JP2547885B2 - Microwave oven with inverter power supply - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an inverter-powered microwave oven capable of controlling the power supplied to a magnetron to be equal to the level set by a cook.

[Prior art]

Generally, a microwave oven equipped with an inverter power supply inputs high-frequency power (high frequency of several tens KHz) and cathode filament current to the magnetron by the inverter power supply. Also,
At the same time, the inverter power supply detects the high-voltage power input to the magnetron, and controls the high-voltage power and the cathode filament current so that the high-voltage power falls within the allowable range. The magnetron has a filter box integrally on the input side. The high-voltage power and the cathode filament current are supplied from the high-voltage coil of the high-voltage power transformer and the cathode filament driving coil to the magnetron through the high-frequency noise control choke coil provided in the filter box. Conventionally, these high-voltage coils and cathode filament driving coils are connected to the filter box as they are by wiring, or they are connected by wiring, and then ferrite beads are fitted to the wiring to limit the input to reduce inductance. I'm giving. In the filter box, the lead wires on both ends of the choke coil are directly connected to the input terminal of the filter box and the magnetron as wiring.

[Problems to be Solved by the Invention]

By the way, the magnetron generates heat due to power conversion loss of microwaves during oscillating operation, and also generates heat by receiving microwave reflected waves generated by impedance mismatch with the load in the oven. Therefore, the air-cooled fan motor is used to force air cooling so as to equilibrate at an appropriate temperature (hereinafter referred to as "operation equilibrium temperature"). Under such a design, as indicated by the alternate long and short dash line I ₀ f, I ₀ l or broken lines I ₁ f, I ₁ l in FIG. 12, a large amount of cathode filament current of the magnetron flows immediately after the start of operation. And, the oscillation operation is stable and the magnetron body reaches from the room temperature to the operation equilibrium temperature,
The cathode filament current decreases and reaches a stable value at the operating equilibrium temperature. Here, I ₀ f and I ₀ l are the case where the cathode filament drive coil is directly connected to the filter box by wiring, and when the microwave oven is operated at the maximum rating, the microwave oven has the minimum power and light load. It shows the cathode filament current when operated at. Also,
I ₁ f and I ₁ l are the case where ferrite beads are fitted to the above wiring to give inductance.When the microwave oven is operated at the maximum rating, the microwave oven is operated at the minimum power and light load. It shows the cathode filament current at the time. As can be seen from the figure, in the conventional microwave oven equipped with an inverter power supply, the cathode filament drive coil is directly connected to the filter box by wiring,
When operating at the maximum rating, the cathode filament current I ₀ f exceeds the upper limit UL immediately after the start of operation and becomes excessive. Immediately after the start of operation, the cathode filament current I ₀ f becomes the upper limit U
If it exceeds L, a lattice defect occurs in the metal forming the surface of the cathode filament, and a moding phenomenon, which is an abnormal oscillation operation of the magnetron, occurs, so that the life of the magnetron is significantly shortened. On the other hand, when ferrite beads are fitted to the above wiring and inductance is applied, when operating at minimum power and light load, when the operating equilibrium temperature is reached, the cathode filament current I ₁ l falls below the lower limit LL. Run short. When the cathode filament current I ₁ l falls below the lower limit LL when the operating equilibrium temperature is reached, due to the self-heating due to the microwave reflected wave caused by the light load inside the oven chamber The moding phenomenon will occur, and as in the case described above, the life of the magnetron will be significantly shortened. As described above, in the conventional microwave oven equipped with an inverter power supply, the cathode filament current of the magnetron excessively flows immediately after the start of operation, or the cathode filament current becomes insufficient when the magnetron reaches the operating equilibrium temperature, and the life of the magnetron is shortened. There is a problem of shortening. Therefore, an object of the present invention is to provide an inverter-powered microwave oven capable of keeping the cathode filament current of the magnetron within an allowable range at all times during operation and thus extending the life of the magnetron.

