JP2834610B2 - High frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a high-frequency heating apparatus for performing so-called dielectric heating such as a microwave oven. More specifically, an inverter circuit is used as a power supply unit, and high-frequency power is supplied by the inverter circuit. The present invention relates to a high-frequency heating device configured to generate and raise a voltage by a magnetron driving transformer to drive the magnetron.

[0002]

2. Description of the Related Art Conventionally, in this kind of high-frequency heating apparatus, voltage feedback means and current feedback means using a winding of a magnetron driving transformer in order to stably control a magnetron output and protect a semiconductor switching element at the same time. And an overvoltage detection circuit are provided, and the feedback of these circuits controls the on-pulse width of the inverter circuit.

However, since the life of the magnetron in the component parts is relatively short, it is necessary to stop safely when the life of the magnetron is reached. If the magnetron is replaced, it is desirable that normal operation be resumed.

Conventionally, when a so-called moding phenomenon in which the oscillation of the magnetron operates in an unstable manner occurs, the resonance of the inverter circuit is disturbed, and the above-described feedback may stop the motor. It did not function properly, such as being destroyed. That is, the life of the magnetron, which is a component, is relatively short, and the oscillation becomes unstable as the electron emission ability of the cathode filament of the magnetron decreases with use time.

Further, when a user attempts to heat an inappropriate container / heated object, the Q factor of the resonator inside the magnetron is reduced, so that the oscillation cannot be maintained in a normal mode, and the oscillation does not occur. It will be stable. At this time, the loss of the magnetron increases due to the oscillation in the abnormal mode, resulting in abnormal heat generation. In addition, due to abnormal heat generation, electrode deformation inside the magnetron and wear of the filament are remarkable, resulting in a shorter life.

Further, at the start of heating, since the filament is not sufficiently heated, electron emission is insufficient, and transiently unstable oscillation occurs for a short time.
In this regard, since the magnetron does not generate abnormal heat, it does not easily cause deterioration.

That is, unstable oscillation is allowed at the start of heating, and oscillation is stopped during another heating period.
It is necessary to suppress input power and prevent abnormal heat generation.

Therefore, in the technique of Japanese Patent Application Laid-Open No. 3-78995, a search antenna is provided in a heating chamber by utilizing the fact that the oscillation frequency of a magnetron is doubled when the magnetron exhibits a moding phenomenon, and a higher-order frequency component is provided. When the microwave is detected and rectified and the level thereof reaches a predetermined value, the switching signal of the inverter circuit is turned off to stop the oscillation.

[0009]

SUMMARY OF THE INVENTION The above-mentioned JP-A-3-78
The technique of No. 995 employs a method of detecting an abnormality when the oscillation frequency at the time of abnormal oscillation is significantly different from that at the time of steady oscillation, so that the above-described problem can be solved. However, a search antenna is provided in the oven cavity. For,
If the oven cavities were different, the level had to be adjusted each time. In addition, there is a risk of malfunction due to high frequency spurious of the magnetron.

Furthermore, it is desirable that the substrate forming the inverter circuit and the oven cavity in which the antenna is mounted be isolated so that the substrate reduces the thermal effect of the cavity. Therefore, since the signal line from the antenna is routed from a position separated from the substrate, there is a problem in noise resistance and detection reliability.

In view of the above, the present invention allows unstable oscillation / moding to be detected at the start of heating and to stop the oscillating operation during another heating period or to suppress the input power and to generate abnormal heat even if heating is detected. It is an object of the present invention to provide a high-frequency heating device capable of preventing the occurrence of the above-mentioned problem and improving the detection reliability.

[0012]

The present invention provides a rectifying and smoothing circuit 101 for rectifying and smoothing a commercial power supply 100 to form a DC power supply, an inverter circuit 102 connected to the rectifying and smoothing circuit, and an inverter. a control circuit 108 for driving and controlling circuit 102, a magnetron driving circuit 112 and the magnetron 113 is driven and controlled by the inverter circuit 102, the output of current of the commercial power source 100
An output setting circuit 107 for setting timing, and a current detection circuit for detecting an instantaneous value of the current of the magnetron 113
And 106, and a current feedback means 11 1 for feeding back the detected current or power supply current of the current detecting circuit 106, the inverter circuit 102 includes a magnetron driving transformer 104 connected to the rectifying and smoothing circuit 101, the drive transformer Vessel 10
4 parallel young properly resonant capacitor connected in series 103
And a high-frequency heating device composed of the driving transformer 104 and a semiconductor switching element 105 connected in series, the control circuit 108 includes the inverter circuit 1
The duration of the driving output signal to 02, wherein the output setting times
A time width according to the set output of the path 107 and the current detection circuit
The control is performed to a smaller time width of the time width detected by 106 .

