JP3240792B2 - High frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a food or liquid
The present invention relates to a high-frequency heating device for heating.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional high-frequency heating apparatus includes a magnetron 1 for high-frequency heating an object to be heated such as food, and a high-voltage rectifier circuit 2 for supplying power to the magnetron 1.
A transformer 3 for supplying high-voltage power to the heater 15 of the magnetron 1 at the same time as supplying power to the magnetron 1, an inverter circuit 5 for rectifying the AC power supply 4, converting the AC power supply 4 to an AC having a predetermined frequency, and supplying the AC to the transformer 3; Power detection means 6 for detecting the input power or output power of the power supply, an output setting section 7 for outputting an output setting signal corresponding to the heating output setting, and a power adjustment signal for comparing the output of the power detection means 6 with the output setting signal. , A reference voltage generating circuit 9, an inverting amplifier circuit 11 for inverting and amplifying an output of a rectifying circuit 10 for rectifying the AC power supply voltage 4 using the output voltage of the reference voltage generating circuit 9 as a comparison reference voltage. , Inverting amplifier circuit 11
A signal superimposing means 12 for superimposing the output of the power control signal on the power adjustment signal to output a pulse width control signal; an oscillation circuit 13; and an output of the oscillation circuit 13 being pulse width modulated by the pulse width control signal. The configuration includes an inverter control circuit 14 for driving the circuit 5.

In the above-mentioned high-frequency heating device, the power supplied to the magnetron 1 is adjusted by the width of the output pulse of the inverter control circuit 14. When the output voltage of the signal superimposing means 12 increases, the output pulse width of the inverter control circuit increases, and the power supplied to the magnetron 1 increases. By changing the output voltage of the signal superimposing means 12 by this configuration, the magnetron 1
It was possible to continuously change the heating output of the apparatus.

[0004] The heater 15 also serves as the cathode of the magnetron 1 and generates heat by a heater current.
It becomes high temperature around K. Thermoelectrons are emitted from the heater. The maximum current IaMAX of the current Ia flowing through the magnetron 1 is determined from this emission capability (electron emission capability). When the magnetron is driven in a state exceeding IaMAX, the life is sometimes 100 minutes when the drive is performed at IaMAX or less. From 1 to 1000 times or less.

Therefore, as shown in FIG. 3, a rectified signal (FIG. 3 (B)) obtained by rectifying the output (FIG. 3 (a)) of the AC power supply 4 is used to invert the comparison reference voltage which is the output of the reference voltage generating circuit 9. The output signal of the signal superimposing means 12 is inverted by inverting the output voltage of the signal superimposing means 12 by superposing the output signal and the DC output of the power adjusting unit 8 by the signal superimposing means 12 to obtain the pulse width control signal. The power source 4 was lowered only in the vicinity of the maximum amplitude output, and Ia was averaged to keep the maximum value low (FIG. 3 (D)).

FIG. 3 is a view at the commercial frequency level, and the broken lines indicate changes in each signal when the output voltage of the signal superimposing means is DC. The waveform Ia in the figure indicates the envelope of Ia.

The output of the reference voltage generator 9 has been fixed. Alternatively, as described in Japanese Patent Application Laid-Open No. 1-220392, a configuration has been considered in which the output voltage of the reference voltage generator is changed in accordance with the output setting signal, but the purpose is different from the present invention. The input or output power feedback path of the inverter circuit was not specified.

[0008]

The proper temperature for the heater 15 to emit electrons is 1900k to 2100k. Below 1900k, the temperature of the heater is low, so that a moding phenomenon due to insufficient electron emission ability is apt to occur, and the life thereof is significantly shortened. At a temperature of 2100 k or more, a deterioration phenomenon of the heater occurs, and the life is remarkably shortened as in the case of 1900 k or less.

However, in the above-described conventional configuration, since the transformer 3 for supplying power to the magnetron 1 also supplies power to the heater 15, the power supplied to the heater 15 is also changed according to a change in the power supplied to the magnetron 1. Was changing. For this reason, if the heater temperature is set within an appropriate range, only a slight change in the heating output can be obtained, and the advantage that the output when the inverter circuit is used as a power supply can be continuously changed is greatly impaired. There was a problem that there is.

