JP2004327104A - Induction heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating cooker capable of reducing the cost and size of a resonance capacitor by limiting an application voltage to the resonance capacitor. <P>SOLUTION: This induction heating cooker is equipped with: a rectifying circuit 10 for rectifying supply power from the outside; a smoothing circuit 20 for converting it into D.C. power; an inverter circuit 30 having a pair of switching elements 31 and 32 serially connected between output lines of the smoothing circuit 20, and a series load circuit of a heating coil 36 and a resonance capacitor 37 connected in parallel with either of the switching elements; a control circuit 50 for outputting a control signal based on a predetermined power setting value; an inverter drive circuit 60 for outputting drive signals of the respective switching elements 31 and 32 according to the control signal; and a capacitor voltage detection circuit 40 for detecting the application voltage to the resonance capacitor 37. The control circuit 50 varies the duty ratio of each drive signal so as to set a detection signal below a predetermined reference value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an induction heating cooker provided with an inverter circuit.
[0002]
[Prior art]
A conventional induction heating cooker has a current value input to a DC power supply circuit in order to determine the material of a pot as described in page 2, column 1, lines 14 to 17 of JP-A-2002-75623. And a voltage value generated in the inverter circuit to determine whether there is an abnormality on the heating coil.
[0003]
[Patent Document 1]
JP-A-2002-75623 (page 2, column 1, lines 14 to 17, FIG. 1)
[0004]
[Problems to be solved by the invention]
The conventional induction heating cooker detects the voltage value generated in the inverter circuit, but only for determining the material of the pot. Therefore, it is necessary to use a resonance capacitor having a sufficiently high withstand voltage in order to cope with both load fluctuations and power supply voltage fluctuations due to changes in the material of the pan, resulting in an increase in the cost and size of the resonance capacitor. Have been.
[0005]
An object of the present invention is to provide an induction heating cooker in which the voltage applied to the resonance capacitor is limited even when various fluctuations occur, and the withstand voltage margin is reduced to reduce the cost and size of the resonance capacitor. It is to be.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an induction heating cooker according to the present invention includes a rectifier circuit that rectifies AC power supplied from an external power supply,
A smoothing circuit that converts the output of the rectifier circuit into DC power,
A pair of switching elements connected in series between the output lines of the smoothing circuit, and an inverter circuit connected in parallel to any one of the switching elements and having a load circuit including a series circuit of a heating coil and a resonance capacitor;
Control means for outputting a control signal based on a preset power set value,
Inverter driving means for outputting a drive signal for alternately turning on or off each switching element of the inverter circuit according to the control signal,
Capacitor voltage detecting means for detecting the applied voltage of the resonance capacitor,
The control means changes the duty ratio of the drive signal of each switching element so that the detection signal from the capacitor voltage detection means becomes equal to or less than a preset reference voltage value.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a circuit block diagram showing a first embodiment of the present invention. The induction heating cooker includes a rectifier circuit 10, a smoothing circuit 20, an inverter circuit 30, a capacitor voltage detection circuit 40, a control circuit 50, an inverter drive circuit 60, and the like.
[0008]
The rectifier circuit 10 is configured by a diode bridge or the like, and rectifies AC power supplied from an external AC power supply PS such as commercial power.
[0009]
The smoothing circuit 20 is configured by, for example, a π-type filter circuit including an input capacitor 21, a choke coil 22, and an output capacitor 23, smoothes the pulsating current rectified by the rectifying circuit 10, converts the pulsating current into DC power, and converts the ground line Lg into a DC power. Output to the power supply line Lh as a reference.
[0010]
The inverter circuit 30 includes a pair of switching elements 31 and 32 connected in series between the ground line Lg and the power supply line Lh, a load circuit including a series circuit including a heating coil 36 and a resonance capacitor 37, and the like.
[0011]
The switching elements 31 and 32 are composed of, for example, transistors and the like, and diodes 33 and 34 for reverse conduction are respectively connected in parallel to the emitter and the collector of each switching element 31 and 32. The drive signal QA from the inverter drive circuit 60 is supplied to the base of the switching element 31, and the drive signal QB from the inverter drive circuit 60 is supplied to the base of the switching element 32.
[0012]
The collector of the switching element 31 on the high potential side is connected to the power supply line Lh, and the emitter of the switching element 32 on the low potential side is connected to the ground line Lg. One end of the heating coil 36 is connected to an output line Lo to which the collector of the switching element 31 and the collector of the switching element 32 are connected. A resonance capacitor 37 is connected between the other end of the heating coil 36 and the ground line Lg. Note that a noise removing capacitor 35 is connected between the output line Lo and the ground line Lg.
