JP3131530B2 - microwave - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven having an inverter circuit for supplying variable power to a magnetron.

[0002]

2. Description of the Related Art An example of this kind of microwave oven is shown in FIG. In FIG. 4, the magnetron 1 is supplied with high-voltage power from the inverter circuit 2 via the high-voltage circuit 3. The inverter circuit 2 is configured to generate a variable power according to the switching operation of the switching element 4. And the switching element 4
Are controlled by an inverter control circuit 5 so that the inverter control circuit 5 can control the output of the magnetron 1. The inverter control circuit 5 is configured to start the oscillation of the magnetron 1 and receive a control signal designating the oscillation output of the magnetron 1 from, for example, a panel-side control circuit 6, which is an operation control circuit provided on the back side of the operation panel. ing. The panel side control circuit 6 includes a microcomputer.

The high-voltage circuit 3 is provided with a current transformer 7 for detecting an anode current of the magnetron 1. The current transformer 7 detects an anode current as a physical quantity corresponding to the input power of the magnetron 1 and supplies a detection signal to the inverter control circuit 5. Thus, the inverter control circuit 5 performs feedback control so that the output of the magnetron 1 becomes equal to the output specified by the panel-side control circuit 6.

Further, the inverter control circuit 5 has a function of detecting an abnormality such as an abnormally high temperature of the switching element 4, an abnormally high input voltage, or an abnormally low input voltage. And a function to stop the magnetron 1 when the abnormality is detected. Since the panel-side control circuit 6 needs to recognize the operating state of the magnetron 1, that is, whether the magnetron 1 is operating normally or abnormally stopped, the inverter control circuit 5 When the magnetron 1 is stopped abnormally, the fact that the abnormal stop is transmitted to the panel-side control circuit 6 via the transmission line 8.

[0005]

However, in the above-described conventional configuration, the information that the magnetron 1 has been abnormally stopped is stored in the memory.
Since the transmission is performed from the inverter control circuit 5 to the panel-side control circuit 6 via the transmission line 8 and the transmission line 8 needs to be provided with a photocoupler, the transmission line for transmitting abnormal stop information of the magnetron 1 is required. 8 has a high manufacturing cost, and as a result, there has been a problem that the manufacturing cost of the entire microwave oven is high.

SUMMARY OF THE INVENTION An object of the present invention is to provide a microwave oven which can simplify the configuration for notifying the operation control circuit of the abnormal stop of the magnetron and reduce the manufacturing cost of the entire configuration.

[0007]

The microwave oven according to the present invention comprises:
An inverter circuit that supplies variable power to the magnetron, and controls an output of the magnetron by turning on and off a switching element of the inverter circuit; and an inverter control circuit that stops the magnetron when an abnormality is detected. Input power detection means for detecting a physical quantity related to the input power of the
And it has at least a setting function of setting an output of the magnetron in accordance with a key operation of a user, while providing a control signal to the inverter control circuit and receiving a detection signal from the input power detection means, comprising a driving control circuit for feedback control so that the output of the magnetron becomes equal to the set output, further, the operation control circuit, level of the detection signal from said input power detection means
When the magnetron falls below the reference value, the magnetron
It is characterized in that it is configured to determine that it has stopped normally.

In this configuration, the inverter control circuit detects abnormalities such as an abnormally high temperature of the switching element, an abnormally high input voltage, or an abnormally low input voltage. It is also conceivable to have a function of detecting the magnetron and a function of stopping the magnetron when the abnormality is detected. The operation control circuit provides a control signal to the inverter control circuit and receives a detection signal from input power detection means for detecting a physical quantity related to input power to the magnetron, so that the output of the magnetron is controlled. It has a function of performing feedback control so as to be equal to the set output, and determines that the magnetron has stopped abnormally when the level of the detection signal from the input power detection means falls below a reference value during feedback control. And determining that the magnetron has been stopped abnormally by controlling the inverter control circuit not to supply a control signal to the inverter control circuit for a certain period of time when the magnetron has been stopped abnormally. It is also preferable that the inverter control circuit has a function of recognizing it. Arbitrariness.

