JP2001297862A - Induction heating power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating power supply which generates little switching noise, and has little noise of audible frequency, even if two or more sets of the induction heating power supply are installed in the same AC power supply. SOLUTION: In IGBTs 31b, 31d which constitute an inverter circuit 31, generating of a switching noise is suppressed by making the switching turn off or turn on when a sine-wave-like current which flows in an in-series resonance circuit of a capacitor 5 for resonance and a heating coil 6 becomes zero. Moreover, even when a heating electric power to a pan 7 is adjusted with a triac 11, the inverter circuit 31 continues the operation based on the resonance frequency of the in-series resonance circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating power supply for supplying a desired high-frequency power to a series resonance circuit including a heating coil for induction heating a metal pot and a resonance capacitor.

[0002]

2. Description of the Related Art FIG. 9 is a main circuit configuration diagram showing a conventional example of this type of induction heating power supply.

In FIG. 9, 1 is an AC power supply such as a commercial power supply, 2 is a diode rectifier circuit, 3 is a capacitor for smoothing the output of the diode rectifier circuit, and 4 is an IGBT as shown in the figure.
An inverter circuit having upper and lower arms of a switching circuit in which anti-parallel circuits 4a and 4b and diodes 4c and 4d are respectively formed, 5 is a capacitor for resonance, 6 is a heating coil, and 7 is a high-frequency current flowing through the heating coil 6. This is a pot that is induction-heated, and the resonance capacitor 5 and the heating coil 6 form a series resonance circuit.

The operation of the induction heating power supply shown in FIG.
This will be described below with reference to the waveform diagram shown in FIG.

In FIG. 10, (a) shows a current waveform flowing through the heating coil 6, (b) shows a current waveform flowing through the IGBT 4a (thick solid line) and IGBT 4b (thin solid line), and (c) shows a diode 4c ( Thick solid line), diode 4
The current waveform flowing through d (thin solid line) is shown.

First, at time t ₀ , an on signal and an off signal have been already output to the gate of the IGBT 4 a and the IGBT 4 b by the control circuit of the inverter circuit 4 (not shown). The same current (see FIG. 1) as the current (see FIG.
0 (see (b)).

At time t ₁ , the IGBT is controlled by the control circuit.
4a changes from an on signal to an off signal,
When an ON signal is issued to the gate of GBT 4b, IGB
The current of T4a (see FIG. 10B) is cut off, and the current of the series resonance circuit (see FIG.
As shown by the thin solid line in (c), the current is commutated to the diode 4d.

At time t ₂ , the current of the diode 4 d becomes zero (see FIG. 10 (C)), and the current of the series resonance circuit (FIG. 10 (A)) is supplied to the IGBT 4 b for which an ON signal has already been generated by the control circuit. ) Is commutated as shown in FIG.

At time t ₃ , the control circuit controls the IGBT
4b changes from an ON signal to an OFF signal,
When an ON signal is issued to the gate of GBT 4a, IGB
The current of T4b (see FIG. 10B) is cut off, and the current of the series resonance circuit (see FIG.
As shown by the thick solid line in (c), the current is commutated to the diode 4c.

At time t ₄ , the current of the diode 4c becomes zero (see FIG. 10 (c)), and the current of the series resonance circuit (FIG. 10 (a)) is supplied to the IGBT 4a, for which an ON signal has already been generated by the control circuit. ) Is commutated as shown in FIG.

[0011] The time t ₄ and later, repeats the operation of the time t ₀ ~t ₄ of the above-mentioned.

As is well known, the adjustment of the heating power to be injected into the pan 7 via the heating coil 6 is performed at the times t _{0 to} t _4.
Is performed by changing the frequency corresponding to.

[0013]

According to the above-described conventional induction heating power supply, the IG at time t ₁ , t ₃ shown in FIG.
The current of the BTs 4a and 4b changes suddenly as shown in FIG. 10 (b), and this sudden change becomes switching noise, which disturbs other electronic devices connected to the AC power supply 1 and peripheral electronic devices. was there.

Further, when a plurality of induction heating power supplies shown in FIG. 10 are installed in the AC power supply 1, an audible frequency varies due to a difference in frequency of each of the induction heating power supplies at the times t _{0 to} t _4. There is also a problem that a noise near the induction heating power source is generated and discomfort is given to a person near the induction heating power supply.

