JPH07297082A - Coaxial capacitor - Google Patents

Abstract

PURPOSE:To provide a coaxial capacitor which has improved temperature characteristics and can have a large capacitance without being restricted by dimensions. CONSTITUTION:In a metal case 1 with a part for inserting into an enclosure, a second cylindrical dielectric 8 with electrodes 9 and 10 is inserted into the inside of an enclosure insertion part in addition to a cylindrical dielectric which a conventional coaxial capacitor has and is connected to the case 1 and a coaxial terminal 5 by soldering. By using a dielectric with temperature coefficients which are opposite in terms of positive and negative signs and a higher dielectric constant than the dielectric with a zero temperature coefficient for a first cylindrical dielectric 2 and the second cylindrical dielectric 8, the temperature coefficient is canceled out, thus obtaining a temperature characteristic closer to 0ppm/ deg.C C and a large capacitance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedthrough capacitor, and more particularly to a feedthrough capacitor having two dielectrics and having a large capacity.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing an example of a conventional feedthrough capacitor, and FIG. 4 is an exploded perspective view. A cylindrical dielectric (for example, porcelain ceramic) 2 having electrodes 3 and 4 on the outer surface and an inner surface is inserted into a metal case 1 having a threaded portion for inserting and fixing the housing, and The inner wall above the threaded portion and the outer electrode 3 of the cylindrical dielectric are connected by soldering. In addition, the through terminal 5 is inserted into the through hole of the cylindrical dielectric body 2, and the through terminal 5 and the dielectric body 2 are
Inner electrodes 4 of are connected by soldering. Further, the insulating resin 6 is filled in the other space inside the metal case 1.

[0003]

In the conventional feedthrough capacitor, one cylindrical dielectric material inside the metal case forms the capacitor.

Therefore, when forming a feedthrough capacitor having excellent temperature characteristics (for example, CH: 0 ± 60 ppm / ° C.), it is necessary to use a dielectric having the same CH temperature characteristics as the cylindrical dielectric. However, in general, a dielectric having good temperature characteristics has a low dielectric constant and has a dimensional constraint that it must be housed in a metal case. Therefore, C = ε (s / d) (C: capacitance, ε: dielectric Rate, S: surface area of the dielectric, d: thickness of the dielectric), a capacitor having a larger capacity cannot be realized.

For example, when the outer diameter of the cylindrical dielectric of the conventional feedthrough capacitor is φ3 and the length is 3 mm, the capacitance is about 30 pF even when the above ceramic material is used. The temperature characteristic of the capacitance at this time is 10 to 20 pF.
Is. In this type of feedthrough capacitor, the limit is about 40 pF due to the above-mentioned restrictions.

In view of the above-mentioned drawbacks, the present invention is to provide a feedthrough capacitor having excellent temperature characteristics, satisfying dimensional constraints, and having a large capacitance value.

[0007]

In order to solve the above-mentioned problems, the feedthrough capacitor of the present invention has an internal / external type instead of the insulating resin filled inside the housing insertion portion of the feedthrough type capacitor of the conventional structure. A second cylindrical dielectric having an electrode on its side surface.

[0008]

The conventional first cylindrical dielectric and the second cylindrical dielectric above the housing insertion portion have positive and negative inverse temperature coefficients, respectively, and have a dielectric constant larger than that of the zero temperature coefficient. By using a capacitor having the above, it is possible to obtain a large capacity feedthrough capacitor with good temperature characteristics.

[0009]

The present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention,
FIG. 2 is an exploded perspective view. Inside a metal case 1 having a threaded portion for inserting and fixing a housing, a first cylindrical dielectric 2 having electrodes 3 and 4 on the outer and inner surfaces and electrodes 9 and 10 similar to the first Two cylindrical dielectrics 8 and the first and second dielectrics are inserted with a bead-shaped spacer 7 made of an insulating resin that is insulated and separated from each other so as not to give stress to each other. The through terminal 5 is inserted into the through holes of the first and second cylindrical dielectric bodies 2 and 8 and the spacer 7, and the electrode 3 of the first cylindrical dielectric body 2 and the electrode 9 of the second cylindrical dielectric body 8 are inserted. Are connected to the inner wall of the metal case 1 and the electrodes 4 and 10 are connected to the through terminals 5 by soldering. Further, an insulating resin 6 is filled in the space inside the case above the threaded part of the metal case 1.

A dielectric having a temperature coefficient of zero is used for the first cylindrical dielectric 2, and a second cylindrical dielectric 8 is used for the second cylindrical dielectric 8.
A dielectric having a temperature coefficient opposite to that of the first cylindrical dielectric 2 is used. In this embodiment, the first cylindrical dielectric body has a dielectric constant larger than CH (0 ± 60 ppm / ° C.) of ceramic and a negative (or positive) temperature coefficient of ceramic LH (−80 ±). 60 ppm / ° C), but the second cylindrical dielectric has a ceramic AH (+100 ± 60 p)
pm / ° C) has been applied.

