JP5452510B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to a power source for driving a magnetron used in a high-frequency cooking device.

  As a conventional control circuit for driving a magnetron, a method of detecting a rare short on the secondary side of a high-voltage transformer has been proposed.

  For example, in the circuit of the microwave oven shown in Patent Document 1, when a rare short occurs in the secondary coil of the high-voltage transformer, the phenomenon that the value of the resonance voltage applied to the primary coil falls below a specific value. By detecting this, it is possible to detect a rare short circuit occurring in the secondary coil of the high-voltage transformer at an early stage and to stop heating.

  Also, in this document, due to the influence of the characteristics of the magnetron connected to the secondary coil of the high voltage transformer, immediately after the start of heating, this resonance voltage has the same characteristics as when a rare short occurs in the secondary coil of the high voltage transformer. For the sake of illustration, the time until the resonance voltage becomes a normal characteristic is such that heating is not stopped even if the resonance voltage shows a value lower than a specific voltage.

JP 2001-167869 A

  In recent years, the variable range of the high-frequency output of magnetrons used in microwave ovens has increased from low output around 200 W to high output up to 1000 W.

  Therefore, in the configuration of Patent Document 1, in order to detect a rare short generated in the secondary side coil of the high voltage transformer, a rare short occurs in the secondary side coil of the high voltage transformer corresponding to each high frequency output. It is necessary to provide the value of the resonance voltage applied to the primary coil.

  Further, it is known that the magnetron oscillates abnormally when the resonance voltage applied to the primary coil of the high-voltage transformer is suddenly changed in order to suddenly change the high frequency output from the magnetron.

  However, in Patent Document 1 described above, a threshold value of the resonance voltage applied to the primary coil for determining that the secondary coil of the high-voltage transformer has been short-circuited is provided according to the high-frequency output, and the magnetron is heated during heating. When the high-frequency output is changed from 200 W to 1000 W, when the threshold value when the high-frequency output is 200 W is changed to the threshold value when 1000 W and the output value of the magnetron are changed simultaneously, the threshold value is instantaneously switched. The resonance voltage applied to the primary coil of the high-voltage transformer is smoothly changed from a value at which high-frequency output 200 W can be output to a value at which 1000 W can be output in order to avoid a sudden change. Since the resonant voltage applied to the primary coil of the high-voltage transformer is still low, the secondary coil of the high-voltage transformer is rarely short-circuited In which the false judges.

The present invention has been made in order to solve the above-described problem, and includes a magnetron that transmits a high-frequency output to heat an object to be heated, a high-voltage transformer that boosts a voltage to be applied to the magnetron, and the high-voltage transformer. A switching element for turning on / off a current flowing through the primary side coil, a resonance capacitor connected in parallel with the primary side coil for flowing an AC current through the primary side coil, and turning on / off the switching element And an input current detection circuit for measuring power consumption when driving the magnetron, and the detection result of the input current detection circuit so that a high-frequency output oscillated by the magnetron becomes a set value. Control means for changing the ON / OFF ratio of the switching element; voltage detection means for detecting a voltage applied to the primary side coil; A reference voltage switching means for the high voltage transformer of the secondary coil having in accordance with the constant-high-frequency output is set to a reference voltage determined that the short circuit, the detection value of said voltage detecting means and by said reference voltage switching means Comparing means for comparing with a set reference voltage and outputting a signal for stopping the operation of the switching element when the detected voltage value becomes larger than the set reference voltage, and the reference voltage switching means comprises the magnetron After the high-frequency output oscillating is switched to a lower output than the operating output, the time that the power consumption measured by the input current detection circuit stabilizes to a value corresponding to the switched high-frequency output After the elapse of time, the reference voltage is switched.

  According to the present invention, even if the output of the magnetron is changed during heating, it is not erroneously determined that a rare short has occurred in the secondary coil of the high-voltage transformer, and a highly reliable high-frequency cooking device is provided. can do.

It is an external appearance perspective view of the high frequency heating cooking appliance which shows one Example of this invention. It is AA sectional drawing of FIG. The block diagram which shows the control part of the high frequency heating cooking appliance which shows one Example of this invention. Explanatory drawing of the power supply for magnetron drive of the said high frequency heating cooker. Explanatory drawing of the voltage waveform of the circuit principal part. Explanatory drawing of a reference voltage.

