JP3177858B2 - Low pressure discharge lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pressure discharge lamp, such as a cold cathode flat fluorescent lamp, which is lit by applying a DC voltage or a unidirectional pulse voltage between a pair of main electrodes.

[0002]

2. Description of the Related Art Recently, a small-sized liquid crystal display device has been developed as a color view finder for a VTR, and this type of device illuminates a liquid crystal display panel having a size of about 23 mm × 18 mm with a backlight from the back thereof. ing. If a straight tube fluorescent lamp or a U-shaped or W-shaped fluorescent lamp is used as the backlight, it cannot be used because it is too large, and therefore, a very small flat cold cathode fluorescent lamp is used. .

In this type of flat fluorescent lamp, as shown in FIGS. 4 and 5, a fluorescent coating 2 is formed on the inner surface of a flat bulb 1 having a cross section of an oblong cylinder or the like. Openings at both ends of the valve 1 are hermetically closed by flat-plate stems 3 as closing members. These stems 3,
3 are attached with main electrodes 4a and 4b each formed of a cold cathode. The cold cathode main electrodes 4a and 4b are made of, for example, a nickel plate. A getter 5 made of zircon-aluminum is applied to the front surface, and a mercury release structure 6 made of a mercury-titanium alloy is adhered to the back surface. The cold cathode main electrodes 4a, 4b are joined to wells 7, 7, respectively, and the wells 7 pass through the stem 3 airtightly and are led out. The stems 3, 3 are made of a glass adhesive, that is, frit glass 1
The bulb 1 is joined to the open end of the bulb 1 by 2 and 12.

As shown in FIG. 5, the main electrodes 4a and 4b are connected to a lighting circuit 20 including a pulse generating circuit. The pulse generation lighting circuit 20 has a frequency of, for example, 15
A pulse power of about KHz is generated. When a pulse voltage is applied between the cold cathode main electrodes 4a and 4b, an arc discharge occurs between the main electrodes 4a and 4b. The mercury sealed in the bulb 1 is ionized and excited to emit ultraviolet rays, and the ultraviolet rays are converted into visible light by the phosphor coating 2 and irradiated to the outside.

[0005] Such a flat cold cathode fluorescent lamp is
Since the shape is flat, it becomes a thin light source, and it emits light on a relatively large surface despite it, so a flat light emitting surface having the same area as the liquid crystal display panel without using a light reflecting plate or light diffusing plate. And there is an advantage that the whole light source can be made small and thin. In this type of flat fluorescent lamp, when it is pulse-lit, the luminance distribution becomes uniform with high efficiency. Therefore, recently, the pulse lighting method has been increasingly used.

[0006]

However, the flat fluorescent lamp of the pulse lighting type as described above has a drawback that the startability is not good in dark and low temperature. In other words, the initial electrons required for the start of normal discharge are supplied by thermoelectrons, light, or cosmic rays, but no external light can be expected in the dark, and this type of lamp is a cold cathode. Neither can the electrodes be preheated to emit thermoelectrons, thus leaving only cosmic rays. However, when the lamp is accommodated in a casing or the like, the cosmic ray reaches only a very small amount and is unlikely to trigger the start of discharge.

Therefore, a starting auxiliary electrode is provided outside the pair of main electrodes, an auxiliary discharge is generated between the auxiliary electrode and one of the main electrodes, and the auxiliary discharge is generated by the main arc between the pair of main electrodes. A method of shifting to discharge can be considered. This type of starting method using an auxiliary electrode is a method that has been conventionally known for a high-pressure discharge lamp or the like. The starting method using this kind of auxiliary electrode generates an auxiliary discharge between the auxiliary electrode and the main electrode closer to the auxiliary electrode as described above, and emits a large amount of thermoelectrons into the lamp by the auxiliary discharge. These electrons shift to a main arc discharge between the pair of main electrodes,
Since discharge breakdown occurs at an extremely low voltage as compared with the case where no auxiliary electrode is used, there is also an advantage that the starting voltage can be reduced.

However, most of the conventional high pressure discharge lamps using the auxiliary electrode are operated by alternating current, so that there is no distinction between the polarity of the anode and the polarity of the auxiliary electrode. In contrast, the above VT
In the case of the low-pressure discharge lamp used as the light source of the R color view finder, since the DC lighting or the unidirectional pulse lighting method is used, the auxiliary electrode must be set to either the anode or the negative polarity. However, according to our experiments, it was found that when the auxiliary electrode was used as the anode (+) with respect to the main electrode approaching the auxiliary electrode, the start-up time in the dark was delayed.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a low-pressure discharge lamp in which, when a starting auxiliary electrode is provided, startability is improved even in darkness. Things.

