JPH01232691A - Power source for magnetron - Google Patents

Abstract

PURPOSE:To obtain a power source of a small size, a light weight and a high performance applicable to any cooking conditions and conditions for industrial application of a microwave oven by making desired intermittent action possible at a desired output for a power source for a magnetron using an inverter circuit. CONSTITUTION:An inverter circuit for converting DC from a commercial power source rectified at a rectifier 3 into a high frequency AC by a switching element 2 is provided for the primary side, and for the secondary side are provided a transformer including an anode high voltage output coil and a cathode low voltage output coil of a magnetron 6 and a control for controlling the time of opening and closing conditions for the element 2. Adjustment not only of the size of the microwave output for the magnetron 6 but also of intermittent stoppage is performed only by changing the time ratio of opening and closing conditions for the element 2, and current supply is continued to the primary side of the transformer even when the output is stopped. The output of the magnetron can thus be changed in a wide range including an intermittent stoppage without reducing the life of a cathode.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a magnetron in which the life of the magnetron cathode (filament) is not shortened even if the output of the magnetron is changed over a wide range including intermittent stoppage. related to a power supply device.

[Prior Art] A conventional power supply device for Magne 1 Heron uses a commercial frequency transformer to obtain high voltage at the anode of the magnetron.

The output was adjusted by intermittent power supply, but if the magnetron's cathode filament was blinked intermittently, especially if the period of intermittent operation was shortened, the life of the filament would be significantly shortened.

Generally, a separate filament transformer was provided to keep the Neurament ignited at all times. Also.

Commercial frequency transformers are large and heavy, so in recent years, as disclosed in Utility Model Application Publication No. 62-107396, a switching element is used to open and close the DC obtained by rectifying the commercial power supply, The transformer is made smaller and lighter by using a 1R inverter circuit that converts the alternating current at a frequency far higher than the power supply frequency. At the same time, the microwave output of the magnetron is adjusted by adjusting the time ratio of the open/closed state of the switching element. A lightweight inverter-type magnetron power supply device that can be adjusted by changing the power supply has been developed.

[Problems to be Solved by the Invention] The purpose of the above conventional technology is to use a magnetron for high-frequency heating in a microwave oven, etc., and the microwave output given to the object to be heated is delivered at intervals of several seconds using a commercial frequency power supply. Even if the control is performed by intermittent operation or by changing the opening/closing time ratio of switching elements using an inverter type power source, the purpose can be achieved in both cases.

Microwave generators using magnetrons include not only microwave ovens but also industrial equipment such as plasma etching equipment, strobe-type high-intensity light emitting equipment, and minute spot heating equipment used in semiconductor processing processes. In addition to value control, some require fast intermittent output switching.

In order to perform high-speed intermittent output intermittent operation, filament 1
A power supply with a separate transformer installed to open and close only the high voltage anode of the magnetron has been put into practical use, but it is large and expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power supply device for a magnetron that can not only control the magnitude of the microwave output but also can intermittent the microwave output at high speed.

[Means for Solving the Problems] In order to solve the above problems, the present invention converts the direct current obtained by rectifying the commercial power supply into alternating current with a frequency far higher than the commercial power supply frequency by switching on and off using a switching element. an inverter circuit that takes the high-frequency alternating current generated by this circuit as its primary input, and a transformer that has a high-voltage output winding for the anode of the magnetron and a low-voltage output winding for the cathode on the secondary side, and an inverter circuit that opens and closes the switching element. In a magnetron power supply device equipped with a control circuit that controls the state time, the microwave output of the magnetron is adjusted not only in magnitude but also intermittently stopping, and the time ratio of the open and closed states of the switching element is changed. Even when microwave output is stopped, power continues to be supplied to the primary side of the transformer. That is, when the open period of the switching element of the inverter circuit is made relatively long and the closed period is made relatively short, the high voltage value applied to the anode of the magnetron gradually decreases, and when it becomes below the Δ critical value, Anode current stops flowing and microwave output stops.

In this way, high-speed intermittent operation of microwave output can be performed simply by changing the time ratio of the open/close states of the switching elements of the inverter circuit.

[The anode current of the action comagnetron changes greatly with relatively small fluctuations in the voltage applied to the anode, and when the voltage applied to the anode falls below a certain critical value, it stops flowing and no microwave output can be obtained. This critical value is quite high, even when the microwave output is stopped.

A considerable voltage is still applied to the cathode filament. In other words, the microwave output is stopped in a state where the cathode heating power is not very small.

