JP2001196159A - High-frequency heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of the increase of harmonics of power source wave-form caused by the temperature characteristics of a magnetron, for a high-frequency heating device. SOLUTION: The high-frequency heating device comprises an inverter 24 equipped with a modulation part 21, a driving part 22, and a semiconductor switching element 23 and a magnetron 25 driven by the inverter 24. The modulation part 21 generates a modulation signal depending on a power source voltage detecting means 27 detecting the voltage of power source 26 supplied to the inverter 24, and a magnetron operating voltage detecting means 28 detecting the operating voltage of the magnetron 25. The driving part 22 determines the pulse signal to drive the semiconductor switching element 23 depending on the above modulation signal. Accordingly, even if the operating voltage is changed by the temperature characteristics of the magnetron 25, an optimum modulation signal can be obtained and the harmonics of input current are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter power supply for driving a magnetron used in a microwave oven.

[0002]

2. Description of the Related Art A magnetron is a vacuum tube comprising an anode and a cathode. Figure 8 is a graph showing the characteristics of the magnetron, the horizontal axis represents the anode current (hereinafter referred to as I _A) of the magnetron, the vertical axis represents the voltage between the anode and cathode of the magnetron (hereinafter referred to as V _AK) ing. The magnetron is energized with a negative voltage, oscillates at about -4 kV, starts to flow an anode current, and microwaves are radiated from the antenna. Magnetron V _AK has temperature dependence,
It tends to decrease as the temperature increases. It has a characteristic of about −4 kV in a room temperature state, but drops to about −3.2 kV as the temperature increases in continuous operation. The solid line in the figure shows the characteristics at room temperature, and the broken line shows the characteristics when the temperature rises.

FIG. 9 is a block diagram showing a circuit configuration for driving a magnetron. In the figure, 1 is a commercial power supply, 2 is an inverter, and 3 is a magnetron. The inverter 2 includes a full-wave rectifier circuit for full-wave rectifying the voltage of the commercial power supply 1, a filter circuit unit for reducing noise, a semiconductor switching element, a boosting transformer, a driving unit for driving the semiconductor switching element, It comprises a power supply voltage detecting means for detecting a voltage, and a modulation unit. The modulation section generates a modulation signal to be sent to the drive section based on a signal from the power supply voltage detection means. The drive unit determines an ON time of a pulse for driving the semiconductor switching element based on the modulation signal. The frequency of the pulse given from the drive unit to the semiconductor switching element is from 20 kHz to 50 kHz. This is a circuit configuration in which a high-frequency voltage obtained by the operation of a semiconductor switching element is boosted by a boosting transformer to generate a high voltage for driving a magnetron.

FIG. 10 shows the voltage or current waveform of each part of the inverter and the magnetron, and FIGS. 10A to 10D are described together with the time axis. FIG. 3A shows a case where the commercial power supply is subjected to full-wave rectification, and a voltage waveform at a location outputted through a filter circuit is used when a commercial power supply of 60 Hz is used. Solid line in FIG. (B) shows the V _AK of the magnetron at room temperature conditions, in the form in which the voltage is cut at -4kV from V _AK -I _A characteristic of the magnetron as described above. I _A from the time the V _AK reaches about -4kV
Begins to flow. Since the input current of the commercial power supply shown in solid line in FIG. (C) shows a similar waveform and I _A, starts to flow from the time when V _AK reaches -4 kV. As described above, the input current waveform has a pause in which no current flows. When such an input current waveform is subjected to Fourier series expansion, harmonics of orders other than the fundamental wave exist. The magnitude of this harmonic is IE
It is regulated by C1000-3-2. In order to reduce harmonics, it is necessary to make the idle period of the input current as short as possible. To this end, in the low portion of the output voltage waveform of the filter section shown in FIG. 7A, the ON time of the pulse for driving the semiconductor switching element is lengthened so that the voltage output from the step-up transformer is increased as much as possible. Controlling.

Further, the life of the magnetron is dependent on the peak value of I _A, there is a tendency that the life as the peak value of I _A increases becomes short. Therefore it is possible to control the semiconductor switching devices constituting the inverter such that the peak value of I _A does not increase required. I _A from becoming large, since the peak near the output voltage waveform of the filter unit shown in FIG. 6 (a), in this part by shortening the pulse on-time for driving the semiconductor switching element, I
_A is controlled so that it does not increase. Input current waveform shown by the solid line in the figure showing the I _A, similar to a waveform (c) is in a substantially flat peak.

