Abstract:
A plasma display apparatus with small-sized circuits and of a low cost has been disclosed. The apparatus comprises a display panel, having first electrodes and second electrodes adjacently arranged by turns and third electrodes that extend in the direction intersecting the first electrodes and the second electrodes, opposed to each other so as to sandwich a discharge area therebetween, an X drive circuit that drives the first electrodes, a Y drive circuit that drives the second electrodes, an address drive circuit that drives the third electrodes, and a secondary power supply that uses a pulse relating to the drive signal generated in the X drive circuit or the Y drive circuit.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a plasma display (PDP) apparatus. More particularly, the present invention relates to a power supply circuit that generates voltages other than those supplied from the outside of the PDP apparatus. 
     The PDP apparatus has been put to practical use as a plane display, and it is expected that it will be used as a thin high-intensity display. FIG. 1 is a diagram that shows the general structure of a conventional three-electrode AC-driven PDP apparatus. As shown schematically, the PDP apparatus comprises a plasma display panel (PDP)  1  composed of two substrates, between which a discharge gas is enclosed, having plural X electrodes and Y electrodes adjacently arranged by turns with plural address electrodes arranged in the direction intersecting thereto and fluorescent substances arranged at the intersecting points, an address drive circuit  2  that applies such as an address pulse to the address electrode, an X common drive circuit  3  that applies such as a sustain discharge (sustain) pulse to the X electrode, a Vx voltage supply circuit  4  that supplies a voltage Vx, which will be described later, to the X common drive circuit  3 , a scan circuit  5  that sequentially applies such as a scan pulse to the Y electrode, a Y drive circuit  6  that supplies such as a sustain discharge (sustain) pulse, which is to be applied to the Y electrode, to the scan circuit  5 , a reset circuit  7  that supplies a reset voltage Vw, which will be described later, to the Y drive circuit  6 , a control circuit  8  that controls each section, and a power supply circuit  9  that supplies various voltages such as Vs, Vw, Vx, and Va to each section. Since the PDP apparatus is widely known, a more detailed description of the whole apparatus is omitted here, but the power supply circuit that relates to the present invention is further described. 
     FIG. 2 illustrates the drive waveforms that show the signals to be applied to each electrode in the PDP apparatus. In the PDP apparatus, a display cell is formed at the intersecting point of a pair of an X electrode and a Y electrode and of an address electrode. The displaying operation is composed of a reset period in which each cell is put into a uniform state, an address period in which a cell to be displayed is selected, and a sustain (sustain discharge) period in which the selected cell is caused to discharge, and a continuous display is attained by the repetition of this series of operations. 
     As shown schematically, in the reset period, a pulse, the maximum voltage of which is Vw, is applied to the Y electrode while the X electrode and the address electrode are being kept to 0 V (ground level) and a discharge is caused to occur in every cell to attain a uniform state. In the address period, in the state in which the voltage Vx is being applied to the X electrode, a scan pulse, the voltage of which changes from the voltage Vs to the ground level, is sequentially applied to the Y electrode. By applying an address pulse of voltage Va to the address electrode of the cell that is made to emit light in synchronization with the scan pulse, a discharge is caused to occur in the cell that is made to emit light and wall charges are formed. In this way, a state in which all the cells correspond to the display data, that is, a state in which wall charges are formed in the cell that is made to emit light and wall charges are not formed in the cell that is not made to emit light, is attained. In the sustain period, in the state in which 0 V is being applied to the address electrode, a sustain pulse of voltage Vs is applied alternately to the X electrode and the Y electrode. (When the sustain pulse is not applied, 0 V is applied.) In the cell in which wall charges are formed, a discharge is caused to occur because the voltage due to the wall charges is added to the Vs, but no discharge is caused to occur in the cell in which wall charges are not formed. 
     FIG. 2 shows only an example, and various modifications of the drive waveforms are proposed. Moreover, the voltages Vs, Vw, Vx, and Va in FIG. 2 are specified adequately according to the structure and the intensity of the light emission of the plasma display panel and, for example, Vs is 150-180 v, Vw is greater than Vs, and Vx is also greater than Vs in the example shown in FIG.  2 . In any case, it is necessary to apply plural high voltages to each electrode in the PDP apparatus, and the power supply circuit  9  supplies each high voltage. Although not shown schematically, the power supply voltage of the control circuit is 5 V (or 3 V) but this voltage is also supplied from the power supply circuit and a description is omitted below because it does not relate directly to the present invention. 
