Abstract:
A magnetron filter apparatus having a bottom box type filter case which is engaged and fixed with a cathode input side of a magnetron bulb and provided with a cover. A transformer which supplies a cathode current to the magnetron is contained in the filter case and a filter is contained in the filter case for preventing leakage of unwanted electromagnetic waves. Further, an insulation box in which the transformer is embedded and which is provided with integrally formed cylindrical portions through which lead wires to a primary winding of the transformer is disposed in the filter case. The insulation box is positioned by insertion of the cylindrical portions thereof into holes formed in a wall of the filter case.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetron filter apparatus and particularly to a structure of magnetron filter apparatus just suitable for a microwave range to be operated with a high frequency driving power supply. 
     2. Description of the Prior Art 
     FIG. 1 shows a basic concept of a power supply for driving a magnetron. In FIG. 1, numeral 1 denotes a commercial power supply of 50 or 60 Hz which generates a cathode current and a voltage to be supplied to the magnetron 3 with a transformer 2. 4 is a smoothing capacitor and 5 is a rectifying diode. The section enclosed by the dotted line 6 is a magnetron 3 designed with an ordinary structure. The section enclosed by the dotted line 7 is a filter apparatus integrally provided to the magnetron 3, which eliminates unwanted waves (mainly, TV noise) generated for the magnetron 3 with inductance of a choke coil 8 and a through capacitor 9. 
     Recently, development and investigation for practical use of a so-called inverter power supply which converts the frequency of a commercial power supply to the high frequency of 10k˜100 kHz and thereby makes possible remarkable reduction of the size of a transformer required are showing dynamic advancement. 
     FIG. 2 shows a conventional magnetron filter apparatus. A bottomed box type filter case 16 is forced to engage with a cylindrical seal 10 of the magnetron bulb and a couple of leads 12 which support the cathode in the bulb are hermetically brazed together with terminals 13 through a stem ceramic 11 hermetically brazed to the cylindrical seal 10. The terminals 13 are respectively fixed with choke coils 8 wound around the ferrite core, with the other ends thereof connected to a through capacitor 9. This through capacitor 9 is fixed to a filter case 16 through a chassis plate 9a which is earthed. Moreover, a cover 17 is fixed to said filter case 16 by caulking the four sides thereof in order to shield unwanted waves such as harmonics of a magnetron. Above structure corresponds to the section enclosed by a dotted line 7 in FIG. 1. Usually a cathode current to be supplied to the terminals 12 of a cathode in the filter case 16 is comparatively as high as 10˜16 A in the case of a magnetron and therefore a lead wire as thick as 1.0˜1.6φ is necessary. Moreover in case of a commercial power supply it is disadvantage because a transformer itself becomes large in size due to its low frequency (50 or 60 Hz) to attempt to include said transformer which supplies the cathode current within the filter case 16. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a magnetron filter apparatus just suitable to be driven by an inverter power supply which converts the commercial power source to a high frequency power source. 
     Namely, by making the best use of remarkable reduction of the size of a transformer in case of an inverter power supply and thereby housing the whole or at least half of the transformer in a filter case of a magnetron the present invention provides a magnetron filter apparatus comprising a bottomed box type filter case which is engaged and fixed with a cathode input side of a magnetron bulb and is provided with a cover, a transformer which supplies a cathode current to a magnetron and is contained in said filter case, a filter contained in said filter case for preventing leakage of unwanted electromagnetic waves, and an insulation box in which said transformer is embedded and which is provided with integrally formed cylindrical portions through which lead wires to a primary winding of said transformer are inserted, said insulation box being positioned by insertion of said cylindrical portions into holes formed in a wall of said filter case; or a magnetron filter apparatus comprising a bottomed box type filter case which is engaged and fixed with a cathode input side of a magnetron bulb and is provided with a cover, a transformer which supplies a cathode current to a magnetron, and a filter contained in said filter case for preventing leakage of unwanted electromagnetic waves, said transformer having a first U-shaped core for a primary winding outside said filter case and a second U-shaped core for a secondary winding inside said filter case, and open ends of one or both of said first and second U-shaped cores being engaged with extruded portions formed in a wall of said filter case for positioning of said cores. 
     Further objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a basic circuit structure of a driving power supply of a magnetron. 
     FIG. 2 is a conventional magnetron filter. 
     FIG. 3 is an embodiment where a transformer is housed within a magnetron filter case of the present invention. 
     FIG. 4 and FIG. 5 show other embodiments of the section where an insulation box for accommodating a transformer is fixed. 
     FIG. 6 shows an embodiment of the present invention where a closed magnetic loop is formed by placing in close contact the cores of a transformer from the internal and external sides of a side wall of a magnetron filter case. 
     FIG. 7, FIG. 8 and FIG. 9 show the principal section of further embodiments of the transformer coupling section. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 is a structure of a filter apparatus including a transformer within a filter case of an embodiment of the present invention. In this figure, a part of bottom section of an insulation box 23 made of a box type plastic or ceramics including the core 22 of a transformer at the inside of filter case together with a guiding line 21 which is also used as the primary winding of a transformer which supplies a cathode current is extruded through the bottomed box type filter case 16 which is forced to be engaged with the seal 10 of a magnetron bulb. The insulation box 23 is fixed when the cylindrical section 23a formed integrally with said insulation box 23 is engaged into the through hole in the side wall of said filter case 16. The insulation box 23 is provided with a rectangular or circular (rectangular shape in FIG. 3) core 22 which functions as a magnetic core of a transformer and is wound by a secondary winding 24 and is connected to the terminals 13 to the cathode with the arc welding. Herein, a core 22 is made of a ferrite which shows less high frequency loss but it is inferior in insulation property to plastic, etc. Therefore, it is desirable to place said guide wires 21 and winding part of a secondary winding 24 with the insulation sheet 25 interposed between them and the core 22. Moreover, since the components in the insulation box 23 are housed almost without any gap around the core 22 and the secondary winding 24 is formed by comparatively thick wire, movement due to vibration can be suppressed considerably, and when these are fixed by molding with the epoxy resin 26 for improving insulation property, these are integrated to the insulation box 23 making easier the maneuvering. 