[Means for Solving the Problems]

In order to achieve the above object, a first invention has a filter box integrally on an input side, and a high-frequency coil and a cathode filament driving coil are provided through a high-frequency noise control choke coil provided in the filter box. In a microwave oven equipped with an inverter power supply, which includes a magnetron that operates by receiving high-frequency power, and an inverter power supply that detects the high-frequency power input to the magnetron and controls the high-frequency power so that the high-frequency power is within an allowable range, Has a threshold temperature between room temperature and the operating equilibrium temperature of the magnetron, and has an inductance when the temperature of the magnetron is between room temperature and the threshold temperature, while the temperature of the magnetron exceeds the threshold temperature. When the above-mentioned filter is used It is characterized in that fitted to the wiring connecting the choke coil in the box. A second invention is a magnetron which operates by receiving high-frequency power from a high-voltage coil and a cathode filament driving coil via a high-frequency noise control choke coil provided in the filter box, and a high-frequency input to the magnetron. In an inverter-powered microwave oven that includes an inverter power supply that detects electric power and controls the high-frequency power so that the high-frequency power falls within an allowable range, a threshold temperature is provided between room temperature and the operating equilibrium temperature of the magnetron. While having an inductance when the temperature of the magnetron is between room temperature and the threshold temperature,
It is characterized in that a thermosensitive ferrite rod having an inductance of substantially zero when the temperature of the magnetron exceeds the threshold temperature is fitted in the choke coil in the filter box.

[Action]

The first invention operates as follows. The cathode filament driving coil is directly connected to the filter box by wiring, and ferrite beads are not fitted to this wiring. When the temperature of the magnetron is between room temperature and the threshold temperature of the heat-sensitive ferrite beads, the wiring that connects the choke coils in the filter box is provided with the inductance of the heat-sensitive ferrite beads. Therefore, immediately after the start of operation, the cathode filament current is limited by this inductance, and an excessive current does not flow. On the other hand, when the temperature of the magnetron exceeds the threshold temperature, the inductance of the heat-sensitive ferrite beads becomes substantially zero, so that the cathode filament current is hardly limited. Therefore, when the magnetron reaches the operating equilibrium temperature, the cathode filament current will not run short. Thus, during operation, the cathode filament current is always within the allowable range. Therefore, the life of the magnetron is extended as compared with the conventional one. Since the heat-sensitive ferrite beads are fitted to the wiring that connects the choke coils, they can be attached without using a separate member such as a fitting. The second invention operates as follows. Also in this case, the cathode filament driving coil is directly connected to the filter box by wiring. When the temperature of the magnetron is between room temperature and the threshold temperature of the heat sensitive ferrite rod, the inductance of the choke coil in the filter box is increased due to the insertion of the heat sensitive ferrite rod. Therefore, immediately after the start of operation, the cathode filament current is limited by the increased inductance, and the excessive current does not flow. On the other hand, when the temperature of the magnetron exceeds the threshold temperature, the increase in inductance due to the heat-sensitive ferrite rod disappears, so that the cathode filament current is hardly limited. Therefore, when the magnetron reaches the operating equilibrium temperature, the cathode filament current will not run short. Thus, during operation, the cathode filament current is always within the allowable range. Therefore, the life of the magnetron is extended as compared with the conventional one. Since the heat-sensitive ferrite rod is fitted in the choke coil, it can be attached without using a separate member such as a fitting.

