JP2003272932A - Boosting transformer for driving magnetron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a boosting transformer wherein less frequency loss is produced and that is hardly saturated and is compact and easy to manufacture. <P>SOLUTION: A boosting transformer 20 is designed for a microwave oven. A primary winding 21, a secondary winding 22, and a heater winding 23 surround a bar-like ferrite core 26, respectively. They are piled up in the axial direction of the ferrite core 26. The ferrite core 26 is a metallic core that is formed by winding a long metallic thin plate by plural times like a square, and one inner diameter thereof is made larger than an outer diameter of the primary winding 21, the secondary winding 22 and the heater winding 23. The other square inner diameter thereof is made larger than a total piling height of them. Such an iron oxide powder resin core 27 is inserted to the bar-like ferrite core 26 from the outside of the primary winding 21, the secondary winding 22 and the heater winding 23. It is arranged opposite to the ferrite core 26 with a clearance G in-between in this state. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-frequency dielectric heating using a magnetron such as a microwave oven, and more particularly to a step-up transformer for driving the magnetron with a switching power supply.

[0002]

2. Description of the Related Art FIG. 1 is a block diagram of a magnetron drive power source using a step-up transformer, which is the object of the present invention. In the figure, the alternating current from the commercial power supply 11 is rectified into a direct current by the rectifier circuit 13, smoothed by the choke coil 14 and the filter capacitor 15 on the output side of the rectifier circuit 13, and given to the input side of the inverter 16. The direct current is converted into a desired high frequency (20 to 40 kHz) by turning on and off the semiconductor switching element in the inverter 16. The inverter 16 is composed of, for example, two sets of switching element groups in which a plurality of power MOSFETs are connected in parallel for switching direct current at high speed, and a drive circuit for driving these switching element groups. The drains of the power MOSFETs that form the switching element group are connected to one end and the other end of the primary winding 182 of the step-up transformer 18, respectively, and the power MOS that forms these two switching element groups.
The sources of the FETs are connected to each other, and the gates of the power MOSFETs that form the switching element group are connected to the switching element drive circuit.
The switching element group composed of power MOSFETs is driven by the inverter control circuit 61, and the current flowing through the primary side of the step-up transformer 18 is switched on / off at high speed. The input signal of the control circuit 161 detects the primary side current of the rectifier circuit 13 at CT17, and the detected current is input to the inverter control circuit 161 and used for controlling the inverter 16.

In the step-up transformer 18, a high frequency voltage output from the inverter 16 is applied to the primary winding 181, and a high voltage according to the winding ratio is obtained in the secondary winding 182. In addition, the winding 1 having a small number of turns on the secondary side of the step-up transformer 18
83 is provided and is used for heating the filament 121 of the magnetron 12. Step-up transformer 1
The secondary winding 182 of No. 8 includes a voltage doubler half-wave rectifier circuit 19 that rectifies the output. The double voltage half-wave rectifier circuit 19 includes a high voltage capacitor 191 and two high voltage diodes 192.
193, the high voltage capacitor 191 and the high voltage diode 192 are turned on in a positive cycle (for example, the upper end of the secondary winding 182 is positive in the figure), and the electrode plate of the high voltage capacitor 191 is moved to the left side in the figure. Charge the right side plate positively and negatively. Next, in a negative cycle (the lower end of the secondary winding 182 is positive), the high voltage diode 193 conducts, and between the anode 122 and the cathode 121 of the magnetron 12, the voltage of the previously charged high voltage capacitor 191 and the secondary voltage. Winding 18
A voltage twice as large as the voltage of 2 is added.

An example of a magnetron drive power supply using a boosting transformer, which is the subject of the present invention, has been described above, but the drive power supply is not limited to this, and any drive that includes a transformer for boosting high frequencies can be used. It can be anything.

[0005]

With the need for miniaturization of microwave ovens, it is necessary to miniaturize the step-up transformer, so that high frequencies have come to be used from the low frequencies up to then. As a core of a transformer, a metal core (amorphous, silicon steel plate), which is advantageous in terms of downsizing, saturation, and cost, was used at low frequencies, but at high frequencies, the metal core is no longer used because of its large high-frequency loss. Ferrite cores have come to be used instead of.

