JPH03201683A - Ray cathode protecting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention generates an electron beam for each division when a screen on a screen is vertically divided into a plurality of divisions, and generates an electron beam for each division. The present invention relates to a line cathode protection device in an image display device that displays a plurality of lines by vertically deflecting a beam to display a television image as a whole.

2. Description of the Related Art First, a basic configuration of an image display device used here will be explained with reference to FIG. This display device consists of, in order from the back to the front, a back electrode 1°, a line cathode 2 as a beam source, and a line cathode 2. Beam extraction electrode 3° Beam flow control electrode 4. Focusing electrode5. A horizontal deflection electrode 6, a vertical deflection electrode 7, and a screen 8 are arranged in sequence, and these are housed inside a flat vacuum container (not shown).

A line cathode 2 serving as a beam source is stretched horizontally so as to generate an electron beam distributed linearly in the horizontal direction. (Only seven wires, 2A to 2G, are shown). In this example, the spacing between the line cathodes is 3 m, and the number of line cathodes is 30.
It is assumed that the above-mentioned linear cathodes are provided as 2i to 27.

The distance between the line cathodes 2 is not allowed to be increased freely, but is regulated by the distance between the vertical deflection electrode 7 and the screen 8. These line cathodes 2 have a diameter of, for example, 10 to 30 μm.
An oxide cathode material is coated on the surface of a tungsten wire. Then, as will be described later, the electron beams are controlled to be emitted sequentially from the upper line cathode 2a for a fixed period of time. The back electrode 1 suppresses the generation of electron beams from other line cathodes 2 other than the line cathode 2 that is controlled to emit electron beams for a certain period of time, and directs the generated electron beams only in the forward direction. It has the effect of pushing out. This back electrode 1 may be constructed using the inner surface of the rear wall of the vacuum container.

The beam extraction electrode 3 is composed of a conductive plate 11 having a large number of through holes 10 arranged at predetermined intervals in the horizontal direction facing each of the line cathodes 2a to 27, and conducts the electron beam emitted from the line cathode 2. It is taken out through the through hole 10.

Next, the beam flow control electrode 4 is composed of a vertically long conductive plate 15 having a through hole 14 at a position facing each of the line cathodes 2a to 27, and a plurality of conductive plates 15 are arranged in parallel in the horizontal direction at predetermined intervals. has been done. In this example, 120 conductive plates 15a to 15n for control electrodes are provided (only 8 are shown in the figure).

The beam flow control electrode 4 controls the amount of passage of each of the electron beams divided horizontally by the beam extraction electrode 3 in accordance with a video signal for displaying each picture element. One line of video is displayed on the 120 beam flow control electrodes 4 at one time.

The focusing electrode 5 is composed of a conductive plate 17 having a through hole 16 at a position opposite to each through hole 14 provided in the beam flow control electrode 4.
focuses the electron beam that has passed through the

A plurality of horizontal deflection electrodes 6 are electrically conductive plates 1 arranged vertically on each side of the through hole 16 of the focusing electrode 5.
8.18', each conductive plate 18.18'
A horizontal deflection voltage is applied to horizontally deflect the electron beams of each picture element in the horizontal direction.
, H are sequentially irradiated to emit light. In this example, the deflection range is two picture elements wide for each electron beam.

The vertical deflection electrode 7 is a plurality of conductive plates 1 arranged horizontally at intermediate positions between the through holes 16 of the focusing electrode 5.
9.19', each conductive plate 19.19'
A vertical deflection voltage is applied to deflect the electron beam in the vertical direction. In this example, a pair of conductive plates 19 and 19' direct the electron beam generated from one line cathode by 8
Deflect to the position corresponding to the line. The 31 vertical deflection electrodes 7 constitute 30 conductive plate pairs corresponding to each of the 30 line cathodes, and ultimately deflect the electron beam to draw 240 horizontal lines on the screen 8. . The electron beam is mainly bent in the space between the horizontal and vertical deflection electrodes 6 and 7 and the screen 8, but the entire screen is configured with a sufficiently small amount of deflection compared to the distance in this space so that large deflection distortion does not occur. The screen has been split to make it possible.

