JPH0587940B2 - - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to improvements in high pressure discharge lamps such as high pressure sodium lamps used for general lighting, and more particularly to improvements in high pressure discharge lamps in which a starting device is housed inside the outer bulb.

[0002]

BACKGROUND OF THE INVENTION High-pressure discharge lamps such as high-pressure sodium lamps are difficult to start with normal commercial power supply voltage, and therefore require the application of a high-voltage pulse voltage to start them. Lamps in which a device for generating such a pulse voltage is grounded within the outer bulb of the lamp and used in combination with a general high-pressure mercury lamp ballast have become popular.
A lamp basically consists of a ferroelectric ceramic capacitor connected in parallel with an arc tube, and by combining this with a semiconductor switch or diode, a high voltage pulse voltage is generated, which is applied to the arc tube together with the power supply voltage. to start the lamp. Incidentally, in order to start such a high-pressure sodium lamp, it is generally necessary to apply a pulse voltage having a peak value of 2000 V or more, although this depends on the xenon gas pressure within the arc tube that constitutes the lamp. It is effective to use a ferroelectric ceramic capacitor as a means for stably generating such a high voltage pulse voltage. This capacitor is D (charge) - E (coercive electric field) as shown in Figure 4.
have characteristics. By utilizing the rectangular characteristics of this capacitor and performing a switching action, it is possible to generate the above-mentioned high voltage pulse voltage.

[0003] Although the generation of such a high-pressure pulse voltage is very effective for starting a high-pressure sodium lamp, it is necessary to consider problems that occur at the end of the life of a high-pressure sodium lamp. That is, in general, high-pressure sodium lamps tend to leak at the electrode seal portion of the arc tube at the end of their life, and this often causes xenon gas, sodium, and mercury inside the arc tube to come out into the outer bulb. In this case, since the inside of the lamp's outer bulb is in a high vacuum, when a pulse voltage is applied to the lamp, discharge starts throughout the lamp's outer bulb, and naturally a large current flows due to arc discharge. If this condition continues for a long time, the ballast installed outside the lamp may be burnt out, and most dangerously, the outer bulb may be damaged by the arc within the bulb.

[0004]

[Summary of the Invention] The present invention has been made in view of the above points, and is a high-pressure discharge lamp equipped with a safety function to prevent damage to the glass bulb or burnout of the ballast at the end of the lamp's life. The purpose is to provide To achieve this objective, the present invention normally generates a high-pressure pulse to start the arc tube, but detects the leakage of xenon gas into the outer bulb due to arc tube leakage that occurs at the end of the lamp life. It has a structure in which means for stopping the generation of a high voltage pulse for starting is included in the outer sphere.

[0005]

[Description of Embodiments] An example of the circuit configuration of a high-pressure discharge lamp according to the present invention is as shown in FIGS. 1 and 2, and a specific example of the configuration is as shown in FIG. 3. In each case, a ferroelectric ceramic capacitor 2 is connected in parallel to the arc tube 1, and these are housed in an outer bulb 5 with a high vacuum inside. The ferroelectric ceramic capacitor 2 is generally made by adding several mol% of strontium titanate, barium zirconate, barium stannate, etc. and a trace amount of rare earth oxide powder to barium titanate powder, granulating it, and pressing it into a disk shape. A ceramic substrate 7 as shown in FIG. 5 is produced by molding and firing in air, and electrode films 8a and 8b are formed on both surfaces of the ceramic substrate 7 using silver paste or the like. This is overcoated with ferroelectric crystallized glass paste 9 except for the lead terminal portions, and then lead terminals 10a and 10b are adhered to the lead wire terminal portions for finishing. The above-mentioned ferroelectric crystallized glass paste 9 for overcoat is basically
It has a structure of xBaTiO ₃ + (1-x) BaAl ₂ Si ₂ O ₈ , and the relative permittivity ε _S can be adjusted by changing the firing temperature and holding time.
It can be 300-1200.

[0006] If the capacitor is housed in the outer bulb without overcoating as described above, discharge will occur from the entire surface or edge of the silver film electrode when a high voltage pulse voltage is generated, which will not only cause damage to the electrode film, but also cause damage to the electrode film.
It will destroy the ceramic base. This is because a high electric field is concentrated in a narrow electrode film, and because the silver film electrode itself is mixed with oxide, ie glass frit, the work function of the silver film electrode itself is low, making it easier for electrons to emit field. This is because there is. In order to prevent such electrode radiation, as mentioned above, the electric field on the electrode film surface can be lowered by overcoating the basic ceramic capacitor with a material having a higher dielectric constant. In other words, when using such a capacitor, factors such as the distance between the periphery of the silver film electrode and the periphery of the ceramic substrate, the thickness of the ferroelectric crystallized glass film, and the xenon gas pressure as the atmosphere must be selected appropriately. By doing so, it is possible to prevent discharge in the ceramic capacitor during normal lighting of the high-pressure discharge lamp, and to cause discharge to occur at the end of the lamp's life, destroying the high-pressure pulse voltage generation function. Therefore, among the above factors, the inventors focused on the fact that the distance between the periphery of the silver film electrode and the periphery of the ceramic substrate had a particularly large effect, and conducted the following experiment on discharge breakdown of a capacitor.

[0007] As the ceramic substrate 7 shown in FIG. 5, a barium titanate-based material with non-linear characteristics as described above is fired and used as a disc-shaped material with a diameter of 26.0 mm and a thickness of 0.5 mm. By changing the distance d between the periphery of the substrate 7 and the peripheries of the silver film electrodes 8a and 8b, the film thickness t of the ferroelectric crystallized glass 9, and the xenon gas pressure inside the outer sphere in which this capacitor is installed, a high-voltage pulse voltage is generated. was generated, and the state of discharge destruction of the capacitor was investigated. The results of the experiment were as shown below. In addition, in the table showing the experimental results, the symbols ×, ○, and Δ indicate the following conditions, respectively. ×: No discharge damage. ○: Destruction occurred due to discharge. △: Edge discharge occurs but does not lead to destruction.

