JPS6334589B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode ray tube for a light source.
As conventional display light source tubes, various light source lamps,
Small monochrome cathode ray tubes were used. Light source lamps have insufficient luminance, short lifespan, and are difficult to maintain. In addition, small monochrome cathode ray tubes deflect the electron beam emitted from an electron gun enclosed in the cathode ray tube to cause the fluorescent surface of the cathode ray tube to emit light, which requires a deflection circuit system and the drive circuit is complicated, resulting in a large number of small cathode ray tubes. The disadvantage was that it was very difficult to arrange the tubes and drive them simultaneously.

Therefore, the present invention provides a cathode ray tube for a light source that can provide sufficient luminance, eliminates the need for an electron beam deflection system, simplifies the drive circuit for the cathode ray tube, and allows a large number of cathode ray tubes to be easily arranged and driven. The present invention provides a cathode ray tube for a light source that can perform the following steps.

That is, the fluorescent surface voltage of the cathode ray tube is maintained at a high potential,
The electron beam emitted from the electron gun in the cathode ray tube is uniformly diverged so that it hits the entire fluorescent surface, eliminating the electron beam deflection system and simplifying the drive circuit to create a high-brightness light source tube.

Figure 1 shows a conventionally well-known cathode.
This is a schematic cross-sectional view of a three-electrode electron gun consisting of a first grid, a second grid, and a third grid, and the positional relationship of the fluorescent surface of a cathode ray tube.

The electron beam 6 emitted from the cathode 4 containing an electron-emitting substance is controlled by the voltage Ec 1 applied to the first grid 1, accelerated by the voltage Ec ₂ applied to the second grid 2, and further accelerated by the voltage Ec ₂ applied to the second grid 2. It is accelerated by the voltage applied to the fluorescent surface 5 and causes the fluorescent surface 5 to emit light. At this time, the voltage of the fluorescent surface is connected so that it has the same potential as the voltage Ec ₃ of the third grid 3 (not shown).The first grid 1 shown in FIG. 1 faces the cathode 4. Part diameter 0.5~1
A mmφ hole is provided. The same applies to the second grid 2.

The opposing open ends of the second grid 2 and the third grid 3 form an electron lens which is a cylindrical electrode.

Therefore, by varying the voltage Ec ₁ of the first grid 1, the current IK of the electron beam 6 can be varied. Divergence of the electron beam 6 is suppressed by the cylindrical electron lenses of the second grid 2 and the third grid 3, and the electron beam goes straight to the fluorescent surface, causing a circular spot to emit light on the fluorescent surface 5. The diameter of this light emitting spot is defined as D.

FIG. 2 shows the relationship between the current IK of the electron beam emitted from the electron gun shown in FIG. 1 and the diameter D of the light emitting spot on the fluorescent surface of the cathode ray tube.

In this case, since the diameter D of the light emitting spot changes depending on the distance between the fluorescent surface 5 and the second grid 2, it is fixed at a constant value, and the value of _Ec2 is also fixed at an arbitrary value. In this case, for example, if we consider the diameter D of the light-emitting spot on the phosphor surface when the current IK of the electron beam is IK = Ik ₀ , when the phosphor surface voltage Ec ₃ is Ec ₃ = Ea, D = Da, Ec ₃ =Eb
When D=Db, and when Ec ₃ =Ec, D=Dc.
At this time, the _Ec3 voltage relationship is Ec>Eb>Ea.

That is, when the voltage of the fluorescent surface 5 is lowered, the luminous spot diameter D becomes larger, and when the fluorescent surface voltage _Ec3 is increased, the luminous spot diameter D becomes smaller.

Therefore, in order to increase the brightness of the light emitting spot, increasing the phosphor surface voltage _Ec3 and increasing the diameter of the light emitting spot are contradictory. Furthermore, if the value of Ik is small (for example, 0 to 50 .mu.A), the required luminescent spot diameter D cannot be obtained even if the phosphor surface voltage is lowered. The ratio D/Ik of the luminescent spot diameter D to the electron beam current Ik is determined by the material of the fluorescent surface and the voltage of the fluorescent surface, and must be used at a current density below the allowable current density of the fluorescent surface. Generally, when using a cathode ray tube continuously, 3~
4μA/cm2 or ^less , peak when used discontinuously
Must be used at 10 μA/cm ² or less.

