JPH10149876A - Induction-heated cooking device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient control method in an induction-heated cooking device an inverter having a constant-frequency operation, smaller and more inexpensive than the conventional one. SOLUTION: An inadequate pot detecting circuit 12 judges the adequacy or inadequacy of a load based on the output of an iin detecting circuit 10 detecting the input current of an inverter circuit 2 and the output of a vcel detecting circuit detecting the voltage between the collector and emitter of an IGBT5. In case of an inadequate pot, a drive control circuit 3 stops the drive of the IGBT5 and an IGBT7 and stops the operation of the inverter circuit 2, and prevents the heating of an inadequate load such as a small load.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker having an inverter operating at a constant frequency.

[0002]

2. Description of the Related Art Conventionally, this type of induction heating cooker has a configuration disclosed in Japanese Patent Application Laid-Open No. Hei 5-21150. The induction heating cooker is described below with reference to FIGS.
1 will be described.

FIG. 19 is a circuit diagram of a conventional induction heating cooker. In FIG.
Is an inverter circuit for converting DC into high-frequency AC, and 10
A control circuit 3 controls the inverter circuit 102.
The inverter circuit 102 includes a first switching element 104 of a reverse current blocking type, a second switching element 105 of a reverse current conduction type, a heating coil 106, and a first resonance capacitor 10.
7, the second resonance capacitor 108 and the diode 109. The control circuit 103 includes a drive unit 110 and the like that alternately conduct the first switching element 104 and the second switching element 105 at a constant frequency f0.

FIG. 20 shows operation waveforms of respective parts for explaining the operation of the inverter circuit 102 of the conventional induction heating cooker configured as described above.

FIG. 21 shows the input power pin with respect to the conduction ratio D1 (= ton1 / t0) of the conventional induction heating cooker.
It is the characteristic of.

As is clear from FIG. 21, in the conventional induction heating cooker, the operating frequency (f0) of the inverter circuit 102
Under constant conditions, the input power (Pin) is changed by changing the conduction ratio D1 (= ton1 / t0), which is the ratio of the ON time (ton1) of the first switching element 104 to the fixed period (t0), and 20, the first switching element 104 and the second switching element 105 were able to realize the zero volt switching operation.

[0007]

Such a conventional induction heating cooker is provided with an inverter circuit capable of varying input power under a constant operating frequency. Can solve the problem of pot interference noise caused by the above, and since the two switching elements can realize the zero volt switching operation, the circuit was excellent in that the circuit was reduced in cost and size by reducing loss and noise. In order to spread multi-port induction heating cookers, it is necessary to establish a new low-cost and compact inverter and its control system.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide an induction heating cooker using a low-cost and small-sized inverter system operating at a constant frequency.

[0009]

In order to solve the above-mentioned problems, the present invention provides a DC power supply, a heating coil connected to one end of the DC power supply, the other end of the heating coil and the other end of the DC power supply. A first switching element connected to the first resonance capacitor forming a resonance circuit with the heating coil,
An inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor; an improper load detection unit for detecting an improper load; and the inverter circuit. A drive control circuit for alternately controlling the conduction of both switching elements at a constant frequency, the inappropriate load detection means detects an inappropriate load, and the drive control circuit detects that the inappropriate load detection means Is detected, the operation of the inverter circuit is stopped.

[0010]

The invention according to claim 1 is a DC power supply, a heating coil connected to one end of the DC power supply, and a heating coil connected to the other end of the heating coil and the other end of the DC power supply. A switching element, a first resonance capacitor forming a resonance circuit with the heating coil, and a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor. An inverter circuit, an improper load detecting means for detecting an improper load, and a drive control circuit for alternately controlling conduction of both switching elements of the inverter circuit at a constant frequency, wherein the improper load detecting means comprises an improper load. To detect
The drive control circuit conducts the two switching elements alternately at a constant frequency, and temporarily stops the operation of the inverter circuit when the inappropriate load detecting means detects an inappropriate load.

According to a second aspect of the present invention, there is provided a heating coil connected to one end of a DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply,
A first resonance capacitor forming a resonance circuit with the heating coil; an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor; An improper load detecting means for detecting an appropriate load, an operating state detecting means for detecting an operating state of the inverter circuit, and a drive control circuit for alternately controlling conduction of both switching elements of the inverter circuit at a constant frequency, The improper load detecting means detects an improper load from an output of the operation state detecting means, and the drive control circuit alternately conducts the two switching elements at a constant frequency, and the improper load detecting means detects an improper load. When a load is detected, the operation of the inverter circuit is temporarily stopped.

According to a third aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, Input current detecting means for detecting an input current of the inverter circuit, first switching element voltage detecting means for detecting a voltage of the first switching element, improper load detecting means, and both switching elements of the inverter circuit being fixed. A drive control circuit for alternately controlling conduction at a frequency, wherein the inappropriate load detection means is detected by the input current detection means The drive control circuit detects the inappropriate load from the value of the input current of the inverter circuit and the value of the voltage of the first switching element detected by the first switching element voltage detection means, When the improper load detecting means detects an improper load by conducting alternately at a constant frequency, the operation of the inverter circuit is temporarily stopped.

According to a fourth aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, Input current detecting means for detecting the input current of the inverter circuit, second switching element voltage detecting means for detecting the voltage of the second switching element, improper load detecting means, and both switching elements of the inverter circuit being fixed. A drive control circuit for alternately controlling conduction at a frequency, wherein the inappropriate load detection means is detected by the input current detection means The drive control circuit detects an inappropriate load from the value of the input current of the inverter circuit and the value of the voltage of the second switching element detected by the second switching element voltage detection means, When the improper load detecting means detects an improper load by conducting alternately at a constant frequency, the operation of the inverter circuit is temporarily stopped.

According to a fifth aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, Starting and stopping means for starting and stopping the inverter circuit, starting delay means for delaying the starting of the inverter circuit, and a drive control circuit for alternately controlling conduction of both switching elements of the inverter circuit at a constant frequency; The means is for starting / initiating the inverter circuit.
Controlling the stop, the start delay circuit outputs after a lapse of a predetermined time after the start / stop means outputs the start, and the drive control circuit sets the switching elements to a constant frequency after the output of the start delay circuit. Are conducted alternately to control the conduction ratio.

