JP2003036962A - Cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actuate an inverter circuit at an operation point in which an electric stress and switching noises are low concerning power parts such as a switching element taking the lead, even in case there is the extreme value in a conduction time of the switching element versus characteristics of an input current of the inverter circuit. SOLUTION: Because the extreme value detection means 11 detects its extreme value based on the conduction time of the switching element versus characteristics of an input current of the inverter circuit and an input current control means 8 appropriately selects the operation point in the desired conduction time of the switching means 4a, the inverter circuit 4 can be actuated at useful operation points such as the operation point in which the electric stress of constituting power parts of the inverter circuit 4 becomes less or in which the switching noises become smaller, and a cost increase due to reinforcement of a cooling performance and EMC countermeasures, reduction in the reliability of an equipment, and reduction in using conveniences can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating cooker using an inverter used at home or for business.

[0002]

2. Description of the Related Art In recent years, a heating cooker that uses induction heating and dielectric heating and uses an inverter to make good use of its excellent heat responsiveness and controllability, has a temperature detecting element in the vicinity of a pot or food serving as a load. And a weight sensor, etc. are mounted to detect the temperature of the pan, food, etc. and the weight of the food, etc., and adjust the heating power and the cooking time accordingly to realize fine cooking and to prevent flames. Since it is not used and has high thermal efficiency, it does not pollute indoor air, is safe and clean, and its demand is rapidly increasing.

The operation of the conventional cooking device will be described below with reference to the drawings. FIG. 4 is a block diagram showing the configuration of the conventional example, and FIG. 5 is a characteristic diagram of the conduction time Ton of the switching means of this conventional example versus the input current Iin of the inverter circuit.

In FIG. 4, 21 is a commercial power source, 22 is a rectifying circuit, 23 is a smoothing circuit, and 24 is a switching means 24.
a and a load coil 24b, the inverter circuit for inductively heating the load pan 25 by applying a high frequency current to the load coil 24b, the control circuit 26 is the switching means 2
Input current control means 28 for outputting a signal for driving the switching means 24a to the drive means 27 to control the conduction time of 4a, input detection means 29 for detecting the input current to the inverter circuit 24, and operation of the inverter circuit 24. The operation unit 30 includes a switch for setting the state and the like.

The operation of the above configuration will be described. The inverter circuit 24 rectifies the commercial power supply 21 by the rectifier circuit 22 and converts the direct current smoothed by the smoothing circuit 23 into a high frequency alternating current, and supplies a high frequency current to the load coil 24b, so that the load pan 25 magnetically coupled to the load coil 24b. An eddy current is generated in and the Joule heat heats the load pan 25 by induction.
The input current control unit 28 changes the conduction time of the switching unit 24a of the inverter circuit 24 so that the value detected by the input detection unit 29 becomes the input current value corresponding to the desired thermal power set by the operation unit 28. Control the input current.

In this prior art example, the input current control means 28 is composed of a microcomputer, and if the input current value detected by the input detection means 29 is larger than the set input current value, the conduction time of the switching means 24a is increased. Decreased,
Conversely, if the input current value detected by the input detection means 29 is smaller than the set input current value, the switching means 24
The input current of the inverter circuit is kept substantially constant by increasing the conduction time of a and performing feedback control.

At this time, in the case of the load pan 24 having characteristics as shown in FIG. 5A, the input current Iin characteristic of the inverter circuit 24 with respect to the conduction time Ton of the switching means 24a is monotonically increasing, so that the operating section 30 is used. Therefore, even if the current input current setting is increased or decreased and then set to the input current before it is increased or decreased again, the conduction time T of the switching means 24a is substantially the same.
It can be operated on.

[0008]

However, in the conventional heating cooker as described above, when the load pan 25 having the characteristic B shown in FIG. 5 is operated, the switching means 24a conducts electricity. The input current Iin characteristic of the inverter circuit 24 with respect to the time Ton does not increase monotonically but has an extreme value, and the conduction time of the plurality of switching means 24a exists for one input current.
If the input current is set to 0 before and after the current input current setting is increased / decreased, the input current of the same inverter circuit 24 is operated with different conduction times of the switching means. Then, in general, characteristic A,
Regardless of the difference in B, the voltage across the switching means 24a has a characteristic of monotonically increasing with respect to the conduction time of the switching means 24a. Therefore, in the load pan 25 of characteristic B, with respect to the input current of the single inverter circuit 24. Switching means 24
There is an operating point where the electrical stress of a and other power components constituting the inverter circuit 24 becomes large, and the cost for strengthening the cooling performance of the equipment increases, the noise increases due to the increase of the cooling fan air volume, and the cost for EMC measures. However, there is a problem in that the usability is deteriorated because the heating is temporarily stopped due to the increase in the reliability of the equipment, the deterioration of the reliability of the equipment, and the protection of the power components from abnormally high temperatures.

