KR100375849B1 - Electronic range - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven on which an inverter power source is mounted. Since the primary side of the boost transformer 5 is connected to a half-bridge type inverter power source, no DC component flows through the primary winding of the boost transformer 5. Instead, as the boosting transformer 5, one having a small saturation voltage can be used. In this case, in the boosting transformer 5, the core gap 40 formed of the divided cores 28 and 29 is provided on the secondary winding 22 side. Since the magnetic coupling coefficient of the secondary winding 22 is reduced, the magnetic resonance frequency of the secondary winding 22 side moves to the high frequency side, and as a result, the resistance of the secondary winding 22 side increases, Since the Q value of the magnetic resonance on the secondary winding 22 side of the boosting transformer decreases, the occurrence of ringing due to the magnetic resonance can be prevented, and it is insulated as a boosting transformer in a microwave oven using a half-bridge type inverter power supply. While using a small internal pressure It characterized in that it prevents the swing start-up time longer torch.

Description

Microwave oven {ELECTRONIC RANGE}

The present invention relates to a microwave oven on which an inverter power source is mounted.

Background Art Conventionally, in the electronic lens, a one-stage voltage resonance type inverter power supply called "quasi-E class" has been used as an inverter power source for driving magnetrons.

However, this one-type voltage resonant inverter power source has advantages such as simple configuration, but since a direct current component flows in the boost transformer, it is necessary to use a large one to increase the saturation voltage of the boost transformer. It was difficult to miniaturize more than this.

For this reason, it is considered to adopt a half-bridge type inverter voltage capable of miniaturizing the boost transformer. That is, since the half-bridge type inverter power supply is made by connecting two switching elements and two resonant capacitors half bridge, and outputting no DC component, a small one can be used as a boosting transformer.

However, when a half-bridge type inverter power supply is adopted, the ringing is caused by magnetic resonance with the floating (parasitic) capacitance generated in the secondary winding of the boost transformer at the start of the magnetron (the cathode is not sufficiently heated yet). Unnecessary resonance called ringing sometimes occurs. When ringing occurs in this way, since a high pressure equal to or higher than the boost ratio is generated on the secondary side of the boost transformer, it is necessary to use a large insulation breakdown voltage as the boost transformer.

On the other hand, if the control circuit is to suppress the high voltage caused by the ringing occurring in the secondary winding of the boost transformer, it causes a problem that the cathode heating current at the magnetron start-up is relatively small and the magnetron start-up time is long.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a microwave oven capable of preventing the magnetron starting time from being prolonged while using a small insulation breakdown voltage as a boosting transformer in a configuration using a half-bridge type inverter power supply. To provide.

1 is a cross-sectional view of a boost transformer in an embodiment of the present invention,

2 is a perspective view of the microwave oven shown in the open state of the door,

3 is an electrical circuit diagram schematically showing the overall electrical configuration;

4 is a perspective view of a boost transformer,

5 is an exploded perspective view of the boost transformer;

6 is a perspective view showing the structure of a litz wire,

7 is a waveform diagram showing a primary voltage of a boost transformer;

8 is a waveform diagram showing a secondary voltage corresponding to a primary voltage of a boost transformer;

FIG. 9 is a diagram corresponding to FIG. 8 showing in a state where the Q values are different. FIG.

* Explanation of symbols for main parts of the drawings

5: boost transformer 7: magnetron

10: switching unit (inverter power) 11: rectifier

14: switching element 15: resonant capacitor

19: primary winding 20: high voltage condenser

22: secondary winding 22a: unit winding

26: bobbin 28: first split core

29: second split core 38: the Ritz line

40: core gap

The present invention provides an inverter power supply having a switching unit formed by connecting two switching elements and two resonant capacitors to a half bridge, a boosting transformer for receiving a high frequency current from the inverter power supply by boosting the secondary winding and outputting the secondary winding; In a microwave oven having a high voltage rectifier for rectifying a high-voltage high-frequency current boosted by a transformer and a magnetron for irradiating microwaves to the cooking chamber in a state where the high-voltage rectifier voltage rectified by the high-voltage rectifier is applied, the boost transformer is a primary pressure transformer. A bobbin wound in parallel with a winding and a secondary winding, and inserted into a core insertion hole of the bobbin, wherein the core gap is composed of a first split core and a second split core in which the core gap is located on the secondary winding side. (Claim 1).

