JPH05129074A - High frequency heating device - Google Patents

Abstract

PURPOSE:To output an electromagnetic wave output larger than a rated output at steady time for a determined time in a high frequency heating device. CONSTITUTION:A high frequency heating device is formed of a magnetron 32, a power converter 33 for supplying a power to the magnetron 32, a control part 34 for controlling the operation of the power convertor 33, and a high output control part 42 for controlling the control part 34 to form an output higher than a rated output for a determined time. According to this constitution, an output higher than the rated output can be outputted for a determined time. Thus, the enlargement of a cooling structure accompanying an output increase can be prevented, and cooking time can be shortened.

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 and the like, 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 device such as a microwave oven for home use has a structure as 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, it is configured to maintain the radio wave output P ₀ (for example, 500 W) defined as the rated output of the device.

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 rise 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 300 W for the magnetron 7 and about 100 W for the high-voltage transformer 3 in the case of a device having an actual radio wave output rating of 500 W. Occurs. For this reason, 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 made of an insulating material or a constituent material capable of maintaining sufficient safety even if such a heat loss occurs. Therefore, the structure of the cooling condition and the specifications of each part are specified. It is designed to meet such guarantee conditions. That is, at t = t ₃ in FIG. 7B, the constituent materials, the parts specifications, and the cooling structure are determined in due consideration of the temperature rise that has occurred.

Therefore, the rated output is 500 W 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 the size and cost are increased, and the high voltage transformer 3 is inevitably increased in size and 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 by 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 reheating, which is often used in ordinary households, usually requires 5 hours.
It is extremely often used with a heating time of about a minute or less. That is, in FIG. 7 (b), there are very many usages such as ending the usage at a time of t = t ₀ ,
Usually, cooking that reaches t ₃ is rarely performed. 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. In terms of quality, it is of excessive quality. However, in rare cases t
Since = may also use conditions reaching the t ₃ inevitably such substantial excess quality one.

[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 supplied with electric power from the outside, a high-voltage power conversion unit including a boosting unit for converting the power from the power supply unit into high-voltage power, and an electromagnetic wave radiated by receiving the output of the high-voltage power conversion unit. A radio wave radiating unit, a control unit that controls the operation of the high-voltage power conversion unit, and a high-power control unit that controls the control unit so that the electromagnetic wave output is larger than the rated output in the steady state for a predetermined time. It is composed.

Further, the high-voltage power converter is composed of an inverter including a semiconductor element, and the radio wave radiation part is composed of a magnetron.

Furthermore, the display unit for displaying that the electromagnetic wave output is larger than the rated output in the steady state is provided.

[0016]

With the above construction, the high frequency heating apparatus according to the present invention has the following functions.

The high output control unit controls the operating state of the control unit to output an electromagnetic wave output larger than the rated output in the steady state for a predetermined time, which makes it possible to significantly shorten the heating time, and The cooling structure, heat-resistant specifications, and quality performance can be made appropriate without being excessive.

Further, the configuration using the inverter and the magnetron facilitates the control of the inverter, which is the high-voltage power conversion section, by the high-output control section, so that the high-output control section can generate a higher output than the steady state for a predetermined time. The control by the output control unit can also be easily realized by controlling the operation of the inverter.

Further, by providing the display unit, the user can easily be informed that the output state is higher than the steady state, and the usability can be improved by preventing misuse.

[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 source 20, a diode bridge 21, an inductor 22 and a capacitor 23 constitutes a power source section 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
And a high-voltage rectifier circuit that includes a diode 31 and a capacitor 30 that rectifies the output of the step-up transformer 27, 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 to perform 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 unit 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 to a predetermined value by so-called pulse width control.
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 structure, 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. Upon receiving the heating start command, the activation control unit 41 sends a rising signal to the control unit 34 to operate at an output (eg, 600 W) larger than the rated output (eg, 500 W) in the steady state for a predetermined time at the start of operation. give.