FIG. 6 shows an example of a step-up transformer using a ferrite core. In FIG. 6, the primary winding 6
1, the secondary winding 62, and the heater winding 63 were placed in parallel on the same axis of the two opposing U-shaped ferrite cores 64 and 65. In the case of a magnetron driving power source that often handles a large amount of power, a zero volt switching method (hereinafter, ZVS method) based on voltage resonance is mainly used to reduce the load on the power semiconductor. In this ZVS method, the resonance voltage is changed. In order to obtain the coupling coefficient of the step-up transformer from 0.6 to 0.
It is necessary to set it to about 85, and a gap G is provided. However, in the case of the conventional step-up transformer using the two opposed U-shaped ferrite cores 64 and 65, it is necessary to further increase the peak current flowing in the primary side of the step-up transformer in order to further increase the output of the magnetron. If so, the saturation magnetic flux density characteristic of the ferrite core is poor, so that the ferrite core is easily saturated, and it is necessary to increase the size of the ferrite core to prevent saturation. This has been an obstacle to the premise of downsizing the power supply. The present invention solves these problems, and it is an object of the present invention to provide a step-up transformer that contributes to downsizing of a power supply and does not saturate even at high output.

[0007]

According to the invention of a step-up transformer for driving a magnetron as set forth in claim 1, there is provided a step-up transformer for supplying a drive voltage to the magnetron, wherein the primary winding and the secondary winding are rod-shaped respectively. In a magnetron driving step-up transformer surrounding a ferrite core, a letter-shaped core is inserted from the outside of the primary winding and the secondary winding toward the rod-shaped ferrite core, and the air gap is formed between the rod-shaped ferrite core. Is placed to face each other. According to the invention of the step-up transformer for driving a magnetron as set forth in claim 2, the step-up transformer for supplying a drive voltage to the magnetron, wherein the primary winding and the secondary winding respectively surround a rod-shaped ferrite core for driving the magnetron. In the step-up transformer, one of the square-shaped inner diameters is larger than the outer diameter of either the primary winding or the secondary winding, and the other square-shaped inner diameter of the primary winding and the secondary winding is overlapped. A square-shaped core formed to have a size larger than the length is inserted into the rod-shaped ferrite core from the outside of the primary winding and the secondary winding, and is opposed to the rod-shaped ferrite core with a gap. It is characterized by consisting of. According to the above two inventions, since the ferrite core having a small high frequency loss is used as the main core, and the void-shaped core is provided so as to face the main core so as not to be saturated, and the square-shaped core is used for the magnetic path, the manufacturing is simple and the size is small. Thus, there is an effect that it is firm and also acts as a mechanical protection on the outside of each winding. According to the invention of the step-up transformer for driving a magnetron as set forth in claim 3, there is provided a step-up transformer for supplying a drive voltage to the magnetron, wherein the primary winding and the secondary winding respectively surround the rod-shaped ferrite core and the rod-shaped ferrite core. In a step-up transformer for driving a magnetron, which is juxtaposed side by side in the axial direction, a metal core is formed by winding a long thin metal plate in a square shape a plurality of times, and one inner diameter of the square shape is the primary winding. And a secondary winding, the inner diameter of which is larger than the outer diameter of any of the secondary windings and the inner diameter of the other of the square brackets is larger than the overlapping length of the primary winding and the secondary winding. And a state in which the rod-shaped ferrite core is fitted from the outside of the secondary winding toward the rod-shaped ferrite core and is opposed to the rod-shaped ferrite core with a gap. According to the above invention, a ferrite core having a small high frequency loss is used as a main core, and a void is provided so as not to be saturated, and a metal core that is small and has a saturation magnetic flux density characteristic higher than that of a ferrite core is used. Moreover, by stacking thin metal plates in the direction in which eddy currents flow to prevent eddy currents from flowing and taking measures against high-frequency loss, and by making the metal core into a square shape, it is easy to manufacture, is small in size, and is solid. It also has the effect of acting as a mechanical protection on the outside of the line.
