JP2589159Y2 - Induction heating device for cooking - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooking induction heating apparatus for supplying high-frequency power to an induction heating coil to generate eddy current in a member to be heated by electromagnetic induction, thereby performing induction heating.

[0002]

2. Description of the Related Art An induction heating device for cooking uses an eddy current generated when a magnetic flux passing through a magnetic member is greatly changed. The eddy current is generated by heat generated by electric resistance of the magnetic member. The member can be heated.

[0003] Therefore, in general, an induction heating device for cooking is provided with an induction heating coil, and a member to be heated mainly made of a magnetic material, for example, a steel pot or the like is installed near the induction heating coil. It supplies a high-frequency current (high-frequency power).

The induction heating coil generates a magnetic flux in response to the supplied high-frequency current, and the magnetic flux passes through the member to be heated. Then, an eddy current is generated in the magnetic material forming the heated member in response to the change in the magnetic flux, and heat is generated by the electric resistance of the magnetic material, so that the heated member is heated.

In the above-described induction heating apparatus for cooking, a high-frequency current is supplied to the induction heating coil to heat the member to be heated. However, it is necessary to adjust the amount of heating according to the cooking content. There is known a device provided with a control circuit for adjusting the output.

That is, the cooking induction heating device comprises a rectifier circuit for converting an AC current from a commercial AC power supply into a DC current, a high-frequency switching element for converting the DC current to a high-frequency current, and an on-state of the high-frequency switching element. It comprises an inverter circuit consisting of a resonance capacitor and an induction heating coil that are charged during operation and discharged during off operation, and a control circuit that controls on / off of a high-frequency switching element of the inverter circuit. The output of the high-frequency current has been adjusted by the on-time and off-time in the on / off control of the element.

When the high-frequency switching element is, for example, a high-frequency NPN transistor, on / off control of the transistor by the control circuit is performed by outputting a control signal to a base terminal of the transistor. This control signal is generated by a control circuit including a control circuit, for example, a reference voltage setting circuit, a sawtooth wave generation circuit, and a drive circuit.
The signal is input from the control circuit to the base terminal of the transistor.

That is, the driving circuit compares the reference voltage set by the reference voltage setting circuit to obtain a desired amount of heating with the voltage of the sawtooth signal generated by the sawtooth generation circuit, and outputs the sawtooth signal. Is high when the voltage of the sawtooth signal is higher than the reference voltage, and is output to the base terminal of the transistor as a control signal that becomes low when the voltage of the sawtooth signal is lower than the reference voltage.

Therefore, if the reference voltage set by the reference voltage setting circuit is set high, the high-level time of the control signal, that is, the on-time of the transistor, can be shortened. Can be lengthened. However, the off time is a condition that the discharge time of the resonance capacitor is secured.

In the conventional cooking induction heating apparatus, the reference voltage setting circuit is constituted by a microcomputer, and the microcomputer outputs the output from a volume for setting the cooking temperature and the thermistor for detecting the temperature of the member to be heated. , And a reference voltage is set by the microcomputer, and the reference voltage is output from an output port of the microcomputer.

However, most of the commercially available cooking microcomputers hardly have a D / A output port for converting digital data of the reference voltage set as described above into analog data and outputting the analog data.

Therefore, in order to output a set reference voltage, a method of converting digital data of the reference voltage into analog data using a plurality of output ports of a microcomputer has been used.

In this method, one terminal of a resistor having a different value is connected to each output port used by the microcomputer, and the other terminal of the resistor is connected in common, and the connection terminal connected in common is used. Is connected to a power supply or ground via a reference resistor to form a series voltage dividing circuit. Therefore, if the digital data of the reference voltage is output as a combination of the output levels of the respective output ports, the divided output of the series voltage dividing circuit determined by the combination of the output levels becomes the reference voltage.