According to a sixth aspect of the present invention, there is provided a commercial power supply, a rectifier for rectifying the commercial power, a smoothing capacitor connected to the rectifier, a heating coil connected to one end of the smoothing capacitor, and the heating coil. And a first switching element connected to the other end of the smoothing capacitor,
A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, A commercial power supply monitoring means for monitoring commercial power supply, and a drive control circuit for alternately controlling conduction of both switching elements of the inverter circuit at a constant frequency, the commercial power supply monitoring means detects a power state of the commercial power supply, The drive control circuit conducts the two switching elements alternately at a constant frequency, and temporarily stops the operation of the inverter circuit when the commercial power supply monitoring unit detects an abnormality of the commercial power supply.

According to a seventh aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, An input setting means for setting input power of the inverter circuit, a soft start circuit, and a drive control circuit for alternately controlling conduction of both switching elements of the inverter circuit at a constant frequency, wherein the input setting means comprises The soft start circuit gradually sets a predetermined minimum input power when starting the inverter circuit. Increasing the input power, the drive control circuit, the two switching elements conduct alternately at a constant frequency, and controls the conduction ratio.

The invention according to claim 8 is a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, Input setting means for setting the input power of the inverter circuit, a reference voltage setting circuit, an oscillation circuit, comparison means for comparing the output of the reference voltage setting circuit with the output of the oscillation circuit, and both switching of the inverter circuit A drive control circuit for alternately controlling conduction of the element at a constant frequency, wherein the input setting means sets input power of the inverter circuit; The reference voltage setting circuit gradually changes the reference voltage from an initial value of the reference voltage to a reference voltage set based on the output of the input setting means, the oscillation circuit generates a triangular wave, and the comparing means Comparing the output of a reference voltage setting circuit with the output of the oscillation circuit, wherein the drive control circuit alternately conducts the two switching elements at a constant frequency, and controls the conduction ratio based on the output of the comparison means. It is.

According to a ninth aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, A drive control circuit for alternately controlling conduction of both switching elements of the inverter circuit at a constant frequency, and a dead time setting means, wherein the drive control circuit alternately conducts the switching elements at a constant frequency, and the dead time The setting means sets both of the two switching elements during the conduction period of the two switching elements to be alternately conductive. Conduction become period (hereinafter, referred to as dead time.) Is intended to provide.

According to a tenth aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, A drive control circuit that alternately controls conduction of both switching elements of the inverter circuit at a constant frequency,
An operation state detection unit for detecting an operation state of the inverter circuit; and a dead time setting unit, wherein the drive control circuit alternately conducts the switching elements at a constant frequency, and the operation state detection unit includes the inverter The operation time of the circuit is detected, and the dead time setting means provides a dead time between the conduction periods of the two switching elements which are turned on alternately based on the output of the operation state detection means.

According to an eleventh aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, A drive control circuit that alternately controls conduction of both switching elements of the inverter circuit at a constant frequency,
The drive control circuit includes a dead time setting unit, wherein the drive control circuit alternately conducts the switching elements at a constant frequency, and the dead time setting unit determines that the switching time is constant during a conduction period of the switching elements that alternately conduct. The dead time is provided.

According to a twelfth aspect of the present invention, there is provided a DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply. A first resonance capacitor forming a resonance circuit with the heating coil, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, A drive control circuit that alternately controls conduction of both switching elements of the inverter circuit at a constant frequency,
The drive control circuit alternately conducts the two switching elements at a constant frequency; and the dead time setting means performs a conduction period of the first switching element and a conduction period of the second switching element. A dead time of a first predetermined value is provided between the first predetermined value and a dead time of a second predetermined value is provided between a conduction period of the second switching element and a conduction period of the first switching element. And setting the second predetermined value to a different value.

[0022]

【Example】

(Embodiment 1) FIG. 1 shows a circuit configuration diagram of an induction heating cooker according to a first embodiment. In FIG. 1, reference numeral 1 denotes a DC power supply, and 2 denotes an inverter circuit connected to the DC power supply 1. .

The inverter circuit 2 is connected to the heating coil 4 having one end connected to the plus side which is one end of the DC power supply 1, and to the other end of the heating coil 4 and the minus side being the other end of the DC power supply 1. An IGBT 5 with a built-in reverse conducting diode as a first switching element, a first resonance capacitor 6 connected in parallel with the IGBT 5 so as to form a resonance circuit with the heating coil 4, and a second switching element connected in parallel with the heating coil 4 And a series circuit of an IGBT 7 with a built-in reverse conducting diode and a second resonance capacitor 8.

The plus side of the DC power supply 1 and the inverter circuit 2
Is connected to the current sensor 9, and the output of the current sensor 9 is connected to the iin detection circuit 10. The current sensor 9 and the iin detection circuit 10 constitute an input current detection unit of the inverter circuit 2. Also,
The vce1 detection circuit 11, which is the first switching element voltage detection means, is connected to the collector terminal of the IGBT5.
The current sensor 9, the iin detecting circuit 10, and the vce1 detecting circuit 11 constitute an operation state detecting means of the inverter circuit 2. iin detection circuit 10 and vce1 detection circuit 1
1 are connected to an improper pan detecting circuit 12 which is an improper load detecting means, and an output of the improper pan detecting circuit 12 is connected to a drive control circuit 3, and the drive control circuit 3 is connected to the IGBT 5
And the gate terminal of the IGBT7.

The operation of the induction heating cooker configured as described above will be described. When the induction heating cooker operates, the input current detecting means constituted by the current sensor 9 and the iin detecting circuit 10 outputs the input current i of the inverter circuit 2.
and the iin detection circuit 10 detects the input current iin
Output according to the size of. vce1 detection circuit 11
Detects the collector-emitter voltage vce1 of the IGBT 5 and outputs an output according to the magnitude of vce1. The improper pan detection circuit 12 detects the input current iin of the inverter circuit 2 detected by the current sensor 9 and the iin detection circuit 10.
The load control circuit 3 determines whether the load is appropriate or not based on the collector-emitter voltage vce1 of the IGBT 5 detected by the vce1 detection circuit 11, and the drive control circuit 3
2 outputs a signal indicating that the appropriate pan has been determined, the IGBT 5 and the I
When the GBT 7 is alternately driven at a constant frequency to operate the inverter circuit 2 and the inappropriate pan detection circuit 12 outputs an output indicating that the improper pan has been determined, the driving of the IGBT 5 and the IGBT 7 is stopped and the operation of the inverter circuit 2 is stopped. Stop.

