JPH11135248A - Induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safe and simple-structured heating device which can prevent a switching element from destroying without requiring any protection circuit, by providing the switching element with a self short means for causing self short at both ends' voltage over a given value. SOLUTION: A chock coil 12 is connected with a direct current power 11 in series, and its inductance is set to be less than 1 mH, for example, 300 μH. A resonance capacitor 16 is connected with a heating coil 15 in series, and these two components form a resonance circuit 20. A control circuit 17 including an oscillating circuit 19 controls a switching element 13. A self short means 18 provide the switching element with self short when voltage on the both sides of the switching element 13 becomes more than a given value (concretely, it is higher than a voltage generated during normal operation, and is lower than a withstand voltage of the switching element 13). Thus, loss of the switching element 13 is reduced, and even during abnormal time, withstand voltage destroy of the switching element 13 is prevented.

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 such as an induction heating cooker used in ordinary households and restaurants, and more particularly to an inverter circuit configuration and a control method thereof.

[0002]

2. Description of the Related Art A conventional inverter circuit configuration and control method of an induction heating apparatus will be described with reference to FIGS.

FIG. 19 shows a basic circuit of an inverter of an induction heating device. Reference numeral 1 denotes a DC power supply, which is obtained from a commercial AC power supply via a rectifier. Reference numeral 2 denotes a heating coil, on which an object to be heated is placed.
Induction heating is performed by a high-frequency magnetic field from the heating coil 2.
3 is a resonance capacitor connected in parallel with the heating coil 2;
Is a switching element.
A high frequency current is supplied to the heating coil. The switching element 4 uses an IGBT that requires much less driving power than a bipolar transistor or the like, and has a withstand voltage of 900 V and a current rating of 60 A. Reference numeral 5 denotes a reverse conducting diode connected in parallel to the switching element 4, and reference numeral 6 denotes a control circuit that detects a collector-emitter voltage of the switching element 4 and controls on / off of the switching element 4.

FIG. 20 is a diagram showing waveforms at various points during the operation of the inverter of FIG. (A) is a drive signal of the switching element 4 output from the control circuit 6, which is HIGH.
At this time, the switching element 4 is turned on. (A) shows the current flowing through the switching element 4 and the reverse conducting diode 5. (C) is a voltage generated between the collector and the emitter of the switching element 4.

FIG. 21 is an enlarged view of the collector current and the collector-emitter voltage during the period when the switching element 4 changes from on to off (ie, at the time of turning off) in the operation waveform of FIG. In the figure, the tail current is a phenomenon peculiar to the IGBT. The lower the switching speed of the element, the longer the generation period. The temperature characteristic of the tail current is positive, and the higher the temperature of the switching element, the longer the generation period and the greater the loss.

As described above, the loss of the switching element 4 caused by the operation of the present inverter includes the conduction loss generated during the HIGH period of the drive signal in FIG. 20 and the conduction loss in FIG.
, Ie, turn-off loss.

[0007] The conduction loss is determined by the product of the collector current of the switching element 4 and the on-voltage correlated with the collector current. In general, the loss temperature characteristic of the conduction loss is almost flat or negative depending on the performance of the switching element.

In the present inverter, the switching element 4
Is turned on and off at a frequency of about 20 kHz to 30 kHz, and the generated loss depends on the element performance.
It is about 40W. Further, the ratio of the turn-off loss to the generated loss depends on the operating frequency, but is approximately 30 to 50.
%. Since the generated loss is large, the switching element 4 is attached to a heat sink and is forcibly cooled by a cooling fan.

[0009]

However, the conventional induction heating apparatus has the following problems.

A first problem is that since the cooling fan is driven at the time of operation, the noise is large and the user feels uncomfortable. This noise is a problem particularly when the user surrounds and uses a cooking device such as a pan. In the case of application to a rice cooker, when the timer rice cooker or the like is operated in the early morning or late at night, the noise similarly gives a user discomfort. This problem is not a general electric heater type or a cooking device such as a gas stove, and is therefore a serious problem unique to an induction heating device. In addition, the temperature characteristic of the turn-off loss is dominant in the temperature characteristic of the entire loss, and when the element temperature of the switching element 4 increases, the loss also increases. Therefore, the design of the forced air cooling by the fan needs to be sufficiently studied. There is also a problem with development man-hours.