The screen 8 is constructed by applying a phosphor 20 that emits light when irradiated with an electron beam to the back surface of a glass plate 21, and adding a metal back layer (not shown) if necessary. The phosphors 20 of the three colors R, G, and B are attached to one through hole 14 of the beam flow control electrode 4, that is, to each one electron beam divided in the horizontal direction. They are provided in two pairs and are applied in stripes in the vertical direction. The broken lines drawn on the screen 8 in FIG. 3 indicate vertical divisions displayed corresponding to each of the plurality of line cathodes 2, and the two-dot chain lines indicate each of the plurality of beam flow control electrodes 4. Shows the horizontal divisions displayed corresponding to. As shown in an enlarged view in FIG. 4, one section partitioned by these two pixels has two picture elements of R1+Gl+B, R2, G2, . B
There are two phosphors 20, and the width is eight lines in the vertical direction. The size of one block is, for example, 1 block in the horizontal direction and 3TM in the vertical direction. R, G, H 3
The colored phosphors may be applied in arrangements other than vertical stripes, such as delta arrangements.

Note that in FIG. 4, the length in the horizontal direction is enlarged by about twice the length in the vertical direction for clarity.

In this example, two pairs of R, G, and H phosphors 20 are provided for one beam flow control electrode 4, that is, one electron beam, for two picture elements, but of course one picture element is provided with two pairs of R, G, and H phosphors 20. The control electrode 4 may be provided with R, G or more pixels for one picture element or three picture elements or more.
, B video signals are sequentially applied, and horizontal deflection is performed in synchronization with them. Furthermore, the phosphors of the three colors R, G, and H may be applied in an arrangement other than vertical stripes, such as a delta arrangement, in which case horizontal and vertical deflection voltages suitable for the phosphor arrangement may be applied. Apply.

Next, the basic configuration of a drive circuit for displaying images on this display device will be explained with reference to FIG.

First, a driving portion for irradiating the screen 8 with an electron beam to emit raster light will be described.

In FIG. 5, the power supply circuit 22 is a circuit for applying a predetermined bias voltage (operating voltage) to each electrode of the display device.
A DC voltage of V5 is applied to the focusing electrode 5, and a DC voltage of V8 is applied to the screen 8.

The line cathode drive circuit 26 receives a vertical synchronizing signal V and a horizontal synchronizing signal H.
Line cathode drive pulses (a) to (ma) as shown in FIG. 6C are created using the following. FIG. 6 shows the relationship between the vertical synchronizing signal (1), the horizontal synchronizing signal H, and the line cathode drive pulses (A) to (M). That is, as shown in FIG. 2, the line cathode drive circuit 26 generates line cathode drive pulses (a) to (m) in response to the line cathode start pulse 44 from the pulse generating circuit 39, and the line cathodes 2a to 27 , during the high voltage period of drive pulses (a) to (ma) generated by the pulse generation circuit 39, the line cathode switching circuit 49 switches to the side a through which current flows from the line cathode heating power source 46, Line cathodes 2-27 are heated. At this time, the potential of the line cathode becomes more positive than the potential determined by the bias voltage applied to the back electrode 1 and the beam extraction electrode 3.
No electrons are emitted from 7. Drive pulse (a) ~ (ma)
During the low voltage period of 8H, the line cathode switching circuit 49 switches to the emission power source 45, b side, and the line cathodes 2-2
7 emits electrons. At this time, the cutoff power supply 47
Although the voltage is higher than that of the emission power source 45, no current flows through the diode 48. In this way, in the line cathodes 2A to 27, electrons are sequentially emitted from the upper line cathode 2I to the lower line cathode 27 every 8H period during the effective vertical scanning period.

Here, if the diode 48 is short-circuited for some reason, an excessive current flows from the cut-off power supply 47 through the line cathode to the emission power supply, but this excessive current is detected by the diode short-circuit detection circuit 50, and the detection circuit 50 detects the excessive current. The signal is sent to the line cathode drive pulse changing circuit 5, and all switches for each line cathode in the line cathode switching circuit 49 are switched to the a side to stop the excessive current flowing from the cutoff power supply 47 to the emitter 3 power supply 45. Protect the cathode.

The deflection voltage waveform generation circuit 40 is composed of a direct memory access controller (DMA controller) 41, a memory for storing deflection voltage waveforms (deflection memory) 42, and digital-to-analog converters (D/A converters) 43h and 43v. It generates signals 1, h' and vertical deflection signals v, v'.