An object of the present invention is to provide an induction heating power supply which solves the above problems.

[0016]

According to a first aspect of the present invention, there is provided a rectifier circuit for converting an AC power supply to a DC power, a smoothing circuit for smoothing an output of the rectifier circuit, and a diode which receives an output voltage of the smoothing circuit as an input. And a self-extinguishing element connected in series with an inverter circuit having upper and lower arms as first and second switching circuits, a heating coil supplied with high-frequency power from the inverter circuit, and a resonance capacitor. And a semiconductor AC switch circuit installed in a path from the AC power supply to the rectifier circuit, and controls the opening and closing of the semiconductor AC switch circuit in one-cycle or half-cycle units of the AC power supply. Characterized in that the self-extinguishing elements constituting the first and second switching circuits are respectively turned on and off when the current becomes zero. To.

According to a second aspect of the present invention, in the induction heating power source of the first aspect, the resonance circuit is connected between an intermediate connection point of the inverter circuit and one end of an output of the smoothing circuit. I do.

According to a third aspect, in the induction heating power source according to the first aspect, the smoothing circuit is configured by connecting a plurality of capacitors in series, and an intermediate connection point of the inverter circuit and an intermediate potential point of the smoothing circuit. And the resonance circuit is connected between them.

According to a fourth aspect of the present invention, in the induction heating power supply of the first to third aspects, when the current of the resonance circuit becomes zero, each of the self-power-off circuits constituting the first and second switching circuits is turned off. Among the arc-shaped elements, control is performed to turn off an element that is on, and then to turn on an element that is off.

According to a fifth aspect of the present invention, there is provided an inverter circuit having a DC power supply as an input, and first and second switching circuits formed by connecting a diode and a self-extinguishing element in series to upper and lower arms, respectively. A resonance circuit comprising a heating coil to which high-frequency power is supplied from a circuit and a resonance capacitor, a diode connected in antiparallel to one of the upper and lower arms, and a self-extinguishing element are connected in series. A third switching circuit, wherein the self-extinguishing elements constituting the first to third switching circuits are turned on and off when the current of the resonance circuit becomes zero, respectively. Turn on the power.

According to a sixth aspect, in the induction heating power supply according to the fifth aspect, when the current of the resonance circuit becomes zero,
Among the self-extinguishing elements constituting the first to third switching circuits, the on-state element is turned off, and then the off-state element has a different current polarity with respect to the series resonance circuit. It is characterized in that control for turning on the element or one of the elements having different current polarities is performed.

According to a seventh aspect of the present invention, there is provided an inverter circuit having a DC power supply as an input, and first and second switching circuits formed by connecting a diode and a self-extinguishing element in series as upper and lower arms, respectively. A resonance circuit comprising a heating coil to which high-frequency power is supplied from the circuit and a resonance capacitor; and a third and third elements in which a diode anti-parallel to each of the upper and lower arms and a self-extinguishing element are connected in series. 4
A switching circuit, wherein the self-extinguishing elements constituting the first to fourth switching circuits are turned on and off when the current of the resonance circuit becomes zero. I do.

According to an eighth invention, in the induction heating power supply according to the seventh invention, when the current of the resonance circuit becomes zero,
Of the respective self-extinguishing elements constituting the first to fourth switching circuits, the on-state element is turned off, and then the off-state element has a different current polarity with respect to the series resonance circuit. It is characterized in that control for turning on any one element is performed.

According to the present invention, when the sinusoidal current flowing through the series resonance circuit becomes zero, the current of each of the self-extinguishing elements is switched, so that switching noise generated from the elements is suppressed. can do.

When a plurality of induction heating power supplies are installed in the same AC power supply, the pan is heated by adjusting the resonance frequency of each series resonance circuit by the capacitance value of a resonance capacitor. Even if the heating power injected through the coil is adjusted, the frequency of the heating power at this time substantially maintains a value based on the adjusted resonance frequency.
The above-mentioned audible frequency noise can be suppressed.

[0026]

FIG. 1 is a diagram showing a main circuit configuration of an induction heating power supply according to a first embodiment of the present invention. Components having the same functions as those of the conventional circuit shown in FIG. And a duplicate description will be omitted.

