JP2008292089A - State detecting device for detecting operating state of high-frequency heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation state detecting technology for performing accurate malfunction detection in relation to a change in the operated state of a high-frequency heating device such as a strong or weak output, a heated object, installation conditions and ambient temperatures. <P>SOLUTION: An anode current detected by an anode current detecting resistance 40 of a magnetron is inputted to an A/D converter terminal of a microcomputer 27 on the side of a control panel circuit board. The current is subjected to analog/digital conversion, and then a value of an anode voltage IaDC is obtained. On the basis of the read value for the anode voltage IaDC, the microcomputer 27 determines the operation state. In this case, a threshold used for determining a malfunction in a device is regulated at each device in relation to an output of the radio-frequency heating device or a change in the operation state of the heated object, and store it to perform more accurate malfunction detection. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high-frequency heating technique for a device using a magnetron such as a microwave oven, and more particularly to a state detection device that detects an operating state of the high-frequency heating device.

  FIG. 5 is a configuration diagram of a microwave oven 100 which is an example of a high-frequency heating device. In the figure, AC power from a commercial power source 11 is rectified to DC by a rectifier circuit 13, smoothed by a choke coil 14 and a smoothing capacitor 15 on the output side of the rectifier circuit 13, and supplied to the input side of an inverter 16. The direct current is converted to a desired high frequency (20 to 40 kHz) by turning on and off the semiconductor switching element in the inverter 16. The inverter 16 is controlled by an inverter control circuit 161 that drives and controls a semiconductor switching element that switches direct current at high speed, and the current flowing through the primary side of the step-up transformer 18 is switched on / off at high speed.

  The input signal of the control circuit 161 detects the primary side current of the rectifier circuit 13 by the current transformer 17, and the detected current is input to the inverter control circuit 161 and used for controlling the inverter 16. Further, a temperature sensor (thermistor) 9 ′ is attached to a heat radiation fin for cooling the semiconductor switching element, and temperature information detected by this temperature sensor is input to the inverter control circuit 161 and used for controlling the inverter 16.

  In the step-up transformer 18, a high-frequency voltage that is the output of the inverter 16 is applied to the primary winding 181, and a high-voltage voltage corresponding to the winding ratio is obtained in the secondary winding 182. Further, a winding 183 having a small number of turns is provided on the secondary side of the step-up transformer 18 and is used for heating the filament 121 of the magnetron 12. The secondary winding 182 of the step-up transformer 18 includes a voltage doubler rectifier circuit 19 that rectifies its output. The voltage doubler rectifier circuit 19 includes a high voltage capacitor 191 and two high voltage diodes 192 and 193.

  By the way, when such a microwave oven is not put into the heating chamber or is operated in a light load state, the magnetron temperature rises due to the rebound of microwaves (back bombardment), and the ebm is lowered. As a result, the anode current is reduced. There is a risk that the so-called air-burning or an overheating state due to a light load may occur, and the temperature of the magnetron or the high-voltage diode may increase more than usual. If such a state is left unattended, the high voltage diode or magnetron may be destroyed by temperature.

  As a method to prevent such troubles, a thermistor that detects the temperature is placed in the vicinity of a magnetron, a semiconductor switching element, a high-voltage diode, etc., and the temperature is stopped by stopping the device before thermal destruction of these components. There is.

  As a technique for preventing a temperature rise using a thermistor, there has been a method in which a thermistor is screwed to a radiation fin and the temperature is detected from the radiation fin (see Patent Document 1).

  FIG. 6A is a view showing the attachment method described in Patent Document 1, and is a view showing a state in which the thermistor 9 ′ is screwed to the radiating fin. A heat radiating fin 7 is attached on the printed circuit board 6, and a thermistor 9 ′ is attached immediately above the semiconductor switching element 8 attached in the vicinity of the heat radiating fin 7.

The heat radiating part of the semiconductor switching element (IGBT) 8 that generates high heat is fixed to the heat radiating fin 7, and its three legs are inserted into the through holes of the printed circuit board 6 and soldered on the opposite side. The thermistor 9 ′ is similarly screwed to the radiating fin 7 to extract temperature information of the radiating fin 7.

