JP2006222004A - Microwave generation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave generation device preventing a high voltage diode or a magnetron from thermal breakdown by detecting non-load operation of the magnetron by a current flowing through the high voltage diode, and reducing power, or stopping operation. <P>SOLUTION: The microwave generation device, surely preventing the high voltage diodes 203, 204 from breakdown caused by temperature increase thereof, can be provided by detecting the current flowing through the high voltage diodes 203, 204 directly related with the temperature increase thereof, and by controlling an output of the magnetron. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microwave generator using a magnetron such as a microwave oven, and more particularly to a detection method for overheating protection of a high voltage diode used in an inverter.

  FIG. 4 is a configuration diagram of a conventional magnetron driving power source of a microwave oven.

  In the figure, the alternating current from the commercial power supply 11 is rectified to a direct current by the rectifier circuit 13, smoothed by the choke coil 14 and the smoothing capacitor 15 on the output side of the rectifier circuit 13, and given to the input side of the 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 IGBT (Insulated Gate Bipolar Transistor) that switches DC at high speed and an inverter control circuit 161 that drives and controls the IGBT, and the current flowing through the primary side of the step-up transformer 18 is switched on / off at high speed. Is done.

  The input signal of the control circuit 161 detects the primary side current of the rectifier circuit 13 with the CT 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 radiating fin for cooling the IGBT, and temperature information detected by the 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. A winding 183 with 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 half-wave rectifier circuit 19 that rectifies its output. The voltage doubler half wave 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 does not put a heated object in the heating chamber or is operated in a light load state, the magnetron anode current increases due to the rebound of the microwave, and the temperature of the magnetron and the high voltage diode rises more than usual. Therefore, it is attached to the top, bottom, left, and right five sides in the furniture and the air supply / exhaust port of the microwave oven is blocked, or the motor coil part of the cooling fan of the microwave oven is When a trouble such as disconnection occurs and the cooling fan becomes inoperable, the high-voltage diode or magnetron often breaks down.

  In such a case, as a method of preventing thermal destruction of these parts, it is conventionally placed near the IGBT that correlates with the temperature rise of the magnetron thermistor, temperature switch, high voltage diode or magnetron, and detects the temperature rise of the IGBT. A chip thermistor that can be used was stopped before the thermal breakdown of these high-voltage diodes and magnetrons to prevent temperature rise.

In this case, as a method of detecting the temperature by attaching the thermistor 9 ′,
1) There was a method of fastening the package with a thermistor lead sen U with glasses terminals.

  However, since the method of tightening the package part can be realized only by human work, the number of man-hours is increased and the cost is increased accordingly.

  2) There is also a method in which the thermistor is separately screwed to the heat dissipating fin and detected from the heat dissipating fin (see, for example, Patent Document 1).

  In addition, a thermistor attached to the magnetron is used to stop the high voltage diode or magnetron before thermal destruction to prevent temperature rise, or a chip thermistor placed near the IGBT is used to prevent the high voltage diode or magnetron from being destroyed. There is also a method to prevent the temperature from rising, but this also has the disadvantage that both the high temperature diode has a low temperature detection accuracy and sensitivity because the detection temperature is not a direct temperature but a temperature in the vicinity of the magnetron or IGBT. .

3) Furthermore, there was a method of attaching a radial thermistor in the vicinity of the IGBT 8 on the printed circuit board (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 2-312182 Japanese Patent No. 2892454

  Fig.5 (a) is a figure which shows the attachment method of patent document 1, and is a figure which shows the state which screwed the thermistor to the radiation fin.

  In the figure, 6 is a printed circuit board, 7 is a radiation fin, 8 is an IGBT, and 9 'is a thermistor.

  The heat radiating part of the IGBT 8 that generates high heat is fixed to the heat radiating fins 7, and its three legs are inserted into the through holes of the printed circuit board and soldered on the opposite side. The thermistor 9 ′ is also screwed to the radiating fin 7 and takes out temperature information of the radiating fin.

  However, such a screw fastening method to the heat radiating fin also increases the man-hours and the cost, and the detection temperature is not the direct temperature of the high voltage diode, but the temperature of the heat radiating fin with the IGBT attached. Although there is a certain degree of correlation between the temperature rises, the temperature detection accuracy and sensitivity are both poor.

  FIG. 5B is a view showing the attachment method described in Patent Document 2.

  In the figure, 6 is a printed circuit board, 7 is a radiation fin, 8 is an IGBT, and 9 'is a thermistor. This method is retrofitted in the vicinity of the printed circuit board, and has the disadvantage that the man-hour increases because it is attached by hand, and the thermal time constant of the thermistor deteriorates because it is directly affected by the cooling air. Also in this case, since the detection temperature is not the direct temperature of the high voltage diode but the temperature of the radiation fin with the IGBT attached, the temperature rise of the high voltage diode and the IGBT is correlated to some extent, but the temperature detection accuracy and sensitivity are both poor. There were drawbacks.

