JPH07272674A - Hot cathode discharge tube, hot cathode fluorescent lamp, and lighting device for them - Google Patents

Abstract

PURPOSE:To lessen the power consumption of a small-sized hot cathode discharge tube and prolong its lifetime by forming the electrode in a double coil wind structure where a tungsten wire is used, and giving the ratio of its length to diameter a specified value. CONSTITUTION:A small-sized hot cathode discharge tube is constructed so that the lamp current is discharged with a minor amperage below 50mA, wherein the filament electrode 4 is made from a tungsten wire formed in a double coil wind having a thickness below 2MG, and the surface is coated with an electron emitting substance. The ratio of the length L of the coil to its diameter D is made approx. 3:1. The power to be supplied to the filament electrode 4 is set so that its temp. minimizes or lies near it in the condition that the electrode 4 is in arc discharging, or so that the power supplied to the electrode 4 lessens with smaller lamp amperage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small hot cathode discharge tube, a small hot cathode fluorescent lamp suitable for use as a backlight of a liquid crystal display device, and a lighting device thereof.

[0002]

2. Description of the Related Art Conventionally, small fluorescent lamps are roughly classified into a cold cathode type and a hot cathode type. Generally, a cold cathode type is mainly used in view of a long lamp life. Is still mainstream. However, in the case of the same size, the hot cathode type is superior in brightness, so that the hot cathode type is recently used as a backlight for a liquid crystal display device such as a liquid crystal television, which requires a small size and high brightness. Things are getting attention.

This hot cathode type having a coiled filament electrode coated with an electron emitting substance is
This filament electrode is roughly classified into a constant current type and a non-current type, and since the lighting device does not complicate the lighting circuit and consumes relatively little power, the non-current type is used. Widely adopted. However, this non-conducting type has an advantage that it does not require electric power for preheating because it is not necessary to energize the filament electrode all the time, but since it discharges at one point on the filament electrode, it does not emit electrons. Is easily scattered, resulting in a short lamp life. This is because the electrode temperature is low and the discharge positions on the filament electrode are concentrated at one point in order to partially raise the electrode temperature to a temperature at which thermoelectrons are easily emitted.

On the other hand, the constant current type has a disadvantage that it requires electric power for preheating, but since the entire filament electrode is preheated in advance, sufficient thermoelectrons are supplied from the entire electrode. As a result, the entire electrode is discharged, and as a result, there is almost no scattering of the electron emissive material as described above, and the lamp has a long life.

Since such a long-life always-on hot cathode fluorescent lamp is used in, for example, a liquid crystal television or the like (particularly for portable use), the lamp current is 50 mA in the past.
A small hot cathode discharge tube that discharges below has been developed. Specifically, the tube diameter is φ8 mm, the lamp current is 20 mA,
Preheat power of 1W (2W for one lamp) has been developed.

[0006]

However, this conventionally known hot cathode fluorescent lamp is unsuitable as a small power-saving type because the power consumption of the filament electrode is large and the tube diameter is large. It was Further, since the hot cathode fluorescent lamp including the heretofore known hot cathode fluorescent lamp always heats the filament electrode, it always has a problem of evaporation of the electron emissive substance. That is,
If the filament electrode is overheated, the evaporation of the electron-discharging substance is promoted, which shortens the lamp life, and if the filament electrode temperature is too low, the emission of the electron-emissive substance causes the lamp life to shorten as described above. Is.

Such evaporation and scattering of the electron emissive substance can be dealt with by increasing the amount of the electron emissive substance, but an increase in the amount of the electron emissive substance leads to an increase in preheating power, It is not suitable for suppressing power consumption as much as possible.

When the filament electrode is composed of a tungsten coil and an electrode is designed, the lamp current is reduced (specifically 50 mA or less) and the coil wire diameter is reduced (for example, 2 MG or less). When trying to miniaturize the discharge tube, the shape of the coil and the relationship between the wire diameter and the lamp current subtly affect each other, which makes it very difficult to design the filament electrode.

An object of the present invention is to develop a small filament electrode having good preheating efficiency, and to provide a small-sized hot cathode discharge tube with low power consumption and a hot cathode fluorescent lamp and a lighting device thereof. There is.

