A plasma display panel (hereafter briefly referred to as a “panel”) is a typical AC type surface discharge panel in which many discharge cells are formed between a front plate and a rear plate that are disposed facing each other. In the front plate, multiple display electrode pairs, each including a pair of a scan electrode and a sustain electrode, are formed in parallel on a front glass substrate. A dielectric layer and a protective layer are formed covering these display electrode pairs. In the rear plate, multiple data electrodes are formed in parallel on a rear glass substrate, and a dielectric layer covers these data electrodes. Then, multiple barrier ribs are formed in parallel to data electrodes. A phosphor layer is formed on the surface of the dielectric layer and the side face of the barrier ribs. Then, the front plate and the rear plate are disposed facing each other such that the display electrode pairs and the data electrodes are disposed orthogonal to each other, and sealed. Discharge gas, for example, containing 5% xenon in partial pressure ratio, is filled in an internal discharge space. A discharge cell is formed at an area where the display electrode pair faces the data electrode. In a panel as configured above, an ultraviolet ray is generated by gas discharge in each discharge cell. This ultraviolet ray excites each phosphor of red (R), green (G), and blue (B) to emit light for color display.
In general, a subfield method is adopted as a panel-driving method. More specifically, one field period is divided into multiple subfields. Grayscale display is achieved by combinations of subfields to emit light.
Each subfield includes an initializing period, address period, and sustain period. In the initializing period, an initializing discharge occurs so as to form a wall charge needed for a subsequent address operation on each electrode. At the same time, priming particles (a detonator for discharge=Excited particles) are generated so as to reliably generate address discharge. In the address period, an address pulse voltage is selectively applied to discharge cells to be displayed. This generates address discharge and forms the wall charge (this operation is hereafter also referred to as “address”). In the sustain period, a sustain pulse voltage is applied alternately to the display electrode pair including the scan electrode and the sustain electrode, so as to generate a sustain discharge in the discharge cells where the address discharge has occurred. This makes phosphor layers of corresponding discharge cells emit light, and thus an image is displayed.
In the above operations, heat is generated in the discharge cells in proportion to the number of discharges. Accordingly, a temperature of the panel itself increases by this heat. In addition, a brighter display image requires more number of discharges. A brighter display image thus results in a higher panel temperature. Furthermore, it is generally known that a discharge characteristic changes depending on the discharge cell temperature in this type of panels. Accordingly, too high panel temperature causes unstable discharge. This risks degradation in the image display quality.
Therefore, diversifying methods have been proposed to prevent degradation in the image display quality that may be caused depending on the panel temperature.
For example, one method disclosed is to attach the panel to a chassis with a heat-conducting sheet made of silicone rubber in between. In this method, the heat generated from the panel is efficiently transferred to the chassis so as to prevent a temperature rise in the panel. (For example, refer to Patent Document 1.)
Another method proposed is to detect the panel temperature and apply diversifying corrections depending on detected temperature. For example, one of plasma display devices disclosed is provided with a panel temperature detector for detecting the panel temperature, and an address pulse period is changed depending on temperature information received from the panel temperature detector so as to stabilize the address operation. (For example, refer to Patent Document 2).
Still another method disclosed is to detect an average picture level (APL) of an input video signal and the panel temperature, and control a picture level of a display image depending on the detected APL and detected temperature. The panel temperature is controlled by controlling power consumption in the panel. (For example, refer to Patent Document 3.)
However, since distribution of the panel temperature is not even over a panel area, the entire display area hardly shows uniform temperature. In addition, the panel temperature greatly changes depending on display images. On the other hand, reduction of the number of components configuring the plasma display device has been strongly demanded. It is thus difficult to increase the number of thermal sensors to be installed.
Accordingly, accurate detection of the panel temperature is difficult in a plasma display device in which the number of thermal sensors that can be installed is limited. Still more, a recent trend of larger panel and larger plasma display device makes accurate detection of the panel temperature more difficult.
Furthermore, in recent years, a brighter display is studied in order to improve the image display quality. In a plasma display device that is configured to increase luminance of light emission by increasing the discharge current, the panel temperature increases further easily.
Accordingly, it is becoming more difficult to maintain an appropriate panel temperature in the recent trend of a larger panel for plasma display devices and higher luminance.
However, the control of panel temperature to an appropriate level is becoming more important in order to display high-grade images. Therefore, a simple structure for keeping an appropriate panel temperature in plasma display devices for larger panel and brighter image is strongly demanded.    Patent Document 1: Japanese Patent Unexamined Publication No. H10-254372    Patent Document 2: Japanese Patent Unexamined Publication No. 2004-61702    Patent Document 3: Japanese Patent Unexamined Publication No. 2000-305514