JP2000357617A - Power supply transformer for magnetron drive - Google Patents

Abstract

(57) [Problem] To improve the temperature performance and cooling performance of a transformer of a power supply for driving a magnetron, and to improve the dielectric strength of a primary winding and a secondary winding. SOLUTION: In a transformer having a concentric winding structure in which a large current flows and a primary winding 2 which generates a large amount of heat is disposed on the outside and a secondary winding 3 is disposed on the inside, between the secondary winding 3 and the primary winding 2 By providing the space insulating layer 12 to the outside, the degree of exposure of the primary winding to the outside air is increased, cooling is facilitated, and insulation reinforcement is achieved by the space insulating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating apparatus for performing dielectric heating using a magnetron, such as a microwave oven, and more particularly to a high-frequency high-voltage power supply from a commercial power supply. It is suitable for a transformer of a magnetron drive power supply provided with an inverter for driving the motor.

[0002]

2. Description of the Related Art Conventionally, as this type of inverter power supply, a single-ended single-pole type voltage resonance inverter as disclosed in Japanese Patent Application Laid-Open No. 5-121159 has been disclosed. Inverter power supplies represented by these devices convert high-frequency power from an inverter into high voltage using a step-up transformer, and generate a high-voltage DC voltage suitable for driving a magnetron using a rectifier circuit or a high-voltage circuit using multiplied voltage rectification. I have. By doing so, it is possible to reduce the size of the step-up transformer by increasing the frequency of the power by the inverter, and
By configuring the circuit on a single substrate, a more compact and lightweight magnetron drive power supply (inverter power supply) can be configured.

FIG. 6 is an external view of a conventional step-up transformer. Reference numeral 1 denotes a bobbin made of resin, which is used to heat a primary winding 2, a secondary winding 3, a contact prevention winding 4 for preventing contact between primary and secondary, and a magnetron cathode. The heater winding 5 for supplying the electric power is wound. Bobbin 2
The portion around which the next winding 3 is wound is formed by a partition 6 into four winding grooves. First 2 in the first winding groove
When the next winding is started and wound by a predetermined amount, it is wound over the next second winding groove. When a predetermined amount of winding is performed also on the winding groove, it then passes over the third winding groove. By winding this up to the fourth winding groove, 2
By making the next winding a divided winding configuration, even if it is impossible to wind in alignment in each winding groove and partial winding is generated, each is divided and insulated with resin. Therefore, the configuration is such that the danger of causing dielectric breakdown between the mutual windings can be eliminated. In addition, since the winding is divided, heat generated by copper loss in the secondary winding is distributed to each winding groove and radiated, so that the heat radiation characteristics are excellent and there is an advantage in a temperature portion. Reference numeral 7 denotes a core made of ferrite or the like, which functions as a magnetic circuit for transmitting magnetic energy generated by the current of the primary winding 2 to the secondary winding. A core cover 8 made of resin is mounted to ensure insulation between the core 7 and each winding. The above is the configuration of the conventional step-up transformer.

[0004]

However, such a step-up transformer has a structure in which the primary winding and the secondary winding are arranged in parallel. To increase the exposed area for cooling by increasing the winding width of the primary winding 2, or to increase the winding width or increase the number of divisions for the secondary winding A method of increasing the exposed area to improve the heat dissipation can be considered.

Here, when used in a microwave oven or the like,
Increasing the output is an indispensable factor for speed heating, but in order to achieve that, the energy transmitted by the transformer also increases, it is necessary to suppress the temperature rise and avoid the deterioration of insulation performance . For this reason, there has been a problem that the width of the transformer must be increased to increase the size in order to improve the heat radiation property and lower the temperature.

[0006]

In order to solve the above-mentioned problems, the present invention has a primary winding and a secondary winding concentrically, a primary winding on the outside, and a secondary winding on the inside. The arrangement is such that a predetermined space is provided between the primary winding and the secondary winding.

[0007]

According to the present invention, the secondary winding can be arranged inside the bobbin of the primary winding, and the space factor can be significantly reduced. In addition, an air layer is provided between the primary and secondary windings to strengthen the insulation between the primary and secondary windings, making it difficult for unsafe modes such as PS touching to occur. Since the large primary current of several tens of amperes is exposed to the external atmosphere, the cooling performance is significantly improved, and high output of the microwave oven is realized using a compact step-up transformer. be able to.

[0008]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view from the side of a transformer of a power supply for driving a magnetron according to an embodiment of the present invention. The outer bobbin 10 is wound around the primary winding 2 and the inner bobbin 11 is wound with the secondary winding 3. It is configured. In this fitted state, the outer turbobin 10 is a component for insulating the primary winding 2 and the secondary winding 3. Further, the secondary winding 3 is not wound to the full bobbin winding frame, so that the space insulating layer 12 is formed.
Further, a gap 13 is required to optimize the inverter operation.
The two sets of cores 7 are inserted into the inner diameter of the inner bobbin 11 with the above gap.