As mentioned above, as is clear from Fig. 2, even if the required luminous spot diameter D is obtained by lowering the phosphor voltage, the phosphor voltage is too low (in actual case, it is 5 kV).
(below), the luminance of the light-emitting spot becomes extremely dim, making it impossible to use it as a cathode-ray tube for a light source. In addition, the state where the fluorescent surface voltage is increased (actual case
In order to obtain the luminous spot diameter D required for 10 kV or higher), one method is to unnecessarily lengthen the distance between the fluorescent surface and the electron gun, but this method has the disadvantage that the cathode ray tube for the light source becomes extremely long. Yes, it cannot be put into practical use.

Therefore, in the present invention, the electron beam emitted from the cathode is guided to a three-electrode system consisting of a first grid, a second grid, and a third grid, and the voltage on the fluorescent surface is controlled by changing the electrode length of the second grid. It has been discovered that the diameter of the luminescent spot required on the fluorescent surface can be obtained arbitrarily without lowering the diameter.

3 and 4 illustrate the basic principle of the present invention. In FIG. 3, all cathode ray tubes a to c have the same total length including the electron gun. FIG. 3a shows that the electron beam 6 emitted from the cathode 4 passes through the first grid 1, the second grid 2, and the third grid 3 and forms a luminescent spot _D1 on the fluorescent surface 5. At this time, the electrode length in the axial direction of the second grid 2 is l ₁ , and l ₁ is equal to or less than the inner diameter d of the cylindrical electrode of the second grid 2 . Further, the voltage of the fluorescent surface 5 is at the same potential as that of the third grid 3 as in FIG. When the applied voltage of the second grid 2 is Ec ₂ and the applied voltage of the third grid is Ec ₃ , the voltage ratio N = Ec ₂ /Ec ₃ is an index showing the strength of the electron lens between the second grid and the third grid. becomes. The electron gun of the present invention has Ec ₂ =50 to 100v,
Since it is used at Ec ₃ = about 10 kV, the voltage ratio N = 100 ~
200, which is estimated to be a very strong lens. As shown in FIG. 3a, when the length _l1 of the second grid electrode is less than the inner diameter d of the second grid electrode, the diffusion angle of the electron beam passing through the electron lens decreases, causing underfocus on the fluorescent surface 5. Spot D ₁
Create.

However, as shown in Figure 3b, if the second grid electrode length _l2 exceeds the second grid electrode inner diameter d, the electron lens composed of the second grid 2 and the third grid 3 becomes very strong with a voltage ratio of N. Working as a bipotential lens, the electron beam 6 is focused at the front end 10 of the fluorescent surface 5, and a light emitting spot _D2 , which is an overfocused spot, can be created on the fluorescent surface 5.

Furthermore, as shown in Figure 3c, if the length of the second grid electrode is increased to _l3 , the object point distance will be becomes larger, and the image point position determined by the imaging formula approaches the lens. Therefore, when passing through this strong bipotential lens, only the electron beam diameter increases relative to the lens diameter, so the refractive power received by the electron beam increases, and at the same time, lens aberration increases, and the point 10 where the electron beam 6 is focused becomes a firefly. As the electron beam 6 moves further away from the optical surface 5, the convergence angle of the electron beam 6 increases, so the divergence angle of the electron beam 6 after being focused at the front end 10 of the fluorescent surface 5 increases, causing a number of particles to appear on the fluorescent surface 5. An even larger overfocused emission spot D3 than the emission spot _D2 shown in FIG. _3b is obtained.
As described above, it has been found that when the voltage ratio N between the second grid 2 and the third grid 3 is kept constant and the axial length l of the second grid electrode is varied, the diameter D of the light emitting spot on the fluorescent surface changes. did. This situation can be seen in the fourth
Shown in the figure.

In Fig. 4, the current value of the electron beam is Ik ₁ ,
The graph shows how the luminous spot diameter D changes depending on the second grid electrode length l when Ik ₂ and Ik ₃ increase. For example, if the diameter of the fluorescent surface of a cathode ray tube for a light source is Dx, the current value of the electron beam Ik = Ik ₁
lx ₁ when Ik=Ik ₂ , lx ₃ when _Ik =Ik ₃
The desired second grid electrode length can be determined as follows. Which Ik value to choose is determined by the size of the fluorescent surface and the allowable current density of the fluorescent surface.

As described above, by varying the length of the second grid electrode while maintaining the third grid voltage at a high voltage of 10 kV or more, it is possible to easily obtain a desired light emitting spot on the fluorescent surface.

Next, an embodiment of the present invention is shown in FIG. FIG. 5 is a schematic cross-sectional view of a cathode ray tube for a light source according to the present invention. The electron gun is basically the same as that shown in FIG. The cathode ray tube is a cylindrical glass tube 20 with an outer diameter of 29 mm, and the flat end facing the electron gun is coated with a phosphor to form a phosphor surface 5. The fluorescent surface 5 and the third grid 3 of the electron gun are connected through a contactor 7 and an inner graphite film 8.