[0010]

According to the present invention, a pair of main electrodes are provided in an arc tube bulb so as to face each other, and an auxiliary electrode for starting is provided near one of the main electrodes. in low-pressure discharge lamp to be lighted by the discharge, the start
Auxiliary electrode is the main electrode whose
It is formed so as to be thinner than the auxiliary discharge generation part.
And a negative potential polarity with respect to the adjacent main electrode.

[0011]

According to the present invention, the tip of the auxiliary electrode for starting is provided.
The size of the auxiliary discharge generating part of the main electrode
When the auxiliary electrode for starting is set to a negative (-) potential, the electric field is concentrated on the auxiliary electrode, and the electric field strength at the tip of the auxiliary electrode is set to a positive (+) potential for the auxiliary electrode for starting. In comparison, the effective electric field strength on the electrode surface is increased, so that the auxiliary discharge delay time τ _s1 can be reduced, and as a result, the main discharge delay time can be reduced, and the discharge delay in darkness can be eliminated. In addition, the starting characteristics can be greatly improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The drawing shows a flat cold-cathode fluorescent lamp used as a backlight of a liquid crystal display device applied to a color viewfinder of a VTR.
And the same as the conventional example shown in FIG. 5, but will be described in further detail.

In FIG. 1 and FIG. 2, reference numeral 1 denotes a flat valve having an elliptical cylindrical cross section as in the prior art, and a phosphor coating 2 is formed on the inner surface of the flat valve 1.
Openings at both ends of the flat valve 1 are airtightly closed by plate-shaped stems 3 as closing members. The stems 3 and 3 are made of a glass plate and have a flat plate shape, and thus belong to a so-called button stem type. Such a flat stem 3,
3 are attached with main electrodes 4a and 4b each formed of a cold cathode. The cold cathode type main electrodes 4a and 4b are made of, for example, a nickel plate, are coated with a getter 5 made of zircon-aluminum on the front surface, and have a mercury release structure 6 made of a mercury-titanium alloy adhered on the back surface. . The cold cathodes 4a and 4b facing each other are configured such that the surfaces to which the getters 5 are applied face each other.

Such plate-shaped cold cathodes 4a, 4b
Has one end joined to wells 7, 7, respectively.
The wells 7 pass through the stem 3 airtightly and are led out. A starting auxiliary electrode 10 is pierced through one stem 3 secretly. The start-up auxiliary electrode 10 has a tip with respect to one of the cold cathode main electrodes 4a. The tip is sharpened like a needle to reduce the area of the tip. For example, the dimension d is about 0.3 mm. And faces the cold cathode type main electrode 4a with a discharge gap. Dummy wells 9 are secretly penetrated into the other stem 3, and this
The wells 9 are provided to thermally balance the wells 7 on the main electrode 4b side when the bulb 1 and the stem 3 are heated.

The inner surface of the stem 3 has the stem 3
Bosses 11, 11 for positioning when fitting into the openings at both ends of the flat valve 1 are projected, and the wells 7, 7, the starting aid are penetrated through these bosses 11, 11. Electrodes 10 and dummy wells 9 are arranged. The stems 3, 3 provided with the respective electrodes as described above are joined to the open end of the bulb 1 by a glass adhesive, that is, frit glasses 12, 12. The frit glasses 12, 12 are made of a glass material having a coefficient of thermal expansion similar to that of the glass, and have an oval ring shape corresponding to the opening surface of the bulb 1, and are sandwiched between the inner surfaces of the stems 3, 3. In rare cases, the stems 3 are melted by being heated from the outside, and the stems 3 are air-tightly joined to the opening end surface of the valve 1.

The mercury emitting structure 6 attached to the cold cathodes 4a and 4b is heated from the outside by means such as high-frequency dielectric heating after the bulb is sealed, so that it evaporates into the bulb and is emitted. It has become. A rare gas such as argon Ar is sealed in the valve 1 at a predetermined pressure P (Torr), for example, 30 to 140 Torr. As shown in FIG. 2, the flat cold cathode fluorescent lamp having the above-described configuration is connected to a lighting circuit 20 including a pulse generating circuit to be lit.

The pulse generation lighting circuit 20 is a known circuit having a one-way polarity with a repetition frequency f of, for example, 15 KHz and an on / off duty ratio having a pause period τ of, for example, about 0.1. Good. The plus side of such a pulse generation lighting circuit 20 is connected to one cold cathode type main electrode 4a.
And the negative side is connected to the other cold cathode main electrode 4b. The negative side of the pulse generation lighting circuit 20 is connected to the auxiliary electrode 10 via an impedance 21 of, for example, about 1 MΩ. Accordingly, the auxiliary electrode 10 has the polarity of the negative electrode (-), one main electrode 4a approaching the auxiliary electrode 10 has the polarity of the anode (+), and the other main electrode 4b opposed thereto has the polarity of the negative electrode (-). Has made.