  Furthermore, the thermistor 9 'was also attached to the vicinity A of the leg portion of the IGBT 8, but this was also retrofitted to the vicinity of the printed circuit board, and it was attached by hand, which increased man-hours and the effect of cooling air. Since it was received directly, there was a drawback that the thermal time constant of the thermistor deteriorated. Also in this case, since the detection temperature is not the direct temperature of the high voltage diode but the temperature of the radiation fin with the IGBT attached, the temperature rise of the high voltage diode and the IGBT is correlated to some extent, but the temperature detection accuracy and sensitivity are both poor. There were drawbacks.

In any case, the high-temperature diode has the disadvantage that both the temperature detection accuracy and sensitivity are poor because the detection temperature is not the direct temperature but the temperature of the IGBT or magnetron.
In addition, as described above, when the heated object is not placed in the heating chamber or when it is operated under a light load, the temperature rise value of the magnetron or high-voltage diode is greater than the temperature rise value of other components, and the temperature rise detection is a component destruction. There was also a drawback that it was not in time.

  Therefore, the present invention solves these problems, and does not need to be attached by hand, is not easily affected by cooling air, and more accurately detects the temperature rise of the high-voltage diode, so that the breakdown due to the temperature rise of the high-voltage diode can be further improved. Provided is a microwave generator that reliably prevents the generation.

  The present invention has been made to solve the above-described problems, and includes a detection control circuit that inserts a resistor between the cathode side of the high-voltage diode and the ground and detects and measures a voltage generated between the resistor and the ground. In addition, it is possible to detect the magnitude of the current that flows directly to the high-voltage diode, and it is not necessary to install it by hand, and it is difficult to be affected by the cooling air. It is possible to provide a microwave generator that can detect safely and more reliably prevent destruction of the high-voltage diode due to temperature rise.

  According to the present invention, the current control is performed by detecting the current flowing through the high-voltage diode, which is directly related to the temperature rise of the high-voltage diode. It is possible to provide a microwave generator that can prevent more reliably.

  In addition, a resistor is inserted between the cathode side of the high voltage diode and the ground, and a detection control circuit is provided to detect and measure the voltage generated between the resistor and the ground, but it is dangerous even if the resistor fails and becomes open. It is safe and can avoid the situation. In addition, since it is composed of a plurality of resistors and different types of resistors, it is possible to eliminate all the resistors themselves from being in a failure open state, and this point is also very safe.

  It is not necessary to install a thermistor by hand as in the past, and it is very easy to produce at the production plant. In addition, the indirect detection method at the IGBT temperature is not used. It is possible to provide a microwave generator that can detect the rise more accurately and safely and more reliably prevent the breakdown due to the temperature rise of the high-voltage diode.

  In the first invention, a resistance is inserted between the cathode side of the high voltage diode and the ground, and a detection control circuit for detecting and measuring a voltage generated between the resistance and the ground is provided. It is made to be able to detect.

  According to a second aspect of the present invention, in the microwave generator according to the first aspect of the present invention, the microwave generation power can be controlled so as to be changed by a voltage generated between the resistor and the ground.

  According to a third aspect of the present invention, in the microwave generator of the first or second aspect, a specific method for controlling the power generated by the microwave to be changed by the voltage generated between the resistor and the ground is shown. And

  4th invention shows the concrete method which controls so that the electric power of microwave generation can be changed with the voltage which generate | occur | produces between the said resistance and earth | ground in the microwave generator of any one of 1st-3rd invention. It is characterized by that.

  5th invention shows the concrete method which controls so that the electric power of microwave generation can be changed with the voltage which generate | occur | produces between the said resistance and earth | ground in the microwave generator of any one invention of 1-4. However, a heat stop function is provided for safety.

  According to a sixth aspect of the present invention, in the microwave generator according to any one of the first to fifth aspects, a resistor is inserted between the cathode side of the high-voltage diode and the ground, and a voltage generated between the resistor and the ground is detected and measured. Although it has a configuration equipped with a detection control circuit, when the resistor fails and becomes open, that is, the entire circuit floats from the ground while maintaining a high voltage, which is very dangerous. By providing a plurality of resistors in between, safety against open failures of the resistors is further improved.

  According to a seventh invention, in the microwave generator according to any one of the first to sixth inventions, the voltage of the detection control circuit is detected by a microcomputer with a built-in A / D converter.

  According to an eighth aspect of the present invention, in the microwave generator according to any one of the first to seventh aspects, in the detection control circuit, the detection is different from the resistance between the cathode side of the high-voltage diode and the ground between the circuit input and the ground. One or a plurality of side safety resistances are provided, and a method for improving safety is used.

