JPS62296389A - Radio frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention Industrial Application Field The present invention relates to a high-frequency heating device for performing so-called dielectric heating such as a microwave oven, and more specifically, the present invention relates to a high-frequency heating device for performing so-called dielectric heating such as a microwave oven. This invention relates to an improvement in a high-frequency heating device configured to generate high-frequency power using an inverter and boost the voltage using a step-up transformer to drive a magnetron.

BACKGROUND OF THE INVENTION Various configurations of high-frequency heating devices using this method have been proposed in order to reduce the size, weight, or cost of the power transformer.

FIG. 5 is a circuit diagram of a conventional high frequency heating device. Fifth
In the figure, the power from commercial power supply 1 is connected to diode bridge 2.
A unidirectional power source is formed. 3 is an inductor, and 4 is a capacitor, which serves as a filter for the high frequency switching operation of the inverter.

The inverter is composed of a resonant capacitor 5, a step-up transformer 6, a transistor 7, a diode 8, and a drive circuit 9. The transistor 7 performs a switching operation with a predetermined cycle and duty (ie, on-off time ratio) by a base current supplied from the drive circuit 9. As a result, the current 1c/1d as shown in FIG. 6(a), that is, the collector current 1c of the transistor 7 and the current 1d of the diode 8
flows. On the other hand, when the transistor 7 is off, a voltage Vce as shown in FIG. 6(b) is generated between C and E of the transistor 7 due to resonance between the capacitor 5 and the primary winding 1o.

Therefore, a current as shown in FIG. 6(c) flows through the primary winding 1o, and high frequency power is generated at both ends of the primary winding 1o.

Therefore, high frequency power and high frequency low voltage power are generated in the secondary winding 11 and the tertiary winding 12, respectively. This high frequency high voltage power is rectified by a capacitor 13 and a diode 14 and is supplied between the anode and cathode of the magnetron 15, while the high frequency low power is supplied to the cathode heater.

Therefore, the magnetron 15 oscillates and dielectric heating becomes possible. The magnetron 15 includes a magnetron main body 15a and a capacitor 16.1 that constitutes a filter.
7.18 and a choke coil 19.20. In such a configuration, the core cross-sectional area of the step-up transformer 6 becomes smaller as the frequency of the power supplied to both ends of the primary winding 10 becomes higher.
When operating at a frequency of about Hz to 100kHz, the weight and size of the step-up transformer can be reduced from a few minutes to a dozen times less than when boosting the voltage at the commercial power frequency, making it possible to reduce the cost of the power supply section. It has the following characteristics. Generally, transformers that handle large amounts of power are large because the windings generate heat due to copper loss and the core generates heat due to hysteresis loss. Therefore, various configurations have been proposed for miniaturization.

FIG. 7 shows a cross-sectional view of a conventional high frequency transformer. In the figure, 21 is a ferrite core a, 22 is a ferrite core b, and is held down by a fastener 23. 24 is the primary winding of the transformer, and 25 is the secondary winding. 26ba3
The next winding supplies power to the magnetron's cathode heater.

FIG. 8 shows the frequency characteristics of copper loss. As shown in Figure 8, as the frequency increases, resistance increases due to the skin effect and losses increase, causing the windings to overheat abnormally and burn the insulation film of the wires, making it impossible to maintain insulation between the wires. It may disappear.

Therefore, the influence of the skin effect is reduced by using a so-called litz wire, which is a bundle of thin copper wires, for the primary winding 24.

On the other hand, the 2'-order winding 25 has line-to-line withstand voltage and is wound in multiple layers in order to save space. Face treatment is applied to increase the withstand voltage between each winding and improve heat dissipation.

The tertiary winding 26 is thick and has a thick insulating film 27 in order to supply a high voltage and a large current.

Problems to be Solved by the Invention However, such conventional high frequency heating devices have the following drawbacks.

In the power transformer of the high-frequency heating device, in order to supply power to the magnetron heater, the tertiary winding 26 must have a large wire diameter and a high withstand voltage.

Therefore, it was necessary to increase the cross-sectional area of the core 22 and the insulating material 28 used between the primary winding 24 and the tertiary winding 26. This has resulted in problems in that miniaturization of the transformer has been hindered and costs have also increased. Furthermore, as the frequency to be handled becomes higher, the loss resistance of the winding cannot be reduced even if the cross-sectional area is increased simply by increasing the wire diameter due to the influence of the skin effect, and there is a drawback that reliability is significantly lowered due to heat generation.

Means for Solving the Problems The present invention has been made to solve the drawbacks of such conventional high frequency heating devices, and is a high frequency heating device constructed by the means described below.

In other words, a power source obtained from a commercial power source, etc., and at least one
a power converter for generating high-frequency power having two semiconductor switches and driving means thereof; a magnetron for heating food or fluid; and a high-frequency transformer for supplying the output of the power converter to the magnetron;
The high frequency transformer includes a core, a primary winding, a secondary winding, and a tertiary winding, and the tertiary winding is a flat conductor wound thereon.