     The power supply circuit  9  generates the above-mentioned high voltages Vs, Vw, Vx, and Va by converting the AC input voltage from AC to DC, or first generates the voltage Vs, which needs a large current capacity, by the conversion from AC to DC, then generates Vw and Vx by converting the generated Vs from DC to DC. Generally, the latter method is employed. The voltage Va (Vx is also included when Vx&lt;Vs), which is less than Vs, can be generated from Vs with the aid of a step-down circuit. In this way, the operation is enabled only by the supply of the AC input voltage generally used as a voltage supplied from the outside. The small sized power supply device appropriate for the use in the PDP has been disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-332401. Moreover, in Japanese Unexamined Patent Publication (Kokai) No. 9-325735, a structure has been disclosed, which can reduce the power consumption due to the application of the sustain pulse between the X electrode and the Y electrode in the sustain period. 
     As described above, the power supply circuit in the PDP apparatus generates Vw and Vx by converting Vs from DC to DC, which has been generated by the conversion from AC to DC, therefore, a DC-to-DC conversion circuit composed of such as an oscillator circuit and a switching device is provided, this causing the circuits to be large in the PDP apparatus. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to reduce both the circuit size and the cost by simplifying the structure of the circuit to generate Vw and Vx. 
     In order to realize the above-mentioned object, the plasma display (PDP) apparatus according to a first aspect of the present invention comprises a secondary power supply that utilizes a pulse relating to the drive signal generated in an X drive circuit that drives a first electrode or in a Y drive circuit that drives a second electrode. By this characteristic, an oscillator circuit, a switching device, and so on, which are conventionally necessary to form the secondary power sources such as the power supply voltages Vw and Vx, can be eliminated, resulting in reductions in circuit size and in cost. 
     The pulse appropriate to be used by the secondary power supply is a pulse relating to the sustain pulse generated in the sustain period. 
     The secondary power supply is structured so as to comprise, for example, a charge-pump circuit that is driven by the above-mentioned pulse and a rectifier circuit that generates a direct current voltage by rectifying the output of the charge-pump circuit. In this case, if a charge-pump circuit equipped with plural stages that enter the output of the preceding stage as the base voltage of the subsequent stage is provided, it is possible to generate a voltage two or more times the voltage of the pulse to be used. 
     In another example of structure of the secondary power supply, a transformer, the primary of which is provided with a pulse, and a rectifier circuit that generates a direct current voltage by rectifying the output of the secondary of the transformer, are provided. 
     Moreover, if a voltage stabilizer circuit that converts the output of the rectifier circuit of the secondary power supply into a fixed voltage is further provided, an arbitrary voltage can be stably obtained. 
     The voltage generated by the secondary power supply generates either the voltage Vx to be applied to the first electrode in the address period or the voltage Vw to be applied to the second electrode in the reset period, or both. 
     As described above, conventionally the power supply voltages Vw and Vx are generally generated from the power supply voltage Vs to be used to generate the sustain pulse. However, the power supply voltage Va to be supplied to the address drive circuit is also generated, and it is possible to use Va as well as Vs to generate the power supply voltages Vw and Vx, and in this case, it is necessary to ensure the reliability of the circuit. The PDP apparatus in the second embodiment of the present invention will realize such a structure. 
     In other words, the plasma display (PDP) apparatus according to a second aspect of the present invention is characterized in that: a second power supply voltage (Va) is supplied to the address drive circuit; the second power supply voltage as well as a first power supply voltage (Vs) is supplied to both the X drive circuit and the Y drive circuit; and a circuit is provided, which passes a current from the path through which the second power supply voltage is supplied to the address drive circuit to the path through which the first power supply voltage is supplied to the X drive circuit and the Y drive circuit when the first power supply voltage is less than the second power supply voltage. 
     The circuit, which passes a current from the path through which the second power supply voltage is supplied to the address drive circuit to the path through which the first power supply voltage is supplied to the X drive circuit and the Y drive circuit, is a protection switch. 
