JPH06267653A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To improve the durability as well as to prevent the failure of a magnetron by preventing the rise of the anode temperature of the magnetron in an abnormal oscillation condition. CONSTITUTION:In an inverter method of high-frequency heating device, a detecting winding 25 to grasp the variation of the cathode voltage of a magnetron 10 differentally; an output shaping circuit 80 to generate an abnormal oscillation reporting signal of the magnetron 10 depending on the output signal of the detecting winding 25; and a main controller 90 to lower the output level of the magnetron 10 from the present output level to a specific level responding to the abnormal oscillation reporting signal; are provided. When the magnetron 10 is in the abnormal oscillation condition, its output level is lowered to lower the anode temperature, and the magnetron 10 is protected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type high frequency heating device, and more particularly to the construction of a magnetron drive transformer for protecting a magnetron and improvement of a control circuit system and a control system of a control microcomputer. is there.

[0002]

2. Description of the Related Art A conventional high frequency heating apparatus for driving a magnetron with an inverter power supply will be outlined with reference to FIG.

The commercial power supply 1 is rectified by the rectification bridge 2,
A smoothing circuit 50 is formed by smoothing with the choke coil 3 and the smoothing capacitor 4.

A magnetron driving step-up transformer 6 (hereinafter referred to as a transformer) is connected to the rectifying / smoothing circuit 50, and a resonance capacitor 5 is connected to the transformer 6 in series or in parallel (parallel in the drawing) to form a resonance circuit. An inverter circuit 29 is configured by connecting the semiconductor switching element 7 to this resonance circuit.

Then, the high voltage diode 11 and the high voltage capacitor 12 are connected to the secondary side circuit of the transformer 6 which constitutes the above-mentioned inverter circuit 29 to constitute a voltage doubler circuit,
This becomes a magnetron drive circuit, and the magnetron 10 is further connected.

The cathode of the magnetron 10 is connected to the secondary winding 22 of the transformer 6, and the cathode voltage of the magnetron 10 is connected to the control circuit 40 via the capacitor 12 and the secondary winding 22. The control circuit 40 sends a signal to the drive circuit 30 to perform optimal control by feedback. That is, the control circuit 40
Is a drive pulse of the semiconductor switching element 7 through the drive circuit 30 in order to control the output based on the detection result of the input / output voltage / current in accordance with the magnetron output setting signal from the main controller 70 that controls the entire system. Adjust width and drive timing.

Here, the resistor 14 is for detecting the magnetron anode current, and the voltage across this resistor is input to the control circuit 40 as a current value.

The output of control winding 24 is input to control circuit 40 for synchronization and output voltage sensing.

An input current of the high-frequency heating device is detected from the consumption current detection circuit 60 and input to the control circuit 40.

The above is the outline of the high-frequency heating device for driving the magnetron with the inverter power supply.

[0011]

In the conventional method, when abnormal oscillation of the magnetron 10 occurs, the phenomenon is detected, the information is input to the control circuit 40, and the corresponding adjustment is performed to the magnetron. There is no protection function for stopping the progress of characteristic deterioration of 10.

Therefore, once abnormal oscillation occurs, self-heating becomes excessive and the anode temperature of the magnetron 10 rapidly rises, so that the magnetron 10 itself is destroyed. In FIG. 27, the control winding 24 is provided for detecting the output voltage, but the above-described abnormality occurs rapidly, so that the detection is not sufficient with the control winding 24 arranged on the primary side. There was no practical use.

In view of the above problems, the present invention aims at providing a high-frequency heating device capable of preventing the magnetron from failing by increasing the anode temperature of the magnetron at the time of abnormal oscillation and improving the durability of the magnetron. And

[0014]