【Example】

Hereinafter, a microwave oven equipped with an inverter power supply of the present invention will be described in detail with reference to embodiments. FIG. 3 shows a structure of a microwave oven equipped with an inverter power supply according to an embodiment of the first invention, and FIG. 9 shows a circuit configuration thereof. As shown in FIG. 3, this microwave oven equipped with an inverter power supply includes an operation panel 20 and a door 9 capable of shielding microwaves on the entire surface of a main body 30, and a turntable 7 inside an oven 6. Further, this microwave oven equipped with an inverter power supply includes the inverter power supply 1 shown in FIG. 9 and the magnetron MAG on the right side of the oven chamber 6 on the back side of the operation panel 20. As shown in FIG. 9, the inverter power supply 1 includes a control microcomputer CPU 2 operated by the operation panel 20, an interface transistor Tr ₃ , a drive transformer DT, a power transistor drive circuit PTD, and a power transistor. Transistor PTr
And have. In the high voltage transformer HVT, a pre-coil PC ₀ and a driving coil DC ₀ are wound on the primary side, and a cathode filament driving coil Fi, a high voltage coil HC ₀ and a detection coil SC ₀ are wound on the secondary side. The cathode filament driving coil Fi is directly connected to the input terminals 13 and 13 of the magnetron MAG (without providing ferrite beads) by the high voltage wirings 11 and 12. Further, a high breakdown voltage diode HD and a high breakdown voltage on-denser HCap for rectifying the output of this coil HC ₀ are connected between the terminals of the high voltage coil HC ₀ . One terminal of the high voltage coil HC ₀ has a high withstand voltage capacitor H
It is connected to a part of the high-voltage wiring 11 on the high-voltage transformer HVT side via C _0, and the other terminal of the high-voltage coil HC ₀ is connected to the anode of the magnetron MAG via the ground. The magnetron MAG has an appearance as shown in FIG. 2 and its equivalent circuit is as shown in FIG. As shown in FIG. 2, the magnetron MAG comprises a magnetron body MT, a heat dissipation yoke 2 attached around the magnetron MT, and a filter box 5 integrally attached to the input side of the magnetron body MT. There is. Reference numeral 15 indicates an outlet for microwave output.
As shown in FIG. 1, the filter box 5 has a feedthrough capacitor 14 on the wall surface and a pair of choke coils RFC, RFC for limiting high frequency noise inside. The feedthrough capacitor 14 guides the pair of input terminals 13, 13 into the filter box 5. Choke coil RFC, RFC
Are connected to the input terminal 13 guided into the filter box 5 and the cathode filament 10 incorporated in the magnetron body MT by the wiring 16 formed by extending the coil winding. And in each case, the ferrite rod FC ₁ is inserted as a core. And coincide with the inner diameter and the outer diameter of the ferrite rod FC ₁ of the choke coil RFC, is easy so as not come off. Further, the heat-sensitive ferrite beads FB are fitted to the wiring 16 between the one choke coil RFC and the cathode filament 10. The heat-sensitive ferrite beads FB are fixed to the wiring 16 with an adhesive 17.
In this way, it is mounted without using a separate member such as a mounting bracket. Note that FIG. 4 shows a portion of the wiring 16 in which the heat-sensitive ferrite beads FB are fitted. As shown in FIG. 5, the heat-sensitive ferrite beads FB have a threshold temperature T ₀ (about 70 ° C.) between the room temperature RT and the operating equilibrium temperature Teq of the magnetron MAG. This allows the above wiring
As shown by the solid line L ₂ in FIG. 5, 16 is a magnetron MAG at the operating frequency (several 10 KHz) of the inverter power supply 1.
When the temperature is between room temperature RT and the threshold temperature T ₀ , inductance (about 3 μH) is given, while the magnetron MA
