JP2010182474A - High-frequency heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent spark from occurring between a high-voltage winding and cores, restrain fluctuation of gaps between U-cores and I-cores, and aim at stabilization of transformer characteristics, even if cracks may be generated at a bobbin due to long-hour use in an abnormal installation state. <P>SOLUTION: The cores are so structured to be covered with an insulator before being inserted into the bobbin at primary winding or a high-voltage winding, or at a part opposed to both the primary winding and the high-voltage winding, and at the same time, to prevent high-voltage spark between the high-voltage winding and the core due to cracks of the bobbin, while, the U-core and the I-core are covered with the insulator for a whole periphery, and that, by making a thickness of the insulator at an opposed face of the both cores constant, gaps between the both cores can be made constant, so that characteristics of a boosting transformer may be made stable without fluctuation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique related to a high-voltage transformer for an inverter power source used in a high-frequency heating device such as a microwave oven, and more particularly to a technique for improving the performance and safety of the inverter.

  As an inverter type high frequency heating apparatus, there is one provided with a transformer unit in which a transformer is mounted on a printed circuit board (for example, see Patent Document 1).

  FIG. 6 is a block diagram showing a circuit configuration of a transformer unit in the inverter type high frequency heating apparatus.

  In FIG. 6, the alternating current from the commercial power supply 11 is rectified to direct current by the rectifier circuit 13. The rectified voltage is smoothed by the choke coil 14 and the smoothing capacitor 15 on the output side of the rectifier circuit 13 and is given to the input side of the inverter circuit 102.

  By controlling the semiconductor switching element (IGBT) 17 in the inverter circuit 102 to be turned on / off by the control circuit 29, a desired high-frequency (20 to 50 kHz) bidirectional current is generated on the primary side of the step-up transformer 18. Flowing.

  The high-frequency power generated on the primary side of the step-up transformer 18 is boosted by the step-up transformer 18 and high-voltage high-frequency power is generated on the secondary side. A secondary side of the step-up transformer 18 is connected to a voltage doubler full-wave rectification type high voltage circuit 19 including high voltage diodes 191 and 192 and high voltage capacitors 193 and 194, and a high voltage DC voltage ( For example, −4 kV) is applied.

  In addition, power is supplied from the other high-voltage winding (heater winding) 5 of the step-up transformer 18 to the cathode (filament) 121 of the magnetron 10, and electrons are generated from the heated cathode and reach the anode. Microwave energy is applied to an object to be heated in the heating chamber (not shown).

  The control circuit 29 controls the inverter 102 based on a command from the control unit of the high-frequency heating device through the connector 26. Thus, the control circuit 29 controls the power supply to the secondary side by the on / off control of the IGBT 17 and controls the intensity of the output microwave from the magnetron 10.

  FIG. 8 is a schematic cross-sectional view showing the structure of the step-up transformer 18 mounted on a conventional transformer unit. As shown in FIG. 8, the step-up transformer 18 used in the transformer unit has a bobbin 2 in which a primary winding 3, a high-voltage winding 4, and a heater winding 5 are wound concentrically. The U core 1 and the I core 39 are inserted into the center of the structure.

  The high voltage winding 4 has about 10 times the number of turns of the primary winding so as to obtain a predetermined step-up ratio. The U core 1 is grounded for stabilizing the operation of the transformer and for safety.

In addition, a resin gap spacer 38 protruding from a part of the bobbin 2 is provided between the U core 1 and the I core 39.
JP 2004-304142 A

  FIGS. 7A and 7B are simplified diagrams showing the positional relationship of the main components of the step-up transformer 18. FIG. 7A shows a case where the core is long, and FIG. This is an example of when the height of is short.

  The U core 1 and the I core 39 are inserted into the bobbin 2 so as to face each other, and a primary winding (P winding) is formed on a concentric circle centered on the UI cores 1 and 39 with the bobbin 2 in parallel and outward. Wire) 3 and high voltage winding (S winding) 4 are wound.

  The U core 1 and the I core 39 are inserted into the bobbin 2, but are inserted into the bobbin 2 against the outer wall portions 50 (U core side) and 51 (I core side). In the first place, the core is completed by solidifying and firing a magnetic material such as iron or manganese with a certain size, but the resulting dimensional accuracy is poor because it shrinks during firing. Therefore, the dimensional variation of the gap (gap) g52 facing the U core 1 and the I core 39 increases.

  If the gap g52 varies greatly, the inductance variation of the step-up transformer 18 increases, and the performance and characteristics of the step-up transformer 18 deteriorate. In FIG. 7A, the gap g52 is reduced, and in FIG. 7B, the gap g52 is increased.