     Meanwhile, a lead wire 27a of the inductance element 27 is connected to one end of said secondary winding and the other lead wire 27b to the through capacitor 28, in order to supply a high voltage. In this case, connection can be done by ordinary soldering work but since a current as low as 200˜400 mA flows through the lead wires 27a, 27b of the inductance element 27, it is enough to use a fine lead wire as thin as 0.5φ or less. Accordingly, the wire can be wound using a lapping tool as shown in FIG. 3. Otherwise, said lead wires 27a, 27b may be made of iron, nickel or alloys of them, and the one may be fixed to said cathode while the other is fixed to the center conductor of said through capacitor 28 by the spot welding. In addition, in the case of a through capacitor 28, like the double-element through capacitor shown in FIG. 2, the chassis plate 28a set at the earth potential is fixed to said filter case 16. In the example of FIG. 3, the insulation box 23 and a through capacitor 28 are provided on the opposite walls of a filter case 16, but these may be fixed on the two perpendicular surfaces or on the same surface for convenience of external wirings. 
     Regarding the fixing of insulation box 23, a cylindrical section 23a is inserted to a through hole provided to the filter case 16 as shown in FIG. 3 and the external circumference thereof is fixed with a heat compressive tube 29 together with the guide wire 21 or they can be fixed only with a bonding agent. Moreover, as shown in the partial diagram of FIG. 4, the function to prevent the waves from leaking can be improved by forming through holes with a cylindrical portion 16a through the burring hole in a wall of the filter case 16 and engaging thereto the cylindrical section 23a of the insulation box 23. Moreover, a metal bush 30 having a hat section formed separately as shown in FIG. 5 is engaged with said cylindrical section 23a and thereby the function to prevent the leak of waves can further be improved than in the example shown in FIG. 4. 
     FIG. 6 shows another example of the present invention where a closed magnetic loop is formed by placing in close contact the cores of primary and secondary sides of a transformer from the internal and external surfaces of side wall of the filter case with a wall of the filter case interposed between them. In this figure, the U-shaped core 14 to which the primary winding 31 of the transformer which supplies the cathode current is wound (the ferrite having excellent high frequency characteristic is desirable material for the core) is located on an extruded section 16a provided to said filter case and ends of the U-shaped core 15, to which the secondary winding 24 of said transformer is wound are engaged with the extruded section 16a. These cores are fixed by the bonding agent 32, and a closed magnetic loop is formed together with said cores 14 and 15 with said extruded section 16a interposed between them. Said extruded section 16a is extruded toward the outside of said filter case 16 in the example of FIG. 6, but since the main object of it is positioning of the cores 14, 15, it may be extruded toward the inside. 
     In the example of FIG. 7, the core 14 of the primary side of a transformer is covered with a holder 33 except for the winding section and the flat plate 33a of said holder is fixed by caulking to the side surface of said filter case 16 through the burred holes 33b. Thereby, it is no longer necessary to fix the core 14 with the bonding agent and positioning can also be done easily. The flat section 33a of a holder 33 can also be fixed by rivetting or screwing in place of the caulking. 
     In the example of FIG. 8, a pair of extruded sections 16b extruded to the internal and external sides are provided to the side surface of said filter case 16, one end of respective cores 14, 15 is engaged with corresponding extruded sections 16b in order to make easier the positioning. Therein, a rectangular, ellipse and triangular cross-section of a core other than the circular section is very convenient for preventing displacement in the rotating direction. 
     In the example of FIG. 9, in order to form a transformer, an extruded section 34a is formed of the metal plate 34 separated from said filter case 16. The cores 14, 15 are molded together with a metal plate 34 interposed between them with resin 35 and the metal plate 34 fixed by caulking to said filter case 16. In the figure, a window through which the core 15 of the secondary side of a transformer is to be inserted is provided and holes for caulking are burred in the side wall of the filter case 16 and said metal plate 34 is fixed by caulking to the filter case 16. In this case, it can also be fixed by rivetting, screwing or welding instead of caulking. 
     In above examples of structure, the transformer forms a closed magnetic loop via the wall of the filter case 16. Therefore, a loss of magnetic flux is inevitable but thickness of the wall of the filter case 16 is as thin as 0.5 mm or less and the magnetic flux can be sufficiently compensated for by increasing the number of turns of winding. Generally, as the material of the filter case 16, an economical zinc plated steel plate is used and loss of magnetic flux can be alleviated using non-magnetic metal such as aluminum. 
     In a magnetron filter apparatus of the present invention which is driven by a high frequency power source, a transformer which supplies a cathode current is accommodated within the filter case with good insulation characteristic or a transformer is directly and integrally provided to the filter case and moreover the magnetic core of a transformer is coupled through a metal body. Therefore, leak of electromagnetic waves from the power supply can be prevented perfectly and thereby a highly reliable magnetron filter apparatus ensuring easy assembling can be obtained.