In this example, regarding the vertical deflection signal, there are two sets of memory address areas for storing the vertical deflection signal corresponding to each line of 240H, and by storing regular data in the memory every 8H, Eight levels of vertical deflection signals can be obtained for two fields. In addition, for horizontal deflection signals, IH
Since it is necessary to horizontally deflect the electron beam in 6 stages within the period, 6 deflections are required during IH, and 240Hx6/H during 1.
There are memory address areas corresponding to =1440 horizontal deflection waveforms, and by storing regular data in the memory every IH minute, a horizontal deflection signal with 6-step waves can be obtained.

As mentioned above, the line cathode 2
1 to which a low potential drive pulse is applied among A to 27
The electron beam emitted from the main line cathode is divided horizontally into 120 sections by the beam extraction electrode 3.
It is taken out as a row of 20 electron beams. The amount of electron beam passing through each section is controlled by a beam flow control electrode 4 as described later, and after being focused by a focusing electrode 5, a pair of horizontal deflections that change in six stages as shown in FIG. Horizontal deflection electrode 6 to which signal h' is applied
RI, G++ Bl of the screen 8 during each horizontal period.

R2, G2. B2 (The phosphors corresponding to each conductive plate 15a to 15n of the beam flow control electrode 4 are R, G, and B for two picture elements, but for convenience of explanation, one picture element is RI, G,
i, sl and the other is R2+ G2r B2) are sequentially irradiated by H/6. In this way, each line raster has 120 pixels in the horizontal direction.
The electron beams are divided into RI, Gi, B1 . R2,
G2. Each phosphor 20 of B2 is sequentially irradiated with light. Therefore, for each horizontal section of each line, the electron beam R1+ at,
A color image can be displayed on the screen 8 by modulating it with the video signal of Bll R21G21 B2.

Next, the modulation control portion of the electron beam will be explained. First, R, G, and B primary color signals (hereinafter referred to as R1G and B video signals) applied to signal input terminals 23R, 23G, and 23B are sent to 120 sample and hold circuit sets 31a to 31.
added to n. Each sample and hold circuit set 31a to 3
1n is +02 for R1, Gi, Bl, and R2, respectively.
It has 6 sample and hold circuits for R, G and B2.

The B video signal is applied to each of the R, G, and B sample and hold circuits. The sampling pulse generation circuit 34 generates signals for each RI, G, and G of the 120 sample and hold circuit sets 31a to 31n during an effective horizontal scanning period (approximately 50 μsec) of the horizontal period (63.5 μsec).
120X6 as shown in A in Figure 6 corresponding to the sample and hold circuits for +, B+, R2, G2, and B2.
=720 sampling pulses Ra I'= B n
2 are generated sequentially. Six of these 720 sampling pulses R11-B, , 2 are applied to each of the 120 sample-and-hold circuit sets 31a-31n, and thereby one line is applied to each sample-and-hold circuit set 120 times.
RI, Gi, for each two picture elements when divided into
B1. Each video signal of R2, G2°B2 is individually sampled and held. The sample-held 120 pairs of RI, Cz, B1. R2, G2. The video signal of B2 is 120M after completing the sample hold for one line.
are transferred all at once to the memory sets 32a to 32n by the transfer pulse t, where they are held for the next -horizontal period.

This retained R11 GI+ Bl, R2+G
2. The video signal of B2 is transmitted through 120 switching circuits 35.
Added to a~35n. Switching circuits 35a-3
5n are R1+ GI+ BllR2, G2.
This circuit is composed of a circuit having individual input terminals of B2 and a common output terminal that sequentially switches and outputs them. Each of the switching circuits 35a to 35n receives switching pulses rl+gl+bl, as shown in B in FIG. 6, which are applied from the switching pulse generation circuit 36.
Switching is controlled simultaneously by r2+ g2+ t)2. Switching pulse rl+gl+ bl+ r2
+ g2+ B2 is - H/6 by dividing each horizontal period into 6
Switch two switching circuits 35a to 35n each, and
, Gi, B1. R2, G2. A switching signal rl+ is applied so that each video signal of B2 is time-divisionally outputted sequentially and supplied to pulse width modulation circuits (hereinafter referred to as PWM circuits) 37a to 37n.
g++ t)++ r2+ g2+ B2
occurs. The output of each switching circuit 35a to 35n is applied to 120 sets of PWM circuits 37a to 37n,
Here, sample and hold R1G1. Bl, R2
, G2. The pulse width is modulated according to the magnitude of the B2 video signal and output. The outputs of the PWM circuits 37a-37n are individually applied to the 120 conductive plates 15a-15n of the beam flow control electrode 4 as control signals for modulating the electron beam.

