JPH08117092A - Induction heating apparatus - Google Patents

Abstract

PURPOSE: To surely judge an improper load for preventing respective parts from a risk of overheat when the load other than a specified one on an induction heating apparatus is used. CONSTITUTION: There are provided an induction heating coil, a semiconductor switching element 29 connected in series to the coil and a control circuit 46 for controlling an inverter circuit 32. The control circuit 46 has a voltage detecting means 35 and frequency detecting means 36. The switching frequency of the semiconductor switching element 29 detected by the frequency detecting means 36 is compared with the both end voltage of the semiconductor switching element detected by the voltage detecting means by a load judging means 43 to detect whether or not a specified load is applied. If a load is improper one, the turning on-off time of the switching element 29 is controlled to reduce a power amount of the heating coil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device for heating a rice cooker made of a magnetic material by electromagnetic induction.

[0002]

2. Description of the Related Art In a general household, an electric rice cooker that heats a pot made of only aluminum by heating an ordinary electric heater, or a stainless steel (SUS304) that is sold at a metal cook shop and is heated by a gas stove, etc. ) And aluminum are used in many pots with similar shapes such as deep pots for cooking.

On the other hand, recently, an electromagnetic induction heating rice cooker has been proposed and commercialized in search of more delicious rice. The rice cooker used in this rice cooker is a so-called clad steel made of aluminum and stainless steel which is a magnetic substance. Is used. SUS430 is known as a material of stainless steel most suitable for this induction heating device.

However, the pot used for the induction heating rice cooker is a magnetic material such as stainless steel represented by SUS430 which constitutes a magnetic path, and its size and thickness depend on the output of the inverter. Designed with the specified materials and dimensions (hereinafter referred to as the specified pan), the cooking pot made of aluminum is different in material and does not generate heat because it is not a magnetic substance even if the size and thickness are almost the same. I can't.

Even with a stainless steel pot, a sufficient amount of heat cannot be obtained unless it has a prescribed size and thickness.

However, as described above, in households having many kinds of pans, there are more chances that a user of an induction heating rice cooker will accidentally use a pan other than the prescribed pan of the induction heating rice cooker. As a result, a large current flows in the electric circuit, causing problems such as damage to the switching element and the power supply circuit.

In order to prevent such a problem from occurring, for example, in Japanese Unexamined Patent Publication No. 2-95315 (Prior Art), when an improper pan other than the specified pan (hereinafter referred to as a different pan) is used, the inverter is used. The operation of the circuit is stopped to prevent misuse by the user.

In this prior art, when heated in a different pot made of aluminum, the input current to the inverter circuit is smaller than when it is heated in a regular pot, and the input detection circuit that detects this input current The signal is output to the small object detection circuit. In addition, the voltage detection circuit that detects that the voltage between the terminals of the power switching semiconductor in the inverter circuit is considerably large also outputs the signal to the small object detection circuit, and the small object detection circuit compares the respective signals to detect the input. It is determined that the signal output of the circuit is smaller than the signal output of the voltage detection circuit, and it is determined that the signal output is different.

As a result, in the small article detection circuit, the inverter circuit stops the high-frequency current supply to the heating coil to stop the rice cooking operation.

[0010]

However, the above-mentioned prior art detects whether it is a regulated pot or a different pot by the change of the terminal voltage of the power switching semiconductor and the input current to the inverter circuit. When converting one parameter into a data amount that can be handled by a microcomputer, the operation of each input means converts the detected value by the voltage converting means, and then performs A / D conversion to obtain a digital amount. , There is a problem that conversion error occurs due to variations in component constants and fluctuations in the power supply voltage supplied to the conversion means.
There were drawbacks such as the need to adjust the circuit.

Further, since the detection of the current to the above-mentioned inverter circuit is performed by the current transformer (current transformer) connected in series to the heating coil, the circuit board becomes large and the weight increases, and the handling and assembly thereof are difficult. It was troublesome. Since this current transformer is a winding component, it has a large current-voltage conversion error due to its characteristics, and requires circuit adjustment as described above.

Therefore, according to the present invention, when a load other than the specified load (specified pan) of the induction heating device is used, it is surely determined to be an improper load (different pan) and the overheating of each component is performed. The present invention is intended to prevent the danger due to, and to simplify the circuit by eliminating the need for a current transformer that requires circuit adjustment.