A high-frequency heating apparatus according to the invention of claim 1 is a rectifier circuit, a magnetron for high-frequency heating, a drive transformer, an inverter circuit, a drive circuit, a first control means, and a second control means. It includes control means, detection windings, abnormal oscillation detection means, and output level setting means. The rectifier circuit converts a commercial power supply into a DC power supply. The drive transformer supplies the magnetron with boosted power from the secondary side. The inverter circuit is connected to the primary side of the driving transformer and switches the DC power supply. The drive circuit drives the switching element of the inverter circuit. The first control means sets the output level of the magnetron according to the load and controls the entire system. The second control means controls the output level of the magnetron to be the output level set by the first control means in response to the signal fed back from the secondary side of the driving transformer. The detection winding is the drive transformer 2
It is provided on the secondary side under the same conditions as the secondary winding and differentially captures the fluctuation of the cathode voltage of the magnetron. The abnormal oscillation detection means detects abnormal oscillation of the magnetron based on the level of the output signal of the detection winding, and generates an abnormal oscillation notification signal. The output level setting means generates an output setting signal for lowering the output level of the magnetron set by the first control means to a predetermined output level in response to the abnormal call notification signal, and outputs the second setting signal. Give to the control means.

The high frequency heating apparatus according to the invention of claim 4 is
The invention of claim 1 further includes a notification signal ignoring means and a judging means. The notification signal ignoring means ignores the abnormal oscillation notification signal within a certain period when the magnetron starts up. The determination means counts the abnormal oscillation notification signal input after the elapse of the certain period, and determines that the magnetron is abnormal when the count value reaches a predetermined number.

The high-frequency heating device according to the invention of claim 5 is
A timer means and a dividing means are added to the invention of claim 1 or 4. The timer means causes the abnormal oscillation detection means to perform the abnormal oscillation detection operation of the magnetron at regular time intervals. The dividing means divides the output level when the output level of the magnetron is lowered into a plurality of stages between the output level during normal oscillation and a predetermined finally lowered level, and sets the timer. The output level is decreased by one step each time the abnormal oscillation notification signal is input from the means.

[0017]

According to the invention of claim 1, the detection winding differentially captures the variation of the cathode voltage of the magnetron, and the abnormal oscillation detection means detects the abnormal oscillation of the magnetron based on the output level of the detection winding, thereby causing the abnormal oscillation. A notification signal is generated.
Then, the first control means reduces the output level set by the first control means in response to the abnormal oscillation notification signal. By doing so, when the magnetron abnormally oscillates, it is possible to reduce the output level of the magnetron to prevent the anode voltage of the magnetron from rapidly increasing and to escape from the abnormal oscillation state. Therefore, the failure of the magnetron can be prevented and the durability of the magnetron can be improved.

The detection winding can be provided in parallel with the secondary winding of the drive transformer and on the opposite side of the primary winding. Further, the detection winding can be provided in the arm portion on the secondary side of the driving transformer. The detection windings are provided at these positions because the differential change corresponding to the change in the cathode voltage of the magnetron is the largest.

According to the present invention, the alarm signal ignoring means ignores the abnormal oscillation alarm signal within a certain period when the magnetron rises, so that the abnormal oscillation in the unstable state at the startup of the magnetron is originally intended. It is possible to prevent detection as abnormal oscillation.

According to the invention of claim 5, the output level of the magnetron is lowered stepwise by the dividing means,
In addition to protecting the magnetron and improving its durability, it is possible to maximize the heating function of the magnetron.

[0021]

1 is a circuit diagram showing an embodiment of a high frequency heating apparatus according to the present invention. The high frequency heating device shown in FIG. 1 includes a detection winding 25 provided on the secondary side of a transformer 6 for driving a magnetron, an output shaping circuit 80 for forming a waveform of an output signal of the detection winding 25, and an entire system. And a control device 90 for controlling the output level of the control circuit 40 in response to the output of the output shaping circuit 80. The other circuits are the same as the circuits shown in FIG. 17, and the description thereof will be omitted as appropriate.

Next, the overall operation of the high frequency heating apparatus shown in FIG. 1 will be described. The cathode voltage during normal oscillation of the magnetron 10 and the corresponding output of the detection winding 25 are as shown in FIG. On the other hand, the relationship between the cathode voltage of the magnetron 10 and the output signal of the detection winding 25 during abnormal oscillation is as shown in FIG. 3, and the output signal of the detection winding 25 is the cathode voltage indicated by the arrow in FIG. A differential variation part corresponding to the variation appears.

