JP3837838B2

JP3837838B2 - Positive temperature coefficient thermistor

Info

Publication number: JP3837838B2
Application number: JP15501397A
Authority: JP
Inventors: 吉高長尾; 俊春広田; 康訓並河
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 1997-06-12
Filing date: 1997-06-12
Publication date: 2006-10-25
Anticipated expiration: 2017-06-12
Also published as: JPH113805A

Description

【０００１】
【発明の属する技術分野】
本発明は、正特性サーミスタに関し、特に、過電流保護回路、消磁回路、モータ起動回路等の回路に用いられ、フラッシュ耐圧の大きな正特性サーミスタに関するものである。
【０００２】
【従来の技術】
従来の正特性サーミスタ３１は、図９に示されるように、板状のサーミスタ素体３２の両主面にオーミック性の電極３３、３４が形成されたものである。
【０００３】
【発明が解決しようとする課題】
しかしながら、従来の正特性サーミスタ３１に電圧を印加すると、印加直後は正特性サーミスタ３１が低抵抗であるため、突入電流が多く流れて、ジュール熱によって正特性サーミスタ３１が高温になり主面と略平行な面で割れる層状割れという現象が発生する（正特性サーミスタに突入電流を流したとき、正特性サーミスタが層状割れに至る直前の電圧をフラッシュ耐圧と呼ぶ）。特に、正特性サーミスタ３１を小型化すると、フラッシュ耐圧が小さくなるという問題点を有していた。
【０００４】
本発明の目的は、上述の問題点を解消すべくなされたもので、フラッシュ耐圧が大きい正特性サーミスタを提供することにある。
【０００５】
【課題を解決するための手段】
上記目的を達成するために、本発明の正特性サーミスタは、正の抵抗温度特性を有するセラミック体の厚みがその主面の周縁部の一部が中央部に比べて厚い正特性サーミスタ素体の両主面に電極が形成されている正特性サーミスタであって、前記正特性サーミスタ素体の両主面の周縁部の一部が中央部に比べて凸状であり、前記電極は下層電極と上層電極からなり、下層電極が前記正特性サーミスタ素体の両主面全面に形成されており、
前記上層電極は前記正特性サーミスタ素体の凸状の周縁部を除く中央部に対応する両主面に形成されている。
【０００６】
さらに、前記正特性サーミスタ素体の周縁の角部が丸みを帯びていることが好ましい。
さらに、前記正特性サーミスタ素体の周縁部の凸部にこのセラミック体の厚み方向に主面側から溝が形成されていることが好ましい。
さらに、前記上層電極はその周縁部で下層電極が露出するように前記下層電極より小さな平面積からなることが好ましい。
【０００７】
これにより、正特性サーミスタのフラッシュ耐圧及びＰmax を向上させることができるものである。
【０００８】
【発明の実施の形態】
本発明による第１の実施の形態の正特性サーミスタについて、図１、図２に基づいて説明する。
正特性サーミスタ１は、正特性サーミスタ素体２の両主面に、オーミック性の例えばＮｉ、Ｉｎ−Ｇａ、Ａｌ、またはＡｇを主成分とする電極３、４が形成されたものである。
【０００９】
正特性サーミスタ素体２は、チタン酸バリウムを主成分とする正特性サーミスタ用セラミック原料を、成形、焼結した正の抵抗温度特性有する略円板状のセラミック体からなり、セラミック体の厚みが、その両主面の異なる周縁部の一部に、中央部に比べて厚い凸状部５、６、７、８が形成されたものである。
【００１０】
本発明による第２の実施の形態の正特性サーミスタについて、図３に基づいて説明する。但し、前述の実施の形態と同様部分については、同様の符号を付し、詳細な説明を省略する。
【００１１】
正特性サーミスタ１ａは、正特性サーミスタ素体２ａの両主面にオーミック性の電極３ａ、４ａが形成されたものである。正特性サーミスタ素体２ａは、略矩形状のセラミック体からなり、セラミック体の厚みが、その両主面の対向する周縁部の一部に、中央部に比べて厚い凸状部５ａ、６ａ、７ａ、８ａが形成されたものである。
【００１２】
なお、第１および第２の実施の形態の正特性サーミスタ素体２、２ａの凸状部５〜８、５ａ〜８ａは、両主面において互いに対向しない位置、および互いに対向する位置のものを示したが、これに限定されるものではなく、両主面の任意な位置に設けられてもよい。また、凸状部の数についても上述した実施の形態に限定されるものではない。
【００１３】
本発明による第３の他の実施の形態の正特性サーミスタについて、図４に基づいて説明する。但し、前述の実施の形態と同様部分については、同様の符号を付し、詳細な説明を省略する。