[0013]
In the present embodiment, an example in which the heating coil 36 is arranged on the output line Lo side and the resonance capacitor 37 is arranged on the ground line Lg side in a series circuit of the heating coil 36 and the resonance capacitor 37 will be described. The heating capacitor 36 may be arranged on the ground line Lg side. In this case, the capacitor voltage detection circuit 40 is arranged so that the voltage across the resonance capacitor 37 can be measured.
[0014]
In this embodiment, an example in which the load circuit is arranged between the output line Lo and the ground line Lg will be described. However, the load circuit can be arranged between the power supply line Lh and the output line Lo.
[0015]
The capacitor voltage detection circuit 40 has a function of detecting a voltage applied to the resonance capacitor 37 and outputting a detection signal D. Here, a voltage dividing circuit including resistors 41 and 42 is connected to both ends of the resonance capacitor 37. In addition, the voltage dividing ratio of the resistor is adjusted to match the input voltage range of the control circuit 50.
[0016]
FIG. 2 is a block diagram showing a circuit configuration of the control circuit 50. The control circuit 50 can be configured by an analog circuit such as an operational amplifier, or a digital circuit such as a microcomputer or a DSP (digital signal processor), and includes an input setting unit 51, an input detection unit 52, a power control unit 53, It comprises a capacitor voltage setting section 54, a capacitor voltage detecting section 55, a comparing section 56 and the like.
[0017]
The input setting unit 51 stores a cooking power value set by a panel operation, an external command signal, or the like, and outputs a power setting signal corresponding to the cooking power value.
[0018]
The input detection unit 52 has a function of detecting power input from the external AC power supply PS and outputting an input power signal, and for example, a current sensor and a filter circuit for detecting a current flowing through an input line of the rectifier circuit 10, an amplifier, and an amplifier. It can be configured by a circuit or the like.
[0019]
The power control unit 53 outputs a control signal SA based on the power setting signal from the input setting unit 51 and the input power signal from the input detection unit 52.
[0020]
The capacitor voltage setting unit 54 stores and outputs a reference voltage value corresponding to the upper limit of the voltage applied to the resonance capacitor 37 in consideration of the withstand voltage rating of the resonance capacitor 37 and the like.
[0021]
The capacitor voltage detection unit 55 receives the detection signal D from the capacitor voltage detection circuit 40, performs signal processing as necessary, and outputs the processed signal.
[0022]
The comparing unit 56 compares the reference voltage value from the capacitor voltage setting unit 54 with the output signal from the capacitor voltage detecting unit 55, and outputs a control signal SB based on the comparison result.
[0023]
FIG. 3 is a block diagram illustrating an example of a circuit configuration of the inverter drive circuit 60. Here, an example using an analog circuit such as an operational amplifier will be described, but a similar function can be realized using a digital circuit.
[0024]
The inverter drive circuit 60 includes an oscillator 61, comparators 62 to 68, and the like. The oscillator 61 determines the reference frequency of the inverter operation, and generates a pulse having a predetermined cycle and a predetermined duty ratio (conduction ratio). The comparator 62 converts the pulse waveform from the oscillator 61 into a sawtooth waveform based on the reference voltage. The comparator 63 compares the control signals SA and SB from the control circuit 50 and outputs a control signal SC. The comparator 64 compares the output of the comparator 62 with the control signal SC from the comparator 63, and outputs a pulse with a variable duty ratio.
[0025]
The comparator 65 converts the pulse waveform from the comparator 64 into a sawtooth waveform based on the reference voltage. The comparator 66 converts the output from the comparator 65 into a pulse having a variable duty ratio based on the reference voltage, and outputs a drive signal QA. The comparator 67 converts the pulse waveform from the comparator 64 into a sawtooth waveform based on the reference voltage. The comparator 68 converts the output from the comparator 67 into a pulse with a variable duty ratio based on the reference voltage, and outputs a drive signal QB.
[0026]
Next, the overall operation will be described with reference to the timing chart shown in FIG. First, as shown in FIG. 4A, the oscillator 61 generates a rectangular pulse s1 having a frequency of 21 kHz (cycle T = about 48 μs) and a duty ratio of 50%, for example. As shown in FIG. 4B, the comparator 62 inverts the rectangular pulse s1 and, after a lapse of a predetermined time (for example, 5 μs) from the fall of the inverted pulse, increases the slope linearly from the low level to the high level. A waveform is generated, and a sawtooth pulse s2 is output.