According to this configuration, the high frequency current output from the inverter power source is boosted by the primary winding of the boost transformer and output as a high voltage high frequency current from the secondary winding. At this time, in the boost transformer, since the core gap between the first split core and the second split core is located on the secondary winding side wound on the bobbin, the magnetic coupling coefficient on the secondary winding side is reduced, and the magnetism on the secondary winding side is reduced. The resonance frequency is moving toward the high frequency side. As a result, since the resistance on the secondary winding side becomes large and the Q value of the magnetic resonance on the secondary winding side of the boost transformer decreases, the occurrence of ringing due to the magnetic resonance can be suppressed.

Therefore, a small voltage having a small insulation breakdown voltage can be used as the boosting transformer, and the boosting ratio does not decrease, so that the current for cathode heating does not decrease and the startup time of the magnetron does not become long.

In the above configuration, it is preferable that the core gap of the boost transformer is located corresponding to approximately the center of the secondary winding (claim 2).

According to this configuration, since the resistance on the secondary winding side of the boost transformer can be maximized, the Q value of the magnetic resonance on the secondary winding side of the boost transformer can be greatly reduced, and the occurrence of ringing can be effectively prevented. Can be.

In addition, the resonance frequency due to the stray capacitance on the secondary winding side of the boost transformer and the inductance is preferably 10 times or more the switching frequency of the inverter power supply (claim 3).

According to this configuration, since the self-resonant frequency due to the stray capacitance on the secondary winding side and the inductance of the boost transformer deviates significantly from the switching frequency of the inverter power supply, the synergistic effect with the increase of the resistance on the secondary winding side due to the core gap is increased. This can greatly reduce the Q value of the magnetic resonance.

The high-voltage rectifier is preferably an onion double voltage rectifier circuit composed of two high-voltage capacitors and two high-voltage diodes (claim 4).

According to such a structure, since the secondary circuit of the boost transformer performs symmetrical operation on both sides and the negative side, all operations can be made symmetrical as well as the symmetrical operation of the half-bridge type inverter power source which is the primary side circuit. As a result, two switching elements and two resonant capacitors used in the half-bridge type inverter power supply and two high voltage capacitors and the high voltage diodes used in the high voltage rectifying unit can each use the same device, and the parts can be easily managed. have.

In addition, it is preferable that the end located on the primary winding side of the secondary winding of the boost transformer is connected to the common connection point of the series-connected high voltage capacitor constituting the onion double voltage rectifier circuit (claim 5).

According to this structure, since the secondary winding electrostatically coupled to the primary winding is connected to the frame of the microwave at high frequency, voltage resonance energy at the magnetic resonance frequency of the secondary winding becomes difficult to leak from the primary side. It is possible to prevent the conversion efficiency of the boost transformer from decreasing.

The secondary winding of the boost transformer is preferably formed by connecting a plurality of unit winding portions in series (claim 6).

According to this structure, since the interlayer voltage of the whole secondary winding is reduced and the capacitance is reduced equivalently, resistance to a high frequency becomes large, the Q value of the magnetic resonance on the secondary winding side is reduced, and ringing is generated. Can be suppressed.

In addition, it is preferable that the primary winding of the boost transformer is formed of a litz wire by combining eight or more small wires of 0.1 mm or less (claim 7).

According to such a structure, the secondary winding resistance value at the operating frequency (for example, 50 Hz) of an inverter power supply can be suppressed about 1.2 times at low frequency, raising the secondary winding resistance value at the start of a magnetron.

That is, since the high frequency current flows through the secondary winding of the boost transformer, the effect of the skin effect and the proximity effect becomes remarkable, but the effect of the skin effect and the proximity effect can be avoided by reducing the wire diameter and increasing the number of wires. Can be.

In this case, it is preferable to make the wire diameter extremely small because the resistance at the self-resonant frequency of the secondary winding becomes large, but on the other hand, since the resistance value of the operating frequency needs to be made small, the wire thinning is in a certain range. You must do it.

Thus, the Litz wire is suitable as a configuration capable of sufficiently reducing the loss at the operating frequency while ensuring a ratio between the resistance component at the operating frequency and the resistance value at the magnetic resonance frequency of the secondary winding.

