US 3622918 A
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United States Patent  Inventors Shiro Ito;
Shoichi lwaya; Mitsuya Honda, all of Tokyo, Japan [21 Appl. No. 4,873  Filed Jan. 22, 1970  Patented Nov. 23, 1971  Assignee TDK Electronics Company, Limited Tokyo, Japan  FILTER 4 Claims, 9 Drawing Figs.
 0.8. (I 333/79, 333/73, 317/242  Int. Cl 1103b 7/04  Field oiSearch 317/242; 333/73, 79, 81
 References Cited UNITED STATES PATENTS 3,456,215 7/1969 Denes 333/79 3,035,237 5/1962 Schlicke 333/79 3,443,251 6/1969 Garstang 333/79 3,521,200 7/1970 Matsushama.... 333/79 3,329,91 l 7/1967 Schlicke 333/79 Primary Examiner-Herman Karl Saalbach Assistant Examiner-C. Baraff Attorney-Wolfe, Hubbard, Leydig, Voit & Osann ABSTRACT: A high-voltage resistive filter of through type, using a ceramic dielectric. The filter comprises a cylindrical ceramic dielectric having electrodes formed on respective both end surfaces of said dielectric cylinders, a conductor penetrating through inner space of said cylinder and mounted at an end to one of said electrodes through a connecting metal fixture, a ferrite ring fitted to said conductor, and a chassis fitting metal fixture adhered to the other one of the electrodes. A synthetic resin is molded around the dielectric, connecting metal fixture, conductor and ferrite ring as assembled so as to bond them integrally.
PAIENTEflnuv 23 l97l ATTENUATION (an) ATTENUA'WON (d) SHEET 2 BF 3 FREQUENCY (MHZ)- FREQUENCY (MHZ) INVENTORS gmao I10 HOICHIIWAYA MITSUYA HONDA Zyzf/ai, W VofiMATToRNEYs PATENTEDNUV 2 3 197! SHEET 3 BF 3 iNVENTORS Sumo 1T0 SHOICHI IWAYA MrrsuvA Honon 5 1W, MAJ, VodifiwwATTonnzvs FILTER This invention relates to filters and more particularly to a through filter for high voltages wherein an electrode is fitted to each end surface of a ceramic cylinder and the electrode on one side is pressed and bonded directly to a chassis so that waves may be well filtered up to a frequency in a very high range.
A high-electric power of a frequency band of ,UHF or a higher range is recently utilized not only for such industrial and communication apparatus as broadcasting apparatus and radars but also for medical apparatus and such domestic apparatus as microwave ovens.
However, with the increase of such utilization, such problems as the receiving disturbances in television and radio apparatus and electric wave obstructions to general communication apparatus by electric wave noises leaking out of such apparatus are considered so serious that measures are being taken against them.
Generally, in the principle of the filter, the impedance at the frequency to be filtered must be high in series but low in parallel. Therefore, an inverted L-type filter consisting of an inductor and capacitor has been so far used. However, for example, the oscillation frequency of a magnetron used for a microwave oven is mostly 2,450 MHz. but the produced lower harmonic and higher harmonic range several MHz. to several 10.000 MHz. and are substantially in a white noise state. However, in the inverted L-type filter, due to the influences of the stray capacitance of the inductor, the terminal of the capacitor and the stray inductance of the electrode, each element produces a self-resonance and, above about 100 MHz., equivalently the capacitor becomes an inductor and the inductor becomes a capacitor, the filter has an impedance low in series but high in parallel in a frequency band above the self-resonance frequency and therefore the filtering characteristics has been dissatisfactory. Further, the voltage and power to be used are so high that the size must be large and the filter has been disadvantageous in this respect.
As a result of making researches by taking such facts particularly into consideration, the present inventors have succeeded in giving a high withstand voltage by applying an electrode to each end surface of a cylindrical ceramic dielectric and molding the inner and outer peripheral surfaces of the dielectric and have been able to minimize the stray inductance with a structure of bonding the earthing side electrode directly to a chassis.
Further, a ring ferrite core high in the electric wave absorbing character is fitted to a central conductor. This core is to absorb noise waves flowing through the central conductor, to make an eddy current within the core and to convert the noise wave into a heat energy with the core loss and dissipate the heat energy.
