JPS63261695A - Electric source for magnetron - 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 Industrial Application] The present invention relates to a power supply device for a magnetron that reduces the rise time required for the cathode temperature of the magnetron to reach the operating temperature after power is turned on.

[Conventional technology]

A method of reducing the size and weight of a power transformer and facilitating output control by using a switching power supply with a high frequency as a power supply device for a magnetron is disclosed, for example, in Japanese Utility Model Publication No. 61-31512 and Japanese Patent Laid-Open No. 60-25058.
Although it is stated in Publication No. 8, etc., it has not yet been widely put into practical use.One reason for this current situation is that, as stated in Publication No. 61-31512, the cathode side exit of the magnetron is It is also necessary to consider the characteristics of the filter, which is made up of an inductor and a capacitor and is installed in the microwave to prevent microwaves from leaking and becoming a noise source.

When operating the magnetron with a switching power supply,
It is not considered how the inductor and capacitor of the filter affect the cathode heating operation of the magnetron, and if you try to drive the magnetron at a switching power supply frequency higher than the commercial power supply frequency, the inductor and capacitor of the filter will be inserted into the cathode outlet of the magnetron. The impedance of the filter inductor increases in proportion to the frequency (therefore, the cathode heating current becomes more difficult to flow than at the commercial frequency. In order to cancel the effect of this impedance increase and obtain a sufficient cathode temperature, Even if the output voltage of the cathode circuit is increased, the rise time from turning on the power until the cathode reaches the operating temperature is longer than when heating at commercial frequency as in the past. To be more specific, for example, in the case of conventional heating at a commercial frequency, microwave output can be obtained in about 3 seconds after the power is turned on (the temperature at which the cathode emits the necessary amount of electrons is reached). On the other hand, when a switching power supply is used, the rise time is about 6 seconds, which is about twice as long.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetron power supply device that solves the problem that the cathode temperature rise time becomes long when the conventional switching power supply is used.

[Means for solving problems]

In order to solve the above problems, in the present invention, a capacitor and an inductor are inserted in series with a low-voltage winding circuit for magnetron cathode heating provided on the secondary side of a power transformer that is small and lightweight with a high switching frequency. The constants of these elements are such that the circuit enters a series resonance state at the high switching frequency, the reactance component almost disappears, and the impedance of the cathode heating circuit seen from the transformer side is almost only the resistance of the magnetron's cathode. I decided to set it up like this.

(For 1 unit) Normally, the switching frequency to be used in a magnetron power supply is, for example, about 1,000 times the commercial power supply frequency, and the microwave frequency is, for example, about tens of thousands of times compared to the switching frequency. Therefore, the value of the inductor of the filter conventionally installed at the outlet of the magnetron's cathode heating circuit to suppress microwave leakage is
In terms of absolute value, it is extremely small.

On the other hand, the cathode of a magnetron, for example in the case of a microwave oven, is made of a tungsten filament, and has an ohm of approximately 0.03 ohm at room temperature and approximately 0.0 ohm at the operating temperature (approximately 1500 degrees Celsius).
It has a resistance of about 3 ohms. The value of the filtering inductor is small and at commercial power frequency it is still negligible compared to the small room temperature resistance of the filament, but at the switching frequency the impedance of this inductor is about 1000 at commercial frequency. This is not only the room temperature resistance of the filament, but also several times the resistance value at the operating temperature, which is about 10 times higher. This will approximately double the time it takes to rise. When heating the magnetron cathode at the commercial power frequency, the resistance at room temperature is small, so once the power is turned on, a large current, so-called inrush current, which reaches a value nearly 10 times the current value during continuous operation, flows. Thereafter, the temperature of the filament gradually rises, the resistance of the filament increases, and the current value gradually decreases, and when the current value reaches the value for continued operation, an equilibrium state is reached. If the impedance of the cathode heating circuit is large, the inrush current value is kept small, the amount of heating power is kept small, and the rise time until the temperature of the filament having a certain heat capacity reaches the operating temperature becomes long.