According to the invention described in claim 4, in the step-up transformer for driving magnetron according to any one of claims 1 to 3, the rod-shaped ferrite core has a rectangular parallelepiped shape. According to the above invention, the voids formed between the rod-shaped ferrite core and the metal core have the same width, which facilitates the design of the coupling coefficient and the like. According to a fifth aspect of the present invention, in the magnetron driving step-up transformer according to the fourth aspect, a protrusion is formed on a part of a surface of the rectangular parallelepiped ferrite core facing the metal core, and the protrusion is formed. Is contacted with the metal core. According to the invention described above, it is not necessary to separately prepare a spacer between the rod-shaped ferrite core and the metal core, and therefore the labor for assembling it can be saved, so that the step-up transformer can be easily assembled and the cost can be reduced. According to the invention of a step-up transformer for driving a magnetron as set forth in claim 6, there is provided a step-up transformer for supplying a driving voltage to the magnetron, wherein the primary winding and the secondary winding respectively surround a rod-shaped ferrite core. In the step-up transformer, one inner diameter of the square shape is larger than both outer diameters of the primary winding and the secondary winding, and the other inner diameter of the square shape is larger than the length of the rod-shaped ferrite core. The rod-shaped ferrite core is inserted into the square-shaped core formed together with the winding, and the rod-shaped ferrite core and the metal core are opposed to each other with a gap between the axial end of the rod-shaped ferrite core and the metal core. According to the above invention, the ferrite core having a small high frequency loss is used as the main core, and the void-shaped core is used to face the main core so as not to be saturated, and the square-shaped core is used for the magnetic path. It has the effect of being robust and also providing mechanical protection on the outside of each winding. According to the invention of a step-up transformer for driving a magnetron as set forth in claim 7, the step-up transformer for supplying a drive voltage to the magnetron, wherein the primary winding and the secondary winding respectively surround a rod-shaped ferrite core. In a step-up transformer, a metal core is formed by laminating a plurality of letter-shaped thin metal plates in the thickness direction, and one of the letter-shaped inner diameters is larger than the outer diameter of either the primary winding or the secondary winding. The rod-shaped ferrite core is fitted together with the winding into a metal core formed by forming the other inner diameter of the rod-shaped ferrite core larger than the length of the rod-shaped ferrite core, and the axial end of the rod-shaped ferrite core and the metal. It is characterized in that it is arranged so as to face the core with a gap therebetween. According to the above invention, a ferrite core with a low high-frequency loss is used as a main core, and a gap is provided so as not to saturate. Since the thin plates are laminated, it becomes difficult for eddy currents to flow, and since the metal core is formed in a square shape, it is easy to manufacture, is robust, and has an effect that it also functions as a guard for each winding. According to the invention described in claim 8, in the step-up transformer for driving magnetron according to claim 6 or 7, the rod-shaped ferrite core has a columnar shape. According to the above invention, the rod-shaped ferrite core has a columnar shape, which has the effect of simplifying the manufacturing. Further, since the voids formed between the rod-shaped ferrite core and the metal core have the same width, it is easy to design the coupling coefficient and the like. According to a ninth aspect of the present invention, in the magnetron driving step-up transformer according to any one of the first to eighth aspects, the magnetic resistance is changed by the rod-shaped ferrite core and the gap between the cores. And According to the above-described invention, it is possible to easily create the coupling coefficient of the step-up transformer to an optimum coefficient.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A step-up transformer of the present invention will be described below with reference to FIGS. FIG. 2 shows the first of the present invention.
5A and 5B are views showing a step-up transformer according to the embodiment of the present invention, FIG. 7A is a front view, FIG. 7B is a plan view, FIG. In the figure, 20 is a step-up transformer according to the first embodiment, 21 is a primary winding, 22 is a secondary winding,
23 is a heater winding. The primary winding 21 is the secondary winding 2
Compared with 2, the winding cross section is large and the number of turns is small. The heater winding 23 has an extremely small number of turns as compared with the secondary winding 22, and is not shown in the drawing. Further, since the heater winding 23 may be configured as a separate component, it is not an essential component here. Reference numeral 26 is a rod-shaped ferrite core, which has a rectangular parallelepiped shape. Around the rectangular parallelepiped ferrite core 26, the primary winding 21, the secondary winding 22, and the heater winding 23
And are respectively surrounded and juxtaposed side by side in the axial direction of the core.