  Embodiments of the present invention will be described below with reference to FIGS. 1 and 2 described above.

  In FIG. 1, reference numeral 1 denotes a main body of a high-frequency heating cooker, in which food to be heated is placed in a heating chamber 17, and the food is heated and cooked using high-frequency energy or heat from a heater. The door 2 is opened and closed to put food in and out of the heating chamber 17, and the heating chamber 17 is hermetically closed by closing the door 2, thereby preventing leakage of high frequency used when heating the food. It is possible to contain the heat and efficiently heat it. The handle 7 is attached to the door 2 and facilitates opening and closing of the door 2, and has a shape that can be easily grasped by a hand. The glass window 4 is attached to the door 2 so that the state of food being cooked can be confirmed, and uses glass that can withstand high temperatures due to heat generated by a heater or the like. The input unit 5 includes a display unit 5a and an operation unit 5b provided on the operation panel 3 below the front surface of the door 2. The operation unit 5b is a heating unit such as high-frequency heating or heater heating, heating intensity, or heating time. The display unit 5a displays the contents input from the operation unit 5b and the progress of cooking. The exhaust port 8 is a place where the steam generated when the components are cooled and the steam generated when the food is heated are discharged.

  In FIG. 2, a machine room 18 is a space provided in the lower part of the heating chamber 17. In the space, a magnetron 31 for heating food, a waveguide 21 connected to the magnetron 31, and a power source for the magnetron 31 are provided. A substrate 9 on which a magnetron driving power supply 30 (FIG. 3) to be supplied and a main control means 6 (FIG. 3) are mounted, various components described later, a cooling means 62 for cooling these various components, and the like are attached.

  A substantially central portion of the bottom surface of the heating chamber 17 is recessed in a concave shape, in which a rotating antenna 19 is installed, and high frequency energy radiated by the oscillation of the magnetron 31 is output from the waveguide 21 and the rotating antenna driving means 23. It flows into the lower surface of the rotating antenna 19 through the coupling hole 22 through which the shaft 23 a passes, diffused by the rotating antenna 19 and radiated into the heating chamber 17. The rotating antenna 19 is connected to the output shaft 23 a of the rotating antenna driving unit 23.

  A hot air unit 11 is attached to the rear part of the heating chamber 17, a hot air fan 15 and a hot air heater 14 for efficiently circulating the air in the heating chamber 17 are attached in the hot air unit 11, and hot air is heated on the back wall of the heating chamber. A hole is provided as a passage. The hot air fan 15 rotates by driving a hot air motor 13 attached to the outside of the hot air unit 11, circulates air between the heating chamber 17 through a hole provided in the inner wall surface of the heating chamber, and circulates in the hot air heater 14. Heat the air.

  On the back side of the top surface of the heating chamber 17, a grill heating means 12 made of a heater is attached. The grill heating means 12 wraps a heater wire around a mica plate to form a flat surface, presses and fixes the heating chamber 17 to the back side of the top surface, and heats the top surface of the heating chamber 17 to remove the food in the heating chamber 17. It is baked by radiant heat. The temperature detection means 16 detects the temperature of the heating chamber 17 heated by each heater, and a thermistor or the like is used as the detection means.

  The table plate 20 is for placing food, has heat resistance so that it can be used for both heater heating and high-frequency heating, has good high-frequency permeability, and has no sanitary problems. It is molded with the material.

  Next, the control unit will be described with reference to the block diagram of FIG. Reference numeral 41 denotes a commercial power source that operates the control unit and each electrical component of the main body 1. A range heating means 60 comprises a magnetron 31 for heating food with high frequency energy and a power source 30 for driving the magnetron. The high frequency setting output from the magnetron is inputted from the input means 5, and the inputted value is the main control means 6. Is converted into a power signal 6a and sent to the control circuit 50 of the magnetron driving power source 30. 61 is an oven heating means, which comprises the above-described hot air unit 11 and the hot air motor 13 attached to the outside of the hot air unit 11, and the main control means so that the temperature of the heating chamber 17 becomes the temperature inputted from the input means 5. 6 is detected by the temperature detection means 16 and adjusts the electric power of the hot air heater 14 based on the temperature of the heating chamber 17. Reference numeral 62 denotes a cooling unit that cools self-heating components and components that are thermally defective due to heat conduction from the heating components during the heating operation. Especially when the range heating unit 60 is operating, The magnetron driving power source 30 is cooled. 6 is a main control means which operates each heating means to cook food according to the contents inputted from the input means 5, and the oven heating means 61 and grill heating means 12 according to the temperature detected by the temperature detection means 16. The power of the heater is adjusted.