[0010]

In order to achieve the above object, the present invention provides a lamp current of 50 m with a coil-shaped electrode coated with an electron emissive material being constantly energized.
In a small hot cathode discharge tube that discharges with a small current of A or less, the electrode is a double coil winding using a tungsten wire of 2 MG or less, and the ratio of the length to the diameter is about 3: 1. It is what constitutes.

According to the present invention, the electrodes constructed as described above are installed at both ends of a glass tube having an inner surface coated with a fluorescent substance and having low-pressure mercury vapor sealed inside, and the double-ended hot cathode is used. It constitutes a fluorescent lamp.

According to the present invention, the electrode constructed as described above is installed at one end of a one-necked glass tube in which a fluorescent substance is applied to the inner surface and low-pressure mercury vapor is sealed inside the one-necked hot cathode. A fluorescent lamp can be constructed.

The present invention further relates to a small hot cathode discharge tube or hot cathode fluorescent lamp which discharges a lamp current with a small current of 50 mA or less in a state where a coiled electrode coated with an electron emitting substance is always energized. In the lighting device, the electrode is a double coil winding using a tungsten wire of 2 MG or less, and the ratio of the length to the diameter is about 3: 1.
In addition, the electric power supplied to the electrode is set so that the electrode temperature is at or near the minimum in the arc discharge state of the electrode.

Further, according to the present invention, a small hot cathode discharge tube or hot cathode fluorescent lamp which discharges a lamp current with a small current of 50 mA or less in a state where a coil-shaped electrode coated with an electron emissive material is always energized. In the lighting device of (1), when adjusting the lamp brightness by varying the lamp current, the electric power supplied to the electrodes is varied in accordance with the lamp current, and the smaller the lamp current, the smaller. is there.

[0015]

When the wire diameter of the filament forming the electrode is set to 2 MG or less and the coil is double-coiled, the core wire does not have to be used, so that the power consumption for preheating can be suppressed as much as possible, as compared with the filament electrode using the core wire.

In the present invention, since the filament electrode is made of a tungsten wire of 2 MG or less and the ratio of the filament length L to the diameter D is about 3: 1, the filament electrode is efficiently heated with a small electric power. Therefore, the discharge tube can be miniaturized (thinned).

In the fluorescent lamp, mercury vapor is excited by the discharge from the electrodes to emit ultraviolet rays, and the fluorescent substance absorbs the ultraviolet rays to generate visible light, which is radiated to the outside of the glass tube.

In the hot cathode type discharge tube and the fluorescent lamp constructed as described in claims 1 to 4, the lighting device is controlled so that the electric power supplied to the electrodes is controlled so that the electrode temperature is at or near the minimum in the arc discharge state. By configuring, the evaporation of the electron emissive material is suppressed as much as possible.

Further, in the hot cathode discharge tube and the fluorescent lamp constructed as described in claims 1 to 5, the electric power supplied to the filament is changed according to the lamp current, and when the lamp current is reduced, the filament is changed to a filament. If it is configured to reduce the preheating current supplied, it prevents the temperature of the filament from rising together with the decrease of the lamp current,
It is possible to suppress the evaporation of electron radioactive materials.

[0020]

[Embodiment] The power consumption of a liquid crystal display device in a liquid crystal television is about 2 to 3 W in consideration of the case of using a battery. In this case, the lamp current of a fluorescent lamp constituting a backlight is within an allowable range of about 20 to 30 mA. Is. Since personal computers, word processors, and the like that use the same liquid crystal display device do not operate on batteries in principle, power consumption is not suppressed as much as liquid crystal televisions. However, the hot cathode type discharge tube and fluorescent lamp according to the present invention, which are intended to use a small glass tube having a tube diameter of 7 mm or less, have a lamp current of 50 mA or less and always energize the filament electrode ( The always energized type was the target.

The drawing shows one embodiment of the present invention. In FIG. 1, a pair of electrode columns 2 and 2 are provided at both ends of a glass tube 1.
・ 3,3 are enclosed, and each of these electrode columns 2,2 ・
Filament electrodes 4 and 4 forming cathodes are suspended on 3 and 3. The glass tube 1 shown in FIG. 1 is made of soda glass, for example, and has a tube length of 200 mm and a tube diameter of 6.2 mm
In addition, a fluorescent substance 8 such as calcium halophosphate is coated inside, and low pressure mercury vapor of 20 Torr is enclosed. Incidentally, argon gas or xenon gas may be used together with or separately from the mercury vapor.
The electrode columns 2, 2, 3, and 3 are made of an alloy containing iron and nickel, and penetrate the inside of the stems 5 and 5 to form a pair of lead wires 6, 6, 7, and 7 to the outside of the glass tube 1. Has been derived.