[0013]

SUMMARY OF THE INVENTION The present invention has a DC power supply circuit for converting a commercial power supply into a DC voltage, an induction heating coil and a semiconductor switching element connected in series to the DC power supply, and the semiconductor switching element. In an induction heating device including an inverter circuit for turning on and off a high-frequency current to the induction heating coil and a control circuit for the inverter circuit, the control circuit is a voltage for detecting a voltage applied to the semiconductor switching element. Detecting means, a frequency detecting means for detecting the switching frequency of the semiconductor switching element, a reference value corresponding to the frequency detected by the frequency detecting means and a value detected by the voltage detecting means are compared and defined. It has a load determining means for detecting whether or not it is a load.

The load determining means determines whether or not the load is a prescribed load based on the reference value corresponding to the frequency detected by the frequency detecting means and the value detected by the voltage detecting means, The on / off time of the switching element of the inverter circuit is controlled based on this determination result.

Further, the control circuit comprises a microcomputer that operates based on a pre-programmed content based on a reference frequency generator, and the frequency detecting means uses the reference frequency of the reference frequency generator to operate the semiconductor. The switching frequency of the switching element is detected.

[0016]

According to the present invention, a control circuit for controlling an inverter circuit for turning on and off a semiconductor switching element to flow a high frequency current to an induction heating coil includes a voltage detecting means for detecting a voltage applied to the semiconductor switching element, and Whether the load is a prescribed load by comparing a value detected by the voltage detection means with a frequency detection means for detecting a switching frequency of the semiconductor switching element and a reference value according to the frequency detected by the frequency detection means The determination is made reliable by having a load determination means for detecting the above, and detecting an improper load by detecting the switching frequency of the semiconductor switching element that does not affect the variation of the component constants.

The load determining means determines whether or not the load is a prescribed load based on the reference value corresponding to the frequency detected by the frequency detecting means and the value detected by the voltage detecting means. By controlling the on / off time of the switching element of the inverter circuit based on the determination result, the control of the improper load is stopped or the user is notified of the misuse.

Further, the frequency detecting means detects the switching frequency of the semiconductor switching element using the reference frequency of a reference frequency generator for operating the microcomputer, and the operation of the frequency detecting means is pulse synchronization. Is transmitted, the detection accuracy is improved without being influenced by the component constant.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An induction heating device according to the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an electric rice cooker which is an embodiment of the present invention, FIG. 2 is a schematic structural sectional view of the same, and FIG. 3 is a graph of a target upper limit voltage of both ends of a semiconductor switching element and a switching frequency of the semiconductor switching element. FIG. 4 is a control flowchart, and FIG. 5 is an improper load (different pot = SUS).
304, aluminum) detection flow chart, FIG. 6 is a relationship diagram between the input current of the power supply and the switching frequency of the semiconductor switching element when the voltage is constant, FIG.
[Fig. 4] is a relationship diagram of a voltage across a semiconductor switching element and a switching frequency when a specified load (specified pan = SUS430) and an improper load (different pan = SUS304, aluminum) are used.

(1) is the electric rice cooker body, the pan body (2)
And a lid body (3).

(4) is a standard pan serving as a load using SUS430 and aluminum as materials, for example, which is molded in conformity with the capacity of the main body of the electric rice cooker provided in the pan main body, which is not shown in detail. The inner side is made of aluminum and the outer side is made of clad steel with SUS430. The specified pan (4) is configured so that electromagnetic coupling becomes constant when it is attached to the rice cooker body (1).

(5) is a metal storage case for storing the specified pan (4), (6) is a bottom case connected to the lower part of the storage case (5), and (7) is the bottom case (6). Two sets of ring-shaped induction heating coils closely fixed to the lower surface of the
(8) is a support plate provided below the induction heating coil (7), and (9) is provided in the central portion of the support plate (8) and is always in close contact with the outer bottom surface of the prescribed pan (4). The thermistor, (10) is a side heater which constitutes a part of the heat insulation heater wound around the outside of the storage case (5), (11)
Is an operation display unit provided on the upper wall surface of the pan body (2),
Reference numeral (12) is a control board provided below the support plate (8) to which various electric components described later are attached.

Reference numeral (13) is a steam vent provided in the lid main body (3) for communicating the inside of the specified pan (4) with the outside air, and rises when the inside of the specified pan (4) exceeds a predetermined pressure. A valve body (15) for opening the steam passage (14) is provided. (1
6) is a lid heater forming a part of the heat retaining heater provided in the lid body (3), and (17) is attached to the lower surface of the lid body (3) and adheres closely to the upper peripheral edge of the regulation pan (4). It is an inner lid provided with a packing (18) for sealing.

