JP2785889B2 - Magnetron for microwave oven - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron for a microwave oven used for a microwave oven or the like.

[0002]

2. Description of the Related Art Conventionally, a magnetron is used by being incorporated in a microwave oven for cooking and thawing foods. By the way, conditions for noise such as a microwave oven have become severe, and suppression of noise has become important. In order to suppress such microwave noise,
Various methods have been proposed. One of them is a method of reducing noise generated by the magnetron itself.

Here, a method for reducing noise generated by the magnetron will be described with reference to FIG. FIG.
Is a diagram showing an input portion of a magnetron used for a microwave oven, and 51a and 51b are input terminals connected to a power supply (not shown). A capacitor 52 and an inductor 53 are connected to the input terminals 51a and 51b. Note that the inductor 53 is provided with a winding 55 around the ferrite core 54.
Is used. The inductor 53 is connected to a cathode (not shown) of the magnetron main body 56. Note that the capacitor 52 and the inductor 53 form a low-pass filter, and the input terminal 5
Noise leaking outside through 1a and 51b is suppressed.

FIG. 6 is a circuit diagram of the above-described configuration. The same reference numerals are given to portions corresponding to those in FIG. 5, and duplicate description will be omitted. As shown in FIG. 6, the capacitors 52 are connected between the input terminals 51a and 51b and between the input terminals 51a and 51b and the ground, respectively. The inductor 53 is connected to each of the input terminals 51a and 51b, and is connected to the cathode F.

[0007] As shown in FIG. 7, the inductor 53 is provided with a winding 55 around an outer periphery of a ferrite core 54 having a high relative magnetic permeability.
Is used. In this case, a formal copper wire or the like is used for the winding 55. Also,
The inductor 53 includes a ferrite core 5 inside the winding 55.
4 and an air core B without the ferrite core 54. Then, the air core B side is connected to the cathode of the magnetron body.

[0006] The magnetron having the above-described configuration is, for example, 24
It oscillates at 50 MHz and most of its energy is output to the outside as microwave power through the magnetron output. However, some of them leak to the input terminal side. If part of the energy leaks to the input side, the microwave energy forms a standing wave on the winding 55, producing high and low power densities. At this time, when a portion having a large power density is located in the core portion A, heat is generated by magnetic loss such as eddy current loss. As a result, the formal coating used for insulation between the windings 55 constituting the inductor 53 may be deteriorated by heat.

In order to avoid such deterioration of the formal coating, an air core B is provided in a part of the inductor 53 so that a portion having a high power density is located at the position of the air core B.

[0008]

Here, the inductor 5
The relationship between the magnetic permeability and the frequency of some materials of the ferrite core used in No. 3 will be described with reference to FIG. FIG.
In the graph, the horizontal axis represents frequency (MHz), and the vertical axis represents magnetic permeability. As shown by the curves a to d, the frequency is increased to about 100 MHz.
At about z, the magnetic permeability of each material decreases. When the magnetic permeability of the ferrite core is reduced as described above, the inductance L of the inductor 53 constituting the filter decreases.

By the way, the cutoff frequency f of the low-pass L-type filter is

(Equation 1) Indicated by In the equation (1), L is the inductance [H] of the inductor 53, and C is the capacitance [F] of the capacitor 52.

Therefore, when the inductance L of the inductor 53 decreases, the cutoff frequency f increases. For example, in the case of a conventional filter, the inductance L of the inductor 53 is 1.2 μH,
Has a capacitance C of 500 PF and a cutoff frequency of 7 MHz. In the filter having such a configuration, the effect of suppressing noise is obtained up to about several tens of MHz. However, due to the recommendations of the CISPR (International Special Committee on Radio Interference) and the like, suppression of radiation noise in the several hundred MHz band has become important.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetron for a microwave oven which solves the above-mentioned drawbacks and suppresses noise in a high frequency band from 500 MHz to 1000 MHz.

[0012]

SUMMARY OF THE INVENTION According to the present invention, an input terminal to which a power supply voltage is supplied is provided with a cored winding portion and a coreless portion.
In a magnetron for a microwave oven to which a filter having a core type inductor formed by an air core winding portion is connected, a length of a winding wound along an outer periphery of a core portion of the winding portion having the core. Is shorter than a length corresponding to a half wavelength of the frequency of the noise to be suppressed.