Further, the control circuit 108 may include one <br/> constant time after the start of heating, and has a means for stopping the function of the current detection circuit 106.

[0014] Alternatively, the control circuit 108, and has a means for stopping the function of the constant value is reached or de current detection circuit 106 that the level value is a current feedback means 111.

[0015]

In the above means for solving the problems, the on / off pulse signal output from the control circuit is supplied to the semiconductor switching element 105. Semiconductor switching element 105
3 is shown in FIG. When the control circuit 108 outputs an ON signal, the semiconductor switching element 105 becomes conductive and supplies power to the magnetron drive transformer 104.

When the control circuit 108 outputs an off signal, the semiconductor switching element 105 becomes non-conductive, and the resonance capacitor 103 and the magnetron driving transformer 1 are turned off.
04 constitutes a resonance circuit, and the resonance voltage appears in the collector voltage Vce of the semiconductor switching element 105.

Here, the next ON signal is issued in synchronization with the fall timing of the resonance voltage. The high-frequency power generated by the inverter circuit 102 is supplied to the magnetron driving circuit 112 by the secondary boosting winding of the magnetron driving transformer 104, and the output heating power of the magnetron 113 is controlled by an on / off pulse signal output by the control circuit 108. Is proportional to the on-time width of.

[0018] That is, the control circuit 108, the output setting times
On the on-time width corresponding to the set output of the road 107, and is synchronized with the resonant frequency of the magnetron driving dynamic transformers 104 -
An off-pulse signal is output to the semiconductor switching element 105 .

When high-frequency power is applied to the magnetron 113, a filament current first flows and the filament temperature rises. Thereafter, a magnetron current starts to flow and microwaves are radiated into the microwave oven. The detection circuit 106 provided in the magnetron current circuit turns off the output of the control circuit 108 at the falling timing of the current waveform.

Usually, the magnetron current is supplied to the control circuit 108.
A current corresponding to the on-time generated by the current flows. However, when the magnetron 113 deteriorates and modding occurs, the anode voltage of the magnetron 113 increases as shown in FIG. 3, and the magnetron current decreases as shown in FIG. 3 regardless of the ON period of the switching signal. The magnetron current is detected by the current detection circuit 106 and output to the control circuit 108. The control circuit 108 switches the control output signal from on to off based on the signal. At this time, since the ON time width of the control output signal is short, the flyback voltage is also low, and the charging voltage of the capacitor of the magnetron drive circuit 112 is low. This indicates that the magnetron current does not flow at the modulating voltage in the next cycle. However, as a phenomenon, the moding is suppressed and the operation shifts to a steady operation, thereby preventing abnormal heating of the magnetron.

Here, when the magnetron 113 exhibits moding, the magnetron current decreases for the following reasons. Magnetron 1 in steady state
The voltage applied to the anode 13 is determined by the constant voltage characteristic shown in the anode voltage-current characteristics of the magnetron 113 in FIG. This constant-voltage property is determined by the drive transformer 1
04 and the capacitor C of the drive circuit 112
3 and the inverter circuit 102 operates at the operating point (A) in FIG.

When the mode of the magnetron 113 is changed, the voltage and current characteristics shown in FIG.
The characteristic of No. 3 changes to the characteristic shown by the broken line. Here, the inverter circuit 102 moves to the operating point (B) in FIG. 2, but without the circuit of the present invention, the operating point (A) is applied to the capacitor C3 of the drive circuit 112 by the flyback energy accumulated at the time of ON. ), The charging is attempted to reach the operating point (C). However, according to the control of the present invention, the current detection circuit 106 detects that the point has moved to the operating point (B) in FIG. 2, and the control circuit 108 cuts off the flyback energy to cut off the ON signal. The operating point returns to (A) again without any increase, and the input power of the magnetron 113 is suppressed. In the present invention, since the switching control by the magnetron current detection circuit 106 is given priority to the current feedback means 111, the control circuit 108 outputs an off signal at the time of moding.

If the filament is not sufficiently heated at the start of heating, no magnetron current flows, and during this time, the brake and magnetron current detection circuit 10 based on the input from the current feedback means 111 is used.
The output of No. 6 is zero, and the control circuit 108 outputs an ON signal with a wide ON pulse width to sufficiently supply filament power.

