JPS63178482A - 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 Field of the Invention The present invention relates to a high-frequency heating device that boosts high-frequency power using a step-up transformer and supplies the boosted high-frequency power to a magnetron.

Conventional technology In recent years, in order to reduce the size, weight, and cost of magnetron power supplies in high-frequency heating equipment, a power supply system has been considered in which the commercial frequency is first raised to a high frequency using an impark circuit, and then the voltage is boosted and applied to the magnetron. This is called an impark power source.8 Generally speaking, the magnetron's cathode stem is connected to the FF115 in order to prevent radio wave leakage from the input terminal side, that is, the cathode stem side.
The filter circuit is composed of a choke coil installed inside the shield coos and a feedthrough capacitor. However, if an inverter power source using a frequency of 20KH2 or more is used as the power source, a problem arises in that this high frequency power itself is suppressed by the filter circuit and becomes difficult to be supplied to the magnetron. Figure 4 is U.K. Showa 61-1.
07190 - Utility Model Application No. 107193, Utility Model Application No. 61-114691, and Utility Model Application No. 61-11469
This is a cross-sectional view of a main part of a high-frequency heating device using an inverter power source as seen in Publication No. 2, which was proposed for the purpose of solving the above problem. In FIG. 4, 14 is an oscillation tube, and the oscillation tube 14 is provided with an antenna 19 at one end and a cathode stem 20 at the opposite end, and each cathode stem 20 is provided with cathode terminals 21 and 22. . A shield case 23 formed of a non-magnetic 3# electric material surrounding the cathode stem 20 and electrically connected to the oscillation tube 14 completely isolates the inside and outside of the shield case 23 in terms of high frequency. The primary winding 6a of the step-up transformer 6 and the winding 1 around which the primary winding 6a of the step-up transformer 6 is wound are exposed through the wall surface 23 & of the shield case 23.
The secondary core 24 is configured such that a high-voltage secondary winding 6b, a low-voltage secondary winding 6C, and a secondary core 25 around which these are wound are disposed facing each other inside. In the case of this reference, the primary core 24 and the secondary core 25 are arranged so as to be electromagnetically coupled to the outside and inside through the wall surface 23a of the shield case 23, respectively, by mutual induction. This aims to simultaneously prevent leakage of high-frequency waves from the magnetron and supply high-frequency power to the magnetron.

Problems to be Solved by the Invention However, the above configuration has the following problems.

That is, according to the explanation in the reference, the shield case 23 surrounding the cathode stem 20 provided at one end of the oscillation tube 14 is made of a non-magnetic conductor, and the shield case 23 is made of a non-magnetic conductor. The primary and secondary sides of the step-up transformer are placed outside and inside. In this case, leakage of high frequency waves from the cathode stem 20 can certainly be prevented, but the primary and secondary sides of the step-up transformer 6 are also shielded at the same time, and no electromagnetic energy is transmitted, resulting in electromagnetic coupling due to mutual induction. There is no such thing as placement. This is because the wall surface 23a of the shield case 23 is made of a conductor, so that the magnetic field generated by the high frequency current flowing through the primary winding 6a of the step-up transformer 6 is transmitted through the shield case 23.
This is because an induced current, that is, an eddy current is generated on the wall surface 23a of the eddy current, and the electrical energy thereof is consumed as Joule heat due to this eddy current and is not transmitted to the secondary windings 6b and 6c of the step-up transformer 6. To explain this phenomenon from another perspective, the shield case 23 made of a conductor is equivalent to adding a short-circuited third secondary winding to the step-up transformer 6; You can think of it as a situation where most of the electrical energy is consumed by the short-circuit current flowing through the wire. In any case, it must be said that the structure of the cited example is a mere imaginary structure in that the shield case 23 has a function that cannot be realized by the technical means understood from the explanation of the cited example.

The present invention has achieved the problem that the cited reference sought to solve in a physically meaningful manner, and is capable of preventing leakage of high frequency waves from the cathode stem 20 side of the magnetron and of supplying power to the magnetron using a high frequency power source. The aim is to achieve both at the same time.

Means for Solving the Problems In order to solve the above-mentioned problems, the high frequency heating device of the present invention connects the secondary of the step-up transformer to the inside and outside of the shield case via the wall surface of the metal shield case that covers the cathode stem of the magnetron. The side and primary side are divided together with the core, and the wall of the shield case has radial slit holes centered on the two points where the primary side core and the secondary side core face each other. .

According to the above-described structure, the present invention can contain microwave and high frequency radio noise leaking from the cathode stem side of the magnetron within the shielding case, while also suppressing the secondary side circuit of the step-up transformer disposed within the shielding case. The primary side circuit placed outside the magnetron operates as a transformer, and the inverter can supply high-frequency power to the magnetron.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a sectional view of a main part of a high-frequency heating device according to an embodiment of the present invention, and FIG. 2 is a circuit configuration of a high-frequency heating device according to an embodiment of the present invention, including the main parts shown in FIG. 1. FIG.

In Fig. 2, power supplied by a commercial frequency power source 1 is rectified by a rectifier circuit 3, and then passed through a low-pass filter consisting of an inductance 5 and a capacitor 4, and is then passed through a capacitor 8, a diode 9, and a switching element. It is supplied to an impark circuit such as a certain transistor 10. The transistor 10 is turned on and off by a high frequency pulse outputted by a control circuit 11.

