JPH11260541A - Induction heating cooking device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the interference noise generation in a multi-port type range by controlling the heating output by keeping the oscillation frequency of an inverter circuit constant. SOLUTION: An inverter circuit 10 of this induction heating cooking device comprises a diode 17 and a transistor 16 connected in series and a capacitor 15 for resonance connected in parallel to the diode and the transistor 16. A control part 20 turns off a transistor 13 after a prescribed time during which the transistor 13 and the transistor 16 are turned on to generate resonance between a heating coil 12 and the capacitor 15. When the collector voltage Vc increases and exceeds an electric power source voltage Vb, the direction of the electric current flowing in the capacitor 15 is turned to the transistor 16 side and the resonance is temporarily stopped. Consequently, the electric current flowing in the heating coil 12 is limited. Due to that, the on time of the transistor 16 is fixed and on the other hand, the heating output is lessened more as the on time of the transistor 13 is shortened more. As a result, without fluctuating the operational frequency of the inverter circuit 10, the heating electric power can be adjusted.

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, and more particularly to an inverter circuit for controlling heating and its control.

[0002]

2. Description of the Related Art In an induction heating cooker, an alternating magnetic flux generated in a coil is passed through a pot, which is a conductor, and an eddy current is generated in the pot to generate heat in the pot itself. FIG. 8 is a schematic configuration diagram of an electric system of a conventional induction heating cooker. A heating coil 12 for heating the pan 30 and a transistor 13 are connected in series to a DC power supply 11 having a voltage Vb. A capacitor 15 for resonance is connected to the heating coil 12 in parallel, and the transistor 13 is turned on in the reverse direction. Are connected in parallel, thereby constituting the inverter circuit 10. An on / off drive signal is input from the control unit 20 to the base terminal of the transistor 13 as a drive signal for the inverter circuit 10.

FIGS. 9 and 10 are waveform diagrams for explaining the operation of the inverter circuit 10 having the configuration shown in FIG. 8, and FIG. 9 shows the input power (that is, heating output) of the inverter circuit 10.
Is relatively large, and FIG. 10 is an example when the input power is relatively small. First, when the control unit 20 turns on the transistor 13, a current flows from the DC power supply 11 to the heating coil 12, and the current increases as shown in FIG. 9B. Next, when the transistor 13 is turned off, resonance occurs in a closed circuit between the heating coil 12 and the capacitor 15. When the value of the capacitor 15 and the like are determined so that this resonance frequency becomes sufficiently higher than the oscillation frequency of the inverter circuit 10, the collector voltage Vc of the transistor 13 becomes
As shown in FIG. 9A, the waveform oscillates around the voltage Vb. When the transistor 13 is turned on during a period from the point B where the collector voltage Vc is inverted to the negative polarity and the diode 14 is turned on to the point C which is delayed for a certain time, the current flowing through the heating coil 12 is as shown in FIG. The waveform is as shown in FIG.

[0004] The input power of the inverter circuit 10 depends on the oscillation cycle, and if the input cycle power is shortened as in the oscillation cycle Tb shown in FIG. 10, the oscillation amplitude of the current flowing through the heating coil 12 decreases (see FIG. See)) Input power decreases. The control unit 20 adjusts the oscillation cycle by controlling the on-time of the transistor 13, and controls the inverter circuit 1.
0 input power is controlled.

[0005]

However, in the inverter circuit according to the above-mentioned conventional configuration, the characteristic of the input power with respect to the oscillation cycle greatly differs depending on the material of the pot 30 as a load. FIG. 11 shows SUS316 which is an austenitic stainless steel and SUS which is a ferritic stainless steel.
430 and a graph showing a relationship between an oscillation cycle and input power when iron is used as a load. For example, in order to obtain an input power of 1 kW, the oscillation cycle of the SUS430 load is 3
Oscillation cycle is 42 μm with iron load, whereas 1 μs.
It is very different from seconds. Such input power characteristics depend not only on the material of the pan, but also on the shape of the pan 30 and the heating coil 1.
It also changes greatly depending on the distance between the two. For this reason,
In a multi-hole stove-type induction heating cooker having a plurality of inverter circuits having the above configuration, there is a problem that when a plurality of stoves are used at the same time, an interference sound is generated due to a shift in the oscillation frequency of each inverter circuit.