[0014]

However, as described above, in the conventional induction heating device for cooking, the number of output ports of the microcomputer for outputting digital data of the reference voltage is limited. There were limits to the combinations. For example, if there are only three output ports for outputting digital data of the reference voltage, there are only eight combinations. Therefore, the reference voltage cannot be changed and set arbitrarily continuously, and only a reference voltage having a stepwise numerical value corresponding to the number of combinations of the output ports can be output. As a result, the heating amount cannot be finely adjusted. There was a problem.

Further, the resistor connected to the output port for outputting the digital data of the reference voltage constitutes a series voltage dividing circuit, and the divided voltage output of the series voltage dividing circuit becomes the analog data of the reference voltage. There is a problem that a resistor with high accuracy must be used.

Accordingly, the present invention provides a cooking apparatus which can precisely and precisely adjust a reference voltage for adjusting a heating amount without using a high-precision resistor, and thus can finely adjust a heating amount. An object of the present invention is to provide an induction heating device.

[0017]

The present invention provides a DC power supply, a switching element, an induction heating coil for heating a member to be heated mainly composed of a magnetic material, and a resonance capacitor connected in parallel to the induction heating coil. An inverter circuit for converting DC power supplied from a DC power supply to high-frequency power, a sawtooth wave generating means for generating a sawtooth signal, an integration circuit for integrating and outputting an input pulse signal, and an integration circuit for integrating the pulse signal. A constant voltage control unit that outputs a pulse signal to an integration circuit based on a comparison between digital data obtained by digitally converting a signal output from the circuit and data of a preset reference voltage; and a sawtooth wave generation unit. Based on the comparison between the voltage of the sawtooth signal and the voltage of the signal output from the integrating circuit.
Switching control means for controlling on / off of the switching element.

[0018]

In the present invention having such a configuration, the constant voltage control means compares the digital data obtained by digitally converting the signal output from the integration circuit with the data of the preset reference voltage based on the comparison. Since the pulse signal is input to the integration circuit, the voltage output from the integration circuit is stabilized at a preset reference voltage.

The switching control means controls on / off of the switching element based on a comparison between the voltage of the sawtooth signal from the sawtooth wave generation means and the reference voltage output from the integration circuit.

At this time, the switching element is turned on / off and the resonance capacitor is charged / discharged, and a counter electromotive force is generated in the induction heating coil, so that the inverter circuit converts the DC power of the DC power supply into high frequency power. I do.

Accordingly, high-frequency power is supplied to the induction heating coil, and the magnetic flux passing through the member to be heated is changed in accordance with the cycle of the high-frequency power to generate an eddy current. Is heated.

Accordingly, the amount of heating of the member to be heated at this time corresponds to the magnitude of the eddy current generated in the member to be heated, and the magnitude of the eddy current depends on the output of the high-frequency power supplied by the switching element. The output of the high-frequency power corresponds to the on-pulse width of the signal for controlling on / off of the switching element. That is, since the on-pulse width of the signal for controlling on / off of the switching element corresponds to the reference voltage, the heating amount corresponds to the reference voltage.

Further, the constant voltage control means controls the pulse signal output to the integration circuit so that the digital data of the signal output from the integration circuit becomes the data of the reference voltage. Since the setting can be changed continuously, and the output of the integration circuit is controlled by feedback, the reference voltage can be output from the integration circuit with high accuracy.

[0024]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a main circuit configuration of a cooking induction heating apparatus to which the present invention is applied. Reference numeral 1 denotes a commercial AC power supply. An AC current supplied from the commercial AC power supply 1 is rectified by a rectifier circuit 2 to obtain a DC current (DC power).

The DC current output from the rectifier circuit 2 is first smoothed by the smoothing capacitor 3. Therefore, the rectifier circuit 2 and the smoothing capacitor 3 constitute a DC power supply.

The rectifying circuit 2 of the smoothing capacitor 3
One end of the induction heating coil 4 is connected to a terminal connected to the positive electrode side of the induction heating coil 4. The other end of the induction heating coil 4 is connected to the collector terminal of a high-frequency NPN transistor 5 serving as a switching element.
Is connected to the terminal of the smoothing capacitor 3 connected to the negative electrode side of the rectifier circuit 2.

