JPS5836793B2 - Protection circuit for discharge display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Discharge display devices using so-called plasma discharge are already known, and an example thereof will be explained with reference to FIG. 1. In the tube, 1a, 1b, Ic, and 1d are X electrodes, which in this case extend in the lateral direction.

2a, 2b>2c, 2d, 2e are husband Y electrodes,
In this case, the 0, X, and Y electrodes are extended in the vertical direction and are arranged to face each other in a state where they intersect with each other.

3 is a spacer made of an insulating material interposed between both the X and Y electrodes, and 4 is a through hole provided in this spacer 3.

Therefore, discharge at the intersection of the X electrode and the Y electrode occurs through the through hole 4.

5 is a spacer placed behind the X electrode, and 6 is a base glass placed further behind it.

Reference numeral 7 denotes a window glass, the inner surface of which is covered with a black mask, and a transparent portion 8 is formed at a portion corresponding to the intersection of the above-mentioned X electrode and Y electrode. There is.

Therefore, the discharge of both electrodes can be seen from the outside through the transparent portion 8 of the window glass 7.

Note that through holes are also provided in the X and Y electrodes at their respective intersection points.

Furthermore, in this structure, Y electrodes 2a, 2b, 2c...
. . . are sequentially scanned, that is, sequentially grounded in a time-division manner,
Meanwhile, in synchronization with this scanning, X electrodes 1a, 1b, Ic...
. . . by simultaneously selecting one, two or more of them and applying a high voltage thereto, the X electrode to which this high voltage is applied, that is, the selected X electrode and the currently grounded Y electrode. A discharge occurs at each intersection.

Therefore, by synchronizing with the time-divisional grounding or scanning of the Y electrodes 2a, 2b, 2c, etc., and then selecting the X electrode and repeating this process repeatedly, based on this discharge, It is possible to display figures, numbers, characters, etc. as a whole.

In FIG. 1, four X electrodes and five Y electrodes are shown.

Figure 2 shows an example of the display by this device, where the white circles indicate the positions of the intersections between each X electrode and the Y electrode, and the black circles indicate the areas where discharge is occurring at the intersections. It shows.

In addition, in Figure 2, the case where the number 8 and the alphabet A are displayed is shown as 0, and one number or letter is shown as 7.
35 intersections between 1 X electrode and 5 Y electrodes, that is 3
It is displayed using 5 dots.

When displaying characters or numbers, one Y electrode between them is paused to provide an interval between the characters or numbers.

Furthermore, Fig. 2 shows the case where, in addition to the X electrode for displaying such characters, one X electrode is provided below the X electrode, and this is used as an electrode for displaying a cursor. There is.

According to such a discharge display device, a desired number or the like can be displayed by selecting a plurality of X electrodes in synchronization with the scanning of a plurality of Y electrodes and repeating this process as described above.

FIG. 3 shows an example of a drive circuit for such a display tube, and numeral 10 indicates a discharge display tube.

In this example, seven X electrodes are used.

Although only 10 Y electrodes are shown in the figure,
Usually, about 100-odd or several hundred pieces are used.

11 is a cathode drive signal generating circuit for scanning the Y electrode, and includes output terminals 11a, 1lb, 11c...
. . 0 is the switching signal Sa, Sb with different times as shown in Fig. 4 κ, B', C', . . .
, Sc... are obtained.

The time width of the switching signals Sa, Sb, Sc, . . . can be selected to be, for example, 100 μsec.

This switching signal SaySby...... is the switching transistor 1 2 a t 1 2, respectively.
b and 1 2 c, and in a state where these signals are supplied, each transistor 12 a t 1
2b, 1, 2c, . . . are each turned on (conducting), and therefore each collector is configured to be grounded.

Note that each of these transistors 12a, 12b, 12c...
The DC voltage from the power supply terminal 13 to O is applied to the collectors of the terminals 13 through resistors 14a, 14b, 14c, . However, upon arrival of the switching signals 1 2 a , 1 2 b . . . described above, this becomes the ground potential.

