch is unable to be configured with a diode which allows the current to flow in one direction only. The Vad separation switch must be configured with a switching element, such as MOSFET, which allows the current to flow in bi-directions and can control the conduction. 
     The high-side power recovery circuit is arranged in any of blocks H, K, and L, and the low-side power recovery circuit is arranged in any of blocks H, K, and L. 
     In the present pattern, the Vset separation circuit can be configured with a diode. 
     3-4 Pattern  4   
     In this pattern, the high-side sustain switch is arranged in block B, the low-side sustain switch in block D, the Vset separation switch in block A, and the Vad separation switch in block C, respectively. The high-side power recovery circuit is arranged in either one of blocks H, I, and L, and the low-side power recovery circuit is arranged in either one of blocks H, I, and L, too. 
     In the present pattern, the Vset separation circuit and the Vad separation circuit can be configured with a diode, thereby resulting in an effect that the mounting area can be reduced. 
     3-5 Pattern  5   
     In this pattern, the high-side sustain switch is arranged in block B, the low-side sustain switch in block C, the Vset separation switch in block A, and the Vad separation switch in block D, respectively. The high-side power recovery circuit is arranged in either one of blocks H and L, and the low-side power recovery circuit is arranged in either one of blocks H or L, too. 
     In the present pattern, the Vset separation circuit and the Vad separation circuit can be configured with a diode thereby resulting in an effect that the mounting area can be reduced. 
     3-6 Pattern  6   
     In this pattern, the high-side sustain switch is arranged in block A, the low-side sustain switch in block D, the Vset separation switch in block E, and the Vad separation switch in block C, respectively. Since in such event, the Vset separation switch is inserted in the main discharge path, the Vset separation switch is unable to be configured with a diode which allows the current to flow in one direction only. It must be configured with a switching element, such as MOSFET, which allows current to flow in bi-directions and can control the conduction. 
     The high-side power recovery circuit is arranged in any of blocks H, I, J, and L, and the low-side power recovery circuit is arranged in any of blocks H, I, J, and L, too. 
     In the present pattern, the Vad separation circuit can be configured with a diode. The Vset separation circuit must be configured with a switching element. 
     3-7 Pattern  7   
     In this pattern, the high-side sustain switch is arranged in block A, the low-side sustain switch in block C, the Vset separation switch in block E, and the Vad separation switch in block D, respectively. Since in such event, the Vset separation switch may be inserted in the main discharge path, the Vset separation switch is unable to be configured with a diode which allows the current to flow in one direction only. It must be configured with a switching element, such as MOSFET, which allows the current to flow in bi-directions and can control the conduction. 
     The high-side power recovery circuit is arranged in any of blocks H, J, and L, and the low-side power recovery circuit is arranged in any of blocks H, J, and L, too. 
     In the present pattern, the Vad separation circuit can be configured with diodes. The Vset separation circuit must be configured with a switching element. 
     3-8 Pattern  8   
     In this pattern, the high-side sustain switch is arranged in block A, the low-side sustain switch in block D, the Vset separation switch in block B, and the Vad separation switch in block F, respectively. Since in such event, the Vad separation switch is inserted in the main discharge path, the Vad separation switch is unable to be configured with a diode which allows the current to flow in one direction only. It must be configured with a switching element, such as MOSFET, which allows the current to flow in bi-directions and can control the conduction. 
     The high-side power recovery circuit is arranged in any of blocks G, H, K, and L, and the low-side power recovery circuit is arranged in any of blocks G, H, K and L, too. In the present pattern, the Vset separation circuit can be configured with a diode. The Vad separation circuit must be configured with a switching element. 
     As one example of the pattern, the switching element S 5  is arranged in block A, diode D 11  and the switching element S 11  connected to it in parallel in block B, a switching element S 6  in block D, a switching element S 9  in block F, the high-side power recovery circuit in block G, and the low-side power recovery circuit in block H. 
     3-9 Effects 
     Even when the positive peak voltage Vset of the reset period is applied to PDP  10  in the pattern  1  through pattern  8 , voltage applied to the Vset separation switch rises upto the voltage obtained by subtracting address voltage (Vscn) from voltage Vset at most, and thus the withstand voltage of the separation switch can be reduced. In addition, since the discharge current does not flow in either the Vset separation circuit or the Vad separation circuit, circuit loss can be reduced. 