  Next, operations of the magnetron 31 and the magnetron driving power source 30 will be described with reference to a control block diagram for explaining the magnetron driving power source in FIG. 4 and a voltage waveform diagram of the main part in FIG. Reference numeral 42 denotes a rectifier circuit for converting the AC power supplied from the commercial power supply 41 into a DC. A power supply smoothing circuit 43 smoothes the power rectified by the rectifier circuit 42. A high voltage transformer 46 boosts a voltage applied to the primary coil (this voltage is called a resonance voltage) to induce a high voltage in the secondary coil. Reference numeral 44 denotes a switching element. The switching element 44 turns on and off the current flowing through the primary side coil of the high-voltage transformer 46 at a high frequency (20 K to 40 KHz). Reference numeral 45 denotes a resonance capacitor, and even after the switching element 44 is turned off from ON due to the inductance of the resonance capacitor 45 and the primary coil of the high voltage transformer 46, a current flows through the primary coil of the high voltage transformer 46 in an alternating current manner. A voltage is induced in the secondary side coil. The voltage applied to the primary side is changed by adjusting the ratio of the ON / OFF time of the switching element 44 to adjust the magnitude of the voltage generated on the secondary side. The power supply smoothing circuit 43, the switching element 44, the resonance capacitor 45, and the high voltage transformer 46 described above constitute an inverter circuit 48.

  Reference numeral 47 denotes a high-voltage circuit that rectifies the high-frequency voltage induced in the secondary coil of the high-voltage transformer 46 by double voltage rectification. Reference numeral 31 denotes a magnetron. The electrical configuration includes a cathode (also used as a heater) 31a and an anode 31b. An electric current is supplied to the heater 31a to heat the heater, the heater is warmed, and the voltage between the cathode 31a and the anode 31b is an oscillation voltage. When reaching the above (about 4 kV), the magnetron 31 starts to oscillate and radiates high frequency energy as high frequency output to heat the food in the heating chamber 17.

  6a is a power signal. The strength of heating the food input from the operation unit 5b is converted into the power signal 6a by the main control means 6, and this power signal 6a is transmitted to the control circuit 50 of the magnetron driving power source 30 for control. The circuit 50 sets the power supplied to the magnetron 31 based on the power signal 6a.

  Reference numeral 51 denotes a power supply synchronization timing detection circuit for detecting the timing at which the voltage of the commercial power supply 41 (shown in FIG. 5 (a) 1/2 cycle of the commercial power supply) changes periodically and the voltage becomes zero volts. is there. As shown in FIG. 5B, the output of the power supply synchronization timing detection circuit 51 is set to output as a pulse when the voltage of the commercial power supply 41 is a certain voltage or less. And the control means 53 mentioned later is set so that the midpoint of the output pulse may be recognized as zero. However, if the control means 53 is equipped with a zero cross detection means that can detect the timing when the voltage of the commercial power supply becomes zero, it is possible to use the zero cross detection means in place of the power supply synchronization timing detection circuit 51. .

  An input current detection circuit 52 measures the power consumed by the operation of the magnetron 31, and detects the current flowing through the circuit here. The current measurement is calculated from the difference in voltage generated between both ends of the resistor 52a and the resistance value of the resistor 52a. Then, by confirming in advance the correlation between the high-frequency output when the magnetron 31 is oscillating and the current detected by the input current detection circuit 52, the control means 53 detects the detected value of the input current detection circuit 52. Thus, it is possible to confirm whether or not the high frequency output oscillated by the magnetron 31 matches the request from the main control means 6.