[0006] As shown in the circuit book diagram of FIG. 9, such control is instructed by a modulation signal given to a drive unit for generating a pulse for driving a semiconductor switching element. The modulation section generates a modulation signal based on the signal of the power supply voltage detecting means, and supplies the modulation signal shown in FIG. The output voltage waveform of the modulator in FIG. 3 acts so that the ON time of the pulse for driving the semiconductor switching element becomes longer as the voltage becomes higher.

[0007] As shown in FIG. 9, the driving section determines the driving pulse by adding the signal of the output command means and the signal of the modulating section. The signal of the output command means is a DC voltage, and when the output is increased, the DC voltage increases.

[0008]

However, the conventional method has the following problems.

As mentioned above, the magnetron V _AK -I
_{The A} characteristic has a temperature characteristic, and V _AK tends to decrease as the temperature rises. The waveform shown by the broken line in FIG. 10B shows V _AK when the temperature rises, and is approximately −3.
This shows a state where oscillation occurs at 2 kV. With such a change in the characteristics of the magnetron, the input current waveform changes as shown in FIG.
As indicated by the broken line. Since V _AK starts to oscillate at about -3.2 kV, the input current starts to flow and sharply increases,
From the place where the output voltage waveform of the modulation section in FIG. 4D starts to fall, a peak is formed where the input current in FIG. When such a waveform is subjected to Fourier series expansion, there is a problem that a waveform to a higher order exists and its amplitude also increases.

Further, when varying the output of the magnetron, the magnitude of the DC voltage, which is a signal from the output command means, changes, and the driving section adds this signal and the modulation signal to generate a pulse for driving the semiconductor switching element. decide.
Therefore, even when varying the output of the magnetron, there are the the generation of the pile of the input current waveform due to the temperature characteristic of V _AK -I _A characteristics as described above, a similar condition occurs,
There has been a problem that harmonics are increased.

[0011]

Means for Solving the Problems] high frequency heating apparatus of the present invention has been made to solve the problems described above, first, harmonic of the input current caused by the temperature characteristic of the V _AK -I _A characteristics of the magnetron for improvement of the wave, the change information due to the temperature of the operating voltage of the magnetron is reflected in the modulated signal, even during the change with temperature of the V _AK and resulting construction proper modulation signal.

Further, the output information is reflected on the modulation signal so that an appropriate modulation signal can be obtained when the output of the magnetron changes.

[0013]

The invention according to claim 1 includes an inverter having a modulator, a driver, and a semiconductor switching element, and a magnetron driven by the inverter, wherein the inverter controls power by the inverter. Power supply voltage detection means for detecting the voltage of the obtained power supply, and magnetron operation voltage detection means for detecting the operation voltage of the magnetron, and the drive section modulates a pulse for driving the semiconductor switching element by the modulation. with the configuration determined based on the signal, the change information due to the temperature of the operating voltage of the magnetron is reflected in the modulated signal, so that a proper modulation signal even when changes due to temperature of the magnetron voltage V _AK is obtained.

According to a second aspect of the present invention, there is provided an inverter having a modulator, a driver, and a semiconductor switching element;
The inverter includes a magnetron driven by the inverter, and an output command unit.The modulation unit generates a modulation signal from a power supply voltage detection unit that detects a voltage of a power supply from which the inverter obtains power, and the output command unit. The drive section determines a pulse for driving the semiconductor switching element based on the modulation signal, so that an appropriate modulation signal can be obtained when the output of the magnetron changes.

Further, the invention according to claim 3 comprises a power supply current detecting means for detecting a current of a power supply, an output command means, and a comparing means for comparing the power supply current detecting means with the output command means. The comparing means is configured to control the drive unit so that the signal from the output command means and the signal from the power supply current detecting means are equal, in other words, the input current constant control is constant. Is correlated with the operating voltage of the magnetron, the signal of the comparing means is transmitted to the modulation section as the signal of the magnetron operating voltage detecting means, so that the input power of the inverter is kept constant and To reflect the change in the operating voltage of the magnetron due to temperature in the modulation signal without providing a means for newly detecting the operating voltage of the magnetron It can be.