     In addition, in  FIG. 21A , the block  90  that supplies voltage Vsus is connected to the high-voltage side input end of scan IC (IC 31 ). However, similar to the block  91  which supplies voltage Vad, it may be connected to the low-voltage side input end of the scan IC (IC 31 ) (in such event, the configuration of  FIG. 1 , etc. is obtained). In such event, of the above-mentioned combinations, the combination in which the power recovery circuit is disposed to block L is eliminated. 
     In the above-mentioned patters  1  through  8 , the following effects are obtained in accordance with the location of the power recovery circuit. By disposing the power recovery circuit in blocks G or I, withstand voltage of the diode of the high side power recovery circuit or the switch of the low side power recovery circuit can be lowered. In addition, by disposing the power recovery circuit to block H, K or L, the recovery current does not pass the separation circuit, and consequently, loss in separation circuit loss can be reduced and as a result, the recovery efficiency can be improved. 
     In short, when the separation circuit is not disposed between a block to which the power recovery circuit is disposed and the PDP  10  (for example, when the power recovery circuit is disposed in block K or L), the recovered current does not pass the separation circuit, and consequently, loss in separation circuit can be reduced, and as a result, the recovery efficiency can be improved (this effect is called the “current advantage”). In addition, when the block in which the power recovery circuit is arranged is disposed on the PDP side with respect to the block in which the separation circuit is disposed (for example, when the power recovery circuit is disposed at block G, H, or I), the electric power recover circuit is applied with the sustain voltage Vsus at a maximum, and thus the withstand voltage of a diode or a switch contained in the power recovery circuit can be reduced (this effect is called the “voltage advantage”). The foregoing points are the same in the following embodiments. For example, the optimum drive conditions require high initialization voltages (Vset, Vad), a configuration with priority given to the voltage advantage is suited. When the panel capacity is large and the electric power to be recovered is high (recovery current is large) and/or when time allowed for recovery is short (when a recovery circuit is large), a configuration with priority given to the current advantage is suited. The size of the recovery current depends on the product among sustain voltage, panel capacity, and inverse of rise or fall time of sustain voltage. 
     Embodiment 4 
       FIG. 22  is an illustration that indicates another example of circuit topology in the PDP drive circuit. 
     In the example of  FIG. 22 , the high-voltage side input terminal P 1  of the scan IC (IC 31 ) is connected to block  90  which supplies voltage Vsus and the low-voltage side input terminal P 2  of the low-voltage side switch is connected to block  91  that supplies voltage Vad. In addition, the high-voltage side output (Vsus) of the sustain pulse generation circuit is connected to the high-voltage side input terminal P 1  of scan IC (IC 31 ) and the low-voltage side output (ground) is connected to the low-voltage side input terminal P 2 . That is, during the sustain period, current is supplied to the PDP  10  via the high-voltage side input terminal P 1  of the scan IC (IC 31 ) and current from the PDP  10  is swept via the low-voltage side input terminal P 2 . 
     In the circuit topology as shown in  FIG. 22 , variations with the following arrangements could be considered. 
     4-1 Pattern  1   
     In this pattern, a high-side sustain switch is arranged in block A, a low-side sustain switch is arranged in block D, a Vset separation switch is arranged in block B, and a Vad separation switch is arranged in block C, respectively. The high-side power recovery circuit is arranged in either one of blocks E, F, G or H, and the low-side power recovery circuit is arranged to either one of blocks E, F, G or H, too. 
     4-2 Pattern  2   
     In this pattern, the high-side sustain switch is arranged in block B, the low-side sustain switch in block D, the Vset separation switch to block A, and the Vad separation switch in block C, respectively. The high-side power recovery circuit is arranged in either one of blocks F, G, or H, and the low-side power recovery circuit is arranged in either one of blocks F, G, or H, too. 
     4-3 Pattern  3   
     In this pattern, the high-side sustain switch is arranged in block A, the low-side sustain switch in block C, the Vset separation switch in block B, and the Vad separation switch in block D, respectively. The high-side power recovery circuit is arranged in any of blocks E, G, and H, and the low-side power recovery circuit is arranged in any of blocks E, G, and H, too. 
     4-4 Pattern  4   
     In this pattern, the high-side sustain switch is arranged in block B, the low-side sustain switch in block C, the Vset separation switch in block A, and the Vad separation switch in block D, respectively. The high-side power recovery circuit is arranged in block G or H, and the low-side power recovery circuit is arranged in block G or H. 
     In the above-mentioned patterns  1  through  4 , the Vset separation circuit and the Vad separation circuit can be configured with a diode thereby resulting in an effect that the packaging area can be reduced. In addition, since the discharge current does not flow in either the Vset separation circuit nor the Vad separation circuit, circuit loss can be reduced. 