(19) is a low-frequency commercial AC power source, (2
0) is a current fuse, (21) is the AC power supply (19)
Bridge diode for full-wave rectification of (22) (23)
Is the capacitor and coil that make up the noise filter, and (2
4) is a coil (25) and a capacitor (26) for smoothing the DC voltage converted by the bridge diode
(26) is a smoothing circuit.

The current fuse (20), capacitor (22) and coil (23), bridge diode (2)
1) and the smoothing circuit (24) form a DC power supply circuit (27).

(28) is a resonance capacitor connected to both ends of the heating coil (7), and (29) is a heating coil (7).
A semiconductor switching element (hereinafter referred to as a transistor) including a turn-off controllable transistor connected in series to the transistor, (30) is a diode connected in parallel to the transistor (29) in a direction opposite to its conduction direction, and (31) is an oscillation circuit described later. It is a transistor drive circuit for controlling the drive of the transistor (29) (on / off) by the pulse of (34).

The resonance capacitor (28), the transistor (29), the diode (30), and the transistor drive circuit (31) constitute an inverter circuit (32) for supplying a high frequency current to the heating coil (7).

Reference numeral (33) is an oscillation synchronization circuit for generating an ON pulse of the transistor (29) when the voltage (Vce) across the transistor (29) becomes 0V.

Reference numeral (34) is an on-pulse control circuit (4) described later for controlling the on-pulse width of the transistor (29).
8) is an oscillator circuit for controlling the on-time of the transistor (29) by the output, the input terminal of which is connected to the oscillation synchronization circuit (33) and the on-pulse control circuit (48),
The output terminal is connected to the transistor drive circuit (31).

Reference numeral (35) is a voltage detecting means connected to the collector of the transistor (29) to detect the voltage (Vce) across it, and reference numeral (36) is connected to the output side of the oscillation circuit (34) and the transistor ( 29) Frequency detecting means for detecting the switching frequency.

(37) is a control circuit (hereinafter referred to as "microcomputer") including a microcomputer for executing a series of rice cooking steps such as water absorption-rice cooking-heat retention step based on pre-programmed contents. Has been done.

(38) is a control means for storing the above-mentioned program contents and performing arithmetic processing based on the temperature information of the thermistor (9), etc. (39) is based on the contents programmed in advance for the microcomputer (37). A reference frequency generator that is operated accurately and timewise, and (40) is a pulse counter that counts the output pulses of the frequency detecting means (36) based on the reference frequency generated by the reference frequency generator (39). The output level is changed depending on whether or not the number of output pulses of the detection means (36) is within a predetermined number range. (41) is a threshold conversion circuit,
Based on the output of the frequency detecting means (36) counted by the pulse counter (40), the transistor (2
9) If the voltage across both ends (Vce) is below that,
If it is more than that, a threshold value for determining that the pot is different is determined. Reference numeral (42) is a switching frequency correction circuit for the transistor (29), which determines the level of a frequency correction straight line shown in FIGS. 3 and 7, which will be described later, and the stainless steel (SUS304) having the closest characteristics to the stainless steel (SUS430) standard pan. ) Is determined as a different pot, and the voltage (Vc) between both ends of the transistor (29) that sets the electric power for the water absorption process, the rice cooking process, the heat retention process, etc. to this straight line.
e) becomes like the broken line of FIG.

Reference numeral (43) is a load judging means for comparing the value detected by the voltage detecting means (35) with a reference value corresponding to the switching frequency detected by the frequency detecting means (36), which is an improper aluminum. Load (different pot)
In the case of a different pot, the first load determination means (44) makes a determination, and in the case of an inappropriate load (different pot) of stainless steel (SUS304), a second load determination means (45) makes a determination.

Each determination in this case is particularly made of stainless steel (S
In the case of different type of US304), the level value according to the voltage of the voltage detecting means (35) and the level according to the correction straight line of the frequency correction circuit (42) on the input side of the second load determining means (45) are compared with each other. Power setting circuit (4
Compare the target values in 9).

Particularly, when using a different pot of aluminum, similarly, the level value of the voltage detecting means (35) and the first load judging means (4)
4) The reference value of the reference value set by the input side threshold conversion circuit (41) is compared.