  The control means 53 has a time measuring means and a storage means 53a, and the time measuring means measures the pulse width of the pulse signal (FIG. 5B) sent from the power supply synchronization timing detection circuit 51 and determines the middle of the pulse. The frequency of the connected power supply 41 is determined by calculating and measuring the time between pulses. In the storage means 53a, the switching element 44 is turned on / off so that the output of the magnetron driving power supply 30 can generate a voltage to be applied to the primary side of the high voltage transformer 46 so that the magnetron 31 can oscillate the high frequency output efficiently. ON / OFF data for storing data is stored. This data differs depending on the frequency of the commercial power supply 41 to be connected, and two types are prepared for commercial power supplies of 50 Hz and 60 Hz when used in Japan. The length of the data signal generated by this data is the commercial power supply 41. The data corresponding to the half cycle is stored, and the frequency is set to be about 16 KHz. And the control means 53 calls the data corresponding to the frequency of the commercial power supply 41 from the storage means 53a, and creates the data signal (c) (FIG. 5 (c)) to be output to the next smoothing circuit 54. The data signal (c) starts counting from the midpoint of the pulse input from the power supply synchronization timing detection circuit 51 (the zero volt point of the AC power supply), and the OFF time that is called after the OFF time of the first data has elapsed. And a pulse based on the ON time data. When the half-cycle pulse has been output, the next pulse input from the power supply synchronization timing detection circuit 51 is awaited, and the operation of generating the pulse based on the recalled OFF time and ON time data is repeated. Heating is continued.

  Further, in order to change the high frequency output oscillated by the magnetron 31 in response to the power signal 6a sent from the main control means 6, the pulse of the data signal (c) outputted from the control means 53 is turned ON / OFF. Change the time ratio as follows: The data signal (c) is changed so that the voltage applied to the magnetron 31 is increased when the current value detected by the input current detection circuit 52 is small so that a current corresponding to the required high frequency output flows through the resistor 52a. The ratio of the ON time is increased, and the high frequency output generated by the magnetron 31 is increased. When the detected current is large, the ON time ratio of the data signal is shortened so as to reduce the voltage applied to the magnetron 31, and the high frequency output generated by the magnetron 31 is reduced. The ratio is gradually changed, and the change to the final setting output is made in about 1 second so that the magnetron 31 does not oscillate abnormally.

  The data stored in the storage means 53a is characterized in that the output of the magnetron driving power supply 30 oscillates at the maximum high frequency output from the magnetron 31 and the power factor and efficiency can be improved to the maximum when the magnetron 31 is oscillated. This is data for generating (FIG. 5H). Specifically, in order to improve the power factor and efficiency, in the part A of FIG. 5A corresponding to the bottom of the sine wave where the voltage of the commercial power supply 41 is low, By increasing the ON time ratio (shown in FIG. 5E), the induced voltage of the secondary coil of the high-voltage transformer 46 is quickly raised (maintained), the temperature of the heater 31a of the magnetron 31 is quickly raised, and the magnetron 31 The start of outgoing is quick.

  In order to improve the power supply efficiency, the voltage of the commercial power supply 41 suddenly increases from the A part of FIG. 5A corresponding to the base of the low sine wave (the B part of FIG. 5A), and then the voltage In the C portion of FIG. 5A at the apex portion where the fluctuations are gentle, in order to prevent an excessive voltage from being applied to the magnetron 31, the front portion of the C portion of the apex portion (in the B portion where the voltage is rapidly increased). The ratio of the ON time of the switching element 44 is shortened from the latter half) (as shown in FIG. 5 (e)) to suppress the rate of increase of the voltage applied to the magnetron 31, and an excessive voltage (magnetron 31) is applied to the C portion at the apex. (The current waveform suddenly flows when the applied voltage exceeds the magnetron oscillation voltage (about 4 kV)) is not applied (the voltage waveform applied to the magnetron is shown in FIG. 5 (h)).

  The high frequency output is changed by changing the ratio of the ON / OFF time of all the pulses of the data signal (c) at the same ratio, so that the power factor and power efficiency of the power source applied to the magnetron 31 are not lowered. .