After being converted into a high frequency of about 20KH2 by the inverter circuit, the voltage supplied to the primary winding 7& of the step-up transformer 7 is induced in the secondary windings 7b and 7c as magnetron anode voltage and heater voltage, respectively. and is applied to the magnetron 13.

In FIG. 2, 14 is an oscillation tube which is the tube body of the magnetron, and this oscillation tube 14 has anti+t9 at one end,
A cathode stem 20t is provided at the end of the capacity. This cathode stem 2o has cathode terminals 21 and 22, respectively.
The shield case 28 that covers the cathode stem 20 has a lid 28 which is a part of its wall surface, and is composed of a shield plate 28b made of a non-magnetic metal plate and a structural support body 28c made of a dielectric material. The external pressure transformer 7 has its core separated into the inside and outside of the shield case 28 by the lid 28a, which is a part of the wall surface of the shield case 28, and the outer primary core 7P has a primary winding 7a. However, secondary windings 7b and 7c are wound around the inner secondary core 7s. Furthermore, the shield plate 28b has two points, centered on the opposing primary core 7P and secondary core 7S,
It has a configuration in which a plurality of radial slit holes 29 are provided. Regarding each winding, the already explained primary winding is supplied with a voltage converted to a high frequency by an inverter circuit, and the high voltage and low voltage generated in the secondary windings 7b and 7c are generated by a magnetron. is applied as the anode voltage and heater voltage through the cathode terminal 20.21.

FIG. 3 shows a detailed structure of the slit hole 29, and FIG. 3(a) shows the cover 28 of the shield case 28.
FIG. 3(bHc) is a plan view of FIG. 3(a) viewed from the outside, and is a cross-sectional view of the b-vi section and CC' section of FIG. 3(a), respectively, viewed from the direction of the arrow.

In the above configuration, the eddy current on the metal wall 28a of the shield case 28, which is induced by the magnetic field generated by the high frequency current flowing through the primary coil 7a of the step-up transformer 7, flows through the core 7P,
The current flows in a circumferential direction centered on two opposing points of 7S, and the radial slit holes 2 are provided approximately at right angles to the direction of this induced current, thus blocking the induced current.
It is 9. The presence of this slit hole 29 prevents the induced current flowing in the circumferential direction, and therefore the power consumption, which is consumed as Joule heat of this induced current, can be basically eliminated. As a result, the step-up transformer 7 fully exhibits its function as a step-up transformer, even though the primary side and the secondary side are divided by the lid 28a, which is a part of the wall surface of the shield case 28. One hand power sword stem 2
Regarding the leakage electromagnetic waves from the slit hole 29, the shield function is basically exerted, although the shielding performance is weakly reduced for frequencies where the length of the slit hole 29 is equal to or greater than I/4.

However, if higher shielding performance is required, the slit hole 29 may be divided into shorter parts, or in some cases, a second shield plate made of a non-magnetic metal plate may be inserted between the shield plate 28b and an insulating sheet. This shield plate is provided with radial slit holes similarly to the shield plate 28b, and the slit is located between adjacent slit holes 29 of the shield plate 28b. By adopting such a configuration, it is possible to improve the shielding performance of the shield case 28 while maintaining the function of the step-up transformer 7.

As can be understood from the above description, according to the configuration of the embodiment described above, the shield case 28 has a function of preventing leakage of high frequency waves from the cathode stem 2o side of the magnetron, and the wall surface of the shield case 28 The divided step-up transformer 7 also fully exhibits its function as a transformer.

As described in the detailed description of the invention, the high frequency heating device of the present invention provides the following effects.

(1) The microwave and high frequency radio noise leaking from the magnetron's cathode stem side can be contained within the shielding case, while the secondary circuit of the step-up transformer placed inside the shielding case and the primary side circuit placed outside. The two act as a transformer, and the impark high-frequency power can be efficiently supplied to the magnetron.

(2) As a result, it is possible to eliminate the filter circuit consisting of inductance and capacitance that was conventionally installed inside the shield case of the magnetron to prevent high-frequency leakage, and therefore the voltage drop and power loss caused by this filter circuit can be eliminated. Furthermore, since the anode voltage of the magnetron is a high voltage of around 4KV, it is possible to reduce the cost of capacitance and inductance, which are conventionally high in voltage and therefore expensive.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the main parts of a high-frequency heating device according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing the circuit configuration of the same high-frequency heating device, and Fig. 3 (, j to (C) are sectional views of the same lid Fig. 4 is a cross-sectional view of main parts of a conventional high-frequency heating device. 7...Step-up transformer, 7P...Primary side core, 7S... ...Secondary side core, 28...
Shield cous, 28a... Lid, 28b...
...Shield plate, 29...Slit hole. Name of agent: Patent attorney Toshio Nakao and one other person C
-Low pressure 2 you alley Figure 1'/P/ZD core Figure 3b? ? Figure 4

Claims (1)

[Claims] A magnetron, a high frequency inverter circuit, a primary winding connected to the output thereof, a high voltage secondary winding that supplies the anode voltage of the magnetron, a low voltage secondary winding that supplies the cathode voltage of the magnetron, and these 1 It consists of a step-up transformer consisting of a core around which a secondary winding and a secondary winding are wound, and a metal shield case that covers the cathode stem portion of the magnetron. It is divided into an outside and an inside, with the outside as a primary core and the inside as a secondary core, and the primary and secondary windings are wound around each of the primary and secondary cores. A high-frequency heating device with slit holes in the opposing walls of the shield case.