JPH0775191B2 - Surge absorption element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge absorbing element for protecting electronic components from a surge such as a transient abnormal voltage or a lightning surge that enters an electronic device. More specifically, it relates to a surge absorbing element that can be miniaturized without using a cap electrode.

[0002]

2. Description of the Related Art A surge absorbing element of this type is connected to a pair of input lines of an electronic device in parallel with the electronic device and is configured to operate at a voltage higher than the operating voltage of the electronic device. That is, the surge absorbing element is a resistor having a high resistance value at a voltage lower than the discharge starting voltage, but becomes a resistor having a low resistance value of several tens Ω or less when the applied voltage is equal to or higher than the discharge starting voltage. When a surge voltage such as a lightning surge is momentarily applied to an electronic device, the surge absorbing element discharges and absorbs the surge voltage. As a result, the surge voltage is not applied to the electronic device, and the failure or malfunction of the electronic device due to the surge voltage is avoided.

Among the conventional gap type surge absorbers,
As shown in FIG. 6, the microgap type surge absorbing element has a cylindrical ceramic body 1 whose peripheral surface is covered with a conductive film 1a. A microgap 1b having a width of several tens to 50 μm is formed on the peripheral surface of the central portion of the ceramic body 1 by trimming the conductive film 1a with a laser beam or the like. A pair of cap electrodes 2 and 3 are capped on both ends of the ceramic body 1, and a pair of sealing electrodes 6 having lead wires 4 and 5 welded to the outer surfaces of the cap electrodes 2 and 3 are attached to the respective end surfaces of the cap electrodes 2 and 3. 7 is abutted. The surge absorbing element 9 accommodates the ceramic body 1 with the cap electrodes 2 and 3 and the sealing electrodes 6 and 7 with the lead wires 4 and 5 in contact with each other in the glass tube 8 as shown in the drawing. In this state, the glass tube 8 is filled with an inert gas and the glass tube 8 is sealed to the electrodes 6 and 7.

[0004]

In the above-mentioned conventional microgap type surge absorbing element, since the discharge at the time of surge absorption occurs at the outer surface portion of the ceramic body, the cap electrodes are attached to both ends of the ceramic body. A clearance is created between the outer surface and the inner wall of the glass tube. In order to reduce the size of the surge absorber with the above conventional structure, it is conceivable to reduce the outer diameter of the cylindrical ceramic body. However, when the ceramic body is made small in this way, there arises a problem that it becomes difficult to attach the cap electrode. Therefore, the surge absorbing element cannot be downsized.

The object of the present invention is to provide excellent surge absorption performance,
Another object of the present invention is to provide a surge absorbing element which can be miniaturized and requires a small mounting space.

[0006]

The structure of the present invention for achieving the above object will be described with reference to FIGS. 1 and 2 corresponding to the embodiments. The surge absorbing element 19 of the present invention includes a ceramic element body 11, a pair of cylindrical electrodes 16 and 17, and an insulating tube body 18. In the ceramic body 11, the protrusion 11d is provided on a part of the peripheral surface of the ceramic columnar body 11c.
And a cylindrical body 11 that is integrally formed with the protrusion 11d.
The entire surface of c is covered with the conductive film 11a, and the projection 11
The microgap 11b is formed by removing a part of the film 11a on the peripheral surface of the columnar body 11c where d is not formed.
The pair of electrodes 16 and 17 have an outer diameter slightly larger than the outer diameter of the protruding portion of the ceramic body 11.
Is abutted on both end faces of the. The insulating tube body 18 encloses the ceramic body 11 with which the pair of electrodes 16 and 17 are in contact, and is filled with an inert gas to be sealed on the outer circumference of the electrodes 16 and 17.

The ceramic cylindrical body 11c is not particularly limited as long as it is an insulating material, but is highly insulating with a volume resistivity of 10 ¹⁴ Ωcm or more, such as alumina, mullite, zirconia, steatite, forsterite or beryllia. Ceramics are preferred. The protrusion 11d is provided so that the cylindrical portion of the ceramic cylindrical body 11c does not contact the inner wall of the insulating tubular body 18 when the ceramic body 11 is inserted into the insulating tubular body 18. For this reason, it is preferable to provide the protrusions 11d on both ends of the ceramic columnar body 11c, but it is also possible to provide the protrusions 11d on one end in consideration of die cutting when the ceramic columnar body including the protrusions is injection-molded. As the shape of this projection, in addition to the perfect circular flange 11d as shown in FIGS. 1 and 2, an elliptical flange 11e as shown in FIG. 3 and a triangular flange 1 as shown in FIG.
It may be 1f.

