JPS63208210A - Transformer for magnetron power source - Google Patents

Abstract

PURPOSE:To obtain always a stable microwave output from a magnetron which is operated under various environmental conditions by a method wherein a core is composed of a plurality of types of soft ferrite whose temperature characteristics of permeabilities compensate each other in the operation temperature range. CONSTITUTION:A magnetron power source transformer elevates the voltage of an inverter electric source with a relatively high frequency and supplies the high voltage to a magnetron. A core which is composed of a plurality of types of soft ferrite whose temperature characteristics of permeabilities compensate each other in the temperature range of the transformer operation is used as the core of the transformer. With this constitution, even if the magnetron power source transformer is operated in the wide temperature range, the fluctuation or degradation of the secondary induced voltage caused by the temperature dependent permeability variation can be avoided and a stable output can be always taken out from the magnetron.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetron power supply transformer that has small fluctuations in alternating magnetic flux due to temperature rise, has a high rated temperature, is small in size, and is lightweight.

[Conventional technology]

For example, when supplying high-voltage power to a home microwave oven's magnetron, etc., if you try to step up the voltage while maintaining the commercial AC frequency, you will have to use a large and heavy transformer.

For this reason, conventionally, the DC obtained by rectifying a commercial AC power source is interrupted by an appropriate switching means, converted to high-frequency AC, boosted by a small and lightweight transformer, and then rectified again to generate high-voltage DC. Development of an inverter-type magnetron power supply to supply the magnetron has been progressing.

In the case of an inverter type magnetron power supply like the one above,
Since the main purpose is to make transformers smaller and lighter and to make output control easier, the high frequency is generally around several tens of kHz, and step-up transformers are made of soft ferromagnetic material. Miniaturization is achieved by using a magnetic core with a considerable magnetic flux density. Generally, when the device is intended to be used in a household electric appliance such as a microwave oven, low cost is extremely important, so the entire device is required to be as small and lightweight as possible from a safety standpoint. Therefore, even under a relatively favorable environment, the magnetron power supply transformer is used at a temperature of about 20° C., which is equivalent to room temperature, at the time of initial operation, and at about 60 to 80° C. during operation.

On the other hand, in a magnetron, almost no current flows until the applied voltage reaches a predetermined high voltage determined by the product type, and once that voltage is reached, the current suddenly begins to flow, and after that, it responds to relatively small fluctuations in the applied voltage. It has a unique operating characteristic as shown in Fig. 2, in which the input current fluctuates greatly even when the input current is changed. Because of these characteristics, even if the output voltage of the power transformer varies relatively slightly, the output of the magnetron will vary considerably.

When a magnetron power supply transformer is used in a household microwave oven, for example, it has a high voltage of about 4 kV and a microwave output of about 5 kV.
00W must be generated, but since the design is as short as possible as described above, the temperature of the innermost magnetic core increases significantly due to heat generation due to copper loss in the windings and iron loss in the magnetic core.On the other hand, the magnetron Because of the above-mentioned operating characteristics, it is quite difficult to extract stable microwave output from the magnetron under various usage environments. Incidentally, related devices of this type include, for example, those described in Japanese Utility Model Application Publication No. 50-29552.

[Problem that the invention seeks to solve]

The present invention solves the problems of the conventional magnetron power transformer and provides a magnetron power transformer that can be used in a wide variety of environments and always provide stable microwave output from the magnetron. purpose.

[Means for solving problems]

In order to solve the above problems, the present invention provides a magnetron power supply transformer that is combined with an inverter power supply to step up the voltage at a relatively high frequency and supply high voltage to the magnetron, within the temperature range in which this transformer is used. We decided to use a magnetic core that combines multiple types of soft ferrite whose magnetic permeability changes with temperature compensate for each other.

[Effect]

By taking the above measures, even if the magnetron power transformer is used over a wide temperature range, it will be possible to prevent the secondary side induced voltage from fluctuating or decreasing due to changes in magnetic permeability due to temperature. This makes it possible to always obtain stable output from the magnetron.

Among the magnetic materials currently in widespread use, ferrite is known to be superior in terms of performance to price for most applications, and fortunately, the temperature characteristics of magnetic permeability are also Various things have been obtained.

〔Example〕

FIG. 1 is an external view of one embodiment of the present invention, in which 1 is a primary coil, 2 is a secondary high voltage coil, and 3 is two types of ferrite magnetic cores 3a, 3 whose temperature coefficients act to compensate for each other.
The magnetic core b is a combination of magnetic cores, and the magnetic core 4 is a bypass magnetic core for passing leakage magnetic flux. Although not visible in this figure, there are other bypass cores as well. It is a well-known fact that this type of transformer is of a leakage type.

The magnetic core 3a is made of ferrite having a positive temperature coefficient as shown in FIG. 3, such as GP-5 manufactured by Nippon Ferrite Co., Ltd.
+0.556χ/'C), and the magnetic core 3b is, for example, the third
A ferrite with a negative temperature coefficient as shown in the figure, for example 5B-5 (-0,407χ/'C) manufactured by Nippon Ferrite Co., Ltd.
shall be.

By setting the area to A times the cross-sectional area of the magnetic core 3a, the overall temperature coefficient of the magnetic core 3 becomes almost zero as they are mutually compensated for by using the above two types of ferrite in combination.
Very stable characteristics were obtained in the above-mentioned usage environment, that is, with respect to temperature changes within the range of about 20 to 80°C.

As shown in Figure 2, the characteristics of the magnetron used in combination with this example are as follows: When the voltage changes by 10% around 4kV, the current changes from almost 0 to 300mA, and the output of the magnetron also changes from almost 0 to 90mA. do.

When using a conventional transformer with a magnetic core made of one type of magnetic material in an inverter power supply for a microwave oven, a feedback circuit was installed to stabilize the output, but this significantly increased the cost. . In the present invention, the magnetic core of the transformer is formed of two types of materials, but the increased cost is small compared to the case where a feedback circuit is provided.

〔Effect of the invention〕

As explained above, according to the present invention, by using a relatively inexpensive transformer that uses two types of ferrite as magnetic core materials for the magnetron power supply, the magnetron can be operated without using an output control means such as a feedback circuit. It is possible to obtain stable output against temperature changes.

[Brief explanation of the drawing]

Fig. 1 is an external view of one embodiment of the present invention, Fig. 2 is a side view of the operating characteristics of the magnetron, and Fig. 3 is a diagram showing the temperature coefficient of the magnetron.
FIG. 3 is a diagram showing the temperature characteristics of different types of ferrite. i -111 primary coil, 2-・-secondary coil, 3
．． 3a, 3b--magnetic core, 4--magnetic core for bypass. Fig. 1 Goo - Ingo fill

Claims (1)

[Claims] 1. When converting a commercial AC power supply into high-frequency AC using an inverter circuit, boosting the voltage using a small, lightweight transformer, and rectifying it again to supply power to the magnetron, in the magnetron power supply transformer used for boosting the voltage, A magnetron power supply transformer characterized in that a magnetic core is formed by combining multiple types of soft ferrite whose magnetic permeability temperature change characteristics act to compensate for each other within the temperature range in which the transformer is used.