  A smoothing circuit 54 smoothes the data signal (c) output from the control means 53. In the smoothing circuit 54, as shown by the signal g in FIG. 5D, the smoothed voltage value becomes lower as the ON time ratio of the pulse of the data signal (c) is shorter than the OFF time, and the ON time The longer the ratio is than the OFF time, the higher the voltage value after smoothing. The smoothing circuit 54 determines the circuit multiplier so that the time constant is 1 msec or less so that the smoothed voltage value can be changed corresponding to the change of the data signal (c).

  Reference numeral 55 denotes an ON timing detection circuit, which detects when the voltage applied to the switching element 44 becomes zero after the switching element 44 is turned OFF from ON, and then enables the switching element 44 to be turned ON next. Is output as the signal f in FIG. This signal f is a signal having a frequency of 20 to 40 KHz in the shape of a triangular wave.

  Reference numeral 56 denotes a reference oscillation circuit. The signal g in FIG. 5D obtained by converting the data signal (c) output from the control means 53 by the smoothing circuit 54 and the signal g in FIG. 5D output from the ON timing detection circuit 55. And the point at which the signals intersect is determined as the ON time and OFF time of the switching element 44 (shown in FIG. 5E), and the ON time and OFF time of the switching element 44 are determined. A high frequency of 20 KHz to 40 KHz is output so that the magnetron 31 can oscillate efficiently.

  The ON time and the OFF time of the switching element 44 are determined when the voltage value of the signal g smoothed by the smoothing circuit 54 is high, the intersection with the signal f swings toward the apex side of the triangular wave, so the ON time ratio of the switching element 44 is short. The voltage applied to the magnetron 31 is lowered. Further, when the voltage value of the smoothed signal g is low, the intersection point with the signal f is shifted to the bottom side of the triangular wave, so that the ratio of the ON time of the switching element 44 is increased and the voltage applied to the magnetron 31 is increased.

  Reference numeral 57 denotes a drive circuit that converts the signal from the reference oscillation circuit 56 into a signal that can drive the switching element 44. The output waveform is shown in FIG.

  Next, when the secondary side coil of the high-voltage transformer 46 undergoes a rare short, the configuration of means for detecting the rare short will be described.

  Reference numeral 71 denotes voltage detection means for detecting a voltage (resonance voltage) applied to the temporary coil of the high-voltage transformer 46. Reference voltage switching means 72 is a threshold value for determining whether the resonance voltage applied to the primary coil of the high voltage transformer 46 detected by the voltage detecting means 71 in accordance with the set high frequency output is greater than a specific value. A reference voltage is set. The reference voltage is provided according to the set high-frequency output.If the set high-frequency output is changed during heating, the reference voltage should be set immediately when the high-frequency output is changed from a low value to a high value. In the case of changing the high-frequency output from a high value to a low value, the reference voltage is changed after providing a certain delay time (the delay time set here is 1 second). This delay time is a time period for slowly changing the oscillating output of the magnetron, and is a value corresponding to the output in which the power consumption (current) detected by the input current detection circuit 52 is finally changed. This is the time it takes to stabilize. The reference voltage may be provided according to the set high frequency output, or the high frequency output may be divided into blocks and provided according to the blocks.

  Reference numeral 73 denotes a comparison means for outputting a signal for stopping the operation of the switching element 44 to the drive circuit 57 when the detection value of the voltage detection means 71 becomes larger than the voltage set by the reference voltage switching means 72.

  The present embodiment has the above configuration, and the operation thereof will be described next with reference to FIG. FIG. 6 shows the waveform of the resonance voltage applied to the primary coil when the secondary coil of the high voltage transformer corresponding to the high frequency output 700 W and the high frequency output 200 W is normal, and the primary when the secondary coil is abnormally short-circuited. It shows a waveform of a resonance voltage applied to the side coil and a reference voltage serving as a threshold for detecting a change in the resonance voltage in order to detect the abnormality. Specifically, when the high frequency output is 700 W, the normal resonance voltage waveform (A) applied to the primary side coil of the high voltage transformer 46 and the abnormal time when the secondary side coil has caused a rare short circuit. The resonance voltage waveform (b) and a threshold for detecting the abnormality are applied to the primary coil of the high voltage transformer 46 when the reference voltage A set by the reference voltage switching means 72 and the high frequency output 200 W are being output. The resonance voltage waveform (c) when the voltage to be normal is normal, the resonance voltage waveform (d) at the time of abnormality in which the secondary coil has caused a short-circuit, and the threshold for detecting the abnormality are set by the reference voltage switching means 72. The reference voltage B is shown.