[0027]
On the other hand, the comparator 63 compares the control signal SA from the power control unit 53 with the control signal SB from the comparison unit 56, and outputs the control signal SC as the reference voltage of the comparator 64 as shown in FIG. Output. The comparator 64 compares the sawtooth pulse s2 from the comparator 62 with the control signal SC, and as shown in FIG. 4D, a rectangle which becomes high level only during the period when the sawtooth pulse s2 is equal to or less than the control signal SC. The pulse s4 is output.
[0028]
As shown in FIG. 4E, the comparator 65 generates a ramp waveform that rises linearly from the rising edge of the rectangular pulse s4, and outputs a sawtooth pulse s5. As shown in FIG. 4F, the comparator 66 compares the sawtooth pulse s5 with the reference voltage Va, and outputs a drive signal QA that is at a high level only during a period when the sawtooth pulse s5 is higher than the reference voltage Va. I do. As shown in FIG. 4 (g), the drive signal QA is a rectangular pulse having a period T during the on-period T1 and delayed by a time t3 from the rise of the rectangular pulse s1 of the oscillator 61, and has a duty ratio (= T1 / T1). ) Changes by adjusting the level of the control signal SC.
[0029]
As shown in FIG. 4H, the comparator 67 inverts the rectangular pulse s4, generates a ramp waveform that monotonically increases from the rising point of the inverted pulse, and outputs a sawtooth pulse s7. As shown in FIG. 4 (i), the comparator 68 compares the sawtooth pulse s7 with the reference voltage Vb, and outputs a drive signal QB which is at a high level only during a period when the sawtooth pulse s7 is higher than the reference voltage Vb. I do. As shown in FIG. 4 (j), the drive signal QB is a rectangular pulse having a period T during the on-period T2 with a delay of time t4 from the fall of the rectangular pulse s1 of the oscillator 61, and its duty ratio (= T2 / T) changes by adjusting the level of the control signal SC.
[0030]
Thus, drive signals QA and QB whose duty ratio changes in accordance with the level adjustment of control signal SC are obtained.
[0031]
The switching element 31 is turned on in response to the on-period T1 of the drive signal QA, and is turned off during the remaining off-period. The switching element 32 is turned on in response to the on-period T2 of the drive signal QB, and is turned off during the remaining off-period. The switching elements 31 and 32 alternately turn on or off at a cycle T, so that a high-frequency current flows through a series circuit including the heating coil 36 and the resonance capacitor 37.
[0032]
An object W to be heated such as a pan is arranged near the heating coil 36. When the heating coil 36 generates a high-frequency magnetic field, an induction current flows through the object W to be heated, and heating and cooking are performed by Joule heat.
[0033]
When the on-period of the switching element 31 becomes longer and the on-period of the switching element 32 becomes shorter, the electric power supplied to the heating coil 36 increases, and the amount of heat generated in the heated object W increases. On the other hand, when the ON period of the switching element 31 is short and the ON period of the switching element 32 is long, the electric power supplied to the heating coil 36 is reduced, and the amount of heat generated in the heated object W is reduced. Therefore, by adjusting the level of the control signal SC, the amount of heat generated in the object to be heated W can be controlled.
[0034]
Next, the power control operation will be described. Referring to the timing chart shown in FIG. 5, when the control circuit 50 increases the cooking power value set in the input setting unit 51 by a panel operation or an external command signal, the control signal SA from the power control unit 53 is output. As the level increases, the level of the control signal SC also increases. Then, the ON period T1 of the drive signal QA becomes longer and the duty ratio increases, and the ON period T2 of the drive signal QB becomes shorter and the duty ratio decreases. As a result, the power supplied to the heating coil 36 increases.
[0035]
On the other hand, when the cooking power value set in the input setting unit 51 is reduced, the level of the control signal SA from the power control unit 53 decreases, and the level of the control signal SC also decreases. Then, the ON period T1 of the drive signal QA becomes shorter and the duty ratio decreases, and the ON period T2 of the drive signal QB becomes longer and the duty ratio increases. As a result, the power supplied to the heating coil 36 decreases.
[0036]
In this way, the power supplied to the heating coil 36 is controlled in accordance with the operation of the user, and the heating of the object to be heated W can be controlled.
