JPH07114147B2 - High frequency heating device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating device such as a microwave oven for heating foods, fluids, etc., and more specifically, to improvement of its power supply device.

2. Description of the Related Art Conventionally, as is well known, a power supply device for a microwave oven includes a power supply circuit mainly composed of a ferroresonant transformer 2 as shown in FIG. Since the magnetron 5 normally has an operating voltage of 3 to 4 kV, the circuit voltage of the secondary side circuit of the step-up transformer 2 is very high and dangerous. Therefore, the housing 6 of the microwave oven has always been grounded to the earth ground 7 and used.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the structure of the conventional power supply device for a microwave oven as described above, if the high voltage winding 8 and the primary winding 9 are provided as shown in FIG.
When and are in contact with each other due to some trouble (for example, point P and point Q are in contact with each other), if the ground wire 10 is provided, the housing 6 is kept at the ground potential, and the fuse 11 is Since it melts, there is no danger even if it is touched by humans. However, if the ground wire 10 is not provided or if the way of installing the ground wire is incomplete, when a contact accident at points P and Q occurs, the housing 6 has a very high potential (for example, 2kV), and human beings will be electrocuted if touched. Therefore, the ground wire 10 is indispensable, and the installation work is also troublesome because it is necessary to guarantee a sufficiently low impedance grounding. That is, in the prior art, the microwave oven requires strict earth grounding, which makes the installation work troublesome and the movement after the installation troublesome, resulting in inconvenience.

Means for Solving the Problems The present invention has been made in order to solve the above-mentioned inconvenience, and has a configuration described below.

That is, a power supply unit that receives power from a commercial power supply or a battery, a frequency converter that converts the power of the power supply unit into high frequency power, a step-up transformer that steps up the output of the frequency converter, and an output of the step-up transformer. And a shield member made of a non-magnetic conductive material, which is substantially connected to the housing and is provided between the primary winding and the secondary winding of the step-up transformer. The shield member is provided with groove portions whose one end is open and arranged at an arbitrary interval, and the shield member is configured to be an electrical open circuit along the winding direction of the primary winding.

In addition, two shield members with the width of the groove portion being 1/2 or less of the arrangement interval are provided, and the shield members are placed in such a positional relationship that the groove portions do not overlap each other, and are made of an insulating space or an insulating material. The structure is provided in the step-up transformer through the layers.

Furthermore, a plurality of shield members are provided via an insulating space or an insulating layer made of an insulating material, and the groove portions of these shield members are arranged in different relative positional relations.
The secondary and secondary windings are shielded by a shield member having no opening.

With the above configuration, a shielding member having substantially the same potential as the housing can be provided between the primary winding and the secondary winding of the step-up transformer, and the high-voltage circuit on the secondary side of the step-up transformer has the same potential as the case. It becomes possible to be confined in the shielding space of. Moreover, since it is a step-up transformer for stepping up the electric power whose frequency is increased by the frequency converter, it has an extremely small structure and can easily enclose the high-voltage circuit in the shielding space. The shield member is made of a non-magnetic conductive material having groove portions provided at one end and opened at arbitrary intervals, and
Since the primary winding is electrically opened along the winding direction, the eddy current generated in the shielding member can be suppressed to an extremely small level by the high frequency magnetic flux generated by the primary winding. Therefore, it is possible to prevent the shield member itself from being heated by induction heating to a high temperature and wasteful power consumption, and also to prevent an adverse effect on the frequency converter.

Further, by forming a groove portion having a width of 1/2 or less of the interval and providing two shield members with an insulating layer so that the groove portions do not overlap, the opening of the shield member is substantially eliminated, It is possible to completely prevent inconvenience and instability such as a high voltage lead wire reaching the primary winding side through the shielding member in the event of an abnormality.

Further, a plurality of shielding members are provided via an insulating layer, and the groove portions thereof are arranged so that the relative positional relations thereof are different from each other, and the shielding member having substantially no opening between the primary and secondary windings. By providing the structure, it is possible to achieve the same effect as the above.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a high frequency heating apparatus showing an embodiment of the present invention.

In the figure, a commercial power supply 1, a fuse 11, a diode bridge 20, an inductor 21, and a capacitor 22 form a power supply unit 23 to form a unidirectional power supply. The power supply power is supplied to the control circuit 25 by the resistor 24, and the control circuit 25
The transistor 26 is switched at a high frequency of 20 kHz to 1 MHz, for example. Reference numeral 27 is a diode, and 28 is a resonance capacitor, which constitute a resonance type inverter (frequency converter) 29. Therefore, high frequency power having a frequency equal to the switching frequency of the transistor 26 is supplied to the primary winding 31 of the step-up transformer 30, and a high voltage output is generated in the secondary winding 33 magnetically coupled through the core 32. To do. This output is rectified by the capacitor 34 and the diode 35 and supplied to the magnetron 5. Since the cathode of the magnetron 5 is heated by the heater winding 36, the magnetron 5 oscillates, radio wave output is generated, and dielectric heating becomes possible. The detailed operation of the resonant inverter 29 is already known and will not be described.

