JP2004321462A - Rice cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase high-frequency current supplied to a heating coil by increasing a conduction time of a switching means so as to increase input current, when an AC power supply has low voltage, in a rice cooker for controlling the high-frequency current in the heating coil by the switching means to heat a pot. <P>SOLUTION: The rice cooker has a resonant circuit composed of the heating coil 2 electrically connected with the pot 1 for heating the pot 1 by supplying the high-frequency current, and a resonant capacitor 3 to control the high-frequency current in the heating coil 2 by the switching means 4. The AC power supply 5 for supplying electricity to the heating coil 2 is rectified and smoothed by a rectifying and smoothing means 6, and the conduction time of the switching means 4 is set by a conduction time setting means 12. The conduction time setting means 12 sets the conduction time according to the outputs of a current setting means 10 for setting input current from the AC power supply 5 and an envelope detection means 11 for detecting the envelope of input current from the AC power supply 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rice cooker that controls a high-frequency current flowing through a heating coil by a switching unit to heat a pot.
[0002]
[Prior art]
Conventionally, this type of rice cooker has been configured as shown in FIG. Hereinafter, the configuration will be described.
[0003]
As shown in FIG. 5, the pot 1 contains water and rice, and is shown by an electric circuit model. The pot 1 is constituted by a laminate using a plurality of metals that transmit magnetic flux. The heating coil 2 is composed of a litz wire obtained by bundling a plurality of copper wires, and the pot 1 and the heating coil 2 are electromagnetically coupled. That is, when a current flows through the heating coil 2, a magnetic flux is generated in the heating coil 2, and when the magnetic flux passes through the metal of the pan 1, a current flows through the metal of the pan 1. Pot 1 is heated.
[0004]
The resonance capacitor 3 is connected in parallel to the heating coil 2 and forms a parallel resonance circuit with the heating coil 2. The switching means 4 includes a semiconductor element such as a MOSFET or an IGBT and a reverse connection diode reversely connected to the semiconductor element, and controls a high-frequency current flowing through the heating coil 2.
[0005]
The rectifying / smoothing means 6 includes a diode bridge 7, a choke coil 8, and a capacitor 9, and rectifies the 100 V, 60 Hz AC power supply 5. At this time, since the capacitance of the capacitor 9 is as small as several μF, when a high-frequency current is applied to the heating coil 2, a large ripple is generated, and the waveform becomes the same as the rectified waveform of the AC power supply 5. Can be smoothed.
[0006]
The peak voltage setting means 61 is constituted by a voltage dividing circuit composed of two or more resistors, and sets a reference voltage of a voltage between both ends of the switching means 4. This reference voltage has already been adjusted by trimming and volume control to be around 700V.
[0007]
The peak voltage detecting means 62 includes a voltage dividing circuit for dividing the voltage applied to the switching means 4 by two or more resistors, and a peak hold circuit for holding an output peak value of the voltage dividing circuit. Here, the peak hold circuit includes a transistor for inputting an output of the voltage dividing circuit to a base terminal, an electrolytic capacitor connected to an emitter terminal of the transistor, and a discharge resistor connected in parallel to the electrolytic capacitor. At this time, the time constant of the electrolytic capacitor and the discharge resistance is set to be sufficiently longer than the half cycle of the AC power supply 5.
[0008]
The AD converter 63 is provided in advance in the microcomputer. The AD converter 63 converts the output voltage of the peak voltage detecting means 62 into an A / D signal, and outputs the value to the conduction time setting means 65.
[0009]
The zero voltage detecting means 64 is configured by connecting a photocoupler to both ends of the AC power supply 5. The photocoupler outputs high to the conduction time setting means 65 when the voltage across the AC power supply 5 exceeds a predetermined value, and outputs low when the voltage across the AC power supply 5 is equal to or less than the predetermined value.
[0010]
The conduction time setting means 65 is constituted by a microcomputer. The conduction time setting means 65 compares the output of the peak voltage setting means 61 with the output of the peak voltage detection means 62 every time the output edge of the zero voltage detection means 64 is detected, and sets the conduction time of the switching means 4, It outputs high for the conduction time set in the driving means 13.
[0011]
The driving means 13 is constituted by a push-pull circuit including a PNP transistor and an NPN transistor. The driving unit 13 receives the high and low signals of the conduction time setting unit 64 and outputs a signal to the gate of the IGBT constituting the switching unit 4. The IGBT is turned on and off in response to this signal, and supplies or cuts off current to the heating coil 2.
