JP2000068133A - High voltage transformer for microwave oven - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the high voltage transformer of a microwave oven for substantially reducing radiation noise generated from the microwave oven without adding a separate member. SOLUTION: This high voltage transformer is provided with a core 100 for inducing a magnetic field flux generated by a current, a primary coil 300 wound to the core 100 for generating the magnetic field flux, a secondary side first coil 310 wound to the core 100 for generating a first output voltage by the magnetic field flux inside the core generated by the primary coil 300, a shunt core 110 interposed between the primary coil 300 and the secondary side coil 310 for shunting the magnetic field flux induced in the core 100, and a secondary side second coil 320 interposed between the shunt core 110 and the primary core 100 for generating a second output voltage by the magnetic field flux inside the core 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transformer, and more particularly, to a high-voltage transformer used for a microwave oven.

[0002]

2. Description of the Related Art Generally, a transformer is a device for supplying boosted or depressurized power by an electromagnetic induction action, and is usually supplied with a normal AC voltage from one circuit through a primary winding. The input voltage is boosted or decompressed and output to the other circuit.
Also, since a microwave oven requires a high voltage to drive a magnetron, a high voltage transformer (High Voltage Transformer: 'HVT') is indispensably provided.

Such a high-voltage transformer for a microwave oven has one type.
A common AC power supply of about 10 V / 220 V is input through a primary coil, and the voltage is raised to a high voltage of about 4000 V through a winding ratio of a secondary coil and a half-wave voltage multiplier circuit, and output to a magnetron. The secondary coil is 2
Secondary first coil and secondary second coil (or 1-2)
(Secondary coil and second-secondary coil). The magnetron is driven by a high voltage output from the high-voltage transformer and generates a microwave having a predetermined frequency. The microwaves thus generated vibrate water molecules contained in the food, thereby heating / cooking the food.

FIG. 1 is a perspective view showing a general microwave oven. 1, reference numeral 20 denotes a main body, 21 denotes a door, 22 denotes a cooking chamber, 23 denotes an apparatus room, 24 denotes a rotating tray,
25 is a control panel, 26 is a lamp, 27 is a fan motor, 28 is an air guide, HVT is a high-voltage transformer, HVC
Is a high voltage capacitor, HVD is a high voltage diode, and M
GT is a magnetron.

According to this, the main body 20 has a cooking chamber 22 and an apparatus chamber 23 partitioned on the left and right sides. A control panel 25 for operating a microwave oven and displaying the state of the microwave oven is provided on the front of the device room 23. Inside the equipment room 23, a magnetron MGT, a high-voltage transformer HVT, a high-voltage diode HV
D, a high-voltage capacitor HVC, a lamp 26, a fan motor 27, and an air guide 28 are provided. The lamp 26 illuminates the inside of the cooking room 22, and the fan motor 27
Blow air into the interior. The air guide 28 guides the air blown by the fan motor 27 into the cooking chamber 22.

The front of the cooking chamber 22 is opened and closed by a door 21 formed on one side of the main body 20. A rotating tray 24 on which food to be cooked is placed is provided inside the cooking chamber 22. The rotating tray 24 is rotated by a drive motor (not shown) on the bottom surface of the cooking chamber 22, and makes microwaves emitted into the cooking chamber 22 incident on food placed on the upper stage.

FIG. 2 is a perspective view of a high voltage transformer of a microwave oven according to the prior art, FIG. 3 is a longitudinal sectional view of the high voltage transformer, and FIG. 4 is a secondary coil and a shunt core of the high voltage transformer. FIG. 5 is a detailed perspective view of a high-voltage transformer, and FIG. 6 is a circuit diagram in which a conventional high-voltage transformer is connected. Here, reference numeral 10 is a core, and 11 is a shunt core (sh
unt core), 30 is a primary coil, 31 is a secondary first coil, and 32 is a secondary second coil. Also, 10a shown in FIG. 5 is an outer leg of the EI core having three legs, and 10b is a center leg. Also,
In FIG. 6, HVT is a high voltage transformer, HVC is a high voltage capacitor, HVD is a high voltage diode, MGT is a magnetron, and 40 is a filament inside the magnetron MGT.

