JPH113806A - Positive temperature coefficient thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the flash resistance and Pmax of a positive temperature coefficient thermistor, by forming grooves inside the peripheral edge sections of both main surfaces of a ceramic body having a positive temperature characteristic of resistance along the peripheral section in the thickness direction of the ceramic body and electrodes on the main surfaces. SOLUTION: A positive temperature coefficient thermistor 1 is obtained by respectively forming ohmic electrodes 3 and 4 on both main surfaces of a positive temperature coefficient thermistor element 2. The element 2 is composed of a discoid ceramic body which is formed by molding and sintering a ceramic material for positive temperature coefficient thermistor containing barium titanate as a main component and has a positive temperature characteristic of resistance. Then, grooves 5 and 6 are respectively formed on both main surfaces of the ceramic body inside the peripheral edge sections along the peripheral edge sections in the thickness direction of the ceramic body. Therefore, the flash resistance of the thermistor 1 is remarkably improved and, in addition, the Pmax of the thermistor 1 can be reduced even when the size and weight of the thermistor 1 are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor, and more particularly to a positive temperature coefficient thermistor used in circuits such as an overcurrent protection circuit, a demagnetizing circuit, and a motor starting circuit, and having a high flash breakdown voltage.

[0002]

2. Description of the Related Art A conventional positive temperature coefficient thermistor 31 has ohmic electrodes 33 and 34 formed on both main surfaces of a plate-like thermistor element 32 as shown in FIG.

[0003]

However, when a voltage is applied to the conventional positive-characteristic thermistor 31, immediately after the voltage is applied, since the positive-characteristic thermistor 31 has a low resistance, a large amount of inrush current flows, and the positive-characteristic thermistor 31 is caused by Joule heat. 31
Becomes high temperature, causing a phenomenon of layered cracking that splits on a plane substantially parallel to the main surface (the voltage immediately before the positive characteristic thermistor reaches the layered crack when an inrush current flows through the positive characteristic thermistor is called flash breakdown voltage). In particular, the positive characteristic thermistor 31
There is a problem that when the size is reduced, the flash breakdown voltage is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a positive temperature coefficient thermistor having a large flash breakdown voltage.

[0005]

In order to achieve the above object, in a positive temperature coefficient thermistor of the present invention, a ceramic body having a positive resistance temperature characteristic is provided inside a peripheral portion of a main surface of the ceramic body so as to be along the peripheral portion. In addition, electrodes are formed on both main surfaces of the thermistor body having grooves formed in the thickness direction of the ceramic body. Further, it is preferable that a corner of a peripheral portion of the positive temperature coefficient thermistor body is rounded. Preferably, the electrode comprises a lower electrode and an upper electrode, and the lower electrode is formed over both main surfaces of the positive temperature coefficient thermistor body.

Preferably, the upper layer electrode has a smaller plane area than the lower layer electrode so that the lower layer electrode is exposed at a peripheral portion thereof. Further, it is preferable that the upper layer electrode is formed on both main surfaces corresponding to a central portion surrounded by a groove of the positive temperature coefficient thermistor body. Preferably, the lower electrode is made of a metal mainly composed of nickel, and the upper electrode is made of a metal mainly composed of silver.
As a result, the flash breakdown voltage and P
max can be improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A PTC thermistor according to an embodiment of the present invention will be described with reference to FIG.
The positive temperature coefficient thermistor 1 has ohmic properties such as Ni, In—Ga, Al,
Alternatively, electrodes 3 and 4 mainly composed of Ag are formed.

The positive temperature coefficient thermistor body 2 is made of a ceramic body having a positive resistance temperature characteristic formed by molding and sintering a ceramic material for a positive temperature coefficient thermistor containing barium titanate as a main component. Grooves 5 and 6 are formed inside the peripheral portion of the main surface along the peripheral portion and in the thickness direction of the ceramic body.

Another embodiment of the positive temperature coefficient thermistor according to the present invention will be described with reference to FIG. However, the same portions as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

The positive temperature coefficient thermistor 7 has a structure in which electrodes 3 and 4 are formed on both main surfaces of a positive temperature coefficient thermistor body 8.
The positive-characteristic thermistor element body 8 is formed by forming roundnesses 9 and 10 at the corners of the positive-characteristic thermistor element body 2 shown in FIG. 1, inside the peripheral part of the main surface, along the peripheral part and Grooves 5 and 6 are formed in the thickness direction of the ceramic body.

