JPH01292789A - Inverter power supply for magnetron - Google Patents

Abstract

PURPOSE:To reduce cost by intentionally generating a leakage magnetic flux in the inside of a transformer connected to an inverter circuit while making a winding on the primary side or on the secondary side of the transformer to have inductance acting as a choke coil. CONSTITUTION:A high-tention transformer 3 uses two places of ferrite cores 12 while being provided with a gap so as to adjust inductance. A primary winding 9 is wound only about a core 12 on one side so that many leakage magnetic fluxes may be generated in the part of a gap. In this way, leakage inductance, which similarly acts to the case of connecting a high-frequency choke to the primary side, can be obtained. Further, a secondary winding 10 is wound about the whole of the cores 12 on both sides so that the leakage magnetic fluxes from the gap part may be reduced. Thereby, a special high-frequency choke coil is not needed so that low cost can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an economical inverter power source for a magnetron suitable for a dielectric heating device using a magnetron, such as a microwave oven.

[Prior Art] In order to make the magnetron operate stably, it is necessary to configure a resonant circuit on the power supply side in order to prevent the peak current of the magnetron from becoming unnecessarily large. In an inverter power supply for a magnetron, high voltage generated in a resonant circuit is used when a switching element is cut off (for example, Sanyo Electric Technical Report: Design of an inverter circuit for a magnetron using rCAD J, September 1981 issue, etc.). for that.

- [Problem to be solved by the invention] When inserting a high-frequency choke on the secondary side of a step-up transformer, a high-frequency choke with adequate insulation and withstand voltage is required, and when inserting it on the primary side, Although it is not so high in terms of withstand voltage, the high-frequency primary current is large, so litz wire must be used as a measure against heat generation. In this way, in the conventional method, high frequency chokes are expensive,
It was increasing the cost.

An object of the present invention is to provide an economical inverter power supply for a magnetron that does not require a special high-frequency choke.

[Means to solve the problem] In order to achieve the above object, the present invention.

By intentionally generating leakage magnetic flux inside the transformer connected to the inverter circuit, the transformer's primary or secondary windings are provided with inductance that acts like a choke coil.

[Function] Conventionally, in normal cases, only mutual inductance exists in a transformer, and ideally, leakage inductance entering the primary side or the secondary side is extremely small.

However, in order to make the transformer act like a choke coil as in the present invention, the shape of the transformer's magnetic core and the position of the windings relative to it must be taken into account, and both the primary and secondary windings must be chained. It is necessary to increase the leakage magnetic flux that does not intersect and only interlinks in one direction. Leakage inductance due to leakage magnetic flux enters in series with the winding that generates leakage magnetic flux.

Therefore, if you use a winding method that increases the leakage flux, you can create a larger one-cage inductance.For example, if you use a winding method that increases the leakage flux of only the primary winding, you can It is possible to give it the same characteristics as when it is placed on the side. Single-cage transformers like the one described above have been used in the past for special purposes, but there is no precedent for this in inverter power supplies for magnetrons.

[Example] FIG. 1 is a diagram illustrating the principle of an inverter power supply for a magnetron using a leakage transformer according to the present invention.

Reference numeral 1 denotes a bridge that rectifies commercial alternating current, the positive side of which is connected to the primary winding of a high voltage (step-up) transformer 3, and then returns to one side through a switching element 2. A resonance capacitor 4 is connected in parallel to the switching element, and a high voltage is generated in the secondary winding 10 of the high voltage transformer 3 by turning the switching element 2 on and off by a drive circuit. A high voltage capacitor 6 and a voltage doubler rectifier diode 7 are connected to the secondary winding 10, and a high voltage is applied to the magnetron 5. The magnetron filament is
A voltage is applied by a filament winding 11 wound around a high voltage transformer 3.

Further, 8 is a diode for preventing 0M charging and discharging.

The high voltage transformer 3 uses two ferrite cores 12.

A gap is provided to adjust the inductance.

The primary winding is wound around only one core so that a large amount of leakage flux occurs in the gap. In this way, a one-cage inductance can be obtained that has the same effect as connecting a high-frequency choke to the primary side.

The secondary winding is wound around the entire core on both sides to reduce magnetic flux leakage from the gap.