     Normally, Vs&gt;Va, but it may happen that Vs&lt;Va because Va rises prior to Vs due to the sequence of power on in the transition period such as power on and power off. In this case, it can happen that an abnormal current flows to the X drive circuit and the Y drive circuit via circuits that form the secondary power supply, but such an abnormal current can be prevented and a circuit malfunction, and so on, can be avoided according to the second aspect of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a conventional plasma display (PDP) apparatus; 
     FIG. 2 is a diagram that shows the drive waveforms of the PDP apparatus; 
     FIG. 3 is a block diagram of the PDP apparatus in the first embodiment of the present invention; 
     FIG. 4 is a diagram that shows the circuit structure of the drive section on the Y side in the first embodiment; 
     FIG. 5 is a diagram that shows the circuit structure of the drive section on the X side in the first embodiment; 
     FIG. 6 is a diagram that shows the circuit structure (example 1) of the Vw voltage generator circuit in the first embodiment; 
     FIG. 7 is a diagram that shows the circuit structure (example 2) of the Vw voltage generator circuit in the first embodiment; 
     FIG. 8 is a diagram that shows the circuit structure (example 3) of the Vw voltage generator circuit in the first embodiment; 
     FIG. 9 is a diagram that shows the circuit structure (example 4) of the Vw voltage generator circuit in the first embodiment. 
     FIG. 10 is a diagram that shows the circuit structure (example 5) of the Vw voltage generator circuit in the first embodiment; 
     FIG. 11 is a diagram that shows the circuit structure (example 6) of the Vw voltage generator circuit in the first embodiment; 
     FIG. 12 is a diagram that shows the circuit structure of the drive section of the PDP apparatus in the second embodiment of the present invention; 
     FIG. 13 is a diagram that shows the drive waveforms in the sustaining operation in the second embodiment; 
     FIG. 14 is a rough block structure diagram of the PDP apparatus in the third embodiment of the present invention; 
     FIG. 15 is a circuit diagram that shows the Vx voltage generator circuit in the third embodiment; and 
     FIG.  16 A and FIG. 16B are circuit diagrams that show the Va voltage generator circuits in the third embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 is a block diagram that shows the rough structure of the PDP apparatus in the first embodiment of the present invention. It is obvious, from the comparison with FIG. 1, that the conventional PDP apparatus in FIG. 1, differs from that in the first embodiment in that, while the power supply voltages Vx and Vw are generated in the power supply circuit  9  in the conventional PDP apparatus, in the PDP apparatus in the first embodiment, a Vx voltage generator circuit  11  and a Vw voltage generator circuit  12  are provided, which generate the power supply voltages Vx and Vw, respectively, by utilizing the pulse signal relating to the sustain pulses generated in the X drive circuit  3  and the Y drive circuit  6 , respectively, and the voltages Vx and Vw generated thereby are supplied to the voltage supply circuit  4  and the voltage supply circuit  7 , and other parts are identical with those of FIG.  1 . Therefore, the power supply circuit  9  generates only the power supply voltages Vs and Va in the PDP apparatus in the first embodiment. Although the power supply voltages Vs, Va, Vw, and Vx are specified adequately in accordance with the condition of the panel, the following description of embodiments assumes that Va&lt;Vs&lt;Vx&lt;Vw. It is also assumed that the drive waveforms are identical with the conventional ones shown in FIG. 2 in the following description. 
     FIG. 4 is a diagram that shows the circuit structure of the drive section on the Y electrode side. As shown schematically, each scan drive circuit  5 - 1 , . . . ,  5 -N (N stands for the number of Y electrodes) is provided for each Y electrode. The scan drive circuits  5 - 1 , . . . ,  5 -N are connected commonly to two drive power supply lines  15  and  16 . The drive power supply line  15  is connected to a first scan power supply circuit  51 - 1 , a first reset circuit  7 - 1 , and a first Y drive circuit  6 - 1 . Similarly, the drive power supply line  16  is connected to a second scan power supply circuit  51 - 2 , a second reset circuit  72 , and a second Y drive circuit  6 - 2 . The Vw voltage generator circuit  12  is connected to the output section of the first Y drive circuit  6 - 1 . The scan drive circuits  5 - 1 , . . . ,  5 -N and the first and second scan power supply circuits  51 - 1  and  51 - 2  constitute the scan circuit  5  shown in FIG. 3, the first and second Y drive circuits  6 - 1  and  6 - 2  constitute the Y drive circuit  6  shown in FIG. 3, and the first and second reset circuits  7 - 1  and  7 - 2  constitute the reset circuit  7  shown in FIG.  3 . 