  On the other hand, in FIG. 8, since the step-up transformer 18 is energized during high-frequency heating, the primary winding 3, the high-voltage winding 4, and the heater winding 5 that warms the cathode (filament) of the magnetron 10 (FIG. 6) generate heat. The step-up transformer 18 rises in temperature. Since heat generation stops after the high-frequency heating is finished, the temperature of the step-up transformer 18 decreases.

  That is, the step-up transformer 18 repeats a so-called temperature cycle in which the temperature rises and falls repeatedly. At this time, the material constituting the step-up transformer 18 gradually deteriorates due to thermal fatigue.

  Although it is a deterioration that does not become a problem under normal use conditions, if it is used abnormally under bad conditions that cannot be assumed by the installation conditions and use conditions of the high-frequency heating device, or when other parts for cooling parts fail, When it is placed on the top, bottom, left, or right back of the furniture, the supply / exhaust port of the high frequency heating device is blocked, or the motor coil of the cooling fan of the high frequency heating device is disconnected. Thus, when trouble occurs such that the cooling fan becomes inoperable, there is a concern that a crack 7 may occur in the bobbin as shown in FIG.

  If a crack 7 occurs in the bobbin 2 portion of the step-up transformer 18, a high voltage of about 3000 V is applied between the high-voltage winding 4 and the U core 1 portion connected to the ground, and a spark is generated because the spatial distance is not relatively large. (Enlarged structure part)

  When there is a spark, the high-voltage circuit 19 in FIG. 6 changes greatly electrically, and the influence also causes the inverter circuit portion 102 to change greatly. This change is detected and high-frequency heating is stopped for the purpose of safety and component protection. . Therefore, the generation of spark is also stopped at this time.

  However, when the user tries to perform high-frequency heating again, a spark is generated again, and this is repeatedly detected and stopped. If this is repeated, as shown in FIG. 8, the portion of the high voltage winding 4 is abnormally heated and causes dielectric breakdown, resulting in a rare short state, and further heat is generated in the rare short portion, causing smoke and ignition. In other words, the user may be very uneasy and unsafe.

  As a method of preventing the bobbin 2 from deteriorating and extending its life or preventing sparks, the distance between the high voltage winding 4 and the U core 1 can be increased, or the insulation thickness of the exterior of the high voltage winding 4 can be increased to increase the withstand voltage. There is also a way to raise it.

  However, the shape of the step-up transformer 18 is increased, so that space is not saved, and convenience for the user is impaired. Moreover, the cost is high, which is also contrary to the convenience for the user.

  Further, if the U core 1 is not grounded, no spark is generated between the high voltage winding 4 cores 1 even if cracks 7 occur, but conversely cracks or holes where the cracks of the bobbin 2 continue to progress. Will start to generate sparks between the primary winding 3 and the high-voltage winding 4.

  At this time, if the user does not take the grounding of the high-frequency heating device, a very dangerous situation occurs in which a high-voltage electric shock is caused when the user touches the high-frequency heating device.

  In order to avoid this worst situation, even if the U-core 1 is grounded and the bobbin 2 is cracked or perforated, a spark will surely fly from the high-voltage winding 4 to the U-core 1 that is closest to the U-core 1. The distance and structure of the bobbin 2 from the primary winding.

  That is, when the shortest distance between the high voltage winding and the U core 1 is d1, and the shortest distance between the high voltage winding and the primary winding is d2, the bobbin design is performed in the positional relationship of d1 << d2, and the primary winding and The safety structure is such that there is no real possibility of reducing the probability of sparking directly between the primary winding and the high-voltage winding due to the occurrence of cracks or perforations by providing double partitions between the high-voltage windings. .

  Therefore, the present invention solves the above-mentioned problems, stabilizes the characteristics of the transformer by suppressing gap variation between U cores and I cores, and heats up the bobbin due to abnormal use, abnormal installation conditions, and ultra-long-term use. Fatigue and cracks occur, sparking between the high-voltage winding and the core, eventually causing a dielectric breakdown in the high-voltage winding, resulting in a rare short state, further generating heat in the rare short portion, causing smoke and ignition It is an object of the present invention to provide a device that can surely prevent a user from feeling uneasy or unsafe from occurring.