The second problem is that if the control of the element deviates from a predetermined timing due to some abnormality (power supply abnormality such as instantaneous power failure or lightning surge or external noise), a voltage higher than the withstand voltage of the switching element 4 is obtained. Is likely to occur. Generally, the switching element 4 is immediately destroyed when a voltage higher than the withstand voltage is applied.
Although not particularly shown in the figure, a protection circuit that detects the voltage between both ends of the switching element 4 and the input voltage and immediately stops oscillation when an abnormality occurs is required. This protection circuit includes an inverter constant (heating coil 2 and resonance capacitor 3).
(Electrical constants such as electrical constants) (because the waveform of the collector-emitter voltage during normal operation differs depending on the inverter constant), it is necessary to review the circuit constants for each development of various induction heating devices. This is one of the bottlenecks in the development man-hour.

The present invention solves the above-mentioned conventional problems, and realizes a safe induction heating device with a simple structure capable of sufficiently reducing the noise of a cooling fan and preventing the switching element from being destroyed even though the protection circuit is unnecessary. It is intended to do so.

[0013]

In order to solve the above problems, the present invention provides a DC power supply, a choke coil, a self-extinguishing type switching element, and a reverse conducting diode connected in parallel to the switching element. And a control circuit including an oscillation circuit that generates an on / off signal for the switching element. The choke coil has an inductance of about 1 mH.
In the following, the DC power supply and the choke coil are connected in series, the other end of the choke coil and the other end of the DC power supply are connected in parallel to the switching element and the resonance circuit, and the switching element Is an induction heating device having self-shortening means for self-shortening when the voltage across the terminals is equal to or higher than a predetermined value.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is characterized in that a DC power supply, a choke coil, a self-extinguishing type switching element, a reverse conducting diode connected in parallel to the switching element, a heating coil and a resonance coil. A control circuit including an oscillation circuit that generates an on / off signal for the switching element, wherein the inductance of the choke coil is approximately 1 mH or less, and the DC power supply and the choke coil are connected in series The other end of the choke coil and the other end of the DC power supply are connected in parallel to the switching element and the resonance circuit, and the switching element self-short-circuits when a voltage at both ends is equal to or more than a predetermined value. The induction heating device has a short circuit means. With this configuration, the current flowing through the switching element has a resonance waveform, and turns off while the current is zero or flows through the reverse conducting diode, so that no turn-off loss occurs as a loss of the switching element.
Only conduction loss occurs, and the loss of the switching element can be significantly reduced. Furthermore, since there is no turn-off loss, the loss temperature characteristic becomes almost flat or negative, and an inverter circuit which is extremely stable thermally and can be easily designed for cooling can be obtained. In addition, by setting the above predetermined value lower than the withstand voltage of the switching element, even if a voltage exceeding the withstand voltage of the element is generated due to some abnormality, the switching element itself is short-circuited (self-clamped) and destroyed. Therefore, the protection by the external circuit (the protection operation of detecting the abnormality by the external circuit and turning off the switching element) which is conventionally required is not required.

The invention according to claim 2 is particularly configured such that the switching element is a voltage-driven element such as an IGBT, and a zener diode and a diode connected in series between the collector and the gate are inserted. With this configuration, the clamp voltage of the Zener diode can be reduced by IGB
If it is designed to be lower than the withstand voltage of T, the above-mentioned self-shortening operation can be achieved with extremely few components.

According to a third aspect of the present invention, in particular, the switching element is a voltage-driven element such as an IGBT, and a gate is supplied with a voltage obtained by dividing the voltage between both ends of the switching element by resistance. By designing the resistance division value to be equal to or lower than the threshold voltage and equal to or higher than the withstand voltage of the switching element and equal to or higher than the threshold voltage, the self-short-circuit operation can be realized with extremely few components and at a lower cost than the configuration according to claim 2. can do.

According to a fourth aspect of the present invention, in particular, the configuration is such that a self-short circuit is provided through a drive circuit of the switching element, so that the configuration is inexpensive as compared with the configuration of the second aspect, and compared with the configuration of the third aspect. In addition, since the gate voltage can be sufficiently reduced during the normal operation (at the time of off-state), it is possible to realize an induction heating device that does not need to perform a design related to a difference in threshold voltage of the switching element.