In the lamp having such a configuration, when the lamp is started, the pulse voltage supplied from the pulse generation lighting circuit 20 is applied to one of the cold cathode type main electrode 4a and the auxiliary electrode 10 arranged close to the same. Since the distance between the auxiliary electrode 10 and the cold cathode main electrode 4a is short, discharge breakdown occurs between them and an auxiliary discharge occurs between the auxiliary electrode 10 and the cold cathode main electrode 4a. I do. This auxiliary discharge emits a large amount of electrons, and thus induces a main discharge of the pair of cold cathode main electrodes 4a and 4b facing each other. That is, according to such a lamp, an auxiliary discharge is easily generated between the auxiliary electrode 10 and the cold cathode type main electrode 4a even in a dark atmosphere or a low-temperature atmosphere, and this auxiliary discharge quickly becomes the main discharge. Since the transition is made, the startability is improved.

By the way, the present inventors have proposed the starting auxiliary electrode 1.
When 0 was used, the relationship between the polarity of the starting auxiliary electrode 10 and the starting time was examined. First, the specific structure of the lamp is such that the distance L between the cold cathode main electrodes 4a and 4b is 25 mm, and the discharge gap d between the starting auxiliary electrode 10 and the main electrode 4a close to the auxiliary electrode 10 is 0. 3 mm, the argon gas sealed in the bulb 1 was 80 Torr, and the cold cathode main electrodes 4a and 4b were connected to the pulse generation lighting circuit 20.
The pulse generation lighting circuit 20 has a repetition frequency f of 15 KH.
z, and has a one-way polarity with an on / off duty ratio having a pause period τ of 0.1. With such a configuration, the type A without the auxiliary electrode for starting shown in FIG.
Then, a type B lamp in which the auxiliary starting electrode 10 is connected to the negative electrode as in the present embodiment shown in FIG. 2 and a type C lamp in which the auxiliary auxiliary electrode 10 for starting is connected to the anode as shown in FIG. 3 are produced. In this case, the starting auxiliary electrode 10 was connected to the pulse generation lighting circuit 20 via an impedance 21 of 1 MΩ.

The main discharge time delay τ _s (msec) was measured for each lamp having such a configuration. The time delay τ _s of the main discharge in each type of lamp is shown in FIG.
Is defined as shown below. That is, in the type A without the auxiliary starting electrode shown in FIG. 5, the time from the application of the starting voltage to the start of the main arc discharge between the main electrodes 4a and 4b is set to the time delay τ _{s of the} main discharge. . On the other hand, in the case of the type B of FIG. 2 and the type C of FIG. 3 in which the auxiliary electrode 10 for starting is provided, the time delay τ _s of the main discharge is equal to the applied starting voltage because of the starting behavior described above. The first stage from the time when the auxiliary discharge occurs between the auxiliary electrode 10 and the cold cathode type main electrode 4a, that is, the auxiliary discharge delay time τ _s1, and the pair of cold cathode type main electrodes 4a and 4b from the start of the auxiliary discharge The second stage until the transition to the main discharge, that is, the main discharge transition time τ _s2
(Τ _s = τ _s1 + τ _s2 ).

For each of the above lamps, the ambient temperature was 25
Applied voltage (Vin / V) when started in the dark of
FIG. 7 shows the result of measuring the relationship between s) and the time delay τ _s of the main discharge. The applied voltage is about Vs = 400 V in the A type without the auxiliary electrode. From the results of FIG. 7, FIG.
2 and 3, the type B and the type C provided with the starting auxiliary electrode 10 shown in FIG. 2 and FIG. 3 greatly reduce the time delay τ _s of the main discharge as compared with the type A without the starting auxiliary electrode shown in FIG. Can be. This is apparently because the auxiliary discharge triggers the discharge even in the dark and promotes the main discharge.