According to the present invention, when the peak value V _A larger than the reference value V _N appears in the output signal of the detection winding 25 with the peak voltage level V _N during normal oscillation as the reference value, the abnormal oscillation of the magnetron 10 occurs. determines that the output shaping circuit 8 a potential difference at this time (V _a -V _N)
0 is extracted, and the extracted signal is shaped to generate one magnetron abnormal oscillation notification signal, which is input to the main controller 90.

The main controller 90 includes an output shaping circuit 80.
A signal for lowering the output level of the magnetron 10 to a preset level P ₂ is generated in response to the abnormality notification signal from the control circuit 40. The control circuit 40 controls the drive pulse width or the drive timing of the switching element 7 in order to lower the output level of the magnetron 10 in response to the applied signal.

Next, the temperature of the anode voltage of the magnetron T ° C.
4 shows the relationship between the oscillation output P of the magnetron and the magnetron. Referring to (1) in FIG. 4, when the magnetron 10 abnormally oscillates at time t1, the magnetron anode temperature starts to rise. The main controller 90 judges that the magnetron is abnormally oscillating based on the abnormal neglected signal from the output shaping circuit 80, and at the time of this judgment t2, lowers the output level of the magnetron 10 to P _2. By outputting the magnetron output setting signal of 1 to the control circuit 40, the magnetron oscillation output is reduced from P ₁ to P ₂ as shown in (2) of FIG. As a result, the magnetron anode temperature can also be lowered from T ₁ to T ₂ . By doing so, it is possible to prevent a rapid increase in the anode temperature, escape from the abnormal oscillation state, and prevent the magnetron 10 from being destroyed.

FIG. 5 shows the main controller 90 shown in FIG.
6 is a circuit diagram showing an example of an output shaping circuit 80. FIG.

Referring to FIG. 5, output shaping circuit 80 includes diode 81 for rectifying the output of detection winding 25, zener diode 82 having zener voltage V _Z equal to reference potential V _N , transistor 83, and Transistor 8
3 includes a capacitor 84 and a resistor 85 operatively coupled to the collector.

Next, the operation of the output shaping circuit 80 will be described with reference to FIG. FIG. 6 is a signal waveform of each part of the output shaping circuit 80. The cathode voltage of the magnetron 10 has a waveform as shown in FIGS. 2 and 3 by being differentially captured by the detection winding. The output of the detection winding 25 at the time of abnormal oscillation of the magnetron has the negative side cut by the diode 81 and has a waveform as shown in FIG. Since the Zener voltage V _Z of the Zener diode 82 is set to be substantially equal to the output peak value V _N of the detection winding during normal oscillation, no voltage is applied to the base of the transistor 83 except during abnormal oscillation. During abnormal oscillation, a voltage corresponding to the difference between the peak value V _A during abnormal oscillation and the reference voltage V _N is applied to the base of the transistor 83, as shown in FIG. The capacitor 84 is charged with electric charges from the power supply voltage V _C through the resistor 85, and the voltage across the capacitor 84 is almost the power supply voltage V _C during normal oscillation. However, at the time of abnormal oscillation occurs, base voltage of the transistor 83 (V _A -V _N) is applied, the transistor 83 is driven, the electric charge charged in the capacitor 84 is discharged via the transistor 83, the base No voltage is applied to the transistor 83 and the transistor 83 is turned off. When the transistor 83 is turned off, the operation of charging again via the resistor 85 is performed. Thereby, the transistor 8
The voltage of the collector of No. 3 has a waveform as shown in FIG.

Referring again to FIG. 5, the main controller 90
Includes a microcomputer 71, a key input device 73, a display device 72, and the like. This main controller 90
Conditions such as heating and cooking are externally input to the microcomputer 71 via the key input device 73, and the processing result is displayed on the display device 72.

FIG. 7 is a block diagram showing the operation of the microcomputer 71 shown in FIG. FIG. 8 is a flowchart of the microcomputer shown in FIG.