[0009]

According to the above means, the control signal is supplied from the operation control circuit to the inverter control circuit to control the on / off of the switching element of the inverter circuit, and from the input power detection means for detecting the physical quantity related to the input power to the magnetron. By supplying the operation control circuit with the detection signal of
The operation control circuit is configured to perform feedback control so that the output of the magnetron becomes equal to the set output. In this case, since the operation control circuit receives the detection signal from the input power detection means, it becomes possible to determine that the magnetron has stopped abnormally based on the detection signal. Thereby, a transmission line for transmitting from the inverter control circuit to the operation control circuit can be eliminated. It is necessary to provide a configuration in which a detection signal from the input power detection means is supplied to the operation control circuit. ) Does not increase the configuration. Therefore, the manufacturing cost of the entire microwave oven is reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, in FIG. 1 showing an electric configuration of a microwave oven, a commercial AC power supply 11 is connected to an inverter circuit 12, and the inverter circuit 12
The high voltage circuit 13 is connected to a step-up transformer 14. The inverter circuit 12 includes a full-wave rectifier 15, a choke coil 16, a smoothing capacitor 17, and a switching circuit 1.
8. In this case, the full-wave rectifier 15
It is configured by connecting four diodes in a bridge,
One output terminal is connected to one end of the primary winding 14a of the step-up transformer 14 via the choke coil 16. The other end of the primary winding 14a is connected to a switching element, for example, a collector of a transistor (IGBT) 19, and an emitter of the transistor 19 is connected to the other output terminal of the full-wave rectifier 15.

A smoothing capacitor 17 is connected between the output side of the choke coil 16 and the other output terminal of the full-wave rectifier 15. A resonance capacitor 20 is connected in parallel to both ends of the primary winding 14a of the step-up transformer 14. Further, a diode 21 having the illustrated polarity is connected between the collector and the emitter of the transistor 19. The base of the transistor 19 is connected to the inverter control circuit 22, so that the transistor 19 is controlled to be turned on and off by the inverter control circuit 22.

The step-up transformer 14 is provided with two secondary windings 14b and 14c, of which the secondary winding 14c is a filament winding and is connected to the cathode 23a of the magnetron 23. ing. The other secondary winding 1
4b, the cathode 2 of the magnetron 23 is connected via a high-voltage capacitor 24 and a high-voltage diode 25 having the illustrated polarity at one end.
3a and the other end is grounded. The common connection point between the high-voltage capacitor 24 and the high-voltage diode 25 is grounded via a high-voltage diode 26 having the illustrated polarity. The two high voltage diodes 25, 2
6 constitutes a high-voltage rectifier 27.

Here, for example, a current transformer 28 which is an input power detecting means is provided in an energizing path from the high voltage diode 26 to the ground, and the current transformer 28 supplies a current flowing through the anode of the magnetron 23 (anode current). ) Is detected. In this case, the anode current of the magnetron 23 is a physical quantity related to the input power to the magnetron 23. The detection signal output from the current transformer 28 is supplied to an operation control circuit, for example, a panel-side control circuit 29.

The panel-side control circuit 29 is provided on the back side of the operation panel, and includes a microcomputer 30 and a rectifying / smoothing circuit 31. The rectifying / smoothing circuit 31 receives the detection signal output from the current transformer 28, rectifies and smoothes the detection signal, and supplies the rectified and smoothed voltage signal Vct to the microcomputer 30. The microcomputer 30 has a function of executing operation control of the entire microwave oven, and stores a control program for that. Also, the microcomputer 30
Receives various switch signals from various switches (not shown) provided on the operation panel and drives and controls various indicators (not shown) provided on the operation panel. It is configured.

In this case, when the user operates, for example, a switch for setting the heating output among the various switches,
The microcomputer 30 sets the output of the magnetron 23 according to the operation. Also, when the user operates various switches to select and set a cooking menu for automatic cooking, the microcomputer 30 automatically outputs the output of the magnetron 23 suitable for cooking the selected and set cooking menu. It is configured to be set to. That is, the microcomputer 30 has a setting function of setting the output of the magnetron 23 according to the key operation of the user.