Each of the circuits and means constitutes a control circuit (46) of the inverter circuit (32).

Here, the correction value of the frequency correction circuit (42) will be described in detail. The target upper limit value of the voltage across the transistor and the limit function graph of the switching frequency of the transistor in FIG. 3 will be described. In this graph, if the switching frequency is within a predetermined range within the range (A) in the case of the standard pan, the voltage (Vce) across the transistor (29) corresponding to each power of the water absorption-rice cooking-heat retention step indicated by the broken line is shown. ) Is the target voltage (Vce) across the transistor (29).
It is a value that allows the induction heating coil (7) to operate the transistor (29) within the rated range without loss without any limitation. (The point S indicates one position of the specified pot.) In the case of different pot made of stainless steel (SUS304), the switching frequency becomes higher than the predetermined range and the transistor (29) is applied to limit the voltage across the transistor (29) as shown by the solid line. 29) Reduce power loss. In the present invention, each power of water absorption (power 750W) and heat retention (power 300W) other than rice cooking (power 1200W) is not corrected.

Further, in the case of a different pot of aluminum, since the switching frequency rises significantly over a predetermined range, the voltage across the transistor (29) is limited to a certain limit as shown by the solid line, and power loss is similarly caused. Hold down. However,
Since it does not affect the detection of different pots, which will be described later, the suppression is kept constant above a certain frequency.

That is, in FIG. 3, the specified pan (SUS4) is used.
In 30), since the switching frequency is low and within the predetermined range, the voltage across the transistor (29) is increased to fully control the induction heating coil (7) and
In 304), since the switching frequency is high and out of the predetermined range, the voltage across the transistor (29) is limited to control the on / off time of the transistor and reduce the electric energy of the induction heating coil (7). .

FIG. 6 shows a regular pan (SUS430) and a different pan (S).
The relationship between the circuit current and the switching frequency of the transistor (29) when the voltage across the transistor (29) of the inverter circuit (32) is controlled to be constant when US304, aluminum) is used. It can be seen that the circuit current is small and the switching frequency is low in the case of the specified pan. In the case of a different pot (SUS304), the circuit current is considerably large and the switching frequency is also slightly high, so it can be seen that the power loss of the transistor (29) is large. In the case of different pot (aluminum), the circuit current is small, but the switching frequency is quite high, and it can be seen that the loss of the transistor (29) is also large.

That is, when a different pot is used, both or one of the circuit current and the switching frequency exceeds a predetermined range, which causes a loss in the operation of the inverter circuit (32).

FIG. 7 is a diagram in which a frequency correction straight line and a straight line for judging whether the pan is a normal pan or a different pan are drawn, and a shaded area (P) is shown.
Is a regular pan (SUS430), and the area (Q) is a different pan (SUS)
304), the region (R) indicates a different pot (aluminum), the determination straight line set by the threshold conversion circuit (41) is (Y), and the frequency set by the frequency correction circuit (42). The correction straight line is (X).

The frequency correction straight line (X) is set in consideration of the voltage across the transistor (29) and the switching frequency, especially when a stainless steel pan (SUS304) is used. Similarly, the judgment straight line (Y) is particularly aluminum. It is set in consideration of the voltage across both ends and the switching frequency when is used.

In the above-mentioned FIG. 7 showing the characteristics of each pot, the arc-shaped curved region is drawn. As described above, the series of rice cooking steps basically includes the steps of water absorption-rice cooking-heat retention. In the case of the rice cooking process by the program of the microcomputer (37), the electric energy to the induction heating coil (7) is increased, so that the voltage across the transistor (29) is high and the switching frequency is low. This is because a large amount of heat is not required in the heat retention step, so that the voltage across the transistor is low and the switching frequency is high.

Therefore, from FIG. 7, if the voltage across the transistor (29) and the switching frequency are on the left side of the judgment line (Y), the pot used is stainless steel (SUS43).
It is the standard pan of 0), the pan used on the right is an aluminum pan, and the pan used on the left of the left inflection point of the frequency correction line (X). Can be determined to be a different pot of stainless steel (SUS304).

In FIG. 7, the characteristic diagram of each pot is represented by a hatched area having a width on the left and right. The variation of the AC voltage in each process during use of the pot and the pot itself. It is caused by a slight dimensional variation of the above. In Fig. 7, in the case of different pans made of stainless steel (SUS304) and aluminum, there is overlap due to variation, and in the case of different pans made of stainless steel (SUS304) and standard pans made of stainless steel (SUS430), there is no overlap due to variations. The solid lines tend to overlap when the respective variations become large.

