JP4100333B2 - rice cooker - Google Patents

Description

  The present invention relates to a rice cooker that has a heating coil that operates with at least two different input powers and that induction-heats a pan or a lid.

  Conventionally, in this type of rice cooker, a first switching means is connected in series to a first heating coil that induction-heats the pan, and a second heating coil that induction-heats the inner surface side of the lid that covers the pan is secondly connected. The switching means is connected in series, and the on / off of the first switching means and the second switching means is controlled by the control means, and both the first heating coil and the second heating coil are alternately used in the rice cooking process and the heat retaining process. By operating, water droplets attached to the inner surface side of the lid are evaporated (see, for example, Patent Document 1).

  There is also an induction heating cooker that controls the ON time of the switching means so that the turn-on voltage of the switching means does not exceed a predetermined value (see, for example, Patent Document 2).

  There is also a rice cooker that detects an input current supplied to the rice cooker from the AC power source when the ON time of the switching means reaches the maximum value, and determines that there is no pan if it is below a predetermined value (for example, And Patent Document 3).

  FIG. 11 is a block diagram of the conventional rice cooker shown in Patent Document 1. In FIG. As shown in FIG. 11, the pan 101 is configured to be induction-heated by the pan-side induction heating coil 102, and the pan heating control means 103 controls energization and non-energization of the pan-side induction heating coil 102. The pan temperature detecting means 104 is brought into contact with the bottom surface of the pan 101 and detects the temperature of the pan 101.

The metal plate on the inner surface side of the lid 105 is induction-heated by the lid-side induction heating coil 106 built in the lid 105, and energization / non-energization of the lid-side induction heating coil 106 is controlled by the lid heating control means 107. The lid temperature detecting means 108 is in contact with the inner surface side of the lid 5 and detects a temperature change of the lid due to water vapor generated from the cooking object inside the pan 101. The cooking process storage unit 109 stores cooking sequence information such as the rice cooking process in a ROM in the microcomputer, and outputs this information to the control unit 110. The control means 110 receives the output of the cooking process storage means 109 and evaporates water droplets on the inner surface of the lid while cooking rice by alternately operating the pan-side induction heating coil 102 and the lid-side induction heating coil 106. .
JP-A-8-196417 JP-A-11-111440 JP 2000-166757 A

  However, in the conventional configuration, the input power required to drive the lid-side induction heating coil 106 is smaller than the input power required to drive the pan-side induction heating coil 102. It is necessary to match the minimum on time of the driving switching means with the minimum on time of the switching means for driving the lid-side induction heating coil 106. For this reason, at the time of starting the pan-side induction heating coil 2, the on-time of the switching means connected to the pan-side induction heating coil 2 is shortened, the turn-on voltage of the switching means is increased, and there is a problem that heat is generated.

  Further, there is a problem that the rise time until the input power when driving the pan-side induction heating coil 2 reaches the target value also depends on the input power when driving the lid-side induction heating coil 6.

  FIG. 12 shows operation waveforms when the pot 101 and the lid 105 are alternately heated in the conventional rice cooker shown in FIG. 12A shows the time change of the on-time Ton, and FIG. 12B shows the time change of the input current Iin. As shown in FIG. 12, when the minimum on-time is set to only Tmin2, the larger the target value of the input current, the longer it takes to reach the target value.

  The present invention solves the above-described conventional problems. When there is a heating coil that operates with at least two different input powers, the minimum on-time of each switching means can be set independently, and the switching means at startup The purpose is to reduce the turn-on voltage and suppress heat generation.