In addition, it is preferable to connect a series circuit composed of a resistor and a capacitor between the primary winding of the boost transformer or between the primary winding and the high voltage capacitor of the half-bridge type inverter power supply (claim 8).

According to such a structure, since the voltage change rate of the part in which the voltage change rate of a voltage waveform is large (part in which the absolute value of dV / dt is large) in a primary winding of a boost transformer can be suppressed, High frequency components with respect to the operating frequency can be suppressed. As a result, the vibration amplitude with respect to the magnetic resonance frequency of the secondary winding is reduced, and the ringing component of the secondary winding voltage waveform can be suppressed, so that unnecessary high voltage is not generated and the magnetron can be started quickly. have.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

2 shows the microwave at an angle. In FIG. 2, the cabinet 1 has a box shape in which the front surface is opened. The cooking chamber 2 is provided inside the cabinet 1, and at the side of the cabinet 1, the machine room ( 3) is formed.

The printed wiring board 4 is arrange | positioned at the bottom part of the machine room 3, and the voltage rising transformer 5 is mounted in the printed wiring board 4. As shown in FIG.

In addition, the waveguide 6 facing the cooking chamber 2 is fixed in the machine chamber 3, and microwaves from the magnetron 7 are irradiated to the cooking chamber 2 through the waveguide 6.

3 schematically shows the electrical configuration of the microwave oven. In FIG. 3, the rectifying unit 8, the inverter control unit 9, the switching unit 10, and the high voltage rectifying unit 11 are mounted on the printed wiring board 4 in addition to the boosting transformer 5. And the switching unit 10 constitute an inverter power source.

The rectifier 8 rectifies the entire wave by the diode bridge circuit and then smoothes it by a reactor and a smoothing capacitor (both not shown) to output a DC current to the power supply lines 12 and 13.

The inverter control unit 9 outputs a switching signal of a predetermined frequency (for example, 50 Hz) to the switching unit 10.

The switching unit 10 simultaneously connects in series a series circuit in which two switching elements 14 are connected in series between the power supply lines 12 and 13 and a series circuit in which two resonant capacitors 15 are connected in series, The common connection point of the switching element 14 and the common connection point of the resonant capacitor 15 are formed in the half bridge type which respectively makes an output terminal. In this case, the flywheel diode 16 of the polarity shown is connected between the collector of the switching element 14, and the emitter. In addition, a series circuit composed of a capacitor 17 and a resistor 18 is connected between the common connection point of the switching element 14 and the power supply line 13.

The primary winding 19 of the boost transformer 5 is connected to the output terminal of the switching section 10, respectively.

The high-voltage rectifier 11 is configured as an onion-voltage voltage rectifier circuit in which a series circuit in which two high voltage capacitors 20 are connected in series and a series circuit in which two high voltage diodes 21 are connected in series are connected in parallel. The common connection point of 20 is connected to one of the secondary windings 22 of the boost transformer 5, and the common connection point of the high voltage diode 21 is connected to the other side of the secondary winding 22. As shown in FIG. In addition, both power supply lines 23 through which the high voltage direct current is output from the high voltage rectifying unit 11 are connected to the positive electrode 7a of the magnetron 7, and the negative power supply line 24 is the negative electrode 7b of the magnetron 7. Is connected to.

On the other hand, the secondary winding 25 for cathode heating is connected with the cathode 7b of the magnetron 7.

Since the floating capacity (indicated by the broken line in FIG. 3) is generated on the secondary winding 22 side of the boosting transformer 5, the secondary winding 22 of the boosting transformer 5 is caused by the floating capacity and inductance. The resonance frequency of the side is determined. In this embodiment, by adjusting the inductance of the secondary winding 22, the resonance frequency determined by the stray capacitance and the inductance is set to be 10 times or more of the switching frequency of the inverter section 10 50 kHz.

Next, the structure of the boost transformer 5 will be described.

4 shows the boost transformer 5 at an angle, and FIG. 5 shows the boost transformer in an exploded manner. 4 and 5, the boost transformer 5 includes a bobbin in which a primary winding 19, a secondary winding 22, and a cathode winding secondary winding 25 (omitted in FIGS. 4 and 5) are wound. (26), the core support member 27, the first split core 28 (shown only in FIG. 5), the second split core 29, and the core band 30. As shown in FIG.