When the magnetron 113 is about to oscillate, the mode of the magnetron 113 transiently occurs.
When 06 functions and produces an output, the on-time width is reduced and the magnetron filament power is reduced, which increases the transient moding time, which is undesirable.

Therefore, the control circuit 10 according to the third aspect of the present invention is described.
Reference numeral 8 has a function of turning on / off the input of the current detection circuit 106 based on a signal obtained by the current feedback unit 111 in order to recognize that the magnetron 113 has reached a predetermined current.

That is, as described in claim 2, the time required for the magnetron 113 to operate stably can be obtained in advance as a design value.
08, a time counting circuit 118 is provided to measure the time from the start of heating, and after reaching a predetermined time, the current detection circuit 10
It is also possible to configure so that the signal of No. 6 is turned on.

As described above, when the magnetron 113 exhibits unstable oscillation, that is, a moding symptom, the output can be suppressed by switching the switching signal from on to off based on the falling waveform of the magnetron current, and the abnormality of the magnetron 113 can be suppressed. An inverter control system that suppresses heat generation and suppresses the continuation of moding of the magnetron 113 can be configured.

[0028]

【Example】

(First Embodiment) FIG. 1 is a basic configuration diagram of the present invention. In FIG. 1, reference numeral 101 denotes a rectifying / smoothing circuit of a commercial power supply 100,
Reference numeral 102 denotes an inverter circuit, which is a magnetron driving transformer 104, a resonance capacitor 103 connected in parallel or in series (parallel in the figure) to the transformer 104, and a semiconductor switching element 10 connected in series to the driving transformer 104.
And 5.

Reference numeral 108 denotes a control circuit, and an output setting circuit 107
And the input from the current feedback means 111 for detecting and controlling the power supply current or the magnetron current,
The pulse width given from the PWM circuit 119 to the semiconductor switching element 105 is controlled. 120 is a synchronous circuit, 122
Denotes a comparator, and 118 denotes a clock circuit.

Reference numeral 106 denotes a magnetron current detection circuit which supplies a magnetron abnormal signal to the control circuit 108. 11
Numeral 0 denotes a current transformer for transmitting a magnetron current to the current feedback means 111 and the current detection circuit 106. 1
Reference numeral 12 denotes a magnetron driving circuit, which is a half-wave voltage rectifying circuit including a diode D2 and a capacitor C3 connected in series to the driving transformer 104. 113 is a magnetron.

FIG. 4 shows the basic configuration of FIG. 1 in further detail. FIG. 4 is a block diagram showing the configuration of the high-frequency heating device.
2, a rectifying / smoothing circuit 101 is connected.

The rectifying and smoothing circuit 101 includes a rectifying bridge D1.
And the output terminals thereof are connected to the yoke coil L1 and the smoothing capacitor C2.

The DC output terminal of the rectifying / smoothing circuit 101 has
An inverter circuit 102 is connected. The inverter circuit 102 is connected to a primary winding 104a of a magnetron drive transformer 104 and a parallel resonance circuit of a resonance capacitor 103. The inverter circuit 102 serves as a magnetron drive transformer 104 and a switching element 105. The series circuit of the transistor Q1 is connected, and the damper diode D4 is connected to the transistor Q1.
It is connected in reverse between one collector emitter.

The magnetron drive circuit 112 is connected to a magnetron heater winding 104b, high-voltage diodes D2 and D3 for half-wave rectifying the magnetron input winding 104c, and a high-voltage capacitor C3 via a magnetron driving transformer 104. .

The control circuit 108 includes a flip-flop IC
1 to IC6, shift register IC7, buffer BUF,
It comprises a comparator CMP4 and a counter CNT1.

When this component is matched with the component shown in FIG. 1, a PWM circuit 119 for generating an on / off pulse signal for switching the transistor Q1 at a high frequency comprises a reference timing generation circuit TG and a counter circuit CNT1. Will be.

When the control circuit 108 generates an on / off pulse signal, the synchronization circuit 120 of FIG. 1 for synchronizing with the resonance circuit composed of the driving transformer 104 and the resonance capacitor C1 is a magnetron primary winding of the driving transformer 104. 1
It comprises a comparator CMP2 for inputting a signal divided by a resistor from the resistor 04a, a timing circuit IC4 connected to its output terminal, a flip-flop IC6 and a counter circuit CNT1.