Referring to FIG. 7, the microcomputer 71 includes a comparison section 71a, a timer section 71b, a counter section 71c, an output setting signal generation section 71d and a system control section 71e. The comparison unit 71a detects the abnormality by comparing the level of the abnormal oscillation notification signal with a predetermined threshold value V _{TH according} to the power cycle (see FIG. 6). The timer unit 71b detects the detection of the abnormal oscillation notification signal by stopping the operation of the comparison unit 71a for a certain period after power-on. The counter unit 71c counts the comparison result,
When the count value CNT becomes 3, the system control unit 71e determines that the oscillation is abnormal. The output setting signal generator 71d outputs a signal for setting the output level corresponding to the load to P1 in response to the output setting signal from the system controller 71e, and outputs the signal in response to the output signal of the counter 71c. and outputs a signal for reducing the P _2. The system control unit 71e controls the entire system such as the time for heating and cooking the load in response to the signal from the key input device 73 and the signal from the counter unit 71c, and control for reducing the output level to P _2. Do.

Next, the control operation for heating and cooking by the microcomputer 71 will be described with reference to FIG.

First, in step S1, it is detected that a certain period of time has elapsed after the power was turned on. This is because the oscillation operation of the magnetron 10 is unstable immediately after the power is turned on, and the abnormality detection operation is stopped for a certain period of time.

In step S2, the comparing portion 71a determines whether or not the level of the abnormal oscillation informing signal V _O exceeds the threshold voltage V _TH . If V _TH > V _O , the counter portion in step S3. 71c starts the count-up operation. On the other hand, if V _TH ≤V _O , the counter section 71c is reset in step S6.

In step S4, the counter section 71c
When the abnormal count signal from the comparison unit 71a is counted three times, the system control unit 71e, in step S5,
The output setting signal generator 71d is controlled to output the output level setting signal for lowering the output level of the magnetron 10 to P ₂ , and the counter 71c is reset in step S6.

In step S7, the system controller 71
e determines whether or not the heating operation is completed. If it is determined that the heating operation is completed, the system control operation is stopped, and if it is determined that the heating operation is not completed, the process returns to step S2. .

The reason why the counter section 71c counts the abnormality notification signal from the comparison section 71a three times in succession is that the protection function is provided by only one abnormal oscillation notification in consideration of the influence of noise or the like. This is because the operation causes a malfunction. FIG. 9 shows that if the magnetron 10 continuously abnormally oscillates during three cycles of the commercial power supply, the abnormal oscillation leaving signal V _O is continuously output three times.

In this embodiment, the abnormal oscillation leaving signal V
_{The case where O} is output three times consecutively is determined to be abnormal detection, but the case where abnormal oscillation notification signal is output three times or more consecutively may be determined to be abnormal oscillation.

FIG. 10 is a block diagram showing another embodiment of the present invention. The microcomputer 71 shown in FIG. 10 includes a comparison unit 71a and a first timer unit 71.
b, a counter section 71c, a system control section 71e, a second timer section 71f and a dividing section 71g. Comparison unit 71
a, the first timer unit 71b, the counter unit 71c, and the system control unit 71e are the same as those of the microcomputer shown in FIG. The first timer unit 71f sets the undetected period Δt, and makes the comparison unit 71a perform the comparison operation after Δt time. Dividing unit 71g divides between the output level P ₁ and P ₂ to _{P 1, P 11, P 12} , P 13, P 2, the output level comparison result that abnormal oscillation after Δt time is input Is decreased from P ₁ to P ₁₁ , and when the comparison result of abnormal oscillation is input after the next Δt time has elapsed, the output level P ₁₁
From P to P ₁₂ .

By doing this, the reduction of the magnetron oscillation output at the time of one abnormality detection is made small, and the function by the magnetron protection as the high frequency heating device is compared with the case where the output level is dropped from P ₁ to P ₂ at once. The degree of decrease can be reduced.

FIG. 11 is a flowchart of the microcomputer shown in FIG. FIG. 12 is a graph showing the relationship between the decrease in the output level P of the magnetron and the anode temperature T of the magnetron. The operation of the microcomputer shown in FIG. 10 will be described with reference to FIGS. 11 and 12.