Another embodiment of the positive temperature coefficient thermistor according to the present invention will be described with reference to FIG. However, the same portions as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

The positive temperature coefficient thermistor 11 comprises two layers of electrodes 3 on both main surfaces of the positive temperature coefficient thermistor body 2 shown in FIG.
4 is formed. The electrodes 3 and 4 are composed of lower electrodes 12 and 13 made of Ni formed on the entire surfaces of both main surfaces of the positive temperature coefficient thermistor body, and a gap G is provided from the periphery of the lower electrodes 12 and 13 to form a lower electrode of the periphery. 12, 13
Upper electrode 1 made of Ag formed so as to be exposed
4 and 15.

The upper electrodes 14, 15 shown in FIG.
Are formed on both main surfaces corresponding to the central portion surrounded by the grooves 5 and 6, but are not shown. However, the gap G is smaller than this, and the upper electrodes 14 and 15 are 6 may be formed so as to approach the peripheral side of the ceramic body 2 beyond 6.

[0014]

Embodiment 1 Embodiment 1 of a PTC thermistor according to the present invention
As shown in FIG. 1, the outer diameter is φ8.2 mm,
The thickness T between the two main surfaces is 3.0 mm, the depth d of the grooves 5 and 6 is 0.5 mm, the width h of the grooves 5 and 6 is 0.5 mm, and the position L of the grooves 5 and 6 from the peripheral edge is An approximately disk-shaped PTC thermistor body 2 of about 1 mm was prepared, and electrodes 3 and 4 made of In—Ga were formed on both main surfaces to obtain a PTC thermistor 1. Table 1 shows the results of measuring the flash breakdown voltage of the positive temperature coefficient thermistor 1. The PTC thermistor 6 had a Curie temperature of 120 ° C. and a resistance value of 23Ω at room temperature.

For comparison, a disk-shaped positive temperature coefficient thermistor body 32 having an outer diameter of 8.2 mm and a thickness T of both main surfaces of 3 mm as shown in FIG. And
Electrodes 3 made of In-Ga on both main surfaces as in Example 1.
By forming Nos. 3 and 34, a positive temperature coefficient thermistor 31 was obtained. Table 1 shows the results of measuring the flash breakdown voltage of the positive temperature coefficient thermistor 31. The resistance of the positive temperature coefficient thermistor 31 at the Curie temperature and the normal temperature was the same as that of the first embodiment.

[0016]

[Table 1]

As apparent from Table 1, the flash breakdown voltage of the first embodiment is significantly improved in both the minimum value and the average with respect to the flash breakdown voltage of the conventional example 1.

[0018]

Example 2 In Example 2, the same electrodes 3 and 4 were formed on a PTC thermistor body 2 having the same shape as that of Example 1 described above, and a PTC thermistor 1 was obtained. However, the main material of the PTC thermistor body 2 of Example 2 is different from the main material of Example 1, and the Curie temperature of the PTC thermistor of Example 2 is 70 ° C. It was 9Ω.

Table 2 shows the results of measuring the flash breakdown voltage and Pmax of the PTC thermistor of Example 2. Table 2 shows the result of calculation of the volume of the positive temperature coefficient thermistor.

For comparison, a disk-shaped positive temperature coefficient thermistor body 32 having an outer diameter of φ8.2 mm and a thickness T of both main surfaces of 3 mm as shown in FIG. And
Electrodes 3 made of In-Ga on both main surfaces as in Example 2.
By forming Nos. 3 and 34, a positive temperature coefficient thermistor 31 was obtained. The PTC thermistor 31 of Conventional Example 2 was measured in the same manner as in Example 2, and the results are shown in Table 2. This positive characteristic thermistor 3
The Curie temperature and the resistance value at room temperature were the same as in Example 2. The number of measurement samples in each of Example 1, Conventional Example 1, Example 2, and Conventional Example 2 was 18 each.

Here, Pmax will be described. When a current flows through a degaussing circuit using a positive temperature coefficient thermistor, an alternating decay current as shown in FIG. 4 flows through the degaussing coil by the action of the positive temperature coefficient thermistor. The difference between adjacent peak values of the alternating decay current is called an envelope change amount P, and the envelope change amount P
Is referred to as Pmax.