  To warm the cooking object, the cooking object (not shown) is placed on the table plate 20 of the heating chamber 17 and the door 2 is closed. After the door 2 is closed, the high frequency heating is selected by the operation unit 5b while viewing the display unit 5a of the operation panel 3 provided on the door 2, and the high frequency output indicating the heating intensity and the heating time are set. Then, the heating start button (not shown) of the operation unit 5b is pressed to start heating. In the following description, a case where a high frequency output is input as 700 W and a heating time is input as 1 minute will be described.

  In order to start heating, the main control means 6 sets that the input high-frequency output is 700 W by sending data to the power signal 6 a and sending it to the control means 53 in the magnetron driving power supply 30. . The main control means 6 sends a signal to the rotating antenna driving means 23, rotates the rotating antenna 19, sends a signal also to the cooling means 62, and starts air blowing. The control means 53 receives the power signal 6a, calls out the data corresponding to the frequency of the power source among the data stored in the storage means 53a, generates and outputs a data signal (c). In the detection of the power supply frequency, the detection of the frequency of the connected commercial power supply 41 is completed when the product is connected to the power supply. Also, output information with a high frequency of 700 W output to the reference voltage switching means 72 is sent, and the reference voltage switching means 72 sets the reference voltage A corresponding to the output 700 W.

  Immediately after the start of heating, in order to heat the heater 31a of the magnetron 31 at an early stage to enable early oscillation, the data signal (c) is obtained from data at which the oscillation output of the magnetron 31 stored in the storage means 53a becomes the maximum output. ) And the high voltage generated thereby is applied to the magnetron 31. Then, before the heater 31a is still completely warmed, the ratio of the ON time of the data signal (c) is decreased in the direction of decreasing the voltage applied to the magnetron 31, thereby preventing an unnecessary current from flowing.

  The detailed operation is as follows. After the voltage is applied to the magnetron 31, the input current detection circuit 52 continues to detect the input current. When the detected value is 3A or less in terms of current, the data signal (c) output after the start of heating. The ratio of the ON time to the OFF time is continued, and when the detected current becomes 3 A or more, the ratio of the ON time of the data signal (c) is lowered to lower the voltage applied to the magnetron 31. Thereafter, the ratio of the ON time to the OFF time of the data signal (c) is changed so that a current value corresponding to the set high frequency output 700 W can be obtained. However, when the difference between the target input current value and the detected current value is large, the change width of the ratio between the ON time and the OFF time of the data signal (c) is increased, and when the difference is small, the ratio is changed. Reduce the width.

  The above is the description of the operation of the control circuit 50 at the normal time. Next, the operation at the time of abnormality in which a rare short is caused in the secondary coil of the high-voltage transformer 46 will be described.

  When a rare short occurs in the secondary coil of the high-voltage transformer 46, the input current of the primary coil decreases. When the input current detected by the input current detection circuit 52 decreases, the control means 53 having the circuit configuration described in the present embodiment decreases so as to maintain the input current corresponding to the set high-frequency output. In order to increase the input current, the ON time ratio of the switching element 44 is increased. Therefore, the resonance voltage detected by the voltage detection means 71 detects a high value when the secondary coil of the high voltage transformer 46 causes a rare short. Then, with respect to the reference voltage (reference voltage A) set by the reference voltage switching means 72 for each high-frequency output, the resonance voltage waveform (b) when the resonance voltage is normal is changed to the resonance voltage waveform (b) when it is abnormal. As shown in the figure, when the detection voltage of the resonance voltage detected by the voltage detection means 71 and detected by the comparison means 73 from the reference voltage A becomes higher, a signal for stopping the operation of the switching element 44 is sent to the drive circuit 57. Output and stop the oscillation of the magnetron 31.

  Next, the reference voltage change timing set by the reference voltage switching means 72 when the setting of the high frequency output is changed during heating will be described.

