JP2705084B2 - High frequency heating equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating device configured to obtain a high-voltage power supply to be applied to a high-frequency oscillator (hereinafter, referred to as a magnetron) by an inverter circuit, and particularly to a safety device for the inverter circuit. It is about.

2. Description of the Related Art A high-frequency heating device configured to apply a high-frequency power obtained by an inverter circuit that performs high-frequency switching with a switching element to a unidirectional power obtained by rectifying a commercial power or the like and applying a high-voltage power to a magnetron by a high-voltage transformer. In the power control method, the larger output value of the output of the input current detector for detecting the input current to the inverter circuit and the output of the output voltage detector for detecting the voltage of the high-voltage power supply is set to a predetermined value. Power control method is used.

In this power control method, the magnetron has a high impedance until the magnetron starts oscillating, so that the voltage of the high-voltage power supply does not exceed a certain value. The output is controlled so as to be a predetermined value, and since the magnetron has a low impedance in a period after the start of oscillation, the voltage of the high-voltage power supply is reduced and the output value of the input current detection unit is controlled so as to be a predetermined value. You.

However, if the output voltage detector fails, the correct value of the high-voltage power supply is not detected. Shorten. Conversely, when the applied voltage has a very small value, the time required for the magnetron to oscillate becomes longer, or the magnetron does not oscillate.

In addition, if the current detection unit fails, the input current to the inverter circuit cannot be correctly detected, so that the input current becomes excessive and the switching element is destroyed due to excessive loss of the switching element, and its life is shortened by applying excessive power to the magnetron.

Conversely, when the input current is too small, a predetermined high-frequency output cannot be obtained.

Means for Solving the Problems In a high-frequency heating apparatus according to the present invention, an inverter circuit that performs high-frequency switching of a unidirectional power supply obtained by rectifying a commercial power supply by a switching element and converts the high-frequency power supply to a high-frequency power supply, A high-voltage transformer for converting the high-voltage power supply to a high-voltage power supply, and a high-frequency oscillator for applying the high-voltage power supply to oscillate a high frequency. The inverter circuit includes an output voltage detection unit for detecting the voltage of the high-voltage power supply, and an inverter circuit. A current detection unit for detecting an input current of the switching element, a terminal voltage detection unit for detecting a voltage between both ends of the switching element, and a larger output value of the output of the output voltage detection unit and the output of the current detection unit being a predetermined value. Power control means for controlling so that the high-frequency switching is stopped when the output value is smaller than the output value of the terminal voltage detection unit. Output stopping means.

By the means described above, during the period before the magnetron starts to oscillate, the applied voltage of the magnetron is controlled to a fixed value or less, and after the magnetron starts to oscillate, the input current to the inverter circuit is controlled to a constant value. In addition to the conventional functions, the application of excessive voltage to the magnetron when the output voltage detector fails, the destruction of the switching element when the input current detector fails, or the application of excessive power to the magnetron, etc. Is prevented.

Embodiment FIG. 1 is a configuration diagram of a high-voltage power generation unit of a high-frequency heating device according to the present invention.

A unidirectional power supply 3 obtained from a commercial power supply 1 through a rectifier circuit 2 is turned on / off by a switching element 4 to be converted into a high-frequency power supply 5, input to a high-voltage transformer 6, and a boosted high-voltage power supply 7
Is applied between the anode 8a and the cathode 8b of the magnetron 8 to operate the magnetron 8.

Input current detection unit 9 detects the input current I _in of from the commercial power supply 1 by the input current detecting section 10, and outputs an input current signal 12 by rectifying the output by the input current signal rectifying circuit 11.

The output voltage detector 13 detects the voltage of the high voltage power supply 7 applied to the magnetron 8 by the output voltage detector 14, rectifies the output by the output voltage signal rectifier circuit 15, and outputs the output voltage signal 16.

The input current signal 12 and the output voltage signal 16 are input to the diode circuit 17, respectively, and the larger signal is input to one of the input terminals of the error amplifier circuit 19 as the selected output signal 18.