The present invention is to solve the above-mentioned problems. Even when the conduction time of the switching means vs. the input current characteristic of the inverter circuit does not have a monotonic increase but has some extreme values, the switching means and the other means. By operating the inverter circuit by selecting an operating point where the electrical stress of the power components that make up the inverter circuit is reduced, or an operating point with low switching noise of the switching means, the heating is inexpensive and easy to use. The purpose is to provide a cooker.

[0010]

In order to solve the above-mentioned problems, the present invention is based on the fact that the extreme value detecting means determines the output of the input detecting means and the conduction time of the switching means output by the input current control means to determine the switching means. Since it is possible to detect the extreme value in the characteristic of the conduction time versus the input current of the inverter circuit, the characteristic of the conduction time of the switching means versus the input current of the inverter circuit does not have a monotonic increase but has an extreme value, that is, one input current. On the other hand, even when there is a conduction time of a plurality of switching means, an operating point where the electrical stress of the power components that constitute the inverter circuit, such as the switching means, is low among the extreme values detected by the extreme value detecting means. Or, even if the voltage burden of the switching means is somewhat large,
The input current control means can appropriately select the operating point such that the switching noise generated from the switching means is reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The object of the present invention can be achieved by adopting the configurations described in each claim as an embodiment, and therefore, the action will be described together with the features characterized in each claim. Then, the significance of the embodiment will be explained in an easy-to-understand manner.

According to the first aspect of the present invention, there is provided an inverter circuit which includes a load coil and a switching means, converts a direct current into a high frequency alternating current, and supplies a high frequency current to the load coil, and a control circuit for controlling the operation of the inverter circuit. The control circuit has a driving means for driving the switching means, an input detecting means for detecting an input current of the inverter circuit, an operating section for setting an input current of the inverter circuit, a conduction time of the switching means vs. the inverter circuit. An extreme value detecting means for detecting an extreme value of the characteristic of the input current, and a conduction time or a driving cycle of the switching means is changed according to the output of the input detecting means and the output of the extreme value detecting means to output to the driving means for operation. The input current of the inverter circuit is set so that the input current becomes the value set by the Control means for supplying a high-frequency current to the load coil by driving the switching means of the inverter circuit by the driving means based on the output of the input current control means. The induction coil heats the load such as the pan with the high-frequency magnetic flux generated from the load coil, or drives the magnetron with the high-frequency voltage generated from the load coil, and applies the microwave generated from the magnetron to the cooked food that is the load. It can be heated. The heating power to the load is changed by changing the conduction time or the drive cycle of the switching means so that the input current of the inverter circuit detected by the input detection means becomes equal to the input current set by the operation unit. It can be controlled by changing the amount.

From the output of the input detection means by the extreme value detection means and the conduction time of the switching means output from the input current control means, the extreme value in the characteristic of the conduction time of the switching means versus the input current of the inverter circuit is calculated. Since it can be detected, the characteristic of the conduction time of the switching means versus the input current of the inverter circuit does not increase monotonically but has an extreme value, that is, when the conduction time of a plurality of switching means exists for one input current. However, among the extreme values detected by the extreme value detecting means, even if the operating point where the electrical stress of the power components forming the inverter circuit such as the switching means is low, or the voltage burden of the switching means is a little large, the switching is performed. The input current control means selects an appropriate point such as an operating point at which switching noise generated from the means is reduced. An effect that it is possible to operate the converter circuit.

According to the second aspect of the invention, in addition to the configuration of the first aspect, when the input current set by the operating unit is not reached, the characteristics of the conduction time of the switching means versus the input current of the inverter circuit are It is configured to operate in the vicinity of the maximum value among the extreme values, and if the input current set by the operating unit is not reached even if the conduction time of the switching means is maximized, the extreme value detected by the extreme value detection means. The inverter circuit can be operated near the maximum value among the values, and the input current close to the set input current can be obtained.