[0012]
The operation of the above configuration will be described. When rice cooking is started, when the microcomputer constituting the conduction time setting means 65 detects the output edge of the zero voltage detecting means 64, the microcomputer compares the output of the peak voltage setting means 61 with the output of the peak voltage detecting means 62 and sets the peak voltage. If the output of the means 61 is large, the conduction time of the switching means 4 is made longer than the current setting, and if the output of the peak voltage setting means 61 is small, the conduction time of the switching means 4 is made shorter than the current setting. Then, the conduction time setting means 65 outputs a high for the set time to the driving means 13.
[0013]
The driving unit 13 turns on the switching unit 4 and causes a current to flow through the heating coil 2. Assuming that the conduction time at this time is Td, the voltage applied to the rectifying and smoothing means 6 is V, and the inductance of the heating coil 2 is L, the current IL flowing through the heating coil 2 at Td is:
IL = (V / L) × Td
Can be represented by That is, the current IL of the heating coil 2 is proportional to the conduction time and the voltage applied to the rectifying / smoothing means 6. At this time, if the energy accumulated in the heating coil 2 is WL,
WL = 1/2 × L × IL2
Can be represented by The energy WL of the heating coil 2 becomes the resonance energy with the resonance capacitor 3. Assuming that the energy accumulated in the resonance capacitor 3 is WC and the voltage between both ends of the resonance capacitor 3 is VC,
WC = 1/2 × C × VC2
Can be represented by Since the energy WL of the heating coil 2 is converted into the energy WC of the resonance capacitor 3,
WL = WC
It becomes. The voltage Vsw across the switching means 4 is the sum of the output voltage V of the rectifying / smoothing means 6 and the voltage VC across the resonance capacitor 3.
[0014]
When the above operations are summarized, two main things can be understood. First, as the conduction time of the switching means 4 increases, the current flowing through the heating coil 2 increases and the energy accumulated in the heating coil 2 increases, but the voltage across the resonance capacitor 3 also increases. This means that the voltage between both ends of the means 4 increases. Second, even if the conduction time is the same, if the voltage applied to the rectifying / smoothing means 6 changes, the current flowing through the heating coil 2 changes, so that the voltage across the switching means 4 also changes.
[0015]
FIG. 6 shows an operation waveform of a main part in one cycle of the AC power supply 5. FIG. 6A shows a voltage waveform of the AC power supply 5. FIG. 6B shows an input current waveform of the AC power supply 5. FIG. 6C shows an output voltage waveform of the rectifying / smoothing means 6. FIG. 6D shows an envelope of the voltage between both ends of the switching means 4. FIG. 6E shows the envelope of the current supplied to the heating coil 2 (that is, the current when the IGBT constituting the switching means 4 is conducting).
[0016]
As shown in FIG. 6, the conduction time is constant during the half cycle of the AC power supply 5, so that the current supplied to the heating coil 2 fluctuates in proportion to the output voltage of the rectifying and smoothing means 6. That is, since the output voltage of the rectifying / smoothing means 6 corresponds to the voltage of the AC power supply 5, the current supplied to the heating coil 2 fluctuates in accordance with the voltage of the AC power supply 5.
[0017]
As described above, the conventional rice cooker sets the conduction time of the switching means 4 by comparing the peak value of the voltage between both ends of the switching means 4 with the set value every half cycle of the AC power supply 5, and sets the conduction time of the switching means 4. The voltage is suppressed to a set value (for example, see Patent Document 1).
[0018]
[Patent Document 1]
JP-A-5-114472
[0019]
[Problems to be solved by the invention]
However, in the above-described conventional configuration, the conduction time of the switching means 4 is changed every half cycle of the AC power supply 5, so that the current flowing through the heating coil 2 fluctuates according to the voltage of the rectifying and smoothing means 6. Therefore, even if the current is increased so that a larger high-frequency power can be supplied to the heating coil 2, there is a problem that the voltage across the switching means 4 exceeds the maximum rating when the voltage of the rectifying / smoothing means 6 is at its peak. .