According to the fifth aspect of the present invention, an IGBT is used as a switching element, and an element having a low on-voltage and a low switching speed is selected and provided among variations in switching speed and on-voltage trade-off of the IGBT. With this configuration, the loss at the time of conduction is lower than the general range of variation (because the on-state voltage is low), and as a result, it is possible to realize an induction heating device in which required cooling can be greatly eased.

According to a sixth aspect of the present invention, a voltage-driven thyristor operating element such as an MCT is used as a switching element, and the loss can be further reduced as compared with the fifth aspect. .

The invention according to claim 7 is particularly configured so that the off state is continued for a predetermined time after the recovery from the self-short circuit. With this configuration, it is possible to prevent thermal destruction of the switching element due to continuous self-short circuit.

According to an eighth aspect of the present invention, after the self-short circuit is recovered, the off state is continued for a predetermined time regardless of the on / off signal of the oscillation circuit. With this configuration, it is possible to prevent the switching element from being destroyed even when the ON / OFF signal of the oscillation circuit is abnormal due to some abnormality.

According to a ninth aspect of the present invention, in particular, the off state is continued for a predetermined time after the recovery from the self-short circuit, and the oscillation state is set after the predetermined time. When the operation of the self-short circuit continues for a predetermined number of times due to the occurrence of the above-mentioned voltage, the circuit is turned off for the predetermined time or longer. This configuration makes it possible to reduce unnecessary oscillations, for example, when the object to be heated by induction heating is in an abnormal state,
As a result, the loss of the switching element can be reduced.

According to the present invention, in particular, the off state is continued for a predetermined time after the recovery from the self-short circuit, and the oscillation state is set after the predetermined time. When the voltage of 発 生 自己 発 生 自己 自己 短 絡 自己 所 定 自己 自己 と な り オ フ 自己 自己 自己 自己 自己 自己 自己 自己 自己 自己 自己 自己 自己 所 定 所 定 所 定 所 定 所 定 所 定 所 定 所 定 所 定 所 定. With this configuration, the user can be notified of the state of the load abnormality.

[0024]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described. FIG. 1 is a diagram showing a first embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a DC power supply, specifically, a commercial AC power supply is obtained via a rectifier. Reference numeral 12 denotes a choke coil connected in series to the DC power supply 11, the inductance of which is 300 μH in this embodiment.
A switching element 13 is connected in parallel with the reverse conducting diode 14. Reference numeral 15 denotes a heating coil, though not particularly shown in the figure, on which an object to be heated such as a pot is placed. Reference numeral 16 denotes a resonance capacitor, and the heating coil 1
5, and a resonance circuit is formed by these two components. Reference numeral 17 denotes a control circuit including an oscillation circuit, which controls the switching element 13. Numeral 18 denotes a self-shortening means. The voltage at both ends of the switching element 13 is higher than a predetermined value (specifically, higher than a voltage generated during normal operation.
The switching element 13 self-short-circuits when the voltage becomes equal to or higher than the withstand voltage of the switching element 13).

FIG. 2 shows a drive signal of the switching element 13 and a current (Ic) voltage (Vce) waveform during normal operation. In the figure, the switching element is turned on when the drive signal is HIGH and turned off when the drive signal is LOW. As shown in FIG. 2A, the current waveform becomes a resonance waveform by adopting the present inverter circuit configuration, and the current flowing through the switching element 13 is zero or the current is turned off while the current is flowing through the reverse conducting diode 14. In addition, the conventional turn-off loss does not occur, and the loss can be significantly reduced.

FIG. 3 shows the drive signal of the switching element 13 and the current (Ic) voltage (Vce) waveform when the on / off timing of the switching element 13 is deviated due to some abnormal cause and a surge voltage is generated in the switching element 13.

As shown in the figure, when the switching element 13 is turned off while a current is flowing through the switching element 13, a very high surge voltage is generated in the voltage across the switching element 13. In the value, the switching element 13 is not short-circuited by itself and does not exceed the withstand voltage of the switching element 13.

FIG. 4 shows the switching element 1 during a self-short circuit.
When the voltage across the switching element 13 exceeds a predetermined value due to the self-shortening means 18 in the enlarged waveform of the drive signal 3, the current (Ic) voltage (Vce) and the drive terminal voltage (Vge),
The drive terminal voltage rises and exceeds the threshold voltage of the switching element 13 to cause a self-short circuit.

