JPH07122199A - Magnetron for microwave oven - Google Patents

Abstract

PURPOSE:To continue a stable oscillation even in a power supply having high operating frequency by changing the relative position between a coil and a core constituting a choke coil depending on temperature. CONSTITUTION:Two coils 14a, 14b are connected to a capacitor 12, and cores 15a, 15b are inserted into the inner parts of the coils 14a, 14b, respectively. Movable parts 16a, 16b consisting of a material whose form is changed depending on temperature such as shape memory alloy or bimetal are connected to the cores 15a, 15b, and one-side ends of the parts 16a, 16b are fixed to a filter box 11. When operated, for example by an inverter power supply, the temperature of an oscillating part body 15 is raised, and this heat is transmitted to the parts 16a, 16b, which are then deformed, for example, contracted to pull the cores 15a, 15b in Y-direction, and the inserted parts of the cores 15a, 15b are shortened to reduce the L-value of a choke coil. Consequently, the reduction of the filament current carried to a filament is suppressed, and stable oscillation can be continued.

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 cooking and thawing food.

[0002]

2. Description of the Related Art A magnetron for a microwave oven is provided with a filter circuit at its input terminal portion so that noise does not leak from its input terminal. This filter circuit is usually composed of a choke coil and a capacitor. The choke coil is composed of a core formed of a material that absorbs radio waves and a coil in which a conductive wire is wound around the core. Further, the core and the coil are integrally fixed with silicon or the like.

In the choke coil having such a structure, its inductance (hereinafter referred to as L value) is determined by the relative position between the coil and the core and the number of turns of the coil, that is, the number of turns of the conductive wire wound around the core.

[0004]

By the way, when the input voltage to the filament of the magnetron for a microwave oven is an alternating current, the input voltage is applied to the filament through the choke coil, so that the filament current flowing through the filament is L value of the choke coil. Is small, the value is large, and conversely, it is small when the L value is large. Therefore,
As an electric power source for the filament, for example, when using an inverter power source whose operating frequency is as high as several 10 kHz,
The larger the L value of the choke coil, the larger the voltage drop.

However, since the coils and cores that constitute the choke coil are fixed to each other as described above,
The L value is constant until the operating temperature reaches the Curie point of the core. Therefore, when the magnetron for a microwave oven is operated by an inverter power supply, if the anode voltage drops during operation due to thermal demagnetization, the input terminal voltage also drops. As a result, the filament current flowing through the filament becomes small, and eventually normal oscillation cannot be maintained.

In such a case, even if the input terminal voltage of the magnetron for microwave oven is lowered, normal oscillation can be maintained unless the filament current is lowered. However, in the structure in which the core and the coil forming the choke coil are fixed to each other, the L value is fixed, so that when the input terminal voltage decreases, the filament current becomes small and normal oscillation becomes difficult. Therefore, in the conventional magnetron for a microwave oven, there is a problem in using the inverter power supply as its operation power supply.

The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide a magnetron for a microwave oven capable of sustaining stable oscillation even in the case of a power source having a high operating frequency.

[0008]

SUMMARY OF THE INVENTION The present invention has a coil formed by winding a conductor wire a plurality of times and a choke coil composed of a core arranged inside the coil, and a choke coil having the choke coil to prevent leaking noise. In a magnetron for a microwave oven provided with a filter circuit for blocking, the relative positions of the coil and the core forming the choke coil are changed depending on the temperature.

Further, the core is mechanically connected to a temperature sensitive material whose shape is changed by temperature change so that the relative positions of the coil and the core are changed by temperature.

[0010]

According to the above construction, when the magnetron for a microwave oven is operated by a high operating frequency, for example, an inverter power supply, the relative position between the coil and the core changes due to the temperature rise during operation, The length of the core located at is shortened, and the L value of the choke coil is reduced. Therefore, even if the anode voltage decreases due to thermal demagnetization and the input voltage decreases, the decrease in the L value of the choke coil can suppress the decrease in the filament current flowing in the filament, and the stable oscillation can be maintained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1A shows a filter circuit portion of a magnetron for a microwave oven, and FIG. 1B shows a choke coil portion of the filter circuit in cross section.

Reference numeral 11 is a filter box, and a condenser 12 is attached to the filter box 11.
Further, 13 is an input terminal, and a power source (not shown) is connected to the input terminal 13. The condenser 12 has two coils 1
4a and 14b are connected, and the other ends of the coils 14a and 14b are connected to the filament terminal of the oscillator body 15. Cores 15a and 15b are inserted inside the coils 14a and 14b, respectively. And the core 15
The a and 15b are connected to movable parts 16a and 16b made of a material such as a shape memory alloy or a bimetal whose shape changes depending on the temperature. One ends of the movable parts 16a and 16b are fixed to the filter box 11.