By winding the filament winding across both cores, the degree of coupling with the secondary winding is improved.

The operation of the above transformer will be explained with reference to prior art circuits. FIG. 7 shows a circuit example of a conventional magnetron inverter power supply in which a high frequency circuit is separately connected to the secondary side of a high voltage transformer. In the figure, 13 is a high frequency choke. FIG. 8 shows an example of a conventional circuit in which a high frequency circuit 13 is separately connected to the primary side of a high voltage transformer. Both circuits require a high frequency choke 13, which is clearly different from the circuit of the present invention shown in FIG. 1, which does not use a high frequency choke.

Next, the differences between the conventional circuit and the high voltage transformer of the present invention will be explained in the second to
This will be explained using Figure 6.

FIG. 2 shows a high voltage transformer used in a conventional circuit. The primary and secondary windings have leakage flux φ,.

The winding method is used to reduce φ2, and the leakage inductance L on the primary and secondary sides in the equivalent circuit is extremely small and can be ignored in practice.

Figure 3 shows the primary and secondary windings wound on separate cores.
In this method, the leakage magnetic flux φ□, φ2 at the gap increases, and the leakage inductance L1 shown in the equivalent circuit increases.
, L2 have large values. Furthermore, if a magnetic material is inserted into the leakage flux path, an even larger cage inductance can be obtained.

FIG. 4 is a diagram showing the principle of the transformer used in the embodiment of the present invention shown in FIG. The primary winding is wound around only one core, and the secondary winding is wound around both cores.

When wound in this way, the primary side glue and cage inductance L
It is possible to make i large and to make it small L8 on the secondary side, and in practice it works the same as adding a high frequency choke to the primary side.

FIG. 5 shows a method of increasing the leakage inductance on the secondary side, and the principle is the same.

FIG. 6 shows a case where a UI type core is used.

In the case of any core, the value of leakage inductance is determined not only by the gear Φ position, coil position, and coil winding diameter, but also by the amount of overlap between the primary and secondary coils or the winding density of the secondary coil. Use a method such as adding more to one core and less to the other core.

As a result of using the leakage transformer according to the present invention, it has become possible to operate the magnetron stably without using a separate high-frequency choke.

[Effects of the Invention] As explained above, according to the present invention, a simple and low-cost inverter power supply for a magnetron that does not require a special high-frequency choke coil can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of an inverter power supply for a magnetron using a leakage transformer according to the present invention, and Fig. 2 -
FIG. 5 is a diagram explaining the present invention in detail, FIG. 6 is a diagram showing a technical example similar to the present invention, and FIGS. 7 and 8 are diagrams showing a conventional technique using a separate high-frequency choke coil. 1... Rectifier bridge, 2... Switching element. 3...High voltage transformer, 4...Resonance capacitor,
5...Magnetron, 6...High voltage capacitor,
7... Voltage doubler rectifier diode, 8... 0M charge/discharge prevention diode, 11... Filament winding, 128 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 3-West ft pressure Work 4-f 1st & 1st control tape 5-Macnetron 11-5 top 12-7 Gorai Y core Fig. 4-1 1st wing 5-72th stop Ron 6-voltage control 2nd stage

Claims (1)

[Claims of Claims] 1. Direct current obtained by rectifying a commercial AC power source is intermittently converted into AC with a frequency much higher than the commercial AC frequency using a switching element, and the converted AC is input to the primary side of a transformer. In an inverter power supply for a magnetron that supplies power to the magnetron from the secondary side of the transformer, by intentionally creating leakage magnetic flux inside the transformer, the winding on the primary or secondary side of the transformer is An inverter power supply for a magnetron characterized by having a working inductance. 2. A patent claim in which an EE type ferrite core is used as the magnetic core of the transformer, the primary winding is wound around the middle leg of one E type core, and the secondary winding is wound around the middle legs of two E type cores. Inverter power supply for magnetrons described in scope 1. 3. The inverter power supply for a magnetron according to claim 1, wherein the secondary winding for feeding power to the filament is wound across both middle legs of the two E-shaped cores of the transformer. 4. The inverter power supply for a magnetron according to claim 1, wherein the secondary winding is wound with a different number of turns around each of the two E-type cores.