[0020]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. By changing the setting of the conduction time of the switching means instantaneously in response to a change in the input current of the AC power supply, when the voltage of the AC power supply is low, It is an object of the present invention to increase the conduction time of the switching means so as to increase the current and increase the high-frequency current supplied to the heating coil.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, the present invention forms a resonance circuit with a heating coil and a resonance capacitor, which are electromagnetically coupled to the pan and supplies high-frequency power to heat the pan, and switches a high-frequency current flowing through the heating coil by switching means. And an AC power supply for supplying power to the heating coil is rectified and smoothed by the rectifying and smoothing means, and a conduction time of the switching means is set by the conduction time setting means. The conduction time is set in accordance with the output of the current setting means for setting the current and the output of the envelope detection means for detecting the envelope of the input current of the AC power supply.
[0022]
This allows the setting of the conduction time of the switching means to be instantaneously changed in response to a change in the input current of the AC power supply, so that when the voltage of the AC power supply is low, the conduction time of the switching means is extended to increase the heating coil. The flowing current can be increased, and the high-frequency power supplied to the heating coil can be increased.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention provides a heating coil that is electromagnetically coupled to a pan and supplies high-frequency power to heat the pan, a resonance capacitor that forms a resonance circuit with the heating coil, and the heating coil. Switching means for controlling a high-frequency current flowing to the AC power supply for supplying power to the heating coil; rectifying and smoothing means for rectifying and smoothing the AC power supply; current setting means for setting an input current of the AC power supply; An envelope detection means for detecting an envelope of an input current of the AC power supply, and a conduction time setting means for setting a conduction time of the switching means, wherein the conduction time setting means comprises the current setting means and the envelope detection means. The conduction time is set according to the output of the switching means, and the setting of the conduction time of the switching means is instantaneously changed in response to a change in the input current of the AC power supply. Doing, when the voltage of the AC power supply is low, it is possible to increase the current flowing through the heating coil by increasing the conduction time of the switching means, the high frequency power supplied to the heating coil can be increased.
[0024]
According to a second aspect of the present invention, in the first aspect of the present invention, the conduction time setting means sets an upper limit value for the set value of the conduction time, and sets a frequency range of the high-frequency current flowing through the heating coil. As a result, the frequency of the high-frequency current flowing through the heating coil can be prevented from entering the human audible frequency range.
[0025]
According to a third aspect of the present invention, in the first or second aspect, an average current detecting means for detecting an average value of the input current of the AC power supply, and an average value of the input current of the AC power supply are set. Average current setting means, wherein the current setting means changes the set value of the input current according to the outputs of the average current detection means and the average current setting means, and the input current waveform has distortion. Even if it occurs, the average value of the input current can be controlled to be constant.
[0026]
According to a fourth aspect of the present invention, in the first or second aspect, an effective current detecting means for detecting an effective value of an input current of the AC power supply, and an effective value of the input current of the AC power supply are set. Effective current setting means, wherein the current setting means changes the set value of the input current according to the output of the effective current detection means and the output of the effective current setting means. Even if it occurs, the effective value of the input current can be controlled to be constant.
[0027]
According to a fifth aspect of the present invention, in the third or fourth aspect of the present invention, the current setting means sets an upper limit value for the set value of the input current, and the set value of the input current becomes excessive. In addition, it is possible to prevent the breaker for home use from being cut off and cooking from being interrupted.
[0028]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0029]
(Example 1)
As shown in FIG. 1, the pot 1 contains water and rice, and is shown by an electric circuit model. The pot 1 is composed of a laminate using a plurality of metals that transmit magnetic flux. However, this is only an example, and it is not always necessary to constitute a laminated body, and a pot plated with metal or a pot made of only the same metal may be used. When the pot 1 is composed only of a laminate or the same metal, it is easy to control the thickness of the metal. When the pot 1 is metal-plated, various types of pots can be created only by changing the metal on the surface.
[0030]
The heating coil 2 is composed of a wire in which a plurality of litz wires obtained by bundling a plurality of copper wires are further twisted by more than 20 wires, so that a current distribution when a high-frequency current flows is made uniform. Although not particularly shown, the pan 1 is placed on the heating coil 2 and the pan 1 and the heating coil 2 are electromagnetically coupled. That is, when a current flows through the heating coil 2, a magnetic flux is generated in the heating coil 2, and when the magnetic flux passes through the metal of the pan 1, a current flows through the metal of the pan 1. Pot 1 is heated.