(47) is drive means for outputting based on the output of the judgment result of the load judging means (43), and (48) is oscillation of the oscillation circuit (34) based on the output of the driving means (47). Adjust the frequency to adjust the transistor (2
9) An on-pulse control circuit that controls the on-pulse width.

Next, the operation will be described. First, the setting operation of the target upper limit value of the transistor shown in FIG. 3 will be described.

The AC voltage is converted to DC by the DC power supply circuit (27) and rectified. The reference frequency generator (39) oscillates the reference frequency to operate the microcomputer (37) based on the contents programmed in advance. When a start switch (not shown) is operated to start a series of rice cooking operations, the control means (38) causes the passage of time and the thermistor (9).
The rice cooking process is executed based on the detected temperature of the transistor (2), which corresponds to the power setting value according to the water absorption, rice cooking, and heat retention processes.
The voltage setting value between both ends of 9) is set in the power setting circuit (49).

Further, the oscillation synchronization circuit (33) generates an ON pulse of the transistor when the voltage (Vce) across the transistor (29) becomes 0 V, and inputs the ON pulse to the oscillation circuit (34). The drive circuit (31) is driven to turn on the transistor (29), and the resonance with the resonance capacitor (28) supplies power to the induction heating coil (7) to generate an alternating magnetic flux to heat the pot.

When the temperature of the pan rises with the progress of the rice cooking process, the thermistor (9) detecting this temperature inputs the change in its resistance value to the microcomputer (37), which is not shown in detail, but it is a control means. (38) and so on to control the on-pulse control circuit (4
The signal given to 8) is changed, the signal is converted into the magnitude of voltage, and it inputs into the oscillation circuit (34). The oscillating circuit (34) which receives this signal changes the pulse on time of the transistor (29) according to the water absorption, rice cooking and heat retention processes to control the electric energy of the induction heating coil (7) and change the calorific value of the pan.

Although the above description of the operation is explained as the basic operation, in reality, the transistor (2 shown in FIGS. 3 and 7 is based on the output of the frequency detecting means (36).
9) The target upper limit value of the frequency correction line (X) of the voltage (Vce) across both ends is obtained. (Refer to the flow chart of FIG. 4) That is, when the standard pan (SUS430) is housed in the pan body (2) and used, the switching frequency output from the oscillation circuit (34) is detected by the frequency detecting means (36). , The number of pulses per unit time by the pulse counter (40), that is, the frequency value is converted, and the output is used to determine the upper limit value (Vlim) of the terminal voltage from the frequency correction straight line (X) (S ₂ ). Is larger than the set target value in each process of a series of rice cooking (S ₃ ). For example, since a large amount of electric power is required in the rice cooking process, the reference level of the frequency correction line (X) is on the same line as the solid line position of FIG. 3 by the frequency correction circuit (42) as described above. If the voltage (Vce) across the transistor (29) during the rice cooking process, which is obtained from the reference level of the correction straight line in FIG. 3 based on the detected switching frequency, is smaller than the set target value, the target value is reached. The control target value is calculated by the control means (38), the voltage across the transistor is detected by the voltage detection means (35), and the switching frequency is controlled so that the voltage becomes equal to the set target value in the rice cooking process (S). ₄ ) (S ₅ ).

Here, when the stainless steel pan (SUS304) closest to the characteristics of the specified pan is used, the reference level of the correction straight line of FIG. 3 based on the switching frequency is determined as in the determination in the above step (S ₃ ). The both-end voltage (Vce) obtained from the second load determination means (4) is smaller than the set target value, and the set target value is equal to the control target value.
It is controlled by the output of 5) (S ₃ ) (S ₆ ).

In the heat retention step, the voltage setting across the frequency correction line (X) is completely lower than the reference level. Therefore, the set target value and the voltage across the transistor during the process are calculated to obtain the control target value. Control to be equal.

Next, the operation of detecting a different pot will be described. (Refer to the flow chart of FIG. 5) For example, an aluminum pot is housed in the pot body and the start switch is operated. In response to the operation, an on-pulse is output from the on-pulse control circuit (48) and an oscillation synchronization circuit (33) and oscillation are generated. The transistor (29) operates by operating the transistor drive circuit (31) by the output of the circuit (34).
Is turned on to supply power to the induction heating coil (7).