There is also a method of attaching a radial thermistor in the vicinity of a semiconductor switching element on a printed circuit board (see Patent Document 2). FIG. 6B is a view showing the attachment method described in Patent Document 2. In the figure, a heat radiation fin 7 for heat radiation is attached on a printed circuit board 6, and a semiconductor switching element 8 is attached adjacent to the heat radiation fin 7. A thermistor 9 ′ is attached to the opposite side of the semiconductor switching element 8.
Japanese Patent Laid-Open No. 2-312182 Japanese Patent No. 2892454

  In the method of Patent Document 1, since it is necessary to tighten the screws to the radiating fins, there is a problem that the number of assembling steps is increased and the cost is increased. Furthermore, since the detection temperature is not the direct temperature of the high-voltage diode but the temperature of the heat radiation fin with the semiconductor switching element attached, the temperature rise of the high-voltage diode and the semiconductor switching element is correlated to some extent, but the temperature detection accuracy and There was a drawback that both sensitivity was bad.

  In the method of Patent Document 2, since the thermistor is retrofitted in the vicinity of the heat dissipating fins, the number of assembling steps is increased, and the thermal time constant of the thermistor is deteriorated because it is directly affected by the cooling air. In addition, the detection temperature is not the direct temperature of the high-voltage diode, but the temperature rise of the high-voltage diode and the semiconductor switching element is correlated to some extent, but there is a drawback that both the temperature detection accuracy and sensitivity are poor.

  Further, the thermistor 9 'is also attached to the vicinity A of the leg portion of the semiconductor switching element 8, but in this case as well, it is retrofitted in the vicinity of the heat radiation fin, and is attached by hand, thereby increasing the number of steps and cooling. Since it is directly affected by the wind, there is a drawback that the thermal time constant of the thermistor is deteriorated. In addition, the detection temperature is not the direct temperature of the high-voltage diode, but the temperature rise of the high-voltage diode and the semiconductor switching element is correlated to some extent, but there is a drawback that both the temperature detection accuracy and sensitivity are poor.

  None of these are improvements in terms of high-voltage diode thermal breakdown protection, but the above-described technology is in any case inferior in temperature detection accuracy and sensitivity, and does not allow heated items to enter the heating chamber or operate under light load conditions. At times, the temperature rise value of the magnetron or the high-voltage diode becomes larger than the temperature rise value of the other component parts, and the temperature rise detection is not performed accurately, and there is a possibility of causing the component destruction.

  In order to accurately determine and grasp the operating state of the high-frequency heating device, the present invention can be applied to different combinations such as the strength of radio wave output, the object to be heated, installation conditions, and the ambient temperature. For the determination, a method using a threshold value adjusted for each device is provided, and an abnormal operation state such as an air-burning state or an overheating state is accurately detected, and each component or high-frequency heating device is protected.

The present invention provides a state detection device that detects an operation state of a high-frequency heating device including a magnetron that generates a microwave, and the state detection device inputs an anode current of the detected magnetron. And a determination unit that reads an anode current input from the anode current input unit and determines an operation state of the high-frequency heating device based on the anode current, and the determination unit includes a storage unit, and the storage The threshold for state determination is changed based on information stored in advance in the unit.

  According to the state detection device of the present invention, it is possible to store a threshold value as a determination criterion for determining the operation state of the high-frequency heating device in a storage unit such as a nonvolatile memory for each device according to the output control of the magnetron. . By setting an appropriate threshold according to the variation of each device, the boundary between abnormal operation and normal operation that changes depending on the ambient temperature, installation conditions, type of object to be heated, etc. can be clearly drawn, It is possible to prevent erroneous determination of the operating state.

  As information to be stored in the storage unit, a current value corresponding to one or more predetermined anode currents is input to the anode current input unit, and a value read from the anode current input from the anode current input unit is stored. By changing the threshold value for determining the state based on the stored information, it is possible to correct variations in components constituting the state detection device such as the anode current input unit and the determination unit.

  The information to be stored may be adjusted and stored by a high-frequency heating device that is a finished product, or may be adjusted and stored by a control panel substrate described later.

