JP2676730B2 - Surge absorption element for low voltage - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surge absorbing element for low voltage, and more particularly to a surge absorbing element for low voltage in which a discharge starting voltage is specially lowered. [Prior art] As a method of using a surge absorbing element, generally, a surge absorbing element having an operating voltage higher than the maximum circuit voltage of a circuit to which the surge absorbing element is attached is attached, and an instantaneous overvoltage such as a lightning surge is attached to the circuit. The surge absorbing element operates only when the intrusion occurs, thereby protecting the electronic components attached to the circuit. In the conventional surge absorption element, the operating voltage, that is, the discharge start voltage, changes the number of micro gaps,
Adjustments were made by changing the shape of the microgap. Therefore, the range of adjustment of the discharge voltage is limited. [Problems to be Solved by the Invention] An object of the present invention is to provide a surge absorbing element in which the discharge starting voltage is lowered and the discharge delay is reduced. That is, an object of the present invention is to provide a surge absorbing element that can be used in parts and circuits having low surge withstand voltage. Another object of the present invention is to provide a surge absorbing element with improved life characteristics. Another object of the present invention is to provide a surge absorbing element with improved reliability of parts. [Structure of the Invention] [Means for Solving Problems] Here, the gist of the present invention is to provide a microgap element provided with a microgap for discharge and an insulating jacket for the discharge. In a surge absorbing element for low voltage, which has an internal space formed between the body, in the internal space, the microgap element is separated from a surface of the microgap element by a certain distance from at least one electrode terminal of the microgap element. Is a surge absorbing element for low voltage, in which an auxiliary electrode extending to at least a microgap position is provided along the surface of the surge absorbing element. Then, it is preferable that at least a part of the surface of the auxiliary electrode is coated with a metal or compound having a low work function. [Operation] According to the present invention, a structure in which an auxiliary electrode is incorporated inside a microgap type surge absorbing element is made to facilitate glow discharge and arc discharge of the surge absorbing element when an overvoltage is applied. is there. In the present specification, a microgap element includes an “insulator and a conductive thin film divided through a plurality of microgaps provided on the surface of the insulator, and a predetermined voltage is a value for the divided conductive thin film. It is called an element that absorbs surges when discharge occurs between them when it takes time. The microgap type surge absorbing element is provided with "an internal space defined by an outer casing, which internally has this microgap element and a pair of metal electrodes that are in close contact with both ends of the divided microgap element of the conductive thin film. , A surge absorption type having an external terminal coupled to each of the pair of electrodes and absorbing a surge by generating a discharge between the metal electrodes in the internal space when a surge overvoltage and overcurrent is applied. Say "element". Therefore, the microgap means a plurality of grooves that divide the conductive thin film formed on the surface of the insulator. According to the present invention, there is provided a microgap type surge absorbing element having an auxiliary electrode made of metal mechanically and electrically connected to a lead wire or a cap of an element in a sealing glass of a conventional microgap type surge absorbing element. To use. By thus inserting the auxiliary electrode into the sealing glass, the electric field distribution in the surge absorbing element tends to be non-uniform, and electrons are easily emitted from the surface of the auxiliary electrode. Therefore, the effects of lowering the discharge start voltage and the discharge delay are produced. Furthermore, the microgap type surge absorber having the auxiliary electrode has the effect of extending the life with respect to repeated application of impulses. That is, in the discharge in the microgap type surge absorbing element having no auxiliary electrode, glow discharge occurs in the vicinity of the microgap, and finally the cap-to-cap arc discharge occurs. This arc discharge deteriorates the gap in the surge absorbing element and the film formation. However, since the surge absorbing element according to the present invention has a structure having an auxiliary electrode, arc discharge occurs between the cap and the auxiliary electrode, and arc discharge occurs at a position above the gap and the film so that the arc discharge passes over the film. Since it does not occur, the life characteristics of the surge absorber are improved. In the structure according to the present invention, the auxiliary electrodes are provided in the surge absorbing element, and the number of the inserted electrodes is one or more. The shape of the auxiliary electrode is not particularly limited, but one having a sharp end face is preferable in order to enhance the electron emission effect and the electric field concentration. In addition, as the auxiliary electrode material, Fe, N with good electrical conductivity is used.
Metals such as i, Ti, Zr, and Ta or alloys thereof, or alloys such as stainless steel can be used, but not limited to them. The method for producing the auxiliary electrode according to the present invention is not particularly limited in connection method, but it is connected to the lead wire or the cap by spot welding, caulking or the like. As described above, according to the present invention, by using the auxiliary electrode,
The discharge starting voltage can be reduced. Furthermore, in the present invention, it is considered to apply a metal or compound having a low work function to the surface of the auxiliary electrode. This is intended to enhance the electron emission effect at the start of discharge by applying a substance having a low work function to the surface of the auxiliary electrode. The substance to be applied to the surface of the auxiliary electrode is a compound of alkali metal or alkaline earth metal, Ba-Al alloy, TiC, ZrC, Ta.