[0031]
The resonance capacitor 3 uses a polypropylene capacitor having a small loss even when a high-frequency current flows, and is connected in parallel to the heating coil 2 to form a parallel resonance circuit with the heating coil 2. The switching means 4 controls a high-frequency current flowing through the heating coil 2 and includes a semiconductor element such as a MOSFET or IGBT and a reverse connection diode reversely connected to the semiconductor element. MOSFETs and IGBTs have the advantages of high withstand voltage, high-frequency switching, and large current flow.
[0032]
The rectifying / smoothing means 6 includes a diode bridge 7, a choke coil 8, and a capacitor 9, and rectifies and smoothes the AC power supply 5 of 100 V and 60 Hz. At this time, the capacitance of the capacitor 9 is as small as several μF, and when a high-frequency current flows through the heating coil 2, ripple occurs. In this embodiment, this ripple voltage is the same as the voltage of the AC power supply 5.
[0033]
The current setting means 10 sets the input current of the AC power supply 5, and is constituted by a ROM, a DA converter and the like in the microcomputer. The rice cooker according to the present embodiment has a plurality of operation modes such as rice cooking and heat retention, and the input current of the AC power supply 5 can be set corresponding to each of these operation modes. The set value of the input current (hereinafter referred to as input current set value) is stored in the ROM in the microcomputer. That is, the current setting means 10 calls the input current setting value from the ROM corresponding to the operation mode, converts the input current setting value into an analog voltage by the DA converter, and outputs the analog voltage to the conduction time setting means 12. I have.
[0034]
The envelope detecting means 11 detects an envelope of an input current in a half cycle of the AC power supply 5, and the envelope detecting means 11 includes a current transformer provided between the AC power supply 5 and the rectifying and smoothing means 6, It comprises a diode bridge for full-wave rectifying the output of the current transformer and a voltage dividing circuit for dividing the output voltage of the diode bridge. In this embodiment, since it is not necessary to smooth the output of the diode bridge, a smoothing capacitor can be omitted and the mounting area can be reduced. However, this is only an example, and a configuration may be adopted in which a current detection resistor is provided between the diode bridge 7 and the capacitor 9 and the voltage between both ends is detected.
[0035]
The conduction time setting means 12 sets the conduction time of the switching means 4 and is composed of an amplifier circuit using an operational amplifier or the like and an oscillation circuit using a comparator or the like. The amplifier circuit amplifies the error of the input current set value set by the current setting means 10 and the envelope of the input current detected by the envelope detection means 11, and outputs the result to the oscillation circuit. The oscillation circuit changes the oscillation frequency by changing the time of the high signal according to the output voltage of the amplification circuit and keeping the time of the low signal constant.
[0036]
As described above, when the conduction time setting means 12 is configured by an analog circuit, a microcomputer having a low operation speed can be used, so that the cost can be reduced and the power consumption of the microcomputer can be reduced.
[0037]
However, this is only an example, and a microcomputer having a high calculation speed can be used, and the conduction time setting means 12 can be constituted by this microcomputer. For example, since recent microcomputers have built-in AD converters and PWM output terminals, the output of the envelope detection means 11 is input to the AD converter, and the digital output of the AD converter is compared with the input current set value. Then, the conduction time is set. The switching means 4 can be turned on and off by outputting a high or low signal from the PWM terminal of the microcomputer according to the conduction time. In this case, the mounting area for analog circuits such as an operational amplifier and a comparator can be reduced.
[0038]
The driving means 13 is constituted by a push-pull circuit including a PNP transistor and an NPN transistor. The driving means 13 receives the high and low signals of the conduction time setting means 11 and outputs a signal to the gate of the IGBT constituting the switching means 4. The IGBT is turned on and off in response to this signal, and supplies or cuts off current to the heating coil 2.
[0039]
The operation of the above configuration will be described. First, when rice cooking is started, the current setting means 10 sets an input current set value Is determined for each operation mode. In this embodiment, there is an input current set value for each operation mode. Here, Is = 10 A is set as an example.