The reference signal 20 is input to the other terminal, and the difference signal
21 is output. The first comparator 22 calculates the difference signal 21
With the sawtooth wave 24 from the sawtooth wave generation circuit 23,
An ON / OFF pulse 25 for the switching element 4 is created.

The more the input current detector 9 to a first comparator 22 constitute an input current control unit 26, the error amplifier circuit 19 output rises when the input current I _in is decreased, a longer ON time of the ON / OFF pulse 25 input to work in the direction to increase the current I _in. Input current I _in the opposite operates to reduce the input current I _in a shorter for the ON time increases. Thus, the input current control unit 26
Operates so that the reference signal 20 selects the output signal 18 matches the input current I _in is a part for controlling to a predetermined value.

The output voltage detector 13 to the first comparator 22 constitute an output voltage controller 27. When the voltage of the high-voltage power supply 7 decreases, the output of the error amplifier 19 increases, and the ON / OFF pulse 25 turns ON.
The time becomes longer and the high voltage power supply 7 operates in the direction of increasing the voltage,
At the same time, the input current I _in also increases. Conversely, when the voltage of the high voltage power supply 7 increases, the ON time is shortened to operate to reduce the voltage of the high voltage power supply 7, and the input current _Iin also decreases. As described above, the output voltage control unit 27 is a part that operates so that the selected output signal 18 matches the reference signal 20 and controls the voltage of the high-voltage power supply 7 to be a predetermined value.

Here, the input current signal 12 and the output voltage signal 16 are input to the diode circuit 17, but as is clear from the figure, the higher input voltage to the diode circuit 17 is selectively output to the error amplifier circuit 19. Although configured to output, this is so that, as the high-voltage power source 7 voltage does not exceed the predetermined value, and also the input current I _in does not exceed a predetermined value.

As described above, the switching element 4, the input current control unit 26, and the output voltage control unit 27 for obtaining the high frequency power supply 5 from the unidirectional power supply 3 are basic components of the inverter circuit 28.
In addition to the above, the present invention further includes an output stop unit 29 as protection means in the event of an abnormal operation.

The output stop unit 29 is connected to the switching element 4 as shown in the figure.
A terminal voltage signal 32 is output by a voltage dividing circuit 30 for stepping down the terminal voltage V _CE and a terminal voltage rectifying circuit 31, and this signal is a selected output when the above-described input current control or output voltage control is performed. The terminal voltage detection unit 33 having a detection sensitivity smaller than the signal 18 is compared with the terminal voltage signal 32 and the selection signal output 18 described above, and when the latter signal is smaller than the former signal, abnormality is detected. It comprises a second comparator 35 that outputs a signal 34 and a latch circuit 37 that latches the abnormality detection signal 34 and outputs an output stop signal 36.

The sawtooth wave 24 from the sawtooth wave generating circuit 23 is stopped by the error detection signal 34 from the output stop unit 29 that is output at the time of this error, and the ON / OFF pulse 25 stops, so the operation of the inverter circuit 28 stops. I do.

That is, when the inverter circuit 28 detects an abnormality, it also has a safety function of stopping its operation and stopping the output of the high-voltage power supply 7.

Next, the principle of detecting an abnormality by comparing the two signals described above will be described.

 First, an operation waveform in a normal state will be described.

FIG. 2 is a voltage waveform diagram of the high-voltage power supply 7 when the magnetron 8 oscillates and when it does not oscillate. This negative voltage is the forward voltage at which the magnetron oscillates. This voltage is defined as the magnetron applied voltage _VAK , and the relationship with the input current _Iin is obtained to obtain an operation characteristic diagram as shown in FIG.

When the commercial power supply 1 is applied at time t ₀ , the magnetron 8
During the period until the oscillation starts, the magnetron applied voltage
Since V _AK is large even though the input current I _in is N etc. not flow殆, as the output voltage signal 16 corresponding to each of the illustrated large, the input current signal 12 decreases. Also, during this period, the output voltage control section 27 operates so that the selection signal output 18 matches the reference signal 20 as described above, so that the output voltage signal 16 becomes substantially the same as the reference signal 20.

