JPH05299167A - Induction-heated cooking apparatus - Google Patents

Abstract

PURPOSE:To prevent an excessive current applied to a switching element by detecting the voltage when the switching element is turned on so that this voltage does not exceed a preset value. CONSTITUTION:An induction-heated cooking apparatus is provided with a turn-on voltage detecting circuit 9 detecting the voltage when a switching element 5 is turned on and an oscillation control circuit 10 controlling the on/off- oscillation of the switching element 5 so that the input power from an AC power source 1 is made a value set by a user within the range that the voltage detected by the turn-on voltage detecting circuit 9 does not exceed a preset value when the switching element 5 is turned on. A spike-like steep current applied when the input power is small or the excessive switching loss can be 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 cooker used in general households.

[0002]

2. Description of the Related Art In recent years, induction heating cookers have come into wide use in general households because of their excellent features such as safety, cleanliness and high efficiency.

A conventional induction heating cooker will be described below. FIG. 4 is a circuit block diagram of a conventional induction heating cooker. As shown in the figure, the AC power supply 1 includes a heating coil 4 that is magnetically coupled to a load pan 3 that is a load via a rectifier circuit 2 that converts the AC power supply 1 into DC, and this heating coil 4
It is connected to the switching element 5 that oscillates on and off. Further, the heating coil 4 has a resonance capacitor 6 connected in parallel. An input power detection circuit 7 detects the input power from the AC power supply 1. The oscillation control circuit 8 inputs a signal from the input power detection circuit 7 so that the input power reaches a value set by the user. It is designed to control the on / off oscillation of the.

The operation of the induction heating cooker configured as described above will be described with reference to FIG. In the figure, the load pan 3 is an enamel pan, and the waveforms of the current (isw) and voltage (vsw) applied to the switching element 5 at this time are shown in FIG.
(A) shows the switching element 5 when the input power is large.
The waveforms of the current and voltage applied to are shown. Also in FIG.
(B) shows the switching element 5 when the input power is small.
The waveforms of the current and voltage applied to are shown. Figure 5
As can be seen from (a), when the input power is large, the switching element voltage when the switching element 5 is turned on has a large amplitude of resonance, so the switching element 5 is turned on at a timing of zero volt or less, and low-loss switching is possible. Has become. However, as shown in FIG. 5B, when the input power is small, the amplitude of resonance is small, so that the switching element 5 cannot be turned on at zero volts or less, and must be turned on with the voltage of the switching element 5 remaining. become.

FIG. 6 shows the relationship between input power and switching element loss in an enameled pot and a copper-clad pot. As shown in the figure, in the enamel pot, the loss is maximum when the maximum power is 1200 W, and the loss gradually decreases as the input power is reduced, but the loss is increased around 600 W with the minimum. On the other hand, in a copper pan that has good coupling with the heating coil 4, the input power at which the loss becomes minimum is around 800 W, and the loss rapidly increases as the input power decreases, and the loss at maximum power exceeds the loss at around 150 W, which is the minimum power. Will be things.

[0006]

As described above, in the above-described conventional configuration, when the input power is small, it cannot be turned on at zero volts or less, and the switching element 5 is turned on with the voltage remaining. As a result, not only a spike-shaped steep current is applied to the switching element 5, but also an excessive switching loss is added at the time of turn-on. In this operation mode, if the load pan 3 has a good coupling with the heating coil 4 such as a copper-clad pan, a significantly larger input power is generated.

As measures against this, it is necessary to adopt a switching element 5 having a large current withstanding capacity and a large cooling mechanism capable of sufficiently reducing switching loss.
Both of them have problems that they are large or costly.

The present invention solves the above-mentioned conventional problems and provides an induction heating cooker that is small in size and low in cost, by reducing excessive current and switching loss applied to a switching element when input power is small. The purpose is to do.

A second object is to realize a smaller input power while reducing an excessive current applied to the switching element and a switching loss.

Further, it is a third object to reduce excessive current and switching loss applied to the switching element by a wider variety of load materials and a wide range of input power.
Has the purpose of.