The filament electrodes 4 and 4 have 1.6 MG (2
It is made of a double-coil-wound tungsten wire having a thickness of MG or less), an electron emissive material (hereinafter also referred to as oxide) is applied to the surface, and the ratio of the length L to the diameter D is as shown in FIG. It is configured to be about 3: 1.

The shape of the filaments forming the electrodes is a double coil winding or a triple coil winding (or a coil winding of a different shape using a core wire) which can adhere a large amount of oxide in order to prolong the service life. And are commonly used.

A triple coil winding (or a coil winding of a different shape using a core wire) is advantageous for downsizing the discharge tube lamp, but requires a large amount of preheating power because the core wire is used. . Therefore, in the present invention, since the double coil winding without using the core wire is adopted, the power consumption for preheating can be suppressed as much as possible as compared with the case where the core wire is used.

When designing an electrode with a double coil wound tungsten wire of 2 MG or less, it is necessary to increase the diameter of the double coil and shorten its length so that a sufficient amount of oxide is applied. Although it is advantageous to reduce the size of the discharge tube while maintaining the above condition, if the length of the coil is too short, the coil cannot be efficiently heated.

More specifically, as shown in FIG. 3, the length of the coil when the double coil (having the same amount of oxide applied) wound with the same wire diameter and the same length of the dangsten wire is preheated. The electrode temperature with respect to the ratio of the length L to the diameter D is extremely lowered when the ratio of the coil length to the diameter is smaller than 3: 1.

Therefore, in terms of the electrode temperature, it is necessary to design the filament so that the ratio of the coil length to the diameter is about 3: 1 or more. However, in order to miniaturize the discharge tube, the coil should be made smaller. Since it is better to have the length as short as possible, the coil length / diameter ratio of about 3: 1 was chosen.

FIG. 4 is a graph showing the relationship between the lamp current and the filament voltage. As shown in this graph,
While the lamp current is constant at 20 mA, that is, in the arc discharge state, when the filament voltage (or current) is lowered, the peak temperature of the filament is lowered, but below a certain voltage (5.5 Vf or less in FIG. 4). Then, the peak temperature of the filament rises. This means that if the filament voltage is 5.5 Vf or higher, the filament temperature can be maintained at a temperature higher than that required for discharging the entire filament electrode, and the filament voltage is 5.5 Vf.
It is shown that when the temperature falls below the range, the temperature of the filament decreases, and the discharge at one point (such as the non-conduction type) is performed as described above.

Therefore, in the arc discharge state of the filament electrode, when the electric power supplied to the filament electrode is set so that the electrode temperature is at or near the minimum, that is, the filament voltage is set to 5.5 Vf or its vicinity ( In the embodiment, in consideration of manufacturing variations, 5.
(It is set slightly higher than 5 Vf), it is possible to suppress the evaporation of oxide as much as possible without excessively heating the filament. In each of the fluorescent lamps having a specific structure, the filament voltage is changed while the lamp current is kept constant, the lowest point of the peak temperature of the filament electrode is determined, and the lighting device is operated as such. It is composed of.

FIG. 5 is a graph showing the relationship between the wire diameter of the dangsten forming the filament electrode and the lamp current. For the manufacturing reason, the diameter D of the coil can be made smaller as the wire diameter of tungsten is made smaller. However, if the wire diameter is made too thin, as shown by the dotted line in FIG. Will be greatly affected by. That is, the thicker the wire diameter of tungsten, the less susceptible it is to the temperature of the lamp current, and the thinner the wire diameter, the more susceptible it is to the temperature of the lamp current.

Therefore, the wire diameter of tungsten is determined in consideration of the lamp current range to be used and the influence of temperature due to the lamp current. When the wire diameter of tungsten is determined, the coil length L and the coil diameter D are determined in consideration of the amount of oxide.