The present invention has been made to solve such a problem, and its main object is to provide:
It is an object of the present invention to provide an induction heating cooker capable of controlling input power of an inverter circuit, that is, heating output to a load while maintaining the same oscillation frequency.

[0007]

Means for Solving the Problems and Embodiments of the Invention The present invention has been made to solve the above-mentioned problems, and comprises a series connection of a DC power supply, a heating coil for induction heating, and a first switching element. In an induction heating cooker having an inverter circuit connected to a heating coil or a first switching element in parallel with a resonance capacitor and connected in parallel with the first switching element to a first diode conducting in the opposite direction, a) A series circuit for circulating a current flowing through the heating coil, which is connected in parallel to both ends of the heating coil, and is configured by connecting a second diode and a second switching element in series; and b) a first and a second switching element. Control means for controlling the on / off operation, wherein the control means sets the off timing of the first switching element to the off timing of the second switching element. It is characterized by adjusting the current flowing through the heating coil by adjusting relative packaging.

In the above configuration, the inverter circuit connects one end of a heating coil to a high potential end of a DC power supply,
By connecting the first switching element so as to conduct from the other end of the heating coil toward the low potential end of the DC power supply, a series closed circuit including the DC power supply, the heating coil, and the first switching element is configured. The heating coil or the first
A configuration in which a resonance capacitor is connected in parallel with the switching element, and a first diode that conducts in the opposite direction is connected in parallel with the first switching element, and the series circuit for reflux includes a second diode and A circuit in which the second switching element is connected in series in the same conduction direction, wherein the circuit is connected in parallel to both ends of the heating coil so as to conduct from the connection end side to the other end side with the first switching element. can do.

In the induction heating cooker according to the present invention, when the control means turns on the first switching element, a current flows from the DC power supply to the heating coil. At this time, since the voltage between both ends of the first switching element is maintained at almost zero, a reverse voltage is applied to the second diode, and there is no return series circuit regardless of whether the second switching element is on or off. Can be regarded as something. When the first switching element is turned off after a lapse of a predetermined time, resonance occurs in the closed circuit of the heating coil and the capacitor, and the voltage across the first switching element oscillates around the power supply voltage of the DC power supply. As a result, the voltage at the connection end between the heating coil and the first switching element rises from near zero, but when the voltage exceeds the power supply voltage, a forward voltage is applied to the second diode, and the current flowing through the capacitor up to that point is reduced to the 2 Commutation to the switching element side, and the resonance temporarily stops. For this reason, the rise of the voltage across the first switching element stops and is maintained near the power supply voltage. Thereafter, when the second switching element is turned off, resonance starts again, and the voltage across the first switching element oscillates. As the on-time of the first switching element is shorter than the on-time of the second switching element, the vibration amplitude due to resonance becomes smaller, and the current flowing through the heating coil also becomes smaller.
Therefore, if the OFF timing of the second switching element is determined by the operating frequency of the inverter circuit, the heating output can be adjusted by changing the ON time of the first switching element while keeping the operating frequency constant. Can be.

The ON timing of the second switching element can be appropriately set in a period from the ON timing of the first switching element to the conduction of the second diode. Since it changes, it is preferable that the reliable timing is set to the ON timing of the first switching element.

In order to perform the above control,
The control means includes: an on-timing detection means for detecting an on-timing of the first and second switching elements based on a voltage across the first switching element; an oscillation means for generating a signal of an operating frequency of an inverter circuit; An on-timing of the first switching element is determined by an output signal of the detecting means, and an off-timing of the first switching element is determined according to input power of the inverter circuit.
ON-time setting means for determining the ON-timing of the second switching element based on the output signal of the ON-timing detecting means, and determining the OFF-time based on the output signal of the oscillating means; May be included.