In order to achieve the above object, the present invention provides a first heating coil for induction heating of a pan, a first resonance capacitor that constitutes a resonance circuit with the first heating coil, and a series of the first heating coil. The connected first switching means, the lid covering the opening of the pan, the second heating coil for induction heating the metal plate on the inner surface side of the lid, and the second heating coil constitute a resonance circuit. A second resonant capacitor, second switching means connected in series to the second heating coil, rectifying means for rectifying an AC power source and supplying power to the first heating coil and the second heating coil; A minimum on-time setting means for setting a minimum value of an on-time of the first switching means and the second switching means; a current detection means for detecting an input current supplied from an AC power supply; and a target of the input current value A current setting means for setting a corresponding value, said first switching means and the second selecting one of the switching means and control means for on-off control, the said first heating coil second The heating coil has a resistance value and an inductance value, and the current setting means has a first current setting value used when heating the pan and a second current value used when heating the metal plate of the lid. The minimum on-time setting means has a first minimum on-time and a second minimum on-time shorter than the first minimum on-time, and the first switching means is activated when the first switching means is activated. set the minimum on-time as an initial value of the on-time, then the control means controls the on time of the first switching means such that said first set current value, said second switching means During movement sets the second minimum on-time as the initial value of the on-time, which is then said control means is configured to control the on-time of the second switching means so that the second current set value It is.

As a result, even when the first heating coil and the second heating coil have different resistance values and inductance values, the minimum on-time of the first switching means and the second switching means can be set independently. In the start-up, the minimum on-time of the first switching means can be made longer than the minimum on-time of the second switching means, the turn-on voltage can be sufficiently reduced, and the heat generation of the switching means can be suppressed. . In addition, by increasing the first minimum on-time, the input power at the time of startup is increased, and the rise time of the input power can be shortened.

  The rice cooker of the present invention sets the minimum on-time of the switching means connected in series to the heating coils that operate with different input powers independently, thereby reducing the turn-on voltage of the switching means at startup and suppressing heat generation. Can do.

A first invention is a first heating coil for induction heating a pan, a first resonance capacitor that constitutes a resonance circuit with the first heating coil, and a first connected in series to the first heating coil. Switching means, a lid covering the opening of the pan, a second heating coil for induction heating the metal plate on the inner surface side of the lid, and a second resonance capacitor constituting a resonance circuit with the second heating coil Second switching means connected in series to the second heating coil, rectifying means for rectifying an AC power source and supplying power to the first heating coil and the second heating coil, and the first switching Means, a minimum on-time setting means for setting a minimum value of the on-time of the second switching means, a current detection means for detecting an input current supplied from an AC power source , and a value corresponding to the target value of the input current Set A current setting unit, the first and control means for selecting and turning on and off the one of the switching means and the second switching means, the first heating coil and the second heating coil resistance The current setting means has a first current setting value used when heating the pan and a second current value used when heating the metal plate of the lid, and the minimum ON The time setting means has a first minimum on-time and a second minimum on-time shorter than the first minimum on-time, and the first minimum on-time is set as the on-time when the first switching means is activated. the set as the initial value, then the control means controls the on time of the first switching means such that said first set current value, said second switching means when starting the second in Set the minimum on time as an initial value of the on-time, and the subsequent ones said control means is configured to control the on-time of the second switching means so that the second current set value, said first wherein the heating coil second heating coil even if the resistance value and the inductance value are different, it is able to independently set the minimum on-time of the first switching means and second switching means, first switching on startup The minimum on-time of the means can be made longer than the minimum on-time of the second switching means, the turn-on voltage can be made sufficiently small, and the heat generation of the switching means can be suppressed. In addition, by increasing the first minimum on-time, the input power at the time of startup is increased, and the rise time of the input power can be shortened.

  According to a second invention, in the first invention described above, a maximum on-time setting means for setting a maximum value of an on-time of the first switching means and the second switching means is provided. 1 having a maximum on-time and a second maximum on-time shorter than the first maximum on-time, the first maximum on-time being used when on / off controlling the first switching means, The maximum ON time of 2 is used when the second switching means is on / off controlled, and a large current flows through the second heating coil and the second switching means for heating the inner surface side of the lid. Thus, the maximum on-time can be set so that the second heating coil and the second switching means are not overheated.