Reference numeral 27 denotes a metal core adopted by the present invention. A long metal thin plate 27a made of an amorphous or silicon steel plate is formed in a letter shape a plurality of times (10 to 10) as shown in FIG. 3 (a).
It is wound around 40 times) to insulate each layer. Moreover, one of the inner diameters of the square-shaped metal core (see FIG.
In (c), the inner diameter of the metal core 27 in the left-right direction is the primary winding 2
The outer diameter is larger than any one of the primary winding 1, the secondary winding 22, and the heater winding 23, and the inner diameter of the other (see FIG. 2).
In (c), the inner diameter of the metal core 27 in the vertical direction) is the primary winding 2
6, the secondary winding 22, and the heater winding 23 are formed to be larger than the overlapping length of the three windings.

Therefore, as shown in FIG. 2 (d), the metal core 27 as shown in the figure is inserted from the outside of the primary winding 21, the secondary winding 22, and the heater winding 23 toward the ferrite core 26, A spacer (not shown) is placed between the rod-shaped ferrite core 26 and the rod-shaped ferrite core 26 to secure a gap G and to face each other. The gap between the ferrite core 26 and the metal core 27 is 0.3.
It is about 0.8 mm.

With the above-described structure, the ferrite core having a small high frequency loss is used as a main core, and a gap is provided so as not to saturate, and a small-sized metal core that is opposed to the ferrite core and is difficult to saturate is connected to the primary winding 21 and the secondary winding. Since it is arranged outside the winding wire 22 and the heater winding wire 23, it contributes to a significant reduction in size as compared with a conventional step-up transformer (FIG. 6) consisting of only a ferrite core. That is, in the conventional step-up transformer, the ferrite core portion 64a disposed outside the primary winding 21, the secondary winding 22, and the heater winding 23,
Since 65a has a cross-sectional area almost the same as that of the main ferrite core portion, it largely protrudes outside the primary winding 21, the secondary winding 22, and the heater winding 23.
Since the step-up transformer 20 according to the first embodiment of the present invention is a metal core, its cross-sectional area can be made extremely smaller than that of the ferrite core portion, so that the primary winding 21 and the secondary winding 2
2 and the outside of the heater winding 23 do not largely protrude (see FIG. 2C).

Regarding the high frequency loss, which is a drawback of the metal core under high frequency, an eddy current flows by using a long thin metal plate 27a wound 10 to 40 times as shown in FIG. 3 (a). Since the direction is aligned with the direction across the sheet metal layer formed by winding a number of times, the eddy current can flow only within the cross sectional area of one sheet metal, and the resistance of the cross sectional area of one sheet metal is Due to the large value, almost no eddy current can flow. Therefore, even under a high frequency, the high frequency loss is reduced only by arranging the metal core having such a configuration as described above, and it is possible to obtain a step-up transformer having advantages of both the ferrite core and the metal core. Further, since the ferrite core of the step-up transformer has a rectangular parallelepiped shape, the mutually facing portions of the ferrite core 26 and the metal core 27 are parallel to each other, and the gap G formed therebetween has the same width, so that the coupling coefficient, etc. The design becomes easy. It is also possible to use a U-shaped metal core instead of the U-shaped metal core, but the U-shaped metal core is easier to manufacture than the U-shaped metal core, and the U-shaped metal core is also used. Since the metal core of (1) wraps each winding part from the outside, it also has a secondary effect of mechanically protecting each winding. In the above embodiment, the primary winding 21, the secondary winding 22, and the heater winding 23 surround the rod-shaped ferrite core and are arranged side by side in the axial direction of the core. The present invention is not limited to this, and the three windings centering around the rod-shaped ferrite core are the second winding outside the first winding and the third winding outside the first winding. May be