  According to the present invention, the anode current of the magnetron in the high-frequency heating device is detected, and the operating state of the high-frequency heating device is determined based on the detected anode current. At this time, it is possible to accurately detect the operating state by correcting the variation of the state detection device based on the anode current information adjusted for each device and more accurately determining the change in the anode current of the magnetron. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit configuration diagram of a high-frequency generator 100 such as a microwave oven according to an embodiment of the present invention, particularly a portion related to detection of an operating state. In FIG. 1, an AC power source from a commercial power source is not shown, but is rectified to DC by a rectifier circuit, smoothed by a smoothing circuit of an output side choke coil and a smoothing capacitor, and supplied to the input side of an inverter. . The direct current is converted to a desired high frequency (20 to 40 KHz) by turning on and off the semiconductor switching element of the inverter. The inverter is driven by an inverter control circuit that controls a semiconductor switching element that switches direct current at high speed, and switches on and off the current flowing through the primary side of the step-up transformer 18 at high speed. A high frequency voltage which is an output of the inverter is given, and a high voltage corresponding to the winding ratio is obtained in the secondary winding. Further, a winding having a small number of turns is provided on the secondary side of the step-up transformer 18 and used for heating the filament of the magnetron 12. The output of the step-up transformer is rectified by a double wave voltage doubler rectifier circuit connected to the secondary winding, and a DC high voltage is applied to the magnetron. This double wave rectifier circuit is composed of two high voltage capacitors 193 and two high voltage diodes 194.

  The basic configuration on the inverter circuit board described above constitutes a part of the high-frequency heating device according to the present invention and is the same as the overall configuration of FIG. 5 (except for the temperature sensor 9 ′), and is not shown. That is, the omitted portion includes at least an inverter unit (including the inverter 16 and the inverter control circuit 161 in FIG. 5) that controls the magnetron. The above parts are basically arranged on an inverter circuit board housed inside the casing of the high-frequency heating device.

  In the configuration of FIG. 1, an anode current detection resistor 40 as an anode current detection unit for detecting the anode current of the magnetron 12 is inserted between the magnetron 12 and the cathode side of the high voltage diode 194 and the ground of the inverter circuit board. ing. However, other elements may be used as the anode current detection unit as long as the current flowing through the anode can be detected.

  When a high voltage is applied to the magnetron during operation of the high-frequency heating device, a microwave is output. At this time, it is known that the anode current of the magnetron increases as the output of the high-frequency heating device increases. In addition, when the load in the heating chamber of the device is light or when the object to be heated is in an baked state where there is no object to be heated, the reflection of microwaves increases, and the anode current increases compared to when there is a certain load. ing. That is, by detecting the anode current flowing through the anode current detection resistor 40, it is possible to grasp the operating state of the high-frequency heating device, in particular, the abnormal operating state such as idling or overheating. Therefore, this current information can be input to the microcomputer 27 of the control panel board described later to control the operation of the apparatus.

  Next, a description will be given of a portion disposed on a control panel circuit board that is housed inside the casing of the high-frequency heating device in the same manner as the inverter circuit board and is configured as a separate substrate from the inverter circuit board. The current information detected by the detection resistor 40 is transmitted from the inverter circuit board through a connector and a communication line IaDC connected to the inverter circuit board via the connector, and is composed of an input resistor 41 and a capacitor 29, and also has high frequency noise. Then, the signal is smoothed through a low-pass filter that removes the signal and input to the A / D converter terminal 49 of the microcomputer 27. The resistor 43 is a surge protection resistor.

Further, the protective element 23 is connected between the output line (a part of the communication line IaDC) from the detection resistor 40 and the ground GND of the control panel circuit board in the preceding stage of the above-described low-pass filter. The protective element 23 is in an abnormal state on the inverter circuit board side (detection resistor 4
It is provided to prevent high voltage from being input to the microcomputer 27 when 0 is opened or when the ground is not connected.

  Further, the ground wire 50 is connected to the main body (housing) of the high-frequency heating device through a metal fixing member 50a such as an eyeglass terminal lead wire or a screw formed on the control panel circuit board. Has been. In other words, a configuration is adopted in which earthing to the control panel circuit board is performed at only one place of the ground wire 50. With this configuration, there is one anode current path of a magnetron as a detection target to be described later, and it is possible to easily detect an error when the ground is not connected.