According to a fourth aspect of the present invention, the modulating unit forms a basic waveform by using a signal from the power supply voltage detecting unit, and an upper limit for setting an upper limit of the basic waveform generated by the basic waveform forming unit. A setting unit A, wherein the upper limit setting unit A sets an upper limit by a signal from the comparing unit.
The change information due to the temperature of the operating voltage of the magnetron is reflected in the modulated signal, so that a proper modulation signal even when changes due to temperature of the magnetron voltage V _AK is obtained.

According to a fifth aspect of the present invention, the modulating section forms a basic waveform by means of a signal from the power supply voltage detecting means, and an upper limit for setting an upper limit of the basic waveform generated by the basic waveform forming means. Since the upper limit setting means B has a configuration in which the upper limit is set by a signal from the output command means, an appropriate modulation signal can be obtained when the output of the magnetron changes.

According to a sixth aspect of the present invention, the modulating unit forms a basic waveform by using a signal from the power supply voltage detecting unit, and an upper limit for setting an upper limit of the basic waveform generated by the basic waveform forming unit. Setting means, wherein the upper limit setting means comprises an amplifier and a reference value, and the reference value is set by a signal of an output command means, and the amplifier sets the reference value and a signal of a comparison means. By amplifying the difference between the two, the change information due to the temperature of the operating voltage of the magnetron is reflected in the modulation signal, so that an appropriate modulation signal can be obtained even when the magnetron voltage V _AK changes due to the temperature, and An appropriate modulated signal can be obtained even when the output changes.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to an embodiment of the present invention. In FIG. 1, reference numeral 26 denotes a power source,
4 is supplied with power. Reference numeral 29 denotes output command means for commanding the magnitude of the output of the magnetron. A magnetron 25 is driven by the inverter 24. The inverter 24 is a power supply voltage detecting means 2 for detecting the voltage of the power supply 26.
7, a magnetron operating voltage detecting means 28 for detecting an operating voltage of the magnetron 25, a modulating section 21 for generating a modulation signal by signals from the power supply voltage detecting means 27 and the magnetron operating voltage detecting means 28, and a modulating section 21 and an output commanding means 29. The driving unit 22 includes a driving unit 22 that generates a driving pulse from a signal, a semiconductor switching element 23 driven by the pulse of the driving unit 22, and a step-up transformer that steps up a high-frequency voltage obtained by the operation of the semiconductor switching element 23. The power of the power supply 26 is supplied to the semiconductor switching element 23 and the boosting transformer via a full-wave rectifier circuit and a filter circuit, but is omitted in the figure.

When the operating voltage of the magnetron 25 is detected, a signal including information in which the operating voltage V _AK has changed due to temperature characteristics can be obtained, and this signal is transmitted to the modulation unit 21. The modulation section 21 can perform processing based on this signal to create an optimal modulation signal. As the magnetron operating voltage detecting means 28, there is a method of specifically detecting with a resistor. In this case, since the magnetron has a high voltage, a large and high-resistance resistor is used. In addition, because of the potential of the circuit, the signal detected by this resistor cannot be directly transmitted to the modulation unit 21, so that it is necessary to interpose an insulating means such as a photocoupler.

Further, since the signal of the output command means 29 is also transmitted to the modulation section, the modulation section can produce an optimum modulation signal for each output.

FIG. 2 is a block diagram of a magnetron drive circuit used in a high-frequency heating apparatus according to another embodiment of the present invention. Components equivalent to those in FIG. 1 are denoted by the same reference numerals.
The description of the function is omitted.

The comparing means 31 compares the signals of the power supply current detecting means 30 for detecting the current of the power supply 26 and the output command means 29, and outputs a signal corresponding to the difference between the two. Comparison means 3
Since the signal of 1 is transmitted to the drive unit 22, the drive unit 22 determines a pulse for driving the semiconductor switching element 23 according to this signal. Thus, the input current of the power supply 26 is controlled so as to have a constant magnitude set by the output command means. That is, the input power to the inverter is determined by the output command means. Further, the comparison means 3
Since the signal 1 is transmitted to the modulation section 22, the modulation section 21 generates a modulation signal from this signal and the signal of the power supply voltage detection means 27. As a result, the modulation section 21 can obtain information in which the operating voltage V _AK has changed due to the temperature characteristics, and can perform processing based on this signal to create an optimal modulation signal. This will be described in more detail.