FIG. 2 shows the input current iin of the inverter circuit 2 and the collector-emitter voltage v of the IGBT 5 when the load to be inductively heated is a standard pot, a pot and a knife.
This is a characteristic of ce1. As shown in the characteristics of FIG. 2, the smaller the bottom area of the load, the larger the vce1 value at the same iin value. When the iin-vce1 characteristic of the load is in the region above the bold line in FIG. 2, the improper pan detection circuit 12 outputs an improper pan detection output. In the case of, it will not be heated.

As described above, the drive control circuit 3 alternately conducts the IGBT 5 and the IGBT 7 under the constant operating frequency f0 (= 1 / t0) and can change the conduction ratio D1 (= ton1 / t0). The input power pin can be variably controlled while the circuit 2 is operated at a constant frequency. The improper pot detection circuit 12 detects the input current iin of the inverter circuit 2 detected by the current sensor 9 and the iin detection circuit 10 and the collector / emitter of the IGBT 5 detected by the vce1 detection circuit 11 at each load. Voltage vce1
The drive control circuit 3 can detect an improper load such as a knife from the difference between the characteristics of the IGBT 5 and the IGBT 5 when the improper load occurs.
In addition, since the driving of the IGBT 7 is stopped and the operation of the inverter circuit 2 is stopped to stop the heating operation, it is possible to prevent heating of an improper load such as a small load.

(Embodiment 2) FIG. 3 is a circuit diagram of an induction heating cooker according to a second embodiment. In FIG. 3, reference numeral 1 denotes a DC power supply, and 2 denotes an inverter connected to the DC power supply 1. Circuit.

The inverter circuit 2 is connected to the heating coil 4 having one end connected to the positive side, which is one end of the DC power supply 1, and to the other end of the heating coil 4 and the negative side, which is the other end of the DC power supply 1. An IGBT 5 with a built-in reverse conducting diode as a first switching element, a first resonance capacitor 6 connected in parallel with the IGBT 5 so as to form a resonance circuit with the heating coil 4, and a second switching element connected in parallel with the heating coil 4 And a series circuit of an IGBT 7 with a built-in reverse conducting diode and a second resonance capacitor 8.

The plus side of the DC power supply 1 and the inverter circuit 2
Is connected to the current sensor 9, and the output of the current sensor 9 is connected to the iin detection circuit 10. The current sensor 9 and the iin detection circuit 10 constitute an input current detection unit of the inverter circuit 2.

Further, the collector terminal of the IGBT 7 is connected to a vce2 detecting circuit 13 which is a second switching element voltage detecting means. The current sensor 9, the iin detection circuit 10, and the vce2 detection circuit 13 constitute an operation state detection means of the inverter circuit 2. The outputs of the iin detection circuit 10 and the vce2 detection circuit 13 are both connected to an improper pan detection circuit 14 which is an improper load detection means, and the output of the improper pan detection circuit 14 is connected to the drive control circuit 3 and the drive control circuit Reference numeral 3 is connected to the gate terminal of the IGBT 5 and the gate terminal of the IGBT 7, respectively.

The operation of the induction heating cooker configured as described above will be described. When the induction heating cooker operates, the input current detecting means constituted by the current sensor 9 and the iin detecting circuit 10 outputs the input current i of the inverter circuit 2.
and the iin detection circuit 10 detects the input current iin
Output according to the size of. vce2 detection circuit 13
Detects the collector-emitter voltage vce2 of the IGBT 7 and outputs an output according to the magnitude of vce2. The improper pan detection circuit 14 detects the input current iin of the inverter circuit 2 detected by the current sensor 9 and the iin detection circuit 10.
And whether the load is appropriate or not based on the collector-emitter voltage vce2 of the IGBT 7 detected by the vce2 detection circuit 13, and the drive control circuit 3
4 outputs the determination of the inappropriate pot, the IGBT 5 and the IG
The driving of the BT 7 is stopped, and the operation of the inverter circuit 2 is stopped.

FIG. 4 shows the input current iin of the inverter circuit 2 and the collector-emitter voltage v of the IGBT 7 when the load to be induction-heated is a standard pot, a pot and a knife.
This is the characteristic of ce2. As shown in the characteristic of FIG. 4, the smaller the bottom area of the load, the larger the vce2 value at the same iin value. When the iin-vce2 characteristic of the load is in the region above the bold line in FIG. 4, the improper pan detection circuit 14 outputs a detection of an improper pan. In the case of, it will not be heated.

As described above, the proper pot detecting circuit 14 detects the input current iin of the inverter circuit 2 detected by the iin detecting circuit 10 and the collector-emitter voltage vce2 of the IGBT 7 detected by the vce2 detecting circuit 13 at each load. The drive control circuit 3 can detect an improper load such as a knife from the difference in the characteristics of the IGBT 5 and the IGBT 5 when the improper load is applied.
Since the driving of the BT 7 is stopped and the operation of the inverter circuit 2 is stopped to stop the heating operation, heating of an improper load such as a small load can be prevented.

(Embodiment 3) FIG. 5 is a circuit diagram of an induction heating cooker according to a third embodiment. In FIG. 5, reference numeral 15 denotes a commercial power supply, and 16 denotes a rectifier connected to the commercial power supply 15. One end of a choke coil 17 is connected to the positive output of the diode bridge 16,
The other end of the choke coil 17 is connected to one end of a smoothing capacitor 18, the other end of the smoothing capacitor 18 is connected to the negative output of the diode bridge 16, and the smoothing capacitor 18 serves as a DC power supply supplied to the inverter circuit 2. have. The choke coil 17 has a role of a filter.

The inverter circuit 2 includes a smoothing capacitor 18
A heating coil 4 having one end connected to the plus side of the heating coil 4, an IGBT 5 with a built-in reverse conducting diode as a first switching element connected to the other end of the heating coil 4 and a minus side of the smoothing capacitor 18, and resonance with the heating coil 4 First resonant capacitor 6 connected in parallel with IGBT 5 to form a circuit
And a series circuit of an IGBT 7 with a built-in reverse conducting diode, which is a second switching element connected in parallel with the heating coil 4, and a second resonance capacitor 8.