FIG. 3A shows the radio wave output P ₀ indicating this state.
FIG. When the transistor 28 starts to operate at t = 0, the magnetron 32 starts to oscillate at t = t ₁ after 1 to 2 seconds, and the radio wave output P ₀ is controlled to be 600 W, which is higher than the steady state (that is, the rated value). And t _S
At the subsequent time t ₄ , its output P ₀ is controlled to be 500 W in the steady state (that is, rated). Such control of the radio wave output P ₀ can be realized by various methods. For example, as shown in FIG. 2, the activation controller 41 controls the signal generated by the reference signal generator 38 of the input current. This can be easily achieved. That is, FIG.
This can be realized by changing the reference signal of the input current after the time t _S so that the output P ₀ of (a) changes.

The time t _S in FIG. 3 (a) is a time for generating a higher output than in a 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 a predetermined temperature may be set as t _S.
From such an idea, t _S is detected by the thermistor 42, for example, the anode temperature of the magnetron 7 and its ambient temperature or the temperature of the radiation fin of the transistor 28 as shown in FIG. The activation control unit 41 configured to compare with the comparator 44 can be configured to determine the temperature control center.
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 component) is provided, and the time t _S is determined by the signal of the stop time counter 45, start modulation counter counts the t _S changes the reference signal 38 of the input current after t _S 4
With the structure provided 6 detects the operation state of the apparatus may be determined the t _S.

Further, of course, the activation control section 41 may be constituted by a simple timer device by limiting and fixing t _S for a short time of, for example, about 5 minutes.

[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.

Further, as shown in FIG. 3 (b), the radio wave output P ₀ is gradually reduced during the time t _S , and a steady radio wave output P ₀ is obtained after the time t _S. It is obvious that the effect of can be obtained.

[0029]

As described above, according to the present invention, the high output control unit controls the control unit to output the electromagnetic wave output larger than the rated output in the steady state for the predetermined time. Therefore, it is possible to obtain a larger electromagnetic wave output than the steady state for a predetermined time. Therefore, in the case of short-time heating that is frequently used when used in general households,
It is possible to provide a high-frequency heating device that can be used with a large electromagnetic wave output, shorten the heating time, and enable faster speed cooking. In addition, since the radio wave output is constant during long-term operation, the cooling structure and heat-resistant specifications of each component are not oversized, and the size is small.
It is possible to realize a high-frequency heating device that is compact, inexpensive, and extremely rational and has high cost performance.

Further, by configuring the high-voltage power conversion unit by using the inverter and driving the magnetron, the control of the control unit by the high output control unit can be performed only by controlling the operating state of the inverter. Therefore, it is possible to realize a high-frequency heating device capable of easily outputting an output larger than the steady state only by controlling signals.

Further, by providing the output display means, it is possible to easily inform the user that the output state is larger than the steady state, so that the inconvenience such as an erroneous heating operation can be prevented and the usability is improved. An excellent high frequency heating device can be realized.

[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 output control unit 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 cross-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 Output Control Section (Startup Control Section) 47 Display Section

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Niwa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor 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 supplied with electric power from the outside, a high-voltage power conversion unit including a boosting unit for converting electric power from the power supply unit into high-voltage power, and an electromagnetic wave receiving the output of the high-voltage power conversion unit. A radio wave radiation unit that radiates energy, a control unit that controls the operation of the high-voltage power conversion unit, and a high output control that controls the control unit so that the electromagnetic wave output is larger than the rated output in the steady state for a predetermined time. High-frequency heating device having a section. 2. The high frequency power generating apparatus according to claim 1, wherein the high-voltage power converter comprises an inverter having at least one semiconductor element and a step-up transformer for stepping up the output of the inverter, and the radio wave emitting means is a magnetron. Heating device. 3. The high-frequency heating apparatus according to claim 1, further comprising a display unit for displaying that the electromagnetic wave output is larger than the rated output in the steady state.