JP5211917B2 - High frequency heating device - Google Patents

Description

  The present invention relates to a high-voltage switching transformer used for an inverter power supply type high-frequency heating device, and more particularly to a technique for protecting the device and improving safety.

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

  In FIG. 5, 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. The secondary side of the step-up transformer 18 is connected to a high voltage circuit 19 of a voltage doubler full wave rectification system composed of 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.

  Further, electric power is supplied from another secondary 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. The microwave energy is irradiated to the 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. 6 is a schematic cross-sectional view showing the structure of a step-up transformer mounted on a conventional transformer unit. As shown in FIG. 6, the step-up transformer 18 used in the above-described transformer unit has a bobbin 2 in which a primary winding 3, a secondary winding 4, and a heater winding 5 are wound concentrically. The core 1 is inserted into the center of the bobbin 2 from both sides.
JP 2004-304142 A

  In FIG. 5, the temperature of the step-up transformer 18 rises due to heat generated by the heater winding 5 that warms the primary winding 3, the high-voltage winding 4, and the cathode 121 of the magnetron 10 during high-frequency heating.

  Since the heat generation stops after the high-frequency heating is finished, the temperature of the step-up transformer 18 decreases. As the temperature rises and falls repeatedly, the material constituting the step-up transformer 18 gradually deteriorates due to thermal fatigue.

  In the case of use under bad conditions that cannot be assumed or failure of cooling parts, for example, the high-frequency heating device is installed vertically, left and right, When the rear five surfaces are placed in contact with the surroundings and the air supply / exhaust port is blocked, or when the motor fan of the cooling fan is disconnected and the cooling fan becomes inoperable, The bobbin 2 may crack.

  In FIG. 6, a high voltage of about 3000 V is applied between the high voltage winding 4 and the core 1 connected to the ground, but the distance is not so large, so that if the crack 7 occurs in the bobbin 2, the high voltage winding A spark may occur between the core 4 and the core 1 (see an enlarged view in FIG. 6).

  When a spark occurs, the inverter circuit portion 102 also fluctuates greatly due to the large fluctuation of the high-voltage circuit 19 in FIG. 5. When this fluctuation is detected, it is designed to stop high-frequency heating for safety. Yes. Accordingly, the generation of sparks is also stopped.

  However, when high-frequency heating is started again, a spark is generated again, and this is detected again and the operation of stopping high-frequency heating is repeated.

  Furthermore, if this repeated operation is continued, the insulation of the high-voltage winding 4 is destroyed by heat generation, the high-voltage winding 4 becomes in a rare short state, further heat is generated in the rare short portion, and in the worst case, smoke and ignition are caused. It can be a situation.

  As a method of preventing the occurrence of sparks, that is, a method of preventing the bobbin 2 from deteriorating, the distance between the high voltage winding 4 and the core 1 is further increased, the insulation thickness of the exterior of the high voltage winding 4 is increased, and the withstand voltage is increased. However, the shape of the step-up transformer 18 is increased and the cost is increased.

  Further, if the core 1 is not grounded, even if a crack 7 occurs, no spark is generated between the high-voltage winding 4 core 1, but conversely, the crack of the bobbin 2 progresses steadily. When a hole starts to be opened, a spark is generated between the primary winding 3 and the high-voltage winding 4 this time.

  At this time, if the high-frequency heating device is not grounded, a dangerous situation occurs in which the user is exposed to a high voltage.

  In order to avoid this situation, the core 1 is grounded, and even if a crack 7 or a hole in the bobbin 2 occurs, a primary winding that always sparks from the high-voltage winding 4 to the core 1 that is closest to the core 1 is used. The distance between the bobbin 2 and the bobbin 2 structure.

  That is, if the shortest distance between the high voltage winding 4 and the core 1 is d1, and the shortest distance between the high voltage winding 4 and the primary winding 3 is d2, the bobbin is designed so that the positional relationship is d1 << d2. Probability that a spark is generated directly between the primary winding 3 and the high-voltage winding 4 due to the occurrence of cracks 7 or perforations by providing double partitions between the winding 3 and the high-voltage winding 4. In some cases, a safety structure is prepared in preparation for a situation that is virtually impossible, such as lowering the pressure.

Therefore, the present invention solves the above-described problem, and provides a high-frequency heating device that prevents the occurrence of a spark between a high-voltage winding and a core even if a crack occurs in a bobbin due to long-term use in an abnormal installation state. Is.