The conductive coating 11a formed on the surface of the ceramic columnar body 11 including the protrusions 11d, 11e or 11f has excellent conductivity such as titanium, nickel, tin oxide or titanium nitride. Metal thin films are preferred. This film is formed by wrapping the entire cylindrical body 11 by sputtering, vacuum deposition or the like. A microgap 11b having a width of about several tens to 50 μm is formed on the peripheral surface of the ceramic body 11 by trimming the conductive film 11a with a laser beam. In order to eliminate the electrical polarity of the surge absorbing element 19, the microgap 11b has the ceramic columnar body 1 excluding the protrusions 11d, 11e or 11f.
It is preferably formed in the central portion of 1c. Electrode 16,
A material 17 having a thermal expansion coefficient close to that of the insulating tubular body 18 is selected so that the tubular body is not cracked when the insulating tubular body 18 is sealed. When the insulating tube is a glass tube made of borosilicate glass, lead glass or the like, a Dumet wire or an amber (Invar) with which the thermal expansion coefficient of the glass tube is matched is preferable. It is possible to weld the lead wires 14 and 15 to the outer surfaces of the electrodes 16 and 17 before the insulating tube 18 is sealed. A rare gas such as argon gas, nitrogen gas, or a mixed gas thereof is sealed in the insulating tube body 18.

The surge absorbing element of the present invention is manufactured by the following method. First, if necessary, one electrode 16 having the lead wire 14 welded thereto is inserted into one end of the insulating tube body 18 so that the other end of the insulating tube body 18 is positioned above. Stand the body 18 vertically. Then, the conductive film 1
The ceramic body 11 covered with 1a and having the microgap 11b formed therein is dropped into the insulating tubular body 18. Next, if necessary, the other electrode 17 having the lead wire 15 welded thereon is inserted into the insulating tubular body 18. With the ceramic body 11 held between the electrodes 16 and 17, the inside of the insulating tube body 18 is evacuated to remove air, and an inert gas is introduced instead. When the insulating tubular body 18 and the electrodes 16 and 17 are heated by a carbon heater (not shown) in this state, the insulating tubular body 18 is sealed to the electrodes 16 and 17.

[0010]

When the surge voltage is applied to the electrodes 16 and 17,
A creeping discharge occurs in the conductive film 11a through the microgap of the ceramic body 11, and then the electrode 16 and the electrode 1
An arc discharge is generated between the target and the target. Since the projections 11d to 11f play the role of the conventional cap electrode, the surge absorbing element 19 of the present invention can secure the clearance between the outer surface portion of the ceramic body 11 and the inner wall of the insulating tube body 18, and thus the conventional surge absorbing element. While having the same surge absorption performance as
The surge absorber 19 can be miniaturized.

[0011]

EXAMPLES Next, examples of the present invention will be described together with comparative examples. The invention is not limited to this example. <Example> As shown in FIGS. 1 and 2, a ceramic body 11 having a perfect circular flange 11d formed at its end is prepared. The element 11 has a total length of about 1.5 mm, a ceramic columnar portion has a length of about 1.0 mm, and a flange portion has a length of about 0.5 mm. The outer diameter of the cylindrical portion is about 0.6 mm, and the outer diameter of the flange portion is about 0.9 mm. The flange is an alumina sintered body integrally molded with the cylindrical body. The ceramic body 11 is covered with a conductive coating 11a made of titanium. The film 11a is formed by sputtering. A microgap 11b having a width of about 30 μm is formed by trimming the conductive film 11a with a laser beam in the central portion of the ceramic columnar body 11c excluding the protrusion 11d. The electrode 16 having the lead wire 14 welded to the outer surface is in contact with one end surface of the ceramic body 11, and the electrode 17 having the lead wire 15 welded to the outer surface is in contact with the other end surface of the ceramic body 11. The pair of electrodes 16 and 17 are formed by cutting a Dumet wire having a diameter of about 1.0 mm into a length of about 1.8 mm. The ceramic body 11 is held between electrodes 16 and 17 in a glass tube 18 made of lead glass having an inner diameter of about 1.02 mm, and in this state, the insulating tube 18 is filled with argon gas so that the insulating tube 18 surrounds the electrodes 16 and 17. Is sealed to. The dimensions of the surge absorbing element 19 after sealing are about 2.0 mm in outer diameter and about 5.0 m in length.
m.

<Comparative Example> The aforementioned surge absorbing element 9 shown in FIG. 6 was used as a comparative example. Here, the ceramic body 1 has a length of about 3.1 mm and a diameter of about 1.0 mm, and is a mullite sintered body. A conductive film 1a made of the same material and having the same thickness as that of the embodiment is formed on this surface, and a microgap 1b having a width of about 30 μm is formed on the outer peripheral surface of the central portion thereof. The end electrodes of the stainless steel cap electrodes 2 and 3 are in contact with the sealing electrodes 6 and 7 having a length of about 1.8 mm and a diameter of about 1.5 mm and made of the same material as the embodiment. The ceramic body 1 with the cap electrodes 2 and 3 and the sealing electrodes 6 and 7 with the lead wires 4 and 5 are housed in a glass tube 8 having an inner diameter of about 1.55 mm, and the glass tube 8 contains argon gas inside. It is filled and sealed to the electrodes 6 and 7. Surge absorbing element 9 after sealing
The outer diameter is about 2.6 mm and the length is about 7.0 mm.