  According to a ninth invention, in the microwave generator according to any one of the first to eighth inventions, the resistor and the detection-side safety resistor are mounted on different printed boards.

  According to a tenth aspect of the present invention, in the seventh microwave generator, a protective diode is provided between the output circuit from the detection control circuit to the microcomputer and the microcomputer power supply.

  Hereinafter, a resistance is inserted between the cathode side of the high voltage diode of the present invention and the ground, and a detection control circuit for detecting and measuring the voltage generated between the resistance and the ground is provided, and the magnitude of the current flowing directly to the high voltage diode is detected. A microwave generator that can be used will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram of a magnetron driving power source according to the present invention. In the figure, the alternating current from the commercial power supply 11 is rectified to a direct current by the rectifier circuit 13, smoothed by the choke coil 14 and the smoothing capacitor 15 on the output side of the rectifier circuit 13, and given to the input side of the 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 IGBT in the inverter 16. The inverter 16 is driven by an IGBT 16a that switches DC at high speed and an inverter control circuit 161 that controls the IGBT 16a, and the current flowing through the primary side of the step-up transformer 18 is switched on / off at high speed.

  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. A winding 183 with 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 full wave rectification circuit 20 that rectifies its output. The voltage doubler full-wave rectifier circuit 20 includes high-voltage capacitors 201 and 202 and two high-voltage diodes 203 and 204.

  According to the present invention, the resistor 211 is inserted between the cathode side of the high-voltage diode 204 and the ground, and the voltage generated in the resistor 211 is transmitted to the detection control circuit 26 formed on another printed circuit board 25 via the connector 24. .

  Next, each circuit operation on the detection control circuit 26 will be described. The generated voltage transmitted through the connector 24 is electrically connected to the input having the A / D converter function of the microcomputer 27 through the input resistor 221, and the generated voltage is the detection circuit side at the point where the connector 24 comes out. When the resistance 211 on the high-voltage diode 204 side is opened due to an abnormal state such as disconnection, the detection circuit-side safety resistor 23 connected to the ground by the safety resistor 23 is broken due to a high voltage being input to the detection control circuit 26 side. It is provided to prevent a dangerous situation.

  Further, a plurality of detection circuit side safety resistors 23 (for example, three 231, 232, and 233) are provided in order to ensure safety. On the A / D converter input side of the microcomputer 27, noise malfunction and microcomputer 27 protection For this purpose, the protective diode 28 is connected to the positive power supply side of the microcomputer 27, and the smoothing capacitor 29 is connected between the ground and the A / D converter input side to smooth the generated voltage, thereby preventing erroneous detection and detecting with high accuracy. Like that.

  During the microwave operation, a high voltage is applied to the magnetron 12 from the drive circuit 20 including the step-up transformer 18 and a microwave is output. At this time, an anode current flows through the high-voltage diode 204. It is known that this diode current increases as the microwave high-frequency output increases, and that the lighter the load in the heating chamber of the microwave oven, the greater the reflection of microwaves, resulting in a larger current value. That is, the temperature rise of the high-voltage diode 204 means that the higher the microwave high-frequency output, the higher the lighter the load in the heating chamber of the microwave oven. Further, since the current value flowing through the high voltage diode 204 is the same value as the current value flowing through the resistor 211 connected in series, the voltage (generated voltage) generated between the resistor 211 and the ground increases as the current value increases. The voltage is transmitted to the detection control circuit 26 configured on another printed circuit board 25 through the connector 24. The generated voltage is directly input to the A / D converter input terminal of the microcomputer 27 through the input resistor 221. The On the basis of the generated voltage (input information correlated with the temperature rise of the high voltage diode 204) input to the A / D converter input terminal, the microcomputer 27 performs control for preventing destruction of components such as the high voltage diode 204. .

  As described above, when the microwave oven is not put into the heating chamber or is operated in a light load state, the magnetron anode current increases due to the rebound of the microwave, and the temperature of the magnetron and the high voltage diode rises more than usual. In addition, if the installation conditions are very poor, such as when the furniture is placed on the top, bottom, left, or right side of the furniture and the air supply / exhaust port of the microwave oven is blocked, or the motor coil of the cooling fan of the microwave oven When a trouble occurs such that the part is disconnected and the cooling fan becomes inoperable, the high voltage diode 204 often exceeds the temperature rise limit, and the parts may be destroyed.

  FIG. 3 is a sequence diagram showing the control of the detection control circuit. When the microwave oven is operated, the temperature of the high voltage diode rises and the generated voltage increases accordingly. While the generated voltage is low, the generated voltage is the first threshold value. When the value is lower, since the temperature rise of the high-voltage diode is low and the temperature is not destroyed, microwaves are output at 100% of the preset output without output limitation, and microwave heating is executed.