  The present invention has been made in order to solve the above-described problems. An inverter that rectifies an AC power source to increase the frequency, a step-up transformer that boosts high-frequency power output from the inverter, and an output of the step-up transformer is a high-voltage DC voltage. In a high-frequency heating apparatus having a high-voltage circuit for converting to a high-voltage circuit and a magnetron that receives the high-voltage DC voltage and radiates microwaves, the step-up transformer has a bobbin provided concentrically around a grounded core. The bobbin is wound with a primary winding on the inverter side and a high-voltage winding on the high-voltage circuit side, and an insulator is disposed between the bobbin and the core.

  According to the present invention, even when a crack occurs in the bobbin due to long-term use in an abnormal installation state, it is possible to prevent the occurrence of a spark between the high voltage winding and the core.

  A first aspect of the invention is an inverter that rectifies an AC power source to increase the frequency, a step-up transformer that boosts high-frequency power output from the inverter, a high-voltage circuit that converts the output of the step-up transformer into a high-voltage DC voltage, and the high-voltage In a high-frequency heating apparatus having a magnetron that receives a direct current voltage and radiates microwaves, the step-up transformer has a bobbin provided concentrically around a grounded core, and the bobbin includes the inverter A primary winding on the side and a high-voltage winding on the high-voltage circuit side are wound, and an insulator is disposed between the bobbin and the core.

  According to a second invention, in the first invention, the insulator is disposed only in a portion facing the bobbin around which the high-voltage winding is wound.

  According to a third invention, in the first or second invention, the insulator is aramid paper, and the aramid paper is attached to the core.

  According to a fourth invention, in the first or second invention, the insulator is an insulating tape, and the insulating tape is attached to the core.

  According to a fifth invention, in the first invention, the insulator is formed integrally with the bobbin in a concentric manner with a predetermined distance from the bobbin.

  The above invention provides a safer high-frequency heating device that can prevent the occurrence of sparks between the high-voltage winding and the core even if the bobbin cracks due to long-term use in an abnormal installation state. it can.

  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, and the description thereof is omitted. Further, the present invention is not limited by this embodiment.

(Embodiment 1)
1 and 2 show the structure of the step-up transformer 18 of the high-frequency heating device according to the first embodiment of the present invention, and are sectional views of the step-up transformer 18 at the normal time and when a crack is generated, respectively.

1 and 2, the primary winding 3 on the inverter unit 102 side and the high-voltage winding 4 on the boosting side are the core 1.
The core 1 is rotated by a number of turns of about 10 times so that a predetermined step-up ratio (winding ratio) is obtained in a concentric manner around the bobbin 2 in parallel to the outside, and the core 1 stabilizes the operation of the step-up transformer 18 and For safety, it is grounded (reference numeral 195 in FIG. 2).

  In FIG. 2, as described above, the material constituting the step-up transformer 18 may deteriorate due to the temperature rise and fall of the step-up transformer 18, and cracks may occur in the bobbin 2. Therefore, even if a crack 7 occurs in the bobbin 2 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 connected to the ground, the insulator 6 surrounds and surrounds the core 1. To prevent sparks.

  The insulator 6 can be inserted into a narrow gap between the bobbin 2 and the core 1 and is a thin, high insulating performance, stable material with long humidity, temperature environment and long life, such as aramid paper and high pressure resistance Insulating tape is desirable.

  In addition, as an insulator to be inserted into the narrow gap between the bobbin 2 and the core 1, aramid paper, which is a thin, high insulating performance, stable material with high humidity, temperature environment and long life, and insulating tape with high pressure resistance performance can be used on one side. If it is pasted on the core 1 in advance and inserted into the bobbin, the manufacturing becomes easy.

  In this way, since it is a simple method in which a thin insulator is inserted into the gap between the bobbin 2 and the core 1, not only space saving but also high cost can be prevented.

  In particular, as shown in FIG. 3, the insulator 6 is arranged only in a portion facing the bobbin 2 portion around which the high-voltage winding 4 is wound, and in a portion facing the primary winding 3 on the inverter 102 side. Do not place an insulator.

Specifically, the attachment position of the insulator tip, that is, the distance from the bobbin 2 to the core 1 (symbol b) is the distance at which the high voltage winding 4 does not discharge to the core 1 even if a crack occurs in the bobbin 2. (Reference a) or more, which is shorter than the distance between the high voltage winding 4 and the primary winding 3 (reference e) or the sum of the distance c and the distance d in FIG. That is, a <b <c + d and a <b <e.