A resonance capacitor 6 is connected to the induction heating coil 4 in parallel, and a diode 7 is connected between the collector terminal and the emitter terminal of the transistor 5 in an anti-parallel relationship. Therefore, the induction heating coil 4, the transistor 5, and the resonance capacitor 6 constitute an inverter circuit.

A positive terminal and a negative terminal of the smoothing capacitor 3 are connected to a positive input terminal 8a and a negative input terminal 8b provided in the control circuit 8, respectively. It is connected to a collector voltage input terminal 8c provided in the control circuit 8. The base terminal and the emitter terminal of the transistor 5 are connected to a base output terminal 8d and an emitter connection terminal 8e provided in the control circuit 8, respectively. FIG. 2 shows a block diagram of a main configuration of the control circuit 8. As shown in FIG.

The control circuit 8 includes a first comparing section 11, a sawtooth wave generating section 12 as a sawtooth wave generating means, a microcomputer 13 as a constant voltage control means, an integrating circuit 14,
, And a driving unit 16. In addition,
The second comparison unit 15 and the driving unit 16 constitute a switching control unit.

The first comparator 11 compares the voltage of the signal A input to the positive input terminal 8a with the voltage of the signal B input to the collector voltage input terminal 8c, and compares the voltage of the signal A with the collector voltage input. A signal C having a low level when the input voltage of the terminal 8c is higher than the input voltage of the positive input terminal 8a, and a high level when the input voltage of the collector voltage input terminal 8c is lower than the input voltage of the positive input terminal 8a. Is output to the sawtooth wave generator 12.

The sawtooth wave generator 12 generates a sawtooth signal D in response to a rising edge of the signal C input from the first comparator 11 and generates the sawtooth signal D.
Is output to the comparison unit 15.

The microcomputer 13 has A /
An A / D input port 13a and an output port 13b having a built-in D (analog / digital) converter are provided. The signal E output from the integration circuit 14 is input to the A / D input port 13a. The digital data inputted and converted into digital data is compared with data of a preset reference voltage, and when the digital data from the A / D input port 13a is higher than the data of the reference voltage, the digital data is set to a low level.
When the digital data from the A / D input port 13a is lower than the reference voltage data, a pulse signal which is set to a high level is output from the output port 13b to the integration circuit 14.

The integration circuit 14 integrates the pulse signal input from the output port 13b of the microcomputer 13 over time with a signal E obtained by integrating the pulse signal into the second comparison unit 1.
5 and an A / D input port 13a of the microcomputer 13.

That is, the microcomputer 13
Controls the pulse signal output to the integration circuit 14 so that the voltage of the signal E output from the integration circuit 14 always becomes the reference voltage. The voltage stabilizes at the reference voltage.

The second comparator 15 compares the voltage of the sawtooth signal D input from the sawtooth generator 12 with the integration circuit 1.
The voltage is compared with the voltage of the signal E input from 4, that is, the reference voltage. When the voltage of the sawtooth signal D is higher than the reference voltage, the signal is set to the high level. When the voltage of the sawtooth signal D is lower than the reference voltage, the signal is set to the low level. The signal F is output to the driving unit 16.

The driving section 16 outputs the base output terminal 8 d based on the signal F output from the second comparing section 15.
(And the emitter connection terminal 8e) outputs a control signal for controlling on / off of the transistor 5.

In this embodiment having such a configuration, when a reference voltage is set in the microcomputer 13, a high-level signal is input to the integration circuit 14. Then
When the voltage of the signal E output from the integration circuit 14 gradually rises and the voltage of the signal E output from the integration circuit 14 rises above the reference voltage, the signal input to the integration circuit 14 from the microcomputer 13 goes low. When the voltage of the signal E output from the integrating circuit 14 falls below the reference voltage, the microcomputer 13 sends the signal to the integrating circuit 1
4 becomes high level. Therefore, the voltage of the signal E output from the integrating circuit 14 is stabilized at the reference voltage.