The oscillating means is an oscillating frequency variable oscillating means, wherein the oscillating frequency is changed according to a time difference between an off timing of the first switching element and an off timing of the second switching element. Is preferred. According to this configuration, for example, when the off-timings of the first and second switching elements substantially match, the input power can be further increased by reducing the oscillation frequency.

Furthermore, in the induction heating cooker provided with a plurality of the inverter circuits, the control means is provided corresponding to each of the inverter circuits, and only the oscillating means included in the plurality of control means is commonly used. It is preferable to have a configuration. In this configuration, even when a plurality of heating units, that is, inverter circuits are used at the same time, no interference sound is generated because each inverter circuit operates with a signal of the same frequency given from a common oscillation unit.

In this configuration, when only one of the plurality of inverter circuits is operated, the control means corresponding to the inverter circuit always makes the off timings of the first and second switching elements substantially coincide with each other. Maintained
Preferably, the input power of the inverter circuit is adjusted by changing the oscillation frequency of the oscillating means. That is, under such conditions of use, there is no danger of generating interference noise, so that the inverter circuit can be driven by the most efficient method with little switching loss.

Further, the oscillating means reduces the oscillating frequency when the time difference between the off-timing of the first switching element and the off-timing of the second switching element is eliminated in any of the plurality of operating control means, When there is the time difference in all of the plurality of operating control means, the oscillation frequency may be increased. According to this configuration, even if there is a possibility that the input power is insufficient in any one of the inverter circuits, the shortage is quickly resolved and appropriate heating can be performed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an induction heating cooker according to the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram of the induction heating cooker of the present embodiment, and FIG. 2 is a block diagram showing details of the control unit 20 in FIG.

In the inverter circuit 10 in the induction heating cooker of this embodiment, in addition to the components of the conventional inverter circuit, a series circuit of a second transistor 16 and a second diode 17 is provided in parallel with a resonance capacitor 15. Is connected. The positions of the second transistor 16 and the second diode 17 may be interchanged. A second ON / OFF signal is supplied from the control unit 20 to the base terminal of the second transistor 16.
The off drive signal φ2 is input. (Hereinafter, the conventionally provided transistor 13 and diode 14 will be referred to as the first
The signal input to the base terminal of the first transistor 13 is referred to as a first on / off drive signal φ1. )

Next, the configuration of the control unit 20 will be described with reference to FIG. The input setting section 21 sets the input power of the inverter circuit 10 by a user operation, while the input detection section 22 detects the actually obtained input power. For example, when the DC power supply 11 of the inverter circuit 10 is configured to convert a commercial AC power supply to DC, the input detection unit 22 may be configured to detect the current of the commercial AC power supply. The on-time setting unit 23 compares the set power value set in the input setting unit 21 with the detected power value detected by the input detection unit 22, and determines the on-time of the first transistor 13 so that both match. I do. The first driving unit 24
The first transistor 1 according to the output of the on-time setting unit 23
3 is supplied with a first on / off drive signal φ1.

The on-timing detector 25 detects the voltage across the first transistor 13 (when the emitter of the first transistor 13 is grounded, it is the collector voltage of the first transistor 13; ) Based on Vc and power supply voltage Vb of DC power supply 11,
The ON timing of the transistor 13 is detected, and a detection signal is given to the ON time setting unit 23 and the constraint time setting unit 26. The ON-time setting unit 23 raises the output to a high level at the timing of the ON detection, and lowers the output after the ON time determined as described above elapses. Also,
When the output of variable frequency oscillator 28 transitions from low to high, reset the output if it was high.