According to a third aspect of the present invention, in addition to the configuration of the second aspect, when there are a plurality of maximum values of the characteristic of the conduction time of the switching means versus the input current of the inverter circuit, the larger maximum value is close to the maximum value. It is possible to operate the inverter circuit in the vicinity of the maximum value that is the largest among the extreme values detected by the extreme value detection means, and obtain the input current that is closest to the set input current. It has the effect of being able to.

According to a fourth aspect of the present invention, there is provided an inverter circuit which includes a load coil and a switching means, converts direct current into high frequency alternating current, and supplies a high frequency current to the load coil, and a control circuit for controlling the operation of the inverter circuit. The control circuit has a driving means for driving the switching means, an input detecting means for detecting the input current of the inverter circuit, an operating section for setting the input current of the inverter circuit, and the switching according to the output of the input detecting means. Input current control means for controlling the input current of the inverter circuit such that the input time of the inverter circuit is controlled so that the input current set by the operating portion is output by varying the conduction time or drive cycle of the means, and the input current of the inverter circuit in the operating portion. When the setting of is changed, the conduction time of the switching means is reduced to a predetermined value and then increased until the set input current is reached. Are those provided with the re-start means for, by the means, based on the output of the input current control means, the switching means of the inverter circuit is driven by the drive means, by supplying a high-frequency current to the load coil,
Induction heating of a load such as a pan by high-frequency magnetic flux generated from the load coil, or driving of a magnetron by the high-frequency voltage generated from the load coil, and microwaves generated from the magnetron are applied to the food to be loaded to perform dielectric heating. be able to. The heating power to the load is changed by changing the conduction time or the drive cycle of the switching means so that the input current of the inverter circuit detected by the input detection means becomes equal to the input current set by the operation unit. It can be controlled by changing the amount.

When there is an extreme value in the characteristic of the conduction time of the switching means versus the input current of the inverter circuit, the maximum value of all the extreme values is equal to or greater than the input current set by the operation section. When there are multiple operating points of the inverter circuit with respect to the input current set in step 1, when the input current setting is changed in the operating section, the restarting means causes the restart time to reach a predetermined conduction time, for example, the set input current value. In the following, the conduction time can be reduced to a conduction time shorter than the initial maximum value or less, and then increased until the input current reaches the set input current. If the detected input current value is large, the conduction time of the switching means is reduced. Conversely, if the input current value detected by the input detection means is smaller than the set input current value, the conduction of the switching means is decreased. Has an effect of the input current of the inverter circuit can be maintained substantially constant by using a feedback control that may be a microcomputer makes easy to say to increase between.

As a result, even with a load having such an extreme value, the voltage across the switching means monotonically increases with respect to the conduction time of the switching means, so that the conduction time is always small below the set input current. The operating point can be selected, and it becomes possible to operate the inverter circuit while reducing the electrical stress of the power components such as the switching means.

[0019]

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention, and FIG. 3 is a characteristic diagram of the conduction time Ton of the switching means of the first embodiment of the present invention versus the input current Iin of the inverter circuit and the switching means. Conduction time To
It is a characteristic view of the voltage Vce across the n-pair switching means.

In FIG. 1, 1 is a commercial power source, 2 is a rectifier circuit, 3 is a smoothing circuit, 4 is a switching means 4a and a load coil 4b, and a load pan 5 is induced by applying a high frequency current to the load coil 4b. Inverter circuit to heat,
The control circuit 6 includes an input current control unit 8 that outputs a signal for driving the switching unit 4a to the driving unit 7 to control the conduction time of the switching unit 4a, and an input detection unit 9 that detects the input current to the inverter circuit 4. And the operating section 10 composed of a switch for setting the operating state of the inverter circuit 4, the switching time based on the conduction time output of the switching means 4a output by the input current control means 8 and the output of the input detection means 9. The characteristic of the conduction time Ton of the means 4a versus the input current Iin of the inverter circuit 4 (hereinafter referred to as Ton versus I
The extremal value detecting means 11 for detecting the extremal value from the (in characteristic) and the switching means 4a when the input current setting of the inverter circuit 4 set by the operation unit 10 is changed.
It has restarting means 12 for outputting to the input current control means 8 a signal for increasing the set input current value again as a target after reducing the conduction time to a predetermined value.