【００１４】
正特性サーミスタ１ｂは、正特性サーミスタ素体２ｂの両主面にオーミック性の電極３ｂ、４ｂが形成されたものである。正特性サーミスタ素体２ｂは、略円形状のセラミック体からなり、セラミック体の厚みが、その両主面の対向する周縁部に、切り欠き９、１０を除いて中央部に比べて厚い凸状部５ｂ、７ｂが形成されたものである。
【００１５】
切り欠き９、１０は、正特性サーミスタ素体２ｂの両主面に図示しないリード線を接続する場合に、リード線を嵌入させることによって、正特性サーミスタ素体２ｂの表面に接続しやすくするためのものである。
【００１６】
本発明による第４の実施の形態の正特性サーミスタについて、図５に基づいて説明する。但し、前述の実施の形態と同様部分については、同様の符号を付し、詳細な説明を省略する。
【００１７】
正特性サーミスタ１ｃは、正特性サーミスタ素体２ｃの両主面にオーミック性の電極３ｃ、４ｃが形成されたものである。正特性サーミスタ素体２ｃは、図３に示した正特性サーミスタ素体２ａの両主面の角部に丸み１１、１２が形成されたものである。つまり、略矩形状のセラミック体の両主面の対向する周縁部の一部に、凸状部５ｃ、６ｃ、７ｃ、８ｃが形成されており、この凸状部５ｃ〜８ｃの角部およびこの凸状部５ｃ〜８ｃより厚みが薄い両主面の角部に丸み１１、１２が形成されている。
【００１８】
電極３ｃ、４ｃは、正特性サーミスタ素体２ｃの両主面全面に形成されたＮｉからなる下層電極１３、１４と、さらにこの下層電極１３、１４の周縁からギャップＧを設けて周縁部の下層電極１３、１４が露出するように形成されたＡｇからなる上層電極１４、１５の２層から構成されたものである。
【００１９】
なお、図５に示した上層電極１５、１６は、凸状部５ｃ〜８ｃを除く中央部に対応する両主面に形成されたものであるが、この他に図示しないが、ギャップＧがこれより小さく、上層電極１５、１６が凸状部５ｃ〜８ｃを越えてセラミック素体２ｃの周縁側に近づいて形成されてもよい。
【００２０】
本発明による第５の実施の形態の正特性サーミスタについて、図６に基づいて説明する。但し、前述の実施の形態と同様部分については、同様の符号を付し、詳細な説明を省略する。
【００２１】
正特性サーミスタ１ｄは、正特性サーミスタ素体２ｄの両主面にオーミック性の電極３ｄ、４ｄが形成されたものである。正特性サーミスタ素体２ｄは、図３に示した正特性サーミスタ素体２ａの周縁部に溝１７、１８，１９，２０が形成されたものでる。つまり、正特性サーミスタ素体２ｄは、略矩形状のセラミック体からなり、セラミック体の厚みが、その両主面の対向する周縁部の一部に、中央部に比べて厚い凸状部５ｄ〜８ｄが形成されており、この凸状部５ｄ〜８ｄの厚み方向に溝１７〜２０が形成されている。
【００２２】
なお、図３に示した第２の実施の形態の正特性サーミスタ２ａに基づいて、正特性サーミスタ素体２ａの周縁部に溝１７〜２０を形成した例を示したが、これに限定されるものではなく、他の実施の形態の正特性サーミスタ素体の周縁部に溝を形成したものであってもよい。
【００２３】
【実施例１】
本発明による正特性サーミスタの実施例１として、図１に示されるように、外径がφ８．２ｍｍ、両主面間の厚さＴが３．０ｍｍ、凸状部５〜８を含む高さＨが４．０ｍｍ、凸状部５〜８の幅ｈが１．０ｍｍ、凸状部５〜８の弧長の中心角αが９０°の略円板状の正特性サーミスタ素体２を準備し、両主面にＩｎ−Ｇａからなる電極３、４を形成して、正特性サーミスタ１を得た。この正特性サーミスタ１のフラッシュ耐圧を測定した結果を表１に記す。なお、実施例１の正特性サーミスタ１のキュリー温度は１２０℃、常温における抵抗値は２３Ωであった。
【００２４】
【実施例２】
本発明による正特性サーミスタの実施例２として、図４に示されるように、外径がφ８．２ｍｍ、両主面間の厚さＴが３．０ｍｍ、凸状部５ｂ、７ｂを含む高さＨが４．０ｍｍ、凸状部５ｂ、７ｂの幅ｈが１．０ｍｍ、切り欠き９、１０の幅ｈ１が１．０ｍｍの略円板状の正特性サーミスタ素体２ｂを準備し、両主面に実施例１と同様にＩｎ−Ｇａからなる電極３ｂ、４ｂを形成して、正特性サーミスタ１ｂを得た。この正特性サーミスタ１ｂのフラッシュ耐圧を測定した結果を表１に記す。なお、実施例２の正特性サーミスタ１ｂは、実施例１と同様にキュリー温度が１２０℃、常温における抵抗値が２３Ωであった。
【００２５】
【従来例１】
比較のために、従来例１として、図９に示されるような、外径がφ８．２ｍｍ、両主面の厚さＴが３ｍｍの円板状の正特性サーミスタ素体３２を準備し、両主面に実施例１と同様にＩｎ−Ｇａからなる電極３３、３４を形成して、正特性サーミスタ３１を得た。この正特性サーミスタ３１のフラッシュ耐圧を測定した結果を表１に記す。
【００２６】
なお、従来例１の正特性サーミスタ３１は、実施例１、２の正特性サーミスタ１、１ｂと同様にキュリー温度が１２０℃、常温における抵抗値が２３Ωであった。
【００２７】
【表１】