As is apparent from the above description, according to the first embodiment, an induction heating apparatus which can reduce the loss of the switching element 13 with a simple configuration and has no breakdown voltage of the switching element 13 even in an abnormal condition. Obtainable.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described. FIG. 5 is a view showing a second embodiment of the present invention. In FIG. 2, reference numeral 21 denotes a self-shortening means 18 according to the first embodiment, in which a Zener diode and a diode connected in series are inserted between the collector and the gate of the switching element 13. The switching element 13 uses an IGBT as a voltage control type element. Other parts are the same as in the first embodiment. The clamp voltage of the Zener diode has the same predetermined value as in the first embodiment. The operation of this embodiment is the same as the operation of the first embodiment. As described above, the self-shortening means 18 can be realized with an extremely simple component configuration.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described. FIG. 6 is a diagram showing a third embodiment of the present invention. In FIG. 3, reference numeral 22 denotes the switching element 1
3 is divided by a resistor, and the divided voltage is supplied to the gate of the switching element 13 to realize the self-shortening means 18 of the first embodiment. The switching element 13 uses an IGBT as a voltage control type element. Other parts are the same as in the first embodiment. As in the first embodiment, the voltage divided by the resistance is the switching element 1 during the normal operation.
3 and the switching element 1
It is designed to have a value less than the withstand voltage of 3 and more than the threshold voltage. FIG. 7 shows a drive signal of the switching element 13 at the time of self-short circuit, a current (Ic) voltage (Vce), and a drive terminal voltage (V
Ge) is an enlarged waveform. The operation of this embodiment is almost the same as that of the first embodiment, but the driving terminal voltage waveform (Vge) at the time of self-short circuit is slightly different due to resistance division.
As described above, the self-shortening means 18 can be realized with an extremely simple component configuration, and can be realized with only the resistance as compared with the second embodiment, so that the cost is low.

(Embodiment 4) Hereinafter, a fourth embodiment of the present invention will be described. FIG. 8 is a diagram showing a fourth embodiment of the present invention. In FIG. 8, reference numeral 23 denotes a voltage detection circuit for both ends of the switching element 13, and reference numeral 24 denotes a driving circuit for the switching element 13. The both-ends voltage detection circuit 23 is configured to self-short-circuit the switching element 13 via the drive circuit 24 when a voltage equal to or higher than a predetermined value is generated.
The switching element 13 is a voltage control type element,
BT is used. Other parts are the same as in the first embodiment. FIG. 9 is an enlarged waveform of the drive signal of the switching element 13, the current (Ic) voltage (Vce), and the drive terminal voltage (Vge) at the time of self-short circuit. The drive circuit 24 does not have a steep drive terminal voltage waveform, but has a gentle waveform as shown in FIG. 9 because the limiting resistance for limiting the turn-on and turn-off of the switching element 13 is sufficiently large.
The operation of this embodiment is almost the same as the operation of the first embodiment. As described above, the configuration is inexpensive as compared with the second embodiment (the voltage detection circuit at both ends is possible with simple components such as a resistor and a transistor), and the switching element is compared with the third embodiment. Therefore, it is not necessary to design the thirteenth threshold voltage.

(Embodiment 5) Hereinafter, a fifth embodiment of the present invention will be described. FIG. 1 is a diagram showing a fifth embodiment of the present invention. In FIG. 1, the switching element 13 is an IGBT, and the element performance selection method of the IGBT is shown in FIG.
0 is shown. FIG. 10 shows a trade-off curve between the switching speed and the on-voltage variation of a general IGBT. As shown in the figure, the on-voltage is high when the switching speed is high and the on-voltage is low when the switching speed is low. In the case of the present embodiment, the selection range is such that the ON voltage is low and the switching speed is low. In this embodiment, the loss mode of the switching element 13 is only conduction loss, and the conduction loss is correlated with the ON voltage. Therefore, by this selection, it is possible to easily obtain an induction heating device having a lower loss than normal variation. Become. In the induction heating device having the conventional configuration, when this embodiment is selected, the turn-off loss becomes large and the device becomes thermally unstable. However, in this embodiment, there is no turn-off loss and the switching element 13 This selection is optimal for the present embodiment, since the lower the switching speed is, the smaller the surge voltage becomes, even when the current is erroneously interrupted when a current is flowing through the current.

