JPS6346434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display device, and particularly to a display device using a plasma display panel.

A plasma display panel consists of two sets of electrodes arranged in a matrix, facing each other with a dischargeable gas medium in between.The surface of each electrode in contact with the gas medium is covered with a dielectric layer, and the externally applied voltage is is configured to couple with a gas medium via a capacitor. Therefore, in order to cause a desired gas cell to discharge and emit light, an AC voltage is applied between a pair of opposing electrodes that narrow the gas cell and intersect with each other.
Each time the polarity of the applied voltage changes, the cell intermittently discharges once and emits light.

In order to drive this type of plasma display panel in a time-sharing manner, first, a voltage pulse train consisting of a plurality of pulses is sequentially applied to each electrode of a group of electrodes in either rows or columns facing each other. It is applied sequentially and scanned at a repetition rate of about 60 times or more per second.

When a voltage pulse train is applied to one particular electrode among these electrodes, that is, when it is in a selected state,
Among the rows of gas cells determined by this electrode, a pulse train with an opposite phase to the above pulse train is applied to all the other opposing electrodes that determine which cells are to be emitted according to the display data content to select them. By setting this state, only desired cells can be caused to discharge and emit light. By repeating the above operation each time each electrode in the former electrode group is scanned one by one, the desired display will appear on the entire screen.

Now, if the number of repetitions of scanning is R times per second and the number of pulses assigned to each electrode in one scan is a, then the number of pulses applied to the cell to discharge light is Ra per second. As mentioned above, the gas cell discharges and emits light every time the polarity of the applied voltage changes, so one pulse voltage causes two discharges, and therefore 2Ra times per second. In order to obtain a luminance that is of a practical level, it is necessary to perform discharges approximately 50 times or more per second.

On the other hand, when the number of electrodes to be scanned is n, in order to cause the gas cell to discharge 2Ra times per second, the repetition frequency of the voltage pulse is nRa (Hz). In order to put the panel into practical use, the frequency nRa must be
is nRa=n・2Ra/2=120×5000/2=300 (KHz).

Currently, plasma display panels for character displays, which have a display capacity of about 12 lines with 40 characters per line, have approximately 5 x 7 dot matrices for each character, and the number of column electrodes (X electrodes) is approximately
Consists of 200 electrodes and approximately 120 row electrodes (Y electrodes).
Its total capacitance between opposing electrodes ranges from 1000 to 2000 picofuaratu. Further, the capacitance between two adjacent electrodes of a column or row electrode group is also 20 to 40 picofarad.
When driving this plasma display panel,
As mentioned above, between opposing electrodes and adjacent electrodes,
Although a pulse voltage of 300 KHz or more is applied, the impedance of the interelectrode capacitance at this frequency is quite low. Further, the discharge starting voltage of a plasma display panel is 100 to 120 volts, and the amplitude of the pulse voltage for driving it is required to be about 150 volts. Therefore, the high voltage pulse voltage is applied to a low impedance load, and the power loss flowing out from the pulse voltage source is relatively large. At maximum load, the power loss will be 20 watts.

By the way, in the practical use of display devices, it is extremely rare for characters or symbols to be displayed in the entire area of the display screen, and it is normal for the characters or symbols to be displayed in at most 50 to 60% of the area.

In this type of display device, it is important to design the power supply in order to cope with the extremely rare maximum load.
I have to say it's extremely wasteful.

An object of the present invention is to provide an apparatus that can drive a plasma display panel having a large display capacity even with a small-scale power supply unit. Furthermore, it is another object of the present invention to provide a very compact display device that suppresses power loss, that is, internal heat generation even when displaying a full screen, and thus takes advantage of the characteristics of a panel-shaped display device.

The present invention provides a plasma display panel having a plurality of row and column electrodes, a plurality of row and column drivers that respectively excite the row and column electrodes according to row and column selection signals, and two row and column drivers having opposite phases to each other. In a display device consisting of a high-voltage, high-frequency oscillator circuit that supplies high-voltage, high-frequency pulses of each phase, and a power supply unit that supplies power to the circuit,
This objective was achieved by installing a current sensor in the middle of the power supply line from the power supply unit to the high-voltage, high-frequency oscillation circuit, and configuring the oscillation frequency of the high-voltage, high-frequency oscillation circuit to be varied by the output of the current sensor.