When the temperature of G exceeds the threshold temperature T ₀ , the inductance becomes almost zero. Here, the dashed-dotted line L ₀ shows the inductance when there is no heat-sensitive ferrite bead FB, and the broken line L ₁ is provided with a general ferrite bead (one having no threshold temperature between room temperature RT and operating equilibrium temperature Teq). It shows the inductance when it is turned on. The ferrite cores FC ₁ and CF ₁ are general ones that do not have a threshold temperature between room temperature RT and operating equilibrium temperature Teq. The inverter power supply 1 is a commercial power supply (for example, 120V, 60H
z) is passed through the line noise filter LNF, then the diode bridge BD ₁ , choke coil L and capacitor SC
Power is supplied to the power transistor PTr by making DC through ap. Further, an alternating current is taken out from the diode bridge BD ₁ by a current transformer CT, converted into a direct current through the diode bridge BD ₂ , a resistor R ₁ and a capacitor C ₁ , and a current is supplied to the control microcomputer CPU2. The control microcomputer 2 drives the power transistor drive circuit PTD through the interface transistor Tr ₃ and the drive transformer DT according to the instruction from the operation panel 20. Power transistor drive circuit PTD
Drives the power transistor PTr through the driving coil DC ₀ . Power transistor PTr is a high voltage transformer HVT
2 through the primary side pre-coil PC ₀ and capacitor RCap
High frequency power is generated in the cathode filament drive capacitor Fi and the high voltage coil HC ₀ on the next side. Magnetron MAG
Receives the high frequency power as an input and generates a microwave. In addition, the control microcomputer 2
Is the sensing coil SC ₀ , on the secondary side of the high voltage transformer HVT.
Through a resistor R ₂ and diodes D ₁ detects a high-frequency power, and controls each part of the inverter power supply 1 as the high frequency power is acceptable. In the start-up direct image, the temperature of the magnetron MAG is a value between the room temperature RT and the threshold temperature T ₀ of the heat-sensitive ferrite beads FB. At this time, due to the characteristics shown in FIG. 5 of the heat-sensitive ferrite bead FB, wiring of one choke coil RFC 1
Since 6 is given an inductance of about 3 μH,
Compared with the case where the wiring 16 is directly connected to the cathode filament 10, the cathode filament current is reduced by 1 to 2A. Therefore, even if the microwave oven is operated at the maximum rating, the cathode filament current I ₂ f will not exceed the upper limit UL, as indicated by the solid line in FIG. Note that I ₂ f, I ₂ l
Shows the cathode filament current when the microwave oven equipped with the inverter power supply is operated at the maximum rating and when it is operated at the minimum power and the light load. As the operation continues, the temperature of the magnetron MAG exceeds the threshold temperature T ₀ of the thermal ferrite beads FB and the operating equilibrium temperature Te
At q, the inductance of the heat-sensitive ferrite beads FB becomes almost zero. Therefore, the cathode filament currents I ₂ f and I ₂ l respectively match the cathode filament currents I ₀ f and I ₀ l when the ferrite beads are not provided. Therefore, even when the microwave oven is operated with the minimum power and the light load, the cathode filament current I ₂ l does not fall below the lower limit LL. The points α and β on the solid lines I ₂ f and I ₂ l are the threshold temperatures T of the magnetron MAG when the microwave oven equipped with the inverter power supply is operated at the maximum rating and when it is operated at the minimum power and light load. _It shows the time when it becomes _zero . In this way, this microwave oven equipped with an inverter power supply