The constrained time setting unit 26 raises the output to a high level at the timing of the ON detection, and resets the output to a low level when the output of the variable frequency oscillator 28 changes from a low level to a high level. The second drive unit 27
The second transistor 1 according to the output of the constraint time setting unit 26
6 is supplied with a second on / off drive signal φ2. The frequency increase / decrease instructing section 29 measures the time difference between the falling point of the output of the constrained time setting section 26 and the output of the on-time setting section 23, and issues a frequency increase / decrease command according to the time difference.
8

The operation of the induction heating cooker according to the present embodiment having the above configuration will be described in detail with reference to FIG. FIG. 3 is a waveform diagram showing the operation of each unit when the inverter circuit 10 is in a steady state. Immediately before time t1, the first and second transistors 13 and 16 are both off, and resonate in a closed circuit of the heating coil 12 and the capacitor 15. At this time,
The collector voltage Vc is in the process of decreasing as shown in FIG. At time t1, the collector voltage Vc
Is lower than the power supply voltage Vb, the output of the on-timing detector 25 rises as shown in FIG. In response to this, as shown in FIGS. 3C and 3E, the outputs of the on-time setting unit 23 and the constraint time setting unit 26 also rise. As a result, the output signals φ1, φ1 of the first and second driving units 24, 27
2 changes in the same manner, and as a result, the first and second transistors 13 and 16 are turned on. When the first transistor 13 is on, the collector voltage Vc is maintained at the collector-emitter saturation voltage of the first transistor 13 (substantially close to 0).

The ON time of the first transistor 13, that is, the time during which the output of the first drive unit 24 is maintained at a high level, is set by the ON time setting unit 23 to the input power of the inverter circuit 10 (ie, the detected input power). It is controlled so as to match the input power, and falls, for example, at time t2. As a result, when the first transistor 13 is turned off, resonance occurs in the loop between the heating coil 12 and the capacitor 15, and the collector voltage Vc rises sharply. When the collector voltage Vc is lower than the power supply voltage Vb, the second diode 17
Since the reverse voltage is applied to the first transistor, although the second transistor 16 is turned on, no current flows to the second transistor 16 side, and the resonance is maintained. As shown in FIG. 3A, when the collector voltage Vc sharply increases due to resonance and exceeds the power supply voltage Vb, a forward voltage is applied to the second diode 17 and the second diode 17 conducts, and the current flowing through the capacitor 15 is reduced. Commutation flows to the second transistor 16 side. Therefore, the closed circuit of the resonance is broken, and the collector voltage Vc maintains the value at that time.

As shown in FIG. 3D, when the output of the variable frequency oscillator 28 rises at time t3, the output of the constraint time setting unit 26 falls, and the output signal φ of the second drive unit 27
2 also goes low. Thereby, the second transistor 1
6 is turned off, resonance occurs again in the closed circuit between the heating coil 12 and the capacitor 15, and the collector voltage Vc becomes lower than that in FIG.
As shown in (a), the oscillation waveform is substantially centered on the power supply voltage Vb. Thus, the current flowing through the heating coil 12 is
As shown in FIG. 3 (g), the voltage rises in the positive direction after the first transistor 13 is turned on, reaches a plateau when the first transistor 13 is turned off, and remains constant until the second transistor 16 is turned off. , Gradually decrease due to the influence of the combined resistance component of the heating coil 12 and the pan 30 and the like. And the second
After the transistor 16 is turned off, it follows the above resonance.

When the on-time of the first transistor 13 is shorter than the on-time of the second transistor 16, the output of the frequency increase / decrease instructing section 29 becomes the time difference from time t2 to time t2 as shown in FIG. It goes high during the period t3. When the detected input power is smaller than the set input power, the on-time of the first transistor 13 is sequentially extended by the on-time setting unit 23, so that the time t2 is changed to the time t3.
Approach. When the ON time of the first transistor 13 is further extended, the time t2 finally coincides with the time t3. As described above, since the output of the on-time setting unit 23 is reset by the rise of the output of the variable frequency oscillator 28, the longest on-time of the first transistor 13 is equal to the on-time of the second transistor 16. When both are the same, the output of the frequency increase / decrease instructing unit 29 is maintained at a low level instead of a high level.