Thus, by the actions of the capacitor in which the stray inductance is minimum and the ferrite core as a wave absorber, an ideal characteristic can be obtained.
A main object of the present invention is to provide a filter having an excellent attenuation characteristic in the range of 100 to 1.000 MHz.
Another object of the present invention is to provide a filter which is high in the withstand voltage and dampproofness and is made small. 7
A further object of the present invention is to provide a filter easy to assemble.
Other objects and advantages of the present invention will become clear upon reading the following disclosures of the present invention detailed with reference to the accompanying drawings, in which:
FIG. I is a partly sectioned elevation of a through filter for high voltages according to the present invention.
FIG. 2 is a sectioned view on line lI-II in FIG. 1 as attached to a chassis.
FIG. 3 is a side view of the same.
FIG. 4 shows a circuit of the same according to the present invention.
FIG. 5 is a graph showing the relations between the attenuation and frequency of the through filter for high voltages according to the present invention.
FIG, 6 is a graph showing the relations between the attenuation and frequency by a conventional circuit consisting of a mere condenser and coil.
FIGS. 7 to 9 show another embodiment.
FIG. 7 is partly sectioned elevation.
FIG. 8 is a partly sectioned elevation of the same as made a block.
FIG. 9 is a sectioned view on line IXIX in FIG. 7.
It should be understood here that, while the present invention will be disclosed with reference to certain preferred embodiments as illustrated, the invention should not be limited to the particular embodiments but rather should include all of possible modifications, alternations and equivalent arrangements within the spirit and scope of the invention as defined in the appended claims.
In FIGS. 1 to 3, l is a cylindrical ceramic dielectric having metallic electrodes 2 and 3 formed on the respective end surfaces. 4 is a substantially disk-shaped connecting fixture provided with a stepped projection 5 in the center part and a hole in the projection. The disk-shaped part of the above-mentioned connecting metal fixture is bonded to the metallic electrode 2. 6 is a chassis fitting metal fixture which is substantially disk-shaped and is provided with a projection 7 in the center part. The projection 7 is provided with a hole in the center and is threaded on the outer periphery. 8 is a through conductor threaded at both ends and provided with a part 9 of a large diameter in the intermediate part. A ferrite ring 10 (three ferrite rings in the illustrated case) is passed to one end of the part 9 and is fixed to the through conductor with a nut 11. The other end of the part 9 of the above-mentioned through conductor is inserted and fixed in the hole of the connecting metal fixture 4. 12 is a synthetic resin mold bonding integrally the ceramic dielectric 1, connecting metal fixture 4, through conductor 8, ferrite-ring l0 and nut 11. The mold is made of a mixture of such synthetic resin as an epoxy resin or silicone resin with such filler as SiO TiO AI O or Fe O as molded by casting and is to improve the insulation, withstand voltage, dampproofness and mechanical strength.
13 is a chassis. The projection 7 of the chassis fitting metal fixture 6 is inserted into a hole made in the chassis and the filter is fitted to the chassis with a nut 15 through a washer 14.
By the way, the through conductor 8, connecting metal fixture 4, chassis fitting metal 6, washer l4 and nut 15 are made of such metal easy to work as iron or brass and are plated in advance with such metal as Ni, Ag, Cr or Cd.
FIG. 4 shows an example of the use.
It has been recognized that the through filter for high voltages according to the present invention shows such excellent attenuation characteristic as 60 db. near 600 MHz. as shown in FIG. 5.
On the other hand, the conventional inverted L-type LC filter is of such attenuation characteristic as about 40 db. at most as shown in FIG. 6. It is thus evident that the present invention is superior enough.
As described above, the operation effects obtained by the present invention are that, with a through filter for high voltages characterized in that an electrode is formed on each end surface of a cylindrical ceramic dielectric, a central conductor is connected to one electrode through a connecting metal fixture, a ring-shaped ferrite core is fitted to the above-mentioned central conductor and is pressed with a metal fixture, a chassis fitting metal fixture is bonded to the other electrode of the cylindrical ceramic dielectric and the above-mentioned cylindrical ceramic dielectric and ring-shaped ferrite core are enclosed with a synthetic resin molding, a very excellent attenuation characteristic is obtained in a range of I00 to 1,000 MHz., the leakage of electromagnetic waves out of such electronic apparatus as a microwave oven is nearly zero, the manufacture is easy and the number of working steps can be reduced, the withstand voltage is high, the dampproofness and the so-called heat dissipation from the dielectric is favorable, the space can be advantageously utilized, a strong impact can be endured, the reliability is greatly improved, no trouble is caused to other apparatus by the so-called electromagnetic waves even when it is used in an apparatus of a large electric power and no public damage is caused.