FIG. 4 is a diagram showing a step-up transformer according to a second embodiment of the present invention. (A) is a front view, (b) is a plan view, (c) is a side view, and (d) is a perspective view. It is a figure. In the figure, reference numeral 40 is a step-up transformer according to the second embodiment.
Reference numeral 1 is a primary winding, 22 is a secondary winding, and 23 is a heater winding, which are the same as those in FIG. That is, the primary winding 21
Has a larger winding cross section and a smaller number of turns than the secondary winding 22. The heater winding 23 has an extremely small number of turns as compared with the secondary winding 22, and is not shown in the drawing. Reference numeral 26 denotes a rectangular parallelepiped-shaped ferrite core, which is surrounded by a primary winding 21, a secondary winding 22, and a heater winding 23, and is arranged side by side in the axial direction of the core. 27 is a metal core which is the same as that of FIG. That is, as shown in FIG. 3 (a), the long thin metal plate 27 a is wound in a square shape about 10 to 40 times, and the inside diameter of the square metal core is
One of the inner diameters (the inner diameter in the left-right direction of the metal core 27 in FIG. 4C) is equal to the primary winding 21, the secondary winding 22, and the heater winding 23.
Is larger than any of the outer diameters, and the inner diameter of the other (the inner diameter of the metal core 27 in the vertical direction in FIG. 4C).
There are 3 of the primary winding 26, the secondary winding 22, and the heater winding 23.
It is formed larger than the lap length of the winding.

The step-up transformer according to the second embodiment of the present invention has a rectangular parallelepiped ferrite core 26.
The protrusion 26 a is formed on a part of the surface facing the metal core 27. The height of the protruding portion 26a is substantially the same as the height of the gap G in FIG. A gap G to be secured between the rectangular parallelepiped-shaped ferrite core 26 and the metal core 27 is formed in the protrusion 2
Since it can be secured by 6a, it is not necessary to use the spacer as in the case of FIG. 2, and the step of assembling the spacer when it is separately prepared can be omitted, so that the step-up transformer can be easily assembled. Further, the projecting portion 26a is designed to be saturated with a slight magnetic flux by selecting a small cross-sectional area in the passage direction of the magnetic path, so that a magnetic short circuit is not formed.

In FIG. 4, one protrusion 26a is formed at the center of the side surface of the rectangular parallelepiped ferrite core 26.
It is also possible to further improve the stability of assembly by forming one at each end of the side surface of the rectangular parallelepiped-shaped ferrite core 26 and contacting the metal core 27 at two points.

FIG. 5 is a diagram showing a step-up transformer according to a third embodiment of the present invention. (A) is a front view, (b) is a plan view, (c) is a side view, and (d) is a perspective view. It is a figure. In the figure, reference numeral 50 is a step-up transformer according to the second embodiment.
Reference numeral 1 is a primary winding, 22 is a secondary winding, and 23 is a heater winding, which are the same as those in FIG. That is, the primary winding 21
Has a larger winding cross section and a smaller number of turns than the secondary winding 22. The heater winding 23 has an extremely small number of turns as compared with the secondary winding 22, and is not shown in the drawing.

Then, in the step-up transformer according to the third embodiment of the present invention, the cylindrical ferrite core 56 is used,
A primary winding 21, a secondary winding 22, and a heater winding 23 surround this periphery, and are arranged side by side in the axial direction of the core. Furthermore, the metal core of the step-up transformer is shown in FIG.
As shown in (b), a plurality of (10 to 40) square-shaped metal thin plates 57a are laminated in the thickness direction using an insulating adhesive. And, of the inner diameter of the square-shaped metal core,
One inner diameter (the inner diameter in the left-right direction of the metal core 57 in FIG. 5C) is the primary winding 21, the secondary winding 22, the heater winding 23.
The inner diameter (the inner diameter in the vertical direction of the metal core 27 in FIG. 5C) of any one of them is larger than the length of the cylindrical ferrite core 56. Such a metal core 57 is inserted into the cylindrical ferrite core 56 as shown in FIG. 5D, and is arranged so as to face the axial end of the cylindrical ferrite core 56 with a gap G therebetween.