The primary coil 30 and the secondary second coil 3
2, a shunt core 11 is interposed. The shunt core 11 converts a part of the flux from the secondary coils 31 and 32. In addition, the shunt core 11 is configured such that when the magnetron MGT is in use or in operation, the shunt operation by the shunt core 11 limits the current available in the secondary coils 31 and 32, and Overdrive of magnetron MGT (ov
erdriving).

The structure and arrangement of the high-voltage transformer HVT will be described.
Core 10 having three legs laminated on an "I core"
However, as shown in FIG. 5, only the shape of the 'E' core is shown, and the 'I' core is connected to the opening of the 'E' in a subsequent assembling process. Also, virtual lines a,
b indicates the direction of the shunted magnetic flux and the direction of the normal shunted magnetic flux, respectively. The three legs are composed of one central leg 10b and two outer legs 10a, and the primary coil 30 is connected to the central leg 10b.
And the secondary side coils 31 and 32 are wound.

The main operation of the conventional high voltage transformer of the microwave oven configured as described above is as follows. The high voltage transformer HVT of the microwave oven is
A normal AC power supply AC of about / 220 V is input. In order to prevent the non-oscillation phenomenon of the magnetron MGT, the secondary side second coil 32 generates an AC power supply of usually about 3.3 V, and supplies the AC power to the filament 40 of the magnetron MGT to preheat the filament 40. at the same time,
The secondary first coil 31 generates a high voltage of about 2000 V depending on the winding ratio with the primary coil 30. The high voltage generated in this way is passed through a half-wave doubler circuit composed of a high voltage capacitor HVC and a high voltage diode HVD.
After being boosted to a DC voltage of about 000 V, the DC voltage is supplied to the filament 40 of the magnetron MGT.

Actually, in the positive half cycle, the current flows through the secondary first coil 31, the high-voltage capacitor HVC, and the high-voltage diode HV.
D and ground, the high-voltage capacitor HVC is charged with a voltage of about 2000 V, and the current flows in the negative half cycle of the filament 4 of the magnetron MGT.
0, the current flows to the high voltage capacitor HVC, the secondary side first coil 31, and the ground, and a half-wave DC voltage of about -4000V is applied to the filament 40 of the magnetron MGT. Accordingly, the magnetron MGT is driven by the high voltage (-4000 V) supplied as described above, and generates a microwave of approximately 2450 MHz, as is known. Thereafter, the microwave is introduced into the cooking chamber 22 to heat / cook the food placed therein.

In the state where the food is heated / cooked as described above, various electric components of the microwave oven, in particular, the magnetron MGT or the high-voltage transformer HVT provided in the device room 23.
For example, noise causing electromagnetic interference is emitted. Here, an electromagnetic interference (hereinafter referred to as "EMI") is a signal or noise that is actually generated for a desired signal and obstructs the use effect of the original signal. The types of noise include radiated noise transmitted to space and conducted noise transmitted to electric wires. It has been reported that if such EMI noise is radiated or transmitted to the outside, it adversely affects other electric / electronic devices, and if severe, it is harmful to the human body as well known. Therefore,
In various countries, various regulations for suppressing such EMI noise below a specified value are implemented, and various countermeasures are taken. In particular, in a microwave oven, radiation noise in a 30 MHz to 1000 MHz band is the biggest problem, and the measured values of such radiation noise are shown in FIGS. 7 and 8.

Here, FIGS. 7 and 8 show noises in a state in which a secondary second coil is wound between a secondary first coil and a primary coil in a high-voltage transformer of a microwave oven according to the prior art. It is measurement data showing characteristics. Here, FIG. 7 shows a noise receiving antenna (not shown) located at a predetermined distance from the high voltage transformer HVT in order to measure radiated noise.
8 is experimental data obtained by providing the antenna in the horizontal direction, and FIG. 8 is experimental data obtained by providing an antenna for noise reception (not shown) in the vertical direction. The vertical axis of each drawing is the magnitude of radiation noise expressed in decibels (dB).
The horizontal axis is the frequency band. The line b shown is noise accompanying the frequency in the 30 MHz to 1000 MHz band radiated from the microwave oven, and the line a represents a specified value for limiting the effective limit of the EMI noise. As shown in each drawing, it can be seen that a large amount of noise is generated in the conventional microwave oven, and the noise exceeds the specified value a in some sections.