In this embodiment, a wire diameter of 1.6 MG is adopted in consideration of the influence of the lamp current on the temperature (FIG. 5).
Solid line). In this case, when trying to adjust the lamp current over a wide range, a problem arises in the portion where the filament temperature rises rapidly in the figure. Therefore, in this portion, if the lighting device is configured such that the electric power supplied to the filament electrode becomes smaller as the lamp current becomes smaller, it is possible to prevent the electrode temperature from unnecessarily rising.

With the above structure, the present invention has a glass tube diameter of 6.2 mm and a lamp current of 20 m.
A, 20,000 cd / m ² , and the power consumption of the filament electrode was 0.
4W (0.8W with one double-ended fluorescent lamp), life 2
It was possible to achieve a small-sized hot-cathode fluorescent lamp of 10,000 hours (luminance half-life), and no decrease in life was observed even after dimming.

In the above embodiments, the hot cathode discharge tube is not shown or described, but the one not coated with fluorescent paint on the inside of the glass tube is a discharge tube that radiates ultraviolet rays. The description was omitted. Also, a single-mouthed type is not shown. In this one, the filament electrode and the positive electrode constituting the cathode are placed at a predetermined interval at one end of the sealed glass tube, and the structure is the same as that of the previous embodiment. In the same way, the electrode temperature of the filament electrode can be controlled by the lighting device.

[0035]

Since the present invention is constructed as described above,
The glass tube can be made smaller and the brightness of the lamp can be increased. As a result, the thermal efficiency of the filament electrode is increased,
The power consumption is suppressed as much as possible, and the preheating temperature of the filament electrode is optimized to suppress the scattering and evaporation of oxide as much as possible, thereby extending the lamp life.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining a preheating type fluorescent lamp according to the present invention.

FIG. 2 is an enlarged partial sectional view of the preheating type fluorescent lamp shown in FIG.

FIG. 3 is a graph showing the relationship between the filament temperature and the ratio of the filament electrode length L and diameter D.

FIG. 4 is a graph showing a relationship between a lamp current and a filament voltage.

FIG. 5 is a graph showing the relationship between the wire diameter of tungsten and the lamp current.

[Explanation of symbols]

 1 Glass tube 4 Filament electrode 8 Fluorescent substance L Length D Diameter

Claims (6)

[Claims] 1. A small hot cathode discharge tube which discharges a lamp current with a small current of 50 mA or less in a state in which a coil-shaped filament electrode (4) coated with an electron emissive material is always energized. (4) is a double coil winding using a tungsten wire of 2 MG or less, and its length
A hot cathode discharge tube, characterized in that the ratio of (L) to diameter (D) is about 3: 1. 2. The filament electrode (4) according to claim 1 is installed on both ends of a glass tube (1) having an inner surface coated with a fluorescent substance (8) and a low pressure mercury vapor sealed inside. A hot cathode fluorescent lamp, which is characterized in that 3. The filament electrode (4) according to claim 1, wherein the inner surface is coated with a fluorescent substance and is installed at one end of a single-ended glass tube in which low-pressure mercury vapor is sealed. A hot cathode fluorescent lamp. 4. The hot cathode fluorescent lamp according to claim 2, wherein the glass tube (1) has a diameter of 7 mm or less. 5. The small hot cathode according to claim 1, wherein the lamp current is discharged with a small current of 50 mA or less while the coil-shaped filament electrode (4) coated with the electron emissive material is always energized. In a lighting device of a discharge tube or a hot cathode fluorescent lamp, the filament electrode (4) is a double coil winding using a tungsten wire of 2 MG or less, and its length
(L) and the diameter (D) are set to be about 3: 1, and the power supplied to the filament electrode (4) is supplied to the filament electrode (4) in an arc discharge state. 5. The lighting device for a hot cathode discharge tube or hot cathode discharge lamp according to claim 1, wherein the value is set to be at least or in the vicinity thereof. 6. The small hot cathode according to claim 1, wherein the lamp current is discharged with a small current of 50 mA or less in a state where the coiled filament electrode (4) coated with the electron emissive material is always energized. In a discharge tube or a hot cathode fluorescent lamp lighting device, when adjusting the lamp brightness by changing the lamp current, the power supplied to the filament electrode (4) is changed in accordance with the lamp current, the lamp current is 6. The hot cathode discharge tube or hot cathode fluorescent lamp lighting device according to claim 1, wherein the smaller the power, the smaller the power supplied to the filament electrode (4).