(Embodiment 6) Hereinafter, a sixth embodiment of the present invention will be described. FIG. 11 is a diagram showing a sixth embodiment of the present invention. In FIG. 11, the switching element 2
Reference numeral 5 uses a voltage-driven thyristor operating element such as an MCT. Other parts are the same as in the first embodiment. In general, these devices have a property that the ON voltage is lower than that of the IGBT, but the switching speed is lower than that of the IGBT. However, in this embodiment, as described in the fifth embodiment, In addition, extremely low loss can be achieved, and the surge voltage can be reduced. As described above, according to the present embodiment, it is possible to obtain an induction heating device having lower loss than that of the fifth embodiment.

(Embodiment 7) Hereinafter, a seventh embodiment of the present invention will be described. FIG. 12 is a diagram showing a seventh embodiment of the present invention. In FIG. 12, 26 is a drive circuit for driving the switching element 13, and 27 is an oscillation circuit having a drive terminal voltage detection circuit for the switching element 13 and a time measuring means. Other parts are the same as in the first embodiment.

FIG. 13 shows a drive signal and a current (Ic) voltage (Vce) waveform of the switching element 13 when a surge voltage occurs in the switching element 13 due to some abnormality. When a surge voltage is generated, the drive terminal voltage of the switching element 13 becomes higher than the threshold voltage despite that the oscillation circuit outputs an off signal.
7 detects the voltage and stops the next transmission signal for a predetermined time set in the timer. The reason why the predetermined time is provided is that the switching element 13 causes an instantaneous loss due to the self-short circuit, and the junction temperature increases transiently. 13 is to be protected.
Therefore, the design of the predetermined time is a guideline from the rise of the junction temperature due to the self-shortening of the switching element 13 to the return to the steady state.
About 0 ms is sufficient. According to the above operation, even in a mode in which a surge voltage may continuously occur, such as in the case of a power supply abnormality, the switching element 13 can be prevented from being destroyed by only one self-short circuit.

Embodiment 8 Hereinafter, an eighth embodiment of the present invention will be described. FIG. 14 shows an eighth embodiment of the present invention. In FIG. 14, 28 is an oscillation circuit, 2
Reference numeral 9 denotes a driving circuit for driving the switching element 13, and reference numeral 30 denotes a protection circuit which detects a driving terminal voltage of the switching element 13 and lowers the driving terminal voltage to LOW for a predetermined time. Other parts are the same as in the first embodiment.

FIG. 15 shows a drive signal and a current (Ic) voltage (Vce) drive terminal voltage (Vge) waveform of the switching element 13 when a surge voltage occurs in the switching element 13 due to some abnormality. When a surge voltage is generated, the drive terminal voltage of the switching element 13 becomes equal to or higher than the threshold voltage despite the fact that the oscillation circuit outputs an OFF signal. For a set predetermined time, the drive terminal voltage of the switching element 13 is reduced to LOW regardless of the presence or absence of a drive signal from the oscillation circuit side. The reason for providing the predetermined time is that the switching element 13 instantaneously has a large loss due to a self-short circuit, and the junction temperature transiently increases.
This is for protecting the switching element 13. Therefore, when designing the predetermined time, the time from when the switching temperature of the switching element 13 rises due to the self-short circuit to when the switching element 13 returns to the steady state becomes a standard, and generally about several ms to several hundred ms is sufficient. With the above operation, in addition to the mode in which a surge voltage may continuously occur, such as when there is a power failure, the self-shortening of the switching element 13 can be performed even if the operation of the oscillation circuit temporarily becomes improper for some reason. Is required only once to prevent the switching element 13 from being destroyed.

Embodiment 9 Hereinafter, a ninth embodiment of the present invention will be described. FIG. 16 shows the ninth embodiment of the present invention. In FIG. 16, reference numeral 31 denotes a protection circuit, the operation of which is the same as that described in the eighth embodiment. 32 is a drive circuit for driving the switching element 13, 33 is an oscillation circuit for detecting the protection operation of the protection circuit 31, and 34 is a counting means for counting the number of protection operations of the protection circuit 31. Other parts are the same as in the first embodiment. FIG.
Reference numeral 7 denotes a drive signal of the switching element 13 and a current (Ic) voltage (Vce) waveform when the object to be heated is in the above state such as a no-load state.