[0014] On the other hand, in order to prevent such noise, a conventional microwave high voltage transformer is not illustrated in the drawings, but usually, a line extending from the high voltage transformer HVT is provided with noise such as ring tight. The EMI noise is prevented by covering the shielding member or connecting an expensive EMI filter composed of another circuit to the circuit of the microwave oven.

As an example, Korean Patent Publication No. 91-6
No. 366 (filed on Sep. 1, 1989) discloses a "noise cut-off transformer". According to this, a secondary winding is arranged at the center of the iron core, and one above and below this secondary winding.
By disposing the secondary winding and sealing the primary and secondary windings with a shielding metal layer, transmission of conduction noise and impact voltage that intrudes from or is transmitted to the outside along the power supply side wire is prevented. Become like

As another example, Korean Utility Model Publication No. 9
No. 8-039017, "Transformer with ferrite bead (noise filter)" (Jan. 1996
(Filed February 18, 2008). According to this, the ferrite bead similar to the ringtite described above, that is, the noise filter is sandwiched between the lead wires of the transformer, thereby reducing the installation space of the noise filter in the printed circuit board and facilitating the design. it can.

However, the conventional high-voltage transformer for a microwave oven as described above is configured by attaching another shielding member to the high-voltage transformer to reduce, in particular, radiation noise among various noises, or by using another circuit in the microwave oven. In addition, there is a problem that the cost of the microwave oven is increased by connecting the expensive EMI filter obtained, and there is another problem that the manufacturing process is complicated and the productivity is reduced.

[0018]

SUMMARY OF THE INVENTION Accordingly, the present invention has been devised to solve the above-mentioned problems of the prior art, and the first object of the present invention is to provide a method without adding another member. It is an object of the present invention to provide a high-voltage transformer for a microwave oven that significantly reduces radiation noise generated from the microwave oven.

A second object of the present invention is to reduce the radiation noise without using another shielding member or an expensive noise filter, thereby reducing the manufacturing cost and improving the productivity. It is to provide a manufacturing method.

[0020]

According to the present invention, there is provided a high-voltage transformer for a microwave oven according to the present invention for achieving the above object. And a secondary-side second coil is arranged in the second position. Here, the secondary second coil is disposed between the primary coil and the secondary first coil. It is preferable that a shunt core is interposed between the secondary-side second coil and the secondary-side first coil. Further, the secondary side second coil is more preferably a coil for preheating the filament of the magnetron.

A high-voltage transformer for a microwave oven according to another aspect of the present invention includes a core for inducing a magnetic field flux generated by an electric current, a primary coil wound on the core to generate a magnetic field flux, A secondary-side first coil that is wound around a core and generates a first output voltage by a magnetic flux in the core generated by the first coil; and between the first coil and the secondary-side first coil. A shunt core interposed in the core and shunting the magnetic flux induced by the core; and a second shunt core wound adjacent to the primary coil and wound around the core, the second magnetic flux being generated by the magnetic flux inside the core.
A secondary side second coil for generating an output voltage is included. here,
The secondary second coil is interposed between the shunt coil and the primary coil. Preferably, the secondary side second coil is a coil for preheating a magnetron filament. More preferably, the core includes a central leg and two outer legs, and the primary coil and the two secondary coils are wound around the central leg.

The method of manufacturing a high-voltage transformer for a microwave oven according to the present invention is characterized in that a core for inducing a magnetic flux generated by an electric current, and a primary coil wound on the core to generate a magnetic flux. A secondary first coil wound on the core and generating a first output voltage by a magnetic flux inside the core generated by the primary coil; the primary coil and the secondary first coil; A high-voltage transformer for a microwave oven, comprising: a shunt core interposed between the core and a shunt core for shunting the magnetic flux induced by the core; and a secondary-side second coil for generating a second output voltage by the magnetic flux inside the core. And manufacturing the secondary side second coil so as to be interposed between the shunt core and the primary coil.