As described above, the first and second transistors 13,
The on-time of 16 corresponds to that the input power of the inverter circuit 10 is insufficient for the set input power at the oscillation frequency of the variable frequency oscillator 28 at that time. Frequency increase / decrease instruction unit 29
If the high-level output is lost, it operates to lower the oscillation frequency. As the variable frequency oscillator 28,
A well-known voltage controlled oscillator can be used.

FIG. 4 is a waveform chart showing the operation of each unit when the ON time of the first transistor 13 is controlled. Here, the oscillation frequency of the variable frequency oscillator 28 is set to 20 kHz.
, And the ON time of the first transistor 13 is changed in a range of 10 μsec to 35 μsec. At this time, the equivalent impedance of the heating coil 12 is an inductance component L = 40 μH and a resistance component R = 0.85Ω. When the on-time of the first transistor 13 is 35 μsec, the on-time of the first transistor 13 and the on-time of the second transistor 16 substantially match, and as shown in FIG. The amplitude of the flowing current is maximized. That is, under the oscillation frequency, the input power becomes maximum at this time.

When the ON time of the first transistor 13 is shortened, as shown in FIG. 4A, the time during which the collector voltage Vc is maintained near the power supply voltage Vb becomes longer, and the current flowing through the heating coil 12 is lower. Levels off at the level.
That is, the input power decreases as the on-time decreases. As described above, by adjusting the ON time of the first transistor 13, control of the input power is achieved.

FIG. 5 is a graph showing the relationship between the on-time of the first transistor 13 and the input power under two load (pot) conditions having different inductances. The oscillation frequency of the variable frequency oscillator 28 is fixed at 20 kHz, and the resistance component R of the equivalent impedance of the heating coil 12 is
Is 0.85Ω. As is clear from FIG. 5, for example, when the inductance component L is 40 μH, the input power can be adjusted in a wide range of 300 to 1350 W by changing the ON time of the first transistor 13 in the range of 10 to 35 μsec. We can see that we can do it. That is, it is possible to sufficiently control the input power while keeping the oscillation frequency constant.

FIG. 6 is a graph showing the relationship between the oscillating frequency (oscillation cycle in the figure) of the variable frequency oscillator 28 and the input power under the above two load conditions. In the figure,
(i) is a case where the ON time of the first transistor 13 and the ON time of the second transistor 16 are the same, and (ii) is a case where the ON time of the first transistor 13 is the same.
This is a case where the on time of the transistor 13 is set to be always 9 μs shorter than the on time of the second transistor 16. Since the curve in the case of (i) means that the input power is adjusted by changing the oscillation frequency, it corresponds to the control of the conventional inverter circuit shown in FIG.

As shown in FIGS. 5 and 6, regardless of the ON time and the oscillation frequency of the first transistor 13, the curve under the load condition where the inductance L = 45 μH is represented by the inductance L.
= 40 μH at all times below the curve. This means that by appropriately adjusting the ON time of the first transistor 13, the input power characteristic in the pot with the inductance L = 40 μH can be changed while maintaining the same oscillation frequency, and the input power characteristic in the pot with the inductance L = 45 μH. Means that you can match. In other words, the same input power can be obtained even if the conditions of the pot are different.

As described above, in the induction heating cooker according to the present embodiment, the first transistor 1 is maintained while the oscillation frequency is kept constant.
In addition to controlling the input power by controlling the on-time of No. 3, it is also possible to adjust the input power by changing the oscillation frequency, if necessary, as in the conventional case. it can.

In the above embodiment, the condenser 15 is connected in parallel with the heating coil 12. However, in the AC operation, the DC power supply 11 can be regarded as short-circuited.
Even when the capacitor 15 is connected in parallel with the first transistor 13, the same effect as described above can be obtained.