  The resonance voltage is higher than the value applied to the primary coil when the high voltage transformer 46 is normal, as described above, when the secondary coil of the high voltage transformer 46 is rarely short-circuited. Therefore, the reference voltage set by the reference voltage switching means 72 is set to a voltage value higher than the normal resonance voltage, and a rare short is detected by the resonance voltage being higher than the reference voltage when abnormal. Since this reference voltage increases as the high-frequency output increases, the normal resonance voltage also increases, so the value of the reference voltage serving as a threshold is also increased according to the oscillating high frequency. For example, as shown in FIG. 6, a reference voltage A higher than that at 200 W is set when the high frequency output is 700 W with respect to the reference voltage B when the high frequency output is 200 W.

  With the above configuration, when the high-frequency output is changed from 200 W to a high setting of 700 W during heating, the reference voltage switching means 72 sets the high-frequency output to 200 W even if the reference voltage B is immediately switched from the reference voltage B to the reference voltage A. The reference voltage A when the high frequency output is set to 700 W is higher than the reference voltage B when it is in the normal state, and when normal, the resonance voltage corresponding to 700 W applied to the primary coil of the high voltage transformer 46 is also the reference voltage A. It will never be higher.

  In addition, when the high frequency output is changed from 700 W to a low setting of 200 W during heating, the reference voltage switching means 72 has a certain delay time for switching to the reference voltage B corresponding to 200 W. Thus, even when the high frequency output is gradually changed to a low setting without abruptly changing the voltage applied to the magnetron 31, the transmission of the magnetron 31 is stabilized at an output of 200 W, and the primary side of the high voltage transformer 46 The reference voltage is maintained at the reference voltage A corresponding to 700 W for the high-frequency output until the resonance voltage is stabilized after being applied to the coil, and the reference time after the delay time has elapsed by providing the time until the stabilization as the delay time. By changing the voltage to the reference voltage B corresponding to the high frequency output 200 W, the normal resonance voltage does not reverse with respect to the reference voltage.

  Also, since the voltage applied to the primary side coil is always detected in response to the high frequency output during heating, if the secondary side coil of the high voltage transformer 46 is rarely short-circuited, it will immediately fail. Can be detected.

  The cooking object is heated stably by repeating the above operation. When one minute of the heating time elapses, the main control means 6 issues a stop command to the control means 53 and each load, and the heating is finished. The heating is finished with the signal to do.

  As described above, according to the present embodiment, even if the output of the magnetron 31 is changed during heating, it is not erroneously determined that a rare short has occurred in the secondary side coil of the high-voltage transformer 46. A high-frequency high-frequency cooking device can be provided.

30 Magnetron drive power supply 31 Magnetron 44 Switching element 45 Resonance capacitor 46 High voltage transformer 50 Control circuit 52 Input current detection circuit 53 Control means 71 Voltage detection means 72 Reference voltage switching means 73 Comparison means

Claims (1)

A magnetron that emits high-frequency output to heat the object to be heated;
A high-voltage transformer that boosts the voltage to be applied to the magnetron;
A switching element for turning ON / OFF the current flowing through the primary coil of the high-voltage transformer;
A resonant capacitor connected in parallel with the primary side coil in order to flow an alternating current through the primary side coil;
An input current detection circuit that measures power consumption when the magnetron is driven by turning on / off the switching element;
Control means for changing an ON / OFF ratio of the switching element based on a detection result of the input current detection circuit so that a high-frequency output oscillated by the magnetron becomes a set value;
Voltage detecting means for detecting a voltage applied to the primary coil;
Reference voltage switching means for setting a reference voltage for determining that the secondary coil of the high-voltage transformer has a short- circuit according to the set high-frequency output;
Compare the detection value of the voltage detection means and the reference voltage set by the reference voltage switching means,
Comparing means for outputting a signal for stopping the operation of the switching element when the detected voltage value is larger than a set reference voltage,
The reference voltage switching means switches the high-frequency output oscillated by the magnetron to a lower output than the operating output, and then the power consumption measured by the input current detection means corresponds to the switched high-frequency output. A high-frequency cooking device, wherein the reference voltage is switched after a time period until the value stabilizes.

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