With this configuration, the area of the primary winding 2 where a large amount of high-frequency current flows and generates a large amount of heat is exposed to the outside atmosphere, and the wind of the cooling fan as the cooling means generates heat from the entire surface. The cooling effect is remarkably improved. On the other hand, since the secondary winding 3 is a step-up type transformer, the number of windings is larger than that of the primary winding 2;
Since it does not generate heat as much as the next winding, it is stored in a closed state inside the outer turbo bin 10 and there is no large temperature rise even if cooling air does not hit. In addition, the space insulating layer 12 exerts a heat insulating effect, and it is possible to avoid that the heat on the primary side interferes with the secondary side and raises the temperature abnormally.

Further, regarding the most deadly part of the step-up transformer of the microwave oven, which generates a high voltage on the secondary side, that is, a short circuit between PS due to insulation breakdown, the outer turbo bin 1
Since the resin has a double insulation structure of the resin thickness of the bottom surface of the winding surface and the space insulation layer 12, the reliability is greatly improved. Incidentally, the litz wire is used for the primary winding 2 to prevent an increase in copper loss peculiar to a high frequency such as a skin effect and a proximity effect due to a high frequency large current. As the secondary winding, it is common to use a single wire or a simple litz wire winding using several wires.

As a step-up transformer for a microwave oven, a magnetic leakage type transformer having a gap in a core is used.
The reason will be described below.

First, the operation of a magnetron driving power supply using an inverter will be briefly described with reference to FIG. The commercial power supply 14 is converted to a unidirectional power supply by a full-wave rectification stack 15 (unidirectional power supply unit). The rectifying filter unit 26 for rectifying and smoothing the unidirectional power supply includes the choke coil 16 and the smoothing capacitor 17. The DC voltage of the rectifying filter unit 26 is converted into high frequency power by the inverter unit 27.

When the semiconductor switching element 18 is turned on, a DC voltage is applied to the primary side of the step-up transformer 9. During this time, a current flows through the leakage inductance and the exciting inductance, and energy is accumulated. As the semiconductor switching element 18, an IGBT which is an insulated gate bipolar transistor is generally used.

After a certain time, the semiconductor switching element 18
Is turned off, the inductance component and the resonance capacitor 24
Resonance occurs in the tank circuit, and a resonance voltage is generated on the primary side of the transformer. An AC voltage is applied to the step-up transformer 9 by the ON / OFF cycle. Here, the switching control circuit 22 sends on / off signals to the semiconductor switching element 18.

By increasing the speed of the ON / OFF cycle, a high-frequency AC voltage is applied to the primary side of the step-up transformer 9. Thus, commercial power is converted to high frequency power. And a capacitor 19 and diodes 20, 2
The high-voltage circuit 28 composed of a half-wave voltage doubler composed of
Converts the high-frequency high-voltage on the secondary side into a high-voltage high-voltage DC
Applied to the magnetron 22. The operation of the half-wave voltage is well known, and the detailed operation principle is omitted.
Then, the temperature of the cathode of the magnetron 22 becomes high due to the electric power supplied from the heater winding 5, and electrons are excited to generate microwaves.

Here, the operation of the inverter is changed by providing a leakage magnetic flux in the gap 13 of the core. FIG.
FIG. 5 is a diagram showing waveforms of a collector-emitter voltage Vce and a current Ic of the semiconductor switching element 18. (A)
Is a state where the gap 13 is provided in the core and the leakage inductance is large. When a current is flowing to the negative side of Ic, it is a period in which a current is flowing to a flywheel diode (FWD) attached to the IGBT.
This is a period during which a current flows through the BT. Here, IGBT
Is on, the current increases in the form of a ramp wave. When the current is turned off for a certain period of time, a resonance mode is entered. When the resonance voltage swings negatively, a current flows through the FWD again. Meanwhile IGB
When T is turned on, zero volt switching can be realized, and the IGBT does not take too much responsibility.

FIG. 2B shows a state in which the leakage inductance is small. At this time, the excitation of the resonance circuit is damping,
Excitation shifts to a rising mode as shown by a dotted line in the figure without Vce being equal to or lower than 0 voltage. At this time, IG
When the BT is turned on, the IGBT is
Since the IGBT is turned on, hard switching occurs, an excessive current flows, and the responsibility of the IGBT increases, possibly leading to thermal destruction.

If the leakage inductance is not appropriate from such a point of view, a phenomenon leading to such hard switching occurs. In the present invention, since the secondary winding is wound below the primary winding, the direct transmission of magnetic energy between the windings is high and the coupling is tightly coupled, and the state shown in FIG.
However, by providing a space insulating layer between the primary winding and the secondary winding and physically separating the windings, the state approaches the loosely coupled state, and the state shown in FIG. The IGBT will not be overcharged.