[Table 1] ■■■ Turtle shell [0007] ■■■

[Table 2] ■■■ Turtle shell [0008] ■■■

[Table 3] ■■■ Turtle shell [0009] ■■■

[0008] These experiments were conducted using the circuit shown in FIG. In this circuit, when the input of the AC power supply 11 is 200V/50Hz, the output side of the chiyoke coil 6 is 2000~
A high voltage pulse voltage with a peak value of 2600V is generated. 2 is a ceramic capacitor, 4 is a diode, 12 is a resistor, and 3 is an SSS element. Next, the relationship between the diameter of the coated surface of the silver film electrode of this ceramic substrate and the peak value of the high voltage pulse voltage was measured, and the result was as shown in FIG. The diameter of the silver film electrode is 24
mm, and the pulse voltage decreases when the distance d between the periphery of the electrode and the periphery of the ceramic substrate exceeds 1.0 mm. Therefore, increasing the non-bonding area of the electrode is necessary to ensure that the lamp lights up. This is disadvantageous in generating high-voltage pulses. Therefore, it is desirable that the non-stick distance between the peripheral edges be 1.2 mm or less.

[0009] In addition, if the thickness t of the coating film of ferroelectric crystal glass exceeds 30 μm, the ceramic capacitor cannot be destroyed at the stage where slow leakage of the arc tube 1 starts, and 10 ^-3 to 10 ^-2 torr When the gas pressure is on the order of magnitude, the current flowing through the ballast 10 is 1.2 to 1.4 times as much as normal, and if this time is prolonged, an overcurrent will flow to the ballast windings, potentially causing the windings to burn out. Therefore, it is desirable that the thickness of the coating film of ferroelectric crystallized glass be 10 to 20 μm.

[0010] The present invention was actually implemented using a high-pressure sodium lamp with a rated input of 360W. The internal volume of the arc tube was 5.1 cc, and xenon gas was sealed therein with appropriate amounts of mercury and sodium at a pressure of 150 torr. Since the outer sphere is 1000 c.c., this arc tube 1
If all the xenon gas leaks into the outer sphere 5
The pressure will be 0.8torr. Inside this outer sphere, a ferroelectric ceramic capacitor having a structure as shown in FIG. 5 and having the conditions confirmed in the experiment described above, that is, the distance between the peripheral edges of the ceramic substrate and the silver film electrode was 0 to 1.2 m, was housed. When a high pulse voltage was generated, the ferroelectric ceramic capacitor was reliably destroyed by the xenon gas leaking from the seal of the arc tube 1 at the end of the lamp's life.

[0011]

Effects of the Invention As is clear from the above description, according to the present invention, by appropriately selecting the structure and dimensions of the ferroelectric ceramic capacitor constituting the starting device, high voltage pulse voltage can be applied at the end of the lamp life. It is possible to effectively prevent damage to the glass bulb and burnout of the ballast caused by this.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a high-pressure discharge lamp according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a high-pressure discharge lamp according to a second embodiment of the present invention.

FIG. 3 is a detailed structural diagram of the lamp.

FIG. 4 is a voltage-charge characteristic diagram of a ferroelectric ceramic capacitor used in the present invention.

FIG. 5 is a cross-sectional view of a ferroelectric ceramic capacitor used in the present invention.

[Figure 6] This is a test circuit for the same capacitor.

FIG. 7 is a diagram showing the relationship between the distance between the ceramic substrate and the periphery of the electrode of the same capacitor and the peak value of the high-voltage pulse voltage.

[Explanation of symbols]

1 arc tube, 2 Ferroelectric ceramic capacitor, 5 outside ball, 7 Ceramic substrate, 8a, 8b silver film electrode, 9 Ferroelectric crystallized glass.

Claims (5)

[Claims] 1. An arc tube 1 in which a discharge gas is sealed, an outer bulb 5 having a vacuum interior for accommodating the arc tube, and an outer bulb 5 housed inside the outer bulb for generating a high-voltage pulse for starting the arc tube. In the high-pressure discharge lamp comprising means 2, 3, and 4, the high-pressure pulse generating means for starting the arc tube detects when the inside of the outer bulb reaches a predetermined gas pressure or more due to discharge gas leaking from the arc tube. A high-pressure discharge lamp characterized in that the generation of the high-pressure pulse for starting the arc tube is stopped in response to the above. 2. The high pressure discharge lamp according to claim 1, wherein the predetermined gas pressure is a high pressure selected to be less than or equal to the gas pressure at which arc discharge occurs within the outer bulb when the high pressure pulse is generated. discharge lamp. 3. The high-pressure discharge lamp according to claim 2, wherein the arc tube starting high-pressure pulse generating means includes means for discharging when the predetermined gas pressure is reached. 4. In the high-pressure discharge lamp according to claim 1, the high-pressure pulse generating means includes a switching ferroelectric ceramic capacitor having hysteresis characteristics with respect to polarization and applied voltage; A high-pressure discharge lamp that is destroyed by discharge by the starting high-pressure pulse at the predetermined gas pressure. 5. In the high-pressure discharge lamp according to claim 3, the capacitor comprises a flat ceramic substrate 7 and electrodes 8a and 8b attached on both sides of the substrate except for the periphery of the substrate. Consisting of
A high-pressure discharge lamp, wherein the discharge breakdown is due to discharge in the peripheral area.