The present invention solves the above-mentioned problems, and stabilizes the heater current regardless of the magnitude of the heating output, obtains a large change range of the radio wave output of the magnetron of, for example, 200 w to 800 w or more, and has a long life and high reliability. The purpose of the present invention is to realize a high-frequency heating device capable of guaranteeing performance.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a magnetron for heating an object to be heated at a high frequency, a high voltage power supply from a secondary winding to the magnetron, and a tertiary winding for the magnetron. A transformer for supplying power to the heater, an inverter circuit for rectifying an AC power supply voltage, converting the AC power supply voltage into an alternating current having a predetermined frequency, and supplying the AC to a primary winding of the transformer, and a power for detecting input power or output power of the inverter circuit; A detection unit, an output setting unit that outputs an output setting signal corresponding to a heating output setting, a power adjustment unit that compares an output of the power detection unit with the output setting signal and outputs a power adjustment signal, and the heating output setting. And a rectifier for rectifying the AC power supply voltage having a voltage corresponding to
An inverting amplifier circuit for inverting and amplifying the output of the current circuit, a signal superimposing unit for superimposing an output of the inverting amplifier circuit on the power adjustment signal and outputting a pulse width control signal, an oscillation circuit, and an output of the oscillation circuit. An inverter control circuit for performing pulse width modulation by a pulse width control signal and driving the inverter circuit with the modulated output, wherein the pulse width control signal is configured such that when the heating output setting is low output compared to high output, the AC power supply , The output level of the AC power supply is low near the maximum amplitude, and the output level of the AC power supply is high at a low level.

[0012]

According to the present invention, the output of the inverting amplifier circuit having the rectified voltage of the AC power supply as an input and having a reference signal having a level corresponding to the heating output setting signal, the heating output setting signal and the power detection are provided. By superimposing the output of the power adjustment unit, which is determined by comparing with the output of the means, the pulse width control signal, which is the output signal of the signal superimposing means, becomes as shown in FIG. The solid line in the middle indicates each signal when the high heating output is set, the broken line indicates each signal when the low heating output is set, and the solid line indicates the signal when the high heating output is set.

As described above, the pulse width control signal is at a low level near the maximum amplitude of the AC power supply when the heating output setting is low compared to when the heating output is high, and is higher when the output of the AC power supply is low. Level.

As a result, the envelope of each waveform of the inverter circuit is as follows. The primary winding voltage of the transformer is shown in FIG.
As shown in FIG. 2B, the voltage generated by the secondary winding of the transformer is a waveform that is obtained by boosting the voltage applied to the primary winding and clipped by the oscillation voltage of the magnetron, as shown in FIG. 2C. . The voltage applied to the heater of the magnetron, that is, the voltage generated by the tertiary winding of the transformer is shown in FIG.
As shown in (d), the waveform is strongly influenced by the secondary winding. Here, since the area enclosed by the dashed line or the solid line envelope shown in FIG. 2D corresponds to the power supplied to the heater of the magnetron, the power supplied to the heater has a large heating output. The change between the small time and the small time is reduced as compared with the conventional configuration.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same parts as those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 1, a power detecting means 6, a power adjusting section 8 for outputting a power adjusting signal by comparing with an output level of an output setting section 7, and a voltage corresponding to an output of the output adjusting section 8 are generated. A comparison voltage generation circuit 16, an inversion amplification circuit 11 that inverts and amplifies an output of a rectification circuit 10 that rectifies the AC power supply voltage 4 using an output voltage of the comparison voltage generation circuit 16 as a comparison reference voltage, and an output of the inversion amplification circuit 11. The power control signal is superimposed on the power adjustment signal by a signal superimposing means 12 to form a pulse width control signal.

The structure of the signal superimposing means 12 is such that only the fluctuation signal of the inverting amplifier circuit 11 is superimposed on the DC output voltage of the power adjusting section 8.

According to this configuration, the rectified voltage of the AC power supply 4 is input, and the output of the inverting amplifier circuit 11 having the reference voltage as the reference voltage generating circuit 16 for generating a reference signal having a level corresponding to the heating output setting signal, By superimposing the output of the power adjustment unit 8 for comparing the output setting signal with the output of the power detection means 6, the pulse width control signal, which is the output signal of the signal superimposition means 12, is obtained as shown in FIG. The result is as shown in FIG. Therefore, the oscillation period of the magnetron 1 becomes longer, and at the same time, the output of the inverter circuit 5 during the non-oscillation period of the magnetron 1 becomes larger. Therefore, as shown in FIG. 2D, the area inside the envelope shown by the solid line is almost equal to the area inside the envelope shown by the wavy line. That is, the change in the power supplied to the heater between the high output setting and the low output setting can be reduced.