The output setting circuit 107 is a current input circuit 124 consisting of a resistor and a capacitor in FIG.
Indicated by The input voltage of the output setting circuit 107 and the voltage detected by the current transformer CT1 are compared with the comparator C
MP4 (comparator 122 in FIG. 1), and the result is sent to the counter circuit CN via the shift register IC7.
Set to T1. Therefore, the current feedback means 111
Are the shift register IC7 and the counter circuit CNT1.
And so on.

The magnetron current detection circuit 1 shown in FIG.
Reference numeral 06 includes a comparator CMP1, a flip-flop IC5, and the like in FIG.

The timekeeping circuit 118 shown in FIG.
Comprises an oscillator OSC and a timing generator TG.

Further, in FIG. 4, the overvoltage circuit 12
5 is provided, and this circuit 125 includes a comparator CMP
3 and a flip-flop IC3.

In the above configuration, a resonance circuit voltage signal composed of the driving transformer 104 and the resonance capacitor C1 is input to the comparator CMP3 by a signal obtained by dividing the voltage from the magnetron primary winding 104a of the magnetron driving transformer 104 by a resistor. When the threshold voltage is exceeded, the counter circuit CNT1, the timing generator TG, and the output flip-flop IC2 are reset.

In order to drive the magnetron 113 for heating, the switch SW is operated according to operation information given separately.
After the I, SW2, etc. are closed and converted to DC by the rectifying and smoothing circuit 101, the resonance capacitor C1, the driving transformer 10
4. Inverter circuit 1 including switching element 105
02 is supplied with power.

When the transistor Q1 is turned on, a current flows through the driving transformer 104 and a voltage is applied to the magnetron 113 to start oscillation.

Here, as shown in FIG.
When a moding abnormality occurs, the anode voltage increases and the magnetron current is turned off. When the magnetron current is turned off, the output of the current transformer 110 also becomes zero, and the comparator CMP1 and the flip-flop IC5
Resets the flip-flop IC6.

While the magnetron 113 is operating, the counter circuit CNT1 is counting down and the flip-flop IC2 is set, but the flip-flop I
When C6 is reset, flip-flop IC2 is also reset.

As a result, the counter circuit CNT in the normal state
The flip-flop IC2 and the counter circuit CNT1 are reset prior to the ON data set to 1,
The transistor Q1 is turned off.

As described above, when the magnetron 113 exhibits unstable oscillation, that is, a moding symptom, the output can be suppressed by switching the switching signal from on to off based on the falling waveform of the magnetron current, and abnormal heating of the magnetron 113 can be suppressed. And the continuation of the moding of the magnetron 113 is suppressed. Note that FIG.
In the graph, the waveforms indicated by broken lines in the control output, collector and anode voltages are virtual waveforms when the circuit of the present invention is not provided.

(Second Embodiment) The second embodiment of FIG. 5 is a circuit diagram for controlling the output of the control circuit 108, that is, the switching signal output, based on the outputs of the magnetron current detection circuit 106 and the current input circuit 124. I have.

The product of the magnetron current and the anode voltage is the input power. As described above, since the anode voltage is determined by the magnetron 113, the integral value of the magnetron current is input from the current transformer 110. The input voltage and the DC voltage given by the operation information from the output setting circuit 107 are compared with a comparator CMP.
By comparing at 4, the above-described configuration can be performed.

(Third Embodiment) FIG. 6 shows an example of a control circuit for making the output of the magnetron current detection circuit 106 valid when a certain time has elapsed from the start of heating. here,
The operation information generates a reference DC voltage of the current input circuit 124 based on, for example, a PWM signal based on the power supply cycle. The frequency divider 126 generates a delay time of several seconds by the frequency divider 126, and resets the flip-flop IC5. I have. The frequency divider 126 is internally fed back so as to perform a one-shot operation.

In the above configuration, the output of the flip-flop IC5 is LOW until the input of the PWM signal starts heating and the output of the frequency divider 126 becomes LOW, and the input of the magnetron current detection circuit 106 is invalid. become.

Therefore, at the start of heating, since the filament is not sufficiently heated, electron emission is insufficient, and unstable oscillation occurs transiently for a short time. Since the input of the circuit 106 is invalidated, the magnetron 113 does not generate abnormal heat and operates normally.