  When the load is light as described above or when the installation conditions are slightly bad, the generated voltage will also exceed the first threshold value. At that time, the output is limited for the first time and the microwave is output at 80% of the preset output. Perform microwave heating. In addition, the second threshold value may be exceeded when operated under worse heating conditions. At that time, a larger output limit is applied and microwaves are output at 50% of the preset output to execute microwave heating. To do. Also, when operating under worse heating conditions, for example, when operating for a long time with no load or when the cooling fan motor fails, or when other parts fail, the second threshold is exceeded and the MAX threshold is further increased. At that time, heating is stopped.

  The microcomputer 27 transmits the output control information of the microwave oven to the inverter control circuit 161 through the photocoupler 30 for voltage separation and information transmission according to the information of the generated voltage that is input. When notified from the computer 27, the output control of the microwave oven is executed by controlling the on / off time to the IGBT 16.

  The high-voltage diode 204 is connected to the ground by the resistor 211 and the detection circuit side safety resistor 23. However, when the resistance 211 and the detection circuit side safety resistor 23 are all opened in an abnormal state such as disconnection, the detection control circuit 26 side When a high voltage is input and a failure or a dangerous situation occurs, a plurality of detection circuit side safety resistors 23 (for example, three 231, 232, 233) are provided to ensure safety, and the resistor 211 is opened. 2 is safe because the generated voltage becomes a value far exceeding the MAX threshold value and the microwave output is stopped as described above.

  In general, delivered parts and manufacturing processes often have defects concentrated in the same lot, so the resistance 211 and the detection circuit side safety resistance 23 are all different types of resistance and different processes such as axial resistance, radial resistance, surface mounting. The chances of opening all will be lower if they are made up of different processes such as type resistors and manual insertion type resistors.

  As described above, the microwave generator according to the present invention is configured to detect the current flowing through the high voltage diode, which is directly related to the temperature increase degree of the high voltage diode, and to control the output, so that the temperature increase of the high voltage diode can be detected more accurately. However, it is possible to more reliably prevent the high-voltage diode from being destroyed due to a temperature rise, and it can be applied not only to a microwave oven but also to various microwave generators.

Configuration of microwave generator according to the present invention Explanatory drawing of the safe stop when the resistance of the microwave generator according to the present invention is open Sequence diagram showing the control of the detection control circuit according to the present invention Configuration of conventional microwave generator with thermistor (A) Front view of printed circuit board with thermistor described in Patent Document 1 (b) Perspective view of printed circuit board with thermistor described in Patent Document 2

Explanation of symbols

12 magnetron 13 rectifier circuit 18 step-up transformer 201, 201 high voltage capacitor 203, 204 high voltage diode 211 resistance 221 input resistance 23 detection circuit side safety resistance 231, 232, 233 each detection circuit side safety resistance 25 printed circuit board 26 detection Control circuit 27 Microcomputer 28 Protection diode

Claims (10)

Microwave generation comprising a step-up transformer for generating a high voltage, a high-voltage diode for rectifying a secondary high voltage generated from the step-up transformer, a high-voltage capacitor, and a magnetron for generating a microwave by applying the high voltage The microwave generator provided with the detection control circuit which inserts resistance between the cathode side of the said high voltage | pressure diode and earth | ground, and detects and measures the voltage which generate | occur | produces between the said resistance and earth | ground in the apparatus. The microwave generator according to claim 1, wherein the microwave generator can be controlled so that the electric power generated by the microwave can be changed by a voltage generated between the resistor and the ground. The detection control circuit for detecting and measuring the voltage generated between the resistor and the ground is configured to control so as to reduce the power generated by the microwave when the voltage generated between the resistor and the ground exceeds a preset threshold value. The microwave generator according to claim 1 or 2. A plurality of the preset threshold values are provided, and the power generated for the microwave generation can be controlled according to which threshold voltage between the resistor and the ground is between. The microwave generator of any one of Claims 1-3. A plurality of the preset threshold values are provided, and the power generated by the microwave is stopped when the voltage generated between the resistor and the ground exceeds a threshold value set to the maximum value. Item 5. The microwave generator according to any one of Items 1 to 4. The microwave generator according to any one of claims 1 to 5, comprising a plurality of resistors inserted between the cathode side of the high-voltage diode and the ground. The microwave generator according to any one of claims 1 to 6, wherein voltage detection of the detection control circuit is performed by a microcomputer with a built-in A / D converter. 8. The detection control circuit according to claim 1, wherein one or more different detection-side safety resistors different from the cathode-side resistance of the high-voltage diode are provided between the circuit input and the ground. The microwave generator according to item. The microwave generator according to claim 1, wherein the resistor and the detection-side safety resistor are mounted on different printed boards. 8. The microwave generator according to claim 7, wherein a protection diode is provided between an output circuit from the detection control circuit to the microcomputer and a microcomputer power supply.

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