An electrostatic life test and a pseudo surge response test were conducted on the surge absorbing elements of the examples and comparative examples. <Electrostatic life test> Output terminal 21 of the circuit shown in FIG.
An electrostatic life test was conducted by connecting the lead wires of the surge absorbing element to Nos. 22 and 22. In FIG. 5, 23 is a 10 kV DC power source, 24 is a capacitor having an electrostatic capacity of 500 pF, 25 is a resistor of 500Ω, and 26 is a charge / discharge changeover switch. The switch 26 is switched to the contact a as shown by the solid line in the figure, and a voltage of 10 kV is applied to the capacitor 24 to charge the capacitor 24. Then, the switch 26 is switched to the contact b as shown by the broken line in the figure to discharge the capacitor 24. Then, static electricity was applied to the surge absorbing element. The above static electricity was repeatedly applied 2000 times to the surge absorbing elements of Examples and Comparative Examples, and the discharge starting voltage, insulation resistance, and capacitance of each surge absorbing element before and after the test were measured. As a result, the surge absorption element of the comparative example before the test had an average discharge starting voltage of about 2
50 V, standard deviation 15 V (the number of samples is 50), while the surge absorption element of the example has an average discharge starting voltage of about 250.
V, the standard deviation was 15 V (the number of samples was 50), the insulation resistance was 10 ¹⁰ Ω or more, and the capacitance was 0.5 pF.
When measured after the test, the surge absorption elements of the example and the comparative example each had an average discharge start voltage of about 250 V, an insulation resistance value of 10 ¹⁰ Ω or more, and a capacitance of 0.5 pF. There was no

<Pseudo Surge Response Test> A voltage surge of (1.2 × 50) μsec−2 kV was repeatedly applied 100 times to the surge absorbing elements of Examples and Comparative Examples, and the operating voltage was measured. The surge absorbing elements of Examples and Comparative Examples were designed to have a DC discharge inception voltage of 250V. The surge absorbing element of the comparative example started discharging at an average of about 350 V and its standard deviation was 50 V (the number of samples was 20), whereas the surge absorbing element of the example also had an average of about 350 V.
Discharge started at 50V with a standard deviation of 50V (25 samples)
Met. From the above, it was found that the surge absorbing element of the example is not inferior in durability and surge absorbing characteristics to the surge absorbing element of the comparative example.

[0015]

As described above, in the surge absorbing element of the present invention, the protrusion is used instead of the conventional cap electrode to secure the clearance between the outer surface portion of the ceramic body and the inner wall of the insulating tube. The surge absorbing element can be downsized while having the same surge absorbing performance as the surge absorbing element of, and as a result, the mounting space of the surge absorbing element can be further reduced. In particular, the miniaturized surge absorber is a standard of the Japan Electronic Machinery Manufacturers Association (Standards of Electronic I
ndustries Association of Japan, abbreviated EIAJ standard)
Metal Electrode Face Bonding
The surge absorbing element of the present invention can be easily adapted to a melf type element because it can meet the dimensional standard of Device).

[Brief description of drawings]

FIG. 1 is a sectional view of a surge absorber according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view thereof.

FIG. 3 is a perspective view of a ceramic body according to another embodiment of the present invention.

FIG. 4 is a perspective view of a ceramic body according to still another embodiment of the present invention.

FIG. 5 is an electrostatic life test circuit of Examples and Comparative Examples.

FIG. 6 is a sectional view of a conventional surge absorber.

[Explanation of symbols]

 11 Ceramic Element 11a Conductive Film 11b Micro Gap 11c Ceramic Column 11d, 11e, 11f Protrusion 14, 15 Lead Wire 16, 17 Electrode 18 Insulation Tube 19 Surge Absorption Element

Claims (7)

[Claims] 1. A projection (11d, 11e, 11f) is integrally formed with the cylinder (11c) on a part of the peripheral surface of the ceramic cylinder (11c), and the projection (11d, 11e, 11f) is formed. The entire surface of the columnar body (11c) including is covered with a conductive film (11a), and the protrusions (11d, 11
e, 11f) a ceramic body (11) in which a microgap (11b) is formed by removing a part of the film (11a) on the peripheral surface of the cylindrical body (11c) where the ceramic body (11c) is not formed. A pair of cylindrical electrodes (16, 17) having an outer diameter slightly larger than the outer diameter of the protruding portion of (11) and abutting on both end surfaces of the ceramic body (11), and the pair of electrodes ( (16, 17) abutted ceramic body (1
A surge absorbing element comprising (1) and an insulating tube (18) which is filled with an inert gas and sealed around the electrodes (16, 17). 2. The projection (11d, 11e, 11f) has a ceramic columnar body.
The surge absorber according to claim 1, wherein the surge absorber is formed at the end of (11c). 3. The surge absorbing element according to claim 2, wherein the projections (11d, 11e, 11f) are flanges. 4. The conductive film (11a) comprises titanium, nickel,
The surge absorbing element according to claim 1, which is tin oxide or titanium nitride. 5. The microgap (11b) has protrusions (11d, 11e,
The surge absorbing element according to claim 2, wherein the surge absorbing element is formed in a central portion of the ceramic columnar body (11c) excluding 11f). 6. The surge absorbing element according to claim 1, wherein the insulating tube body (18) is a glass tube. 7. The surge absorbing element according to claim 1, wherein the inert gas is a rare gas, a nitrogen gas, or a mixed gas thereof.