That is, in the circuit configuration shown in FIG. 1, a triac 11 that forms a semiconductor AC switch circuit is provided on a path from the AC power supply 1 to the diode rectifier circuit 2,
Diodes 12a and IGBT 12b as first switching circuits forming the upper arm, and diodes 12c and IG as second switching circuits forming the lower arm
An inverter circuit 12 including a BT 12d and a control circuit 13 for controlling the ignition of the triac 11 and the gate of the IGBTs 12b and 12d are provided. The diodes 12a and 12c are connected in series with an IGB
It is provided to prevent application of a reverse voltage to T12b and 12d.

The operation of the induction heating power supply shown in FIG. 1 will be described below with reference to the waveform diagrams shown in FIGS.

First, the triac 11 is provided for adjusting the heating power injected into the pot 7 via the heating coil 6, and the heating power is set to a rated value as shown in FIG. At times, the voltage of the AC power supply 1 is directly input to the diode rectifier circuit 2 by the ignition control of the triac 11 in the gate drive circuit not shown in FIG. 1, and as a result, the rated DC voltage smoothed by the capacitor 3 is supplied to the inverter circuit 12. Is entered. FIG.
As shown in (b), for example, the heating power is about 1 of the rated value.
When the voltage is set to / 2, conduction (solid waveform in FIG. 2B) and non-conduction (solid line in FIG. 2B) are performed every cycle of the AC power supply 1 by firing control of the triac 11 in the gate drive circuit. As a result, the input voltage to the inverter circuit 12 via the diode rectifier circuit 2 and the capacitor 3 becomes approximately の of the rated DC voltage. Further, as shown in FIG. 2C, for example, when the heating power is set to about 1/3 of the rated value, the ignition control of the triac 11 in the gate drive circuit causes the AC power supply 1 to be turned on for half a cycle. (The solid-line waveform in FIG. 2C) and the one-cycle non-conduction of the AC power supply 1 (the broken-line waveform in FIG. 2C). As a result, the input voltage to the inverter circuit 12 via the diode rectifier circuit 2 and the capacitor 3 becomes about 1/3 of the rated DC voltage.

Here, the firing control of the triac 11 is as follows.
Voltage detection circuit 13b of control circuit 13 for monitoring power supply voltage
By detecting the time point at which the power supply voltage becomes zero, the triac 11 is supplied with an ON signal by the gate drive circuit 13a at this time point, whereby the current can be turned on at zero. The triac 11 is turned off when the current automatically becomes zero due to the characteristics of the element.

The firing control of the triac 11 can also be performed by detecting the voltage across the triac 11.

Next, the inverter circuit 12 determines the period of the resonance frequency of the series resonance circuit (from time t ₀ to time t shown in FIG. 3).
₁ and performs the inverter operation based on a sum) between the time t ₃ ~ time t _4, the time t ₀ at Given an ON signal to IGBT12b by the inverter control circuit (not shown) in FIG. 1 (FIG. 3 (b) see) The current of the heating coil 6 is shown in FIG.
Rising sinusoidally as shown in (c), then the current of the heating coil 6 at time t ₁ becomes zero.

[0033] At time t ₂ that some time from time t ₁ of the above has elapsed, by the inverter control circuit IGBT1
2b to give off signals (see FIG. 3 (b)), given a slight ON signal IGBT12d confirmation timed at time t ₃ when passed (see FIG. 3 (b)), the current of the heating coil 6 3 falls sinusoidally as shown in (c), then the current of the heating coil 6 at time t ₄ becomes zero.

[0034] At time t ₅ a slight time from time t ₄ of the aforementioned has elapsed, by the inverter control circuit IGBT1
2d to give off signals (see FIG. 3 (b)), given a slight ON signal IGBT12b confirmation timed at time t ₆ has elapsed (see FIG. 3 (b)), the current of the heating coil 6 3 It rises in a sine wave shape as shown in (c).

That is, when the sinusoidal current flowing through the series resonance circuit becomes zero, the IGBTs 12b, 12b
d Since each current is switched, these IGBTs
The switching noise generated from the above can be suppressed.

Here, the IGBTs 12b and 12d are turned on,
The off control is performed as follows.