The bobbin 26 has a shape in which the supporting portions 33 and 34 are integrated on both sides of the connecting bobbin bobbin portion 31 and the secondary winding bobbin portion 32 (shown in FIG. 1 only). The U-shaped core support part 35 is formed in the side surface of 33 and 34. As shown in FIG. The partition between the primary winding bobbin portion 31 and the secondary winding bobbin portion 32 is partitioned by a large partition portion 36. The primary winding 19 is wound around the bobbin portion 31 for the primary winding, and the end of the primary winding 19 is held by a holding portion (not shown) formed on the side of the support portion 33 to be shown below. Protruding.

The secondary winding bobbin portion 32 is partitioned into three unit winding portions 32a (shown in FIG. 1 only) by two small partition portions 37, and each unit winding. One secondary winding 22 is wound so as to extend over the periphery 32a. That is, the secondary winding 22 is divided into three unit winding portions 22a, and is formed by connecting the divided unit winding portions 22a in series. One end of the secondary winding 22 is connected to a terminal portion (not shown) provided to protrude from the bottom surface of the large partition portion 36 of the bobbin 26, and the other end thereof is the bottom surface of the support portion 34. It is connected to a terminal portion (not shown) provided so as to protrude from.

6 shows the structure of the Litz wire 38 constituting the primary winding 19. In FIG. 6, the litz wire 38 is formed by combining eight element wires (outer periphery is insulated) 38a of 0.1 mm or less.

4 and 5, the cable holding portion 39 is formed on the side surface of the support portion 34 of the bobbin 26, and the cable holding portion 39 has two secondary windings for cathode heating. 25) (omitted in Figs. 4 and 5) are retained and projected downward, respectively. In this case, the ends of the two cathode heating secondary windings 25 held by the holding portion 39 are connected to one by soldering to the printed wiring board 4, and the cathode heating 2 is connected in the connected state. The primary winding 25 is intended to support the core support 35 formed in the bobbin 26. In addition, a connector (not shown) is connected to one end of the secondary winding 25 for cathode heating, so as to be connected to the cathode 7b of the magnetron 7.

The core support member 27 has a c-shape having an arm portion 27a, and the arm portion 27a is integrated into the bobbin 26 by fitting into the opening of the core support portion 35 formed on the bobbin 26. have.

On the other hand, the first split core 28 and the second split core 29 each have a C shape. The arm portions 28a and 29a of these split cores 28 and 29 are formed in a circumferential shape, and the arm portion 28a of one split core 28 is longer than the arm portion 29a of the other split core 29. Formed. The arm portions 28a and 29a of the split cores 28 and 29 are inserted into the core insertion holes 26a of the bobbin 26. In the inserted state, the arm portions 28a and 29a of the respective split cores 28 and 29 are inserted. ) Abuts on the stopper portion (not shown) formed in the core insertion hole 26a and the stopper portion (not shown) formed on the core support member 27, and the core support portion 35 formed on the bobbin 26. And the core support member 27 for positioning.

1 shows a cross section of the boost transformer 5. In FIG. 1, the first split core 28 and the second split core 29 inserted into the bobbin 26 are formed in the core insertion hole 26a and the core support member 27 of the bobbin 26. The core gap 40 is formed in contact with the stopper portion which is not in contact. In this case, the core gap 40 is located corresponding to approximately the center of the secondary winding 22.

The boosting transformer 5 constructed as described above is provided on the inside of the printed wiring board 4 with respect to the screw fixing part 41 (shown in FIGS. 4 and 5 only) formed on the supporting portions 33 and 34 of the bobbin 26. It is mounted on the printed wiring board 4 by screwing it. In this case, grooves 28b and 29b are formed on the outer surfaces of the first and second split cores 28 and 29, and the core bands 30 are fitted into the grooves 28a and 29b to thereby divide each division. The cores 28 and 29 are integrated with the bobbin 27. In addition, the core band 30 is to be soldered to the printed wiring board 4, and in the state where the boost transformer 5 is inclined to the printed wiring board 4, the respective divided cores 28 and 29 are inclined. It is supposed to be mounted.