【００２８】
表１を見れば明らかなように、実施例１および実施例２のフラッシュ耐圧は最小値および平均ともに従来例１のフラッシュ耐圧より大幅に向上した。なお、フラッシュ耐圧試験において、実施例２の正特性サーミスタ１ｂは、１８個中８個、８１０Ｖで破壊しなかったため、８１０Ｖとして平均値を求めた。
【００２９】
【実施例３】
実施例３は、実施例１と異なる主原料を用いて前述の実施例１と同一形状の正特性サーミスタ素体２を準備し、両主面に実施例１と同一のＩｎ−Ｇａからなる電極３、４を形成して、正特性サーミスタ１を得た。実施例３の正特性サーミスタ１のキュリー温度は７０℃、常温における抵抗値は９Ωであった。
【００３０】
実施例３の正特性サーミスタ１についてフラッシュ耐圧及びＰmax を測定した結果を表２に記す。更に、正特性サーミスタ１の体積を計算によって求めた結果を表２に記す。
【００３１】
【実施例４】
実施例４は、実施例３と同一の主原料を用いて前述の実施例２と同一形状の正特性サーミスタ素体２ｂを準備し、両主面に実施例３と同様のＩｎ−Ｇａからなる電極３ｂ、４ｂを形成して、正特性サーミスタ１ｂを得た。実施例４の正特性サーミスタ１ｂは、実施例３と同じキュリー温度が７０℃、常温における抵抗値が９Ωであった。
【００３２】
実施例４の正特性サーミスタ１ｂについても、実施例３と同様に、フラッシュ耐圧及びＰmax を測定した結果、および、正特性サーミスタ１ｂの体積を表２に記す。
【００３３】
【従来例２】
比較のために、従来例２として、実施例３、４と同一の主原料を用いて図９に示されるような、外径がφ８．２ｍｍ、両主面の厚さＴが３ｍｍの円板状の正特性サーミスタ素体３２を準備し、両主面に実施例３、４と同様にＩｎ−Ｇａからなる電極３３、３４を形成して、正特性サーミスタ３１を得た。この従来例２の正特性サーミスタ３１を実施例３、４と同一の測定をし、結果を表２に記す。なお、従来例２の正特性サーミスタ３１のキュリー温度および常温における抵抗値は、実施例３、４と同一であった。
なお、上述した実施例１〜４および従来例１、２の測定試料数はそれぞれ１８個であった。
【００３４】
ここでＰmax について説明すると、正特性サーミスタを用いた消磁用回路に電流を流すと、正特性サーミスタの働きによって消磁コイルに図７に示すような交番減衰電流が流れる。この交番減衰電流の隣り合うピーク値の差を包絡線変化量Ｐと呼び、包絡線変化量Ｐの最大値をＰmax と呼ぶ。
【００３５】
Ｐmax の測定条件は、図８に示すように、消磁コイルの代替として２０Ωの抵抗７３を用い、この抵抗７３と正特性サーミスタ７４との直列回路にＡＣ２００Ｖ、６０Ｈｚの電圧７５を印加した。
【００３６】
【表２】