That is, since the voltage stored in the capacitor 5 of the resonance circuit is maintained without discharging by the diodes 12a and 12c, no current flows. Therefore, the gate control circuit 13c of the control circuit 13 is longer than the resonance frequency.
When the IGBT is turned on, the resonance current between the heating coil 6 and the resonance capacitor 5 becomes zero, and the voltage is stored in the resonance capacitor 5. If the IGBT is turned off at this point, the IGBT can be turned off when the current becomes zero. Thereafter, by turning on the other off IGBT, the IGBT can be turned on when the current is zero.

Instead of turning the IGBT on and off at a period longer than the period of the resonance frequency as described above, the current of the heating coil 6 is monitored by CT or the like, and when the current becomes zero, the IGBT is turned off. Can be realized by turning on and off.

FIG. 4 is a diagram showing a main circuit configuration of an induction heating power supply according to a second embodiment of the present invention, in which components having the same functions as those of the embodiment shown in FIG. , Overlapping description will be omitted.

The circuit configuration shown in FIG. 4 is different from the circuit configuration shown in FIG. 1 in that a smoothing circuit composed of a reactor 21a and capacitors 21b and 21c having substantially the same capacitance is used instead of capacitor 3 as a smoothing circuit. 21
One end of the heating coil 6 is connected to the condenser 21b and the condenser 2
1c, that is, connected to the intermediate potential point of the smoothing circuit 21.

In the circuit configuration shown in FIG.
When either of b and 12d is turned on, the DC power from the AC power supply 1 is supplied to the series resonance circuit.
The current ripple rate from the AC power supply 1 can be improved as compared with the circuit configuration of FIG.

The operations of the triac 11 and the inverter circuit 12 are the same as those of the waveform diagrams shown in FIGS.

FIG. 5 is a diagram showing the main circuit configuration of an induction heating power supply according to a third embodiment of the present invention. Components having the same functions as those of the conventional circuit shown in FIG. , Overlapping description will be omitted.

That is, in the circuit configuration shown in FIG. 5, the diodes 31a and IGBT 31b as the first switching circuits forming the upper arm, and the second switching circuit forming the lower arm
Diode 31c as switching circuit, IGBT
And a diode 32a and an IGBT 32b as a third switching circuit 32 connected in antiparallel to the lower arm. The diodes 31a, 31c and 32a are provided to prevent application of a reverse voltage to the IGBTs 31b, 31d and 32b connected in series. Further, the second switching circuit and the third switching circuit form a semiconductor AC switch circuit.

The operation of the induction heating power supply shown in FIG.
This will be described below with reference to the waveform chart shown in FIG.

First, when the heating power injected into the pan 7 via the heating coil 6 is set to the rated value,
As shown in (A) of [A], the IGBT 31b is set at time t ₀ ,
It is turned on at the timing of t ₂ ,.
As shown in (b) of [A], the IGBT 31d is set at time t ₁ ,
When turned on at the timing of t ₃ ,..., a sinusoidal current flows through the series resonance circuit as shown in (d) of FIG. The IGBT 31b and the IGBT at this time are
The detailed timing of the ON signal of 31d is the same as the waveform diagram of the circuit of the first embodiment shown in FIG.

Next, when the heating power injected into the pan 7 via the heating coil 6 is set to a rated value or less,
The IGBT 31b is set to the time t as shown in FIG.
₀ is turned on at the timing, similarly, when turned on at time t ₁ the IGBT31d as shown in (b) of FIG. 6 (B), as shown in (d) of FIG. 6 (B), the time t ₀ until to time t ₂ Figure 6 [a] (d) a similar sinusoidal current flows in the series resonant circuit.

At time t ₂ , when an ON signal is given to the IGBT 31 b as shown in FIG.
As shown in (d), a sine-wave current flows through the series resonance circuit. At this time, since no DC power is supplied from the AC power supply 1, a part of the energy stored in the resonance capacitor , The amplitude of the sinusoidal current flowing through the series resonance circuit decreases.

At time t ₃ , when an ON signal is given to the IGBT 32 d as shown in FIG.
As shown in (d), a sinusoidal current flows through the series resonance circuit. However, since no DC power is supplied from the AC power supply 1 at this time, part of the energy stored in the resonance capacitor 5 is lost. It becomes the heating power to be injected into the pan 5, and as a result, the amplitude of the sinusoidal current flowing through the series resonance circuit is further reduced.

