JPH0246693A - Inverter power source for magnetron - Google Patents

Abstract

PURPOSE:To prevent any accident from becoming more serious even in the case that a capacitor on the switching circuit side of pi type filters is openly broken down by specifying inductance in a dc inductor connected to a rectifying circuit. CONSTITUTION:In pi type filters 3, 4 and 5, inductance in a dc inductor 3 is set at 200muH or more. In the case that the inductance value of a coil 3 is set at 200muH or more within the range of 20-60kHz of a switching frequency, even if a capacitor 5 is openly broken down, the absolute value of a high frequency current supplied to the coil 3 is restrained by the effect of the inductance of the coil. Therefore, even in the case that the coil is single, heat generation can be limited to the troubleless extent, thereby preventing any accident from becoming more serious.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is designed to prevent the accident from progressing further to the point of burning out the series inductor of the filter, even if the switching noise elimination capacitor of the filter is broken open. Regarding inverter power supplies for magnetrons.

[Conventional technology] As a power source for magnetrons such as household microwave ovens, this step-up converts power obtained from a commercial power source into high-frequency AC that is approximately 1,000 times the commercial AC frequency and supplies DC high voltage to the anode of the magnetron. Inverter power supplies for magnetrons, which are lighter and more compact transformers, have become widely used.

FIG. 1 is a diagram showing an example of such a magnetron inverter path (for example, substantially similar to FIG. 2 described in Japanese Patent Application Laid-Open No. 61-211987). In the diagram, commercial AC power supply 1
The output is rectified by a rectifier 2, and the output is passed through a π-shaped low-pass filter consisting of capacitors 4 and 5 and an inductor coil 3 to a switching circuit consisting of an input winding 6a of a transformer 6 and a switching section 7. It is supplied to The switching unit 7 is a 20k signal outputted by one oscillation circuit lO.
The boosted high-frequency AC heavy voltage from the first output winding fi6b of the transformer 6, whose opening and closing are controlled by high-frequency pulse signals of Hz to 60kHz, is converted into a DC high voltage by the 1x voltage rectifier circuit 8 and then connected to the magnetron. 9 is supplied to the anode. The second output winding 6c of the transformer 6 also heats the cathode filament of the magnetron 9.

In this way, the input winding 6a of the transformer 6 receives a high frequency voltage and current approximately 1,000 times the frequency of the commercial AC power supply, which causes switching noise. In order to remove this switching noise, capacitor 4,
A π-shaped low-pass filter consisting of a coil 3 and a coil 3 smoothes high frequency components.

FIG. 2 shows the voltage and current waveforms of the low-pass filter, and during normal operation, the first capacitor 4 is connected to the voltage and current waveforms shown in FIG.
A voltage vcm shown in 1) is applied, and a current with a peak shown in FIG. 2 (2) flows through the coil 3.

[Problems to be Solved by the Invention] If the capacitor 5 on the switching circuit side of the low-pass filter as described above is opened and destroyed, there is a risk that an even bigger accident will develop. That is, when the capacitor 5 is opened and destroyed, the current i' whose frequency has been increased by the switching section 7 flows into the coil 3 as shown in FIG. 2(3). Since a single wire is normally used for the winding of the coil 3, when the high-frequency current iL' flows as described above, the coil 3, whose resistance has substantially increased due to the skin effect etc., will become abnormally heated, and in the worst case This may lead to smoke and fire.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter circuit for a magnetron that suppresses abnormal heating of the series inductor of the filter and prevents the development of an accident even if the capacitor on the switching circuit side of the π-type filter is opened and destroyed. do.

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

The inductance of the series inductor of the π-type filter is 20
It was decided to set it to 0 μH or more. however.

The current capacity of the inductor winding is appropriately selected as DC, as in the conventional case, depending on the capacity of the magnetron.