Therefore, it is possible to perform high-speed intermittent operation of the microwave output simply by changing the time ratio of the open/close states of the switching elements of the inverter circuit. It is not large and does not require a separate transformer for cathode heating.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which 1 is a high-frequency transformer having a high-voltage winding for the anode of a magnetron and a low-voltage winding for the cathode, and 2 is a switching element.

3 is a rectifier, 4 is an output adjustment circuit that can adjust the microwave output from a stopped state to a maximum output state by changing the switching element open/close period ratio of the inverter circuit, and 5 is an intermittent that determines the microwave output time and stop time during intermittent operation. The operating circuit 6 is a magnetron.

Figure 2 shows the conventional method where power supply is intermittently interrupted on the primary side.
A circuit for adjusting microwave output is shown.

In this system, when the primary side becomes energized, the magnetron operates and generates microwave output, and when the primary side becomes energized, it stops operating. In this method, as shown in FIG. 3, the filament of the magnetron is also energized and de-energized, so the filament temperature fluctuates significantly. If this change in filament temperature is repeated many times, the life of the filament and therefore the life of the magnetron will be significantly shortened.

Normally, the number of blinking times of the filament 1 of a magnetron is controlled and manufactured under certain quality conditions, and if the number of intermittent operations is large, the life of the filament will be shortened due to the thermal cycle of the filament. For these reasons, the intermittent operation time in a system in which the filament winding and the high voltage winding are provided in the same transformer is about 10 seconds at the shortest. If intermittent operation is performed for a shorter time than this, the number of cycles will increase and the life will be shortened. Therefore, it is necessary to provide a separate transformer exclusively for the filament to keep the filament ignited at all times even when the microwave output is intermittent.

In the embodiment shown in FIG. 1, by increasing or decreasing the conduction time of the switching elements of the inverter circuit, the scale values shown in FIG. characteristics are obtained. When the conduction time of the switching element is 25 μs, an output of 500 W is obtained, and as the conduction time is shortened, the output decreases. When the conduction time reaches 10 μS, the output becomes O. At this time, the transformer output voltage was only lower than the magnetron's starting voltage (approximately 3.8 kV in this example), and was not that low. On the other hand, since the filament current of a magnetron is approximately proportional to the filament voltage, a considerable amount of filament current flows even if the anode voltage of the magnetron falls below the operation start voltage.

Therefore, based on the above, the conduction time of the switching element should be set to a length that allows the desired microwave output to be obtained, or it should be shortened until the high voltage output of the transformer falls below the magnetron's operation start voltage and the microwave output stops. By repeating such operating conditions, intermittent operation with less change in filament temperature as shown in FIG. 5 becomes possible, and the life of the magnetron is not shortened. Therefore, with the conventional method of flowing commercial frequency AC directly to the transformer and adjusting the microwave output by intermittent input on the primary side, intermittent operation within 10 seconds could not be put to practical use, but according to the present invention, Intermittent operation within seconds is now possible.

[Effects of the Invention] As explained above, according to the present invention, a power supply device for a magnetron using an inverter circuit can perform intermittent operation within 1 second, continuously variable microwave output, and can operate at any microwave output. Arbitrary intermittent operation is now possible. As a result, a compact, lightweight, and high-performance power source for a magnetron can be obtained that is compatible with any cooking conditions required of a microwave oven and any industrial usage conditions.

[Brief explanation of the drawing]

Fig. 1 is a diagram of an embodiment of the present invention, Fig. 2 is a diagram explaining the conventional technique, Fig. 3 is a diagram explaining the operation of the conventional example, Fig. 4 is a characteristic diagram of the embodiment of the present invention, Fig. 5 is an explanatory diagram of the operation of the embodiment. 1...High frequency transformer, 2...Switching element. 3...'! 1 current device, 4...output adjustment circuit, 5.
... Intermittent motion 2nd factor 1-high (5) 5 pox 9 each 2-sui Rjite Saiko 3-¥=? -6 Roman sequence) ℃ Fig. 3 Fig. 4 Fig. 5 LrFJI -

Claims (1)

[Claims] 1. An inverter circuit that converts the direct current obtained by rectifying the commercial power supply into alternating current with a frequency far higher than the commercial power supply frequency by switching on and off using a switching element, and the high-frequency alternating current generated by this circuit as the primary input. A magnetron power supply device comprising, on a secondary side, a transformer having a high-voltage output winding for the anode of the magnetron and a low-voltage output winding for the cathode, and a control circuit that controls the open/close state time of the switching element. Adjustment of the microwave output, including not only the magnitude but also intermittent stopping, is carried out by simply changing the time ratio of the open and closed states of the switching element,
A power supply device for a magnetron, characterized in that power continues to be supplied to the primary side of the transformer even when microwave output is stopped.