     In each scan drive circuit, two transistors are connected in series between the drive power supply lines  15  and  16  and their connection nodes are connected to the Y electrode and, simultaneously, a diode is connected in parallel to each transistor, respectively. The first scan power supply circuit  51 - 1  is a circuit in which a transistor is connected between the drive power supply line  15  and the grounding line (0 V). The second scan power supply circuit  51 - 2  is a circuit in which a transistor is connected between the drive power supply line  16  and the power supply line of the voltage Vs. A pre-drive circuit to drive each transistor is omitted. The first Y drive circuit  6 - 1  comprises a transistor  62 , one end of which is connected to the power supply line of the voltage Vs and the other end is connected to the drive power supply line  15 , via a diode, and a pre-drive circuit  61  that drives the transistor  62  according to a CU control signal. The second Y drive circuit  62  comprises a transistor  64  connected between the grounding line (0 V) and the drive power supply line  15  and a pre-drive circuit  63  that drives the transistor  64  according to a CD control signal. The first reset circuit  7 - 1  comprises a transistor  72  connected between the drive power supply line  15  and the output line of the Vw voltage generator circuit  12  and a pre-drive circuit  71  that drives the transistor  72  according to a reset signal  1 . The reset circuit  7 - 2  comprises a transistor  74  connected between the drive power supply line  16  and the grounding line (0 V) and a pre-drive circuit  73  that drives the transistor  74  according to a reset signal  2 . The operation will be described later. 
     FIG. 5 is a diagram that shows the circuit structure of the drive section on the X electrode side. As shown schematically, the X electrode is connected to the Vx voltage supply circuit  4 , a first X drive circuit  3 - 1 , and a second X drive circuit  3 - 2 . To the first X drive circuit  3 - 1 , the Vx voltage generator circuit  11  is connected. The first and the second X drive circuits  3 - 1  and  3 - 2  constitute the X drive circuit  3  shown in FIG.  3 . The first X drive circuit  3 - 1  comprises a transistor  32 , one end of which is connected to the power supply line of the voltage Vs and the other end, to the X electrode via a diode, and a pre-drive circuit  31  that drives the transistor  32  according to the CU control signal. The second X drive circuit  3 - 2  comprises a transistor  34  connected between the grounding line (0 V) and the X electrode and a pre-drive circuit  33  that drives the transistor  34  according to the CD control signal. The Vx supply circuit  4  comprises a transistor  42  connected between the X electrode and the output line of the Vx voltage generator circuit  11  and a pre-drive circuit  41  that drives the transistor  42  according to a Vx control signal. 
     The operations of the circuits shown in FIG.  4  and FIG. 5 are briefly described here with reference to FIG.  2 . In the reset period, while all the transistors of the first and second scan power supply circuits  51 - 1  and  512 , the first and second Y drive circuits  6 - 1  and  6 - 2 , the first X drive circuit  3 - 1 , and the Vx supply circuit  4  are being kept switched off, the transistor of the second X drive circuit  3 - 2  is turned on and 0 V is applied to the X electrode. At this time, the address drive circuit  2  applies 0 V to each address electrode. In this state, if the transistor  74  of the second reset circuit  7 - 2  is turned off and the transistor  72  of the first reset circuit  7 - 1  is turned on, the voltage Vw is applied to the Y electrode via the diode of each scan drive circuit and the potential of the Y electrode is raised toward the voltage Vw until Vw is reached. Then, if the transistor  72  of the first reset circuit  7 - 1  is turned off and the transistor  74  of the second reset circuit  7 - 2  is turned on, the Y electrode is lowered to 0 V via the diode. In this way, a discharge is caused to occur in all the cells regardless of the previous display status, the generated charges neutralize each other, and all the cells enter a uniform state. 