The positive output of the diode bridge 16 is connected to a v + detection circuit 19 which is a commercial power supply monitoring means. The output of the v + detection circuit 19 is connected to a start / stop circuit 20 which is a start / stop means. Is connected to a start delay circuit 21 as start delay means, an output of the start delay circuit 21 is connected to a drive control circuit 22, and an output of the drive control circuit 22 is connected to respective gate terminals of the IGBT5 and the IGBT7. .

The operation of the induction cooking device configured as described above will be described. First, when the induction heating cooker starts operating with the commercial power supply 15 in a normal state, the v + detection circuit 19 detects that the commercial power supply 15 is in a normal state and outputs the detected result. The start / stop circuit 20 receives a detection output of a normal state of the commercial power supply 15 from the v + detection circuit 19,
A start signal is output to start the operation of the inverter circuit 2. Upon receiving the start signal from the start / stop circuit 20, the start delay circuit 21 outputs the start signal after a lapse of a predetermined time of 2 seconds. The drive control circuit 22 receives the start-up signal from the start-up delay circuit 21 and then drives the IGBT 5 and the IGBT.
7 and the operation of the inverter circuit 2 is started.

Next, the operation when the commercial power supply 15 becomes abnormal will be described. For example, when a lightning surge voltage is applied to the commercial power supply 15, the diode bridge 16
The voltage of the plus side output rises above the steady state value due to the energy of the lightning surge. v + detection circuit 19
Detects that the commercial power supply 15 has abnormally risen and becomes large, and outputs the detected result. The start / stop circuit 20 receives a detection output of an abnormal state of the commercial power supply 15 from the v + detection circuit 19 and outputs a stop signal to stop the operation of the inverter circuit 2. Upon receiving the stop signal from the start / stop circuit 20, the start delay circuit 21 instantaneously outputs the stop signal. When the drive control circuit 22 receives the stop signal from the start delay circuit 21, the drive control circuit 22 stops driving the IGBT 5 and the IGBT 7 and stops the operation of the inverter circuit 2.

Thereafter, when the energy of the lightning surge is extinguished and the voltage of the commercial power supply 15 returns to a normal state, the v + detection circuit 19 detects that the commercial power supply 15 has become normal and outputs it. The start / stop circuit 20 includes the v + detection circuit 1
The detection output of the normal state of the commercial power supply 15 is input from 9 and an activation signal is output to restart the operation of the inverter circuit 2. Upon receiving the start signal from the start / stop circuit 20, the start delay circuit 21 outputs a start signal after a lapse of 2 seconds, and the drive control circuit 22 inputs the start signal from the start delay circuit 21 and then turns on the IGBT5 and the IGBT7. Driving is resumed and the operation of the inverter circuit 2 is resumed.

As described above, the v + detection circuit 19 is
5 can be monitored, and the start / stop circuit 20 can control the start / stop of the inverter circuit 2 in accordance with the output of the v + detection circuit 19. Therefore, when the commercial power supply 15 becomes abnormal due to lightning surge application or the like, The operation of the inverter circuit 2 is stopped, and the destruction of the inverter circuit 2 can be prevented.

When the start signal is input from the start / stop circuit 20, the start delay circuit 21 transmits the start signal to the drive control circuit 22 after a lapse of a predetermined time of 2 seconds, and outputs the stop signal from the start / stop circuit 20. When input, the stop signal is immediately transmitted to the drive control circuit 22. Therefore, when the v + detection circuit 19 detects an abnormality of the commercial power supply 15, the operation of the inverter circuit 2 stops immediately, and thereafter, the v + detection circuit 1
If the commercial power supply 9 detects that the commercial power supply 15 returns to the normal state, the operation of the inverter circuit 2 restarts after a lapse of 2 seconds. Even when the abnormal state is repeated, the startup delay time of 2 seconds can wait until the commercial power supply 15 is completely stabilized, so that the breakage of the inverter circuit 2 can be prevented regardless of the start, stop, and restart.

(Embodiment 4) FIG. 6 is a circuit diagram of an induction heating cooker according to a fourth embodiment. In FIG. 6, reference numeral 1 denotes a DC power supply, and 2 denotes an inverter connected to the DC power supply 1. Circuit.

The inverter circuit 2 is connected to the heating coil 4 having one end connected to the plus side, which is one end of the DC power supply 1, and to the other end of the heating coil 4 and the minus side, which is the other end of the DC power supply 1. An IGBT 5 with a built-in reverse conducting diode as a first switching element, a first resonance capacitor 6 connected in parallel with the IGBT 5 so as to form a resonance circuit with the heating coil 4, and a second switching element connected in parallel with the heating coil 4 And a series circuit of an IGBT 7 with a built-in reverse conducting diode and a second resonance capacitor 8.

An input setting circuit 23 is input setting means for setting the input power pin of the inverter circuit 2.
The output of the input setting circuit 23 is connected to a reference voltage setting circuit 24, and the output of the reference voltage setting circuit 24 and the output of the oscillation circuit 25 are both connected to a comparator 26 which is a comparing means.
The output of the comparator 26 is connected to the drive control circuit 27, and the output of the drive control circuit 27 is connected to the gate terminal of the IGBT5 and the gate terminal of the IGBT7, respectively. Reference voltage setting circuit 24, oscillation circuit 25, and comparator 26
Constitutes a soft start circuit.

The operation of the induction heating cooker configured as described above will be described. When the input power pin1 is set by the input setting circuit 23, the input setting circuit 23
The output is set to n1. The oscillation circuit 25 generates a triangular wave having a constant frequency. The reference voltage setting circuit 24 gradually increases the level from the minimum DC voltage which is the initial value, and finally outputs a DC voltage having a level corresponding to the input power pin1. The comparator 26 compares the triangular wave voltage output from the oscillation circuit 25 with the DC voltage output from the reference voltage setting circuit 24, and outputs a high-level signal while the DC voltage is larger than the triangular wave voltage. A low level signal is output during a small period. Since the output of the reference voltage setting circuit 24 gradually increases its level from the minimum DC voltage to a DC voltage corresponding to the input power pin1, the pulse width of the high-level signal output from the comparator 26 gradually increases, The pulse width of the low-level signal gradually narrows, and becomes constant at a pulse width determined by a DC voltage corresponding to the input power pin1. The drive control circuit 27 determines, based on the output of the comparator 26, the conduction time t of the IGBT 5 with respect to the constant operation cycle t0.
The IGBTs 5 and 7 are driven so that the duty ratio D1 that is the ratio of on1 gradually increases from the minimum value, and the duty ratio D1 is controlled so that the input power pin1 set by the input setting circuit 23 is finally obtained.