For this reason, the change in the heater temperature between the high heating output and the low heating output is reduced, and a wide range of output adjustment is possible without impairing the life of the magnetron.

Further, since the high-voltage rectifier circuit is a full-wave rectifier circuit, the peak of Ia can be suppressed sufficiently lower than IaMAX. Therefore, especially at the time of high heating output, the waveform of the pulse width control signal is changed as in the conventional example. , Ia need not be focused on the peak reduction, and it is possible to obtain a waveform in which the heater current is most stable when the output is changed.

In the above embodiment, the inverted reference signal is obtained from the output setting signal. However, the inverted reference signal may be any signal as long as the voltage level corresponds to the set heating output. May be obtained.

Also, the input voltage of the inverter circuit is rectified as an inversion signal and inverted with reference to the inversion reference signal.
What is necessary is just to correspond to the input voltage of the inverter circuit, and it may be obtained by using other means.

Further, the power detecting means is configured to detect the input power of the inverter circuit. However, any means can be used as long as it corresponds to the heating output, and the power detecting means may be obtained by using other means.

The present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention.

[0025]

As described above, the high-frequency heating apparatus of the present invention drives the inverter circuit by the pulse width control signal corresponding to the heating output, and stabilizes the heater current so that it does not fluctuate even if the heating output fluctuates. The heater temperature can be set so that the magnetron can be driven most stably with a wide heating output. Therefore, there is an effect that the feature that the power of the inverter circuit can be continuously adjusted can be sufficiently extracted and a high-frequency heating device with high reliability can be realized.

Furthermore, the pulse width control signal is at a low level near the maximum amplitude of the AC power supply when the heating output setting is lower than that at the time of high output, and is higher when the output of the AC power supply is low. The power supplied to the heater is less changed when the heating output is large and small compared to the conventional configuration, and the heater current is stabilized regardless of the heating output. Can be done.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a high-frequency heating device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between signals of the high-frequency heating device.

FIG. 3 is a diagram showing a relationship between signals of a conventional high-frequency heating device.

FIG. 4 is a configuration diagram of a conventional high-frequency heating device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetron 3 Transformer 5 Inverter circuit 6 Power detection means 7 Output setting part 8 Power adjustment part 11 Inverting amplifier 12 Signal superposition means 13 Oscillation circuit 14 Inverter control circuit

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kazuho Sakamoto 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Toyotsugu Matsukura 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Makoto Shibuya 1006 Oji Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Person Yoshiro Ishio 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-220392 (JP, A) JP-A 64-71092 (JP, A) JP-A 63- 178485 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 6/66-6/68

Claims (2)

(57) [Claims] 1. A magnetron for heating an object to be heated such as food at a high frequency, a transformer for supplying high-voltage power to the magnetron and supplying power to a heater of the magnetron at the same time; An inverter circuit that converts the power into an alternating current and supplies the converted power to the transformer; power detection means for detecting input power or output power of the inverter circuit; an output setting unit for outputting an output setting signal corresponding to a heating output setting; A power adjustment unit that compares the output of the means with the output setting signal and outputs a power adjustment signal; and a reference voltage that corresponds to the heating output setting.
Wherein an inverting amplifier circuit for inverting amplifying the output of the rectifier circuit for rectifying an AC power supply voltage, a signal superimposing means for outputting a pulse width control signal superimposed on the power adjustment signal output of the inverting amplifier circuit having the oscillation A circuit, and an inverter control circuit for pulse width-modulating the output of the oscillation circuit with the pulse width control signal and driving the inverter circuit with the modulated output, wherein the pulse width control signal is when the heating output setting is high output. A high-frequency heating apparatus provided so that, when the output is relatively low, the level is low near the maximum amplitude of the AC power supply, and is high when the output of the AC power supply is low. 2. The high-frequency heating apparatus according to claim 1, wherein the signal superimposing means superposes a voltage fluctuation component of an output signal of the inverting amplifier circuit on the power adjustment signal.