Note that the collectors of each of these transistors 12a, 12b, . . . are connected to the above-mentioned Y electrodes, respectively.

Reference numeral 15 denotes an anode drive signal generation circuit, which includes output terminals 15a > 15bt 15c corresponding to the number of X electrodes l a t 1 b . . . 1g.
. . 15g, which are connected to the base of the switching transistor 1 6 a > 1 6 b . . . 16 g.

Output terminal 1 of such anode drive signal generation circuit 15
5a, 15b...15g are the signals Sa, Sb...
For example, in synchronization with..., Fig. 4 A, B, C...
Letters, numbers, figures, etc. shapes or signals Ea, Eb as shown in G
...Eg is obtained.

These signals Ea, Eb...Eg are always at a high voltage, so the transistors 16a, 16b,
...16g is always on (conducting), and in synchronization with the signals Sa, Sb..., any one or more signals are received within the required time. Zero potential 01
During this period, the transistor is turned off (non-conductive).

Note that the period (11 to t2) in which the signal Sa is obtained is set as output 1, and the period in which the signal Sa is not obtained is set as output O.

Signals Sb, Sc..., Ea, Eb...
The same applies to Eg.

Further, the power supply terminal 13 is connected to resistors 17a, 18a, 17b, respectively.
18b117c, 18c...17g, 18g O
Transistors 16a, 16b, 1 through a series circuit of
6C---16g are connected to the collectors, and their emitters are grounded.

Further, a connection point between resistors connected in series, for example 17a and 18a, is connected to the X electrode 1a.

Thereafter, the X electrodes 1b, 1c, . . . , 1g are connected to the connection points of the corresponding resistors in the same manner.

The terminal 13 is supplied with a voltage necessary for starting a discharge between the X electrode and the Y electrode, that is, a voltage higher than the starting voltage, for example, 300 cm, and when the transistor 16a is on, the resistor 1
The resistor 17a is set so that the voltage at the connection point between 7a and 18a is a pre-bias voltage lower than the discharge sustaining voltage, for example, 150 cm.
, 18a are determined.

The same applies to other corresponding parts.

Therefore, these transistors 16a, 16b...16
No discharge occurs in the on state of g.

Now the signal Sa is 1, and in synchronization with this, the signal E a ,
Ed and Eg are each 1, so transistor 1
2a is on, transistors 16a, 16d and 1
6g are off (period t1 to t2 in FIG. 4), the voltage of the tenon terminal 13 is applied to the X electrodes 1a, Id and 1g, and only the Y electrode 2a is grounded, so during this period Then, a discharge will occur at the intersection of the X electrodes 1a, 1d, 1g (!: Y electrode 2a).

Thereafter, the Y electrodes 2b, 2c, etc. are selected as the signals Ea, Eb,...Eg become 1 or O in synchronization with the signals Sb, Sc, Sd... A discharge is generated between the X electrode and the X electrode, and this operation is repeated, thereby displaying numbers, characters, figures, etc. on the display tube 10.

In such a configuration, if the cathode drive signal generation circuit 11 fails for some reason and the scanning operation stops while the signal Sa is obtained at a certain terminal, for example, 11a,
If only the Y electrode 2a is to discharge continuously (that is, direct current ignition), this Y electrode will sputter in a short period of time, and this will adhere to the inner surface of the display tube, contaminating it, or causing local damage. The glass may be damaged due to excessive heat generation, resulting in a defective product.

The present invention avoids such drawbacks, and the protection circuit according to the present invention will be explained below with reference to FIG. 5. In this example, parts corresponding to those in FIG. Omitted.

In the present invention, a detection circuit 19 is provided to detect the operating state of the drive signal generation circuit 11 for sequential scanning of the Y electrodes,
The control circuit 20 is controlled by the output of the detection circuit 19-0 obtained when the drive signal generation circuit 11 is in an inactive state, and the voltage applied between the X and Y electrodes is determined by the output signal of the control circuit 20-0. It is designed to descend.