That is, during the period from time t ₁ to time t ₆ shown in FIG. 6B, since no DC power is supplied from the AC power supply 1 side, part of the energy stored in the resonance capacitor 5 is 5, and as a result, the amplitude of the sinusoidal current flowing in the series resonance circuit gradually decreases. During this time, the semiconductor AC switch circuit in which the IGBT 31d and the IGBT 32b alternately turn on.

That is, the adjustment of the heating power injected into the pan 7 via the heating coil 6 is performed by changing the ratio of the period during which the inverter circuit operates and the period during which the semiconductor AC switch circuit operates. Can be. The IGBT 31b, IGBT 31d, IG
The detailed timing of the ON signal of the BT 32b is the same as the waveform diagram of the circuit of the first embodiment shown in FIG.

FIG. 7 is a diagram showing the main circuit configuration of an induction heating power supply according to a fourth embodiment of the present invention. Components having the same functions as those of the embodiment shown in FIG. , Overlapping description will be omitted.

That is, the difference between the circuit configuration shown in FIG. 7 and the circuit configuration shown in FIG.
A third switching circuit 41 comprising a BT 41b is connected to the first switching circuit side;
The first switching circuit and the third switching circuit form a semiconductor AC switch circuit.

In the induction heating power supply shown in FIG.
The adjustment of the heating power injected through the heating coil 6
This can be performed by changing the ratio of the period during which the inverter circuit operates and the period during which the semiconductor AC switch circuit operates.

During the period in which the semiconductor AC switch circuit is operating, the series resonance circuit operates at a voltage obtained by subtracting the voltage of the capacitor 3 from the voltage of the resonance capacitor 5, so that the circuit shown in FIG. As compared with the configuration, the amplitude of the sinusoidal current flowing through the series resonance circuit decreases more quickly, and therefore, the adjustment of the heating power becomes easier.

FIG. 8 is a diagram showing a main circuit configuration of an induction heating power supply according to a fifth embodiment of the present invention. Components having the same functions as those of the conventional circuit shown in FIG. , Overlapping description will be omitted.

That is, in the induction heating power supply shown in FIG.
Instead of the inverter circuit 4 shown in FIG. 9, a power conversion circuit including a first switching circuit 51, a second switching circuit 52, a third switching circuit 53, and a fourth switching circuit 54 each having a diode and an IGBT connected in series is provided. Have.

As is clear from the circuit configuration shown in FIG. 8, in adjusting the heating power injected into the pan 7 via the heating coil 6, the functions described in the circuit configuration in FIG. 5 and the circuit configuration in FIG. Both of the described functions are possible, so that fine adjustment of the heating power is easier.

In the circuits shown in FIGS. 1, 5, 7 and 8, as a general configuration example, one end of the heating coil 6 is connected to the negative polarity side of the diode rectifier circuit 2. Although shown, one end of the heating coil 6 may be connected to the positive side of the diode rectifier circuit 2.

In the embodiment of the present invention, a single-phase AC power supply is used as the AC power supply, but a three-phase AC power supply may be used.

[0061]

According to the present invention, the induction heating power supply is operated on the basis of the point in time at which the sinusoidal current flowing in the series resonance circuit comprising the heating coil and the resonance capacitor becomes zero. The switching noise generated from the above can be suppressed.

Further, when a plurality of induction heating power supplies are installed in the same AC power supply, audible noise can be suppressed by adjusting the resonance frequency of each series resonance circuit.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main circuit of an induction heating power supply according to a first embodiment of the present invention;

FIG. 2 is a waveform chart illustrating the operation of FIG.

FIG. 3 is a waveform chart for explaining the operation of FIG. 1;

FIG. 4 is a main circuit configuration diagram of an induction heating power supply showing a second embodiment of the present invention.

FIG. 5 is a main circuit configuration diagram of an induction heating power supply showing a third embodiment of the present invention.

FIG. 6 is a waveform chart for explaining the operation of FIG. 5;

FIG. 7 is a main circuit configuration diagram of an induction heating power supply showing a fourth embodiment of the present invention.