Further, comparing type B and type C,
It is recognized that the type B shown in FIG. 2 can shorten the time delay τ _s of the main discharge. This is for the following reason. That is, the time delay τ _s of the main discharge when the starting auxiliary electrode is used is the sum of the auxiliary discharge delay time τ _s1 and the main discharge transition time τ _s2 (τ _s = τ _s1 + τ _s2 ) as described above. is there. When the auxiliary electrode 10 is an anode, the main discharge transition time τ _s2 is related to the drift time until electrons emitted from the auxiliary electrode 10 reach the opposite main electrode 4b.
When 0 is a negative electrode, it is related to the drift time until ions emitted from the auxiliary electrode 10 reach the opposite main electrode 4b. Here, the drift time is defined by (distance between electrodes / drift speed), and is a time required for electrons or ions to travel a predetermined distance at a speed obtained by an electric field, and is compared with ions. Electrons tend to have a shorter drift time. Therefore, if the main discharge transition time is limited to τ _s2 , it may be advantageous to connect the auxiliary electrode 10 to the anode in order to shorten the rise of the starting time. However, the main discharge transition time τ _s2 is much shorter than the auxiliary discharge delay time τ _s1 , and the influence of the main discharge transition time τ _s2 on the main discharge time delay τ _s is small and negligible. . Therefore, in the case of starting in the dark, it is only necessary to pay attention to the auxiliary discharge delay time τ _s1 . Considering the auxiliary discharge delay time τ _s1 , the type B in which the starting auxiliary electrode 10 is set to the negative electrode (−) is more advantageous from the difference in the effective electric field strength on the electrode surface. In other words, the starting auxiliary electrode 10 has a thin and sharp tip, and the size of the auxiliary discharge generating point is smaller than that of the auxiliary discharge generating portion of the main electrode 4a close to the auxiliary discharge generating point. When the electrode 10 is set to a negative (-) potential, an uneven electric field is generated and the electric field is concentrated on the auxiliary electrode 10, and the electric field strength at the tip of the auxiliary electrode 10 is reduced.
The positive (+) as compared to the B type and the potential, the effective electric field strength of the electrode surface increases, thus assisting the discharge delay time tau _s1
Can be shortened.

Therefore, as shown in FIGS. 1 and 2, if the starting auxiliary electrode 10 is connected to the negative electrode (-), the discharge delay in the dark can be eliminated, and the main electrode can be turned on in a short time. Discharge is induced, and the starting characteristics are greatly improved.

In the above embodiment, the cold cathode fluorescent lamp is lit by applying a unidirectional pulse voltage by the pulse generation lighting circuit 20. However, the present invention is not limited to this. As shown in FIG. 8, an AC voltage from an AC power source 30 is applied between the main electrodes 4a and 4b so that the main electrode 4a and the main electrode 4b are turned on. The present invention can be implemented even if the connection is made to have a negative polarity with respect to 4a.

Further, the present invention is not limited to a fluorescent lamp in which mercury is sealed in a bulb, but may be a rare gas discharge lamp using no mercury. The inert gas sealed in the valve is not limited to argon, but may be xenon Xe or krypton K.
The lamp may be a lamp in which at least one known inert gas generally used in discharge lamps such as r and neon Ne is filled.

[0027]

According to the present invention, as described above, according to the present invention, beginning
Adjust the size of the tip of the moving auxiliary electrode
The electric field is concentrated on the auxiliary electrode, and the electric field strength at the tip of the auxiliary electrode is increased. Discharge is generated, and the delay time τs1 of the auxiliary discharge can be reduced. Therefore, the main discharge delay time can be reduced, the discharge delay in darkness can be eliminated, and the starting characteristics can be greatly improved.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a flat cold cathode fluorescent lamp according to an embodiment of the present invention.

FIG. 2 is a sectional view of the lamp shown together with the lighting circuit in the embodiment.

FIG. 3 is a sectional view of a lamp shown together with a lighting circuit showing a bad example.

FIG. 4 is an exploded perspective view of a flat cold cathode fluorescent lamp showing a conventional example.

FIG. 5 is a sectional view of a lamp shown together with a lighting circuit in a conventional example.

FIG. 6 is a diagram illustrated to define a main discharge delay time.

FIG. 7 is a characteristic diagram showing a relationship between a main discharge delay time and an applied voltage.

FIG. 8 is a sectional view of a lamp shown together with a lighting circuit according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flat valve, 2 ... Fluorescent coating, 3 ... Stem, 4
a, 4b: cold cathode type main electrode, 10: auxiliary electrode, 20: pulse generation lighting circuit, 21: impedance.

Claims (3)

(57) [Claims] 1. A low-pressure discharge lamp in which a pair of main electrodes are provided in an arc tube opposed to each other, and a starting auxiliary electrode is provided in the vicinity of one of the main electrodes, and is turned on by a main discharge between the main electrodes. The starting auxiliary electrode is close in size at its tip.
It is formed so as to be thinner than the auxiliary discharge generation part of the main electrode.
Low-pressure discharge lamp, characterized in that the polarity of the negative potential with respect to which is, and the main electrode in proximity. Wherein said low-pressure discharge lamp, a low-pressure discharge lamp according to claim 1, characterized in that so as to light by applying a DC voltage or a unidirectional pulsed voltage between the main electrodes. 3. A low-pressure discharge lamp according to claim 1, wherein said low-pressure discharge lamp is a flat fluorescent lamp whose main electrode is a cold cathode.
Alternatively, the low-pressure discharge lamp according to claim 2 .