[0013] A winding portion having a core and a winding portion having an air core without a core, wherein the winding is divided and wound on a common core.
In a magnetron for a microwave oven, wherein a filter having a core-shaped inductor formed by a coil and a power supply voltage is supplied to an input terminal, a winding having the core is provided.
The length of each winding divided and wound around the outer periphery of the core part of the part is the length corresponding to half the wavelength of the noise frequency to be suppressed .
It is also characterized by being shorter .

[0014]

The filter having the configuration described in the background art may be effective in suppressing noise in a specific high frequency band of about 500 MHz to about 1000 MHz. The analysis is as follows.

Here, the attenuation characteristic of the filter will be described. A measurement circuit as shown in FIG. 9 is used for measuring the attenuation characteristic of the filter. A sweep oscillator 91 applies a sweep signal generated from the sweep oscillator 91 to a filter 92. The output of the filter 92 is measured by the frequency analyzer 93.

An example of a filter whose attenuation characteristics have been measured by the above-described measuring circuit will be described with reference to FIGS. FIG. 10 shows the structure of the measured filter box, and FIG. 11 shows the structure of the inductor constituting the filter.

In FIG. 10, 101a and 101b are input terminals, and 102 is a capacitor. An inductor 103 is formed by winding a winding 105 around a ferrite core 104. Then, the capacitor 102 and the inductor 1
03 constitutes a filter, and the inductor 103 is connected to the cathode of the magnetron body 105.

As shown in FIG. 11, the inductor is formed of a core portion A having a ferrite core 104 inside a winding 105 and an air core portion B having no ferrite core 104.

The winding 10 formed on the core portion A
La is the length of 5a, Lb is the length of the winding 105b formed in the air core B, D is the outer diameter of the winding of each of the windings 105a and 105b, d is the wire diameter of the winding, and the spacing between the windings. Is g, La = 14.8 mm, Lb = 12.7 mm, and D =
7.6 mm, d = 1.4 mm, g = 0.08 mm.

The ferrite core 104 is moved in the direction of arrow Y in FIG.
The length H of the portion (Ao) inserted in a is changed to 11.4 mm, 9.6 mm, and 8.3 mm, respectively.
The length Lc of the ferrite core 104 is 18 mm, and the core diameter Dc is 4.5 mm.

FIG. 1 shows the attenuation characteristics of the filter having the above-described configuration.
2 to 14. The horizontal axis is frequency (M
Hz), the center is 520 MHz, and one division is 10
0 MHz, and the vertical axis indicates the attenuation. Ferrite core 1
FIG. 12 shows the case where the length H of the portion (Ao) in which 04 is inserted into the winding 105a is 11.4 mm, FIG. 13 shows the case where the length is 9.6 mm, and FIG. 14 shows the case where the length H is 8.3 mm.

Based on the measurement results, the frequency fo having an attenuation effect, the number of turns T of the winding 105a in the portion (Ao) where the ferrite core 103 is inserted, and the portion (where the ferrite core 104 is inserted) Ao) winding 10
Table 1 shows the relationship between the developed length 1 when the length 5a is extended to one long line and the frequency fc at which the developed length 1 becomes a half wavelength.

[0023]

[Table 1] Then, the frequency fo (MHz) having the damping effect is plotted on the horizontal axis and the frequency fc (M
Hz) on the vertical axis, as shown in FIG. Thus, there is a correlation between the frequency fo and the frequency fc. In this case, it is considered that the difference between fo and fc is that a part of the magnetic field generated in the winding 105b of the air core B is applied to the ferrite core 104.

When a half-wavelength of the frequency fo having an attenuating effect is l ′ and a metal wire having a length corresponding to the half-wavelength l ′ is wound so that the winding outer diameter D is 7.6 mm, Table 2 shows the winding length H 'in the direction of the ferrite core 104 and the number of turns T'.

[0025]

[Table 2] Here, the length l of the winding portion (Ao) of the ferrite core 104 is inserted into the winding 105a, when comparing the length l'corresponding to a half wavelength of a frequency fo which is damping effect, l is 2.67 to 3.42 turns shorter than l '
Thus, it can be seen that there is a suppression effect.

It is considered that the above result is due to the fact that the magnetic field generated by the noise current flowing through the winding is consumed as magnetic loss inside the ferrite core, and the noise propagating outside the magnetron is reduced.