【００３７】
表２において、従来例２と比較すれば理解できるように、正特性サーミスタ素体２、２ｂの主面の周縁部の一部に凸状部５〜８を設けた実施例３、および凸状部５ｂ、７ｂを設けた実施例４は、従来例２と比較してフラッシュ耐圧が大幅に向上すると共に、Ｐmax が小さくなる。これにより、同じ大きさのフラッシュ耐圧に耐えるためには、正特性サーミスタ素体の体積を従来例２より小さくすることが可能となる。なお、フラッシュ耐圧試験において、実施例４の正特性サーミスタ１ｂは、１８個中８個、８１０Ｖで破壊しなかったため、８１０Ｖとして平均値を求めた。
【００３８】
なお、本発明に係る正特性サーミスタは前記第１〜第５の実施の形態に限定するものでなく、その要旨の範囲内で種々に変形することができる。
例えば、正特性サーミスタの形状は、外形が略円板状のもの、および略矩形状の平板状のものを示して説明したが、その他の任意の形状の略平板状のものでもよいことはいうまでもない。また、正特性サーミスタ素体の周縁部の一部に形成する凸状部は、一方の主面に形成されていてもよく、又凸状部の位置や大きさも任意に選ぶことができる。さらにまた、正特性サーミスタ素体に形成される溝は、一方の主面に形成されているものでもよく、また、凸状部又は凸状部が形成されていない切り欠きの主面に形成されていてもよい。
【００３９】
また、下層電極１３、１４の材質については、上述したＩｎ−Ｇａ、Ｎｉ等に限定されるものでなく、Ａｌ、Ｃｒ、Ｃｒ合金又はオーミックＡｇ等オーミック性を有するものであればよい。
また、電極の形成方法についても、スパッタ、印刷、焼き付け、溶射、めっき等いずれの方法であってもよい。
【００４０】
さらに、正特性サーミスタ素体の両主面に形成される電極は、前述した１層からなるもの、および２層からなるもの以外に、例えば、下層電極にＣｒ、上層電極として第２層目にモネル、第３層目にＡｇを主成分とする３層からなる電極から構成されるもの、およびそれ以上の複数層からなる電極から構成されてもよい。
【００４１】
【発明の効果】
以上述べたように、本発明による正特性サーミスタは、電極が形成される正特性サーミスタ素体の主面の周縁部の一部に凸状部を設けてあるために、フラッシュ耐圧が著しく向上する。さらに、比抵抗を下げることなく電極間距離を大きくすることができるため、電極間によるスパークの発生が減少する。
【００４２】
また、本発明による正特性サーミスタは、電極が形成される正特性サーミスタ素体の主面の周縁部近傍に溝を設けてあるために、フラッシュ耐圧が向上する。
また、本発明による正特性サーミスタは、Ｐmax を小さくすることなく、小型、軽量にすることができる。
さらに、本発明による正特性サーミスタは、下層電極と上層電極との間にギャップを設けてあるために、銀マイグレーションが防止される。
【図面の簡単な説明】
【図１】本発明に係る第１の実施の形態の正特性サーミスタ素体１の斜視図である。
【図２】図１の正特性サーミスタ１の縦断面図である。
【図３】本発明に係る第２の実施の形態の正特性サーミスタ１ａの斜視図である。
【図４】本発明に係る第３の実施の形態の正特性サーミスタ１ｂの斜視図である。
【図５】本発明に係る第４の実施の形態の正特性サーミスタ１ｃの縦断面図である。
【図６】本発明に係る第５の実施の形態の正特性サーミスタ１ｄの縦断面図である。
【図７】消磁回路の消磁コイルに流れる交番減衰電流を示す図である。
【図８】Ｐmax を測定する回路図である。
【図９】従来の正特性サーミスタの斜視図である。
【符号の説明】
１正特性サーミスタ
２正特性サーミスタ素体
３、４電極
５、６、７、８凸状部
１１、１２丸み
１３、１４下層電極
１５、１６上層電極
１７、１８，１９，２０溝
Ｇギャップ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive temperature coefficient thermistor, and more particularly to a positive temperature coefficient thermistor that is used in circuits such as an overcurrent protection circuit, a demagnetization circuit, and a motor start circuit, and has a high flash withstand voltage.
[0002]
[Prior art]
As shown in FIG. 9, the conventional positive temperature coefficient thermistor 31 is one in which