The comparison means 31 compares the signal of the output command means 29 with the signal of the power supply current detection means 30 and instructs the drive section 22 to eliminate the difference, so that the power supply current is kept constant. In other words, the input power of the inverter 24 is kept constant.

Here, the magnetron operates at the same temperature T as the room temperature.
A magnetron operating voltage V _AK1 when a _A, considering the case of the magnetron operating voltage V _AK2 at temperature T _H the temperature rises, even if the semiconductor switching element 23 is any, when operating under the same conditions, The power supply current is not kept constant. Specifically, when operating under the same conditions, the power supply current increases. Therefore, the comparing means 31 detects a difference between the signal of the output command means 29 and the signal of the power supply current detecting means 30, and gives a command to the drive unit 22 so that the difference disappears. Therefore, the signal of the comparing means 31 is based on the temperature change T of the magnetron.
Accompanied from _A to T _H, so that they have information V _AK2 from the change V _AK1 of the magnetron operating voltage. Therefore, by transmitting the signal of the comparison means 31 to the modulation section 22, the modulation section 21 can obtain information in which the operating voltage V _AK has changed due to the temperature characteristic. Can produce a signal.

FIG. 3 is a block diagram of a magnetron drive circuit used in a high-frequency heating apparatus according to another embodiment of the present invention. Components equivalent to those in FIGS. 1 and 2 are denoted by the same reference numerals, and their functions are described. Description is omitted.

The modulating section 21 forms a fundamental waveform forming means 3 for forming a fundamental wave of modulation based on the signal of the power supply voltage detecting means 27.
2 and upper limit setting means A33 for setting the upper limit value of the fundamental wave obtained thereby. The upper limit setting means A33 sets an upper limit value by the signal of the comparing means 31. With such a configuration, the signal of the comparison means 31 including the information that the operating voltage V _AK has changed due to the temperature characteristic of the magnetron 25,
By manipulating the modulation signal, an optimum modulation signal can be created.

FIG. 4 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to another embodiment of the present invention. Components equivalent to those in FIGS. 1, 2 and 3 are denoted by the same reference numerals. The description of the function is omitted.

The upper limit setting means B34 sets an upper limit value by the signal of the output command means 29. With such a configuration, it is possible to create an optimal modulation signal for each output.

FIG. 5 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to another embodiment of the present invention. Components equivalent to those in FIGS. 1 to 4 are denoted by the same reference numerals, and their functions are described. Description is omitted. In the present embodiment, FIG.
The upper limit setting means A and the upper limit setting means B shown in FIG. 4 are integrated as the upper limit setting means in a configuration described below. The upper limit setting means 43 includes the reference value 36 and the amplifier 3
5

The reference value 36 is set by a signal from the output command means 29. The signal of the reference value 36 is provided to the amplifier 35. The amplifier 35 receives the signal from the comparing means and the reference value 3
6 is set so as to amplify the difference between the signal and the upper limit of the fundamental wave generated by the fundamental wave forming means 32. With such a configuration, the modulation signal can be operated by the signal of the comparison means 31 including the information on the change of the operating voltage _VAK due to the temperature characteristic of the magnetron 25, and the output command means 2
9 can produce an optimal modulation signal according to the signal of No. 9.

Next, the operation of each component will be described with reference to the waveforms of the components shown in FIG. The waveforms (a) to (h) in FIG. Further, the waveform of the symbol from the waveform shown in FIG. 5 indicates the waveform where the symbol of the waveform is described from the waveform shown in FIG. That is, the waveform is the output waveform of the power supply voltage detecting means 27, the waveform is the output waveform of the fundamental wave forming means 32, the waveform is the output waveform of the output command means 29, the waveform is the output waveform of the power supply current detecting means 30, and the waveform is the waveform of the comparing means 31. The output waveform and waveform are the output waveform of the reference value 36, the waveform is the output waveform of the amplifier 35, and the waveform is the output waveform of the output of the fundamental wave forming means 32 from the amplifier 35 and the upper limit of the voltage is set.