What should be noted here is that the switching circuits 35a to 3
R1.5n. G+, Bl, R2, G2. B2 video signal supply switching and horizontal deflection electrode 6 conductive plate 18.
18', electron beams R+, G+, B1. R2°G2. B
The horizontal deflection signal (h') applied to switch the irradiation to the phosphor 20 of No. 2 is synchronously controlled so that they completely match both in timing and order. As a result, when the electron beam is irradiating the R1 phosphor, the irradiation amount of the electron beam is controlled by the RI video signal, and at, Bl, R21G2
182 is controlled in the same way, and the B+ of each picture element is
, G+, B+.

R2, G2. The emission of B2 phosphor is the RI, G+ of that picture element.
.

Bl, R2, G2. Each picture element is controlled by the B2 video signal, and each picture element is displayed by emitting light according to the input video signal. Such control is performed simultaneously for 120 sets of one line (2 picture elements each) to display an image of 240 picture elements per line, and is also performed sequentially for 240 lines starting from the upper line.
One image will be displayed on the screen 8.

The above-mentioned operations are repeated for each field of the input video signal, and as a result, a moving image is displayed on the screen 8 in the same way as in a normal television receiver. The lock required to control this image display device is
It is supplied from a pulse generating circuit 39 whose timing is controlled by a horizontal synchronizing signal H and a vertical synchronizing signal V.

Problem to be Solved by the Invention However, in the above configuration, when the diode 48 is short-circuited for some reason, the cut-off power supply 47
The overcurrent flowing from the line cathode to the emission power source 45 through the line cathode is prevented by always switching the line cathode switching circuit 49 to side a using the diode short circuit detection circuit 50 and the line cathode drive pulse changing circuit 51. Since the current is prevented, the number of components is large, leading to increased costs and decreased reliability, and there is a risk that the protection circuit may malfunction due to noise such as static electricity.

The present invention solves the above problems, and reduces costs by reducing the number of components in the line cathode protection circuit when a diode is shorted.
The present invention provides a line cathode protection device for an image display device that improves reliability and does not malfunction due to noise.

Means for Solving the Problems In order to solve the above problems, the present invention provides a screen coated with a phosphor that emits light when irradiated with an electron beam, and a screen for each vertical division of the screen on the screen in the vertical direction. Equipped with multiple line cathodes that generate electron beams,
A closed circuit is configured such that the linear cathode, the linear cathode heating power source, and a reverse current prevention diode are electrically connected to each other so that the plurality of linear cathodes are heated, and when an electron beam is emitted from the linear cathode, the linear cathode is connected to the linear cathode. Cut off the wire cathode connected to the positive side of the cathode heating power source, connect it to the positive side of the emission power source, and install a current suppressing element at the connection point between the negative side of the wire cathode heating power source and the cathode side of the diode. This is a line cathode protection device that connects the positive side of the cut-off power supply through the cable to form a closed circuit.

With this configuration, if the diode is short-circuited for some reason, the current flowing from the cut-off power supply through the line cathode to the emission power supply is suppressed by the current suppressing element, such as a resistor or constant current diode, and an excessive current flows into the line cathode. prevent current from flowing. As a result, even if the diode is shorted, the line cathode will not break or performance will deteriorate.

When the diode is normal and the line cathode is heated, the cut-off power is
The purpose of this is to apply a potential to the heated wire cathode that will prevent it from emitting electrons, so the current that flows from the cut-off power source is minute. There is almost no voltage drop in the current suppressing element due to this minute current, and the wire cathode can be heated without emitting electrons. Therefore, when the diode is short-circuited, the function of protecting the line cathode can be achieved with only one resistor or constant current diode which is activated by the current insertion element, and a circuit that is free from malfunction due to noise can be realized.