During operation, the cathode filament current can always be kept within an allowable range. Therefore, the life of the magnetron can be extended as compared with the conventional one. FIG. 6 shows a magnetron MAG ₂ that constitutes a microwave oven equipped with an inverter power supply according to an embodiment of the second invention.
The figure shows the equivalent circuit of this magnetron MAG ₂ . Except for this magnetron MAG ₂ , it has the same structure as the microwave oven with the inverter power supply described above. As shown in FIG. 6, the filter box 5 of the magnetron MAG ₂ has a feed-through capacitor 14 on the wall surface, like the magnetron MAG shown in FIG. 1, and has a pair of chokes for limiting high frequency noise inside. Equipped with coil RFC, RFC. The feedthrough capacitor 14 guides the pair of input terminals 13, 13 into the filter box 5. Choke coil RF
Both C and RFC are wirings that extend the coil winding.
Input terminal 13 led into the filter box 5 by
And the cathode filament 10 built into the magnetron body MT
Is connected between and. Then, as shown in FIG. 7, a thermosensitive ferrite rod FC ₂ is fitted as a core into each choke coil RFC. Choke coil RFC
The inner diameter of and the outer diameter of the ferrite rod FC ₂ are the same, and they cannot be easily removed. In this way, it is mounted without using a separate member such as a mounting bracket. As shown in FIG. 8, the heat-sensitive ferrite rod FC ₂ has a threshold temperature T ₁ (about 68 ° C.) between the room temperature RT and the operating equilibrium temperature Teq of the magnetron MAG ₂ . Heat-sensitive ferrite rod FC
By inserting ₂ in the above choke coil RFC, the temperature of the magnetron MAG ₂ is room temperature RT and the threshold temperature T at the operating frequency (several 10 KHz) of the inverter power supply 1 as shown by the solid line L ₄ in FIG. When it is between ₁ and ₁ , it is in a state where the inductance is increased (about 3.4 μH). On the other hand, when the temperature of the magnetron MAG ₂ exceeds the threshold temperature T ₁ , the increase in inductance due to the provision of the heat-sensitive ferrite rod FC ₂ becomes almost zero. The alternate long and short dash line L ₃ shows the inductance (about 1 μH) of the choke coil RFC without the heat-sensitive ferrite rod FC ₂ . Immediately after the start of operation, the temperature of the magnetron MAG ₂ is a value between the room temperature RT and the threshold temperature T ₁ of the heat-sensitive ferrite rod FC ₂ . At this time, due to the characteristics shown in FIG. 8 of the heat-sensitive ferrite rod FC ₂ , since the two choke coils RFC, RFC each have an inductance of about 3.4 μH, the choke coils RFC, RFC are directly applied to the cathode filament 10 as they are. The cathode filament current is reduced by 1 to 2 A as compared with the case of connection. Therefore, similarly to the above-described microwave oven equipped with an inverter power supply, even when the microwave oven is operated at the maximum rating, the cathode filament current I ₂ f does not exceed the upper limit UL as shown by the solid line in FIG. As the operation continues, the temperature of the magnetron MAG ₂ exceeds the threshold temperature T ₁ of the thermal ferrite beads FB and the operating equilibrium temperature Te
At q, the increase in inductance due to the heat-sensitive ferrite rod FC ₂ becomes almost zero. Therefore, the cathode filament currents I ₂ f and I ₂ l respectively match the cathode filament currents I ₀ f and I ₀ l when the heat-sensitive ferrite rod FC ₂ is not provided. Therefore, even if the microwave oven is operated at maximum power and light load, the cathode filament current I ₂ l will not fall below the lower limit LL. In this way, this microwave oven equipped with an inverter power supply
During operation, the cathode filament current can always be kept within an allowable range. Therefore, the life of the magnetron can be extended as compared with the conventional one.