With the above-described structure, the ferrite core having a small high frequency loss is used as the main core, and the air gap is provided so as not to be saturated, and the small and hard metal core which is opposed to this is provided with the primary winding 21 and the secondary winding. Since the winding 22, the heater winding 23, and the ferrite core 56 are arranged outside the ferrite core 56, the size of the coil can be greatly reduced as compared with a conventional step-up transformer (FIG. 6) including only the ferrite core 56. That is, the step-up transformer 5 according to the third embodiment
In 0, since it is a metal core, the cross-sectional area can be made extremely smaller than that of the ferrite core portion, and the primary winding 21 and the secondary winding 2
2 and the outside of the heater winding 23 do not largely protrude (see FIG. 2C).

As for the high frequency loss, which is a drawback of the metal core 57 under high frequency, a stack of 10 to 40 metal thin plates 27a is used as shown in FIG. Since the metal thin plate layers formed by stacking the individual metal plates are aligned in the direction crossing, the eddy current can flow only within the cross sectional area of one metal thin plate, and the resistance value of the cross sectional area of one metal thin plate is large. Therefore, almost no eddy current can flow. Therefore, even under a high frequency, the high frequency loss is reduced only by arranging the metal core 57 having such a configuration as described above, and a step-up transformer having the advantages of both the ferrite core and the metal core can be obtained. . Further, since the ferrite core of the step-up transformer has a columnar shape, it is easier to manufacture than the rectangular parallelepiped, and the air gap G through which the magnetic flux passes is defined by the ferrite core 56.
Since the opposing portions of the metal core 57 and the metal core 57 are parallel to each other,
Since the gap G formed between them has the same width, the design of the coupling coefficient and the like becomes easy. Furthermore, a bracket-shaped metal core 5
7 is a ferrite core 56 and each winding 21, 22, 23
It also wraps a part of it from the outside, so it also serves as a mechanical protection for these. Although the square-shaped metal cores 27 and 57 in FIG. 3 are in the best mode from the viewpoint of high-frequency loss and the like, they may not necessarily be metal cores and may be made of a material with low high-frequency loss, such as ferrite. It is needless to say that a square-shaped core may be formed by using the above method and used as shown in FIG. 2, FIG. 4, and FIG.

[0020]

As described above, according to the step-up transformer of the present invention,
Ferrite core with less high frequency loss is used as the main core,
A void is provided to prevent saturation, and a metal core that is small and has a saturation magnetic flux density characteristic higher than that of a ferrite core is used to face it, and it is difficult to flow eddy current by laminating thin metal plates in the direction of eddy current flow. In addition, since the metal core is formed in a square shape, it is easy to manufacture, is small in size, is solid, and has the effect of mechanically protecting the outside of each winding. Further, since the protrusion is formed on a part of the surface of the rectangular parallelepiped-shaped ferrite core that faces the metal core, it is not necessary to separately prepare a spacer and the labor for incorporating the spacer can be omitted, so that the step-up transformer can be easily assembled. . Further, by appropriately selecting the air gap formed between the rod-shaped ferrite core and the metal core, it becomes possible to easily create the coupling coefficient of the step-up transformer to an arbitrary optimum coefficient.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a magnetron drive power source using a step-up transformer, which is a target of the present invention.

FIG. 2 is a diagram showing a step-up transformer according to a first embodiment of the present invention, (a) is a front view, (b) is a plan view, and (c).
Is a side view, and (d) is a perspective view.

FIG. 3 is a diagram illustrating a method for forming a metal core used in the present invention.

FIG. 4 is a diagram showing a step-up transformer according to a second embodiment of the present invention, (a) is a front view, (b) is a plan view, and (c).
Is a side view, and (d) is a perspective view.

FIG. 5 is a diagram showing a step-up transformer according to a third embodiment of the present invention, (a) is a front view, (b) is a plan view, and (c).
Is a side view, and (d) is a perspective view.

FIG. 6 is a diagram showing a conventional ferrite core step-up transformer that is a mainstream transformer.

