JPH01286231A - Filter for magnetron - Google Patents

Abstract

PURPOSE:To prevent the leakage of the microwave power by combining the wires exciting a filament, guiding them in an annular magnetic body as an inductor only once, and storing and integrally molding them in the case of a capacitor. CONSTITUTION:Filament leads 4 and 4a are guided in an annular magnetic material 1, a porcelain dielectric substance 7 and an insulator 8 are molded with a resin insulator 9. An inductor using the magnetic material 1 is combined with a through capacitor 2 and integrated as a low-pass filter. To adjust the frequency characteristic of the filter, the distance between the fitting section of the dielectric substance 7 and the magnetic material 1 is changed, or the inner and outer diameters, length and magnetic permeability of the magnetic material 1 are changed. Side effects by heating or the inductance are completely eliminated when the filament is heated by an inverter power source at a high frequency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an inductor that forms a low-pass filter.
The present invention relates to a magnetron filter for preventing microwave leakage, which does not act as an inductor for power feeding to a magnetron filament.

[Prior Art] Currently, magnetrons are used for generating microwaves in household microwave ovens and the like. FIG. 2 shows the external appearance of this type of magnetron. In the figure, 2 is a feedthrough capacitor, and 3 is a filament terminal to which wiring for filament power supply from a power source is connected.

Fig. 3 shows an example of a low-pass filter for this kind of magnetron. In Fig. 1, 3.3a is a filament terminal, 4
．． 4a is a filament lead, 5 is a magnetron stem, 6 is a filter case, and 11 and lla are inductors. In this example, unnecessary microwave radiation is prevented by a low-pass filter consisting of an inductor 11.11a using a ferrite core and a feedthrough capacitor 2.

In recent years, the direct current obtained by rectifying a commercial AC power supply is used intermittently at high speed to convert it into alternating current, which has a much higher frequency than the commercial frequency, and then inputs this high frequency alternating current to a transformer. Inverter power supplies that are lighter in weight and smaller in size have begun to become popular as power sources for the above household magnetrons.

When an inverter power source is used, the microwave output of the magnetron is normally controlled by controlling the conduction time of the switching circuit of the inverter power source. Due to the circuit configuration, the cut-off time of the switching circuit is approximately constant, so when the microwave output of the magnetron is controlled, the frequency of the inverter power source changes.

The low-pass filter circuit shown in FIG. 3 is connected as shown in FIG. In this figure, 1° is the filament of the magnetron, 13 is the anode of the magnetron, and other symbols are as described above.

When inputting directly to a transformer from a commercial AC power source, the frequency is low, so there were no problems with separate installation of such a circuit. However, the filament current is large, for example, about 11 A in the case of a household microwave oven, and the filament current is high at 1 frequency when using an inverter power supply (for example, 500 to 1
000 times), so the inductor 11 of the low-pass filter.
Combined with the increase in the impedance of lla,
Heat generation in the inductor has become a problem. Further, as described above, as the output of the magnetron changes, the impedance of the inductor changes, causing a problem that the filament current value changes.

As a countermeasure to this problem, Japanese Patent Application Laid-Open No. 62-66534
No. 62-262344 discloses a structure that does not act as an inductor for filament current, but acts as an inductor only for microwaves. These principles are as shown in Figures 5 and 6. Depending on the filament current, magnetic fields in opposite directions are generated and cancel each other out, so they do not act as an inductor.
Acts as an inductor only against microwave leakage.

[Problems to be Solved by the Invention] However, the above-mentioned conventional measures have drawbacks such as increased external dimensions and difficulty in winding the magnetic core.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide a magnetron filter using an inductor that does not have large external dimensions and is not difficult to manufacture.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, the inside of the annular magnetic body is connected by combining two reciprocating wires that feed power to the filament.
It was decided that the inductor would be made into an inductor by passing through it only once, and then this inductor would be further housed in a capacitor case and molded with resin as a filter.

[Operation] By doing the above, the magnetic fields caused by the filament current in the reciprocating wire cancel each other out, so they do not act as an inductor with respect to the filament current. However, in the case of microwave leakage, since there is only one direction from the stem side of the magnetron toward the feedthrough capacitor, magnetic flux is generated within the annular magnetic body and acts as an inductor.

Further, since the inside of the annular magnetic body is passed through only once, there is no need to perform so-called winding work, and workability is good because it is integrally molded together with the feedthrough capacitor as a filter.

[Example] FIG. 1 is a diagram showing an example of the present invention. 1 is a ring-shaped magnetic body made of ferrite, 2 is a feed-through capacitor similar to the conventional one, 3.3a is a filament terminal to which the filament power supply wiring from the power supply is connected, and 4.4a is connected to the filament terminal of the magnetron stem. A filament lead, 6 a filter case, 7 a capacitor dielectric (porcelain), 8 an insulator (a pipe made of silicone rubber, etc.), and 9 an insulator (resin). Conventional feedthrough capacitors do not have the annular magnetic material 1 built-in, and a low-pass filter is constructed by combining it with a separately attached inductor, but in the present invention, the inductor using the annular magnetic material 1 is used as a feedthrough capacitor. 2 and integrated as a low-pass filter, and can be used as is.

We also experimented with molding an inductor with a conventional structure in which a ferrite core is wound with a feedthrough capacitor as an inductor.

It was difficult due to many structural and dimensional problems. According to the present invention, there is no need to wind the magnetic material, making assembly work very easy.

Furthermore, in terms of performance, it becomes possible to take the following procedure in order to obtain desired characteristics of the insertion loss with respect to the frequency of the filter, which is effective in preventing unnecessary radiation.

As a means of adjusting the frequency characteristics of the filter, (1) changing the distance between the dielectric attachment part and the magnetic body; and (2) changing the inner and outer diameters, length, and magnetic permeability of the magnetic body.

(3) A plurality of annular magnetic bodies are arranged at intervals.

You can take the following methods.

As a result of experiments using the filter according to the present invention, there were no side effects due to heat generation or inductance even when the filament was ignited at a high frequency using an inverter power source. Furthermore, in preventing leakage of microwave power, performance equivalent to or better than that of conventional low-pass filters was obtained.

[Effects of the Invention] As described above, according to the present invention, a magnetron filter that can be used in combination with an inverter power source without any problems can be manufactured very easily and in a short time.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is an external view of an example of a magnetron, and FIGS. 3 to 6 are diagrams explaining a conventional technique. 1... Annular magnetic body, 2... Feedthrough capacitor, 3
．． 3a... filament terminal, 4.4 a-filament lead, 5... magnetron stem,
6... Filter case, 7... Capacitor dielectric, 8... Insulator (pipe), 9... Insulator (
resin). Figure 1 Figure 2 Figure 3 Figure 5 Figure 6

Claims (1)

[Claims] 1. In order to prevent unnecessary radiation of microwaves from the magnetron, in a low-pass filter consisting of an inductor and a capacitor installed on the filament side, the two round-trip wires that feed the filament are combined and passed through the inside of the annular magnetic body only once. A magnetron filter characterized in that the inductor is further housed in a capacitor case and integrally molded with resin as a filter.