In the above structure, the coils 14a, 14a
b and the cores 15a and 15b form a choke coil, and the choke coil and the capacitor 12 form a filter circuit for blocking noise leaking from the input terminal 13.

When the magnetron for a microwave oven having the above structure is operated by, for example, an inverter power source, the temperature of the oscillator body 15 rises and the anode voltage drops due to thermal demagnetization. At this time, the input voltage supplied from the input terminal 13 also drops, and the filament current decreases. FIG. 2 shows how the anode voltage and the filament current decrease as the anode temperature rises. In FIG. 2, the vertical axis represents the decrease rate of the anode voltage or filament current, and the anode temperature, and the horizontal axis represents time. Where A is the anode temperature,
B is the filament current reduction rate, and C is the anode voltage reduction rate.

By the way, when the temperature of the oscillator main body 15 rises, the heat of the oscillator main body 15 is transferred to the movable parts 16a and 16b, and as shown in FIG.
6b is deformed and reduced, for example, and the cores 15a and 15b are pulled in the arrow Y direction. At this time, the coils 14a, 14b
The length of the cores 15a and 15b inserted in the core becomes short, and the L value of the choke coil decreases. As a result,
A decrease in filament current flowing through the filament is suppressed, and stable oscillation can be maintained. FIG. 3 shows the pattern of the reduction rate of the anode voltage and the filament current at this time. In FIG. 3, the vertical axis represents the decrease rate of the anode voltage and filament current, and the anode temperature, and the horizontal axis represents time. A is the anode temperature, B is the filament current decrease rate, and C is
Is the anode voltage drop rate.

FIG. 4 shows the relationship between the amount of movement of the cores 15a and 15b and the L value. In FIG. 4, the horizontal axis represents the movement amount of the core 4, and the vertical axis represents the L value.

Next, another embodiment of the present invention will be described with reference to FIG. Note that in FIG. 5, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and overlapping description will be omitted. In this embodiment, a core disposed inside the coils 14a and 14b is provided with a cylindrical portion 51 and a center rod portion 52 inserted into the cylindrical portion 51.
It consists of and. Then, the cylindrical portion 51 is connected to the coil 14
It is fixed to the inside of a and 14b, and the center rod portion 52 is fixed to the bottom side of the cylindrical portion 51 via the movable part 53. The movable part 53 is made of a material having a property of expanding when the temperature rises. Therefore, when the temperature rises, the movable part 53 expands and moves the central rod portion 52 in the arrow Y direction. As a result, the L value of the choke coil decreases, and the decrease in filament current is suppressed.

Another embodiment of the present invention will be described with reference to FIG. In FIG. 6, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and overlapping description will be omitted. In the case of this embodiment, the center rod portion 61 has different characteristics.
It is formed by bonding different kinds of materials. For example, the right side portion of the center rod portion 61 is made of a material 61a having a high magnetic permeability so that the L value is high, and the left side portion is made of a material 62b having a lower magnetic permeability. According to this configuration, even when the center rod portion 61 moves little in the direction of the arrow Y, the portion of the material 61a having a high magnetic permeability moves to the outside of the coils 14a and 14b, so that the change in the L value can be increased. Therefore, it is effective when it is desired to make a large change in the L value of the choke coil, or a large change in the L value with a small amount of movement.

[0019]

According to the present invention, it is possible to provide a magnetron for a microwave oven capable of sustaining stable oscillation even when a power source having a high operating frequency is used.

[Brief description of drawings]

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

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

FIG. 3 is a characteristic diagram illustrating an example of the present invention.

FIG. 4 is a characteristic diagram illustrating an example of the present invention.

FIG. 5 is a diagram illustrating another embodiment of the present invention.

FIG. 6 is a diagram illustrating another embodiment of the present invention.

[Explanation of symbols]

 11 ... Filter box 12 ... Capacitor 13 ... Input terminal 14a, 14b ... Coil 15a, 15b ... Core 16a, 16b, 53 ... Movable part

Claims (2)

[Claims] 1. A choke coil comprising a coil formed by winding a conductor wire a plurality of times and a core arranged inside the coil, and a filter circuit having the choke coil for preventing leaking noise. In the magnetron for a microwave oven, the relative position of the coil and the core forming the choke coil is changed depending on the temperature. 2. The core is mechanically connected to a temperature sensitive material whose shape changes with temperature.
The described magnetron for a microwave oven.