JPH06101381B2 - High frequency heating device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency heating device for heating foods, fluids, etc., and more particularly to a high frequency heating device using a semiconductor power converter for generating high frequency power in its power supply device. is there.

[0002]

2. Description of the Related Art A power supply circuit of a high-frequency heating apparatus such as a microwave oven for home use has a structure shown in FIG. In FIG. 6, when the operation switch 1 is turned on, the commercial power supply 2 is connected to the high voltage transformer 3. The output of the secondary winding 4 of the high voltage transformer 3 is rectified by the capacitor 5 and the diode 6 and supplied to the magnetron 7. The heater winding 8 of the high voltage transformer 3 is connected to the cathode of the magnetron 7 to heat the cathode. Therefore, the magnetron 7 oscillates and outputs high-frequency electromagnetic waves (radio waves) to enable dielectric heating.

FIG. 7 (a) is a diagram showing the passage of time of the radio wave output P ₀ of the magnetron 7 after turning on the switch 1 at time t = 0.

When the switch 1 is turned on at t = 0, the cathode heater power and the high voltage power are simultaneously applied to the magnetron 7. At t = t ₁ after about 1 to 2 seconds, the temperature of the cathode rises sufficiently and the radio wave output P ₀ rises, and thereafter, it is kept substantially constant as shown in the figure. Of course, due to the temperature characteristics of the magnetron 7 and the high-voltage transformer 3, there may be a slight decrease in radio wave output over time,
Basically, the rated output of the device (maximum continuous operation
Telecommunications defined as output) Output P ₀ (for example, 500
W) is maintained.

FIG. 7B is a diagram showing a temperature rise of components inside the apparatus when the high frequency heating apparatus is operated as described above. For example, the temperature T _{M of the} magnetron 7 and the temperature T _a of the air around the high-voltage transformer 3 increase as shown in FIG.

FIG. 8 is a sectional view of the high frequency heating apparatus. An oven 10, a magnetron 7, a high-voltage transformer 3 and the like are arranged inside the housing 9 as shown in the figure, and are forcedly cooled by a cooling fan 11. Since the efficiency of the magnetron 7 is about 60% and the efficiency of the high-voltage transformer 3 is about 90%, the loss of about 300W for the magnetron 7 and about 100W for the high-voltage transformer 3 is required in the case of an apparatus having an actual radio wave output rating of 500W. Occurs. Therefore, the temperature of these parts gradually rises during operation as shown in FIG. 7 (b), and the temperature rises relatively fast until time t = t ₂ (for example, 15 minutes) determined by the thermal time constant of each part. After that, at t = t ₃ (for example, 60 to 120 minutes), the temperature of the entire apparatus reaches the maximum temperature and becomes saturated.

As described above, the high-frequency heating device has many components with relatively low conversion efficiency such as the magnetron 7 and the high-voltage transformer 3, and accordingly, the heat loss is large, so that the temperature rise during operation is relatively large and it takes a long time. It reaches a stable temperature.

The guarantee of the rated output P ₀ of the device must be an insulating material or constituent material capable of maintaining sufficient safety even if such heat loss occurs. It is designed to meet such guarantee conditions. That is, at t = t ₃ in FIG. 7 (b), the constituent material, the parts specifications, and the cooling structure are determined with due consideration of the temperature rise that has occurred.

Therefore, the case of the rated output 500W and 6
In the case of 00 W, the cooling conditions and the parts specifications are largely different. For example, in the magnetron 7, since the generated loss is different, the cooling structure becomes large and becomes large in size and high in price, and the high voltage transformer 3 is inevitably large in size and high in price.

[0010]

As described above, the conventional high-frequency heating device is a component that can ensure the safety and reliability of the device under temperature conditions when the temperature rise due to heat loss of the device is stable. It was configured using the specifications of.

However, since the high-frequency heating device is a unique heating method called dielectric heating, the heating time is relatively short, and it is necessary to use the heating time of about 5 minutes or less for reheating which is usually used in ordinary households. Is extremely large. That is, in FIG. 7 (b), there are many usages such that the usage is finished in a time of t = t ₀ , and t =
Cooking that reaches t ₃ is rarely done in general. Therefore, in most cases, the high-frequency heating device that guarantees the temperature rise at t = t ₃ , which does not need to be guaranteed under many usage conditions, is used for the usage time of t = t ₀ in most cases. The quality is excessive. However, in rare cases t =
Since there may be use conditions up to t ₃ , there is no choice but to have such a substantially excessive quality.

[0012]

The present invention has been made in order to solve the problems of the conventional high-frequency heating apparatus, and has the structure described below.