ohmic electrodes

33 and 34 are formed on both main surfaces of a plate-like thermistor body 32.
[0003]
[Problems to be solved by the invention]
However, when a voltage is applied to the conventional positive temperature coefficient thermistor 31, since the positive temperature coefficient thermistor 31 has a low resistance immediately after the application, a large amount of inrush current flows, and the positive temperature coefficient thermistor 31 becomes high temperature due to Joule heat and is substantially the same as the main surface. A phenomenon called a layer crack that breaks in parallel planes occurs (when an inrush current is passed through the positive temperature coefficient thermistor, the voltage immediately before the positive temperature coefficient thermistor reaches the layer crack is called the flash withstand voltage). In particular, when the positive temperature coefficient thermistor 31 is downsized, there is a problem that the flash withstand voltage is reduced.
[0004]
An object of the present invention is to solve the above-described problems, and is to provide a positive temperature coefficient thermistor having a high flash withstand voltage.
[0005]
[Means for Solving the Problems]
To achieve the above object, the positive characteristic thermistor of the present invention, the positive thickness of the ceramic body having a resistance temperature characteristic part of the peripheral portion of the main surface of the thick positive characteristics thermistor element as compared with the central portion A positive temperature coefficient thermistor in which electrodes are formed on both main surfaces , wherein a part of the peripheral portion of both main surfaces of the positive temperature coefficient thermistor body is convex compared to the central portion, the electrode being a lower electrode It consists of an upper layer electrode, and a lower layer electrode is formed on both main surfaces of the positive temperature coefficient thermistor body,
The upper layer electrode is formed on both main surfaces corresponding to the central portion excluding the convex peripheral portion of the positive temperature coefficient thermistor body.
[0006]
Furthermore, it is preferable that the corner of the periphery of the positive temperature coefficient thermistor body is rounded.
Furthermore, it is preferable that a groove is formed from the main surface side in the thickness direction of the ceramic body in the convex portion at the peripheral edge of the positive temperature coefficient thermistor body.
Furthermore, it is preferable that the upper layer electrode has a smaller planar area than the lower layer electrode so that the lower layer electrode is exposed at the peripheral edge thereof.
[0007]
As a result, the flash breakdown voltage and Pmax of the positive temperature coefficient thermistor can be improved.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
A positive temperature coefficient thermistor according to a first embodiment of the present invention will be described with reference to FIGS.
The positive temperature coefficient thermistor 1 is formed by forming electrodes 3 and 4 mainly composed of ohmic Ni, In-Ga, Al, or Ag as main components on both main surfaces of a positive temperature coefficient thermistor body 2.
[0009]
The positive temperature coefficient thermistor body 2 is made of a ceramic material for positive temperature coefficient thermistors mainly composed of barium titanate, which is formed and sintered, and has a substantially disk-shaped ceramic body having a positive resistance temperature characteristic. The

convex portions

5, 6, 7, and 8 that are thicker than the central portion are formed on part of the peripheral edge portions of the two main surfaces different from each other.
[0010]
A positive temperature coefficient thermistor according to a second embodiment of the present invention will be described with reference to FIG. However, parts similar to those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
[0011]
In the positive temperature coefficient thermistor 1a, ohmic electrodes 3a and 4a are formed on both main surfaces of the positive temperature coefficient thermistor body 2a. The positive temperature coefficient thermistor body 2a is formed of a substantially rectangular ceramic body, and the thickness of the ceramic body is thicker than the central portion on a part of the opposed peripheral portions of the two main surfaces. 7a and 8a are formed.
[0012]
The convex portions 5 to 8 and 5a to 8a of the positive temperature coefficient

thermistor element bodies

2 and 2a of the first and second embodiments are located at positions that do not face each other and positions that face each other. Although shown, it is not limited to this, You may provide in the arbitrary positions of both main surfaces. Further, the number of convex portions is not limited to the above-described embodiment.
[0013]
A positive temperature coefficient thermistor according to a third other embodiment of the present invention will be described with reference to FIG. However, parts similar to those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
[0014]
In the positive temperature coefficient thermistor 1b,

ohmic electrodes

3b and 4b are formed on both main surfaces of the positive temperature coefficient thermistor body 2b. The positive temperature coefficient thermistor body 2b is formed of a substantially circular ceramic body, and the thickness of the ceramic body is thicker than the central portion except for the

notches

9 and 10 at the opposing peripheral portions of both main surfaces thereof. The parts 5b and 7b are formed.
[0015]
The

notches

9 and 10 are used to facilitate connection to the surface of the positive temperature coefficient thermistor body 2b by inserting the lead wires when connecting lead wires (not shown) to both main surfaces of the positive temperature coefficient thermistor body 2b. belongs to.
[0016]
A positive temperature coefficient thermistor according to a fourth embodiment of the present invention will be described with reference to FIG. However, parts similar to those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
[0017]
The positive temperature coefficient thermistor 1c is obtained by forming ohmic electrodes 3c and 4c on both main surfaces of a positive temperature coefficient thermistor body 2c. The positive characteristic thermistor element body 2c is formed by forming

rounds

11 and 12 at corners of both main surfaces of the positive characteristic thermistor element body 2a shown in FIG. That is, convex portions 5c, 6c, 7c, and 8c are formed on a part of opposing peripheral portions of both main surfaces of the substantially rectangular ceramic body, and the corner portions of the convex portions 5c to 8c and this