Embodiment 2 Hereinafter, another embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a transformer of a power supply for driving a magnetron of the present invention. The inner bobbin 11 around which the secondary winding is wound is divided into four parts. If one end starts to be wound, the other end means the end.
In this case, since each is divided and insulated with a resin, the risk of causing dielectric breakdown between the mutual windings can be eliminated. In addition, since the coil is divided and wound, heat generated due to copper loss in the secondary winding is distributed to each winding groove to radiate heat, so that the heat radiation characteristics are excellent and there is an advantage in a temperature portion.

Further, since the space insulating layer 12 is provided, it is not possible to wind the wires in each of the winding grooves in an aligned manner. Because of the insulation, it is possible to eliminate the danger of causing dielectric breakdown between the mutual windings. Of course, the space insulating layer 12 exerts a heat insulating effect, and the heat of the primary side is reduced.
It is possible to prevent the temperature from being abnormally increased by interfering with the secondary side. Further, regarding the most deadly part of the step-up transformer of the microwave oven, which generates a high voltage on the secondary side, that is, a short circuit between PS due to insulation breakdown, the outer turbo bin 1
Since the resin has a double insulation structure of the resin thickness of the bottom surface of the winding surface and the space insulation layer 12, the reliability is greatly improved.

Embodiment 3 Another embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows a structure in which an outer turbobin 10 wound with a primary winding and an inner bobbin 11 wound with a secondary winding are formed of respective pieces, and the pieces are slid and inserted into the inner diameter of the outer turbobin. Reference numeral 25 denotes an insertion stopper, which can temporarily fix the inner bobbin 11 and the outer turbobin 10 at the stage of insertion, so that the workability such as the removal of the bobbin when the core 7 is inserted later does not occur. By doing so, each part can be separately manufactured and docked, the winding of the inner bobbin and the winding of the outer turbobin can be processed simultaneously, the manufacturing time can be reduced, and the mating insertion can be performed. Thus, the relative positional relationship between the primary winding and the secondary winding can be accurately determined with a simple configuration, and variations in the electrical characteristics of the transformer are reduced.

[0022]

As described above, according to the first and second aspects of the present invention, the primary winding and the secondary winding are concentrically provided, and the primary winding and the secondary winding are provided on the outside.
The primary winding and the secondary winding on the inside have a predetermined space between the primary winding and the secondary winding, so that a large current flows and the primary winding with large heat generation can be widely used in the atmosphere. It can be exposed to improve the temperature performance (cooling performance), and the space (air layer) provided between the primary and secondary windings generates heat on the primary side on the secondary side. To increase the temperature performance of the secondary winding without increasing the winding temperature.

The electrical insulation between the primary winding and the secondary winding can be further enhanced by providing an air layer, and a further improvement in safety can be achieved.

According to the third aspect of the present invention, the primary winding bobbin slides into the inner diameter of the secondary winding bobbin to be inserted and fitted, so that each component can be separately provided. It can be made and docked, the inner bobbin winding and the outer turbobin winding can be processed simultaneously, the production time can be shortened, and the primary winding and secondary winding can be inserted by inserting Can be easily and accurately determined, and variations in the electrical characteristics of the transformer are reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a transformer of a power supply for driving a magnetron according to the present invention.

FIG. 2 is a sectional view showing an example of a transformer of a power supply for driving a magnetron according to another embodiment of the present invention;

FIG. 3 is a main circuit diagram of a power supply for driving a magnetron.

FIG. 4A is a waveform diagram of a generated voltage and a current of the semiconductor switching element when the leakage magnetic flux is large. FIG. 4B is a waveform diagram of a generated voltage and a current of the semiconductor switching element when the leakage magnetic flux is small.

FIG. 5 is an explanatory view showing a method for manufacturing a transformer according to the present invention.

FIG. 6 is an external view showing a configuration of a transformer of a conventional magnetron driving power supply.

[Explanation of symbols]

 2 Primary winding 3 Secondary winding 9 Step-up transformer 10 Outer bobbin (bobbin) 11 Inner bobbin (bobbin) 12 Space insulating layer 26 Rectifying filter section 28 High voltage circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuho Sakamoto 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 5H006 AA05 CA07 CB04 CC01 FA02 HA09

Claims (3)

[Claims] A step-up transformer for stepping up an output of an inverter; and a high-voltage circuit for rectifying a voltage of the output of the step-up transformer by double voltage. The step-up transformer concentrically comprises a primary winding and a secondary winding. A transformer for a power supply for driving a magnetron, having a predetermined space between a primary winding disposed outside and a secondary winding disposed inside. 2. The transformer according to claim 1, wherein the secondary winding is wound around a plurality of winding grooves with a predetermined space insulating layer. 3. A structure in which a bobbin of a primary winding slides and is fitted into an inner diameter of a bobbin of a secondary winding.
3. The transformer for a power supply for driving a magnetron according to 1 or 2.