  The present invention has been made to solve the above-described problems, and rectifies an AC power supply and increases the frequency of the inverter, a boosting transformer that boosts high-frequency power output from the inverter, and an output of the boosting transformer A high-voltage circuit including a high-voltage diode that converts a high-voltage DC voltage into a high-voltage DC voltage, and a magnetron that radiates microwaves in response to the high-voltage DC voltage, and the step-up transformer includes a U-core connected to a ground potential and the U-core. A primary winding on the inverter side and a high-voltage winding on the booster side are circulated in parallel on a concentric circle centering on the facing I core with a bobbin therebetween, and the U core and the I core are all around. Is covered with an insulator and then inserted into the step-up transformer main body.

  According to the present invention, the thickness of the insulator on the side facing each of the U cores and I cores is controlled to a constant value by previously covering with an insulator, so that the gap variation between both cores can be kept low and the characteristics of the transformer can be stabilized. At the same time, cracks in the bobbin due to abnormal use or installation for a long period of time and long-term use, sparks between the high-voltage winding and the core, eventually causing the high-voltage winding to break down into a rare short state, The core is covered with another additional insulator other than the bobbin that the rare short part further generates heat and generates smoke and ignition, which makes the user very uneasy and unsafe. Can be prevented.

  A first invention rectifies an AC power supply and increases the frequency of the inverter unit, a step-up transformer that boosts high-frequency power output from the inverter unit, and a high-voltage diode that converts the output of the step-up transformer into a high-voltage DC voltage And a magnetron that radiates microwaves upon receiving the high-voltage DC voltage, and the step-up transformer is centered on a U-core connected to a ground potential and an I-core facing the U-core. The primary winding of the inverter side and the high-voltage winding on the booster side are wound in parallel on the outer side of the concentric circle with a bobbin therebetween. The U core and the I core are covered with an insulator and then the booster Inserted into the transformer body.

  According to a second aspect of the present invention, in the first aspect of the present invention, the thickness of the insulator on the opposing surfaces of the U core and the I core is made constant, and inserted into the step-up transformer body.

  According to a third invention, in the first or second invention, the insulator covering the U core has a minimum value of a distance between the high-voltage side winding and the primary-side winding for the opposing portion on the high-voltage side winding side. When a slit is provided at a position closer to the high-voltage side winding than the U-core and the high-voltage winding, the bobbin serving as an insulation breaks down and the insulation performance deteriorates. A structure that prevents high-voltage spark between the high-voltage winding and the core, and that even when an abnormal voltage occurs, always sparks from the high-voltage side winding to the slit of the U-core and does not spark to the primary winding side It is.

  According to a fourth invention, in any one of the first to third inventions, the material of the cap-like insulator uses a resin of the same material as the material of the bobbin.

  According to a fifth invention, in any one of the first to third inventions, the material of the cap-like insulator uses a resin of a material different from the material of the bobbin.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The block diagram of the magnetron drive power supply (inverter) according to the present invention is the same as that of the conventional one (FIG. 6), and the description thereof is omitted. Further, the present invention is not limited by this embodiment.

(Embodiment)
The structure of the U core and the I core of the step-up transformer 18 according to the embodiment of the present invention is shown in FIG. The U core 1 and I core 39 previously covered with an insulating material 55 such as resin are inserted into the bobbin so as to face each other, and the thickness of the insulating material on the opposing surfaces of the U core 1 and the I core 39 is made constant. Above, it was inserted into the step-up transformer main body, and it was set as the structure where the tip of each other hits.

  The I core 46U core 47 is a case where the core height is low and the I core 48U core 49 is a case where the core height is high. The gap (gap) between 49 and the I cores 46 and 48 is A1 + B1 and both are constant.

  As shown in FIG. 3, when inserting into the bobbin 2 body, the surface (45 for U-core, 44 for I-core) that contacts the bobbin 2 is also fixed so that there is no gap when fitting with the bobbin. (Size).

In other words, the U core is constant as A2 in FIG. 1 and B2 in the I core. The difference in the core height is the dimension of A3 and B3 in FIG. 1, and is adjusted by the thicker and thinner insulators in the A3 and B3 portions. As a result, even if the core height varies, the gap dimension A1 + B1, which is an important management value in terms of characteristics, can be made constant.

  FIG. 2 is a structural diagram (supplementary to FIG. 1) when the U core 1 and the I core 39 whose entire circumference is covered with an insulator are inserted into the transbobbin 2, and the gap between the opposing surfaces of the U core 1I core 39 is shown in FIG. It is shown that it is constant regardless of the dimensional variation of the core.