FIGS. 7 to 9 show another embodiment. l is a ceramic dielectric. 2 and 3 are metallic electrodes formed on the respective end surfaces. 4 is a connecting metal fixture formed by drawing to have a recess and a threaded projection 5. The metallic electrode 2 is bonded to the connecting metal fixture 4. 13 is a chassis bonded to the metallic electrode 3. 16 is a cylindrical ferrite core. 17 is a coil wound on the ferrite core. The ferrite core and coil are contained in the recess'of the above-mentioned connecting metal fixture 4. This coil is connected at one end to the connecting metal fixture 4 and at the other end to the head of a screw l8. I2 is a synthetic resin mold to integrally bond the ceramic dielectric 1, connecting metal fixture 4, chassis l3, ferrite core 16, coil 17 and screw 18.
its effects are the same as in the first embodiment.
1. A filter comprising: a hollow, cylindrically shaped dielectric; a pair of spaced-apart electrodes, one of which is located on each of the respective end surfaces of the dielectric and formed thereon to cover the entire surface area thereof so that the length of the cylindrical dielectric defines the insulating gap between said electrodes along both its inner and outer peripheral surfaces; a conductor passing through said dielectric in a coaxial, spaced relationship therewith for conducting direct and low frequency currents, said conductor being electrically coupled with one of said electrodes; a ferrite member operatively positioned with respect to said conductor for absorbing high frequency noise signals traveling along the length thereof; an electrical connector suitable for connecting the filter to a chassis, connected to the other of said electrodes; and a synthetic resin mold surrounding and integrally bonding the dielectric, the conductor, and the ferrite member but allowing the respective ends of the conductor and a portion of the electrical connector for connecting the filter to thechassis to project out of said resin mold.
2. A filter comprising: a hollow, cylindrically shaped dielectric; a pair of spaced-apart electrodes, one of which is located on each of the respective end surfaces of the dielectric and formed thereon to cover the entire surface area thereof so that the length of the cylindrical dielectric defines the insulating gap between said electrodes along both its inner and outer peripheral surfaces; a conductor threaded at both ends and passing through said dielectric in a coaxial, spaced relationship therewith for conducting direct and low frequency currents; a first electrical connector in contact with one of said electrodes and coupling the electrode with said connector; a second electrical connector suitable for connecting the filter to a chassis, connected to the other of said electrodes; at least one ferrite ring positioned about said conductor for absorbing high frequency noise signals passing along the length thereof; and a synthetic resin mold surrounding and integrally bonding the dielectric, the first electrical connector, the conductor and the ferrite ring but allowing both threaded ends of the conductor and a portion of said second electrical connector to project out of said resin mold.
3. A filter comprising: a hollow, cylindrically shaped ceramic dielectric; a pair of spaced-apart electrodes, one of which is located on each of the respective end surfaces of the dielectric and formed thereon to cover the entire surface area thereof so that the length of the cylindrical dielectric defines the insulating gap between the electrodes along both its inner and outer peripheral surfaces; a first electrical connector, having a cylindrical recessed portion with a threaded member projecting outwardly from the end surface thereof, connected to one of said electrodes; a cylindrical ferrite member projecting into said recessed member and passing through said dielectric in sgaced relationships therewith a conductive coil ositioned a out the ferrite member, said COll being connec ed at one end to said first electrical connector; a second electrical connector suitable for coupling the filter to a chassis. connected to the other of said electrodes; a conductor member having a threaded portion extending outwardly beyond said second electrical connector coupled to the other end of said coil; and
'a synthetic resin mold surrounding and integrally bonding the dielectric, the first and second electrical connectors, the ferrite member, the coil and the conductor member, but allowing the threaded portions of the first electrical connector and the conductor member together with a portion of the second electrical connector to project out of said resin mold.
4. A filter as set forth in claim 3, in combination with a second similar filter wherein, both filters are bonded to a single second electrical connector for coupling the filters to a chassis and integrally bonded in a spaced relationship with one another in said resin mold.
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