The shape of the fluorescent surface is circular and its diameter D is D=23mmφ
It is.

It is desirable that the distance L between the second grid 2 and the fluorescent surface be as short as possible. For example, second grid 2
When the inner diameter of the electrode is do, if the L dimension exceeds 12 do, the standard-produced cylindrical envelope cannot be used. Further, if the L dimension is less than 9do, the getter will scatter and the luminance of the fluorescent surface will decrease, which is not preferable.

Therefore, it is desirable to set the practical L dimension to 9 to 12 do. In this embodiment, L=11do was selected.

Further, the diffused electron beam 6 shown in FIG.
The light emitting spot may shift on the fluorescent surface 5 due to slight eccentricity (for example, eccentricity of 0.5 to 0.0) at the top.

Therefore, it is necessary to set the diameter of the light-emitting spot on the fluorescent surface 5 to be large enough so that the entire area of the fluorescent surface 5 emits light even in the case of this deviation. In our case,
The luminous spot diameter is D+ relative to the diameter D of the fluorescent surface 5.
(1-2) I found that it is good to set it to do.

Based on the above, when setting L = 9 to 12do,
The second grid electrode length l is the diameter of the fluorescent surface D = 3~
The length l of the second grid electrode was determined experimentally so that the electron beam would be sufficiently diffused at 6do and the entire fluorescent surface would emit light. The range is l=(2-4)do. In the embodiment of the present invention, L=11do and D=4do, and the second grid electrode length was set to l=3.5 to 4do.

The voltage applied to the light source cathode ray tube is applied from the stem portion of the cylindrical tube 10, and there are four types: cathode voltage Ek, first grid voltage Ec ₁ , second grid voltage Ec ₂ , and third grid voltage Ec ₃ . In the example Ek
is the driving voltage, Ec ₁ = 0 (earth potential), Ec ₂ = 70v,
Ec ₃ was set to 10kv. The electron beam current has a maximum peak of 30 μA considering the allowable current density of the fluorescent surface.
(7.2 μA/cm ² ) or less.

As described above, by using the embodiments of the present invention, a compact light source cathode ray tube with high brightness can be obtained, and when a large number of light source cathode ray tubes are arranged and used, a deflection system for the cathode ray tube is not required, and a drive circuit The effect is very large because it can be greatly simplified.

Particularly when this type of cathode ray tube for light source is used for electronic bulletin boards, etc., the effect is great.

[Brief explanation of drawings]

FIG. 1 is an enlarged view showing the inside of an electron gun consisting of three electrodes: a cathode, a first grid, a second grid, and a third grid. Figure 2 is a characteristic diagram showing the relationship between the emission spot diameter and electron beam current when the electron beam emitted from the electron gun causes the fluorescent surface to emit light, and Figure 3 is the characteristic diagram for the second grid of the three-electrode electron gun. A configuration diagram showing the relationship between the diameter of the light emitting spot on the fluorescent surface when the electrode length is varied, FIG. 4 is a characteristic diagram showing the relationship between the current value and the diameter of the light emitting spot, and FIG. 5 is an embodiment of the present invention. FIG. In the figure, 1 is the first grid, 2 is the second grid,
3 is a third grid, 4 is a cathode, and 5 is a fluorescent surface.

Claims (1)

[Claims] 1. A single electron gun consisting of a three-electrode configuration of a first grid, a second grid, and a third grid electrically connected to a fluorescent surface is provided, and the electron beam emitted from the cathode is For a light source characterized in that the electron beam is squeezed by the cylindrical electron lenses of the second grid and the third grid, is focused once before reaching the fluorescent surface, and then diffused again, and this diffused electron beam causes the fluorescent surface to emit light. cathode ray tube. 2. A cathode ray tube for a light source according to claim 1, wherein the portion surrounding the single electron gun and the portion provided with the fluorescent surface are all cylindrical envelopes having the same outer diameter. 3 The inner diameter of the open end of the second grid electrode facing the third grid is d ₀ , the second grid voltage is v ₁ ,
When the third grid voltage is _v2 , the distance between the second grid electrode and the fluorescent surface is L, and the diameter of the fluorescent surface is D,
_v2 / _v1 =100~200, L=9~ _12d0 , D=3~ _6d0
and the electrode length l in the axial direction of the second grid is l/d ₀
2. A cathode ray tube for a light source according to claim 1, comprising an electron gun characterized in that the number of electron beams is set to 2 to 4.