The operation of the above configuration will be described. When the user operates a switch or the like of the operation unit 10, the operation unit 10 outputs a signal to the input current control unit 8 to start the operation of the inverter circuit 4 or to set the thermal power (setting of the input current of the inverter circuit 4). In response to this, the input current control means 8 starts the heating operation, or if the heating operation is in progress, causes the driving means 7 to drive the switching means 4a to stop the heating or change the setting of the heating power.

The inverter circuit 4 is turned on / off by the switching means 4a based on the drive signal from the drive means 7,
The commercial power supply 1 is rectified by the rectifier circuit 2 and the direct current smoothed by the smoothing circuit 3 is converted into a high frequency alternating current, and a high frequency current is passed through the load coil 4b to generate an eddy current in the load pan 5 magnetically coupled to the load coil 4b. Generate it and load it with Joule heat 5
Is induction heated.

Next, the input current control means 8 conducts the conduction time of the switching means 4a (hereinafter referred to as Ton) until the input current detected by the input detection means 9 reaches a desired input current corresponding to the thermal power set by the operating section 10. The heating thermal power of the load pan 5 is controlled by changing the high frequency current supplied to the load coil 4b.

At this time, the extreme value detecting means 11 receives the conduction time output of the switching means 4a output by the input current control means 8 and the output of the input detecting means 9 to obtain Ton.
Observing the Iin characteristic. Specifically, when the operation of the inverter circuit 4 is started, the load pan, which is the current heating target, is temporarily increased by increasing the minimum value of Ton to the maximum value or the maximum value at which the inverter circuit 4 operates stably. Read the Ton-to-Iin characteristic of 5. Then, if there is an extreme value in this Ton-to-Iin characteristic, it outputs to the input current control means 8 what Ton and how much Iin is the extreme value.

As a result, Ii set by the operation unit 10 is set.
The input current control means 8 can determine whether or not there are a plurality of operating points for the n value. In this embodiment,
When there are a plurality of operating points, and in the Ton-to-Iin characteristic of FIG. 3, when the Iin value set by the operation unit 10 is Iin1, the conduction time Ton of the switching means of FIG.
As shown in the characteristic of the voltage Vce across the switching means 4a, the voltage Vce across the switching means 4a monotonically increases with the increase in Ton.
In order to increase the air volume of the cooling fan by strengthening the cooling performance more than necessary by allowing the input current control means 8 to operate the inverter circuit 4 by selecting the operating point a in which the voltage burden on a is low and the conduction loss and the switching loss are low. Increase in wind noise, the cooling fins attached to the switching means 4a are increased in size, or the inverter circuit 4 is stopped or the input current is reduced to protect the power parts such as the switching means 4a from abnormal high temperatures due to insufficient cooling capacity. It is possible to avoid a decrease in cooking performance due to the above.

Further, even if the voltage load on the switching means 4a is somewhat large, the operating point at which the switching noise generated from the switching means 4a is reduced is c, not a, and if it is advantageous to EMC, the operating point c is selected. It is possible to suppress the increase in cost such as addition of parts due to EMC measures by selecting.

Further, in the Ton-to-Iin characteristic of FIG. 3, when the Iin value set by the operation unit 10 is Iin2, even if Ton is increased to the maximum value, it does not reach Iin2. The maximum value is selected from the extreme values detected by the value detection means 11, and further, the operating point e which is the maximum value is selected, and the inverter circuit 4 is operated with the maximum thermal power in the load pan 5 having this characteristic. It is possible to prevent the cooking performance from deteriorating as much as possible.

In this embodiment, the input current is controlled by increasing / decreasing only the conduction time of the switching means. However, when the conduction time of the switching means and the driving cycle are combined and increased / decreased. However, it goes without saying that the same effect can be obtained if the Ton-to-Iin characteristic has an extreme value. The above effects can be applied not only to the induction heating cooker but also to a heating cooker having an inverter such as a microwave oven.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing the configuration of the embodiment of the present invention, and FIG. 3 is the conduction time Ton of the switching means of the embodiment of the present invention versus the input current I of the inverter circuit.
FIG. 5 is a characteristic diagram of in and a characteristic diagram of a conduction time Ton of the switching unit versus a voltage Vce across the switching unit.