  According to the present invention, the grounding / floating of both the inverter circuit board and the control panel circuit board is checked before the operation of the apparatus. This is a three-state output built in the microcomputer 27. This is done using circuit 46. The three-state output circuit 46 checks the earthing with the voltage value obtained at the A / D converter terminal 49 in a loop including the anode current detection resistor 40 and the resistors 41 and 42 as Hi output before the inverter operation. If it is confirmed that the connection is secured, the three-state output circuit 46 is opened as an open circuit, and is disconnected from the series of circuits. Only when it is normal, the PMW output command is sent via the communication line (PWM) to the inverter on the inverter circuit board side. Send to control circuit to start inverter operation. On the other hand, when the occurrence of floating of at least one substrate is detected in the earthing check by the three-state output, an error is displayed and the operation of the apparatus is prohibited. The other communication line OSC is a connector that receives a signal indicating the operation status of the inverter from the inverter control circuit. The portion represented by GND constitutes a connection line to the ground pattern of the control panel circuit board.

  Further, the microcomputer 27 is connected to a display unit 48 for displaying the status of the apparatus, and changes the display contents in accordance with instructions from the microcomputer 27. The microcomputer 27 is connected to an operation input unit 82 that accepts user operation input. It should be noted that the distribution of components to each of the illustrated inverter circuit board and control panel circuit board is arbitrary and is not limited to the illustrated example.

  Note that the distribution of the components to the inverter circuit board and the control panel circuit board in FIG. 1 and the above description is merely an example, and the component distribution method is not related to the essence of the present invention. However, in general, drive main circuits of devices such as an inverter circuit and an inverter control circuit are formed on the inverter circuit board and connected to the magnetron. A control circuit such as a microcomputer is formed on the control panel circuit board. In particular, when the apparatus is a microwave oven, it serves as a cooking menu command.

  In the present invention, as described above, the operating state of the high-frequency heating apparatus is grasped by detecting the anode current of the magnetron and its corresponding value (such as the anode voltage IaDC value, but also including the anode current itself). The detection accuracy at the A / D converter terminal 49 of the microcomputer 27 greatly affects the determination.

  In general, the A / D converter of the microcomputer 27 uses the A / D converter reference input voltage AVR as a reference potential, and, for example, in the case of an 8-bit A / D converter, the A / D converter is decomposed into 256 parts. Is converted into a digital output value indicating what number of 256 parts the voltage is input to. FIG. 2 is a diagram illustrating the relationship among the input voltage, digital output value, and A / D converter terminal input voltage of the A / D converter reference input voltage AVR. In general, the voltage applied to the power supply terminal Vcc of the microcomputer 27 and the A / D converter reference input voltage AVR use the same potential, and the power supply terminal Vcc of the microcomputer has a stabilized power supply circuit such as a three-terminal regulator. The voltage created in is applied. However, even with this stabilized power supply circuit, the output accuracy is generally ± 5% for general-purpose products. When such a stabilized power supply circuit is used, the input to the A / D converter reference input voltage AVR varies from 2.85V to 3.15V.

In this embodiment, the corresponding value of the anode current of the magnetron is a digital output value obtained by converting the input voltage of the A / D converter terminal 49 by the A / D converter of the microcomputer 27. For example, when the microcomputer 27 is programmed so that the abnormal state of the anode current of the magnetron is determined at the 63 level, the input voltage of the A / D converter reference input voltage AVR varies as can be seen from FIG. A / D converter terminal input voltage is 0.701V, 0.738V, 0.775V
The case where it recognizes occurs.

  FIG. 3 is a diagram illustrating the relationship between the A / D converter terminal input voltage and the anode current when the anode current detection resistor 40 is 2.4Ω. As can be seen from this figure, when the A / D converter input voltage is 0.701 V, 0.738 V, and 0.775 V, the actual anode currents are 292 mA, 307 mA, and 323 mA. This appears as individual variations of the high-frequency generator.

  The maximum anode current that can be passed through a magnetron used in a general microwave oven for home use is about 350 mA. When such a magnetron is used and the high frequency output of the microwave oven is 1000 W, the anode current is about 310 mA, which varies from device to device. As shown on the left, it is difficult to determine the optimum threshold value for determining the abnormal state of the magnetron.