The waveform of FIG. 6A has a form in which a sine wave is full-wave rectified because the voltage of the power supply 26 using a commercial power supply is detected. The waveform in FIG. 3B sets the lower limit of the waveform, and this waveform is the fundamental wave of the modulation signal.
The waveform in FIG. 9C and the waveform are the same since the magnitude of the power supply current is controlled by the comparing means 31 so that the magnitude is instructed by the output instructing means 29. Figure (d)
Are the output waveforms of the comparison means 31, and the waveforms are the output waveforms of the reference value 36, which are input to the amplifier 35. The amplifier 35 amplifies the difference between these inputs, and FIG.
The waveform of is output. This waveform is the upper limit value obtained by integrating upper limit setting means A and upper limit setting means B.

The upper limit value of the waveform is set by the voltage value of the waveform. However, since the waveform and the waveform are combined via the resistor, the waveform is not cut by the voltage value of the waveform, but is cut by the voltage value of the waveform. , The upper limit is gently limited, and the waveform shown by the broken line becomes a smooth waveform like a waveform. The drive unit 22 is supplied with a signal obtained by inverting the waveform signal,
Is determined. That is, the higher the voltage of the waveform, the shorter the on-time of the pulse for driving the semiconductor switching element 23. The shorter the on-time of the pulse, the more the output of the inverter is suppressed.

Here, the case where the temperature of the magnetron 25 rises and the operating voltage _VAK decreases will be described. It is assumed that the driving pulse of the semiconductor switching element 23 is in the same state as before the temperature rise. At this time, the input current increases.

FIGS. 6F to 6H show the magnetron 25.
Is a diagram showing waveforms of various parts when the temperature rises from the room temperature state, and the waveform of (f) changes to a waveform 'when the temperature of the magnetron 25 rises. Actually, the voltage becomes the same as that of the waveform due to the operation of the comparing means 31, but it is shifted for the sake of explanation. The waveform in FIG. 7G changes to a waveform ′ when the temperature of the magnetron 25 rises. The waveform in FIG. 7G changes to waveforms と and そ れ ぞ れ when the temperature of the magnetron 25 rises.

The waveform obtained in this manner is applied to the driving unit 2.
In order to explain how it is transmitted to the input current waveform 2 and acts on the input current waveform, the waveform is superimposed on the waveform diagram of FIG. 10 used in the description of the prior art, and this is shown in FIG. The waveform of the dotted line shown in FIG. 7 is the same as the waveform of the dotted line shown in FIG. FIG (a) an output voltage waveform of the filter unit, FIG. (B) shows the voltage waveform when the temperature rises by magnetron V _AK. FIG. 3C shows the input current waveform, the dotted line is a conventional waveform, and the solid line is a waveform obtained by using the above-described means. FIG. 6D shows the output voltage waveform of the modulation section, the dotted line shows the conventional waveform, and the solid line shows the output voltage waveform of the modulation section obtained by inverting the waveform ′ of FIG. 6H.

According to such a modulation signal, it is possible to eliminate the peak of the input current shown in FIG. According to the present invention, even when the operating voltage changes due to the temperature change of the magnetron 25, an optimal modulation signal can be generated and the harmonics of the input current can be reduced. Further, an optimal modulation signal can be created even in response to the signal of the output command means 29.

[0040]

As described above, according to the present invention, an optimum modulation signal can be obtained even when the operating voltage changes due to the temperature characteristics of the magnetron, and the harmonics of the input current can be reduced. Can be. In addition, an optimal modulation signal can be generated when the output of the magnetron is variable, and harmonics of the input current can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to another embodiment of the present invention.

FIG. 3 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to another embodiment of the present invention.

FIG. 4 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to another embodiment of the present invention.

FIG. 5 is a block diagram of a magnetron drive circuit used in a high-frequency heating device according to another embodiment of the present invention.