     In the next address period, while all the transistors of the first and second Y drive circuits  6 - 1  and  6 - 2 , the first and second reset circuits  7 - 1  and  7 - 2 , and the first and second X drive circuits  3 - 1  and  3 - 2  are being kept switched off, the transistor of the Vx supply circuit  4  is turned on and the voltage Vx is applied to the X electrode. Then, the transistors of the first and second scan power supply circuits  51 - 1  and  51 - 2  are turned on and Vs and 0 V are applied to the series of the transistors of the scan drive circuits  5 - 1 , . . . ,  5 -N. In this state, if scan signals are sequentially applied to the series of the transistors of the scan drive circuits  5 - 1 , . . . ,  5 -N, the scan signal of voltage Vs is sequentially applied to the Y electrode. In synchronization with this, the address drive circuit  2  applies Va to the address electrode of a cell to be lit and applies 0 V to the address electrode of a cell not to be lit. 
     In the sustain period, while all the transistors of the first and second scan power supply circuits  51 - 1  and  51 - 2 , the first and second reset circuits  7 - 1  and  7 - 2 , and the Vx supply circuit  4  are being kept switched off, a pair of the transistors of the first X drive circuit  31  and the second Y drive circuit  6 - 2  and that of the second X drive circuit  3 - 2  and the first Y drive circuit  6 - 1  are turned on and off alternately. Practically, the X electrode and the Y electrode are controlled so that both become 0 V simultaneously, but a detailed description is omitted here. 
     Next the Vx voltage generator circuit  11  and the Vw voltage generator circuit  12 , which are the characteristics of the present embodiment, are described, but both circuits are identical as to the way they generate a higher power supply voltage by utilizing the pulse signal relating to the sustain pulse, and can be realized by almost the same circuit structure, therefore, the Vw voltage generator circuit is described as an example and the description of the Vx voltage generator circuit is omitted here. 
     FIG. 6 is a diagram that shows an example of the first structure of the Vw voltage generator circuit. As shown schematically, in this example, the transistor  62  of the first Y drive circuit  6 - 1  is turned on and off according to a CU gate pulse output from the pre-drive circuit  61 , and a voltage pulse VCU that varies between Vs and 0 V is output to the output terminal thereof. Therefore, the voltage pulse VCU is output only in the sustain period during which the CU control signal is output. The voltage pulse VCU is output to the scan circuit via the diode, and simultaneously supplied to the Vw voltage generator circuit  12 . 
     As shown schematically, the Vw voltage generator circuit comprises a capacitor C 1 , to the first terminal of which the voltage pulse VCU is applied, a diode D 1 , the anode of which is connected to the power supply terminal of the voltage Vs and the cathode, to the second terminal of the capacitor C 1 , a diode D 2  the anode of which is connected to the second terminal of the capacitor C 1 , and a capacitor C 2  that is connected between the cathode of the diode D 2  and the grounding line (GND). The capacitor C 1  and the diodes D 1  and D 2  constitute the charge-pump circuit, and the capacitor C 2  constitutes the rectifier circuit. When the voltage pulse VCU is 0 V, 0V is applied to the first terminal of the capacitor C 1 , Vs is applied to the second terminal, and the voltage Vs is held by the capacitor C 1 . In this state, if the voltage pulse VCU changes to Vs, Vs is applied to the first terminal of the capacitor C 1  and, therefore, the held voltage Vs is added to the second terminal and the voltage thereof becomes 2 Vs. In this way, the anode voltage of the diode D 2  varies between Vs and 2 Vs and is output from the cathode. By this, the capacitor C 2  is charged and a voltage of about 2 Vs is held by the capacitor C 2 , if the amount of the voltage Vw to be used is small. 
     As described above, the CU gate pulse is output only in the sustain period, and a voltage of about 2 Vs is held by the capacitor C 2  during the period, therefore, this voltage is supplied to the terminal of the transistor  72  in the first reset circuit  7 - 1  to be used as the power supply of Vw. As a result, the maximum voltage the Y electrode can reach when the output of the Vw generator circuit  12  is actually applied thereto via the first reset circuit  7 - 1  and is determined by the relationship between the capacitance of the additional circuits including the capacitance of the Y electrode and the capacitor C 2  and, therefore, these are adequately set so that a desired Vw can be obtained. 
     As described above, the Vw generator circuit in FIG. 6 uses a signal pulse corresponding to a sustain pulse as an input pulse to the charge-pump circuit, and an oscillator circuit and a switching device, which are necessary for a normal charge-pump circuit, can be omitted and, therefore, the circuit structure can be simplified and reduced in size. Moreover, the sustain pulse to be used has a high voltage to a certain level (about 180 V) and has a large amount of electric current, therefore, it can generate a high voltage Vw. 