Step-up transformer 30 primary winding 31 and secondary winding 33, heater winding
A shielding member 37 is provided between 36 and at a position close to the primary winding side, and the shielding member 37 is connected to the core 32 and is substantially connected to the housing 6 of the high frequency heating device. There is. Therefore, the high-voltage circuit on the output side of the high-voltage secondary winding 33 is substantially confined in the shielding space having the same potential as the housing 6 due to the presence of the shielding member 37. Therefore, even if some failure occurs in the high-voltage secondary winding and the insulation is broken, it is possible to prevent contact between the primary winding 31 and so-called contact between the primary and secondary windings. In particular, the step-up transformer 30 has a structure that boosts the output of the resonant inverter 29, and therefore is very compact, so that the structure of the shielding member 37 can be simple and small, and the high-voltage circuit can be enclosed in the shielding space. Is extremely easy. FIG. 2 is a sectional view showing the structure of the step-up transformer 30. In the figure, those having the same reference numerals as those in FIG. 1 are corresponding components, and detailed description thereof will be omitted. The shielding member 37 is the bobbin 40 of the primary winding 31.
The secondary winding 33 is shielded via the space layer 42 between the secondary winding 33 and the bobbin 41. The shield member 37 is connected to the core 32 at its inner diameter portion 43, and is connected to the housing 6 by a lead wire 44.

With this structure, the secondary winding 33 and the heater winding 36 are the primary winding 31
If the secondary winding 33 is shielded further and the insulation breaks down due to some reason, the primary winding 31 and the secondary winding 33 may touch each other and the electric potential of the housing 6 becomes an abnormally high electric potential. It can be prevented.
Therefore, it is not necessary to further ground the housing 6 to the earth ground by a ground wire, and it is possible to provide a safe and easy-to-use high-frequency heating device.

Since it is indispensable to place the shielding member 37 between the primary winding 31 and the secondary winding 33 as shown in the drawing, the adverse effect of the high frequency magnetic flux generated by them must be extremely large.

FIG. 3 is a view showing the structure of the shielding member 37 for preventing the adverse effect of the high frequency magnetic flux. In FIGS. 3 (a) and 3 (b), the shielding member 37 is provided with the groove portions 50 at regular intervals and constitutes an electrical open circuit along the winding direction (arrow in the figure) of the primary winding. Slit part 51 for
Shield plates 52, 53 made of stainless steel, aluminum, copper, etc. and an insulating layer 54 made of insulating paper, etc.
It is composed by. In this embodiment, the two insulating plates 52 and 53 have exactly the same shape, and the groove portions
The width l ₁ of 50 is chosen to be less than 1/2 of its spacing l ₂ . The mutual arrangement relationship is that the center line P ₁ of the groove portion 50 of the shield plate 52 and the center line P ₁ of the groove portion 55 of the shield plate 53.
P ₂ and P ₂ are displaced by θ as shown in the figure. That is, the groove portions 50 and 55 of each other are arranged so that they are all covered with each other through the insulating layer 54. Therefore, when the shield member is viewed in the vertical direction in FIG. 3 (b), even if there is no insulating layer 54, there is no opening other than the hole 56 through which the core 32 passes. If an opening exists in this direction, the following inconvenience will occur. That is,
As shown in FIG. 4, for example, when the bobbin 41 of the secondary winding 33 is melted as shown in FIG.
The part 58 of the secondary winding approaches the primary winding 31 through the opening 59 of the shielding member 37, resulting in so-called contact between the primary and secondary windings, which is extremely dangerous. However, in the case of the present invention, the shielding portion 37 of the conductor can realize a state in which the opening 59 does not exist between the primary and secondary windings, and can prevent the adverse effect of the high frequency magnetic flux. That is, the groove portion 50 as shown in FIG. 3 (a) is provided, and
By providing the slit portion 51 and forming an electrical open circuit in the winding direction of the primary winding, it is possible to suppress the generation of so-called induced current to a small extent and to make the loss generated therein extremely small. The core 32 is made of ferrite, and the shield 52 is
By using a non-magnetic stainless plate having a thickness of about 0.5 mm or less, the loss of the shield plate 52 can be made extremely small even when boosting the power of the frequency of about 100 kHz. Of course, such a structure can be formed by using other materials. For example, the insulating layer 54 is composed of a ceramic plate, and the shielding plates 52, 53
The same effect can be obtained even if the conductive film having the shape of is printed on both sides of the ceramic plate.

FIGS. 5 (a) and 5 (b) are partial plan views and front views of the shield member 37 in which the three shield plates 52a, 52b and 52C are insulated by the two insulating layers 54a and 54b. The shield plates 52a to 52c have the same shape as the shield plate 52 shown in FIG. However, as is clear from FIG. 5 (a), the width of the groove portions of the shield plates 52a to 52c in this case is wide (length corresponding to l ₁ in FIG. 3). Therefore, as shown in the front view of FIG.
By overlapping the shield plates with the insulating layers 54a and 54b interposed therebetween, and gradually shifting the positions of the groove portions as shown in FIG. 7A, the shield member 37 having substantially no opening as a whole can be obtained. It is composed.