Roundnesses

11 and 12 are formed at corners of both main surfaces which are thinner than the convex portions 5c to 8c.
[0018]
The electrodes 3c and 4c are formed of Ni lower layers 13 and 14 formed on the entire main surfaces of the positive temperature coefficient thermistor body 2c, and a gap G is provided from the periphery of the lower electrodes 13 and 14 to form a lower layer at the periphery. It is composed of two layers of upper layer electrodes 14 and 15 made of Ag formed so that the electrodes 13 and 14 are exposed.
[0019]
Although the

upper layer electrodes

15 and 16 shown in FIG. 5 are formed on both main surfaces corresponding to the central portion excluding the convex portions 5c to 8c, the gap G is not shown. The smaller

upper electrodes

15 and 16 may be formed so as to approach the peripheral side of the ceramic body 2c beyond the convex portions 5c to 8c.
[0020]
A positive temperature coefficient thermistor according to a fifth embodiment of the present invention will be described with reference to FIG. However, parts similar to those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
[0021]
The positive temperature coefficient thermistor 1d is obtained by forming ohmic electrodes 3d and 4d on both main surfaces of a positive temperature coefficient thermistor body 2d. The positive temperature coefficient thermistor body 2d has

grooves

17, 18, 19, and 20 formed at the peripheral edge of the positive temperature coefficient thermistor body 2a shown in FIG. In other words, the positive temperature coefficient thermistor body 2d is made of a substantially rectangular ceramic body, and the thickness of the ceramic body is thicker than the central part at a part of the opposing peripheral parts of both main surfaces thereof. 8d is formed, and grooves 17 to 20 are formed in the thickness direction of the convex portions 5d to 8d.
[0022]
In addition, although the example which formed the grooves 17-20 in the peripheral part of the positive characteristic thermistor body 2a based on the positive characteristic thermistor 2a of 2nd Embodiment shown in FIG. 3 was shown, it is limited to this. Instead, the groove may be formed in the peripheral portion of the positive temperature coefficient thermistor body according to another embodiment.
[0023]
[Example 1]
As Example 1 of the positive temperature coefficient thermistor according to the present invention, as shown in FIG. 1, the outer diameter is φ8.2 mm, the thickness T between both main surfaces is 3.0 mm, and the height including the convex portions 5 to 8 is included. A substantially disc-like positive temperature coefficient thermistor body 2 is prepared in which H is 4.0 mm, the width h of the convex portions 5 to 8 is 1.0 mm, and the central angle α of the arc length of the convex portions 5 to 8 is 90 °. And the electrodes 3 and 4 which consist of In-Ga were formed in both main surfaces, and the positive temperature coefficient thermistor 1 was obtained. The results of measuring the flash withstand voltage of the positive temperature coefficient thermistor 1 are shown in Table 1. The Curie temperature of the positive temperature coefficient thermistor 1 of Example 1 was 120 ° C., and the resistance value at room temperature was 23Ω.
[0024]
[Example 2]
As Example 2 of the positive temperature coefficient thermistor according to the present invention, as shown in FIG. 4, the outer diameter is φ8.2 mm, the thickness T between both main surfaces is 3.0 mm, and the height including the convex portions 5b and 7b. A substantially disc-shaped positive temperature coefficient thermistor body 2b in which H is 4.0 mm, the convex portions 5b and 7b have a width h of 1.0 mm, and the

notches

9 and 10 have a width h1 of 1.0 mm is prepared. In the same manner as Example 1,

electrodes

3b and 4b made of In—Ga were formed on the surface to obtain a positive temperature coefficient thermistor 1b. Table 1 shows the result of measuring the flash withstand voltage of the positive temperature coefficient thermistor 1b. The positive temperature coefficient thermistor 1b of Example 2 had a Curie temperature of 120 ° C. and a resistance value at room temperature of 23Ω as in Example 1.
[0025]
[Conventional example 1]
For comparison, a disk-like positive temperature coefficient thermistor 32 having an outer diameter of φ8.2 mm and a thickness T of both main surfaces of 3 mm as shown in FIG. In the same manner as in Example 1,

electrodes

33 and 34 made of In—Ga were formed on the main surface to obtain a positive temperature coefficient thermistor 31. The results of measuring the flash withstand voltage of the positive temperature coefficient thermistor 31 are shown in Table 1.
[0026]
The positive temperature coefficient thermistor 31 of the prior art example 1 had a Curie temperature of 120 ° C. and a resistance value at room temperature of 23Ω, similarly to the positive

temperature coefficient thermistors

1 and 1b of the first and second embodiments.
[0027]
[Table 1]