Next, the configuration and operation of the induction heating cooker of the multi-opening type stove provided with a plurality of inverter circuits having the above configuration will be described. FIG. 7 is a schematic configuration diagram in the case of a two-necked stove. That is, two inverter circuits (first and second inverter circuits 10a and 10b) and two control units (first and second control units 20a and 20b) shown in FIGS. 1 and 2 are prepared. Here, only the variable frequency oscillators 28 of the first and second control units 20a and 20b are used in common, and the output signals of the same oscillation frequency are set to the ON time setting unit and the constraint time setting of the first and second control units 20a and 20b. Give each to the department. The variable frequency oscillator 28 receives the output from each of the frequency increase / decrease instructing units of the first and second control units 20a and 20b, and changes the oscillation frequency according to a combination of the outputs of the two.

Specifically, when there is no longer a high-level output from any of the frequency increase / decrease instructing units, the input power may be insufficient, so that the variable frequency oscillator 28 gradually reduces the oscillation frequency. On the other hand, when a high-level output is obtained from both the frequency increase / decrease instructing units, the input power coincides with the set value. The frequency can be increased. Therefore, the variable frequency oscillator 28 gradually increases the oscillation frequency. Although the oscillation frequency itself rises and falls as described above, the first and second inverter circuits 1
Since 0a and 10b operate at the same frequency, there is no fear that a beat sound is generated due to the difference in frequency.

The first or second inverter circuit 10
When only one of a and 10b is operated, the first or second control unit 20a or 20b forcibly matches the on-time of the first transistor 13 with the on-time of the second transistor 16 to change the variable frequency. The control may be switched so that the input power is adjusted by changing the oscillation frequency of the oscillator 28. The reason is as follows.

A high breakdown voltage IGBT (insulated gate bipolar transistor) element generally used in this type of inverter circuit has particularly poor turn-on and turn-off characteristics. For this reason, as shown in FIGS. 4C and 4D, power loss due to so-called switching loss occurs at the steep rise and fall timings of the collector current of the transistor. Therefore, from the viewpoint of suppressing such power loss as much as possible, it is desirable that the number of times the transistor is rapidly turned on / off per unit time is small. As described above, when power control is performed by adjusting the ON time of the first transistor 13, the current steeps three times in one cycle (one time for the first transistor 13 and two times for the second transistor 16). Rise and fall occur. On the other hand, when the on / off of the first transistor 13 and the on / off of the second transistor 16 are matched,
As shown in FIG. 4D, no current flows through the second transistor 16, and therefore, the current of the transistor rises and falls only once in one cycle. Therefore, even if the oscillation frequency is doubled, the number of sharp changes in the transistor current is reduced, and efficient heating with suppressed power loss can be performed.

[0037]

As described above, in the induction heating cooker according to the present invention, the off timing of the first switching element connected in series with the DC power supply and the heating coil is determined by setting the resonance capacitor to the second diode. In addition, the input power of the inverter circuit is adjusted by adjusting the off timing of the second switching element connected in parallel. Therefore, by determining the off timing of the second switching element based on the operating frequency of the inverter circuit, it is possible to perform heating adjustment while keeping the oscillation frequency of the inverter circuit constant. Therefore, even when a plurality of inverter circuits are mounted in a multi-hole stove, the plurality of inverter circuits can be simultaneously operated using signals of the same oscillation frequency, thereby preventing generation of interference noise due to a shift in oscillation frequency. be able to.

In addition, when the oscillation frequency does not need to be kept constant, the first and second switching elements are turned off at substantially the same timing, and the input power is adjusted by controlling the operating frequency. Since no current due to commutation flows through the two switching elements, switching loss that occurs when the switching elements are turned on and off can be suppressed, and more efficient heating can be performed.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing details of a control unit in FIG. 1;

FIG. 3 is a waveform chart showing the operation of each unit when the inverter circuit of the present embodiment is in a steady state.

FIG. 4 is a waveform chart showing the operation of each unit when the on-time of the first transistor in FIG. 1 is controlled.

FIG. 5 is a graph showing a relationship between an ON time of a first transistor and input power.

FIG. 6 is a graph showing a relationship between an oscillation cycle of a variable frequency oscillator and input power.

FIG. 7 is a schematic configuration diagram when the induction heating cooker of the present invention is applied to a two-necked stove.