     FIG. 7 is a diagram that shows an example of the second structure of the Vw voltage generator circuit. In this example, the part which is composed of capacitors C 4  and C 5  and diodes D 3  and D 4  is the charge-pump circuit same as that shown in FIG. 6, and a voltage of 2 Vs is supplied to the anode of diode D 5 . The part which is composed of capacitors C 3  and C 6 , the diode D 5 , and diode D 6  is also the charge-pump circuit, and a voltage of 2 Vs is supplied to the anode of the diode D 5 , therefore, the voltage to be put out is nearly 3 Vs, which is 2 Vs plus Vs. In this way, an even higher voltage can be obtained by increasing the number of stages of the charge-pump circuit. 
     As described above, a power supply circuit of 2 Vs can be realized by utilizing the power supply voltage Vs, which is the same as that of the sustain pulse, and the charge-pump circuit that uses the sustain pulse, and moreover, a power supply circuit of integer multiples of Vs can be realized by increasing the number of stages of the charge-pump circuit. A required voltage, however, is not always that of integer multiples of Vs, and it may happen that a voltage of 1.5 Vs is required. The example, which will be described below, is an example of a power supply circuit that puts out an intermediate voltage. 
     FIG. 8 is a diagram that shows an example of the third structure of the Vw voltage generator circuit. In this example, a voltage stabilizer circuit  13  is added to the first example in FIG. 6 and a voltage Vw can be obtained arbitrarily between Vs and 2 Vs. The voltage stabilizer circuit  13  comprises a bipolar transistor  81  the collector of which is connected to the capacitor C 2 , an operational amplifier AMP the output of which is connected to base of the transistor  81 , a reference voltage source VREF, a resistor R, and a variable resistor VR. From this circuit, the output voltage Vw expressed as below can be obtained. 
     
       
           Vw=VREF ( VR+R )/ VR.    
       
     
     In the expression, VREF is the value of the reference voltage, VR and R are values of the variable resistor and the resistor, respectively. 
     Therefore, an arbitrary voltage equal to 2 Vs or less can be obtained by adjusting the variable resistor. 
     FIG. 9 is a diagram that shows an example of the fourth structure of the Vw voltage generator circuit. In this example, the voltage stabilizer circuit  13  is added to the second example shown in FIG.  7  and an arbitrary voltage between about 2 Vs and 3 Vs can be obtained as a voltage 2 Vw. A further description is omitted here. 
     FIG. 10 is a diagram that shows an example of the fifth structure of the Vw voltage generator circuit. In this example, a circuit, which is a combination of a voltage ste-up circuit that has a transformer TR and a rectifier circuit, is employed instead of the charge-pump circuit. A voltage is induced on the secondary by applying the voltage pulse VCU, which corresponds to the sustain pulse, to the primary of the transformer TR via a capacitor C 8 . If the number of turns of the secondary winding is increased to a number greater than that of the primary winding, an alternating current with a voltage greater than the voltage pulse VCU can be obtained, therefore, a voltage Vw greater than Vs can be output by rectifying the alternating current by the diode and a capacitor C 9 . 
     FIG. 11 is a diagram that shows an example of the sixth structure of the Vw voltage generator circuit and, in this example, the voltage stabilizer circuit  13  is added to the example of the fifth structure shown in FIG. 10, therefore, a further description is omitted here. 
     The present applicants have disclosed the art to reduce the voltage generated in the PDP apparatus in Japanese Patent Application No.2000-188663. The present invention can be also applied to a PDP apparatus that employs this art and such an example is shown as the second embodiment. 
     FIG. 12 is a diagram that shows the circuit structure in the second embodiment, in which the present invention is applied to the PDP apparatus that employs the voltage reduction drive circuit disclosed in Japanese Patent Application No.2000-188663, and the drive circuits on the X electrode side and the Y electrode side are shown. Since it has been disclosed in Japanese Patent Application No.2000-173056, a detailed description of the entire drive circuit is omitted and only the part relating to the present invention is described here. 
     In this circuit, a pulse of voltage Vs/2 output from the transistor that constitutes switch SW 1  on the X side is used as an input pulse to the Vx voltage generator circuit  11 . Similarly, a pulse of voltage Vs/2 output from the transistor that constitutes switch SW 1 ′ on the Y side is used as an input pulse to the Vw voltage generator circuit  12 . The voltage generator circuit  11  and the Vw voltage generator circuit  12  in this case can be realized by the structures shown as examples in FIG.  6  through FIG.  11 . 