FIG. 8 is a main circuit configuration diagram of an induction heating power supply showing a fifth embodiment of the present invention.

FIG. 9 is a main circuit configuration diagram of an induction heating power supply showing a conventional example.

FIG. 10 is a waveform chart for explaining the operation of FIG. 9;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... Diode rectifier circuit, 3 ... Capacitor, 4 ... Inverter circuit, 5 ... Resonant capacitor, 6 ...
Heating coil, 7 pan, 11 triac, 12 inverter circuit, 13 control circuit, 21 smoothing circuit, 31
Inverter circuit, 32, 41 ... third switching circuit,
51 to 54... First to fourth switching circuits.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshihiro Nomura 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-Terminal F-term (reference) 3K051 AA02 AC17 AC24 AC30 AC43 BD07 CD09 CD10 3K059 AA05 AA06 AA08 AA12 AA15 AB28 AC07 AD07 AD08 BD07 CD09 CD10 5H007 AA01 AA03 BB04 CA01 CB04 CB08 CB12 CB17 CB23 CC07 CC12 DA03 DB01 DC05

Claims (8)

[Claims] 1. A rectifier circuit for converting an AC power supply to a direct current, a smoothing circuit for smoothing an output of the rectifier circuit, an output voltage of the smoothing circuit as an input, and a diode and a self-extinguishing element connected in series. An inverter circuit having first and second switching circuits as upper and lower arms respectively; a resonance circuit including a heating coil to which high frequency power is supplied from the inverter circuit; and a resonance capacitor; And a semiconductor AC switch circuit installed in a path to the AC power supply, and controls opening and closing of the semiconductor AC switch circuit in units of one cycle or half cycle of the AC power supply, and when the current of the resonance circuit becomes zero, 1st, 2nd
An induction heating power supply characterized in that a self-extinguishing element constituting a switching circuit is turned on and off, respectively. 2. The induction heating power supply according to claim 1, wherein the resonance circuit is connected between an intermediate connection point of the inverter circuit and one end of an output of the smoothing circuit. Power supply. 3. The induction heating power supply according to claim 1, wherein the smoothing circuit is configured by connecting a plurality of capacitors in series, and between an intermediate connection point of the inverter circuit and an intermediate potential point of the smoothing circuit. An induction heating power supply, wherein the resonance circuit is connected to the induction heating power supply. 4. The induction heating power supply according to claim 1, wherein when the current of said resonance circuit becomes zero, the respective self-extinguishing of the first and second switching circuits is performed. An induction heating power supply characterized in that among the shaped elements, control is performed to turn off an element that is on and then turn on an element that is off. 5. An inverter circuit having a DC power supply as an input and first and second switching circuits each having an upper arm and a lower arm each having a diode and a self-extinguishing element connected in series; Circuit comprising a heating coil and a resonance capacitor, to which a voltage is supplied, and a diode and a self-extinguishing element connected in series to one of the upper and lower arms in anti-parallel. Wherein the self-turn-off devices constituting the first to third switching circuits are respectively turned on and off when the current of the resonance circuit becomes zero. 6. The induction heating power supply according to claim 5, wherein, when the current of the resonance circuit becomes zero, the self-extinguishing elements constituting each of the first to third switching circuits are provided. The element that is turned on is turned off, and thereafter, control is performed to turn on any one element having a different current polarity or a different current polarity with respect to the series resonance circuit from the element that has been turned off. Induction heating power supply. 7. An inverter circuit having a DC power supply as an input, and first and second switching circuits each having an upper and a lower arm formed by connecting a diode and a self-extinguishing element in series, respectively; A resonance circuit comprising a heating coil and a resonance capacitor supplied with a third and fourth switching circuits comprising a diode and a self-extinguishing element connected in series to each of the upper and lower arms. An induction heating power supply, comprising: turning on and off the self-extinguishing elements constituting the first to fourth switching circuits when the current of the resonance circuit becomes zero. 8. The induction heating power supply according to claim 7, wherein when the current of the resonance circuit becomes zero, the self-arc-extinguishing elements constituting each of the first to fourth switching circuits are provided. An induction heating power supply characterized in that a turned-on element is turned off, and thereafter, a control is performed to turn on any one element having a different current polarity in the series resonance circuit from the turned-off element.