  According to a third invention, in the second invention, the first synchronization signal generating means for outputting the synchronization signal by the voltage across the first switching means and the synchronization signal by the voltage across the second switching means. A second synchronization signal generating means; a first off means for setting the maximum off time of the second switching means; and a maximum off time setting means for setting a maximum off time of the second switching means. And a second maximum off time shorter than the first maximum off time, and the control means is synchronized with the first synchronization signal generating means when the first switching means is selected. When the signal is detected or when the first maximum off time is detected, the first switching means is turned on. When the second switching means is selected, the second synchronization signal is generated. When the stage synchronization signal is detected or the second maximum off time is detected, the second switching means is turned on, and the maximum off time of the second switching means can be shortened. Even when there is no output signal from the second synchronization signal output means, the ratio of the off time to the on time can be kept within a predetermined value, so that, for example, the input power to the second heating coil is extremely Can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a partial block diagram of the rice cooker according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the pan 1 shows an equivalent circuit, and is composed of a laminated body using a plurality of metals through which magnetic flux passes. The first heating coil 2 is magnetically coupled to the pan 1 so as to heat the pan 1. The first heating coil 2 is constituted by a wire obtained by twisting more than 20 litz wires in which a plurality of copper wires are bundled, and the current distribution when a high-frequency current flows is made uniform.

  The first resonance capacitor 3 is connected in parallel to the first heating coil 2 and constitutes a parallel resonance circuit with the first heating coil 2. In the present embodiment, a polypropylene capacitor having a small loss even when a high-frequency current flows is used. The first switching means 4 is composed of a semiconductor element such as a MOSFET or IGBT and a reverse connection diode reversely connected to the semiconductor element. MOSFETs and IGBTs have a high withstand voltage, can switch at high frequencies, and have an advantage that a large current can flow.

  Although the lid 5 is not shown, a metal plate is attached to the inner surface side, and in this embodiment, a stainless metal plate is used so as not to rust. This metal plate may be detachable from the lid 5 for easy washing after cooking.

  The second heating coil 6 is built in the lid 5 and induction-heats the metal plate. The second heating coil 6 is formed in a donut shape in order to uniformly heat the metal plate. Usually, since the first heating coil 2 and the second heating coil 6 are different in shape, number of turns, required electric power, and the like, the inductance and the DC resistance value are also different.

  The second resonance capacitor 7 is connected in parallel to the second heating coil 6, and is composed of a polypropylene capacitor like the first resonance capacitor 3. The second switching means 8 has the same configuration as the first switching means 4. However, since the flowing current value and the both-end voltage value generated at the time of OFF are different, the parts are configured with specifications that satisfy these current value and both-end voltage value.

  The AC power supply 9 supplies power to the rice cooker, and the power supply frequency of the AC power supply 9 is 50 Hz in the eastern Japan region and 60 Hz in the western Japan region. The rectifying means 10 rectifies the AC power supply 9 and supplies power to the first heating coil 2 and the second heating coil 6, and is composed of a diode bridge 11, a choke coil 12, and a smoothing capacitor 13. . Here, the capacity of the smoothing capacitor 13 is as small as several μF, and ripples are generated when a current is passed through the first heating coil 2 and the second heating coil 6. In the present embodiment, this ripple voltage waveform is the same as the voltage waveform of the AC power supply 9.

  The current detection means 14 detects an input current supplied from the AC power supply 9, and converts the output of the current transformer into a DC voltage via a diode bridge and an electrolytic capacitor. The current setting means 15 sets a value corresponding to the target value of the input current, and a plurality of current setting values are stored in the ROM inside the microcomputer. In the present embodiment, there is a first current set value Is1 used when heating the pan 1, and a second current set value Is2 for heating the metal plate of the lid 5, and the first current set value Is1 The second current set value Is2 is stored as 8-bit data in the ROM inside the microcomputer. In the present embodiment, the first current set value Is1 is a value corresponding to the input current 12A, and the second current set value Is2 is a value corresponding to the input current 2A.

  The minimum on-time setting unit 16 sets a minimum value of the on-time of the first switching unit 4 and the second switching unit 8, and the first minimum on-time Tmin1 and the second minimum on-time Tmin2 are micro values. It is stored in a ROM inside the computer.

  The control unit 17 selects one of the first switching unit 4 and the second switching unit 8 and performs on / off control. The control unit 17 includes an input switch 18 that switches a ratio between the output voltage and the input current of the current detection unit 14. The AD converter 19 that converts the analog voltage output from the input switch 18 into a 10-bit digital value, and the output of the AD converter 19 and the output of the current setting means 15 are compared to set the ON time of the switching means. The time calculator 20, the pulse generator 21 that outputs the high pulse of the on time set by the on-time calculator 20, and the output that switches the output of the pulse generator 21 to the first drive means 23 and the second drive means 24. And a switch 22.