[0040]
When the voltage of the AC power supply 5 is low, the output voltage of the rectifying / smoothing means 6 is also low, so that the voltage applied to the heating coil 2 is low. Therefore, the current flowing through the heating coil 2 decreases during the same conduction time as when the output voltage of the rectifying / smoothing means 6 is high. Assuming that the conduction time at this time is Td, the voltage applied to the rectifying and smoothing means 6 is V, and the inductance of the heating coil 2 is L, the current IL flowing through the heating coil 2 at Td is:
IL = (V / L) × Td
Can be represented by
[0041]
If the current supplied to the heating coil 2 is small, the input current Iin from the AC power supply 5 to the rectifying and smoothing means 6 at that time is also small. That is, since the input current value Iin detected by the envelope detection means 11 becomes lower than the input current setting value Is, the amplifier circuit constituting the conduction time setting time 12 increases the output voltage. Then, the oscillation circuit constituting the conduction time setting means 12 lengthens the high signal, so that the conduction time of the switching means 4 is instantaneously increased. As a result, the current flowing through the heating coil 2 increases, and the input current Iin supplied from the AC power supply 5 also approaches the input current set value Is.
[0042]
Conversely, when the voltage of the AC power supply 5 is near the peak value, the output of the rectifying / smoothing means 6 also increases near the peak value, and the voltage applied to the heating coil 2 increases. 6, the current flowing through the heating coil 2 is larger than when the output is low. That is, since the input current value Iin detected by the envelope detection means 11 becomes larger than the input current set value Is, the amplifier circuit reduces the output voltage. Since the oscillation circuit shortens the high signal in accordance with the output voltage, the conduction time of the switching means 4 is shortened, and the input current Iin supplied from the AC power supply 5 decreases to the input current set value Is.
[0043]
FIG. 2A shows a voltage waveform of the AC power supply 5. FIG. 2B shows an input current waveform of the AC power supply 5. FIG. 2C shows a voltage waveform of the rectifying / smoothing means 6. FIG. 2D shows the envelope of the current supplied from the rectifying / smoothing means 6 in the current IL flowing through the heating coil 2. As shown in FIG. 2, the difference between the current flowing through the heating coil 2 when the voltage of the AC power supply 5 is low and when it is high is small.
[0044]
As described above, by controlling the input current of the AC power supply 5 to the input current set value Is, the high-frequency current flowing through the heating coil 2 can be increased even when the voltage of the AC power supply 5 is low. Compared with the case where the conduction time is controlled for each half cycle of the AC power supply 5, the power amount of the entire half cycle of the AC power supply 5 can be increased.
[0045]
Therefore, if the input current is the same as that of the conventional rice cooker, the conduction time of the switching means 4 when the voltage of the AC power supply 5 is high can be shortened, and the voltage across the switching means 4 can be reduced. Thus, a switching means 4 having a lower voltage rating than a conventional rice cooker can be used. When a MOSFET is used for the switching means 4, the on-resistance decreases as the voltage rating decreases, so that the loss can be reduced. Further, since the voltage between both ends of the switching means 4 is reduced, it is possible to cope with the area of the 200V power supply.
[0046]
(Example 2)
FIG. 3 shows a circuit configuration of the conduction time setting means according to the second embodiment of the present invention. This conduction time setting means has an upper limit value for the conduction time setting value. It is configured as an inverting amplifier circuit including an operational amplifier 22 and resistors 23 and 24. This amplifier circuit 21 amplifies the difference between the input current setting value Is set by the current setting means 10 and the input current Iin detected by the envelope detection means 11 by the ratio of the resistance values of the resistors 23 and 24.
[0047]
The lead-lag filter 25 is composed of a series circuit of two resistors 26 and 27 and an electrolytic capacitor 28. The conduction time limiting circuit 29 is constituted by a Zener diode. In the present embodiment, the output value of the lead-lag filter 25 is limited to a predetermined value or less by setting the upper limit with the Zener voltage of the Zener diode.
[0048]
The oscillating circuit 30 includes a plurality of comparators. The oscillating circuit 30 changes the high output time according to the output value of the lead-lag filter 25 and keeps the low output time constant, so that the driving means 13 To change the oscillation frequency of the output signal. Other configurations are the same as those in the first embodiment, and a description thereof will be omitted.
[0049]
The operation of the conduction time setting means in the above configuration will be described. When the output voltage of the rectifying / smoothing means 6 is low, the high-frequency current flowing through the heating coil 2 is small even when the conduction time is the same as when the output voltage is high, so that the input current Iin supplied from the AC power supply 5 is also small.