FIG. 8 is a schematic configuration diagram of an electric system of a conventional induction heating cooker.

FIG. 9 is a waveform chart for explaining the operation of a conventional inverter circuit.

FIG. 10 is a waveform chart for explaining the operation of a conventional inverter circuit.

FIG. 11 is a graph showing a relationship between an oscillation cycle and input power in a conventional inverter circuit.

[Explanation of symbols]

10, 10a, 10b inverter circuit 11 DC power supply 12 heating coil 13 first transistor 14 first diode 15 capacitor 16 second transistor 17 second diode 20, 20a, 20b control unit 21 input Setting unit 22 input detection unit 23 on-time setting unit 24 first drive unit 25 on-timing detection unit 26 restricted time setting unit 27 second drive unit 28 variable frequency oscillator 29 frequency increase / decrease instruction unit

Claims (8)

[Claims] 1. A DC power supply, a heating coil for induction heating, and a first switching element are connected in series, and a resonance capacitor is connected in parallel with the heating coil or the first switching element. An induction heating cooker having an inverter circuit connected to a first diode connected in parallel and in the opposite direction, comprising: a) connected in parallel to both ends of the heating coil, and a second diode and a second switching element connected in series. A series circuit for circulating a current flowing through the heating coil; and b) control means for controlling on / off operations of the first and second switching elements. The current flowing through the heating coil is adjusted by adjusting the off timing with respect to the off timing of the second switching element. Induction heating cooker. 2. The inverter circuit according to claim 1, wherein one end of a heating coil is connected to a high-potential end of the DC power supply, and a first terminal is connected to the other end of the heating coil in a direction from the other end to the low potential end of the DC power supply.
By connecting a switching element, a series closed circuit composed of a DC power supply, a heating coil, and a first switching element is formed, and a resonance capacitor is connected in parallel with the heating coil or the first switching element. It has a configuration in which a first diode that conducts in the opposite direction is connected in parallel with one switching element, and the series circuit for reflux includes a second diode and a second switching element that are connected in series in the same conduction direction. A circuit, wherein the first
The induction heating cooker according to claim 1, wherein the heating coil is connected in parallel to both ends of the heating coil so as to conduct from the connection end side to the other end side with the switching element. 3. The induction heating cooker according to claim 1, wherein the control unit turns on the first and second switching elements substantially simultaneously. 4. The control means includes: a) a first and a second voltage switching circuit based on a voltage across a first switching element;
ON timing detecting means for detecting the ON timing of the switching element; b) oscillating means for generating a signal of the operating frequency of the inverter circuit; c) ON timing of the first switching element based on the output signal of the ON timing detecting means. Decide,
First on-time setting means for determining the off-timing according to the input power of the inverter circuit; d) determining the on-timing of the second switching element based on the output signal of the on-timing detecting means;
4. The induction heating cooker according to claim 3, further comprising: a second on-time setting unit that determines an off timing based on an output signal of the oscillation unit. 5. 5. The oscillating means is an oscillating frequency variable oscillating means, wherein the oscillating frequency is changed according to a time difference between an off-timing of a first switching element and an off-timing of a second switching element. The induction heating cooker according to claim 4, wherein 6. An induction heating cooker comprising a plurality of said inverter circuits, said control means corresponding to each of said inverter circuits, and only an oscillating means included in said plurality of control means is shared. The induction heating cooker according to claim 5, which is used. 7. When only one of the plurality of inverter circuits is operated, the control means corresponding to the inverter circuit always sets the off timings of the first and second switching elements to substantially coincide with each other. 7. The induction heating cooker according to claim 6, wherein the input power of the inverter circuit is adjusted by maintaining and changing the oscillation frequency of the oscillation unit. 8. The oscillating means reduces the oscillating frequency when the time difference between the off-timing of the first switching element and the off-timing of the second switching element in one of the plurality of operating control means disappears, 7. The induction heating cooker according to claim 6, wherein the oscillating frequency is increased when the time difference exists in all of the plurality of operating control means.