  This is only a case, but the user's electric shock that occurs when the primary winding and the high-voltage winding are completely short-circuited due to frequent occurrence of cracks 7 on the bobbin 2, the high-voltage side and the core 1 (ground potential). It aims at preventing by providing the space | interval appropriately.

(Embodiment 2)
The second embodiment of the present invention will be described below. FIG. 4 is a cross-sectional view showing the structure of the step-up transformer 18 according to the present embodiment.

  As shown in FIG. 4, in the step-up transformer 18 according to the present embodiment, the insulator 6 is formed integrally with the bobbin 2 in a concentric manner with a predetermined distance from the bobbin 2 around which the high-voltage winding 4 is wound. Is done.

  That is, an insulating material is not disposed in the gap between the core 1 and the bobbin 2, but the insulation between the high voltage winding 4 and the core 1 is strengthened by adopting a double structure of the bobbin 2. By making the insulation structure double in this way, even if a crack occurs in the first insulation 33, the double insulation 34 can prevent the occurrence of sparks.

According to the present embodiment, safety can be secured in the same manner without arranging another insulator between the core 1 and the bobbin 2, which is advantageous in terms of work process and material costs.

  In addition, since the bobbin can be processed by resin molding, it may be considered that the bobbin has durability, the performance of the step-up transformer, and the ease of processing.

  Further, the thickness of the bobbin 2 on the primary winding 3 side (symbol f in FIG. 4) is not thicker than the thickness on the high-voltage winding 4 side and even compared with the conventional example. This is because if the thickness of the primary side is increased in accordance with the thickness of the high-voltage winding side, it is necessary to increase the material of the bobbin, resulting in an increase in cost and an increase in the size of the step-up transformer.

  In addition, the inner diameter of the primary winding wound around the bobbin is increased, the length of the primary winding necessary to obtain the same number of turns is lengthened, resulting in performance disadvantages such as a temperature rise, and high winding cost. .

  Moreover, since the voltage between the primary winding and the core is lower than that on the high-voltage winding side, it is not necessary to increase the bobbin thickness.

  As described above, according to the present invention, it is possible to prevent occurrence of sparks between the high-voltage winding and the core even if a crack occurs in the bobbin due to long-term use in an abnormal installation state.

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

Sectional drawing which shows the structure of the step-up transformer which concerns on Embodiment 1 of this invention Sectional drawing which shows generation | occurrence | production of a crack in the pressure | voltage rise transformer which concerns on Embodiment 1 Explanatory drawing showing the position of the insulator Sectional drawing which shows the structure of the step-up transformer concerning Embodiment 2 of this invention Block configuration diagram showing the circuit configuration of a conventional high-frequency heating device Sectional drawing showing the structure of a step-up transformer mounted on a conventional high-frequency heating device

Explanation of symbols

1 Core 2 Bobbin 3 Primary Winding 4 High Voltage Winding 5 Heater Winding 6 Insulator 7 Crack 10 Magnetron 11 Commercial Power Supply 13 Rectifier Circuit 14 Choke Coil 15 Smoothing Capacitor 16 Resonance Capacitor 17 Semiconductor Switching Element (IGBT)
18 Step-up Transformer 19 High Voltage Circuit 29 Control Circuit 33 First Insulation 34 Double Insulation 101 Rectifier Circuit 102 Inverter 121 Cathode 191 and 192 High Voltage Diode 193 and 194 High Voltage Capacitor

Claims (5)

An inverter that rectifies an AC power source to increase the frequency, a step-up transformer that boosts high-frequency power output from the inverter, a high-voltage circuit that converts the output of the step-up transformer into a high-voltage DC voltage, and a micro that receives the high-voltage DC voltage In the high-frequency heating apparatus having a magnetron that radiates a wave, the step-up transformer has a bobbin provided concentrically around a grounded core, and the bobbin includes a primary winding on the inverter side and A high-frequency heating device in which a high-voltage winding on the high-voltage circuit side is wound, and an insulator is disposed between the bobbin and the core. The high-frequency heating device according to claim 1, wherein the insulator is disposed only in a portion facing the bobbin around which the high-voltage winding is wound. The high frequency heating apparatus according to claim 1 or 2, wherein the insulator is aramid paper, and the aramid paper is attached to the core. The high frequency heating apparatus according to claim 1 or 2, wherein the insulator is an insulating tape, and the insulating tape is attached to the core. The high-frequency heating device according to claim 1, wherein the insulator is formed integrally with the bobbin in a concentric manner with a predetermined distance from the bobbin.

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