The method for assembling the high voltage transformer for a microwave oven according to the present invention is characterized in that a core having a central leg and two outer legs, and a high voltage transformer for a microwave oven having a shunt core interposed between the cores. In the method of assembling,
A first step of winding a secondary first coil from the inside of the central leg, a second step of coupling the shunt core at a predetermined distance from the secondary first coil, and A third step of winding a secondary second coil adjacent to the shunt core; and a secondary secondary coil on the central leg.
A fourth winding of the primary coil adjacent to the coil;
Stages.

Therefore, in order to prevent EMI noise, particularly radiation noise in the 30 MHz to 1000 MHz band, which is the most problematic in the microwave oven, the winding position of each coil of the high voltage transformer for the microwave oven is changed, that is, 2. By arranging the secondary side second coil at a position separated from the secondary side first coil, since a separate shielding member or an expensive EMI filter is not adopted, radiation noise can be suppressed without increasing the manufacturing cost, Productivity can be improved.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a high-voltage transformer for a microwave oven according to the present invention will be described below with reference to the accompanying drawings. 9 is a perspective view of a high-voltage transformer of a microwave oven according to an embodiment of the present invention, FIG. 10 is a longitudinal sectional view of the high-voltage transformer, and FIG. 11 is a circuit diagram to which the high-voltage transformer is connected.
Here, reference numeral 100 denotes a core, 110 denotes a shunt core, 3
00 is a primary coil, 310 is a secondary first coil, 320
Is a secondary second coil. HVT is a high voltage transformer, HVC is a high voltage capacitor, HVD is a high voltage diode, MGT is a magnetron, and 40 is a filament inside the magnetron MGT.

As shown in FIGS. 9 to 11, the high-voltage transformer of the microwave oven according to the present invention includes a core 100 for inducing a magnetic flux, and a shunt for the magnetic flux to prevent overdrive of the magnetron MGT. One side is connected to a path core 110, a first coil 300 wound around the core 100 to generate a magnetic flux, and a high voltage capacitor HVC, and a secondary side coil that generates a first output voltage associated with the magnetic flux inside the core 100. A second side coil wound between the first coil 310 and the shunt core 110 and the first coil to generate a second output voltage associated with a magnetic flux inside the core 100 to preheat the magnetron MGT 320.

First, the core 100 is made of 'E-
An I ′ structure, which includes one central leg 111 and two outer legs 112 and 113, and has a primary coil 300 and a secondary coil 310,
20 is wound. The core 100 is made of a plurality of planar soft ferrites, and the primary coil 300 and the secondary coils 310 and 320 are made of insulated copper wires. The secondary first coil 310 is connected in series with the high voltage capacitor HVC, and is thereafter branched and connected to the high voltage diode HVD and the magnetron MGT. The primary coil 3
00 is connected to the input side of the AC power supply AC, and the secondary second coil 320 is connected to the filament 40 of the magnetron MGT. At this time, the secondary side second coil 3
20 is preferably interposed between the shunt core 110 and the primary coil 300.

Hereinafter, the main operation of the shunt core high-voltage transformer of the microwave oven according to the embodiment of the present invention will be described as follows. A shunt core 110 is interposed between the secondary first coil 310 and the secondary second coil 320. The shunt core 110 includes the secondary coils 310, 3
From 20 a portion of the flux is converted and operates as described in the prior art. In addition, the high-voltage transformer HVT of the microwave oven according to the present invention is provided with a common AC power supply A of about 110/220 V
C is input. In order to prevent the non-oscillation phenomenon of the magnetron MGT in the secondary-side second coil 320, a trade 3.3V is used.
AC power is generated, and this is supplied to the magnetron MGT.
And the filament 40 is preheated.