As shown in FIG. 16, when the developed length of the winding 162 wound around the ferrite core 161 becomes longer than half the wavelength λ / 2 of the frequency of the noise to be suppressed, the core 1
Magnetic flux 163 is generated in a direction to cancel the magnetic flux inside 61, and the magnetic loss is reduced. In addition, if the winding constituting the inductor does not have an air core, when the development length of the winding wound around the ferrite core is half the wavelength of the noise frequency to be suppressed,
The amount of magnetic flux generated inside the ferrite core is maximized.

A part of the microwave power of, for example, 2450 MHz output from the magnetron leaks to the input side and is transmitted to the inductor. At this time, an air core B is usually provided on the magnetron main body side so that the microwave power is not absorbed by the ferrite core. In this case, a part of the magnetic flux generated by the winding of the air core B enters the ferrite core. Therefore, the length of the core of the winding wound on a ferrite core (Ao) is Ri Saya Cho corresponding to a half wavelength of the frequency of the noise to be suppressed, there is damping effect 2 from 4-turn partial short condition.

If the frequency of the noise to be suppressed is 500
In the case where the frequency is from MHz to 1000 MHz, if the winding is formed of a metal wire having a length corresponding to a half wavelength of the frequency to be suppressed, the winding length H in the ferrite core direction becomes 100
There is a case where the inductance for suppressing the noise in the MHz band is insufficient. In this case, an inductor having a structure in which the coil is divided into a plurality and wound is used. At this time, a common ferrite core is used for each winding so that the inductor is compactly accommodated in the filter box.

Here, an inductor having a structure in which the coil is divided into a plurality of parts and wound is described. Below, 700MH
An example of an inductor having the largest attenuation effect in the 900 MHz band from z will be described with reference to FIG.

The core portion in which the ferrite core 171 is located inside the winding has two stages, a core portion A1 and a core portion A2. A winding 172a is provided in the core portion A1.
2, a winding 172b is formed. The length of the winding 172a is L1, the length of the winding 172b is L2,
G is the distance between the winding 2a and the winding 172b, and the winding 173 of the air core B
, L1 = 7.35 mm, L
2 = 7.35 mm, G = 3.0 mm, L3 = 10.2 m
m, D = 7.6 mm, d = 1.4 mm, g = 0.08 m
m. Also, the length L of the ferrite core 171
c and core diameter Dc are Lc = 20 mm and Dc =
4.5 mm. The distance Gc between the core end and the winding 172a is Gc = 3.0 mm.

The ferrite core 171 has a winding 172.
The length H1 of the portion (Ao1) inserted into the portion a is 7.3.
5 mm (H1 = L1), ferrite core 171 is winding 1
The length H2 of the portion (Ao2) inserted into 72b is 6.65 mm (H2 = Lc-Gc-L1-G).

FIG. 18 shows the attenuation characteristics of the filter having the above-described configuration, which were measured by the measurement circuit of FIG. 9 described above. In FIG. 18, the horizontal axis is frequency (MHz) and the center is 52
0 MHz, one scale is 100 MHz, and the vertical axis is the attenuation.

Here, the frequency fo having an attenuating effect, the number of turns T of the windings of the portions (Ao1) and (Ao2) where the ferrite core 171 is inserted into the windings 172a and 172b,
Winding development length l, frequency f with this development length l as a half wavelength
Table 3 shows the relationship of c.

[0035]

[Table 3] Further, using a metal wire having a length corresponding to a half wavelength l 'of the frequency fo having an attenuation effect, the winding length wound so that the winding outer diameter becomes 7.6 mm is H', and the number of turns is defined as Assuming T ′, the relationship is as shown in Table 4.

[0036]

[Table 4] The winding length l of the portion (Ao1) (Ao2) where the ferrite core 171 is inserted into each of the windings 172a and 172b.
And a length corresponding to a half wavelength of the frequency fo with an attenuation effect
A comparison of the l', l is from 4.62 than l'5.10
It is shorter by the turn.

As described above, when a winding is divided into a plurality of regions of a common ferrite core, the number of turns is smaller than that in a case where the windings are concentrated in one region because each winding has a leakage magnetic flux. The effect is obtained when the number of turns of the winding of each inductance is shorter by 4 to 6 turns than in the case of a metal wire having a length corresponding to a half wavelength of the frequency at which noise is to be suppressed.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing an input portion of a magnetron for a microwave oven. Reference numerals 11a and 11b denote input terminals which are connected to a power supply (not shown). Input terminals 11a, 11b
Is connected to a capacitor 12 and an inductor 13. Note that, as the inductor 13, a core-type inductor in which a winding 15 is wound around an outer periphery of a ferrite core 14 is used.
Then, the inductor 13 is connected to a cathode (not shown) of the magnetron body 16. Note that the capacitor 12 and the inductor 13 form a low-pass filter.
Noise that leaks outside through the input terminals 11a and 11b is suppressed.