[0028]
As is apparent from Table 1, the flash withstand voltage of Example 1 and Example 2 was significantly improved over the flash withstand voltage of Conventional Example 1 both in the minimum value and the average. In the flash withstand voltage test, since the positive temperature coefficient thermistor 1b of Example 2 was not broken at 810V in 8 out of 18, the average value was obtained as 810V.
[0029]
[Example 3]
In Example 3, a positive temperature coefficient thermistor body 2 having the same shape as that of Example 1 described above was prepared using a main raw material different from that of Example 1, and electrodes made of In—Ga that were the same as Example 1 were formed on both main surfaces. 3 and 4 were formed, and the positive temperature coefficient thermistor 1 was obtained. The Curie temperature of the positive temperature coefficient thermistor 1 of Example 3 was 70 ° C., and the resistance value at room temperature was 9Ω.
[0030]
The results of measuring the flash withstand voltage and Pmax for the positive temperature coefficient thermistor 1 of Example 3 are shown in Table 2. Further, Table 2 shows the results obtained by calculating the volume of the positive temperature coefficient thermistor 1.
[0031]
[Example 4]
In Example 4, a positive temperature coefficient thermistor body 2b having the same shape as that of Example 2 described above was prepared using the same main raw material as in Example 3, and both main surfaces were made of In-Ga as in Example 3.

Electrodes

3b and 4b were formed to obtain a positive temperature coefficient thermistor 1b. The positive temperature coefficient thermistor 1b of Example 4 had the same Curie temperature as Example 3 of 70 ° C. and the resistance value at room temperature of 9Ω.
[0032]
As for the positive temperature coefficient thermistor 1b of the fourth embodiment, as in the third embodiment, the results of measuring the flash withstand voltage and Pmax and the volume of the positive temperature coefficient thermistor 1b are shown in Table 2.
[0033]
[Conventional example 2]
For comparison, as a conventional example 2, a disk having an outer diameter of φ8.2 mm and a thickness T of both main surfaces of 3 mm as shown in FIG. 9 using the same main raw materials as in Examples 3 and 4. A positive temperature coefficient thermistor 32 was prepared, and

electrodes

33 and 34 made of In—Ga were formed on both principal surfaces in the same manner as in Examples 3 and 4. Thus, a positive temperature coefficient thermistor 31 was obtained. The positive temperature coefficient thermistor 31 of Conventional Example 2 was measured in the same manner as in Examples 3 and 4, and the results are shown in Table 2. Note that the Curie temperature and normal temperature resistance value of the positive temperature coefficient thermistor 31 of Conventional Example 2 were the same as those of Examples 3 and 4.
The number of measurement samples in Examples 1 to 4 and Conventional Examples 1 and 2 described above was 18 respectively.
[0034]
Here, Pmax will be described. When a current is passed through a degaussing circuit using a positive temperature coefficient thermistor, an alternating attenuation current as shown in FIG. The difference between adjacent peak values of this alternating decay current is called the envelope change amount P, and the maximum value of the envelope change amount P is called Pmax.
[0035]
As shown in FIG. 8, a 20Ω resistor 73 was used as an alternative to the degaussing coil, and a voltage 75 of AC 200 V and 60 Hz was applied to the series circuit of the resistor 73 and the positive temperature coefficient thermistor 74 as Pmax measurement conditions.
[0036]
[Table 2]