As described above, the drive control circuit 27 determines the constant operating frequency f0 (= 0) based on the output of the comparator 26 which is the output of the soft start circuit composed of the reference voltage setting circuit 24, the oscillation circuit 25 and the comparator 26. 1 /
Since the IGBTs 5 and 7 are driven so as to gradually increase the duty ratio D1 (ton1 / t0) from the minimum value under (t0), the value set by the input setting circuit 23 can be obtained immediately for the input power pin. Instead, since the set value gradually increases from the minimum value, the operation at the time of starting the inverter circuit 2 can be safely performed. For example, when the detection means of the aluminum pan is provided in the present invention, the aluminum pan can be detected and stopped before the inverter circuit 2 is broken by gradually increasing the input power from the minimum value. When the operation starts at the duty ratio corresponding to the input power set by the circuit 23, the inverter circuit 2 is destroyed.

(Embodiment 5) FIG. 7 is a circuit diagram of an induction heating cooker according to a fifth embodiment. In FIG. 7, reference numeral 1 denotes a DC power supply, and 2 denotes an inverter connected to the DC power supply 1. Circuit.

The inverter circuit 2 is connected to the heating coil 4 having one end connected to the plus side which is one end of the DC power supply 1, and to the other end of the heating coil 4 and the minus side being the other end of the DC power supply 1. An IGBT 5 with a built-in reverse conducting diode as a first switching element, a first resonance capacitor 6 connected in parallel with the IGBT 5 so as to form a resonance circuit with the heating coil 4, and a second switching element connected in parallel with the heating coil 4 And a series circuit of an IGBT 7 with a built-in reverse conducting diode and a second resonance capacitor 8. A v + detection circuit 28 is connected to the positive side of the DC power supply 1,
The vce1 detection circuit 29 is connected to the collector of the IGBT 5, and these constitute the operation state detection means of the inverter circuit 2. Both the output of the v + detection circuit 28 and the output of the vce1 detection circuit 29 are connected to a dead time setting circuit 30 which is a dead time setting means, and the output of the dead time setting circuit 30 is connected to a drive control circuit 31 and the drive control circuit 31 Are connected to the gate terminal of IGBT5 and the gate terminal of IGBT7, respectively.

The operation of the induction cooking device configured as described above will be described with reference to FIG.

The v + detection circuit 28 detects the voltage of the DC power supply 1 by resistance division, and the vce1 detection circuit 29 detects the voltage of the IGBT.
5 is detected by the resistance voltage division. The dead time setting circuit 30 receives the output of the v + detection circuit 28 and the output of the vce1 detection circuit 29,
A dead time is set based on these two inputs. That is, the gate-emitter voltage v of the IGBT 7
When ge2 becomes 0V and IGBT7 turns off, vce1
Goes down, but after time t1, the value of vce1 becomes v
+, And after a lapse of time t2 from that point, IG
The gate-emitter voltage vge1 of the BT5 goes high, turning on the IGBT5. After that, vge1 becomes 0V
When the IGBT 5 is turned off and vce1 rises, the value of vce1 becomes the same value as v + after time t3, and after a time t4 from that time, vge2 goes high to turn on the IGBT7.

As described above, the dead time setting circuit 30 uses the IGB based on the outputs of the v + detection circuit 28 and the vce1 detection circuit 29 as the operation state detection means of the inverter circuit 2.
The dead time from when T7 is turned off to when the IGBT 5 is turned on is set to the time td1 obtained by adding the time t1 and the time t2, and the dead time from when the IGBT 5 is turned off to when the IGBT 7 is turned on is set to time t3 and time t4. Added time t
Since it can be set to d1, the IGBT5 and the IGBT7 do not conduct at the same time, and the destruction of the inverter circuit 2 can be prevented.

The dead time td1 is set based on the operation state of each load by the operation state detection means of the inverter circuit 2 composed of the v + detection circuit 28 and the vce1 detection circuit 29. Thus, the respective values become appropriate, and a stable switching operation of IGBT5 and IGBT7 can be obtained.

(Embodiment 6) FIG. 9 is a circuit diagram of an induction heating cooker according to a sixth embodiment. In FIG. 9, reference numeral 1 denotes a DC power supply, and 2 denotes an inverter connected to the DC power supply 1. Circuit.

The inverter circuit 2 is connected to the heating coil 4 having one end connected to the plus side, which is one end of the DC power supply 1, and to the other end of the heating coil 4 and the minus side, which is the other end of the DC power supply 1. An IGBT 5 with a built-in reverse conducting diode as a first switching element, a first resonance capacitor 6 connected in parallel with the IGBT 5 so as to form a resonance circuit with the heating coil 4, and a second switching element connected in parallel with the heating coil 4 And a series circuit of an IGBT 7 with a built-in reverse conducting diode and a second resonance capacitor 8.

Reference numeral 32 denotes a dead time setting circuit which is a dead time setting means. The output of the dead time setting circuit 32 is connected to a drive control circuit 33.
It is connected to the gate terminal of BT5 and the gate terminal of IGBT7, respectively.

The operation of the induction cooking device configured as described above will be described with reference to FIG.