In step S1, it is detected that the undetected period Δt has elapsed. This undetected period Δt is provided for the following reason. That is, the reduction of the abnormal oscillation of the magnetron does not stop immediately from the moment when the output is lowered from P ₁ to P ₁₁ , so Δt is set as the time until the abnormal oscillation of the magnetron is converged, and Δt is reduced after the output is reduced. During this period, the microcomputer 71 sets a non-detection period to ignore even if a signal sufficient for determining abnormal oscillation is input, and the operation for reducing the oscillation output of the magnetron is not performed during this period. Is.

In step S2, the threshold voltage V _TH
And the abnormal oscillation notification signal V _O are compared, and V _TH <V
_In the case of _O , the counter section 71c is reset in step S3, and it is determined in step S10 whether or not the heating operation is completed. On the contrary, when V _TH > V _O , the abnormality detection counter unit 71c is caused to count up in step S4.

If the count value CNT is not 3 in step S5, it is determined in step S10 whether or not the heating operation has been completed. Step S5
If the count value is 3, the counter unit 71c is reset in step S6.

Next, in step S7, it is judged whether or not the output of the magnetron has reached the final level P _2, and if it is not the final level, the output level is lowered to the next level in step S8. Then, in step S9, the undetected period Δt is set. Next, in step S10, it is determined whether or not the heating operation is finished,
If the heating operation has not ended, the process returns to step S1 and if the heating operation has ended, the system operation ends.

That is, steps S2 to S1
If the abnormal oscillation is stopped after the undetected period Δt has passed, the operation up to 0 continues the operation until the end of cooking with the output level from P ₁ to P ₁₁ being down, but at this point the abnormal If the oscillation is not stopped, the magnetron oscillation output is lowered again from P ₁₁ to P ₁₂ and the anode temperature of the magnetron is lowered from T ₁₁ to T ₁₂ , whereby the abnormal oscillation of the magnetron is converged.

The above operation is repeated every time the abnormal magnetron oscillation occurs until the level P ₂ of the magnetron oscillation output which is finally lowered is reached. It is possible to escape from the body and extend the operating life.

FIG. 13 is a front view showing an example of the transformer 6 shown in FIG. FIG. 14 is a sectional view taken along the line AA ′ of the transformer shown in FIG. 13 and 14, the transformer 6 includes a bobbin 61, cores 62, 1
The secondary winding 21, the secondary winding 22, the control winding 24 for synchronization and output voltage detection, and the detection winding 25 are provided. Core 6
2 is provided so as to penetrate the hollow portion of the bobbin 61. A primary winding 21, a secondary winding 22, and a control winding 24 are wound around the bobbin 61, and a detection winding 25 is wound on the secondary winding 22 via an insulator (not shown).

The detection winding 25 is provided so as to overlap the secondary winding 22 because the amplitude width (V _A -V _N ) of the differential fluctuation component corresponding to the cathode voltage of the magnetron at this position is maximum. Is.

FIG. 15 is a front view showing another example of the transformer 6 shown in FIG. 16 is a cross-sectional view of the transformer shown in FIG. 15 taken along the line BB '. The transformer 6 shown in FIGS. 15 and 16 is different from the transformers shown in FIGS. 13 and 14 in that the detection winding 25 has a primary winding 3
It is provided on the arm portion of the core 62 on the opposite side. Also in this position, the amplitude width of the differential fluctuation component corresponding to the change in the cathode voltage of the magnetron is the same as in the cases of FIGS. 13 and 14.

[0051]

According to the invention of claim 1, when the magnetron abnormally oscillates, the output level of the magnetron is lowered to prevent the anode temperature of the magnetron from rapidly increasing.
And it is possible to escape from the abnormal oscillation state. As a result, it is possible to prevent the failure of the magnetron and improve the durability of the magnetron.

According to the fourth aspect of the invention, it is possible to prevent the abnormal oscillation in the unstable state at the startup of the magnetron from being detected as the original abnormal oscillation.