Effects The present invention has the following effects due to the above configuration. That is, in the high-frequency heating device of the present invention, since the tertiary winding is composed of a flat conductor, the winding can be wound in a narrow space, and the transformer can be easily miniaturized.

Furthermore, since the insulation distance can be widened by using a flat plate, a high-frequency heating device with high reliability of the transformer can be realized. Furthermore, since flat conductors are less affected by the skin effect, the cross-sectional area of the winding can be made smaller, and the transformer can be made smaller.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a circuit diagram of a high frequency heating device according to an embodiment of the present invention. In FIG. 1, the same components as in FIG. 5 are given the same reference numerals. FIG. 2 is a sectional view of the high voltage transformer shown in FIG. 1. In FIG. 2, the cores 28 and 29 are made of ferrite and form a magnetic path with a gap 30. The cores 28, 29 are secured with fasteners 31. 3
2 uses a litz wire for the primary winding. 33 is a secondary winding wound in alignment. An insulating material 34 is provided between the primary winding 32 and the secondary winding 33. Also, the secondary winding 3
An insulating tape 35 is wrapped around the winding 3, and an insulating material 36 is applied to the creeping surface of the winding.

A tertiary winding 37 is covered with an insulating material 34 and wound in a space between the secondary winding 33 and the core. FIG. 3 shows the flat conductor portion of the tertiary winding 37. 38 is a winding portion, and a lead wire 39 is welded to the end thereof. In the above configuration, the tertiary winding 3
7 is composed of a flat plate, so the secondary winding 33 and the core 28
The transformer can be placed in the gap between the transformer and the transformer, making it possible to reduce the overall size of the transformer. Furthermore, when operating a transformer at high frequencies, copper loss increases due to the increased resistance due to the skin effect of the windings, but since a flat plate is used, the influence of the skin effect is small and losses due to heat generation can be suppressed. .

Next, another embodiment of the present invention is shown in FIG. FIG. 4 is a sectional view of the transformer, and the same components as in FIG. 2 are given the same reference numerals.

In FIG. 4, the tertiary winding 40 has a concentric ring shape and is provided in the gap between the primary winding 32 and the core 29. FIG. 5 shows the flat conductor portion of the tertiary winding 40 of FIG. 4. In FIG. 5, 41 is a ring-shaped winding portion, and 42 is a lead wire. In the configurations shown in FIGS. 4 and 5, the windings can be easily made by punching out a flat plate.

As described above, if the heater winding of the transformer of the high-frequency heating device is made of a flat conductor, a smaller transformer with less heat loss due to the skin effect can be realized, and the cost of the device can be reduced.

Effects of the Invention As described above, according to the high frequency heating device of the present invention, the following effects can be obtained.

(1) Since the tertiary winding of the transformer generates less heat, an insulator with a low heat resistance grade can be used and costs can be reduced.

■ The space required for the tertiary winding is small, the current density in the wire can be higher than before, and a smaller transformer can be realized, resulting in lower equipment costs.

■ Since the amount of heat generated is small, the cooling structure of the high-frequency heating device can be simplified.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the high frequency heating device used in the present invention, Figure 2 is a circuit diagram of the high frequency heating device used in the present invention.
The figure is a cross-sectional view of the transformer of the high-frequency heating device according to the first embodiment of the present invention, FIG. 3 is a perspective view of the tertiary winding of the high-frequency heating device according to the first embodiment of the present invention, and FIG. A cross-sectional view of a transformer of a high-frequency heating device in a second embodiment,
FIG. 5 is a plan view of the tertiary winding of the high-frequency heating device according to the second embodiment of the present invention, FIG. 6 is a circuit diagram of the high-frequency heating device in the conventional example, and FIG. 7 is a circuit diagram of the high-frequency heating device in the conventional example. FIG. 8 is a sectional view of a transformer of a conventional high-frequency heating device, and FIG. 9 is a frequency characteristic diagram of increased resistance due to the skin effect of copper wire. 1...Commercial power supply, 6...Transformer, 7...
...Transistor, 15...Magnetron,
28.29...Core, 32...Primary winding, 33...Secondary winding, 37...Third winding. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Figure 5 Figure 6 Figure 7

Claims (2)

[Claims] (1) A power source obtained from a commercial power source, etc., and at least one
a power converter for generating high-frequency power having two semiconductor switches and driving means thereof; a magnetron for heating food or fluid; and a high-frequency transformer for supplying the output of the power converter to the magnetron;
The high frequency transformer includes a core, a primary winding, a secondary winding, and a tertiary winding, and the tertiary winding is a high frequency heating device in which a flat conductor is wound. (2) The high-frequency heating device according to claim 1, wherein a primary winding, a secondary winding, and a tertiary winding are arranged in parallel on the core, and a space is provided between each winding.