  The AD converter 19, the on-time calculator 20, and the pulse generator 21 can be realized by using a microcomputer AD converter, CPU, and PWM generator. However, this is merely an example, and for example, a dedicated IC including the on-time calculator 20 and the pulse generator 21 may be created and used, and the configuration is not limited.

  FIG. 2 shows the operation waveforms of the current flowing through the first switching means 4 and the voltage across the first switching means 4 when the first switching means 4 is turned on for the second minimum on-time Tmin2 in the rice cooker shown in FIG. Yes. As shown in FIG. 2, since the voltage Von across the switching means 4 is generated at the turn-on time t <b> 2, the turn-on current Ion flows through the switching means 4. The switching means 4 generates heat due to Von and Ion at this time.

  FIG. 3 shows operating waveforms of the current flowing through the first switching means 4 and the voltage across the first switching means 4 when the first switching means 4 is turned on for the first minimum on time Tmin1 in the rice cooker shown in FIG. ing. As shown in FIG. 3, at the turn-on time t2, the voltage across the switching means 4 becomes 0V, so that no turn-on current flows. Therefore, the heat generation of the switching means 4 can be suppressed.

  FIG. 4 shows operation waveforms when the pot 1 and the lid 5 are alternately heated in the rice cooker shown in FIG. FIG. 4A shows the time change of the on-time Ton. FIG. 4B shows the time change of the input current Iin.

  FIG. 5 shows the relationship between the ON time of the switching means, the turn-off voltage, and the input current in the AC power supply 100V. As shown in FIG. 5, in the case of the same on-time, the input current flows more easily when the metal plate of the lid 5 is heated than when the pan 1 is heated, and the turn-on voltage tends not to be generated. This is because the pan 1 and the lid 5 have different electrical characteristics such as a resistance value and an inductance value.

  FIG. 6 is an example of a block circuit diagram of the input switch 18. As shown in FIG. 6, the input switch 18 connects a series circuit of a resistor 63 and a transistor 64 to the contact point between the resistor 61 and the resistor 62, and turns on and off the transistor 64 with the output of the microcomputer 65, thereby detecting current. The output voltage dividing ratio of 14 output voltages is switched. The microcomputer 65 outputs high to turn on the transistor 64 when heating the pan 1, and outputs low to turn off the transistor 65 when heating the metal plate of the lid 5. As shown in FIG. 6, by switching the voltage dividing ratio of the output voltage of the current detection means 14, the voltage dividing ratio can be increased when the input current is small, and the voltage dividing ratio can be decreased when the input current is large. Without widening the input voltage range of the device 19, the input current can be accurately detected in a wide range.

  FIG. 7 is an example of a block circuit diagram of the output switch 22. As shown in FIG. 7, the output switching unit 22 includes a logical inversion element 71 and logical product operators 72 and 73, and outputs the output pulse of the pulse generator 21 to the first driving unit 23 using the output of the microcomputer 65. Switching to the second driving means 24 is performed. In the present embodiment, when the pan 1 is heated, the microcomputer 65 outputs high, outputs the output of the pulse generator 21 to the first driving means 23 via the logical product operator 72, and outputs the logic. Low is output to the AND operator 72 via the inverting element 71, and the second driving means 24 is fixed to low. Conversely, when heating the metal plate of the lid 5, the microcomputer 65 outputs low, fixes the first driving means 23 to low via the logical product operator 72, and passes through the logical inverting element 71. Then, high is output to the logical product operator 73, and the output of the pulse generator 21 is output to the second driving means 24.

  Note that the configuration of the output switching device 22 shown in FIG. 7 is an example, and a circuit may be configured using a plurality of comparators, for example. In this case, the power supply voltage and the reference voltage can be increased as compared with the logic circuit, and the noise resistance can be increased.

  In the present embodiment, the number of ports used for the microcomputer 65 is saved by using a single output terminal for outputting from the microcomputer 65 to the input switch 18 and the output switch 22.