[0037]
Next, a case where the external AC power supply PS fluctuates will be described. Referring to the timing chart shown in FIG. 5, when the input power from external AC power supply PS increases, the level of control signal SA from power control unit 53 decreases, and the level of control signal SC also decreases. Then, the ON period T1 of the drive signal QA becomes shorter and the duty ratio decreases, and the ON period T2 of the drive signal QB becomes longer and the duty ratio increases. As a result, the power supplied to the heating coil 36 decreases.
[0038]
On the other hand, when the input power from external AC power supply PS decreases, the level of control signal SA from power control unit 53 increases, and the level of control signal SC also increases. Then, the ON period T1 of the drive signal QA becomes longer and the duty ratio increases, and the ON period T2 of the drive signal QB becomes shorter and the duty ratio decreases. As a result, the power supplied to the heating coil 36 increases.
[0039]
Thus, even if the external AC power supply PS fluctuates, the power supplied to the heating coil 36 is controlled to be constant, so that the amount of heat generated in the heated object W can be stabilized.
[0040]
Next, the protection operation of the resonance capacitor 37 will be described. When the voltage of the external AC power supply PS changes, the maximum applied voltage of the resonance capacitor 37 also changes. For example, as shown in the graph of FIG. 6, when the rectified voltage of the rectifier circuit 10 increases, the maximum applied voltage of the resonance capacitor 37 increases almost linearly. The maximum applied voltage of the resonance capacitor 37 also changes when the material of the object to be heated W or the magnetic coupling with the heating coil 36 changes.
[0041]
Conventionally, the withstand voltage rating of the resonance capacitor 37 has been set to be relatively high so as to cope with these fluctuation factors, and this has been a factor of increasing the cost and increasing the size of the resonance capacitor 37.
[0042]
In the present embodiment, the applied voltage of the resonance capacitor 37 is monitored, and the duty ratio of the drive signals QA and QB is controlled so that the applied voltage does not exceed the withstand voltage rating. For example, as shown in the graph of FIG. 7, when the duty ratio of the drive signal QA increases, the maximum applied voltage of the resonance capacitor 37 has a relationship of monotonously increasing. Therefore, by controlling the duty ratio of the drive signals QA and QB, The voltage applied to the resonance capacitor 37 can be controlled.
[0043]
Referring to the timing chart shown in FIG. 5, when the voltage applied to the resonance capacitor 37 increases, the detection signal D from the capacitor voltage detection circuit 40 increases, and the output of the capacitor voltage detection unit 55 also increases. When the voltage exceeds the reference voltage value set by the voltage setting unit 54, the control signal SB from the comparison unit 56 increases, and the level of the control signal SC decreases. Then, the ON period T1 of the drive signal QA becomes shorter and the duty ratio decreases, and the ON period T2 of the drive signal QB becomes longer and the duty ratio increases. As a result, the power supplied to the heating coil 36 decreases. , The voltage applied to the resonance capacitor 37 decreases,
[0044]
When the applied voltage of the resonance capacitor 37 exceeds a predetermined reference value, the duty ratio of the drive signals QA and QB is controlled so that the applied voltage decreases. This can prevent the deterioration and destruction of the resonance capacitor 37 due to the above. As a result, the cost and size of the resonance capacitor 37 can be reduced by reducing the withstand voltage margin.
[0045]
For example, as shown in the graph of FIG. 8A, when the rectified voltage of the rectifier circuit 10 becomes higher than a certain value, the control circuit 50 operates to decrease the duty ratio of the drive signal QA. Then, as shown in the graph of FIG. 8B, even if the rectified voltage of the rectifier circuit 10 becomes higher than a certain value, the voltage applied to the resonance capacitor 37 does not exceed the set voltage, and the overvoltage of the resonance capacitor 37 is prevented. it can.
[0046]
Further, a plurality of reference voltage values may be set in the capacitor voltage setting unit 54, and the rate at which the duty ratio of the drive signal is changed according to the range between the reference voltage values may be changed. For example, as shown in the graphs of FIGS. 9A and 9B, when the applied voltage of the resonance capacitor 37 exceeds the first set voltage, the operation of limiting the duty ratio of the drive signal is started, and When the applied voltage exceeds the second set voltage higher than the first set voltage, the duty ratio of the drive signal is limited so that the applied voltage of the resonance capacitor 37 does not exceed the second set voltage. As a result, overvoltage of the resonance capacitor 37 can be prevented without reducing cooking power as much as possible.