In the case of the waveform shown in FIG. 17, since a surge voltage is continuously generated, it is possible to detect a load abnormality on the circuit side. Specifically, the protection operation of the protection circuit 31 is counted by the counting means 34, and when the count reaches a predetermined number or more, the oscillation circuit 33 stops the oscillation for a sufficiently long time. As described above, the unnecessary oscillation can be easily reduced on the circuit side when the heating operation is unnecessary such as when there is no load.

Embodiment 10 Hereinafter, a tenth embodiment of the present invention will be described. FIG. 18 shows the tenth embodiment of the present invention. In FIG. 18, reference numeral 35 denotes a notifying unit for notifying a load abnormality to the outside. In the present embodiment, an LED is turned on to inform a user of the load abnormality. Other parts are the same as in the ninth embodiment. As described in the ninth embodiment, when the protection circuit 31 enters a mode in which the protection operation continues for a predetermined number of times or more, the oscillation circuit 33 stops oscillating for a sufficiently long time. Notifies an abnormality. As described above, the user can immediately know the abnormal load condition.

[0042]

As described above, according to the first aspect of the present invention, the current flowing through the switching element has a resonance waveform,
Since the cutoff is performed at zero current, a turn-off loss does not occur, and an extremely low-loss and thermally stable induction heating device can be obtained with a simple configuration. Also, even when a voltage exceeding the withstand voltage is generated in the switching element due to power supply abnormality, oscillation abnormality, etc., the switching element itself is short-circuited to prevent destruction. In addition, a protection circuit with a large number of development steps for stopping oscillation is not required. In this type of current resonance inverter, generally, the inductance of the choke coil is made sufficiently large (1 mH or more) so that sufficient diode current always flows (escapes from generation of surge voltage as much as possible, or switches thyristors, etc.). However, in this configuration, the self-extinguishing type switching element is used, and the self-short-circuit protection is provided, so that the inductance of the choke coil is small. As a result, the cost can be reduced and the heat generation of the choke coil can be suppressed. Further, in this type of current resonance inverter, there is an example in which a surge absorption is performed using a CR snubber or the like to protect the surge voltage. However, in this configuration, it is needless to say that the snubber circuit cost is not required. And heat generation need not be considered.

According to the second aspect of the present invention, the self-short-circuit operation according to the first aspect can be simply and reliably performed by the two components of the zener diode and the diode.

According to the third aspect of the present invention, the self-short-circuiting operation according to the first aspect can be performed by using only a resistor, which is less expensive than the configuration according to the second aspect.

According to the fourth aspect of the present invention, the self-shortening operation of the first aspect is performed through a drive circuit of the switching element, so that the operation is less expensive than the second aspect, and This can be realized with a simpler design than that of the above configuration.

According to the fifth aspect of the present invention, an IGBT having a low on-voltage and a low switching speed is selected and used as the switching element of the first aspect. It is possible to obtain.

According to the sixth aspect of the present invention, the switching element according to the first aspect has an ON voltage of the fifth aspect.
Since a voltage-driven thyristor operating element lower than the switching element described above is used, an induction heating device with a lower loss than the invention of claim 5 can be obtained. In an induction heating device having a conventional inverter configuration, this type of element tends to have a larger loss than an IGBT even when used, due to the problem of a low switching speed. Since the IGBT is superior to the IGBT on both sides of the surge voltage, the effect used in this configuration is extremely large.

According to the seventh aspect of the present invention, the oscillation is stopped for a predetermined time after the switching element self-short-circuits. Therefore, even when a power supply abnormality such as a lightning surge causes a continuous surge voltage, the switching element is not used. It does not cause thermal destruction.

According to the eighth aspect of the present invention, the switching element is stopped for a predetermined time after the self-short circuit regardless of the presence or absence of a drive signal from the oscillation circuit. Even in the case of an abnormal drive signal, it is possible to prevent the switching element from being destroyed.

Further, according to the ninth aspect of the present invention, it is possible to detect an abnormal load condition such as a no-load condition on the circuit side and prevent unnecessary oscillation from continuing.

According to the tenth aspect of the present invention, in addition to the effect of the ninth aspect, it is possible to immediately notify a user or the like of an abnormal load condition.

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram in the same normal operation.