The gate-emitter voltage vg of the IGBT 7
When e2 becomes 0V and the IGBT 7 is turned off, the dead time setting circuit 32 sets the time t after vge2 becomes 0V.
During d2, a signal for turning off both the IGBT 5 and the IGBT 7 is output to the drive control circuit 33, and the drive control circuit 33
The GBT 5 and the IGBT 7 are both turned off. When the time td2 has elapsed, the drive control circuit 33 sets the gate of the IGBT 5
When the voltage vge1 between the emitters is changed from 0V to a high level, Ige
The GBT 5 is turned on, and after a predetermined ON time, vge1 is set to 0 V from the high level to turn off the IGBT 5. IGB
When T5 is turned off and vge1 becomes 0V, the dead time setting circuit 32 outputs the time td2 after vge1 becomes 0V.
During this period, a signal for turning off both the IGBT 5 and the IGBT 7 is output to the drive control circuit 33, and the drive control circuit 33
Turn off both T5 and IGBT7. When the time td2 elapses, the drive control circuit 33 sets vge2 from 0 V to a high level to turn on the IGBT 7, and after a predetermined ON time elapses, v
geBT is set to 0 V from the high level to turn off the IGBT 7. Thereafter, the operation is repeated.

As described above, the dead time setting circuit 32 can use the operation state detecting means of the inverter circuit 2 without using the operation state detecting means.
The dead time from when the IGBT 7 turns off to when the IGBT 5 turns on is set to time td2, and the dead time from when the IGBT 5 turns off to when the IGBT 7 turns on is t.
Since it can be set to d2, the IGBT 5 and the IGBT 7 do not conduct simultaneously, and the inverter circuit 2 can be prevented from being destroyed by using an inexpensive circuit.

(Embodiment 7) FIG. 11 shows a circuit diagram of an induction heating cooker according to a seventh embodiment. In FIG.
Denotes a DC power supply, and 2 denotes an inverter circuit connected to the DC power supply 1.

The inverter circuit 2 is connected to the heating coil 4 having one end connected to the plus side which is one end of the DC power supply 1, and to the other end of the heating coil 4 and the minus side being the other end of the DC power supply 1. An IGBT 5 with a built-in reverse conducting diode as a first switching element, a first resonance capacitor 6 connected in parallel with the IGBT 5 so as to form a resonance circuit with the heating coil 4, and a second switching element connected in parallel with the heating coil 4 And a series circuit of an IGBT 7 with a built-in reverse conducting diode and a second resonance capacitor 8.

Reference numeral 34 denotes a dead time setting circuit which is a dead time setting means. The output of the dead time setting circuit 34 is connected to a drive control circuit 35, and the drive control circuit 35
It is connected to the gate terminal of BT5 and the gate terminal of IGBT7, respectively.

The operation of the induction heating cooker configured as described above will be described with reference to FIGS.

FIG. 12 shows operation waveforms of the respective parts of the IGBT 5 and the IGBT 7 when the input power pin is small.
As shown in FIG. 12, when vge2 becomes 0V and the IGBT 7 is turned off, the dead time setting circuit 34 sets vge2 to 0V.
IGBT5 and IGBT7 for a time td3 after the voltage becomes V
Is output to the drive control circuit 35, and the drive control circuit 35 turns off both the IGBT5 and the IGBT7. When the time td3 has elapsed, the drive control circuit 35
geBT5 is turned on from 0V to high level to turn on IGBT5, and after a predetermined ON time, vge1 is changed from high level to 0V.
To turn off the IGBT 5.

After vge2 becomes 0V and the IGBT 7 is turned off, vce1 gradually decreases and becomes smaller. However, when the input power pin is small, vce1 does not reach 0V but increases when it exceeds the minimum value. However, the time td3 is v
The time is set from the time when ge2 becomes 0V to the time when the voltage of vce1 becomes the minimum value.

When vge1 becomes 0V and the IGBT 5 is turned off, the dead time setting circuit 34 outputs a signal for turning off both the IGBT5 and the IGBT7 to the drive control circuit 35 for a time td2 after the vge1 becomes 0V and drives the drive control circuit 35. The control circuit 35 turns off both the IGBT 5 and the IGBT 7. When the time td2 has elapsed, the drive control circuit 35
geBT is changed from 0V to a high level to turn on the IGBT 7, and after a predetermined ON time, vge2 is changed from the high level to 0V.
To turn off the IGBT 7. Thereafter, the operation is repeated. Time td2 is from the time when vge1 becomes 0V.
It is set in a period up to almost the middle of the period of the negative current of ic2 (the freewheel diode current built in the IGBT 7).

As described above, the dead time setting circuit 34 can use the operation state detecting means of the inverter circuit 2 without using the operation state detecting means.
The dead time from when the IGBT 7 is turned off to when the IGBT 5 is turned on is set to time td3, the dead time from when the IGBT 5 is turned off to when the IGBT 7 is turned on is set to time td2, and td2 and td3 are different optimal times. IGBT using an inexpensive circuit
In addition to preventing the inverter circuit 2 from being destroyed due to simultaneous conduction of the IGBT 5 and the IGBT 7, optimal switching operations of the IGBT 5 and the IGBT 7 can be realized. That is, when the input power pin is small, vce1 remains at the moment when the IGBT 5 is turned on, and the operation mode is such that the remaining voltage is short-circuited. However, since the short-circuit voltage at this time becomes the minimum value in the present embodiment, As shown in FIG. 13, the loss of the IGBT 5 and the generation of noise can be reduced as compared with the case where the pin is reduced in the sixth embodiment.

In connection with the configuration of the inverter circuit 2 in the above (Embodiment 1) to (Embodiment 7), the connection of the first resonance capacitor 6 is connected in parallel with the heating coil 4 as shown in FIG. However, the present invention can be similarly implemented by connecting both the heating coil 4 and the IGBT 5 in parallel as shown in FIG.

The DC power supply 1, the heating coil 4, and the IGB
The connection of T5 may be such that the IGBT 5 is connected to the plus side of the DC power supply 1 and the heating coil 4 is connected to the minus side of the DC power supply 1, as shown in FIG.

The IGBT 7 and the second resonance capacitor 8
May be connected in parallel with the IGBT 5 as shown in FIG.

Also, the first switching element can be similarly implemented as a reverse current blocking type as shown in FIG.

[0072]

As described above, according to the first aspect of the present invention, the improper load detecting means detects the improper load, and in the case of the improper load, the drive control circuit stops the operation of the inverter circuit. Therefore, heating of small loads such as knives can be prevented, and a safe induction heating cooker can be provided.