Further, the microcomputer 30 gives the inverter control circuit 22 a control signal for starting the oscillation of the magnetron 23 and designating the oscillation output of the magnetron 23 as the setting output, specifically, a PWM signal Sa. Is configured. Further, the microcomputer 30 receives the detection signal from the current transformer 28 and performs feedback control so that the actual output of the magnetron 23 becomes equal to the set output. The microcomputer 30 receives each detection signal from various sensors (for example, a gas sensor, an alcohol sensor, a temperature sensor in a refrigerator, a room temperature sensor, a height sensor, and a shape sensor) provided for performing automatic cooking. It is configured.

The inverter control circuit 22 receives a PWM signal Sa from the microcomputer 30 and receives a PWM signal Sa.
It comprises an integration circuit 33 for converting the M signal Sa into a voltage signal Vin, an inverter control IC 34, and a drive circuit 35. The inverter control circuit 22 is connected to a temperature detector 36 that detects the temperature of the transistor 19 of the inverter circuit 12, is connected to the positive terminal of the smoothing capacitor 17 of the inverter circuit 12, and Connected to 19 collectors. Thus, the inverter control circuit 22 is configured to receive the temperature detection signal from the temperature detector 36, the terminal voltage signal on the positive electrode side of the smoothing capacitor 17, and the terminal voltage signal of the collector of the transistor 19.

Here, the integrating circuit 33 includes a resistor 37,
38 and a capacitor 39. As shown in FIG. 2, the inverter control IC 34 includes a switching pulse generation circuit 40, an abnormality detection circuit 41,
It comprises a PN transistor 42 and a comparator 43. Here, the switching pulse generation circuit 40
Upon receiving the voltage signal Vin from the integrating circuit 33, the switching pulse signal Sb is generated based on the voltage signal Vin, and the generated switching pulse signal Sb is supplied to the transistor 1 of the inverter circuit 12 via the drive circuit 35.
9 is provided. As a result, the transistor 19 is turned on and off according to the switching pulse signal Sb.

The transistor 42 has its collector connected to a connection line connecting the output terminal of the switching pulse generation circuit 40 and the input terminal of the drive circuit 35,
The emitter is grounded and the base is
Output terminal. This abnormality detection circuit 41
Are the temperature detection signal from the temperature detector 36, the terminal voltage signal on the positive electrode side of the smoothing capacitor 17, the transistor 19
Receiving the terminal voltage signal of the collector of
When the temperature of the magnetron 23 becomes abnormally high, when the input voltage becomes abnormally high, or when the input voltage becomes abnormally low, etc., the oscillation environment of the magnetron 23 changes when the abnormality is detected. The operation of the magnetron 23 is stopped when it is determined that the magnetron 23 is abnormal. Specifically, the abnormality detection circuit 41 supplies a high-level signal to the base of the transistor 42 at the time of each abnormality detection described above, turns on the transistor 42, and outputs the switching pulse signal Sb from the switching pulse generation circuit 40 to the drive circuit 35. Thus, the transistor 19 of the inverter circuit 12 is turned off and the magnetron 23 is stopped.

The abnormality detecting circuit 41 is configured to keep the transistor 42 turned on after detecting the abnormality. In this state, when a high-level signal is given to the input terminal as a release signal, for example, Transistor 4
2 is turned off. In this case, the input terminal of the abnormality detection circuit 41 is connected to the output terminal of the comparator 43. The comparator 43 is provided by the integration circuit 33
And when the voltage signal Vin becomes lower than the reference voltage signal VL, a high-level signal (release signal) is output and supplied to the abnormality detection circuit 41. It is configured as follows.

Next, the operation of the above configuration will be described with reference to FIG. First, a case where the magnetron 23 operates normally will be described. In this case, the microcomputer 30 supplies a PWM signal Sa corresponding to the setting output to the inverter control circuit 22. This PWM signal Sa is
The pulse signal is a pulse signal as shown in FIG. 3A, in which the pulse width d of the high level portion corresponds to the magnitude of the set output (heating intensity). In the inverter control circuit 22, the microcomputer 30
Is input to the integration circuit 33 through the photocoupler 32, where the PWM signal is converted into a voltage signal Vin (see FIG. 3B).