The secondary first coil 310 generates a high voltage of about 2000 V depending on the winding ratio with the primary coil 300. The high voltage thus generated is boosted to a DC voltage of about 4000 V through a half-wave voltage doubler circuit composed of a high-voltage capacitor HVC and a high-voltage diode HVD, and then supplied to the filament 40 of the magnetron MGT. Actually, in the positive half cycle, the current flows through the secondary first coil 310, the high-voltage capacitor HVC, and the high-voltage diode H
The high voltage capacitor HVC is charged with a voltage of about 2000 V by flowing to the VD and the ground, and the current flows to the filament 40 of the magnetron MGT, the high voltage capacitor HVC, the secondary first coil 310 and the ground in a negative half cycle. Thus, a half-wave DC voltage of about -4000 V is applied to the filament 40 of the magnetron MGT. Accordingly, the magnetron MGT is driven by the high voltage supplied as described above to generate a microwave of about 2450 MHz, and this microwave is thereafter transmitted to the cooking chamber 22 (FIG. 1).
) To heat / cook the food placed therein.

In the state where the food is heated / cooked as described above, various electric components of the microwave oven, in particular, the magnetron MGT or the high-voltage transformer HVT provided in the device room 23.
At this time, the configuration of the present invention, that is, the configuration in which the secondary side second coil 320 is interposed between the shunt core 110 and the primary coil 300 (FIG. 10) significantly reduces radiation noise. Such secondary side second coil 320
The noise characteristics associated with the winding position can be proved through repeated experiments and the results of experimental data supplemented through many trials and errors, and the measured data are shown in FIGS. 12 and 13.

FIG. 12 and FIG. 13 show the secondary secondary side between the shunt core and the primary coil in the high-voltage transformer according to the present invention.
9 is measurement data showing noise characteristics when a coil is wound. Here, FIG. 12 shows experimental data obtained by providing a noise receiving antenna (not shown) at a predetermined distance from the high-voltage transformer HVT in a horizontal direction in order to measure radiated noise, and FIG. This is experimental data obtained by providing a noise receiving antenna (not shown) in the vertical direction. The vertical axis of each drawing is the magnitude of radiation noise expressed in decibels (dB), and the horizontal axis is frequency. The line b shown is noise accompanying the frequency in the 30 MHz to 1000 MHz band radiated from the microwave oven, and the line a represents a specified value for limiting the effective limit of the EMI noise. It can be confirmed that the high-voltage transformer of the microwave oven according to the present invention can obtain very good noise characteristics as shown in FIGS. Also,
FIGS. 12 and 13 of the present invention are shown in FIG.
8 and FIG. 8, it can be directly confirmed that the result of the noise characteristic according to the present invention is very stable, and that the EMI noise specified value (a) does not exceed the entire section. Can be seen more clearly.

On the other hand, a core 100 having a central leg 111 and two outer legs 112 and 113 according to the present invention.
The method of assembling the high voltage transformer of the microwave oven having the shunt core 110 proceeds in the following order. First, the secondary first coil 310 is wound from inside the central leg 111 of the core 100, and the shunt core 110 is coupled at a predetermined distance from the secondary first coil 310. The secondary second coil 320 is wound on the center leg 111 of the core 100 so as to be adjacent to the shunt core 110, and then adjacent to the secondary second coil 320 on the center leg 111 of the core 100. So that the primary coil 300
Are sequentially wound.

[0033]

As described above, according to the high-voltage transformer for a microwave oven according to the present invention, EMI noise, particularly 30 MHz to 1000 MHz, which is the largest problem in a microwave oven.
In order to prevent radiation noise in the MHz band, the winding position of each coil of the high-voltage transformer for a microwave oven is changed, that is, the secondary-side second coil is arranged at a position separated from the secondary-side first coil. Accordingly, since no separate shielding member or expensive EMI filter is employed, radiation noise can be suppressed without increasing production costs, and productivity can be improved.

While the present invention has been shown and described with respect to certain preferred embodiments, the present invention is not limited to those embodiments and does not depart from the spirit of the invention as set forth in the appended claims. It goes without saying that various modifications can be made by anyone having ordinary knowledge in the field to which the present invention pertains, and such modifications fall within the scope of the appended claims.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a general microwave oven.

FIG. 2 is a perspective view of a conventional microwave high voltage transformer.