     FIG. 13 shows the waveforms of the sustain pulse to be applied to the X electrode and the Y electrode in the sustain period in the second embodiment, and the above-mentioned Vx voltage generator circuit  11  and the Vw voltage generator circuit  12  generate Vx and Vw from this sustain pulse. 
     FIG. 14 is a block diagram that shows the rough structure of the PDP apparatus in the third embodiment of the present invention. The PDP apparatus in the third embodiment is an example case in which the voltage Vx to be applied to the X electrode in the address period is less than the voltage Va of the address pulse. As is obvious, by comparison with FIG. 3, the structure in the third embodiment differs in that the power supply voltage Va, which is to be supplied from the power supply circuit  9  to the address drive circuit  2 , is applied to the Vx voltage generator circuit  11 , instead of the sustain pulse generated in the X drive circuit  3 , and that a diode D 20  is provided between the supply path of the power supply voltage Va and the supply path of the power supply voltage Vs to the X drive circuit  3 . 
     FIG. 15 is an example of the Vx voltage generator circuit  11  and Vs is generated by stepping down Va, because the voltage Vx is less than the voltage Va. 
     FIG.  16 A and FIG. 16B are examples of the structure of the Va voltage generator circuit in the power supply circuit  9 . In the circuit shown in FIG. 16A, an AC input from the outside is rectified in a rectifier circuit  21  to generate a DC power supply, which is used as the power supply of the transformer. The AC output is induced on the secondary by controlling the transistor on and off, which is provided in the current supply path to the transformer, in an oscillator and control circuit  22 , to cut off the current supply to the transformer. The AC output is then rectified in the rectifier circuit composed of diodes and capacitors to obtain the voltage Va. The output voltage Va is detected in a voltage detection circuit  23  and a fixed voltage can be obtained constantly by controlling the oscillator and control circuit  22  to adjust the duty ratio of the current supply to the transformer based on the detection result. 
     In the circuit shown in FIG. 16B, the transistor is ON-OFF controlled by an oscillator and control circuit  31  to intermittently supply the power supply voltage Vs and the power supply voltage Vs is rectified to generate a desired voltage Va. The output voltage Va is detected in a voltage detection circuit  32  and a fixed voltage can be obtained constantly by controlling the oscillator and control circuit  31  to adjust the duty ratio of the current supply to the transformer based on the detection result. 
     In the circuit shown in FIG. 14, the voltage Vx is less than the voltage Va and the power supply voltage Va is supplied to the Vx voltage generator circuit. In this circuit, normally, Vs&gt;Va, but there is a possibility of Vs&lt;Va because Va rises prior to Vs due to the relation of the power turning on sequence in the transition period such as power on and power off. In this case, there is a possibility of current passing from the power supply circuit  9  through the Vx voltage generator circuit  11  and the voltage Vx supply circuit  4  to damage the transistor Q 1  in the Vx voltage generator circuit  11 . Therefore, in the structure in the third embodiment, the protection diode D 20  is provided, and when Vs&lt;Va, the protection diode  20  turns on to prevent current from passing into the transistor Q 1 . 
     As described above, according to the plasma display apparatus of the present invention, the secondary power supply such as the power supply voltages Vw and Vx is generated using the pulse generated in the X drive circuit or the Y drive circuit, therefore, the oscillator circuit and the switching device, which are conventionally necessary to form these secondary power supplies, can be omitted, resulting in reduction in circuit size and cost. 
     Moreover, in the plasma display apparatus of the present invention, the first power supply voltage Vs is used as the power supply voltage to be supplied to the X drive circuit and the Y drive circuit, and at the same time the power supply voltage Va, which is to be supplied to the address drive circuit, is used as the second power supply voltage. When the first power supply voltage Vs is less than the second power supply voltage Va, a circuit is further provided, which passes current from the supply line of the second power supply voltage Va to that of the first power supply voltage Vs, therefore, in such a case, it is possible to avoid such as malfunctions of the circuit by preventing abnormal current that passes into the X drive circuit or the Y drive circuit via the circuits that constitute the above-mentioned secondary power supply. In this way, the reliability of the circuit is improved.