  The operation and action of the above configuration will be described. First, the pan 1 is placed on the first heating coil 2, and rice cooking is started with a metal plate attached to the lid 5. The rice cooking sequence operates based on the data stored in the ROM of the microcomputer constituting the control means 17 and the like. This Embodiment demonstrates especially the operation | movement in the process of heating the metal plate of the pan 1 and the lid | cover 5 alternately in a rice cooking sequence, referring FIG.

  First, at time t0 in FIG. 4, in order to heat the pan 1, the input switch 18 switches to a low voltage dividing ratio, and the output switch 22 switches the output of the pulse generator 21 to the first driving means 23. Next, the current setting means 15 sets the first current set value Is1 in the on-time calculator 20, and the minimum on-time setting means 16 sets the first minimum on-time Tmin1 as the initial value of the on-time Ton. To do. The on-time calculator 20 outputs a first minimum on-time Tmin1 to the pulse generator 21 as an initial value, and the pulse generator 21 sends a high pulse having a pulse width Tmin1 to the first driving means 23 via the output switch 22. Since the first driving means 23 turns on the first switching means 4, a current flows through the first heating coil 2 and the pot 1 is induction-heated.

  During the period from time t0 to t1, the on-time calculator 20 increases the on-time Ton so that the output value of the AD converter 19 becomes the first current set value Is1. During the period from time t1 to t2, the on-time calculator 20 controls the on-time Ton so that the output value of the AD converter 19 becomes the first current set value Is1. When the time t2 is reached, the heating of the pan 1 is stopped by setting the on time Ton = 0, and the heating of the metal plates of the pan 1 and the lid 5 is stopped until the time t3.

  From time t3, the metal plate of the lid 5 is heated based on a predetermined rice cooking sequence. At this time, first, the input switch 18 switches to a high voltage dividing ratio, and the output switch 22 switches the output of the pulse generator 21 to the second driving means 24.

  Next, the current setting unit 15 sets the second current set value Is2 in the on-time calculator 20, and the minimum on-time setting unit 16 sets the second minimum on-time Tmin2 as an initial value of the on-time Ton. . The on-time calculator 20 outputs Tmin2 to the pulse generator 21 as an initial value, and the pulse generator 21 outputs a high pulse having a pulse width Tmin2 to the second drive means 24 via the output switch 22 to obtain the second value. Since the driving means 24 turns on the second switching means 8, a current flows through the second heating coil 6, and the metal plate of the lid 5 is induction-heated.

  During the period from time t3 to t4, the on-time calculator 20 increases the on-time Ton so that the output value of the AD converter 19 becomes the second current set value Is2. During the period from time t4 to t5, the on-time calculator 20 controls the on-time Ton so that the output value of the AD converter 19 becomes Is2. When the time t5 is reached, the on-time Ton = 0 is set and heating of the metal plate of the lid 5 is stopped, and heating of the metal plate of the pot 1 and the lid 5 is stopped for a predetermined period.

  As described above, in the present embodiment, the minimum on-time setting unit 16 has the first minimum on-time Tmin1 and the second minimum on-time Tmin2, and the first switching unit 4 and the second By changing the setting of the initial value of the on-time when the switching unit 8 is started, the turn-on voltage of the first switching unit 4 can be eliminated, the turn-on loss of the first switching unit 4 can be eliminated, and the heat generation can be reduced. it can.

  In addition, by setting the first minimum on-time Tmin1 to be greater than the second minimum on-time Tmin2, the time to reach the input current target value Is1 is shortened, and the pan 1 can be heated in a short time.

(Embodiment 2)
FIG. 8 is a partial block diagram of the rice cooker according to Embodiment 2 of the present invention.

  As shown in FIG. 8, the maximum on-time setting means 81 sets the maximum value of the on-time of the first switching means 4 and the second switching means 8, and the first maximum time is stored in the ROM inside the microcomputer. An on-time Tmax1 and a second maximum on-time Tmax2 are stored.

  Similarly to the first embodiment, the on-time calculator 82 is composed of a microcomputer, and compares the output of the AD converter 19 with the input current target value set by the current setting means 15 to set the on-time Ton. At the same time, when the on time Ton exceeds the maximum on time set by the maximum on time setting means 81, the on time Ton is fixed to the maximum on time. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and description thereof is omitted.