FIG. 3 is an operation waveform diagram at the time of an abnormality.

FIG. 4 is a waveform chart showing a protection operation at the time of abnormality.

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

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

FIG. 7 is a waveform chart showing a protection operation at the time of abnormality.

FIG. 8 is a circuit configuration diagram of an induction heating apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a waveform diagram showing a protection operation at the time of abnormality.

FIG. 10 is a diagram showing a selection range of a switching element of an induction heating device according to a fifth embodiment of the present invention.

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

FIG. 12 is a circuit configuration diagram of an induction heating apparatus according to a seventh embodiment of the present invention.

FIG. 13 is a waveform chart showing a protection operation at the time of abnormality.

FIG. 14 is a circuit diagram of an induction heating apparatus according to an eighth embodiment of the present invention.

FIG. 15 is a waveform chart showing a protection operation at the time of an abnormality.

FIG. 16 is a circuit configuration diagram of an induction heating apparatus according to a ninth embodiment of the present invention.

FIG. 17 is an operation waveform diagram at the time of an abnormality.

FIG. 18 is a circuit configuration diagram of an induction heating apparatus according to a tenth embodiment of the present invention.

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

FIG. 20 is an operation waveform diagram of the same.

FIG. 21 is an operation waveform diagram when the switching element is turned off.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 DC power supply 12 Choke coil 13 Switching element 14 Reverse conduction diode 15 Heating coil 16 Resonant capacitor 17 Control circuit 18 Self-short circuit means 19 Oscillation circuit 20 Resonance circuit 21 Zener diode and diode 22 Resistance 23 Both ends voltage detection circuit 24 Drive circuit 25 Voltage drive Type thyristor operating element

Claims (10)

[Claims] 1. A DC power supply, a choke coil, a self-extinguishing type switching element, a reverse conducting diode connected in parallel to the switching element, a resonance circuit including a heating coil and a resonance capacitor, and the switching element. And a control circuit including an oscillation circuit for generating an on / off signal of the choke coil.
In the following, the DC power supply and the choke coil are connected in series, the other end of the choke coil and the other end of the DC power supply are connected in parallel to the switching element and the resonance circuit, and the switching element Is an induction heating device having self-shortening means for self-shortening when a voltage across the terminals is equal to or higher than a predetermined value. 2. The switching element is a voltage-driven element, and a zener diode and a diode connected in series are inserted between the collector and the gate.
An induction heating device as described. 3. The induction heating apparatus according to claim 1, wherein the switching element is a voltage-driven element, and a voltage obtained by dividing a voltage between both ends of the switching element is applied to a gate. 4. A switching element drive circuit, and a switching element voltage detection circuit, wherein when the voltage across the switching element is equal to or higher than a predetermined value, the switching element self-short-circuits via the drive circuit. Item 7. An induction heating device according to Item 1. 5. The switching element is an IGBT, and the switching element is an IGBT.
2. The induction heating apparatus according to claim 1, wherein an element having a low on-voltage and a low switching speed is selected and provided in the BT switching speed and on-voltage trade-off variation. 6. The induction heating apparatus according to claim 1, wherein the switching element is a voltage-driven thyristor operating element. 7. The switching element, after returning from a self-short circuit,
The induction heating device according to claim 1, wherein the off-state is continued for a predetermined time. 8. The switching element, after recovery from self-short circuit,
2. The induction heating apparatus according to claim 1, wherein the OFF state is maintained for a predetermined time regardless of an ON / OFF signal of the oscillation circuit. 9. The switching element, after recovery from self-short circuit,
When the off state is continued for a predetermined time and the oscillation state is further set after the predetermined time, a voltage equal to or higher than a predetermined value is generated again at both ends of the switching element due to the oscillation, and the operation of self-short circuit continues for a predetermined number of times. 2. The induction heating device according to claim 1, wherein the device is turned off for the predetermined time or longer. 10. The switching element continues to be in an off state for a predetermined time after recovery from the self-short circuit, and further enters an oscillation state after the predetermined time. By the oscillation, a voltage equal to or higher than a predetermined value is generated again at both ends of the switching element. 2. The induction heating apparatus according to claim 1, wherein when the operation of self-short circuit continues for a predetermined number of times, the power supply is turned off for the predetermined time or more, and a load abnormality is notified.