[Explanation of symbols]

11 Commercial power supply 12 magnetron 122 Anode 121 cathode 13 Rectifier circuit 14 choke coil 15 Filter capacitor 16 inverter 161 Inverter control circuit 17 CT 18 step-up transformer 181 primary winding 182 secondary winding 183 Filament heating winding 19 times voltage half-wave rectifier circuit 191 High Voltage Capacitor 192,193 High voltage diode 20 Step-up transformer according to the first embodiment 21 primary winding 22 Secondary winding 23 heater winding 26 Rectangular parallelepiped ferrite core 26a protrusion 27 Metal core 27a Long metal thin plate 56 cylindrical ferrite core 57 Metal core 57a Bracket-shaped thin metal plate G void

Continued front page    (72) Inventor Makoto Mihara             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (9)

[Claims] 1. A step-up transformer for supplying a drive voltage to a magnetron, wherein a primary winding and a secondary winding surround a rod-shaped ferrite core, respectively. A step-up transformer for driving a magnetron, characterized in that the winding transformer and the secondary winding are fitted and inserted from the outside toward the rod-shaped ferrite core and opposed to the rod-shaped ferrite core with a gap. 2. A step-up transformer for supplying a drive voltage to a magnetron, wherein a primary winding and a secondary winding each surround a rod-shaped ferrite core, the step-up transformer for driving the magnetron, wherein one of the inner diameters of the U-shape Is a letter shape in which is larger than the outer diameter of either of the primary winding and the secondary winding and the inner diameter of the other of the letter shape is larger than the overlapping length of the primary winding and the secondary winding. A magnetron driving device, characterized in that the core is fitted and inserted from the outside of the primary winding and the secondary winding toward the rod-shaped ferrite core and is opposed to the rod-shaped ferrite core with a gap. Step-up transformer. 3. A step-up transformer for supplying a drive voltage to a magnetron, wherein a primary winding and a secondary winding surround a rod-shaped ferrite core and are arranged side by side in the axial direction of the rod-shaped ferrite core. A step-up transformer for use in a metal core formed by winding a long thin metal plate a plurality of times in a square shape, and one inner diameter of the square shape is larger than the outer diameter of either the primary winding or the secondary winding. A rod-shaped ferrite core from the outside of the primary winding and the secondary winding, the metal core being formed larger than the primary winding and the secondary winding so that the inner diameter of the other of the square shape is larger than that of the primary winding and the secondary winding. A step-up transformer for driving a magnetron, wherein the step-up transformer for driving a magnetron is arranged so as to be inserted into the core and to face the rod-shaped ferrite core with a gap. 4. The step-up transformer for driving a magnetron according to claim 1, wherein the rod-shaped ferrite core has a rectangular parallelepiped shape. 5. A protrusion is formed on a part of a surface of the rectangular parallelepiped-shaped ferrite core facing the metal core, and the protrusion is brought into contact with the metal core. Step up transformer for driving magnetron. 6. A step-up transformer for supplying a drive voltage to a magnetron, wherein a primary winding and a secondary winding each surround a rod-shaped ferrite core, wherein the step-up transformer for driving the magnetron has one of a square bore Is a rod-shaped ferrite core formed by forming the rod-shaped ferrite core having an outer diameter larger than the outer diameter of either the primary winding or the secondary winding and a second inner diameter larger than the length of the rod-shaped ferrite core. A magnetron driving step-up transformer, characterized in that it is inserted together with the winding and is arranged to face each other with a gap between the axial end of the rod-shaped ferrite core and the metal core. 7. A step-up transformer for supplying a driving voltage to a magnetron, wherein a primary winding and a secondary winding each surround a rod-shaped ferrite core. A plurality of metal cores stacked in the same direction, and one inner diameter of the square shape is larger than the outer diameter of either the primary winding or the secondary winding, and the other inner diameter of the square shape is The rod-shaped ferrite core is fitted together with the winding into a metal core formed to have a length larger than that of the rod-shaped ferrite core, and the metal core and the axial end of the rod-shaped ferrite core are opposed to each other with a gap therebetween. A step-up transformer for driving a magnetron, which is characterized in that 8. The step-up transformer for driving a magnetron according to claim 6, wherein the rod-shaped ferrite core has a cylindrical shape. 9. The step-up transformer for driving a magnetron according to claim 1, wherein the magnetic resistance is changed by the rod-shaped ferrite core and an air gap between the cores.