In this example, the detection circuit 19 connects the output of at least one terminal of the signal generation circuit 11, for example, 11j to O, to a capacitor 2.
1 to the rectifier circuit 22, and the rectified output, that is, the DC voltage E1, is supplied to the comparator circuit 23 to be compared with the voltage E2 of the reference voltage source 24, and when E1>E2, the comparator circuit 23
This is a case where the configuration is such that there is a 0 output (output 1).

The control circuit 20 also includes a power supply terminal 13 and resistors 17a and 17b.
・・・・・・Connect the collector emitter of transistor 25 as an impedance change element between it and 17g,
A case is shown in which the terminal 13 is grounded through a series circuit of resistors 26-27 and the collector-emitter of a switching transistor 28, and the connection point between the resistors 26 and 27 is connected to the base of the transistor 25.

In the embodiment shown in the drawings, Y electrodes 2a, 2b, 2c...
... is provided with an erroneous scanning detection circuit 29 that detects whether two or more electrodes are being scanned (i.e., grounded) at the same time, and this circuit 29 connects the power supply terminal 13 to a bridge circuit. 30 is grounded through a series circuit of resistors 30a and 30b, and resistors 30c and 30d.
The voltages ■2 and ■ obtained at the connection point P of the resistors 30a and 30b and the connection point Q of the resistors 30c and 30d are supplied to the comparator 31, and ■,≦
The configuration is such that an output is obtained from the comparator 31 (output 1) in the state (2), and this output 1 also controls the control circuit 20 described above.

32 is an AND circuit which supplies the output of 01 through an inverter 33 to the base of the transistor 28 of 匍1 and 20.

Furthermore, in this example, the output of the AND circuit 32 is supplied to the base of the switching transistor 34, and the emitters of the transistors 16a, 16b, 16c, . . . , 16g are grounded through the collector emitter of this transistor 34. .

Next, the operation of this circuit will be explained.

In normal operating conditions, the drive signal generation circuits 811 and 0 are connected to each terminal 11a, 1lb, etc., as described in the explanation of FIG.
・11j to 0 are sequentially output as signals Sa)Sb as shown in Figure 4.
, Sc...01 is obtained, so the Y electrode 2a
, 2b, 2c, . . . are grounded in sequence.

Therefore, even at the terminal 11j, a signal Sa or sb or a signal as shown in . voltage E1 is obtained.

In this case, E2 is chosen to be O smaller than E1 (E1>
E2), output 1 is obtained from the comparator 23.

On the other hand, as mentioned above, under normal operating conditions, the transistors 2a,
Since only one of 12b, 12c, etc. is always turned on (conducting), the resistor 14a
, 14b, 14c..., only one of them is connected in parallel with the resistor 30d of the bridge circuit 30, and in this state, the voltages ■ and ■ at points P and Q are Vp ≧■ is selected, the output of the comparator 31 becomes p1.

In this way, since each output of the comparators 23 and 32 becomes 1, an output of 1 is obtained on the output side, which turns on the O transistor 34, while the output through the inverter 33 (which becomes O). ) of the transistor 28 of the control circuit 20
is off.

Therefore, the transistor 25 conducts almost in a state close to saturation, and the transistors 6 a t 1 6 b ~ 16
By turning off one, two, or more selected ones of g, a voltage close to the voltage applied to the power supply terminal 13 (i.e., A voltage higher than the discharge start voltage is applied, and discharge starts between this voltage and the Y electrode.

Assuming that the operation of the drive signal generation circuit 11 has stopped due to the cause mentioned above, the drive signals (shown in FIG. The state obtained at any one of the terminals will continue.

Therefore, in this case, if no signal is obtained at the terminal 11j, the output E1 of the rectifier circuit 22 will be 0 as E1<E2, and even if a signal is obtained at the terminal 11j, this will be a DC voltage, so the output E1 of the rectifier circuit 22 will be 0. It is blocked and is not supplied to the rectifier circuit 22.