The output voltage signal 16 and the input current I _in the magnetron 8 is lowered the magnetron applied voltage V _AK as described above and start oscillation increases, the input current signal 12 becomes the relationship shown in FIG. At this time, as described above, the input current control unit 26 operates so that the selection signal output 18 matches the reference signal 20, so that the input current signal 12 becomes substantially the same as the reference signal 20.

When the terminal voltage signal 32 in the output stop unit 29 is shown in accordance with these signal changes, the value is always smaller than the selection signal output 18 as shown in the figure due to the detection sensitivity setting described above. It has a value larger than the input current signal 12 during the oscillation period, and has a value larger than the output voltage signal 16 during the oscillation period of the magnetron 8.

Therefore, the output voltage detector 13 or the input current detector 9
However, when no signal is output due to failure, the selection signal output 18 has a smaller value than the terminal voltage signal 32, so that the output stop unit 29 can detect an abnormality by comparing the two signals.

Here's has a bias signal 38 to the input current signal rectifying circuit 11 in FIG. 1, as is clear in Figure 3, selection and there is no time t ₀ the bias signal 38 signal output 18 terminal This is because the voltage signal becomes smaller than the voltage signal 32 and is erroneously detected as abnormal. Naturally, the configuration may be such that the bias signal 38 is included in the output voltage signal 16.

In addition, in FIG. 1, the method of detecting the input current, the method of detecting the output voltage, the method of detecting the terminal voltage, the method of the inverter circuit, and the like are not limited to the illustrated configuration.

Further, a configuration may be adopted in which the secondary side output of the high voltage transformer 6 is rectified to obtain the high voltage power supply 7.

The above-described circuit operation is also possible when the unidirectional power supply 3 is configured to be obtained from a battery.

Effect of the Invention As described above, in addition to the conventional functions of the output voltage control means and the input current control means, when the output voltage detection unit or the input current detection unit fails, the present invention Since the operation is stopped, it is possible to prevent the life of the magnetron from being shortened or destroyed due to the application of excessive voltage or excessive power to the magnetron, and to prevent the switching element from being damaged.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a high-voltage power supply generating section of the high-frequency heating device according to the present invention, FIG. 2 is a waveform diagram of the high-voltage power supply voltage, and FIG. 3 ... unidirectional power supply, 4 ... switching element, 5 ... high frequency power supply, 6 ... high voltage transformer, 7 ... high voltage power supply, 8 ...
... magnetron, 9 ... input current detector, 13 ... output voltage detector, 18 ... selection signal output, 20 ... reference signal, 26 ...
... input current control unit, 27 ... output voltage control unit, 28 ... inverter circuit, 29 ... output stop unit, 33 ... terminal voltage detection unit.

Continuing on the front page (72) Inventor Kimiaki Yamaguchi 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Inventor Takahiro Matsumoto 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Daisuke Villa 1006 Kadoma Kadoma, Kadoma City Osaka, Japan 63-184280 (JP, A)

Claims (1)

(57) [Claims] 1. A unidirectional power supply obtained by rectifying a commercial power supply, an inverter circuit for switching the unidirectional power supply to a high-frequency power supply by high-frequency switching with a switching element, and boosting the high-frequency power supply to a high-voltage power supply. A high-voltage transformer for converting, and a high-frequency oscillator for applying the high-voltage power supply to oscillate a high frequency, the inverter circuit includes an output voltage detection unit that detects a voltage of the high-voltage power supply, and an input current of the inverter circuit. A current detection section for detecting, a terminal voltage detection section for detecting a voltage between both ends of the switching element, and a selection signal output of a larger one of an output of the output voltage detection section and an output of the current detection section so as to have a predetermined value. Power control means for controlling, and the terminal voltage detection unit has a detection sensitivity whose output signal is smaller than a selection signal output at the time of the power control, and High-frequency heating device signal output is formed by and an output stop means for stopping said high-frequency switching is smaller than the output signal of the terminal voltage detection unit.