  FIG. 9 shows the relationship between the on-time of the switching means, the turn-off voltage, and the input current when the AC power supply 9 is 100V. As shown in FIG. 9, in the case of the same on-time, the input current tends to flow and the turn-on voltage is less likely to be generated when the metal plate of the lid 5 is heated than when the pan 1 is heated. . This is because the pan 1 and the lid 5 have different electrical characteristics such as a resistance value and an inductance value. In the present embodiment, the input current when heating the lid 5 is as small as 2A, and a large amount of input current flows even during the same on-time as when the pan 1 is heated, so the maximum on-time of the second switching means 8 Tmax2 is set to a value smaller than the minimum on-time Tmin1 of the first switching means 4.

  The operation and action of the above configuration will be described. First, the pan 1 is placed on the first heating coil 2, and rice cooking is started with a metal plate attached to the lid 5. The rice cooking sequence operates based on the data stored in the ROM of the microcomputer constituting the control means 17 and the like.

  This Embodiment demonstrates especially the operation | movement of the rice cooker in the process of heating the metal plate of the pan 1 and the lid | cover 5 alternately in a rice cooking sequence, referring FIG.

  First, at time t0 in FIG. 4, in order to heat the pan 1, the input switch 18 switches to a low voltage dividing ratio, and the output switch 22 switches the output of the pulse generator 21 to the first driving means 23.

  Next, the current setting unit 15 outputs the first current set value Is1 to the on-time calculator 82, and the minimum on-time setting unit 16 sets the first minimum on-time Tmin1 as the initial value of the on-time Ton. The maximum ON time setting means 81 outputs the first maximum ON time Tmax1 to the ON time calculator 82 as the maximum ON time value. The on-time calculator 82 outputs the first minimum on-time Tmin1 to the pulse generator 21 as an initial value, and the pulse generator 21 sends a high pulse having a pulse width Tmin1 to the first driving means 23 via the output switch 22. Since the first driving means 23 turns on the first switching means 4, a current flows through the first heating coil 2 and the pot 1 is induction-heated.

  During the period from time t0 to t1, the on-time calculator 82 increases the on-time Ton so that the output value of the AD converter 19 becomes the first current set value Is1. At this time, the on-time Ton is set based on (Equation 1) when the output value of the AD converter 19 is Iin.

Ton = Ton + α × (Is1-Iin) (1)
Here, α is a coefficient, which is stored in advance in a ROM inside the microcomputer. The value of α may be changed when the pan 1 is heated and when the metal plate of the lid 5 is heated. If Ton> Tmax1 is satisfied, it is output to the pulse generator 21 as Ton = Tmax1.

  During the period of time t1 to t2, the on-time calculator 82 controls the on-time Ton so that the output value of the AD converter 19 becomes the first current set value Is1. Ton at this time is set based on (Equation 1). When the time t2 is reached, the heating of the pan 1 is stopped by setting the on time Ton = 0, and the heating of the metal plates of the pan 1 and the lid 5 is stopped until the time t3. From time t3, the metal plate of the lid 5 is heated based on a predetermined rice cooking sequence. At this time, first, the input switch 18 switches to a high voltage dividing ratio, and the output switch 22 switches the output of the pulse generator 21 to the second driving means 24.

  Next, the current setting unit 15 outputs the second current set value Is2 to the on-time calculator 82, and the minimum on-time setting unit 16 sets the second minimum on-time Tmin2 as the on-time as the initial value of the on-time Ton. The maximum on-time setting means 81 outputs the second maximum on-time Tmax2 to the on-time calculator 82 as the maximum on-time value. The on-time calculator 82 outputs the second minimum on-time Tmin2 to the pulse generator 21 as an initial value, and the pulse generator 21 outputs a high pulse having a pulse width Tmin2 via the output switch 22 to the second driving means 24. Since the second driving means 24 turns on the second switching means 8, a current flows through the second heating coil 6, and the metal plate of the lid 5 is inductively heated.