Therefore, if the operation of the circuit 11 stops, E1<E2,
The output of the comparator 23 becomes O.

As a result, the output of the AND circuit 32 becomes O, the output of the 01 inverter 33 becomes 1, and the 01 transistor 28 is turned on.

Therefore, the voltage divided by the tenon resistors 26 and 27 is applied to the base of the transistor 25, the internal impedance of the transistor 25 is 0, and the potential of the emitter of the transistor 25 is discharged. This is done below the maintenance voltage.

Therefore, since the discharge by the discharge tube 10 is stopped, the above-mentioned drawbacks are avoided.

In this example, in this case, the output of the AND circuit 32 becomes O, thereby turning off the 01 transistor 34, and connecting the terminal 13 to any one of the resistors 17a, 17b to 17g to the resistor 18.
The current flowing through any one of the transistors 34 among the transistors 15a, 15b to 15g which is turned on is cut off.

In other words, in this case, if this current is not cut off, the internal impedance of the transistor 25 will increase and the heat generated by the transistor 25 will increase, potentially destroying it. However, by turning off the transistor 34 as described above, this The drawbacks can be avoided.

Even if the drive signal generation circuit 11 is operating, if for some reason a signal is obtained at two or more terminals at the same time, two or more Y electrodes may be grounded at the same time. This may result in incorrect or unclear display.

However, if a signal is obtained at the terminals 11a and 1lb at the same time, the transistors 12a and 12b will be turned on, so the two resistors 14a and 14b will be connected to the bridge circuit 30. Therefore, the voltages ■ and ■ at points P and Q become ■>■, the outputs of the comparators 31 and 0 become O and pq, and the output of the AND circuit 22 becomes O becomes.

Therefore, the display can be stopped in the same way as in the case described above.

As explained above, according to the present invention, the drive signal generation circuit 1
1 stops its operation, it is possible to appropriately avoid damage caused by splattering in a part based on this.

According to the actual case shown in FIG.
This is a case in which the operating state is determined by the output obtained from the terminal 11j of the terminal 11j, but the present invention is not limited to this.

Further, it is also possible to obtain an output for determining the operating state by connecting terminals other than the terminals 11a to 11j.

[Brief explanation of drawings]

Fig. 1 is a partial perspective view showing an example of a conventional discharge tube, Fig. 2 is a partial front view showing its display state, Fig. 3 is a connection diagram showing an example of a conventional display device, and Fig. 4 is a partial perspective view showing an example of a conventional discharge tube. FIG. 5 is a waveform diagram for explaining the operating state, and FIG. 5 is a protection circuit diagram of the discharge display device according to the present invention. 1a, 1b to 1g are X electrodes, 2a, 2b, 2C...
- indicates a Y electrode, 11 and 15 a drive signal generation circuit, 19 a detection circuit that detects the operating state of the drive signal generation circuit, 20
is the control circuit.

Claims (1)

[Claims] 1 A plurality of Y electrodes and a plurality of Y electrodes that intersect with each other,
a drive signal generation circuit that sequentially generates a plurality of drive signals for applying a predetermined potential to the plurality of Y electrodes in a time-division manner, and an arbitrary X electrode of the plurality of X electrodes; and another drive signal generation circuit for generating a drive signal for selecting an electrode and applying another predetermined potential to the arbitrary X electrode in synchronization with the scanning, the selected X electrode and the Y In a discharge display device that displays characters, numbers, figures, etc. by generating discharge at the intersections of electrodes, any one of the plurality of drive signals from the first drive signal generation time. a rectifier circuit to which two drive signals are supplied via a capacitor; a comparator circuit to which the rectified output of the rectifier circuit is level-compared with a reference voltage; and a control circuit for controlling, in an operation stopped state in which only one drive signal is generated from the one drive signal generation circuit,
The control circuit is controlled according to the comparison output from the comparison circuit based on a decrease in the level of the rectified output of the rectifier circuit to stop the discharge at the intersection of the X electrode and the Y electrode. protection circuit for discharge display devices.