[0050]
Therefore, the input current Iin becomes smaller than the input current set value Is, and the output of the amplifier circuit 21 increases. Therefore, the output of the lead-lag filter 25 also increases, but does not increase beyond the operating voltage of the Zener diode. Since the oscillation circuit 30 changes the output time of the high signal according to the output voltage, the high signal increases only up to a certain time.
[0051]
In the present embodiment, since the oscillation circuit 30 changes the output time of the high signal and keeps the output time of the low signal constant, the oscillation frequency does not drop below a certain value.
[0052]
As described above, by setting the upper limit value for the conduction time set by the conduction time setting means, the lower limit value can be set for the frequency of the high-frequency current flowing through the heating coil 2. It is possible to prevent the frequency from dropping below the upper limit of the human audible frequency range of 20 kHz, and it is possible to realize a rice cooker with low noise.
[0053]
Note that the configuration of the conduction time setting means in the present embodiment is not limited to this, and for example, a microcomputer may be used.
[0054]
(Example 3)
As shown in FIG. 4, the average current setting means 41 sets an average value of the input current of the AC power supply 5, and in this embodiment, is constituted by a microcomputer. The rice cooker according to the present embodiment has a plurality of operation modes such as rice cooking and heat retention. A set value of the average input current (hereinafter, referred to as an average current set value Ias) corresponding to each operation mode is provided. This average current set value Ias is stored in a ROM or the like in the microcomputer. That is, the average current setting means 41 calls the predetermined average current set value Ias from the ROM data for each operation mode.
[0055]
The average current detecting means 42 detects the average value of the input current of the AC power supply 5 and detects the average value of the output voltage of the envelope detecting means 11. The average current detecting means 42 includes an operational amplifier, an electrolytic capacitor for smoothing the output of the operational amplifier, and a resistor connected in parallel to the electrolytic capacitor.
[0056]
The current setting means 43 changes the set value of the input current according to the outputs of the average current detection means 42 and the average current setting means 41, and is constituted by an AD converter and an arithmetic circuit in the microcomputer. The other configuration is the same as that of the first embodiment, and the same reference numerals are given and the description is omitted.
[0057]
The operation of the above configuration will be described. First, when rice cooking is started, the average current setting means 41 sets a current set value Ias determined for each operation mode. Next, an initial value determined for each operation mode by the current setting means 43 is set as a current setting value Is. In this embodiment, the initial value of the current set value Is is set to 10A.
[0058]
Further, the current setting unit 43 compares the average current setting value Ias with the average current value detected by the average current detection unit 42, and sets the fluctuating current value dIs. After that, the current setting means 43
Is = Is + dIs
, The current set value Is is changed. Here, the update timing of the current set value Is is once per half cycle of the AC power supply 5. The conduction time setting means 12 sets the conduction time by comparing the current setting value Is with the input current value detected by the envelope detection means 11.
[0059]
The waveform of the main part shown in FIG. 4 is the same as FIG. That is, although the input current waveform of the AC power supply 5 does not become a sine wave, the average current is detected, so that the influence of the input current fluctuation due to the waveform change can be suppressed.
[0060]
As described above, in the present embodiment, the current setting unit 43 updates the input current set value Is in accordance with the outputs of the average current setting unit 41 and the average current detection unit 42. And variations in the input current can be suppressed.
[0061]
Note that an upper limit value can be set for the input current set value Is. For example, a step of storing the upper limit value of the input current set value in advance in the ROM of the microcomputer constituting the current setting means 43 and comparing the upper limit value with the input current set value Is set by the current setting means 43 is performed. to add. In this comparison step, if the input current set value Is is larger than the upper limit, the current setting means 43 changes the input current set value to the upper limit.
[0062]
In this way, by providing an upper limit value to the input current setting value set by the current setting means 43, the input current can be suppressed so that the breaker in the house is not cut off. Therefore, it is possible to prevent the breaker from falling due to the flow of an excessive current so that rice cannot be cooked.
[0063]
Further, instead of detecting the average value of the input current, an effective current detecting means may be provided to detect the effective value of the input current. In this case, the effective current detecting means is constituted by an effective value detecting circuit for detecting the effective value of the output value of the current transformer. The effective value detection circuit can be constituted by an operational amplifier or the like. In the case of detecting the effective value of the input current, similarly to the case of detecting the average value, it is possible to cope with a change in the input current waveform and easily estimate the input current value. Further, when detecting the effective value, the input power can be accurately grasped by detecting the voltage of the AC power supply 5, so that a rice cooker with more stable power supply can be provided.