[0047]
Embodiment 2 FIG.
FIG. 10 is a circuit block diagram showing a second embodiment of the present invention. In this embodiment, a load circuit including the heating coil 36 and the resonance capacitor 37 is disposed between the power supply line Lh and the output line Lo.
[0048]
The induction heating cooker includes a rectifier circuit 10, a smoothing circuit 20, an inverter circuit 30, a capacitor voltage detection circuit 40, a control circuit 50, an inverter drive circuit 60, and the like. The control circuit 50 and the inverter drive circuit 60 have the same configuration as described above, and a duplicate description will be omitted.
[0049]
The inverter circuit 30 includes a pair of switching elements 31 and 32 connected in series between the ground line Lg and the power supply line Lh, a load circuit including a series circuit including a heating coil 36 and a resonance capacitor 37, and the like.
[0050]
The switching elements 31 and 32 are composed of, for example, transistors and the like, and diodes 33 and 34 for reverse conduction are respectively connected in parallel to the emitter and the collector of each switching element 31 and 32. The drive signal QA from the inverter drive circuit 60 is supplied to the base of the switching element 31, and the drive signal QB from the inverter drive circuit 60 is supplied to the base of the switching element 32.
[0051]
The collector of the switching element 31 on the high potential side is connected to the power supply line Lh, and the emitter of the switching element 32 on the low potential side is connected to the ground line Lg. One end of a resonance capacitor 37 is connected to an output line Lo to which the collector of the switching element 31 and the collector of the switching element 32 are connected. The heating coil 36 is connected between the other end of the resonance capacitor 37 and the power supply line Lh. A capacitor 35 for removing noise is connected between the output line Lo and the power supply line Lh.
[0052]
The capacitor voltage detection circuit 40 has a function of detecting a voltage applied to the resonance capacitor 37 and outputting a detection signal D. Here, a voltage dividing circuit including resistors 41 and 42 is connected to both ends of the resonance capacitor 37. In addition, the voltage dividing ratio of the resistor is adjusted to match the input voltage range of the control circuit 50.
[0053]
In such a circuit configuration, when the on-period of the switching element 31 becomes longer and the on-period of the switching element 32 becomes shorter, the power supplied to the heating coil 36 increases, and the amount of heat generated in the object to be heated W increases. On the other hand, when the ON period of the switching element 31 is short and the ON period of the switching element 32 is long, the electric power supplied to the heating coil 36 is reduced, and the amount of heat generated in the heated object W is reduced. Therefore, by adjusting the level of the control signal SC, the amount of heat generated in the object to be heated W can be controlled.
[0054]
Further, since the applied voltage of the resonance capacitor 37 is monitored and the duty ratio of the drive signals QA and QB is controlled so that the applied voltage does not exceed the withstand voltage rating, the oscillation of the inverter circuit 30 does not stop, The deterioration and destruction of the resonance capacitor 37 due to the overvoltage can be prevented. As a result, the cost and size of the resonance capacitor 37 can be reduced by reducing the withstand voltage margin.
[0055]
In this embodiment, an example in which the resonance capacitor 37 is arranged on the output line Lo side and the heating coil 36 is arranged on the power supply line Lh side in a series circuit of the heating coil 36 and the resonance capacitor 37 will be described. The heating coil 36 may be arranged on the side, and the resonance capacitor 37 may be arranged on the power line Lh side. In this case, the capacitor voltage detection circuit 40 is arranged so that the voltage across the resonance capacitor 37 can be measured.
[0056]
Embodiment 3 FIG.
FIG. 11 is a circuit block diagram showing a third embodiment of the present invention. This embodiment has the same configuration as the first embodiment, except that a diode 38 connected in parallel to the resonance capacitor 37 is added, and the anode of the diode 38 is connected to the high potential side of the resonance capacitor 37. , The cathode of the diode 38 is connected to the low potential side of the resonance capacitor 37.
[0057]
The diode 38 can turn on the switching element 31 when the diode 33 connected in parallel with the switching element 31 conducts by clamping a half-wave of LC resonance with the heating coil 36 and the resonance capacitor 37. As a result, zero voltage switching can be realized, so that the switching loss of the switching element 31 can be reduced, the heat generation of the switching element 31 can be suppressed, and the switching noise can be reduced.