The frequency detection means (36) detects the switching frequency at this time (S ₁₀ ), and the threshold conversion circuit (4
According to 1), the threshold voltage (Vref) obtained from the judgment line (Y) shown in FIG. 7 is obtained (S ₁₁ ). Further, the voltage detecting means (35) detects the peak voltage of the voltage (Vce) across the transistor (29) at this time (S ₁₂ ).

The threshold voltage (Vref) obtained from the above-mentioned judgment line (Y) and the both-end voltage (Vce) are compared by the first load judging means (44) (S ₁₃ ). When Vce is higher than the threshold voltage (Vref), it is determined that a different pot is stored, and the driving means (47) is output by the output of the first load determining means (44).
Of the transistor (2) by controlling the on-pulse control circuit (48) to suppress the output pulse of the oscillation circuit (34).
9) stops controlling controls the on-off time of the (S _14). At this time, although not shown, a different pan notification buzzer sounds to inform the user (S ₁₅ ).

Both-end voltage (Vce) is a threshold voltage (V
If it is lower than ref), it is determined that the pot is a regular pot and the following process is executed.

[0059]

As described above, the present invention compares the switching frequency of the semiconductor switching element with the voltage across the semiconductor switching element to detect whether or not the load is improper. It is possible to simplify the circuit by eliminating the need for a large current transformer and to perform load determination with high accuracy. In particular, it is possible to perform control without increasing the circuit current even with an improper load whose characteristics are close to the specified load.

As a result, even when a wrong load is used by mistake, the switching element in the induction heating device,
There is no problem that the power supply circuit generates heat and the element or circuit is damaged.

In addition, control the ON / OFF time of the switching element based on the load determination result to stop the control of the load, protect the circuit to notify the user of misuse, and call attention. You can

Furthermore, since the switching frequency is detected using the reference frequency of the microcomputer, the detection accuracy is further improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an electric rice cooker that is an example of an induction heating device of the present invention.

FIG. 2 is a schematic structural sectional view of the same.

FIG. 3 is a function graph of the target upper limit value of the voltage across the semiconductor switching element and the switching frequency (switching frequency) of the switching element.

FIG. 4 is a control flowchart of the same.

FIG. 5 is a control flowchart for detecting an improper load (different pan SUS304, aluminum).

FIG. 6 is a diagram showing the relationship between the input current of the power supply and the switching frequency (switching frequency) of the semiconductor switching element when the voltage is constant.

FIG. 7 is a relationship diagram between the voltage across the semiconductor switching element and the switching frequency when a specified load (specified pan SUS430) and an improper load are also used.

[Explanation of symbols]

 4 regulation pan 7 induction heating coil 29 semiconductor switching element 32 inverter circuit 35 voltage detection means 36 frequency detection means 37 microcomputer 39 reference frequency generator 41 threshold conversion circuit 42 frequency correction circuit 43 load determination means 44 first load determination means 45 Second load judgment means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuo Tanigawa 3 201 Minamiyoshikata Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd. (72) Yuji Saito 3201 201 Minamiyoshikata Minamiyoshikata, Tottori City Tottori Sanyo Within the corporation

Claims (3)

[Claims] 1. A direct current power supply circuit for converting a commercial power supply into a direct current voltage, an induction heating coil connected in series to the direct current power supply, and a semiconductor switching element. The semiconductor switching element is turned on and off. In an induction heating device including an inverter circuit for flowing a high-frequency current through the induction heating coil and a control circuit for the inverter circuit, the control circuit includes voltage detection means for detecting a voltage applied to the semiconductor switching element, and the semiconductor. Whether the load is a specified load by comparing the frequency detection means for detecting the switching frequency of the switching element with a reference value corresponding to the frequency detected by the frequency detection means and the value detected by the voltage detection means. An induction heating device having a load determination means for detecting 2. The load determining means determines whether or not the load is a prescribed load based on a reference value corresponding to the frequency detected by the frequency detecting means and a value detected by the voltage detecting means, The induction heating device according to claim 1, wherein the on / off time of the switching element of the inverter circuit is controlled based on the determination result. 3. The control circuit comprises a microcomputer that operates based on a pre-programmed content based on a reference frequency generator, and the frequency detecting means uses the reference frequency of the reference frequency generator to operate the semiconductor. The induction heating device according to claim 1, wherein a switching frequency of the switching element is detected.