     Embodiment 5 
       FIG. 23  is an illustration that indicates another example of circuit topology in the PDP drive circuit. In the example of  FIG. 23 , the high-voltage side input terminal P 1  of the scan IC (IC 31 ) is connected to block  90  which supplies voltage Vset and the low-voltage side input terminal P 2  of the low-voltage side switch is connected to block  91  that supplies voltage Vad. In addition, the high-voltage side output (Vsus) of the sustain pulse generation circuit is connected to the low-voltage side input terminal P 2  of the scan IC (IC 31 ) and the low-voltage side output (ground) is connected to the high-voltage side input terminal P 1 . That is, during the sustain period, current is supplied to the PDP  10  via the low-voltage side input terminal P 2  of scan IC (IC 31 ) and current from the PDP  10  is swept via the high-voltage side input terminal P 1 . 
     In the circuit topology as shown in  FIG. 23 , variations with the following arrangements could be considered. 
     5-1 Pattern  1   
     In this pattern, a high-side sustain switch is arranged in block D, a low-side sustain switch is arranged in block A, and a Vset separation switch is arranged in block C, respectively. No Vad separation circuit is disposed. The high-side power recovery circuit is arranged in either one of blocks E, F, or H and the low-side power recovery circuit is arranged in either one of blocks E, F, or H, too. 
     5-2 Pattern  2   
     The high-side sustain switch is arranged in block C, the low-side sustain switch in block A, and the Vset separation switch in block D, respectively. No Vad separation circuit is disposed. The high-side power recovery circuit is arranged in either one of blocks E or H, and the low-side power recovery circuit is arranged to either one of blocks E or H, too. 
     Because in the above patterns  1  and  2 , the drain voltage of the low-side sustain switch is kept positive even when the negative peak voltage Vad is applied during the reset period, no Vad separation circuit is required. In such event, the high-side switch of scan IC serves a function of the separation switch. However, this is effective to a case where voltage V 4  which is used for selecting discharge of the scan IC (on address operation) is larger than voltage Vad. 
     Embodiment 6 
       FIG. 24  is an illustration that indicates another example of circuit topology in the PDP drive circuit. 
     In the example of  FIG. 24 , the high-voltage side input terminal P 1  of the scan IC (IC 31 ) is connected to block  90  which supplies voltage Vsus and the low-voltage side input terminal P 2  of the low-voltage side switch is connected to block  91  that supplies voltage Vad. In addition, the output of the sustain pulse generation circuit is connected to the high-voltage side input terminal P 1  of the scan IC (IC 31 ). That is, during the sustain period, current is supplied to the PDP  10  or current from the PDP  10  is drawn, via the high-voltage side input terminal P 1  of the scan IC (IC 31 ). 
     In the circuit topology as shown in  FIG. 24 , variations with the following arrangements could be considered. 
     6-1 Pattern  1   
     A high-side sustain switch is arranged in block A, a low-side sustain switch is arranged in block D, and a Vset separation switch is arranged in block B, respectively. No Vad separation circuit is disposed. The high-side power recovery circuit is arranged in either one of blocks E, F, or H and the low-side power recovery circuit is arranged in either one of blocks E, F, and H, too. 
     6-2 Pattern  2   
     In this pattern, the high-side sustain switch is arranged in block B, the low-side sustain switch in block D, and the Vset separation switch in block A, respectively. No Vad separation circuit is disposed. The high-side power recovery circuit is arranged in either one of blocks F and H and at the same time, the low-side power recovery circuit is arranged in either one of blocks F and H, too. 
     Because in the above patterns  1  and  2 , the drain voltage of the low-side sustain switch is kept positive even when the negative peak voltage Vad is applied during the reset period, no Vad separation circuit is required. In such event, the high-side switch of the scan IC serves a function of the separation switch. 
     The present invention has been described on specific embodiments, but for those skilled in the art, other many modification examples, corrections, and other uses are apparent. Consequently, it is to be understood that the invention is not limited to the specific disclosures herein except as defined in the appended claims. 
     The present application is related to Japanese Patent Application No. 2005-149045 (filed on May 23, 2005), of which content is incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     The present invention is useful to a PDP drive circuit and a plasma display apparatus including an electric recovery circuit and capable of reducing invalid power consumption by reducing impedance in the main discharge path, and particularly to those capable of reducing the number of elements that compose the drive circuit to reduce the mounting area and generating drive waveforms with little strain.