That is, a power supply unit obtained from a commercial power supply or the like, a high-voltage power conversion unit having a boosting means for converting the power from the power supply unit into high-voltage power, and a control unit for controlling the operation of the high-voltage power conversion unit. When the operation is started, it has a radio wave radiating section that radiates the output of the high-voltage power converting section as an electromagnetic wave, and a time measuring means
During this time, continuous operation is possible during the time measured by this time measuring means.
And a high voltage control unit for controlling the control unit so that the electromagnetic wave output is larger than the maximum output (hereinafter referred to as rated output) .

Further, after the time measurement by the time measuring means is finished, the control is automatically performed so that the rated output or the electromagnetic wave output lower than the rated output is controlled.

Furthermore, the clocking time of the clocking means can be adjusted.

[0016]

The high-frequency heating apparatus of the present invention having the above structure has the following functions.

The control unit is controlled by the high-voltage control unit having a clocking means to increase the conversion power of the high-voltage power conversion unit and to output an electromagnetic wave output larger than the rated power for a predetermined time. The cooling performance, heat-resistant specifications, and quality performance will not be excessive, but they will be appropriate, and the heating time can be greatly shortened.

Further, when the time measurement by the time measuring means is completed, the rated output or the electromagnetic wave output lower than the rated output is automatically set to automatically cope with the case where the heating operation for a long time is required.

Furthermore, since the timing means can be adjusted, the time for outputting an electromagnetic wave output larger than the rated output can be arbitrarily adjusted according to the state of the high frequency heating device to prevent the setting of necessary heating time and overheating. Therefore, it is possible to limit the operation time of the high output state.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a high frequency heating apparatus showing an embodiment of the present invention. In the figure, a filter circuit including a commercial power supply 20, a diode bridge 21, an inductor 22 and a capacitor 23 constitutes a power supply unit 24, and includes a capacitor 26, a step-up transformer 27, a transistor 28, a diode 29, a capacitor 30, and a diode 3.
1 and power to a power converter 33 consisting of a magnetron 32. The power converter 33 includes a capacitor 26,
Step-up transformer 27, transistor 28, diode 29
Is composed of an inverter, a high-voltage rectifier circuit that rectifies the output of the step-up transformer 27, a high-voltage rectifier circuit that includes a diode 31, and a magnetron 32 that generates high-frequency power. The magnetron 32 radiates this high-frequency power as electromagnetic wave energy. It also functions as a radio wave radiating part. Of course, the power converter 33 is 900 MHz
Alternatively, a semiconductor oscillator that oscillates at 2450 MHz may be used, and an antenna or the like may be provided as a radio wave radiating unit.

The transistor 28 is supplied with a switching control signal of, for example, 20 KHz to 200 KHz from the control unit 34 and performs a switching operation. Therefore, a high frequency voltage is generated in the primary winding 35 of the step-up transformer 27, the high frequency voltage is boosted, rectified and supplied to the magnetron 32, and the magnetron 32 oscillates. A signal proportional to the input current is sent from the input current detector 36 to the control unit 34. This input current detection signal is sent to the operational amplifier 37 in the control section 34 as shown in FIG. 2, compared with the signal of the reference signal generator 38, and its error signal is sent to the pulse width control circuit 39. Has been done. Therefore, the conduction time of the transistor 28 is controlled, and the input current is controlled by the so-called pulse width control so as to have a predetermined value.
As a result, the electromagnetic wave (radio wave) output P ₀ of the magnetron 32 is constantly controlled to a predetermined value (for example, 500 W).

In such a configuration, when the high frequency heating device is operated, a heating start command is sent from the heating start circuit 40 to the activation control section 41. When activation control unit 41 receives the heating start command, for a predetermined time at the start of operation, communication
A rising signal is given to the control unit 34 so that the controller 34 operates at an output (eg, 600 W) larger than the maximum output (rated output, eg, 500 W) capable of continuous operation .

FIG. 3A shows the radio wave output P ₀ indicating this state.
FIG. When the transistor 28 starts operating at t = 0, the magnetron 32 starts oscillating at t = t ₁ after 1 to 2 seconds, and the radio wave output P ₀ becomes the rated output (that is, 500).
It is controlled to be 600 W, which is larger than W) . Then, at time t ₄ after t _S , the output P ₀ is controlled to be the rated output of 500 W. Such control of the radio wave output P ₀ can be realized by various methods. For example, as shown in FIG. 2, the activation control unit 41 controls the generated signal of the reference signal generator 38 of the input current. Can be easily realized. That is, FIG. 3 (a)
Can be realized by changing the reference signal of the input current after the time t _S so that the output P _{0 of} P.