FIG. 1 is a block diagram showing an embodiment of the present invention.

First, a power supply line from a power supply unit 1 is connected to a high voltage high frequency oscillation circuit 3 via a sensor 2. The high-voltage, high-frequency oscillation circuit 3 includes a circuit that oscillates two-phase pulses having opposite phases to each other, and two power amplifier circuits that increase the amplitude of these two-phase pulses to a level sufficient to control the lighting of a plasma display panel. The high voltage, high frequency pulse outputs of the two power amplifier circuits are given to the row driver 5 and the column driver 7, respectively. The row driver 5 is
According to the information from the row selection signal source 4, the high voltage high frequency pulse is delivered to the row electrode to be selected on the plasma display panel 8 to excite it. Similarly, the column driver 7 follows the information from the column selection signal source 6 and
A high-voltage, high-frequency pulse having a phase opposite to that of the row electrode is delivered to the selected column electrode of the plasma display panel 8, and excited. Then, the gas cells located at the intersections of the excited row electrodes and the excited column electrodes discharge and emit light, thereby producing a display.

By the way, in this embodiment, the sense information of the sensor 2 is transmitted to the high voltage high frequency oscillation circuit 3 via the signal line 9.
given to. The sensor 2 is configured to detect the amount of current flowing out from the power supply unit 1 and control the oscillation frequency of the high voltage high frequency oscillation circuit 3.
One specific example is shown in FIG.

Referring to FIG. 2, the sensor is composed of a resistor 11 inserted in series with the power supply line 10 and an amplifier 12 that amplifies the amount of voltage drop caused by the resistor 11. Note that the amplifier 12 is an inverting amplifier in which the larger the voltage drop across the resistor 11, the smaller the amplifier output. On the other hand, the oscillation frequency of the high voltage high frequency oscillation circuit is determined by the resistor 13.
However, since the output voltage of the amplifier 12 is applied to the resistor 13, the charging time of the capacitor 14 changes depending on the output voltage of the amplifier 12, and as a result, the oscillation frequency is variable. be forced to do so. In FIG. 2, a resistor 15 and a capacitor 16 are used to adjust the response time of the oscillation frequency change.

According to the configuration described above, as the number of characters displayed on the plasma display panel 8 increases, the load on the high voltage high frequency oscillation circuit 3 increases, and therefore the current supplied from the power supply unit 1 to the high voltage high frequency oscillation circuit 3 increases. Therefore, the amount of voltage drop across the resistor 11 increases. The effect appears as a reduction in the oscillation frequency of the high-voltage high-frequency oscillation circuit 3, and since the plasma display panel 8 exhibits capacitive load characteristics as described above, the load current decreases. This operation is a type of constant current control operation.

In this way, according to this embodiment, even when the number of displayed characters increases, it is possible to suppress the increase in power loss in the display device, and this achieves the initial objective of reducing the scale of the power supply unit and reducing the amount of heat generated by the device. can be achieved.

Incidentally, in the present invention, since means for reducing the high-voltage, high-frequency pulse frequency is taken to stop the increase in power, the display brightness naturally becomes darker. However, it is extremely rare to display characters in the entire screen area. The display device according to the present invention, whose sensor sensitivity is adjusted to obtain optimal brightness when displaying in the 50 to 60% range, which is the most frequently used area, reduces maximum power consumption to 12 watts, about half of the conventional display device. It became possible to reduce the In the above explanation, the matrix type was taken as an example, but the present invention can also be applied to segment type display.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a circuit diagram showing one specific example for controlling the oscillation frequency shown in FIG.

Claims (1)

[Claims] 1. A display device comprising a plasma display panel including a plurality of opposing electrodes, a high-voltage, high-frequency oscillation circuit that supplies high-voltage, high-frequency pulses to the electrodes, and a power supply unit that supplies power to the oscillation circuit, in which the A display using a plasma display panel, characterized in that a current sensor is provided in the middle of a power supply line to a high-voltage, high-frequency oscillation circuit, and the oscillation frequency of the high-voltage, high-frequency oscillation circuit can be varied by the output of the current sensor. Device.