In FIG. 2, 1 is a commercial power supply, 2 is a rectifier circuit, 3 is a smoothing circuit, 4 is a switching means 4a and a load coil 4b, and a load pan 5 is induced by applying a high frequency current to the load coil 4b. Inverter circuit to heat,
The control circuit 6 includes an input current control unit 8 that outputs a signal for driving the switching unit 4a to the driving unit 7 to control the conduction time of the switching unit 4a, and an input detection unit 9 that detects the input current to the inverter circuit 4. And an operating section 10 composed of a switch or the like for setting the operating state of the inverter circuit 4, and when the input current setting of the inverter circuit 4 set by the operating section 10 is changed, the conduction time of the switching means 4a is predetermined. It has a restarting means 12 for outputting to the input current control means 8 a signal for increasing again with the set input current value as a target after decreasing to the value of.

The operation of the above configuration will be described. When the user operates a switch or the like of the operation unit 10, the operation unit 10 outputs a signal to the input current control unit 8 to start the operation of the inverter circuit 4 or to set the thermal power (setting of the input current of the inverter circuit 4). In response to this, the input current control means 8 starts the heating operation, or if the heating operation is in progress, causes the driving means 7 to drive the switching means 4a to stop the heating or change the setting of the heating power.

The inverter circuit 4 is turned on / off by the switching means 4a based on the drive signal of the drive means 7,
The commercial power supply 1 is rectified by the rectifier circuit 2 and the direct current smoothed by the smoothing circuit 3 is converted into a high frequency alternating current, and a high frequency current is passed through the load coil 4b to generate an eddy current in the load pan 5 magnetically coupled to the load coil 4b. Generate it and load it with Joule heat 5
Is induction heated.

Next, the input current control means 8 causes the input current detected by the input detection means 9 to reach a desired input current corresponding to the thermal power set by the operating section 10 until the switching means 4a conducts (hereinafter referred to as Ton). The heating thermal power of the load pan 5 is controlled by changing the high frequency current supplied to the load coil 4b.

When the input current set by the operation unit 10 is Iin3 in FIG. 3 and the inverter circuit 4 is operating at the operating point f at the operating point f, the restarting means 12 changes the input current setting to Iin1. Reference numeral 12 outputs to the input current control means 8 a signal for once reducing Ton to a conduction time shorter than the operating point a. After that, the input current control means 8 increases the conduction time again to the first operating point a at which Iin1 is reached.

Without the restart means 12, when the input current set by the operation unit 10 is Iin3 in FIG. 3 and the inverter circuit 4 is operating at the operating point f, the input current setting is Ii.
If it is changed to n1, Ii at the operating point c before reaching the operating point a.
Since it is n1, it cannot be operated at the operating point a.

By the operation of the restart means 12,
When there are a plurality of operating points, the switching means 4 of FIG.
The conduction time Ton of a versus the input current Ii of the inverter circuit 4
In the characteristic of n (hereinafter referred to as Ton vs. Iin characteristic),
When the Iin value set by the operation unit 10 is Iin1, as shown in the characteristic of the conduction time Ton of the switching means versus the voltage Vce across the switching means 4a in FIG.
With the increase of n, the voltage Vc across the switching means 4a
Since e is a monotonic increase, the input current control means 8 selects the operating point a where the voltage burden on the switching means 4a is low and the conduction loss and the switching loss are low, and the inverter circuit 4
Is operated to increase the wind noise by increasing the cooling fan air volume by increasing the cooling performance more than necessary, the cooling fins attached to the switching means 4a are increased in size, or the switching means 4 is caused by insufficient cooling capacity.
It is possible to avoid deterioration of cooking performance and usability due to stop of the inverter circuit 4 for protection against abnormally high temperature of power components such as a and reduction of input current or temporary stop.

If the input current value detected by the input detecting means 9 is larger than the set input current value by the operation of the restarting means 12, the conduction time of the switching means 4a is reduced and the reverse setting is made. If the input current value detected by the input detection means 9 is smaller than the input current value, the input current of the inverter circuit is changed by the feedback control that can be easily performed by the microcomputer that the conduction time of the switching means 4a is increased. It can be kept almost constant.

In this embodiment, it is explained that only the conduction time of the switching means is increased or decreased to control the input current. However, when the conduction time of the switching means and the driving cycle are combined to increase or decrease. However, it goes without saying that the same effect can be obtained if the Ton-to-Iin characteristic has an extreme value. The above effects can be applied not only to the induction heating cooker but also to a heating cooker having an inverter such as a microwave oven.