The time t _S in FIG. 3 (a) is the time for generating a higher output than in the steady state while the temperature of the device and each component is sufficiently low. Therefore, FIG.
As is clear from (b), the time when the internal temperature of the device or the temperature of each component is lower than the predetermined temperature may be set as t _S.
From such an idea, t _S detects, for example, the anode temperature of the magnetron 7 or its ambient temperature or the temperature of the radiation fin of the transistor 28 by the thermistor 42 as shown in FIG. 4, and the signal of the reference signal generator 43 is detected. The continuous operation is possible based on the above-mentioned temperature detection signal by the activation control unit 41 configured to compare with the comparator 44.
It can be configured to determine as the time to operate at maximum power . Further, as shown in FIG. 5, a stop time counter 45 for counting the operation stop time of the equipment (that is, the time for cooling the device or the parts) is provided, and the time t _S is determined by the signal of the stop time counter 45. , T _S is counted and a start modulation counter 46 that changes the reference signal 38 of the input current after t _S is provided as a time element, so that the operating state of the device is detected and this t _S is determined. May be.

Of course, it is also possible to limit and fix t _S for a short time of, for example, about 5 minutes, and provide a simple timer device as a time-limiting element to constitute the activation control section 41.

[0027] In order to notify that it is controlled to thus increase the radio wave output P ₀ from the steady state to the user, as shown in FIG. 2, the display unit 47 is provided, the activation control unit 41 of this By making it operate with the signal of, the user can recognize the power-up state (that is, 600W) or the steady state (500W) to perform cooking, which is extremely convenient and high-speed cooking. It can be performed.

[0028]

As described above, according to the present invention, a power supply unit obtained from a commercial power supply, a high-voltage power conversion unit, a control unit, a radio wave emission unit, and a high-voltage control unit having a clocking means are provided. , Continuous operation is possible during the time measured by this time measuring means
Since it is configured to generate an electromagnetic wave output that is larger than the maximum output that can be used continuously, it is possible to obtain a radio wave output that is larger than the maximum output that can be continuously operated for a predetermined period of time. In case of cooking for hours,
A high-frequency heating device capable of heating and cooking with a large radio wave output can be provided, and speed cooking can be further speeded up. Moreover it is possible to control reliably the original continuous operable maximum output or less output in the case of heating during time length since the large output time is configured to be controlled by the timer means, the cooling structure It is possible to provide a high-frequency heating device that does not have excessive quality such as heat resistance performance of components and parts, is small, compact, and low in cost and guarantees high reliability.

Further, since the timekeeping means can be adjusted, the large output time can be adjusted according to the state of the high-frequency heating device before use, so that the large output time as much as possible is ensured while ensuring high reliability. Can be set to realize a high-frequency heating device that enables speed cooking.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a main part of a control unit of the circuit.

FIG. 3 is a waveform diagram showing a temporal change in radio wave output of the high frequency heating device.

FIG. 4 is a circuit diagram of a main part of a high-voltage controller of the high-frequency heating device.

FIG. 5 is a block diagram showing another embodiment of the same circuit.

FIG. 6 is a circuit diagram of a conventional high frequency heating device.

FIG. 7 (a) is a diagram showing a time change of a radio wave output of the high frequency heating apparatus, and (b) is a waveform diagram showing a temperature rise of parts and the like in the high frequency heating apparatus.

FIG. 8 is a sectional view showing the configuration of a high-frequency heating device

[Explanation of symbols]

 24 Power Supply Section 27 Step-up Transformer 28 Semiconductor Element 32 Radio Wave Emission Section 33 High Voltage Power Conversion Section (Power Converter) 34 Control Section 41 High Voltage Control Section (Startup Control Section) 46 Timekeeping Means

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takashi Niwa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Takahiro Matsumoto 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor Villa Daisuke 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Koji Yoshino, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A power supply unit to which electric power is supplied from the outside, a high-voltage power conversion unit that has a booster and converts the power from the power supply unit into high-voltage power, and radiates an electromagnetic wave when energized by the high-voltage power conversion unit. Has a radio wave radiating section, a control section for controlling the operation of the high-voltage power conversion section, and a clocking means, and the maximum continuous operation is possible during the time counted by the clocking means at the start of the operation.
High-frequency heating apparatus having a high voltage control unit for controlling the control unit so as to be larger than the output electromagnetic wave output. 2. The high-frequency heating apparatus according to claim 1, wherein the electromagnetic wave output is automatically controlled so as to be a maximum value of output capable of continuous operation or a value less than the maximum value after the time measurement by the time measuring means is completed. 3. The high frequency heating apparatus according to claim 1, wherein the time measured by the time measuring means is adjustable, and the time for outputting an electromagnetic wave output larger than the maximum value of continuously operable output is adjustable.