According to the second aspect of the present invention, the operating state detecting means detects the operating state of the inverter circuit, and the inappropriate load detecting means detects the inappropriate load from the output of the operating state detecting means. Inappropriate load can be accurately detected based on the difference in operation state due to the load of the load, and in the case of an inappropriate load, the drive control circuit stops the operation of the inverter circuit, so that heating of small loads such as knives can be prevented, and safe induction A heating cooker can be provided.

According to the third aspect of the invention, the input current detecting means detects the input current of the inverter circuit, the first switching element voltage detecting means detects the voltage of the first switching element, and the improper load detecting means. Can accurately detect an improper load from a difference in characteristics corresponding to the load of the input current detected by the input current detecting means and the load of the first switching element voltage detected by the first switching element voltage detecting means. In this case, the drive control circuit can stop the operation of the inverter circuit, prevent heating of a small object load such as a knife, and provide a safe induction heating cooker.

According to the present invention, the input current detection means detects the input current of the inverter circuit, the second switching element voltage detection means detects the voltage of the second switching element, and the improper load detection means Can accurately detect an improper load from a difference in characteristics corresponding to the load of the input current detected by the input current detecting means and the load of the second switching element voltage detected by the second switching element voltage detecting means. In this case, the drive control circuit can stop the operation of the inverter circuit, prevent heating of a small object load such as a knife, and provide a safe induction heating cooker.

According to the fifth aspect of the present invention, the start / stop means outputs a start signal or a stop signal of the inverter circuit, and the start delay means outputs the start signal after a predetermined time has passed when the start signal is inputted. When a stop signal is input, a stop signal is output immediately, so that when starting or restarting the inverter circuit, the drive control circuit can wait for a predetermined time to elapse and start up after the state has stabilized, and any abnormalities will occur. If the inverter stops, the operation can be stopped immediately, so that a highly reliable induction heating cooker that can safely operate the inverter circuit when starting or stopping can be provided.

According to the invention, the commercial power supply monitoring means can detect the power supply state of the commercial power supply. Therefore, when the commercial power supply monitoring means detects the abnormal state of the commercial power supply, the drive control circuit switches the inverter circuit. Since the inverter is stopped, the inverter circuit can be protected when the commercial power supply is abnormal, and a safe and reliable induction heating cooker can be provided.

According to the seventh aspect of the present invention, the input setting means sets the input power, and the soft start circuit gradually increases the input power from the minimum input power at the time of starting and sets the input power set by the input setting means. The drive control circuit is controlled so as to obtain, for example, even in the case of an aluminum pan in which the operating voltage and current of the inverter circuit at the time of the rated power consumption become excessive, by gradually increasing the input power from the minimum value, An aluminum pan can be detected before the voltage / current rating of the components constituting the circuit is exceeded, and the operation of the inverter circuit can be stopped, thereby providing a safe and reliable induction heating cooker.

According to the present invention, the input setting means sets the input power, and the reference voltage setting circuit gradually sets the reference voltage from the initial value of the reference voltage to the reference voltage corresponding to the input power set by the input setting means. The oscillation circuit generates a triangular wave, the comparison means compares the output of the reference voltage setting circuit with the output of the oscillation circuit and outputs a signal, and the drive control circuit is activated based on the output of the comparison means. Sometimes, the input power is gradually increased from the minimum input power, and the inverter circuit is controlled so as to obtain the input power set by the input setting means.For example, the operating voltage and current of the inverter circuit at the time of rated power consumption become excessive. Even in the case of an aluminum pan, by gradually increasing the input power from the minimum value, the aluminum pan is detected and the inverter is detected before the voltage and current ratings of the components that make up the inverter circuit are exceeded. Can stop the operation of the motor circuit, it is possible to provide a safe and reliable induction heating cooker.

According to the ninth aspect of the present invention, since the dead time setting means can set the dead time when the conduction period of both switching elements is switched, it is possible to prevent both switching elements from conducting at the same time and to destroy the inverter circuit. And a highly reliable induction heating cooker capable of preventing the occurrence of the heat.

According to the tenth aspect, the operating state detecting means detects the operating state of the inverter circuit, and the dead time setting means detects the timing corresponding to the operating state of each load detected by the operating state detecting means. Setting the dead time of both switching elements, it is possible to prevent both switching elements from conducting at the same time, and to set the conduction start timing of both switching elements to an appropriate value corresponding to each load, thereby destroying the inverter circuit. Can provide a highly reliable induction heating cooker that can prevent
An optimal switching operation of both switching elements can be obtained.

According to the eleventh aspect of the present invention, since the dead time setting means can set a constant dead time when the conduction period of both switching elements is switched, both switching elements are simultaneously turned on without using the operation state detecting means. And a reliable induction heating cooker that can prevent the inverter circuit from being destroyed at a low cost can be provided.

According to the twelfth aspect of the present invention, the dead time setting means sets the dead time of the first predetermined value between the end of the conduction period of the first switching element and the start of the conduction period of the second switching element. The dead time of the second predetermined value is provided between the end of the conduction period of the second switching element and the start of the conduction period of the first switching element, and the dead time of the first predetermined value and the second Since the predetermined dead times are set to different values so as to be appropriate, it is possible to prevent both switching elements from conducting simultaneously without using the operation state detecting means. Provide a reliable induction heating cooker that can set the start timing to the optimum value and prevent the inverter circuit from being destroyed at low cost With wear, optimal switching operation of both the switching element is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an induction heating cooker according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of an input current and a first switching element voltage of the induction heating cooker.

FIG. 3 is a circuit configuration diagram of an induction heating cooker according to a second embodiment of the present invention.

FIG. 4 is a characteristic diagram of an input current and a second switching element voltage of the induction heating cooker.

FIG. 5 is a circuit configuration diagram of an induction heating cooker according to a third embodiment of the present invention.

FIG. 6 is a circuit configuration diagram of an induction heating cooker according to a fourth embodiment of the present invention.

FIG. 7 is a circuit configuration diagram of an induction heating cooker according to a fifth embodiment of the present invention.

FIG. 8 is a timing chart for explaining the operation of the induction heating cooker.

FIG. 9 is a circuit configuration diagram of an induction heating cooker according to a sixth embodiment of the present invention.

FIG. 10 is a timing chart for explaining the operation of the induction heating cooker.

FIG. 11 is a circuit configuration diagram of an induction heating cooker according to a seventh embodiment of the present invention.