6A is an output voltage waveform diagram of a power supply voltage detecting means of the high-frequency heating device. FIG. 6B is an output voltage waveform diagram of a basic waveform forming device of the high-frequency heating device. (D) Comparison means of the high-frequency heating device, output voltage waveform diagram of the reference value (e) Output of the basic waveform forming means in which the upper limit of the voltage is set by the amplifier of the high-frequency heating device Voltage waveform diagram (f) Output voltage waveform diagram of power supply current detecting means when magnetron temperature rises in the high-frequency heating device (g) Output voltage waveform diagram of comparison means when magnetron temperature rises in the high-frequency heating device device (H) Output voltage waveform diagram of the basic waveform forming means in which the upper limit of the voltage is set by the amplifier when the temperature of the magnetron rises in the high-frequency heating device

FIG. 7 (a) is an output voltage waveform diagram of a filter section of the high frequency heating device. (B) is a _VAK waveform diagram of a magnetron of the high frequency heating device. (C) is an input current waveform diagram of the high frequency heating device. Output voltage waveform diagram of the modulation section of the heating device

[8] characteristic diagram showing a relationship between magnetron V _AK and I _A

FIG. 9 is a block diagram of a magnetron drive circuit used in a conventional high-frequency heating device.

FIG. 10 (a) is an output voltage waveform diagram of a filter section of a conventional high frequency heating device. (B) is a _VAK waveform diagram of a magnetron of the high frequency heating device. (C) is an input current waveform diagram of the high frequency heating device. Output voltage waveform diagram of modulation section of high-frequency heating device

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Modulation part 22 Drive part 23 Semiconductor switching element 24 Inverter 25 Magnetron 26 Power supply 27 Power supply voltage detection means 28 Magnetron operation voltage detection means 29 Output command means 30 Power supply current detection means 31 Comparison means 32 Fundamental wave formation means 33 Upper limit setting means A 34 Upper limit setting means B 35 Amplifier 36 Reference value 43 Upper limit setting means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiro Ishio 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 3K086 AA10 BA08 CC02 DB03 DB11 DB15 DB16 FA02 FA03 FA04

Claims (6)

[Claims] 1. An inverter having a modulator, a driver, and a semiconductor switching element, and a magnetron driven by the inverter, wherein the modulator detects a voltage of a power source from which the inverter obtains power. Means,
A high-frequency heating apparatus configured to generate a modulation signal from magnetron operation voltage detection means for detecting an operation voltage of the magnetron, and the driving unit determines a pulse for driving the semiconductor switching element based on the modulation signal. 2. An inverter having a modulator, a driver, and a semiconductor switching element, a magnetron driven by the inverter, and output command means, wherein the modulator controls a voltage of a power supply from which the inverter obtains power. A high-frequency heating apparatus having a configuration in which a modulation signal is generated from a power supply voltage detection unit to be detected and the output command unit, and the drive unit determines a pulse for driving the semiconductor switching element based on the modulation signal. 3. A power supply current detection means for detecting a current of a power supply, an output command means, and a comparison means for comparing the power supply current detection means with the output command means, wherein the comparison means comprises the output command means. And a signal from the power supply current detection means is controlled to be the same, and a signal from the comparison means is transmitted to the modulation section as a signal from the magnetron operation voltage detection means. 2. The high-frequency heating device according to 1. 4. A modulating section comprising: a basic waveform forming means for forming a waveform with a signal from a power supply voltage detecting means; and an upper limit setting means A for setting an upper limit of the basic waveform generated by the basic waveform forming means.
The high frequency heating apparatus according to claim 3, wherein the upper limit setting means A is configured to set an upper limit by a signal from a comparing means. 5. A modulating section comprising: a basic waveform forming means for forming a waveform by a signal from a power supply voltage detecting means; and an upper limit setting means B for setting an upper limit of the basic waveform generated by said basic waveform forming means.
The high frequency heating apparatus according to claim 2, wherein the upper limit setting means (B) sets the upper limit by a signal from an output command means. 6. The modulation section has basic waveform forming means for forming a waveform with a signal from a power supply voltage detecting means, and upper limit setting means for setting an upper limit of the basic waveform generated by the basic waveform forming means. The upper limit setting means comprises an amplifier and a reference value, the reference value is set to a reference value by a signal of an output command means, and the amplifier amplifies a difference between the reference value and a signal of a comparison means. The high-frequency heating device according to claim 3.