  During the period of time t0 to t1, the on-time calculator 82 increases the on-time Ton so that the output value of the AD converter 19 becomes Is2. At this time, the on-time Ton is set based on (Equation 2) when the output value of the AD converter 19 is Iin.

Ton = Ton + α × (Is2-Iin) (2)
Here, when Ton> Tmax2, it is output to the pulse generator 21 as Ton = Tmax2.

  During the period from time t3 to t4, the on-time calculator 20 increases the on-time Ton so that the output value of the AD converter 19 becomes the second current set value Is2. During the period from time t4 to t5, the on-time calculator 20 controls the on-time Ton so that the output value of the AD converter 19 becomes the second current set value Is2. When the time t5 is reached, the on-time Ton = 0 is set and heating of the metal plate of the lid 5 is stopped, and heating of the metal plate of the pot 1 and the lid 5 is stopped for a predetermined period.

  As described above, in the present embodiment, the first maximum on-time Tmax1 and the second maximum on-time Tmax2 are provided. When the first switching means 4 is turned on and the second switching means 8 is turned on. When the maximum value of the on-time is changed, the on-time of the second switching means 8 becomes extremely long, and it is possible to prevent a large current from flowing through the second heating coil 6. It is possible to prevent the heating coil 6 and the second switching means 8 from becoming overheated.

(Embodiment 3)
FIG. 10 is a partially block circuit diagram of the rice cooker according to Embodiment 3 of the present invention.

  As shown in FIG. 10, the first synchronization signal generating means 91 outputs a synchronization signal by the voltage across the first switching means 4, and two or more that divide the voltage across the first switching means 6. A first series circuit composed of two resistors, a second series circuit composed of two or more resistors for dividing the voltage across the smoothing capacitor 13, an output of the first series circuit, and an output of the second series circuit And a comparator that outputs high or low.

  The second synchronizing signal generating means 92 outputs a synchronizing signal by the voltage across the second switching means 8, and the third synchronizing signal generating means 92 includes a third resistor composed of two or more resistors that divide the voltage across the second switching means 6. The comparator includes a series circuit, a comparator that compares the outputs of the second series circuit and the third series circuit and outputs high or low.

  The maximum off time setting means 93 sets the maximum value of the off time of the first switching means 4 and the second switching means 8, and the first maximum off time Toff1 and the second maximum time are stored in the ROM inside the microcomputer. The maximum on-time Toff2 is stored. The maximum off time setting means 93 sets a first maximum off time Toff1 when heating the pan 1, and sets a second maximum off time Toff2 when heating the metal plate of the lid 5.

  The off-time timer 94 is configured by using a timer inside the microcomputer, and outputs high to the pulse generator 95 when the off-time Toff reaches the set maximum off-time Toff1 (or Toff2). The pulse generator 95 outputs a high pulse to a predetermined driving means via the output switch 22 when the first synchronizing signal generating means 91, the second synchronizing signal generating means 92, and the off-time timer 94 become high. It is composed. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and description thereof is omitted.

  Configuration in which the voltage across the first switching means 4 and the second switching means 8 is detected and the synchronization signal is output based on the output value, like the first synchronizing signal generating means 91 and the second synchronizing signal generating means 92 At the time of start-up with a short on-time, as shown in FIG. 2, the turn-on voltage Von may not be sufficiently lowered and a synchronization signal may not be output.

  When the off-time timer 94 measures the maximum off-time and outputs high when the synchronization signal is not output in this way, the pulse generator 95 detects this and outputs a high pulse during the Ton period. In particular, it is possible to set an optimum off time for each heating coil by changing the setting of the maximum off time when the pan 1 is heated and when the metal plate of the lid 5 is heated.

  Thereby, for example, when the metal plate of the lid 5 is heated, since the off time is long, the ratio of the off time to the on time at the time of startup increases, the amount of power supplied to the second heating coil 6 decreases, and the lid 5 It is possible to prevent the temperature rise of the metal plate from slowing down.

  As described above, in the present embodiment, the first maximum off time Toff1 and the second maximum on time Toff2 are provided, and the first switching means 4 and the second switching means 8 are driven. When the maximum value of the off time is changed, the off time of the second switching means 8 becomes extremely long at the time of start-up, the amount of power supplied to the second heating coil 6 is reduced, and the metal plate of the lid 5 It is possible to prevent the temperature rise from becoming gradual.