The inductor 13 is a radio wave absorber, and as shown in FIG. 2, the ferrite core 1 having a high relative magnetic permeability.
4 is composed of a core-type inductor in which a winding 15 is wound on the outer periphery. Note that the winding 15 is composed of a winding 15a of the core portion A in which the ferrite core 14 is located, and a winding 15a.
The winding 15b of the air core B is connected to the cathode of the magnetron body 16.

[0040] In the above configuration, the length of the winding length H portion of the winding 15a of the core portion A, corresponds to the length Saya are two from four turns partial short half wavelength of the frequency of the noise to be suppressed I have.

Next, another embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 3 is a diagram showing an input portion of the magnetron for a microwave oven. Reference numerals 31a and 31b denote input terminals, which are connected to a power supply (not shown). Input terminal 31a,
A capacitor 32 and an inductor 33 are connected to 31b. Note that the inductor 33 is a ferrite core 34
A core-type inductor in which a winding 35 is wound on the outer periphery is used. The inductor 33 is connected to the magnetron body 36.
(Not shown). Note that the capacitor 3
2 and the inductor 33 form a low-pass filter, and suppress noise leaking outside through the input terminals 31a and 31b.

Incidentally, the core portion of the inductor in which the ferrite core is located inside the winding is, as shown in FIG.
1 and a core portion A2. A winding 35a is wound around the core A1, and a winding 35b is wound around the core A2. A winding 36 is wound around the air core portion B where the ferrite core 34 is not provided, and the winding 36 is connected to the magnetron body.

In the above configuration, the length of the winding length H1 of the winding 35a of the core A1 and the length of the winding 3 of the core A2
The length of the winding length H2 portion of 5b is Ri Saya Cho corresponding to a half wavelength of the frequency of the noise to be suppressed, 4-6 turns partial short
They are phrases.

[0044]

According to the present invention, it is possible to suppress noise particularly in the frequency band of 500 MHz to 1000 MHz.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram illustrating an embodiment of the present invention.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

FIG. 4 is a diagram illustrating another embodiment of the present invention.

FIG. 5 is a diagram illustrating a conventional example.

FIG. 6 is a diagram illustrating a conventional example.

FIG. 7 is a diagram illustrating a conventional example.

FIG. 8 is a diagram illustrating characteristics of a ferrite core.

FIG. 9 is a diagram showing a circuit for measuring an attenuation characteristic.

FIG. 10 is a diagram illustrating another conventional example.

FIG. 11 is a diagram illustrating another example of the related art.

FIG. 12 is a diagram illustrating an attenuation characteristic of a filter.

FIG. 13 is a diagram illustrating an attenuation characteristic of a filter.

FIG. 14 is a diagram illustrating an attenuation characteristic of a filter.

FIG. 15 is a diagram illustrating characteristics of a filter.

FIG. 16 is a diagram illustrating characteristics of an inductor.

FIG. 17 is a diagram illustrating a conventional inductor.

FIG. 18 is a diagram illustrating an attenuation characteristic of a filter.

[Explanation of symbols]

 11a, 11b Input terminal 12 Capacitor 13 Inductor 14 Ferrite core 15 Winding 16 Magnetron body

Claims (2)

(57) [Claims] An input terminal to which a power supply voltage is supplied is provided with a core.
Formed by a winding part with a core and an air core winding part without a core
In a microwave oven magnetron for a filter is connected with a core type inductor, a said core
The length of the winding wound along the outer periphery of the core part of the winding part is the length corresponding to a half wavelength of the frequency of the noise to be suppressed .
A magnetron for a microwave oven characterized in that it has a shorter length . 2. A winding part having a core and a winding part having an air core without a core, wherein a winding is divided and wound on a common core.
In a magnetron for a microwave oven connected to an input terminal to which a power supply voltage is supplied, a filter having a core-type inductor formed in the above is divided around the outer periphery of a core portion of a winding portion having the core. The length of each wound coil is shorter than the length corresponding to half the wavelength of the noise to be suppressed.
Magnetron for a microwave oven, characterized in that Ku was.