Subsequently, the switching pulse generation circuit 40 of the inverter control IC 34 receives the voltage signal Vin from the integration circuit 33, and switches the switching pulse signal Sb based on the voltage signal Vin (see FIG. 3E). Is generated, and the generated switching pulse signal Sb is applied to the base of the transistor 19 of the inverter circuit 12 via the drive circuit 35, whereby the transistor 19
Are turned on and off according to the switching pulse signal.
As a result, electric power corresponding to the switching operation of the inverter circuit 12 is supplied to the magnetron 23 via the high voltage circuit 13, and the magnetron 23 oscillates at the set output. Then, at this time, the magnitude of the anode current of the magnetron 23 (that is, the magnitude of the input power to the magnetron 23, which corresponds to the magnitude of the actual output of the magnetron 23) is determined by the current transformer 28. The detected signal from the current transformer 28 is converted into a voltage signal Vct (see FIG. 3F) by the rectifying / smoothing circuit 31, and the microcomputer 30 receives the converted voltage signal Vct. I have. Thereby, the microcomputer 30 performs feedback control based on the voltage signal Vct so that the actual oscillation output of the magnetron 23 becomes equal to the set output.

During the normal operation of the magnetron 23, as shown in FIG.
Between 1 and t2, if an abnormality such as an abnormally high temperature of the transistor 19, an abnormally high input voltage, or an abnormally low input voltage occurs,
The abnormality detection circuit 41 detects the abnormality and supplies a high-level signal (FIG. 3D) to the base of the transistor 42.
As a result, the transistor 42 is turned on, and the switching pulse signal from the switching pulse generation circuit 40 is not supplied to the drive circuit 35.
The second transistor 19 is turned off, and the magnetron 23 is stopped.

Then, as shown in FIG. 3 (f), the detection signal from the current transformer 28, that is, the rectifying / smoothing circuit 3
1, the level of the converted voltage signal Vct gradually decreases. Then, the level of the voltage signal Vct is equal to the reference value Vth.
In this case, at time t3, the microcomputer 30 determines that the magnetron 23 has stopped abnormally. At the same time, the microcomputer 30 is configured to stop outputting the PWM signal Sa at time t3.

Then, the microcomputer 30 sends P
When the WM signal Sa is no longer output, the level of the voltage signal Vin output from the integration circuit 33 gradually decreases. Therefore, when the voltage signal Vin becomes lower than the reference voltage signal VL at a time t4 when a predetermined time has elapsed after the output of the PWM signal is stopped, a high-level signal is supplied from the comparison circuit 43 to the abnormality detection circuit 41. As a result, the abnormality detection circuit 41 supplies a low level signal to the base of the transistor 42 to turn off the transistor 42.
Thus, when the microcomputer 30 outputs the PWM signal Sa again at time 5 in order to cause the magnetron 23 to re-oscillate, the magnetron 23 is driven to oscillate again. In this case, the microcomputer 30 controls the inverter control circuit 22 so that the PWM signal is not supplied to the inverter control circuit 22 for a certain period of time.
In this case, the inverter control circuit 22 recognizes that the abnormal stop has been determined.

According to this embodiment having such a configuration, the microcomputer 30 of the panel-side control circuit 29 supplies the PWM signal Sa to the inverter control circuit 22 to control the on / off of the transistor 19 of the inverter circuit 12 and the magnetron 23 The microcomputer 30 is provided with a detection signal from the current transformer 28 for detecting the anode current as a physical quantity related to the input power to the microcomputer 30 so that the output of the magnetron 23 is feedback-controlled so as to be equal to the set output. The microcomputer 30 is configured to determine that the magnetron 23 has stopped abnormally based on a detection signal from the current transformer 28. This eliminates the need for a transmission line for transmission from the inverter control circuit 12 to the panel-side control circuit 29, unlike the conventional configuration (see FIG. 4), and thus causes the microcomputer 30 to stop the magnetron 23 abnormally. The configuration for notifying can be simplified.