On the other hand, the primary winding 19 and the secondary winding 22 of the boost transformer 5 are connected to a predetermined electronic component through a pattern formed on the printed wiring board 4.

That is, the primary winding 19 is connected to the common connection point of the switching element 14 of the switching unit 10 and the common connection point of the resonant capacitor 15 by soldering to the printed wiring board 4.

In addition, the terminal portion which is connected to the secondary winding 22 and protrudes from the bottom surface of the bobbin 26 is soldered to the printed wiring board 4 so that the common connection point of the high voltage condenser 20 of the high voltage rectifying portion 11 is patterned. It is connected with the common connection point of the high voltage diode 21.

The secondary winding 25 for cathode heating is connected to the common connection point of the high voltage capacitor 20 and the high voltage diode 21 through a pattern by soldering to the printed wiring board 4.

Next, the operation of the above configuration will be described.

When the start switch is operated while the commercial AC power is turned on, the inverter control unit 9 outputs a switching signal to the switching unit 10, so that the switching unit 10 sets the DC voltage at the rectifying unit 8 at 50 kV. Switch. At this time, in the on state of the first switching element 14, the current through the second resonant capacitor 15 flows to the primary winding 19 of the boosting transformer 5, and the first resonant capacitor 15 As it discharges, current flows. In the ON state of the second switching element 14, the current through the second resonant capacitor 15 flows in the opposite direction to the primary winding 19 of the boosting transformer 5, and the first resonant capacitor 15 The current flows in the opposite direction as).

In this way, since the high-frequency current of 50 mA flows through the primary winding 19 of the boosting transformer 5 in accordance with the switching operation of the switching element 14, the high-voltage high-frequency current according to the boost ratio is generated from the secondary winding 19. Is output. In addition, since the high frequency current is output from the secondary winding 25 for the cathode heating to the cathode 7b of the magnetron 7, the cathode 7b is heated.

At this time, since the series circuit composed of the capacitor 17 and the resistor 18 is connected to the output terminal of the switching section 10, the voltage change rate of the voltage waveform in the primary winding 19 of the boost transformer 5 is increased. The voltage change rate of this large portion (the portion where the absolute value of dV / dt is large) can be suppressed (see FIG. 7).

On the other hand, the onion double voltage rectifying circuit constituting the high voltage rectifier 11 performs a combination of half-wave voltage rectifier circuits, the high-voltage high-frequency current generated according to the step-up ratio in the secondary winding 22 of the boost transformer (5) Is increased by using charging of the high voltage capacitor 20 to output the high voltage DC voltage.

Then, when the magnetron 7 starts up in a state where a high-voltage DC voltage is applied to the magnetron 7 from the high-voltage rectifier 11, the magnetron 7 starts to oscillate and microwaves are irradiated from the magnetron 7 into the cooking chamber 2. do.

However, since the stray capacitance is generated in the secondary winding 22 of the boost transformer 5 as indicated by the broken line in FIG. 3, the voltage generated in the secondary winding 22 of the boost transformer 5 is the stray capacitance. There is a fear that unnecessary resonance, called ringing, may occur due to magnetic resonance with the magnetic resonance.

Fig. 8 shows the primary side voltage and secondary side voltage of the boost transformer 5 at the start of the magnetron. In addition, the voltage level between the primary side voltage and the secondary side voltage is different. In this case, ideally, the secondary voltage of the boost transformer 5 becomes a voltage obtained by multiplying the primary voltage by the boost ratio (indicated by a solid line in Fig. 8B), but when ringing occurs, the secondary winding voltage is ringing. (Indicated by a broken line in Fig. 8B), a voltage higher than the voltage which is supposed to be generated is generated, and the magnitude of the voltage is determined by a predetermined parameter. That is, the generated voltage of the ringing is determined by the primary voltage, the boost ratio and the Q value of the magnetic resonance. Among these, since the primary side voltage and the step-up ratio are determined by the conditions in the normal operation of the switching operation, only the Q value of the magnetic resonance is an independent parameter, and it is possible to suppress the generated voltage of the ringing by controlling the Q value of the magnetic resonance. Become.