On the other hand, the first sawtooth wave is generated from the sawtooth wave generating section 12 that is triggered at the same time as the power is turned on. When the voltage of the sawtooth signal D rises above the reference voltage (signal E), the transistor 5 is turned on. Is done. At this time, the induction heating coil 4 is energized, and the collector voltage (signal B) of the transistor 5 drops to the ground.

When the voltage of the sawtooth signal D drops below the reference voltage (signal E), the transistor 5 is turned off. At this time, the back electromotive force of the induction heating coil 4 and the discharge of the resonance capacitor 6 cause the collector voltage (signal B) of the transistor 5 to rise higher than the voltage (signal A) of the positive terminal of the smoothing capacitor 3.

Eventually, the capacitance of the resonance capacitor 6 decreases, and the back electromotive force of the back electromotive force generated in the induction heating coil (direct current and forward direction from the rectifier circuit 2) causes the collector voltage of the transistor 5 to increase. When (signal B) drops below the voltage (signal A) of the positive terminal of the smoothing capacitor 3, a trigger is applied from the first comparison unit 11, and the next sawtooth wave is generated from the sawtooth wave generation unit 12.

When the voltage of the sawtooth signal D rises above the reference voltage (signal E), the transistor 5 is turned on,
At this time, the induction heating coil 4 is energized, and the collector voltage (signal B) of the transistor 5 drops to the ground.

When the voltage of the sawtooth signal D drops below the reference voltage, the transistor 5 is turned off. At this time, the back electromotive force of the induction heating coil 4 and the discharge of the resonance capacitor 6 cause the collector voltage of the transistor 5 to decrease. (Signal B) is higher than the voltage (signal A) of the positive terminal of the smoothing capacitor 3.

Eventually, the capacitance of the resonance capacitor 6 decreases and the back electromotive force of the back electromotive force generated in the induction heating coil causes the collector voltage (signal B) of the transistor 5 to increase.
Falls below the voltage (signal A) of the positive terminal of the smoothing capacitor 3, the first comparator 11 triggers, and the sawtooth generator 12 generates the next sawtooth.

As described above, the transistor 5 is turned on / off by the control signal generated by the sawtooth signal D generated by being triggered by the collector voltage (signal B) and the reference voltage (signal E). A high-frequency current (high-frequency power) for generating a desired heating amount is supplied to the induction heating coil 4.

FIG. 3 shows the timing of various signals. FIG. 3A shows that the first comparison unit 11 includes the smoothing capacitor 3.
3B shows a signal A input from the positive terminal of the control circuit 8 via the positive input terminal 8a of the control circuit 8 and a signal B input from the collector terminal of the transistor 5 via the collector voltage input terminal 8c. Is the signal C input from the first comparison unit 11 to the sawtooth wave generation unit 12, and FIG.
3D, the sawtooth signal D input from the sawtooth wave generation unit 12 and the signal E input from the integration circuit 14 to the comparison unit 15 of FIG.
5 shows a signal F input from the second comparing unit 15 to the driving unit 16.

As described above, at time T1, when the collector voltage (signal B) of the transistor falls below the voltage (signal A) of the positive terminal of the smoothing capacitor 3, the first
The signal C from the comparison unit 11 becomes high level and a trigger is applied, so that a sawtooth wave D is generated.

At time T2, when the sawtooth signal D rises above the reference voltage (signal E), the control signal F for driving the transistor 5 goes high. Eventually, at time T3, when the sawtooth signal D falls below the reference voltage (signal E),
The control signal F for driving the transistor 5 becomes low level, and the collector voltage (signal B) of the transistor 5 rises.

At time T4, when the collector voltage (signal B) of the transistor 5 rises above the voltage (signal A) of the positive terminal of the smoothing capacitor 3, the signal C from the first comparison unit 11 goes low. , The sawtooth wave generator 12 is ready for trigger input.