[0039]

As is apparent from the above description, according to the invention described in claim 1, the conduction time of the switching means vs. the input current characteristic of the inverter circuit does not increase monotonically, but there is an extreme value, and the operating portion is present. Even when the conduction time of the switching means is not fixed at one point for the input current set in step 1 and there are a plurality of operating points, the operating point at which the electrical stress of the constituent power components of the inverter circuit such as the switching means becomes small, It is possible to select a useful operating point such as an operating point where the switching noise of the switching means is small,
It is possible to suppress an increase in cooling performance, an increase in cost due to EMC measures, a decrease in device reliability, and a decrease in usability.

According to the second aspect of the present invention, the operating point near the maximum value is selected from the extreme values in the conduction time of the switching means vs. the input current characteristic of the inverter circuit, and a high thermal power is generated with a load having this characteristic. It is possible to operate the inverter circuit in a state in which the above can be obtained, and it is possible to suppress deterioration of cooking performance.

According to the third aspect of the present invention, the maximum value is selected from the extreme values in the conduction time of the switching means vs. the input current characteristic of the inverter circuit, and the operating point in the vicinity of the maximum value is selected. Then, the inverter circuit can be operated with the maximum thermal power under the load having this characteristic, and the deterioration of cooking performance can be suppressed.

According to the fourth aspect of the present invention, the input current of the inverter circuit can be kept substantially constant by using the feedback control which can be easily performed by the microcomputer, and the input current at the set input current value can be constantly maintained. By minimizing the conduction time of the switching means, it is possible to operate the inverter circuit at an operating point where the electrical stress of the power components that make up the inverter circuit including the switching means is reduced, and the cost increase due to the enhanced cooling performance, It is possible to suppress a decrease in reliability of the device and a decrease in usability.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a heating cooker according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a heating cooker according to a second embodiment of the present invention.

FIG. 3 is a characteristic diagram of the conduction time Ton of the switching means of the cooking device of the first and second embodiments of the present invention versus the input current Iin of the inverter circuit, and the conduction time Ton of the switching means versus the voltage Vce across the switching means. Characteristic diagram of

FIG. 4 is a block diagram showing a configuration of a conventional cooking device.

FIG. 5 is a characteristic diagram of the conduction time Ton of the switching means of the heating cooker of the conventional example versus the input current Iin of the inverter circuit.

[Explanation of symbols]

4 Inverter circuit 4a switching means 4b load coil 6 control circuit 7 Drive means 8 Input current control means 9 Input detection means 10 Operation part 11 Extreme value detection means 12 Restart means

Claims (4)

[Claims] 1. An inverter circuit including a load coil and a switching means for converting a direct current into a high frequency alternating current to supply a high frequency current to the load coil, and a control circuit for controlling the operation of the inverter circuit. The circuit includes a driving means for driving the switching means, an input detecting means for detecting an input current of the inverter circuit, an operation section for setting an input current of the inverter circuit, a conduction time of the switching means vs. the inverter circuit. Extreme value detecting means for detecting the extreme value of the characteristic of the input current, and the conduction time or the driving cycle of the switching means is changed according to the output of the input detecting means and the output of the extreme value detecting means and output to the driving means. Then, the input current is set by the operation unit and becomes equal to or less than the extreme value selected from the extreme values detected by the extreme value detecting means. A heating cooker comprising: an input current control means for controlling an input current of the inverter circuit. 2. When the input current set by the operating section is not reached, the operation is performed in the vicinity of the maximum value of the conduction time of the switching means and the extreme value of the characteristic of the input current of the inverter circuit. Cooking device. 3. The heating cooker according to claim 2, wherein when there are a plurality of maximum values of the characteristic of the conduction time of the switching means versus the input current of the inverter circuit, the cooking device is operated near the larger maximum value. 4. An inverter circuit, which includes a load coil and a switching means, converts a direct current into a high frequency alternating current and supplies a high frequency current to the load coil, and a control circuit for controlling the operation of the inverter circuit. The circuit includes a driving unit that drives the switching unit, an input detecting unit that detects an input current of the inverter circuit, an operation unit that sets an input current of the inverter circuit, and the switching unit according to an output of the input detecting unit. Input current control means for controlling the input current of the inverter circuit such that the conduction time of the means or the drive cycle is varied and output to the drive means to obtain the input current set by the operation part; When changing the setting of the input current of the inverter circuit, set it after reducing the conduction time of the switching means to a specified value. A cooker comprising restarting means for increasing until a defined input current is reached.