By making series resonance occur in the cathode heating circuit at the switching frequency according to the present invention, the effect of the actance component on the cathode heating circuit is almost eliminated, and the rise time of the heating current is determined only by the resistance of the cathode filament. Become,
In other words, the rise time is almost the same as when heating with a commercial power source.

〔Example〕

FIG. 1 shows a schematic circuit diagram of an embodiment of the present invention.
is a transformer, 2 is a series inductor according to the present invention, 3 is a series capacitor according to the present invention, 4 is a magnetron with a filter, 5 is a filter capacitor, 6 is a filter inductor, 7 is a filament of the magnetron, and B is a direct current This is a switching element that opens and closes to convert alternating current at a high frequency of 50 kHz. The high voltage circuit of this embodiment is a voltage doubler rectifier circuit. Also, when controlling the output power of the magnetron using a switching power supply, the filament heating power is not interrupted in long cycles (as was done previously), so once the filament reaches operating temperature, Thereafter, the heat capacity of the filament maintains approximately the desired operating temperature. In this example, the resistance value of the filament at room temperature is about 0.03Ω, and the resistance value at operating temperature is about 0.3Ω. Although the inductance value of the filter inductor 6 is small as mentioned above, it is still 50k.
At a switching frequency of 1Lz, the total impedance due to inductance in the cathode heating circuit is approximately 1.5Ω (note that the resistance and inductance of the transformer winding that supplies voltage to the cathode heating circuit can be ignored), so The impedance of the entire cathode heating circuit is overwhelmingly large due to inductance, and even when the filament resistance value is 0.3Ω, the combined impedance is 1.53Ω.

If you try to make the desired current of 11A flow through the filament without implementing the present invention, the electromotive force required for this circuit would be about 3.3V at the commercial power frequency, but if the switching frequency is 50kHz, the electromotive force required for this circuit would be about 3.3V. Approximately 17V is required for this, and on top of that, the current that flows immediately after the power is turned on is approximately 11A, so the time it takes for the filament to reach a temperature sufficient to emit electrons is extended to approximately 6 seconds. ,
When heating with a switching power supply, depending on the method, if the peak value is constant, 50 or 60Hz? There are various cases, such as when the switching frequency is modulated, when the switching frequency is constant, and when the switching frequency fluctuates to some extent, but in all cases, the total impedance of the cathode heating circuit is approximately 1000 times the impedance of the inductance. The impedance value of the filter capacitor is still sufficiently large even at a switching frequency of 50 kHz, so that no effect such as bypassing of the filament current occurs.

However, according to the present invention, if the cathode heating circuit is brought into a series resonant state at the switching frequency, the actance of this circuit becomes almost zero, which is almost the same as heating at the commercial power frequency. In the case of a method in which the switching frequency varies, it is sufficient to create a series resonance state at a frequency that is most frequently used in practical conditions. For example, in order to achieve a series resonance state at approximately 50 kHz, if the inductance is approximately 1.5 Ω, it is sufficient to insert a capacitor of approximately 2.1 μF.

Such a capacitor can be conveniently handled if it is installed as shown in FIG. 2 inside a filter case, which has conventionally been handled as an integral part of a magnetron.

〔Effect of the invention〕

As described above, according to the present invention, when a switching power supply is used, it is possible to prevent an increase in the rise time when starting the magnetron.

[Brief explanation of the drawing]

FIG. 1 is a schematic circuit diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the insertion position of a series capacitor according to the present invention. 2-Series inductor, 3...Series capacitor, 5
- Filter capacitor, 6...Filter inductor.

Claims (1)

[Claims] 1. Direct current obtained by rectifying a commercial power source is opened and closed by a switching element, converted into alternating current whose frequency is higher than that of the commercial power source, and supplied to the primary side of a power transformer, and this transformer In a magnetron power supply device that supplies power from a high voltage winding provided on the secondary side of the magnetron to the anode of the magnetron, and from a low voltage winding to the cathode of the magnetron, a capacitor and an inductor are connected in series with the low voltage winding circuit. By inserting the A power supply device for a magnetron, characterized in that it is set so that only the resistance of 2. A power supply device for a magnetron according to claim 1, wherein the capacitor and inductor are integrally attached to the magnetron.