FIG. 12 is a timing chart for explaining the operation of the induction heating cooker.

FIG. 13 is a timing chart for explaining another operation of the induction heating cooker.

FIG. 14 is a circuit configuration diagram of an induction heating cooker according to another embodiment of the present invention.

FIG. 15 is a circuit configuration diagram of an induction heating cooker according to still another embodiment of the present invention.

FIG. 16 is a circuit configuration diagram of an induction heating cooker according to still another embodiment of the present invention.

FIG. 17 is a circuit configuration diagram of an induction heating cooker according to still another embodiment of the present invention.

FIG. 18 is a circuit configuration diagram of an induction heating cooker according to still another embodiment of the present invention.

FIG. 19 is a circuit configuration diagram of a conventional induction heating cooker.

FIG. 20 is an operation waveform diagram of each part of the inverter circuit of the induction heating cooker.

FIG. 21 is a characteristic diagram of the conduction ratio and input power of the induction heating cooker.

[Explanation of symbols]

Reference Signs List 1 DC power supply 2 Inverter circuit 3 Drive control circuit 4 Heating coil 5 IGBT (first switching element) 6 First resonance capacitor 7 IGBT (Second switching element) 8 Second resonance capacitor 9 Current sensor (input current detection means, inverter circuit) 10 iin detecting circuit (input current detecting means, operating state detecting means of inverter circuit) 11 vce1 detecting circuit (first switching element voltage detecting means, operating state detecting means of inverter circuit) 12 Inappropriate pot detection Circuit (improper load detection means) 13 vce2 detection circuit (second switching element voltage detection means, operation state detection means of inverter circuit) 15 commercial power supply 16 diode bridge (rectifier) 18 smoothing capacitor 19 v + detection circuit (commercial power supply monitoring means) 20 Start / stop circuit Start-up stop means 21 Start-up delay circuit (Start-up delay means) 22 Drive control circuit 23 Input setting circuit (Input setting means) 24 Reference voltage setting circuit (Soft start circuit) 25 Oscillator circuit (Soft start circuit) 26 Comparator (Comparison means, (Soft start circuit) 27 Drive control circuit 28 v + detection circuit (operation state detection means of inverter circuit) 29 vce1 detection circuit (operation state detection means of inverter circuit) 30 dead time setting circuit 31 drive control circuit 32 dead time setting circuit 33 driving Control circuit 34 Dead time setting circuit 35 Drive control circuit

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hidekazu Yamashita 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (12)

[Claims] 1. A DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply, and a resonance with the heating coil. A first resonance capacitor forming a circuit, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, and detecting an improper load. An improper load detection means, and a drive control circuit that alternately controls conduction of both switching elements of the inverter circuit at a constant frequency, wherein the drive control circuit detects when the improper load detection means detects an improper load. An induction heating cooker in which the operation of the inverter circuit is stopped. 2. The induction heating according to claim 1, further comprising an operation state detection means for detecting an operation state of the inverter circuit, wherein the inappropriate load detection means detects an inappropriate load based on an output of the operation state detection means. Cooking device. 3. An input current detecting means for detecting an input current of an inverter circuit, and a first switching element voltage detecting means for detecting a voltage of a first switching element, wherein the improper load detecting means is configured to detect the input current. 2. An induction heating cooker according to claim 1, wherein an improper load is detected based on an input current value detected by said means and a voltage value detected by said first switching element voltage detecting means. 4. An apparatus according to claim 1, further comprising an input current detecting means for detecting an input current of the inverter circuit, and a second switching element voltage detecting means for detecting a voltage of the second switching element. 2. An induction heating cooker according to claim 1, wherein an improper load is detected based on an input current value detected by said means and a voltage value detected by said second switching element voltage detecting means. 5. A DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply, and a resonance with the heating coil. A first resonance capacitor forming a circuit, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, and starting up the inverter circuit. Starting and stopping means for stopping, and a drive control circuit for alternately controlling conduction of both switching elements of the inverter circuit at a constant frequency, wherein the drive control circuit delays the inverter by delaying a predetermined time after the start and output of the starting and stopping means. An induction heating cooker that starts the circuit. 6. The DC power supply includes a commercial power supply, a rectifier for rectifying the commercial power, and a smoothing capacitor connected to an output of the rectifier, and includes a commercial power monitor for monitoring a power state of the commercial power. 6. The induction heating cooker according to claim 1, wherein the drive control circuit stops the operation of the inverter circuit when the commercial power supply monitoring unit detects an abnormal state of the commercial power supply. . 7. A soft start circuit for outputting a signal for gradually increasing the input power from a predetermined minimum input power when the inverter circuit is started, and a drive control circuit based on an output of the soft start circuit for controlling both switching elements. The induction heating cooker according to any one of claims 1 to 6, wherein a conduction ratio is controlled. 8. A DC power supply, a heating coil connected to one end of the DC power supply, a first switching element connected to the other end of the heating coil and the other end of the DC power supply, and a resonance with the heating coil. A first resonance capacitor forming a circuit, an inverter circuit including a series circuit of a second switching element and a second resonance capacitor connected in parallel with the heating coil or the first resonance capacitor, and an input power of the inverter circuit. Input setting means for setting the reference voltage, a reference voltage setting circuit for gradually changing the reference voltage to a reference voltage set based on the output of the input setting means, an oscillation circuit for generating a triangular wave, and an output of the reference voltage setting circuit. And a comparing means for comparing the output of the oscillation circuit with the driving circuit. An induction heating cooker including a circuit, wherein the drive control circuit controls a conduction ratio of both switching elements based on an output of the comparison means. 9. The method according to claim 1, wherein a period in which both of the switching elements are non-conductive (hereinafter, referred to as a “dead time”) is provided when the conduction periods of the two switching elements are alternated. 2. The induction heating cooker according to claim 1. 10. The induction heating cooker according to claim 9, further comprising dead time setting means for setting a dead time of both switching elements based on an operation state of the inverter circuit. 11. The induction heating cooker according to claim 9, wherein the dead time is a fixed time. 12. A dead time between the end of the conduction period of the first switching element and the start of the conduction period of the second switching element, and the first switching from the end of the conduction period of the second switching element. 10. The induction heating cooker according to claim 9, wherein the dead time until the start of the conduction period of the element is made different.