[0058]
In such a circuit configuration, since the applied voltage of the resonance capacitor 37 is monitored and the duty ratio of the drive signals QA and QB is controlled so that the applied voltage does not exceed the withstand voltage rating, the oscillation of the inverter circuit 30 is stopped. Thus, it is possible to prevent the deterioration and destruction of the resonance capacitor 37 due to the overvoltage. As a result, the cost and size of the resonance capacitor 37 can be reduced by reducing the withstand voltage margin. Therefore, in the present embodiment, not only the withstand voltage of the resonance capacitor 37 but also the withstand voltage of the diode 38 can be reduced.
[0059]
【The invention's effect】
As described in detail above, since the duty ratio of the drive signal is controlled so that the applied voltage of the resonance capacitor does not exceed the predetermined reference value, the oscillation of the resonance capacitor 37 due to the overvoltage can be performed without stopping the oscillation of the inverter circuit 30. Deterioration and destruction can be prevented. As a result, the cost and size of the resonance capacitor can be reduced by reducing the withstand voltage margin.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a first embodiment of the present invention.
FIG. 2 is a block diagram showing a circuit configuration of a control circuit 50.
FIG. 3 is a block diagram illustrating an example of a circuit configuration of the inverter drive circuit 60.
FIG. 4 is a timing chart showing an operation.
FIG. 5 is a timing chart showing an operation.
FIG. 6 is a graph showing a relationship between a rectified voltage and a maximum voltage of a resonance capacitor.
FIG. 7 is a graph showing a relationship between a duty ratio of a drive signal and a maximum voltage of a resonance capacitor.
8A is a graph showing a relationship between a rectified voltage according to the present invention and a duty ratio of a drive signal, and FIG. 8B is a graph showing a relationship between a rectified voltage according to the present invention, a maximum voltage of a resonance capacitor, and FIG. 6 is a graph showing the relationship of.
9A is a graph showing the relationship between the rectified voltage according to the present invention and the maximum voltage of the resonance capacitor, and FIG. 9B is a graph showing the relationship between the rectified voltage and the duty ratio of the drive signal according to the present invention. 6 is a graph showing the relationship of.
FIG. 10 is a circuit block diagram showing a second embodiment of the present invention.
FIG. 11 is a circuit block diagram showing a third embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 10 rectifier circuit, 20 smoothing circuit, 21 input capacitor, 22 choke coil, 23 output capacitor, 30 inverter circuit, 31, 32 switching element, 33, 34, 38 diode, 35 capacitor, 36 heating coil, 37 resonance capacitor, 40 capacitor Voltage detection circuit, 41, 42 resistance, 50 control circuit, 51 input setting section, 52 input detection section, 53 power control section, 54 capacitor voltage setting section, 55 capacitor voltage detection section, 56 comparison section, 60 inverter drive circuit, 61 Oscillator, 62-68 comparator.

Claims (3)

A rectifier circuit for rectifying AC power supplied from an external power source;
A smoothing circuit that converts the output of the rectifier circuit into DC power,
A pair of switching elements connected in series between output lines of the smoothing circuit, and an inverter circuit connected in parallel to any one of the switching elements and having a load circuit including a series circuit of a heating coil and a resonance capacitor;
Control means for outputting a control signal based on a preset power set value,
Inverter driving means for outputting a drive signal for alternately turning on or off each switching element of the inverter circuit according to the control signal;
Capacitor voltage detecting means for detecting the applied voltage of the resonance capacitor,
The induction heating cooker, wherein the control means changes a duty ratio of a drive signal of each switching element so that a detection signal from the capacitor voltage detection means becomes equal to or less than a preset reference voltage value. The inverter circuit has a diode connected in parallel to the resonance capacitor, the anode of the diode is connected to the high potential side of the resonance capacitor, and the cathode of the diode is connected to the low potential side of the resonance capacitor. The induction heating cooker according to claim 1, wherein An input setting unit for setting a power set value,
An input detection unit that detects power input from an external power supply,
A power control unit that outputs a first control signal based on a power set value set by the input setting unit and an output from the input detection unit;
A capacitor voltage setting unit for setting a reference voltage value,
A capacitor voltage detection unit that receives a detection signal from the capacitor voltage detection means,
A comparison unit that outputs a second control signal based on a reference voltage value set by the capacitor voltage setting unit and an output from the capacitor voltage detection unit,
3. The induction heating cooker according to claim 1, wherein the inverter driving unit changes a duty ratio of a drive signal of each switching element based on the first control signal and the second control signal. 4.

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