In the case of this configuration, it is necessary to provide a configuration in which the detection signal from the current transformer 28 is supplied to the panel-side control circuit 29. This is a substitute for the configuration (necessary in the configuration (see FIG. 4)), so that the configuration does not increase as compared with the conventional configuration. Therefore, the manufacturing cost of the entire microwave oven can be reduced by the amount of eliminating the transmission line.

Further, in the conventional configuration (see FIG. 4), since the panel side control circuit (microcomputer) 6 is configured to serially transfer an 8-bit power code as a control signal to the inverter control circuit 5, signal transmission is performed. Required three photocouplers. On the contrary,
In the above embodiment, since the PWM signal Sa is transmitted from the microcomputer 30 to the inverter control circuit 22, only one photocoupler 32 is used for signal transmission. The number of points can be reduced and the manufacturing cost can be further reduced.

[0029]

As is apparent from the above description, the present invention provides a control signal from the operation control circuit to the inverter control circuit to control the switching element of the inverter circuit to turn on and off, and relates to the input power to the magnetron. By providing a detection signal from the input power detection means for detecting a physical quantity to the operation control circuit, feedback control is performed so that the output of the magnetron becomes equal to the set output, and the operation control circuit receives the detection signal from the input power detection means. When the level of the detection signal falls below the reference value.
Since the magnetron is determined to have stopped abnormally, a transmission line for transmission from the inverter control circuit to the operation control circuit can be eliminated, and the configuration for notifying abnormal stoppage of the magnetron can be simplified. , And an excellent effect that the production cost of the whole microwave oven can be reduced.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing one embodiment of the present invention.

FIG. 2 is an electric circuit diagram of an inverter control circuit.

FIG. 3 is a time chart

FIG. 4 is a diagram corresponding to FIG. 1 showing a conventional configuration.

[Explanation of symbols]

11 is a commercial AC power supply, 12 is an inverter circuit, 13 is a high voltage circuit, 19 is a transistor (switching element), 2
2 is an inverter control circuit, 23 is a magnetron, 28 is a current transformer (input power detection means), 29 is a panel side control circuit (operation control circuit), 30 is a microcomputer, 31 is a rectifying and smoothing circuit, 32 is a photocoupler, 33
Denotes an integration circuit, 34 denotes an inverter control IC, 40 denotes a switching pulse generation circuit, 41 denotes an abnormality detection circuit, 42 denotes a transistor, and 43 denotes a comparator.

Claims (2)

(57) [Claims] An inverter circuit for supplying variable power to the magnetron; an inverter control circuit for controlling the output of the magnetron by turning on and off a switching element of the inverter circuit, and stopping the magnetron when an abnormality is detected; Input power detection means for detecting a physical quantity related to the input power to the magnetron; and at least a setting function for setting an output of the magnetron in response to a key operation by a user, and providing a control signal to the inverter control circuit. And an operation control circuit that receives a detection signal from the input power detection means and performs feedback control so that the output of the magnetron becomes equal to a set output.The operation control circuit includes: level of the detection signal becomes lower than the reference value Said Magne to come
A microwave oven that determines that TRON has stopped abnormally . 2. A function of the inverter control circuit for detecting an abnormality such as an abnormally high temperature of the switching element, an abnormally high input voltage, or an abnormally low input voltage. And having a function of stopping the magnetron when the abnormality is detected, and the operation control circuit provides a control signal to the inverter control circuit and detects a physical quantity related to input power to the magnetron. It has a function of performing feedback control so that the output of the magnetron becomes equal to a set output by receiving a detection signal from the input power detection means, and the level of the detection signal from the input power detection means during the feedback control. It is determined that the magnetron has stopped abnormally when is lower than the reference value. Has ability, further, when it is determined the abnormal stop of the magnetron by controlling the control signal to the inverter control circuit so as not to give a fixed time,
2. The microwave oven according to claim 1, further comprising a function of causing the inverter control circuit to recognize that the magnetron has been stopped abnormally.