  FIG. 3 is also a simplified diagram showing the positional relationship of the main components of the step-up transformer 18 according to the present invention (a simplified diagram for the combination of FIG. 1 and FIG. 2). When the height of the I core 39 is long, FIG. 3B shows the case where the heights of the U core 1 and the I core 39 are low. In either case, the gap g52 between the faces inserted into the bobbin 2 and facing each other is shown to be constant.

  The structure of the step-up transformer 18 is shown in FIGS. 2 and 4 have the same contents (structure), but FIG. 1 shows a normal time and FIG. 4 shows a time when a crack is generated. In FIG. 6, the primary winding 3 on the inverter unit 102 side and the high-voltage winding 4 on the boost side are concentrically centered on the U core 1 and the I core 39, with a bobbin 2 and parallel to the outside, with a predetermined step-up ratio. In order to obtain (winding ratio), it is circulated with about 10 times the number of turns, and the U core 1 is connected to the ground potential for the stabilization of operation of the step-up transformer (noise prevention) and safety.

  In FIG. 4, since the step-up transformer 18 is energized during high-frequency heating, the heater winding 5 that warms the cathode portion (filament) of the primary winding 3 and the high-voltage winding 4 magnetron 10 (FIG. 6) generates heat. Rises in temperature. Since heat generation stops after the high-frequency heating is finished, the temperature of the step-up transformer 18 decreases.

  That is, the step-up transformer 18 repeats a so-called temperature cycle in which the temperature rises and falls repeatedly. At this time, the material constituting the step-up transformer 18 gradually deteriorates.

  Although it is a deterioration that does not become a problem under normal use conditions, if it is used abnormally under bad conditions that cannot be assumed by the installation conditions or use conditions of the high-frequency heating device, or if other parts for cooling parts fail, for example, furniture If the air supply / exhaust port of the high-frequency heating device is blocked by placing it on the top, bottom, left, or right side of the inside, or the motor coil of the cooling fan of the high-frequency heating device is disconnected, cooling When a trouble occurs such that the fan becomes inoperable, there is a concern that a crack 7 may occur in the bobbin as shown in FIG.

  However, even if a crack 7 is generated in the bobbin 2 portion of the step-up transformer 18 and a high voltage of about 3000 V is applied between the high-voltage winding 4 and the core 1 portion connected to the ground, the cap-like shape surrounds and surrounds the core 1. Since the insulator 6 exists, no spark is generated (expanded structure portion).

  Therefore, sparks are generated many times through the crack 7 as in the conventional case, the high voltage winding 4 is abnormally heated and breaks down and becomes a short circuit. However, it can be avoided so as not to make the user very uneasy or unsafe.

  The insulator 6 that covers the entire circumference of the core is close to the bobbin 2 that is in contact with the windings 3 and 4 that are heated to a high temperature while being applied with a high pressure. For example, an aramid paper or an insulating tape having a high pressure resistance is used, which is different from the resin material used for the bobbin 2, for which a stable material having a long life is desirable.

That is, since the thermal expansion coefficient and thermal conductivity when the heat changes due to different materials are different, the risk of thermal fatigue of the material due to a sudden thermal change due to thermal stress can be reduced. This is because even if one of the insulating performances is greatly deteriorated due to deterioration, the other material can protect it.

  On the other hand, it is possible to reduce the influence due to the difference in temperature expansion coefficient when the insulator 6 and the bobbin 2 are made of the same material and thermally changed. Whether the two materials are the same or different is optimally selected depending on the purpose of use and structure.

  In FIG. 5, the insulator 6 covering the entire circumference of the U core 1 has a slit 40 in the middle, and the distance from the bobbin 2 to the slit 40 of the U core 1 (distance b in the figure) is the bobbin 2. Even if a crack occurs, the distance from the high-voltage winding 4 to the U-core 1 is not less than 32 (distance a in the drawing), and the distance 30 from the high-voltage winding 4 to the primary winding 3 (distance c + distance d in the drawing) Or it is below the path | route of 31 (distance e in the figure). That is, a <b <c + d and a <b <e.

  This is only a case, but the bobbin 2 is frequently cracked, the primary side (winding) and the high voltage side (winding) are short-circuited, and the user is exposed to a high voltage electric shock. The purpose is to absolutely prevent by controlling the distance of the ground potential. Prioritizing the safety of electric shock over the smoke and ignition from the step-up transformer 18. The reason is that when a high-frequency heating device is used, the user is always in the vicinity and notices smoke and fire and does not cause expansion damage.

  On the other hand, the gap accuracy of the I core 39 facing the U core 1 of FIG. 8, which is the conventional structure, that is, the gap distance between both cores is an important factor that affects the characteristics of the step-up transformer 18 such as inductance. Conventionally, a gap spacer 38 is formed by a protruding resin portion extending from a part of the bobbin 2, and the gap distance between the U core 1 and the I core 39 is determined.