[0011]

To achieve the first object, an induction heating cooker according to the present invention comprises an AC power supply, a rectifying circuit for converting the AC power supply into DC, a load pan, and a load. A heating coil that is magnetically coupled to the pan, an input power detection circuit that detects the input power from the AC power supply, a switching element that oscillates on and off in the heating coil, a resonance capacitor that is connected to the heating coil, and the switching element. A turn-on voltage detection circuit for detecting the voltage at the time of turn-on, and within a range in which the voltage at the turn-on of the switching element detected by the turn-on voltage detection circuit does not exceed a preset set value, input power from the AC power supply. And an oscillation control circuit for controlling on / off oscillation of the switching element so that the value becomes a value set by the user. Is a problem solving means.

Further, in order to achieve the second object, the first
When the voltage at turn-on of the switching element detected by the turn-on voltage detection circuit exceeds a preset set value, the duty control of the input power at that time realizes the input power set by the user. The second problem solving means is provided with a duty control circuit for

Further, in order to achieve the third object, the resonance capacitor of the first problem solving means is constituted by a parallel circuit of the first resonance capacitor and a second resonance capacitor which can be opened and closed by the opening / closing means. However, when the turn-on voltage of the switching element detected by the turn-on voltage detection circuit exceeds a predetermined set value, a switching means control circuit for switching the switching means is provided.
To solve the problem.

[0014]

According to the first means for solving the above problems, the present invention provides:
Controls the on / off oscillation of the switching element so that the input power from the AC power supply reaches the value set by the user within the range where the voltage at turn-on of the switching element detected by the turn-on voltage detection circuit does not exceed the preset value. Therefore, the switching element voltage at turn-on can be suppressed to a predetermined value or less. As a result, it becomes possible to reduce the excessive current and switching loss applied to the switching element when the input power is small.

Further, according to the second means for solving the problems, when the voltage at turn-on of the switching element exceeds a predetermined set value, a small input power can be realized by the duty control of the input power at that time. It becomes possible to control the input power to a value set by the user in a state where the excessive current applied to the switching element and the switching loss are reduced.

Further, according to the third means for solving the problem, the constant of the resonance capacitor can be changed by switching the switching means when the voltage at the turn-on of the switching element exceeds a predetermined set value. By this operation, the amplitude of resonance of the switching element voltage can be increased and the voltage when the switching element is turned on can be lowered. As a result, it becomes possible to reduce the excessive current and switching loss applied to the switching element with a wide variety of load materials and a wide range of input power.

[0017]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the accompanying drawings. The same parts as those in the conventional example are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, 1 is an AC power supply, 2 is a rectifying circuit, 3 is a load pan, 4 is a heating coil, 5 is a switching element, 6 is a resonance capacitor, and 7 is an input power detection circuit, which is different from the conventional example. The point is that the switching element 5 is provided with a turn-on voltage detection circuit 9 for detecting the voltage when the switching element 5 is turned on, and the voltage when the switching element 5 is turned on detected by the turn-on voltage detection circuit 9 is predetermined. Provided is an oscillation control circuit 10 for controlling ON / OFF oscillation of the switching element 5 so that the input power from the AC power supply 1 detected by the input power detection circuit 7 reaches a value set by the user within a range not exceeding the set value. That is the point.

With the above configuration, the turn-on voltage of the switching element 5 is detected by the turn-on voltage detection circuit 9, and the oscillation control circuit 10 controls the voltage of the switching element 5 when the turn-on voltage does not exceed a preset value.
Since the on / off oscillation of the switching element 5 is controlled so that the input power from the AC power supply 1 becomes a value set by the user, the switching element voltage at turn-on can be suppressed to a predetermined value or less. As a result, it is possible to reduce the excessive current and switching loss applied to the switching element 5 when the input power is small.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIG. As shown in the figure, the difference from the first embodiment is that when the voltage at the turn-on of the switching element 5 detected by the turn-on voltage detection circuit 9 exceeds a predetermined set value. The point is that the duty control circuit 11 that realizes the input power set by the user by the duty control of the input power at that time is provided.

With the above structure, when the voltage when the switching element 5 is turned on exceeds a predetermined set value,
Since a small input power can be realized by controlling the duty of the input power at that time, the input power can be set to a value set by the user in a state where the excessive current applied to the switching element 5 and the switching loss are reduced. Can be controlled.

(Embodiment 3) Furthermore, a third embodiment of the present invention will be described with reference to FIG. As shown in the figure, the difference from the first embodiment is that the resonance capacitor 6
Is constituted by a parallel circuit of a first resonance capacitor 12 and a second resonance capacitor 13 that can be opened and closed by an opening / closing means 14, and the voltage at the turn-on time of the switching element 5 detected by the turn-on voltage detection circuit 9 is predetermined. An opening / closing means control circuit 15 for switching the opening / closing means 14 when the set value is exceeded is provided.