[0037]
In Table 2, as can be understood by comparing with Conventional Example 2, Example 3 in which convex portions 5 to 8 are provided on a part of the peripheral portion of the main surface of the positive temperature coefficient thermistor bodies 2 and 2b, and the convex shape In the fourth embodiment provided with the portions 5b and 7b, the flash withstand voltage is significantly improved and Pmax is reduced as compared with the conventional example 2. As a result, the volume of the positive temperature coefficient thermistor element can be made smaller than that of the conventional example 2 in order to withstand the flash withstand voltage of the same size. In the flash withstand voltage test, since the positive temperature coefficient thermistor 1b of Example 4 was not broken at 810V in 8 out of 18, the average value was obtained as 810V.
[0038]
The positive temperature coefficient thermistor according to the present invention is not limited to the first to fifth embodiments, and can be variously modified within the scope of the gist thereof.
For example, although the shape of the positive temperature coefficient thermistor has been described by showing a substantially disk-shaped outer shape and a substantially rectangular flat plate shape, it may be a substantially flat plate shape having any other shape. Not too long. Moreover, the convex part formed in a part of the peripheral part of the positive temperature coefficient thermistor body may be formed on one main surface, and the position and size of the convex part can be arbitrarily selected. Furthermore, the groove formed in the positive temperature coefficient thermistor body may be formed on one main surface, and is formed on the main surface of the notch where the convex portion or the convex portion is not formed. It may be.
[0039]
In addition, the material of the lower layer electrodes 13 and 14 is not limited to the above-described In—Ga, Ni, or the like, and may be any material having ohmic properties such as Al, Cr, Cr alloy, or ohmic Ag.
Also, the electrode formation method may be any method such as sputtering, printing, baking, thermal spraying, and plating.
[0040]
Furthermore, the electrodes formed on both main surfaces of the positive temperature coefficient thermistor body are, for example, Cr as the lower layer electrode and the second layer as the upper layer electrode, in addition to the one layer and the two layers described above. Monel, the third layer may be composed of an electrode composed of three layers mainly composed of Ag, and an electrode composed of more than one layer.
[0041]
【The invention's effect】
As described above, in the positive temperature coefficient thermistor according to the present invention, the flash withstand voltage is remarkably improved because the convex portion is provided at a part of the peripheral edge of the main surface of the positive temperature coefficient thermistor body on which the electrode is formed. . Furthermore, since the distance between the electrodes can be increased without reducing the specific resistance, the occurrence of sparks between the electrodes is reduced.
[0042]
In addition, the positive temperature coefficient thermistor according to the present invention is improved in the flash withstand voltage because the groove is provided in the vicinity of the peripheral edge of the main surface of the positive temperature coefficient thermistor body on which the electrode is formed.
Further, the positive temperature coefficient thermistor according to the present invention can be reduced in size and weight without reducing Pmax.
Furthermore, since the positive temperature coefficient thermistor according to the present invention has a gap between the lower layer electrode and the upper layer electrode, silver migration is prevented.
[Brief description of the drawings]
FIG. 1 is a perspective view of a positive temperature coefficient thermistor element body 1 according to a first embodiment of the present invention.
FIG. 2 is a longitudinal sectional view of the positive temperature coefficient thermistor 1 of FIG.
FIG. 3 is a perspective view of a positive temperature coefficient thermistor 1a according to a second embodiment of the present invention.
FIG. 4 is a perspective view of a positive temperature coefficient thermistor 1b according to a third embodiment of the present invention.
FIG. 5 is a longitudinal sectional view of a positive temperature coefficient thermistor 1c according to a fourth embodiment of the present invention.
FIG. 6 is a longitudinal sectional view of a positive temperature coefficient thermistor 1d according to a fifth embodiment of the present invention.
FIG. 7 is a diagram showing an alternating decay current flowing in a degaussing coil of a degaussing circuit.
FIG. 8 is a circuit diagram for measuring Pmax.
FIG. 9 is a perspective view of a conventional positive temperature coefficient thermistor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive characteristic thermistor 2 Positive characteristic thermistor body 3, 4

Electrodes

5, 6, 7, 8

Convex part

11, 12 Round 13, 14

Lower electrode

15, 16

Upper electrode

17, 18, 19, 20 Groove G Gap

Claims

A positive temperature coefficient thermistor thickness of the ceramic body is a part of the periphery of the main surface are formed electrodes on both main surfaces of the thick positive characteristics thermistor element as compared with the central portion having a positive resistance-temperature characteristics ,
A part of the peripheral part of both main surfaces of the positive temperature coefficient thermistor body is convex compared to the central part,
The electrode is composed of a lower layer electrode and an upper layer electrode, the lower layer electrode is formed on the entire surface of both main surfaces of the positive temperature coefficient thermistor body,
2. The positive temperature coefficient thermistor according to claim 1, wherein the upper layer electrode is formed on both main surfaces corresponding to the central portion excluding the convex peripheral edge of the positive temperature coefficient thermistor body .

2. The positive temperature coefficient thermistor according to claim 1 , wherein corners of the periphery of the positive temperature coefficient thermistor body are rounded.

3. The positive temperature coefficient thermistor according to claim 1 , wherein a groove is formed from a main surface side in a thickness direction of the ceramic body at a convex portion of a peripheral edge portion of the positive temperature coefficient thermistor body.

4. The positive temperature coefficient thermistor according to claim 1, wherein the upper layer electrode has a smaller planar area than the lower layer electrode so that the lower layer electrode is exposed at a peripheral portion thereof. 5.

5. The positive temperature coefficient thermistor according to claim 1, wherein the lower electrode is made of a metal containing nickel as a main component, and the upper electrode is made of a metal containing silver as a main component.