  However, the gap spacer 38 formed extending from the bobbin 2 has a problem that the flow of the resin tends to be sparse, the thickness variation is large, and as a result, the variation of the transformer characteristics is greatly affected.

  Therefore, in FIGS. 1 and 2 which are the structure of the step-up transformer of the present invention, the core is covered with an insulator 6 independent of the formation of the bobbin 2, and the gap between the opposing U core 1 and I core 39 is set to a certain thickness in advance. Therefore, the gap variation between the U core 1 and the I core 39 can be made constant, and the characteristics of the step-up transformer 18 can be stabilized.

  The present invention is applied to a high-frequency heating apparatus that heats food, such as a microwave oven.

Combination structure diagram of transformer U core and I core according to an embodiment of the present invention Structural drawing when U core 1 and I core 39 with the entire circumference covered with an insulator are inserted into the transbobbin 2 Positional relationship diagram of main components of the step-up transformer according to the present invention Structural diagram of step-up transformer according to the embodiment of the present invention (including enlarged view of crack portion) Configuration explanatory diagram of the slit position provided in the insulator covering the entire circumference of the core Circuit configuration diagram of control part of conventional and high frequency heating apparatus of the present invention Positional relationship diagram of main components of conventional step-up transformer Structure of conventional step-up transformer (including enlarged view of crack)

1 U core 2 Bobbin 3 Primary winding 4 High voltage winding 5 Heater winding 6 Cap-shaped insulator (shape example 1)
7 Bobbin crack part 8 High frequency heating device 9 Inverter unit board 10 Magnetron 11 Commercial power supply 13 Diode bridge 14 Choke coil 15 Smoothing capacitor 16 Resonance capacitor 17 Power transistor (IGBT)
18 Step-up transformer 19 Double voltage full-wave rectifier circuit 27 Control board (High-frequency heating device controller board)
29 Inverter control circuit 33 Heating chamber 35 Object to be heated 38 Projection resin part extended from bobbin, gap spacer 39 I core 40 (for discharge) slit 44 Surface which is in contact with bobbin when inserted into bobbin body of I core 45 U The surface that is in contact with the bobbin when it is inserted into the bobbin body of the core 46 I core with low height 47 U core with low height 48 I core with high height 49 U core with high height 50 On the bobbin main body with I core The surface that contacts the bobbin 2 when inserted 51 The surface that contacts the bobbin 2 when inserted into the bobbin main body of the U core 52 The gap g between the surfaces of both cores facing each other
55 Insulator that covers the core 101 Rectifier filter part 102 Inverter part
121 Magnetron cathode (heater)
191, 192 High voltage diode 193, 194 High voltage capacitor 197 Core ground plate

Claims (5)

An inverter unit that rectifies an AC power supply and increases the frequency, a step-up transformer that boosts high-frequency power output from the inverter unit, and a high-voltage circuit that includes a high-voltage diode that converts the output of the step-up transformer into a high-voltage DC voltage; A magnetron that radiates microwaves upon receiving the high-voltage DC voltage, and the step-up transformer has a bobbin on a concentric circle centered on the U core connected to the ground potential and the I core facing the U core. A primary winding on the inverter side and a high-voltage winding on the step-up side are wound in parallel on the outside, and the U core and the I core are covered with an insulator and then inserted into the step-up transformer main body. Heating device. The high frequency heating device according to claim 1, wherein the thickness of the insulator on the opposing surfaces of the U core and the I core is fixed and inserted into the step-up transformer body. The insulator covering the U-core is slit at a position where the distance from the high-voltage side winding is closer than the minimum value of the distance between the primary-side windings from the high-voltage side winding in the opposing portion on the high-voltage side winding side. When the bobbin that plays a role of insulation between the U core and the high voltage winding is broken and the insulation performance is deteriorated, a high voltage spark between the high voltage winding and the core is prevented at a normal operating voltage. The high-frequency heating device according to claim 1 or 2, wherein the high-frequency heating device has a structure, and even when an abnormal voltage occurs, the high-voltage side winding always sparks to the slit portion of the U core and does not spark to the primary winding side. The high-frequency heating device according to any one of claims 1 to 3, wherein the cap-shaped insulator is made of a resin that is the same material as the bobbin material. The high-frequency heating device according to any one of claims 1 to 3, wherein the cap-shaped insulator is made of a resin having a material different from that of the bobbin.