(Fourth Embodiment) FIG. 7 shows that the magnetron 11
3 shows an example of a control circuit that makes the output of the magnetron current detection circuit 106 valid by detecting that the current is flowing through the circuit 3.

This is because the magnetron current detection circuit 106
And the integration time constant circuit (delay circuit 128) composed of a resistor and a capacitor is configured. When the threshold value of the comparator CMP3 is set to a predetermined value and exceeds the level, the flip-flop IC5 can be set. It is configured to be.

Therefore, even if unstable oscillation occurs transiently for a short time at the start of heating, since there is an integration time constant circuit (delay circuit 128), no abnormality is determined during that time. It will work normally.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention.

[0058]

As is apparent from the above description, according to the present invention, the time width of the drive output signal to the inverter circuit is determined by the time width corresponding to the set output of the output setting circuit and the current detection.
Since the time width is controlled to be smaller than the time width detected by the circuit , the oscillation operation can be stopped or the input power can be suppressed to suppress abnormal heat generation during unstable oscillation / moding.

[0059] Further, to stop the function of the predetermined time current detection circuit from the start of heating, since the stop functioning until de current detection circuit reaches a predetermined value the level value is a current feedback means, not Stable oscillation / moding is allowed at the start of heating, and normal oscillation operation can be performed.

Further, compared with the conventional case where a search antenna is provided in the oven cavity, even if the oven cavities are different, it is not necessary to adjust the level each time, and the oven cavities can be heated at the output set level, and the oven cavities can be heated. Even if a search antenna is not provided, a circuit is formed on a substrate forming an inverter circuit, so that noise resistance and detection reliability can be ensured. Therefore, a reliable and inexpensive high-frequency heating device can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a high-frequency heating device according to the present invention.

FIG. 2 shows the anode voltage / magnetron current characteristics of the magnetron and the load characteristics of the inverter circuit.
Diagram showing characteristic transitions during magnetron moding

FIG. 3 is a diagram showing a waveform output of a main part of the inverter circuit of the present invention.

FIG. 4 is a configuration diagram of an inverter circuit according to a first embodiment to which a magnetron current detection circuit is added.

FIG. 5 is a configuration diagram of an inverter circuit according to a second embodiment in which an input of a current feedback means is obtained by a magnetron current;

FIG. 6 is a block diagram showing a control circuit according to a third embodiment for enabling the output of the magnetron current detection circuit when a predetermined time has elapsed from the start of heating.

FIG. 7 is a configuration diagram showing a control circuit according to a fourth embodiment for detecting that a predetermined current is flowing to the magnetron from the start of heating and for enabling the output of the magnetron current detection circuit.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 Commercial power supply 101 Rectifier smoothing circuit 102 Inverter circuit 103 Resonant capacitor 104 Magnetron drive transformer 105 Switching element 106 Magnetron current detection circuit 107 Output setting circuit 108 Control circuit 110 Current transformer 111 Current feedback means 112 Magnetron drive circuit 113 Magnetron 119 PWM circuit 120 Synchronous circuit 124 Current input circuit 125 Overvoltage circuit 126 Divider

Claims (3)

(57) [Claims] 1. A rectifying and smoothing circuit for rectifying and smoothing a commercial power supply to generate a DC power supply, an inverter circuit connected to the rectifying and smoothing circuit, a control circuit for driving and controlling the inverter circuit, and a driving control by the inverter circuit. Magnetron drive circuit and magnetron, and current of the commercial power supply
An output setting circuit for setting an output timing of the magnetron; a current detection circuit for detecting an instantaneous value of a current of the magnetron ;
And a current feedback means to feed back the detected current or power source current of the current detection circuit, said inverter circuit, and connected magnetron drive transformer rectifier smoothing circuit, parallel young properly with the drive transformers are connected in series A high-frequency heating device comprising a resonance capacitor and a semiconductor switching element connected in series with the drive transformer, wherein the control circuit sets a time width of a drive output signal to the inverter circuit by setting the output setting circuit. According to the output
Of the time width and the time width detected by the current detection circuit.
A high-frequency heating device characterized in that the time is controlled to be short . 2. A high frequency heating apparatus according to claim 1, wherein the control circuit, high-frequency heating apparatus characterized by comprising means for stopping the predetermined time, the current detection circuit feature from the start of heating. 3. A high-frequency heating apparatus according to claim 1, wherein the control circuit is characterized in that it comprises means for stopping the function of the Mas des current detection circuit reaches a predetermined value the level value is a current feedback means High frequency heating device.