Here, the inner diameter of the first cylindrical dielectric 2 is defined as a
1 [m], the outer diameter is b1 [m], the length is 11 [m], the relative permittivity is εS1, and the inner diameter of the second cylindrical dielectric 8 is a2.
[M], outer diameter is b2 [m], length is 12 [m], relative permittivity is εS2, vacuum permittivity is ε0, and relative permittivity of a dielectric having a temperature coefficient of zero is εS0. 1 cylindrical dielectric 2
The capacity Cr1 obtained from C1 = 2πεS1ε011 / {2.3 × log10 (b1 / a1)} (1) Similarly, the capacitance C2 obtained from the second cylindrical dielectric 8 is represented by C2 = 2πεS2 · ε0 · 12 / {2.3 × log10 (b2 / a2)} (2). Therefore, the amount of change with each temperature is dc1 / dT = 2πε0 · l1 / {2.3 × log10 (b1 / a1)} · dεS1 / dT dc2 / dT = 2πε0 · l2 / {2.3 × log10 (b2 / A2)} · dεS2 / dT In the above equation, a1, b1, l1, dε1 / dT, a2, b such that dC1 / dT = −dC2 / dT.
By selecting 2, 12, and dε2 / dT, it is possible to obtain a feedthrough capacitor having temperature characteristics close to zero by canceling each other's temperature characteristics.

The capacitance C of the feedthrough capacitor is
Since it is given by C = C1 + C2, it is given by the following equation.

C = C1 + C2 = 2π · ε0 / 2.3 × {εS1 · l1 / log10 (b1 / a1) + εS2 · 12 / log10 (b2 / a2)} (5) Next, the first and second cylinders When the dielectrics 2 and 8 having the same temperature coefficient of 0 (0 ppm / ° C.) are used, the capacitance C0 of the feedthrough capacitor is C0 = 2π · ε0 / 2.3 · εS0 × {b1 / log10 (b1 / a1) + b2 / log10 (b2 / a2)} (6) In equations (5) and (6), εS1> εS0, εS2>
From εS0, C> C0 As described above, it is possible to obtain a larger capacitance by providing the second cylindrical dielectric having a positive and negative dielectric constant in the metal case in addition to the first cylindrical dielectric. become. When the size and shape are the same as the conventional one except that the second cylindrical dielectric is provided and a second cylindrical dielectric having φ2.2 and a length of 4.5 mm is provided, the capacitance of the entire capacitor is about 100 pF. Become. Further, the temperature characteristic is maintained at the same level as the conventional one.

As described above, according to the feedthrough capacitor of the present invention, the temperature characteristic is maintained at the same level as that of the conventional one, and moreover, the capacitance of about 100 pF which is more than double that of the conventional one can be realized.

[0016]

As described above, since the feedthrough capacitor according to the present invention has the structure having the second dielectric inside the housing insertion portion of the metal case, the first dielectric and the second dielectric are also provided.
It is possible to select and use a material having a positive and negative temperature coefficient, which has a larger dielectric constant than the dielectric material having a zero temperature coefficient, as the dielectric material. As a result, a feedthrough capacitor having excellent temperature characteristics and a large capacitance value can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a feedthrough capacitor according to the present invention.

FIG. 2 is a perspective exploded view showing an embodiment of a feedthrough capacitor according to the present invention.

FIG. 3 is a sectional view showing an example of a conventional feedthrough capacitor.

FIG. 4 is a perspective exploded view showing an embodiment of a conventional feedthrough capacitor.

[Explanation of symbols]

 1 ... Metal case 2 ... 1st cylindrical dielectric 3 ... Electrode 4 ... Electrode 5 ... Penetrating terminal 6 ... Insulating resin 7 ... Spacer 8 ... 2nd Cylindrical Dielectric 9 ・ ・ ・ Electrode 10 ・ ・ ・ Electrode

Claims (6)

[Claims] 1. A first dielectric having a metal case having a threaded portion, a penetrating terminal connected to the outside, and a first electrode on an outer surface and an inner surface connected to the metal case and the penetrating terminal. A body, a first insulator filled in a space inside the metal case, and a second dielectric having a second electrode inside the threaded portion of the metal case. Characteristic feedthrough capacitor. 2. The first dielectric and the second dielectric are both cylindrical in shape.
The feedthrough capacitor described. 3. The feedthrough capacitor according to claim 2, further comprising a second insulator between the first dielectric and the second dielectric. 4. The feedthrough capacitor according to claim 3, wherein the first dielectric and the second dielectric are dielectrics having temperature coefficients whose positive and negative are opposite to each other. 5. The feedthrough capacitor according to claim 4, wherein the temperature coefficient of the capacitance of the feedthrough capacitor is substantially zero. 6. The method according to claim 5, wherein the first dielectric and the second dielectric are made of ceramics.
The feedthrough capacitor described.