【The invention's effect】

As is clear from the above, in the microwave oven equipped with the inverter power supply of the first invention, the heat-sensitive ferrite beads are fitted to the wiring provided in the input path and connecting the choke coils in the filter box on the input side of the magnetron. Therefore, the cathode filament current can be prevented from flowing excessively immediately after the start of operation, and the cathode filament current can be prevented from becoming insufficient when the magnetron reaches the operating equilibrium temperature. Therefore, during operation, the cathode filament current can always be kept within the allowable range, and the life of the magnetron can be extended as compared with the conventional one. Also,
The heat-sensitive ferrite beads can be attached without using a separate member such as an attachment fitting. Further, in the microwave oven equipped with the inverter power supply of the second invention, since the thermosensitive ferrite prevention is fitted in the choke coil provided in the input path in the filter box on the input side of the magnetron, the cathode filament is immediately after the start of operation. It is possible to prevent the current from flowing excessively and prevent the cathode filament current from becoming insufficient when the magnetron reaches the operating equilibrium temperature. Therefore, during operation, the cathode filament current can always be kept within the allowable range, and the life of the magnetron can be extended as compared with the conventional one. Further, the heat-sensitive ferrite rod can be attached without using a separate member such as an attachment fitting.

[Brief description of drawings]

1 and 2 are diagrams showing a magnetron of an inverter-powered microwave oven according to an embodiment of the first invention, FIG. 3 is an external view of the inverter-powered microwave oven, and FIG. 4 is the inverter. FIG. 5 is a diagram showing a heat-sensitive ferrite bead of a microwave oven equipped with a power source, FIG. 5 is a diagram showing a temperature characteristic of an inductance of a wiring fitted with the heat-sensitive ferrite bead, and FIG. 6 is an inverter power source mounting of an embodiment of the second invention. FIG. 7 is a diagram showing a magnetron of a microwave oven, FIG. 7 is a diagram showing a choke coil and a ferrite rod of the above-mentioned microwave oven equipped with an inverter power source, and FIG. 8 is a diagram showing temperature characteristics of inductance of a choke coil in which the ferrite rod is inserted. FIG. 9 shows the circuit configuration of the above-mentioned microwave oven equipped with an inverter power source, and FIGS. 10 and 11 show the equivalent circuits of the above magnetrons, respectively. FIG. 12 and FIG. 12 are views showing the time course of the cathode filament current in each of the above-mentioned microwave ovens equipped with an inverter power supply and the conventional microwave oven equipped with an inverter power supply. 1 ... Inverter power supply, 2 ... Magnetron yoke, 3 ... Air cooling fan, 5 ... Filter box, 6 ... Oven chamber, 7 ... Turntable, 9 ... Door, 10 ... Cathode filament, 11, 12 …… High voltage wiring, 13 …… Input terminal, 14 …… Penetrating capacitor, 15 …… Microwave output outlet, 16 …… Wiring, 17 …… Adhesive, 20 …… Operation panel, 30 …… Main body, CPU2 ...... Control microcomputer, DC ₀ ...... Drive coil, FB ...... Heat-sensitive ferrite beads, FC ₁ ...... General ferrite core, FC ₂ ...... Heat-sensitive ferrite rod, Fi ...... Cathode filament drive coil, HC ₀ …… High voltage coil, HVT …… High voltage transformer, MAG, MAG ₂ …… Magnetron, MT …… Magnetron body, PC ₀ …… Precoil, PTD …… Power transistor drive circuit, PTr …… Power transistor, RFC …… cho Coil, SC ₀ ... Sensing coil.

Claims (2)

(57) [Claims] 1. A filter box is integrally provided on the input side,
The magnetron that operates by receiving high-frequency power from the high-voltage coil and the coil for driving the cathode filament through the high-frequency noise control choke coil provided in the filter box, and the high-frequency power that is input to the magnetron is detected and the high-frequency power is In an inverter-powered microwave oven equipped with an inverter power supply that controls the high-frequency power so as to be within an allowable range, a threshold temperature is provided between room temperature and the operating equilibrium temperature of the magnetron, and the temperature of the magnetron is room temperature. While having an inductance when it is between the threshold temperature, a thermosensitive ferrite bead having an inductance of substantially zero when the temperature of the magnetron exceeds the threshold temperature, in the wiring that connects the choke coil in the filter box. Inverter characterized by being fitted Microwave with power supply. 2. A filter box is integrally provided on the input side,
A magnetron that operates by receiving high-frequency power from a high-voltage coil and a coil for driving a cathode filament through a high-frequency noise control choke coil provided in the filter box, and the high-frequency power input to the magnetron is detected and the high-frequency power is detected. In the microwave oven equipped with an inverter power supply that controls the high-frequency power so that is within an allowable range, a threshold temperature is between room temperature and the operating equilibrium temperature of the magnetron, and the temperature of the magnetron is room temperature. When the temperature of the magnetron exceeds the threshold temperature, the inductance is substantially zero while having a inductance when it is between the temperature threshold value and the threshold temperature, a thermosensitive ferrite rod is inserted into the choke coil in the filter box. Inverter power supply-equipped electronic characterized by range.