[Function] When the inductance value of the inductor coil 3 of the low-pass filter is small, the peak value of the waveform of the high-frequency current iL' shown in FIG. 2 (3) increases, and the resistance of the winding of the coil 3 increases. (including the increase due to the skin effect caused by the high frequency), the heat generation also increases. In contrast,
If the inductance value of coil 3 is large, iLl
The peak value of the waveform can be suppressed to a small value, and the coil 3
The amount of heat generated in the winding can be kept small. According to the inventor's experimental results, the switching frequency is 20kHz.
.

However, if the inductance value of the coil 3 is too large, the shape will become large and the winding length will become long, which will increase the loss due to the increase in resistance. There are many problems such as a decrease in
is the upper limit.

[Example] An example of the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 shows a very general circuit that drives a magnetron with an inverter power supply.The output of a commercial AC power supply 1 is rectified by a rectifier 2, and the DC output is
5 and an inductor coil 3, the signal is supplied to a switching circuit in which an input winding 6a of a transformer 6 and a switching section 7 are connected in series. The switching unit 7 receives the 2 output from the oscillation circuit 10.
Opening/closing is controlled by a high frequency pulse signal of 0kllz to 60kHz. In this way, direct current is inverted into high-frequency alternating current, which is approximately 1,000 times the commercial alternating current frequency, and this high-frequency alternating current is transformed into a light and compact transformer! The voltage is boosted by l5I-6 and output from the first output winding 6b, converted to a DC high voltage by the voltage doubler rectifier circuit 8, and supplied to the anode of the magnetron 9. The second output winding 6c of the transformer 6 also heats the cathode filament of the magnetron 9.

During normal operation, a voltage vcm shown in FIG. 2 (1) is applied to the capacitor 4 on the rectifier side of the π-type filter.
A current as shown in FIG. 2 (2) flows through the coil 3.

Without the present invention, if the inductance value of the coil 3 of the filter is set to about 50 μH, if the capacitor 5 on the switching circuit side of the filter is opened and destroyed, a high frequency current i1 will flow into the coil 3. , its peak value is approximately 2OA in the case of a household microwave oven, for example.
The winding of the coil 3, which is made of a single wire, may become abnormally heated due to the skin effect etc., resulting in smoke and burnout. On the other hand, according to the present invention, when the inductance value of the coil 3 is set to 200 μm1 or more, even if the switching side capacitor 5 of the filter is opened and destroyed, the absolute value of the high frequency current flowing through the coil 3 is The peak value is at most about IOA, and even if the coil winding is a single wire, the heat generation can be suppressed to an acceptable level.

[Effects of the Invention] As explained above, according to the present invention, even if the capacitor on the switching circuit side of the π-type filter of the magnetron inverter power supply is opened and destroyed, the accident will not spread further.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a circuit that drives a magnetron using an inverter power supply, Figure 2 (1) is a diagram showing the voltage applied to the rectifier side capacitor of the filter in the same circuit during normal operation, and Figure 2 (2) is the same diagram. A diagram showing the current flowing through the inductor coil of the filter in the circuit during normal operation, and FIG. 2 (3) is a diagram showing the high-frequency current flowing into the inductor coil when the switching circuit side capacitor of the filter in the same circuit is opened and destroyed. 1... Commercial AC power supply, 2... Rectifier, 3...
Inductor coil, 4... Capacitor on the rectifier side of the π-type filter, 5... Capacitor on the switching circuit side of the π-type filter, 6... Transformer, 7... Switching section, 8... Voltage doubler rectifier Circuit, 9...Magnef Figure 1 Figure 2'': j-1 Qui 1 Delon

Claims (1)

[Claims] 1. A rectifier circuit that rectifies a commercial AC power source, a π-type filter consisting of a series inductor connected to this circuit and a capacitor at both ends, and a switching section connected in series with the transformer input winding that is input through this filter. The switching circuit connected to the
An inverter power supply for a magnetron, comprising an oscillation circuit that opens and closes at Hz and converts the transformer input into high-frequency alternating current, and supplies the transformer output to the magnetron, characterized in that the inductance of the series inductor is set to 200 μH or more. Inverter power supply.