At time T5, when the collector voltage (signal B) of the transistor 5 drops below the voltage (signal A) of the positive terminal of the smoothing capacitor 3, the signal C from the first comparator 11 goes high. When a trigger is applied, a saw-tooth wave is generated in the saw-tooth wave signal D, and the above is repeated one after another.

As described above, according to the present embodiment, the microcomputer 13 and the integration circuit 14 are provided, and the integration circuit 1
Output signal from the microcomputer 13 to the A / D
It is input to the input port 13a, and the digital data obtained by digitally converting the input signal is compared with data of a preset reference voltage. When the output signal from the integration circuit 14 is lower than the reference voltage, Level and integration circuit 1
By inputting a pulse signal which is set to a high level when the output signal from the reference signal 4 is higher than the reference voltage from the microcomputer 13 to the integration circuit 14, the reference voltage output from the integration circuit 14 and the set reference voltage are always output. By comparing with the microcomputer 13, the reference voltage can be set with high accuracy without using a highly accurate resistor. Further, since the signal output from the integrating circuit 14 is A / D converted and input and compared with the reference voltage by digital data, the reference voltage can be arbitrarily and continuously changed and set. The voltage can be finely adjusted. Therefore, the ON time of the high-frequency current supplied to the induction heating coil can be finely adjusted, so that the heating amount can be finely adjusted.

Further, since the microcomputer 13 feeds back and monitors the reference voltage signal output via the integration circuit 14, the microcomputer 13 can also detect a failure of the microcomputer 13 itself.

In this embodiment, the first comparison unit 11
And when the collector voltage of the transistor 5 falls below the voltage of the positive terminal of the smoothing capacitor 3 as the voltage of the DC power supply, a trigger of the sawtooth signal generated by the sawtooth generator 12 is generated. As a result, the transistor 5
The on-time is kept constant even if the on-time is freely changed, so that an efficient high-frequency operation is automatically performed in accordance with the discharge time of the resonance capacitor 6 and the state of the back electromotive force of the induction heating coil. The effect that a current can be supplied is obtained, and the effect that a circuit configuration can be simplified without the necessity of providing an oscillation circuit for generating a sawtooth signal is also obtained.

In this embodiment, the integrating circuit 14
A signal of the reference voltage is directly input to the second comparison unit 15 from the input unit. However, a differential is provided in front of the second comparison unit 15 to further smooth the output signal from the integration circuit. The information may be supplied to the second comparison unit 15.

[0054]

[Effect of the invention] As described in detail above, according to the invention,
It is possible to provide a cooking induction heating device capable of adjusting a reference voltage for adjusting a heating amount with high precision and finely without using a resistor with high precision, and thus capable of finely adjusting a heating amount.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main circuit configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a main configuration of a control circuit according to the embodiment.

FIG. 3 is a view showing timings of various signals of the embodiment.

[Explanation of symbols]

4 ... Induction heating coil, 5 ... Transistor, 6 ... Resonant capacitor, 8 ... Control circuit, 12 ... Saw wave generator, 13 ... Microcomputer, 14 ... Integration circuit, 15 ... Second comparison unit.

Claims (1)

(57) [Scope of request for utility model registration] 1. A DC power supply, comprising a switching element, an induction heating coil for heating a member to be heated mainly made of a magnetic material, and a resonance capacitor connected in parallel to the induction heating coil, and supplied from the DC power supply. An inverter circuit for converting DC power to high-frequency power, a sawtooth wave generating means for generating a sawtooth signal, an integration circuit for integrating and outputting an input pulse signal, and a signal output from the integration circuit. A constant voltage control unit that outputs a pulse signal to the integration circuit based on a comparison between digital data obtained by digital conversion and data of a preset reference voltage; and a sawtooth wave signal from the sawtooth wave generation unit. Switching control means for controlling on / off of the switching element based on a comparison between a voltage and a voltage of a signal output from the integration circuit; Cooking induction heating device.