According to the invention of claim 5, the output level of the magnetron is stepwise reduced by the dividing means to protect the magnetron and improve its durability, and to maximize the heating function of the magnetron. Can be made.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram of a magnetron cathode voltage and a detection winding output during normal oscillation.

FIG. 3 is a waveform diagram of a magnetron cathode voltage and a detection winding output during abnormal oscillation of the magnetron.

FIG. 4 is a graph for explaining the relationship between the temperature rise of the magnetron and the oscillation output of the magnetron.

5 is a circuit diagram showing an example of a main controller and an output shaping circuit shown in FIG.

FIG. 6 is a waveform diagram showing an output waveform of each part of the output shaping circuit.

7 is a block diagram when the microcomputer shown in FIG. 5 is viewed from the operation side.

FIG. 8 is a flowchart for explaining the operation of the microcomputer.

9 is a waveform chart for explaining the operation of the counter shown in FIG.

FIG. 10 is a block diagram showing another embodiment of the present invention.

11 is a flowchart of the microcomputer shown in FIG.

FIG. 12 is a graph showing the relationship between the decrease in output level P of the magnetron and the magnetron anode temperature T.

FIG. 13 is a front view showing an example of the transformer shown in FIG.

14 is a cross-sectional view taken along the line AA ′ of the transformer shown in FIG.

FIG. 15 is a front view showing another example of the transformer shown in FIG.

16 is a cross-sectional view taken along the line BB ′ of the transformer shown in FIG.

FIG. 17 is a circuit diagram of a conventional high-frequency heating device.

[Explanation of symbols]

 1 Commercial Power Supply 50 Rectifier Circuit 6 Transformer 7 Switching Element 10 Magnetron 25 Detection Winding 40 Control Circuit 80 Output Shaping Circuit 71 Microcomputer 71a Comparison Section 71b Timer Section 71c Counter Section 71d Output Setting Signal Generation Section 71e System Control Section 71f Second Timer 71g division

Claims (5)

[Claims] 1. A rectifier circuit for converting a commercial power source into a DC power source, a high-frequency heating magnetron, a drive transformer for supplying boosting power from the secondary side to the magnetron, and a primary side of the drive transformer. An inverter circuit for switching the DC power supply, a circuit for driving a switching element of the inverter circuit, and first control means for setting the output level of the magnetron corresponding to the load and controlling the entire system. A second control for controlling the output level of the magnetron to the output level set by the first control means in response to a signal fed back from the secondary side of the driving transformer,
And a detection winding which is provided on the secondary side of the drive transformer under the same conditions as the secondary winding, and which detects differentially the variation of the cathode voltage of the magnetron, and the detection winding. An abnormal oscillation detecting means for detecting an abnormal oscillation of the magnetron and generating an abnormal oscillation notification signal based on the output level of the magnetron; and an output level of the magnetron set by the first control means in response to the abnormal transmission notification signal. A high-frequency heating device, comprising: an output level setting means for generating an output setting signal for decreasing the output level to a predetermined level and giving the output setting signal to the second control means. 2. The detection winding is connected to the driving transformer.
The high-frequency heating device according to claim 1, wherein the high-frequency heating device is provided in parallel with the secondary winding and on the opposite side of the primary winding. 3. The detection winding is connected to the drive transformer.
The high-frequency heating device according to claim 1, wherein the high-frequency heating device is provided on the arm portion on the next side. 4. The high frequency heating apparatus according to claim 1, wherein the abnormal oscillation notification signal is ignored during a certain period when the magnetron starts up, and the abnormal oscillation notification signal input after the certain period has elapsed is counted. A high-frequency heating apparatus comprising: a determining unit that determines that the magnetron is abnormal when the count value reaches a predetermined number. 5. The high-frequency heating apparatus according to claim 1, wherein the abnormal oscillation detection means performs timer abnormal oscillation detection operation of the magnetron at regular intervals, and the output level of the magnetron is lowered. The output level of the normal oscillation is divided into a plurality of levels between the output level at the time of normal oscillation and a predetermined level to be finally reduced, and is set every time an abnormal oscillation notification signal is input from the timer means. A high-frequency heating device comprising: a dividing unit that reduces the output level step by step.