Substances such as C are effective, but are not particularly limited as long as they have a low work function. As the coating method, a vapor deposition method, an organic solvent suspension method or the like can be used, but the coating method is not particularly limited. Further, in the present invention, a substance that needs to be reduced after coating can be reduced by heating with radiant heat, high frequency induction heating, or the like. Next, the surge absorbing element for low voltage of the present invention will be described with reference to specific examples, but the present invention is not limited by the description. Example 1 This example is shown in FIG. In this embodiment, a microgap element 3 having two caps 2 and 2a enclosed in a sealing glass tube 1 is used, and the lead wires 4 and 4a of the microgap element 3 have auxiliary electrode lead wires 5 and 5a. Auxiliary electrodes 6 and 6a are attached through and are spot welded. The metal line auxiliary electrodes 6 and 6a are spaced apart from each other and extend on the surface of the microgap element 3 at regular intervals, as shown in the figure. When an electric field is applied to the surface of the microgap element, electrons are likely to be emitted from the surface of the auxiliary electrode, the discharge start voltage is lowered, and the discharge delay is less likely to occur. The discharge start voltage V _S and the impulse discharge voltage V _imp when the material used for the auxiliary electrode was changed were measured. Table 1 shows the results. Table 1 Electrode material V _S (V) V _imp (V) Ti 165 620 Ni 160 610 Ta 160 630 Zr 155 630 None 180 800 V _S is discharge start voltage, V _imp is standard shock impulse (wave front length) This is the impulse discharge voltage when a pulse with a peak value of 5 kv is applied for 1.2 μs and a wave tail length of 50 μs.
That is, in the conventional surge absorbing element, the lower limit of the discharge start voltage is 180 V and the lower limit of the standard impulse applied impulse discharge voltage is 800 V. However, the structure of the present invention significantly improved them. Is clear. Next, this impulse was repeatedly applied to carry out a life test. The results are shown in the graph of FIG. The vertical axis indicates the firing voltage, and the horizontal axis indicates the number of times of application. The surge absorbing element deteriorates due to repeated impulse application.
It is clear that the surge absorption element according to the present invention has a smaller decrease in discharge starting voltage and improved life characteristics as compared with the conventional product having no auxiliary electrode. [Embodiment 2] It has the structure shown in FIG. 2, the structure is almost the same as that of the first embodiment, and the reference numerals are the same as those of the first embodiment. That is, a sealing glass tube (lead glass) 1, a cap 2, 2a, a microgap element 3, a lead wire 4 (Dumet wire), an auxiliary electrode lead wire 5, an auxiliary electrode 6, and a caulking 7 (metal band). Ni plate is used for the auxiliary electrode 6, and the auxiliary electrode lead wire 5
It was caulked to the Dumet wire 4 via. For this auxiliary electrode 6, a Ni plate is used, which is obtained by immersing a Ba-Al alloy powder in an ethyl acetate solution containing 2% by weight of ethyl cellulose and immersing it in a dry state. When this was sealed in glass, high-frequency dielectric heating was performed to decompose ethyl cellulose, which is an adhesive agent, and
Are diffused to the surface of the auxiliary electrode. This treatment further reduced the discharge start voltage and reduced the discharge delay. That is, when the discharge start voltage and the impulse discharge voltage were measured, respectively, V _S = 110
V, V _imp = 460V. EFFECTS OF THE INVENTION In the surge absorbing element of the present invention, the auxiliary electrode arranged inside the surge absorbing element firstly provides the surge absorbing element having a reduced discharge start voltage, and secondly, simultaneously. It is possible to provide a surge absorbing element with improved discharge delay characteristics. Thirdly, the present invention can be used for parts and circuits having low surge withstand voltage. Fourthly, the structure of the present invention can provide life characteristics. The technical effect such as the improvement of was obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing the structure of a microgap type discharge tube as an example of a surge absorbing element of the present invention. FIG. 2 is a sectional view showing the structure of another example of the micro-gap type discharge tube of the surge absorbing element of the present invention. FIG. 3 is a graph showing a result of measuring a change in a discharge starting voltage by repeated application of an impulse by a surge absorbing element having a structure according to the present invention. [Explanation of symbols of main part] 1 ... Sealing glass 2 ... Cap 3 ... Micro gap 4 ... Lead wire 5 ... Auxiliary electrode lead wire 6 ... Auxiliary electrode 7 ... Caulking (metal band)

   ────────────────────────────────────────────────── ─── Continuation of front page    (56) References JP-A-60-167293 (JP, A)                 Actual Development Sho 58-52787 (JP, U)                 Actual public Sho 61-16603 (JP, Y2)

Claims (1)

(57) [Claims] In a surge absorbing element for low voltage having a microgap element provided with a microgap for discharge and an internal space formed between the insulating jackets for the discharge, a microgap in the internal space is provided. The auxiliary electrode is provided at a distance from at least one of the electrode terminals of the gap element and at a distance from the surface of the microgap element, so as to cover the microgap element, and along the surface thereof, an auxiliary electrode extending to at least a microgap position is provided. Surge absorption element for voltage. 2. The surge absorbing element for low voltage according to claim 1, wherein a metal or a compound having a low work function is coated on at least a part of the surface of the auxiliary electrode.