Specifically, when the Q value of the magnetic resonance on the secondary winding 22 side of the boost transformer 5 is large, as shown in Fig. 9B, the ringing is large, but when the Q value of the magnetic resonance decreases, As shown in Fig. 9C, the ringing becomes small. Therefore, it can be seen that it is effective to reduce the Q value of the magnetic resonance to reduce the ringing.

Therefore, in this embodiment, the occurrence of ringing is suppressed by reducing the Q value of the magnetic resonance on the secondary side of the boost transformer 5 as follows.

That is, when focusing on the boosting transformer 5, the core gap 39 between the first and second split cores 28, 29 inserted into the bobbin 26, as shown in FIG. Since it is located on the 22) side, compared with the case where the core gap 39 is located on the primary winding 19 side, the magnetic coupling coefficient of the secondary winding 22 can be reduced, and the secondary winding 22 ), The magnetic resonance frequency moves to the high frequency side. Since the resistance of the secondary winding 22 becomes large by this, the Q value of the magnetic resonance of the secondary winding 22 of the boost transformer 5 becomes small, and generation | occurrence | production of ringing by magnetic resonance can be suppressed effectively.

In the experiment, when the core gap 39 is positioned on the secondary winding 22 side and the primary winding 19 side in the boost transformer 5, each core gap is formed as a primary winding ( It was confirmed that the leakage secondary inductance value can be reduced from 12 mH to 10 mH under the condition that the leakage inductance (primary winding inductance when the secondary winding 22 is opened) becomes the same value.

That is, since the leakage secondary inductance decreases, the resonance frequency on the secondary winding 22 side of the boost transformer 5 can be increased accordingly, so that the Q of the magnetic resonance can be relatively reduced.

According to this embodiment, the core gaps 39 of the first and second split cores 28 and 29 inserted into the core insertion holes 26a of the bobbin 26 of the boosting transformer 5 are closed. Since the leakage secondary inductance is made small by being located on the secondary winding 22 side, the magnetic resonance frequency of the secondary winding 22 side of the boost transformer 5 becomes high, and the Q value of the magnetic resonance can be relatively reduced. Can be. Therefore, ringing can be suppressed from occurring in the secondary winding 22 of the boost transformer 5 at the start of the magnetron, and a small one can be used as the boost transformer 5.

In this case, since the ringing occurring on the secondary side is suppressed without adjusting the primary side voltage, the boosting ratio of the boost transformer 5 is lowered and the cathode heating current of the magnetron 7 can be carried out without decreasing. Therefore, there is no problem that the startup time of the magnetron 7 becomes long.

In addition, since the core gap 39 between the first and second split cores 28 and 29 is located approximately in the center of the secondary winding 22 of the boost transformer 5, the secondary winding of the boost transformer 5 is increased. The resistance on the (22) side can be maximized, and the occurrence of ringing can be most suppressed.

Further, the secondary winding 22 of the boost transformer 5 so that the resonance frequency due to the stray capacitance on the secondary winding 22 side of the boost transformer 5 and the inductance is 10 times or more the switching frequency of the switching unit 10. Since the inductance on the) side is adjusted, the resonant frequency of the secondary winding 22 side of the boosting transformer 5 greatly deviates from the switching frequency of the switching unit 10, so that the core gap of the boosting transformer 5 described above ( The synergistic effect with the lowering of the Q value of the magnetic resonance due to the position adjustment in 39) can greatly reduce the Q value of the magnetic resonance and further suppress the occurrence of ringing.

In addition, since the onion double voltage rectifying circuit is used as the high voltage rectifying section 11, the high voltage rectifying section 11 serving as the secondary side of the boosting transformer 5 operates symmetrically with respect to both sides and the negative side, and the switching section of the primary circuit. All operations can be made symmetrical in accordance with the symmetrical operation in (10). Therefore, two switching elements 14 and two resonant capacitors 15 used in the half-bridge type switching unit 10 and two high voltage capacitors 20 and high voltage diodes 21 used in the high voltage rectifying unit 11 are provided. ) Can use the same element, and can manage parts easily.