Example Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a principle diagram for explaining a line cathode drive circuit in an image display device according to an embodiment of the present invention.

As shown in FIG. 1, the pulse generating circuit 39 outputs line cathode drive pulses (a) to (ma), which are applied to the line cathode switching circuit 49. When the line cathode driving pulse is at a high potential, the line cathode switching circuit 49 is connected to the a side of the line cathode heating power supply 46 that heats the line cathodes 2a to 27, and when the line cathode driving pulse is at a low potential, the line cathode switching circuit 49 switches electrons It is connected to the b side of an emission power source 45 that provides an emission potential to the line cathode for emission. During the line cathode heating period, a cutoff power supply 47 provides a potential that does not cause electron emission from the line cathode, and during the electron emission period, a diode 48 stops the current flowing from the cutoff power supply 47 to the emission power supply 45.

If the diode 48 is short-circuited for some reason, the cut-off power supply 47 will be
Since the voltage doubler is high, an excessive current flows from the cutoff power supply 47 to the emission power supply 45 through the shorted diode and line cathode. This excessive current flowing through the wire cathode is three times or more larger than the heating current flowing through the wire cathode during the wire cathode heating period, and therefore exceeds the current capacity of the wire cathode, resulting in breakage or performance deterioration. By inserting a resistor or a constant current diode as the electron suppressing element 52 between the intersection of the negative side of the line cathode heating power source 46 and the cathode of the diode 48 and the positive side of the cut-off power source 47, it is possible to prevent the diode from short-circuiting. An excessive current of It can be prevented.

During the line cathode heating period when the diode 48 is normal, the cutoff power supply 47 functions to provide a potential that prevents the heated line cathode from emitting electrons, so the current flowing from the cutoff power supply is minute, and the current is suppressed by this current. There is almost no voltage drop in the element, and the heated wire cathode can be kept at the cutoff potential, without adversely affecting the heating of the wire cathode and the electron emission function. Alternatively, a constant current diode can be used to protect the diode 48 from short circuits, and it is also possible to realize a circuit that is free from malfunction due to static electricity or the like.

Effects of the Invention As is clear from the description of the embodiments above, in the line cathode driving device according to the present invention, in order to emit electrons during the low potential period of the line cathode pulse, a diode is used to switch off the cut-off power supply. However, if the diode is short-circuited for some reason, the current flowing from the cut-off power supply to the emission power supply is suppressed by a resistor or constant current diode, which is a current suppressing element. This eliminates the possibility of excessive current flowing through the line cathode and causing it to break or degrade its performance.The function of protecting the line cathode can be realized with a single current suppressing element, reducing the number of parts, reducing costs, and improving reliability. Accordingly, it is possible to realize a device that has a high resistance to noise and does not malfunction due to noise.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the principle of a line cathode drive circuit of an image display device according to an embodiment of the present invention, Fig. 2 is a block diagram of a conventional line cathode drive circuit, and Fig. 3 is a circuit diagram to which the present invention is applied. 4 is an enlarged front view of the screen of the conventional image display device, FIG. 5 is a drive circuit diagram of the same image display device, and FIGS. 6(A), (B), ( C) is the fifth
FIG. 7 is a waveform diagram for explaining the operation. 2 I~Ma... Line cathode, 39... Pulse generation circuit, 45... Emission power supply, 46...
... Line cathode heating power supply, 47... Cutoff power supply, 48... Diode, 4 9... Line cathode switching circuit, 2... Current suppression element.

Claims (1)

[Claims] A screen coated with a phosphor that emits light when irradiated with an electron beam, and a plurality of line cathodes that generate electron beams in each vertical section of the screen above the screen, the line cathode A closed circuit is formed between a line cathode heating power source and a reverse current prevention diode such that the diode conducts and heats the plurality of line cathodes, and when an electron beam is emitted from the line cathode, the line cathode heating power source Cut off the wire cathode connected to the positive side of the wire, connect it to the positive side of the emission power source, and cut it through a current suppressing element to the connection point between the negative side of the wire cathode heating power source and the cathode side of the diode. A line cathode protection device that connects the positive side of an off-power source to form a closed circuit.