The conditions for measuring Pmax are as shown in FIG.
A 20 Ω resistor 73 is used as a substitute for the degaussing coil, and AC2 is connected to a series circuit of the resistor 73 and the positive temperature coefficient thermistor 74.
A voltage 75 of 00 V, 60 Hz was applied.

[0023]

[Table 2]

In Table 2, as can be understood from comparison with the conventional example 2, the embodiment 2 in which the grooves 5, 6 are provided near the periphery of the main surface of the positive temperature coefficient thermistor body 2 is compared with the conventional example 2. As a result, the flash breakdown voltage is greatly improved, and Pmax is reduced. Thus, the volume of the positive temperature coefficient thermistor can be made smaller than that of the second conventional example. Further, the volume of the positive temperature coefficient thermistor body 2 can be reduced.

The PTC thermistor according to the present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the invention. For example, the shape of the positive temperature coefficient thermistor has been described by exemplifying a substantially disc-shaped outer shape. However, the shape is not limited thereto. It goes without saying that it may be the same. Further, the grooves 5 and 6 of the positive temperature coefficient thermistor element body 2 may have a groove formed on at least one main surface, or may have a plurality of grooves formed on the main surface.

The material of the lower electrodes 13 and 14 is not limited to In-Ga, Ni or the like described above, but may be any material having ohmic properties such as Al, Cr, Cr alloy or ohmic Ag. . Also, the electrode may be formed by any method such as sputtering, printing, baking, thermal spraying, and plating.

Further, the electrodes formed on both main surfaces of the positive temperature coefficient thermistor body may be, for example, Cr as a lower electrode and a second electrode as an upper electrode, in addition to the above-described one-layer and two-layer electrodes. The third layer may be composed of Monel, the third layer may be composed of an electrode composed of three layers containing Ag as a main component, or may be composed of an electrode composed of more than two layers.

[0028]

As described above, in the positive temperature coefficient thermistor according to the present invention, since the groove is provided in the vicinity of the periphery of the main surface of the positive temperature coefficient thermistor body on which the electrodes are formed, the flash breakdown voltage is significantly improved. I do. Further, even if the positive temperature coefficient thermistor is small and lightweight, Pmax can be reduced.
Further, since a gap is provided between the lower electrode and the upper electrode, silver migration is prevented.

[Brief description of the drawings]

FIG. 1 is a half sectional perspective view of a positive temperature coefficient thermistor according to one embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a PTC thermistor according to another embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a PTC thermistor according to another embodiment of the present invention.

FIG. 4 is a diagram showing an alternating decay current flowing through a degaussing coil of a degaussing circuit.

FIG. 5 is a circuit diagram for measuring Pmax.

FIG. 6 is a perspective view of a conventional PTC thermistor.

[Explanation of symbols]

 2 Positive thermistor element 3, 4 Electrode 5, 6 Groove 12, 13 Lower electrode 14, 15 Upper electrode G Gap

Claims (6)

[Claims] 1. A thermistor body having grooves formed along the periphery and in the thickness direction of the ceramic body inside the periphery of the main surface of the ceramic body having a positive resistance temperature characteristic. And a positive temperature coefficient thermistor, wherein electrodes are formed. 2. The positive temperature coefficient thermistor according to claim 1, wherein a corner of a peripheral portion of said positive temperature coefficient thermistor body is rounded. 3. The positive temperature coefficient thermistor according to claim 1, wherein said electrode comprises a lower layer electrode and an upper layer electrode, and said lower layer electrode is formed on the entire both main surfaces of said positive temperature coefficient thermistor body. 4. The positive temperature coefficient thermistor according to claim 3, wherein said upper layer electrode has a smaller plane area than said lower layer electrode such that a lower layer electrode is exposed at a peripheral portion thereof. 5. The positive temperature coefficient thermistor according to claim 4, wherein said upper layer electrode is formed on both main surfaces corresponding to a central portion surrounded by a groove of said positive temperature coefficient thermistor element body. 6. The positive temperature coefficient thermistor according to claim 3, wherein the lower electrode is made of a metal mainly containing nickel, and the upper electrode is made of a metal mainly containing silver. .