FIG. 3 is a longitudinal sectional view of a conventional high-voltage transformer.

FIG. 4 shows a secondary side secondary of a high-voltage transformer according to the prior art.
It is a perspective view of a coil and a shunt core.

FIG. 5 is a detailed perspective view of a conventional high-voltage transformer.

FIG. 6 is a circuit diagram in which a high-voltage transformer according to the related art is connected.

FIG. 7 shows a high voltage transformer according to the prior art and a secondary side first.
9 is measurement data showing noise characteristics when a secondary-side second coil is wound below the coil.

FIG. 8 is a view similar to FIG. 7;

FIG. 9 is a perspective view of a high-voltage transformer of the microwave oven according to the embodiment of the present invention.

FIG. 10 is a longitudinal sectional view of the high-voltage transformer according to the embodiment of the present invention.

FIG. 11 is a circuit diagram to which a high-voltage transformer according to the embodiment of the present invention is connected.

FIG. 12 is measurement data showing noise characteristics when a secondary-side second coil is wound below a shunt core in the high-voltage transformer according to the present invention.

FIG. 13 is a view similar to FIG.

[Explanation of symbols]

 100 core 110 shunt core 111 central leg 112, 113 external leg 300 primary coil 310, 320 secondary coil 40 filament HVT high voltage transformer HVC high voltage capacitor HVDD high voltage diode MGT magnetron

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 31/00 Q

Claims (10)

[Claims] 1. A high-voltage transformer for a microwave oven, wherein a secondary-side second coil is arranged on a primary coil side divided from a secondary-side first coil. 2. The high-voltage transformer of a microwave oven according to claim 1, wherein the secondary-side second coil is disposed between the primary coil and the secondary-side first coil. 3. The secondary side second coil and the secondary side first coil.
The high voltage transformer of a microwave oven according to claim 1, wherein a shunt core is interposed between the coil and the coil. 4. The high-voltage transformer according to claim 1, wherein the secondary second coil is a coil for preheating a magnetron filament. 5. A core for inducing a magnetic flux generated by a current, a primary coil wound on the core to generate a magnetic flux, and a core wound on the core and generated by the primary coil. A secondary first coil for generating a first output voltage by an internal magnetic flux, and a magnetic flux interposed between the primary coil and the secondary first coil and shunting the magnetic flux induced by the core. A shunt core to be wound around the core so as to be adjacent to the first coil;
A high-voltage transformer for a microwave oven, comprising: a secondary-side second coil for generating a second output voltage by a magnetic flux in the core. 6. The high voltage transformer according to claim 5, wherein the secondary second coil is interposed between the shunt core and the primary coil. 7. The high-voltage transformer according to claim 5, wherein the second secondary coil is a coil for preheating a magnetron filament. 8. The core according to claim 5, wherein the core includes a center leg and two outer legs, and the primary coil and the two secondary coils are wound on the center leg. High pressure transformer for microwave oven. 9. A core for inducing a magnetic flux generated by a current, a primary coil wound on the core to generate a magnetic flux, and a core wound on the core and generated by the first coil. A secondary first coil for generating a first output voltage by an internal magnetic flux, and a magnetic flux interposed between the primary coil and the secondary first coil and shunting the magnetic flux induced by the core. A method of manufacturing a high-voltage transformer for a microwave oven, comprising: a shunt core to be generated; and a secondary-side second coil that generates a second output voltage by a magnetic flux inside the core. A method of manufacturing a high voltage transformer for a microwave oven, wherein the high voltage transformer is manufactured so as to be interposed between a shunt core and the primary coil. 10. A method of assembling a high-voltage transformer for a microwave oven comprising a core having a central leg and two outer legs, and a shunt core interposed between the cores, wherein A first step of winding one coil, a second step of coupling the shunt core at a predetermined distance from the secondary first coil, and a second step of adjoining the shunt core on the central leg. A high-voltage transformer for a microwave oven, comprising: a third step of winding a secondary coil on the secondary side; and a fourth step of winding a primary coil on the central leg so as to be adjacent to the secondary second coil. Assembly method.