In addition, one of the ends of the secondary winding 22 of the boosting transformer 5, the end of which is located on the primary winding 19 side, is a series circuit of the high voltage condenser 20 of the onion double voltage rectifying circuit constituting the high voltage rectifying unit 11. Since it is connected to the common connection of, the secondary winding 22 which is electrostatically coupled with the primary winding 19 is connected to the frame of the microwave at high frequency. As a result, voltage resonant energy at the magnetic resonance frequency of the secondary winding 22 is less likely to leak to the primary side, and the conversion efficiency of the boost transformer 5 can be prevented from being lowered.

In addition, since the secondary windings 22 of the boost transformer 5 are connected in series in a state in which they are divided into a plurality of unit winding portions 22a, the interlayer voltage of the entire secondary windings 22 is reduced and is equivalent. As a result, the capacitance decreases, so that the resistance to high frequency is increased, and the Q value of the magnetic resonance on the secondary winding side 22 side can be reduced.

In addition, since the primary winding of the boost transformer 5 is a litz wire in which eight or more element wires of 0.1 mm or less are combined, the ratio between the resistance component at the operating frequency and the resistance value at the magnetic resonance frequency of the secondary winding is ensured. The loss at the operating frequency can be made sufficiently small.

In addition, since a series circuit composed of a capacitor 17 and a resistor 18 is connected between the primary winding 19 of the boost transformer 5 and the resonance capacitor 15 of the half-bridge type switching unit 10. , The high frequency component with respect to the operating frequency of the voltage waveform applied to the primary winding 19 can be suppressed, the vibration amplitude with respect to the magnetic resonance frequency of the secondary winding 22 is reduced, and the voltage of the secondary winding 22 is reduced. The ringing component of the waveform can be suppressed. Therefore, the magnetron 7 can be started quickly without generating unnecessary high voltage.

The present invention is not limited to the above embodiment, and can be modified or expanded as follows.

A half-wave voltage rectifier circuit may be used as the high voltage rectifier 11.

A series circuit composed of the capacitor 17 and the resistor 18 may be connected between the primary winding 19 of the boost transformer 5.

As can be seen from the above description, according to the microwave oven of the present invention, the core gap is positioned on the secondary winding side between the first divided core and the second divided core inserted into the core insertion hole of the boost transformer. Since the magnetic coupling coefficient is reduced to move the magnetic resonance frequency on the secondary winding side to the high frequency side, the magnetron starting time is long while using a small insulation breakdown voltage as a boosting transformer in a microwave oven using a half-bridge type inverter power supply. It shows an excellent effect that can prevent losing.

Claims (8)

An inverter power source having a switching unit formed by connecting two switching elements and two resonant capacitors to a half bridge, a boost transformer for receiving a high frequency current from the inverter power source in a primary winding and boosting the secondary winding and outputting the same; In the microwave oven provided with a high-pressure rectifier for rectifying the boosted high-frequency high-frequency current and a magnetron for irradiating microwaves to the cooking chamber in the state that the high-voltage DC voltage rectified by the high-voltage rectifier is applied, The boost transformer has a bobbin wound in parallel with the primary winding and the secondary winding, and is inserted into the core insertion hole of the bobbin so that the core gap is located at the secondary winding side in the insertion state, and the first division core and the second division. Microwave oven comprising a core. The method of claim 1, The core gap of the boost transformer is located in correspondence with approximately the center of the secondary winding. The method of claim 1, 2. A microwave oven characterized in that the resonance frequency due to stray capacitance and inductance on the secondary winding side of a boost transformer is more than 10 times the switching frequency of the inverter power supply. The method of claim 1, The high-voltage rectifier is a microwave oven, characterized in that the onion double voltage rectifier circuit consisting of two high-pressure capacitors and two high-voltage diodes. The method of claim 4, wherein An end of the secondary winding of the boost transformer, the end of which is located on the primary winding side is connected to a common connection point of the series-connected high voltage capacitor constituting the onion double voltage rectifier circuit. The method of claim 1, The secondary winding of the boost transformer is formed by connecting a plurality of unit windings in series. The method of claim 1, The primary winding of the boost transformer is a microwave oven characterized in that it is formed of a litz wire combined with eight or more small wires of 0.1 mm or less. The method of claim 1, A microwave oven is characterized in that a series circuit consisting of a resistor and a capacitor is connected between a primary winding of a boost transformer or between a primary winding and a resonant capacitor of a half-bridge type inverter power supply.