JPH10106740A - Magnetron drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce unnecessary radiation at the operation starting time by connecting a switching element in series between a capacitor of a half-wave voltage doubler rectifier circuit and a cathode of a magnetron. SOLUTION: A cathode 2a of a magnetron 2 is connected between a capacitor 3 and a diode 4 which are connected to the secondary terminal side of a high voltage power source transformer 1b and constitute a half-wave voltage doubler rectifier circuit. Output of the magnetron 2 is adjusted by ON-OFF time of a switching element 7 connected in series between the capacitor 3 and a cathode 2a. Even if the element 7 is turned off just after the operation is started, since voltage is always supplied to the cathode 2a, time till a normally oscillating temperature is shortened, and the time easily generating unnecessary radiation is shortened. Since an electric current is always carried to the cathode 2a even at the output adjusting time, unstable oscillation at the transient time to ON from OFF is eliminated. Preferably, the element 7 is turned on after a necessary time up to becoming a cathode temperature at which the magnetron 2 normally oscillates at the operation start time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a magnetron used in a microwave oven or the like.

[0002]

2. Description of the Related Art Conventionally, for example, a drive circuit shown in FIG. 2 has been known as this type of magnetron drive circuit.

In FIG. 2, reference numeral 1 denotes a power transformer, which has a heater power transformer 1a and a high-voltage power transformer 1b. A magnetron 2 connects the cathode 2a to the heater power transformer 1a. Reference numeral 3 denotes a capacitor, and reference numeral 4 denotes a diode, which is connected to the high-voltage power transformer 1b. A connection between the capacitor 3 and the diode 4 is connected to the cathode 2a of the magnetron 2. 5 is a switching element,
Reference numeral 6 denotes an AC power supply.

In the above circuit, when the output of the magnetron 2 is adjusted, the voltage applied to the magnetron 2 is turned on / off by the switching element 5 and the magnetron 2 is adjusted.
Output microwaves intermittently. Therefore, the average output of the magnetron 2 can be adjusted by adjusting the ON time and the OFF time of the switching element 5. For example, by setting the ON time to 10 seconds and the OFF time to 5 seconds, the output of the magnetron 2 is reduced to 2/3 of the rated value.
It can be.

[0005]

However, in the magnetron 2, immediately after the operation is started, the filament constituting the cathode 2a is not sufficiently heated, so that the electron emission from the filament is not sufficiently performed, and the magnetron 2 operates normally. Until the start of oscillation, there is an unstable oscillation time of about 2 to 4 seconds. During this period, there is a problem that unnecessary radiation of a frequency different from the normal oscillation frequency is likely to occur.

Accordingly, when the driving circuit shown in FIG. 2 is used, the filament is turned off when the switching element 5 is turned off, so that it takes a long time until the filament is heated to a sufficient temperature at the start of operation. Therefore, there is a problem that the state in which unnecessary radiation is easily generated becomes longer, and the receiving state of the television becomes worse due to the unnecessary radiation leaking from a microwave oven or the like.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and has as its object to provide a magnetron drive circuit capable of reducing unnecessary radiation at the time of starting operation of the magnetron.

[0008]

According to the present invention, a capacitor and a diode constituting a half-wave voltage rectifier circuit are connected in series to a secondary terminal of a power transformer, and a cathode of a magnetron is provided between the capacitor and the diode. And a switching element is connected in series between the capacitor and the cathode of the magnetron.

Preferably, the switching element is turned on after a time required for the cathode of the magnetron to reach a temperature at which normal oscillation occurs at the start of operation.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIG. The same parts as those in the related art are denoted by the same reference numerals, and description thereof will be omitted.

Reference numeral 7 denotes a switching element which is connected between the connection between the capacitor 3 and the diode 4 and the cathode 2a of the magnetron 2.

The output of the magnetron 2 is adjusted by adjusting the on / off time of the switching element 7.

In a state immediately after the start of the operation, in which the filament has not reached the temperature at which the magnetron 2 normally oscillates immediately after the start of the operation, the voltage is supplied to the cathode of the magnetron 2 even when the switching element 7 is off. The time required for the filament to reach the temperature at which the magnetron 2 normally oscillates is shortened, and the state in which unnecessary radiation is easily generated is shortened.

In addition, even when the output of the magnetron 2 is adjusted, the cathode of the magnetron 2 is always energized, so that unstable oscillation does not occur at the time of transition from OFF to ON. Therefore, it is not necessary to consider the on / off time of the magnetron 2 at the time of output adjustment, it is possible to perform the duty control in a short time, and it is possible to prevent the food from being burned or uneven when incorporated in the microwave oven. ,
Cooking performance can be improved.

When the switching element 7 is turned on after the time required for the filament to reach a temperature at which the magnetron 2 normally oscillates at the start of operation, generation of unnecessary radiation at the start of operation is more reliably achieved. Can be suppressed.

[0016]

As described above, according to the configuration of the first aspect of the present invention, the generation of unnecessary radiation at the start of operation can be suppressed, and the influence on other electric equipment can be reduced. Has the effect of

According to the configuration of the second aspect of the present invention, the generation of unnecessary radiation at the start of operation can be more reliably prevented, and the influence on other electric equipment can be more reliably suppressed. Has the effect of

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power transformer 1a Heater power transformer 1b High voltage power transformer 2 Magnetron 2a Cathode 3 Capacitor 4 Diode 7 Switching element

Claims (2)

[Claims] 1. A capacitor and a diode constituting a half-wave voltage rectifier circuit are connected in series to a secondary terminal of a power transformer. A cathode of a magnetron is connected between the capacitor and the diode. A magnetron drive circuit, wherein a switching element is connected in series between the cathode of the magnetron and the magnetron. 2. The magnetron drive circuit according to claim 1, wherein the switching element is turned on after a time required until the cathode of the magnetron reaches a temperature at which the cathode of the magnetron normally oscillates at the start of operation.