FIG. 6 is a partial cross-sectional view of a step-up transformer 30 showing another embodiment of the present invention, and those having the same reference numerals as those in FIGS. 2 and 3 are the corresponding components. This step-up transformer 30 is
The bobbin 41 of the secondary winding 33 is provided for the core 32, the shielding member 37 including the shielding plates 52, 53 and the insulating layer 54 is provided outside the insulating cylinder 60, and the primary is further provided outside thereof. Winding
A bobbin 40 having 31 is provided. Shield 52,53
Has a groove portion 50 as shown in FIG. 7 (a) or (b) showing a partial view thereof, and is formed so as to form a slit portion 51 as shown in FIG. 7 (c). . If the shield plate 52 having such a shape is manufactured so that the inner diameters thereof are different, the shield member 37 as shown in FIG. 6 can be configured. If the relative positional relationship of the shield plates 52 and 53 is configured so that the groove portions 50 do not overlap each other, the same operation and effect as the embodiment described with reference to FIGS. 2 and 3 can be obtained. it can.

As described above, according to the present invention, the output of the frequency converter is boosted by the boosting transformer and supplied to the magnetron,
A shield member made of a non-magnetic conductive material is provided between the primary winding and the secondary winding of the step-up transformer, and a groove portion having one end opened and provided at an arbitrary interval is provided in the shield member, and Since this shielding member is configured to be an electrical open circuit along the winding direction of the primary winding, the step-up transformer is small, so that the shield between the primary and secondary windings is very simple and compact. Realized, the high-voltage circuit can be confined in the shielded space. Therefore, high safety can be assured without grounding the housing to the ground, so that a high-frequency heating device that is extremely easy to use and does not require grounding work can be realized. In particular, the shield member is provided with groove portions whose one end is open at an arbitrary interval,
Moreover, since the circuit is electrically opened along the winding direction of the primary winding, the shielding member is induction-heated by the high-frequency magnetic flux to prevent the disadvantage that it is overheated or a large amount of power is lost. In addition, the problem of destabilizing the operation of the frequency converter is also prevented from occurring, grounding work is not required, and a convenient high-frequency heating device that maintains high safety and efficiency is provided. You can

In addition, by providing two shield members having a width of the groove portion that is 1/2 or less of the arrangement interval and providing the shielding portions through the insulating layer in a relative positional relationship such that the groove portions do not overlap each other. Since a shielding member having substantially no opening can be provided between the primary winding and the secondary winding,
Even in the event of an abnormality, it is possible to safely prevent contact between the primary and secondary windings and ensure extremely high safety.

Furthermore, the groove portions of the plurality of shielding members are arranged through an insulating layer so as to have a relative positional relationship different from each other, and substantially no openings are provided between the primary and secondary windings, so that the groove is formed. It is possible to provide a shielding member having substantially no opening without being restricted by the width of the portion and to provide a high-frequency heating device having high safety.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a high-frequency heating apparatus showing an embodiment of the present invention, FIG. 2 is a sectional view showing the structure of a step-up transformer of the apparatus, and FIGS. 3 (a) and 3 (b) are shielding members of the apparatus. And FIG. 4 is a partial sectional view of a step-up transformer for explaining the inconvenience that occurs when the apparatus is abnormal, and FIG. 5 (a).
7B is a partial plan view and a front view showing another configuration of the shielding member of the device, FIG. 6 is a sectional view of a step-up transformer showing another embodiment of the device, and FIGS. ) (C) is
FIG. 8 is a circuit diagram of a conventional high-frequency heating device, which is a partial view showing a configuration of a groove portion of a shielding member of the step-up transformer, a partial view showing the other configuration, a perspective view, and FIG. 5 ... Magnetron, 6 ... Housing, 23 ... Power supply section, 29 ...
… Frequency converter, 30 …… Boosting transformer, 31 …… Primary winding, 32 …… Core, 33 …… Secondary winding, 37 …… Shielding member,
50 …… groove part, 51 …… slit part, 59 …… opening.

Claims (3)

[Claims] 1. A power supply unit that receives power from a commercial power supply or a battery, a frequency converter that converts the power of the power supply unit into high-frequency power, a boosting transformer that boosts the output of the frequency converter, and the booster. A magnetron energized by the output of the transformer, and a shielding member made of a non-magnetic conductive material, which is substantially connected to the housing and is provided between the primary winding and the secondary winding of the step-up transformer. A high-frequency heating device, wherein the shield member is provided with groove portions having one end opened and arranged at an arbitrary interval, and the shield member is an electrical open circuit along the winding direction of the primary winding. 2. A pair of shield members having a width of the groove portion that is 1/2 or less of the arrangement interval thereof are provided, and the two shield members are in a positional relationship such that the groove portions do not overlap each other, and an insulating space or The high-frequency heating device according to claim 1, wherein the high-frequency heating device is provided in the step-up transformer via an insulating layer made of an insulating material. 3. A plurality of shielding members are provided via an insulating space or an insulating layer made of an insulating material, and the groove portions of the plurality of shielding members are arranged in different relative positional relations, and substantially,
The high frequency heating apparatus according to claim 1, wherein the primary and secondary windings are shielded by a shield member having no opening.