With the above structure, the constant of the resonant capacitor can be changed by switching the opening / closing means 14 when the voltage when the switching element 5 is turned on exceeds a predetermined set value. By this operation, the resonance amplitude of the switching element voltage is increased to increase the switching element 5
The voltage at turn-on can be reduced. As a result, it is possible to reduce an excessive current applied to the switching element 5 and a switching loss due to a wider variety of load materials and a wide range of input power.

In the above embodiment, the circuit of each function is shown by the circuit block diagram, but it is obvious that a part of these functions may be combined with a microcomputer.

[0025]

INDUSTRIAL APPLICABILITY As described above, the induction heating cooker according to the present invention has an input from an AC power source within a range in which the voltage at the turn-on of the switching element detected by the turn-on voltage detection circuit does not exceed a predetermined set value. Since the on / off oscillation of the switching element is controlled so that the electric power has a value set by the user, the switching element voltage at turn-on can be suppressed to a predetermined value or less. As a result, it is possible to prevent a spike-shaped steep current and excessive switching loss that were applied when the input power is small, and it is possible to provide a small-sized and low-cost induction heating cooker.

Further, when the voltage at turn-on of the switching element exceeds a predetermined set value, duty control of the input power at that time is performed to prevent excessive current and switching loss applied to the switching element. In the reduced state, it is possible to realize smaller input power and improve usability.

Further, the resonance capacitor is constituted by a parallel circuit of the first resonance capacitor and the second resonance capacitor which can be opened and closed by the opening / closing means, and the voltage at the turn-on time of the switching element detected by the turn-on voltage detection circuit is The constant of the resonant capacitor can be changed by switching the switching means when the preset value is exceeded. By this operation, the amplitude of resonance of the switching element voltage can be increased and the voltage when the switching element is turned on can be lowered. As a result, it is possible to reduce an excessive current applied to the switching element and a switching loss due to a wide variety of load materials and a wide range of input power, and to further improve usability.

[Brief description of drawings]

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

FIG. 2 is a circuit block diagram of the induction heating cooker according to the second embodiment.

FIG. 3 is a circuit block diagram of an induction heating cooker according to the third embodiment.

FIG. 4 is a circuit block diagram of a conventional induction heating cooker.

FIG. 5 (a) is a timing chart for explaining an operation when the input power of the induction heating cooker is large. (B) is a timing chart for explaining an operation when the input power of the induction heating cooker is small.

FIG. 6 is a diagram showing a relationship between input power and switching element loss of the induction heating cooker.

[Explanation of symbols]

 1 AC power supply 2 Rectifier circuit 3 Load pan 4 Heating coil 5 Switching element 6 Resonance capacitor 7 Input power detection circuit 9 Turn-on voltage detection circuit 10 Oscillation control circuit 11 Duty control circuit 12 First resonance capacitor 13 Second resonance capacitor 14 Opening and closing Means 15 Opening / closing means control circuit

Claims (3)

[Claims] 1. An AC power supply, a rectifier circuit for converting the AC power supply into DC, a load pan, a heating coil magnetically coupled to the load pan, and an input power detection circuit for detecting the input power from the AC power supply. A switching element that oscillates on and off in the heating coil, a resonance capacitor connected to the heating coil, a turn-on voltage detection circuit that detects a voltage at the time of turning on the switching element, and a turn-on voltage detection circuit. An oscillation control circuit that controls ON / OFF oscillation of the switching element so that the input power from the AC power supply has a value set by the user within a range in which the voltage at turn-on of the switching element does not exceed a predetermined set value. Induction heating cooker equipped with. 2. When the turn-on voltage of the switching element detected by the turn-on voltage detection circuit exceeds a predetermined set value, the duty for controlling the input power at that time realizes the input power set by the user. The induction heating cooker according to claim 1, further comprising a control circuit. 3. A resonance capacitor is constituted by a parallel circuit of a first resonance capacitor and a second resonance capacitor which can be opened / closed by an opening / closing means, and a voltage at turn-on of a switching element detected by a turn-on voltage detection circuit is The induction heating cooker according to claim 1, further comprising an opening / closing means control circuit for switching the opening / closing means when a preset value is exceeded.