  In this embodiment, in order to eliminate the above-described variation in detection of the anode current, a nonvolatile memory 80 is provided as a storage unit, and a digital output value corresponding to a predetermined anode current is stored in the nonvolatile memory 80, The determination is made with a threshold value calculated based on the stored value. FIG. 4 is a diagram illustrating an example thereof, and is a diagram illustrating a relationship among an A / D converter terminal input voltage, an anode current, and a threshold value. A voltage generated by the anode current detection resistor 40 when the anode current flows 350 mA is applied to IaDC of FIG. 1 of the control panel substrate, and the digital output value a recognized by the microcomputer 27 at that time is stored in the nonvolatile memory 80. . Similarly, the digital output value b when the anode current is 200 mA is also stored in the nonvolatile memory 80. The microcomputer is programmed to use a value obtained by using the values of a and b stored in advance in the nonvolatile memory 80 as a threshold value. In the case of this embodiment, the relationship between the A / D converter terminal input voltage and the digital output value can be approximated by a linear expression. Therefore, when the threshold is set to 310 mA, the microcomputer 27 sets the threshold to (40a + 110b). ) / 150. Thereby, even if the A / D converter terminal input voltage differs depending on the device, it can be corrected.

  In the above-described embodiment, the output value to be stored in the nonvolatile memory 80 is stored at two points. However, the approximation accuracy of the relationship between the A / D converter terminal input voltage and the digital output value is increased by using more points. Needless to say to raise it. Alternatively, when the approximate expression representing the relationship between the A / D converter terminal input voltage and the digital output value is high in accuracy, the point to be stored in the nonvolatile memory 80 may be one point, and the adjustment work may be omitted.

  Further, in the present embodiment, the nonvolatile memory 80 has been described in the storage unit. However, the nonvolatile memory 80 in the microcomputer 27 may be stored.

  Moreover, although one threshold value was demonstrated in a present Example, it cannot be overemphasized that several suitable threshold values may be provided for every several cooking sequence programmed by the microcomputer 27 previously. In particular, it is possible to set a plurality of fine threshold values by increasing the detection accuracy that is the effect of the present invention.

  Further, the method of storing the digital output value in the embodiment of the present invention may be performed by the control board or by the apparatus as a finished product. By adjusting with the apparatus, there is an effect that the variation in the detection resistance can be eliminated by this adjustment.

  In this embodiment, the case where a microcomputer is used as the determination unit has been described. However, the determination may be performed by a logic circuit other than the microcomputer.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the matters shown in the above-described embodiments, and those skilled in the art can make modifications and applications based on the description and the well-known techniques. Is also within the scope of the present invention, which is intended to be protected.

  As described above, according to the present invention, it is possible to detect anomaly of an anode current with high accuracy corresponding to the value corresponding to the anode current of a magnetron by a combination of different radio wave output, installation conditions, an object to be heated, an environmental temperature, and the like. Therefore, it is possible to achieve higher-precision control, safe operation, and protection of the high-frequency generator.

1 is a circuit configuration diagram of a high-frequency heating device according to an embodiment of the present invention, and in particular, a circuit configuration diagram showing a portion related to a state detection device of the high-frequency heating device The figure showing the relationship between the input voltage of A / D converter reference input voltage AVR which concerns on embodiment of this invention, a digital output value, and A / D converter terminal input voltage The figure showing the relationship between the A / D converter terminal input voltage and anode current in case anode current detection resistance 40 concerning the embodiment of the present invention is 2.4 ohms The figure showing the relationship between the A / D converter terminal input voltage which concerns on embodiment of this invention, an anode current, and a threshold value Configuration diagram of high-frequency heating device with thermistor (A) and (b) are the figures which show the state which attached the thermistor to the printed circuit board and the radiation fin.

Explanation of symbols

12 Magnetron 23 Protection element 27 Microcomputer 29 Capacitor 40 Anode current detection resistor 41, 42, 43 Resistor 46 Three-state output circuit 47 Three-state terminal 48 Display unit 49 A / D converter terminal 50 Ground wire 80 Storage unit 82 Operation input Part 100 High-frequency heating device (microwave oven)

Claims (4)

A state detection device that detects an operating state of a high-frequency heating device including a magnetron that generates a microwave, and is input by an anode current input unit that inputs the detected anode current of the magnetron and the anode current input unit And a determination unit that determines an operating state of the high-frequency heating device based on the anode current. The determination unit includes a storage unit that is stored in advance in the storage unit and based on information. A state detection device that changes a threshold for state determination. The state detection apparatus according to claim 1, wherein a nonvolatile memory is used as the storage unit. 3. The state detection device according to claim 1, wherein the determination unit that determines the operation state is a state determination unit based on information stored in the storage unit at a predetermined one or more anode current values. A state detecting device for changing a threshold value for the purpose. The state detection device according to claim 3, wherein the information stored in the storage unit is adjusted and stored for each device.