[0064]
【The invention's effect】
As described above, according to the first aspect of the present invention, the conduction time setting means for setting the conduction time of the switching means includes the current setting means for setting the input current of the AC power supply and the input current of the AC power supply. Since the conduction time is set according to the output of the envelope detecting means for detecting the envelope, the current flowing to the heating coil is increased when the voltage of the rectifying / smoothing means is low, that is, when the voltage of the AC power supply is low. Therefore, the supply of high-frequency power from the heating coil to the pot can be increased while the voltage across the switching means remains low.
[0065]
According to the second aspect of the present invention, since the conduction time setting means sets the upper limit value for the set value of the conduction time, it can set the lower limit for the operating frequency of the high-frequency current flowing through the heating coil. Operating frequency out of the audible frequency range, and a low-noise rice cooker can be provided.
[0066]
According to the third aspect of the present invention, there is provided an average current detecting means for detecting an average value of the input current of the AC power supply, and an average current setting means for setting an average value of the input current of the AC power supply, The current setting means changes the set value of the input current according to the outputs of the average current detection means and the average current setting means, so that even if the input current waveform is distorted, the average value of the input current is changed. It can be controlled to be constant, and the input power of the rice cooker can be controlled to be constant.
[0067]
Further, according to the invention of claim 4, there is provided an effective current detecting means for detecting an effective value of the input current of the AC power supply, and an effective current setting means for setting an effective value of the input current of the AC power supply, The current setting means changes the set value of the input current according to the outputs of the effective current detection means and the effective current setting means, so that even if the input current waveform is distorted, the effective value of the input current is changed. It can be controlled to be constant, and the input power of the rice cooker can be controlled to be constant.
[0068]
According to the fifth aspect of the present invention, since the current setting means sets an upper limit value for the set value of the input current, the input current can be suppressed to a constant value. Can be prevented from being interrupted.
[Brief description of the drawings]
FIG. 1 is a partial circuit diagram of a main part of a rice cooker according to a first embodiment of the present invention.
FIG. 2 is a waveform diagram of a main part voltage and current of the rice cooker.
FIG. 3 is a circuit diagram of a conduction time setting unit of a rice cooker according to a second embodiment of the present invention.
FIG. 4 is a partial circuit diagram of a main part of a rice cooker according to a third embodiment of the present invention.
FIG. 5 is a circuit diagram of a main part of a conventional rice cooker, which is partly blocked.
FIG. 6 is a voltage and current waveform diagram of a main part of the rice cooker.
[Explanation of symbols]
1 pot
2 Heating coil
3 Resonant capacitor
4 Switching means
5 AC power supply
6 Rectifying smoothing means
10 Current setting means
11 Envelope detection means
12 Conduction time setting means

Claims (5)

A heating coil that is electromagnetically coupled to the pan to supply high-frequency power to heat the pan, a resonance capacitor that forms a resonance circuit with the heating coil, a switching unit that controls a high-frequency current flowing through the heating coil, An AC power supply for supplying power to the heating coil, rectifying and smoothing means for rectifying and smoothing the AC power supply, current setting means for setting an input current of the AC power supply, and an envelope for detecting an envelope of the input current of the AC power supply Line detecting means, and a conduction time setting means for setting a conduction time of the switching means, wherein the conduction time setting means sets a conduction time according to outputs of the current setting means and the envelope detection means. Cooked rice cooker. The rice cooker according to claim 1, wherein the conduction time setting means sets an upper limit value for the set value of the conduction time. An average current detection means for detecting an average value of the input current of the AC power supply, and an average current setting means for setting an average value of the input current of the AC power supply, wherein the current setting means includes the average current detection means and the average 3. The rice cooker according to claim 1, wherein a set value of the input current is changed according to an output of the current setting means. An effective current detecting means for detecting an effective value of the input current of the AC power supply, and an effective current setting means for setting an effective value of the input current of the AC power supply, wherein the current setting means comprises the effective current detecting means and the effective current 3. The rice cooker according to claim 1, wherein a set value of the input current is changed according to an output of the current setting means. 5. The rice cooker according to claim 3, wherein the current setting means sets an upper limit value for the set value of the input current.

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