  As described above, the rice cooker according to the present invention reduces the turn-on voltage of the switching means at startup by independently setting the minimum on-time of the switching means connected in series to the heating coils that operate with different input powers. And since it can suppress heat generation, it has a heating coil that operates with at least two different input powers, and is useful as a rice cooker that induction-heats a pan or lid.

The circuit diagram which made the partial block diagram of the rice cooker of Embodiment 1 of this invention Voltage current waveform diagram of the first switching means when the on-time of the first switching means of the rice cooker is shortened Voltage current waveform diagram of the first switching means when the on-time of the first switching means of the rice cooker is lengthened Operation waveform diagram of main parts of the rice cooker The characteristic figure which shows the relation between the ON time of the switching means of the rice cooker, the input current, and the turn-on voltage of the switching means Block circuit diagram of the input switching device constituting the control means of the rice cooker Block circuit diagram of the output switching device constituting the control means of the rice cooker The circuit diagram which made the block diagram of the rice cooker of Embodiment 2 of this invention The characteristic figure which shows the relation between the ON time of the switching means of the rice cooker, the input current, and the turn-on voltage of the switching means The circuit diagram which made the block diagram of the rice cooker of Embodiment 3 of this invention Block diagram of a conventional rice cooker Waveform diagram of the main parts of a conventional rice cooker

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pan 2 1st heating coil 3 1st resonance capacitor 4 1st switching means 5 Lid 6 2nd heating coil 7 2nd resonance capacitor 8 2nd switching means 9 AC power supply 10 Rectification means 16 Minimum on-time Setting means 17 Control means

Claims (3)

A first heating coil for inductively heating the pan, a first resonant capacitor that constitutes a resonance circuit with the first heating coil, first switching means connected in series to the first heating coil, and the pan A lid that covers the opening of the lid, a second heating coil that induction-heats the metal plate on the inner surface side of the lid, a second resonance capacitor that constitutes a resonance circuit with the second heating coil, and the second Second switching means connected in series to the heating coil, rectifying means for rectifying an AC power source and supplying power to the first heating coil and the second heating coil, the first switching means, and the second switching means the minimum on-time setting means for setting a minimum value of the oN time of the switching means, a current detecting means for detecting an input current supplied from the AC power source, the current setting means for setting a value corresponding to the target value of the input current , And control means for selecting and turning on and off the one of said first switching means and said second switching means, wherein the first heating coil second heating coil has resistance and inductance values Differently, the current setting means has a first current set value used when heating the pan and a second current value used when heating the metal plate of the lid, and the minimum on-time setting means is , Having a first minimum on-time and a second minimum on-time shorter than the first minimum on-time, and when starting the first switching means, the first minimum on-time is used as an initial value of the on-time. set, then the control means controls the on time of the first switching means such that said first set current value, the minimum on-time and the second at the time of activation of the second switching means And set to the initial value of the down time, then cooker said control means is configured to control the on-time of the second switching means so that the second current set value. Maximum on-time setting means for setting a maximum value of the on-time of the first switching means and the second switching means, wherein the maximum on-time setting means includes a first maximum on-time and the first maximum on-time. The first maximum on-time is used for on-off control of the first switching means, and the second maximum on-time is used for controlling the second switching means. The rice cooker according to claim 1, which is used for on-off control. A first synchronizing signal generating means for outputting a synchronizing signal according to a voltage across the first switching means; a second synchronizing signal generating means for outputting a synchronizing signal according to a voltage across the second switching means; Switching means and maximum off time setting means for setting a maximum value of the off time of the second switching means, wherein the maximum off time setting means is based on the first maximum off time and the first maximum off time. The controller has a short second maximum off time, and the control means detects the synchronization signal of the first synchronization signal generating means or selects the first maximum off time when the first switching means is selected. When it is detected, the first switching means is turned on, and when the second switching means is selected, the synchronization signal of the second synchronization signal generating means is detected or the second switching means is detected. Cooker according to claim 2, wherein which is adapted to turn on said second switching means and for detecting the off-time.

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