JP3265975B2 - Induction heating cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction cooking device.

[0002]

2. Description of the Related Art In recent years, induction heating cookers have placed a temperature detecting element or the like in the vicinity of a pot or the like serving as a load to detect the temperature of the pot or the like by taking advantage of its good heating response. By making adjustments, it is possible to realize fine cooking, and because it does not use flames, it does not pollute indoor air, so it is safe and clean, and its demand is rapidly increasing. .

Hereinafter, this conventional induction heating cooker will be described with reference to the drawings. FIG. 5 shows a configuration of a conventional induction heating cooker. In FIG. 5, a rectifier circuit 2 rectifies a commercial power supply 1 into a direct current. The inverter circuit 3 includes a switching unit 3a, a heating coil 3b, and the like. The control circuit 4 includes a driving unit 6 for driving the switching unit 3a, and a driving signal generating unit 5 for generating a signal for causing the driving unit 6 to output a signal for driving the switching unit 3a. Reference numeral 3c denotes a load such as a pan heated by the heating coil 3b.

The operation of the above configuration will be described with reference to FIG. FIG. 6 shows the output of the drive signal generation means 5 and the output of the drive means 6. As shown in FIG. 6A, the driving means 6 gives the driving signal shown in FIG. 6B to the switching means 3a by the signal generated and output by the driving signal generating means 5 to drive the switching means 3a, thereby converting the commercial power supply 1 into a rectifier circuit. 2. Convert the rectified DC into high-frequency AC,
A high-frequency current is supplied to the heating coil 3b, and the high-frequency magnetic flux generated by the high-frequency current is applied to the pot 3c of the load for heating. The heating power of the load pan 3c is controlled by changing the drive timing of the switching means 3a based on the output of the drive signal generation means 5. The drive means 6 drives the switching means 3a when the output of the drive signal generation means 5 reaches a predetermined value Vx.

[0005]

However, in the above-mentioned conventional induction heating cooker, the output of the drive signal generation means 5 is determined by the impedance of the signal line from the drive signal generation means 5 to the drive means 6, the input impedance of the drive means 6, and the like. The signal waveform is deformed as shown in FIG. 6A, so that the timing at which the driving means 6 outputs a signal for driving the switching means 3a becomes the time t0 from when the output of the driving signal generating means 5 rises at Z and reaches Vx. There is a problem in that the switching operation is delayed and the switching operation cannot be performed at a desired timing, a desired heating power cannot be obtained, and cooking performance is deteriorated.

When the switching means 3a is driven to supply a high-frequency current to the heating coil 3b to heat the load, external noise or noise due to its own switching causes a signal from the drive signal generation means 5 to the drive means 6 to be generated. When the driving means 6 is superimposed on the line, the driving means 6 drives the switching means 3a at a timing at which the driving means is not originally driven, or does not drive at the driving timing. Had the disadvantage that an electrical stress was applied to it. Further, when a capacitor or the like is added to a signal line from the drive signal generation means 5 to the drive means 6 for removing these noises, the output signal waveform of the drive signal generation means 5 is deformed by the impedance of the capacitor or the like, The timing at which the driving means 6 outputs the signal for driving the switching means 3a is shifted due to a delay or the like, so that the switching operation cannot be performed at a desired timing. Even in the case of performing the heating, the degree of deformation of the output signal waveform of the drive signal generating means 5 changes due to the variation of the capacitor capacity and the like, so that the switching means 3a cannot be driven at a desired timing and a desired heating power cannot be obtained, so that There was a problem that performance deteriorated.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and suppresses a shift in switching timing of a switching means to prevent a deterioration in cooking performance. The purpose of the present invention is to prevent the malfunction of the heating operation, thereby making the heating operation unstable and applying electrical stress to the switching means and the like.

[0008]

In order to solve the above-mentioned problems, the present invention provides a control circuit comprising: a driving signal generating unit;
Is larger than 0, smaller than a predetermined value, and the predetermined
The amplitude of the output of the drive signal generation means is set to be close to the value.
A level shift means for changing the level shift means;
When the output signal reaches the predetermined value, the switching means
By comprising a driving means for driving the stage, Rino timing drive means rising of the output of the drive signal generating means for suppressing the shift of the timing for driving the switching means.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a switch.
That has a heating means and supplies a high-frequency current to the heating coil.
Controlling the operation of the inverter circuit and the inverter circuit
A control circuit, wherein the control circuit includes a drive signal generation unit.
And the minimum value is larger than 0, smaller than a predetermined value , and
Level shift means for changing the amplitude of the output of the drive signal generation means so as to be close to the predetermined value ;
When the output signal of the shift means reaches the predetermined value, the switch
And a driving unit for driving the switching unit.The driving unit drives the switching unit to supply a high-frequency current to the heating coil by a driving signal generated by the driving signal generation unit. A load such as a pot can be induction-heated by the generated magnetic flux. The heating power of the load is controlled by changing the drive timing of the switching means based on the output of the drive signal generating means and changing the high-frequency current supplied to the heating coil. Further, since the level shift means is provided, the amplitude of the output of the drive signal generation means can be changed, and the minimum value and the maximum value of the output of the level shift means are set close to a predetermined input value at which the drive means outputs the drive signal. Even if the output of the drive signal generation means is deformed by the influence of the impedance of the signal line or the input impedance of the drive means, the output of the drive signal generation means corresponds to the drive timing of the switching means. This has the effect that the timing at which the drive means outputs a signal for driving the switching means from the waveform portion can be hardly shifted.

According to the second aspect of the present invention, since the level shift means is provided with noise prevention means, it is possible to suppress noise from being superimposed on a signal line from the drive signal generation means to the drive means and to output the level shift means. If the minimum value and the maximum value are set close to a predetermined input value at which the drive means outputs a drive signal, the output of the drive signal generation means will be the impedance of the noise prevention means, the impedance of the signal line and the output of the drive means. Even if deformed due to input impedance,
This has an effect that a waveform portion corresponding to the drive timing of the switching means of the signal output by the drive signal generation means and a timing at which the drive means outputs a signal for driving the switching means can be prevented from being shifted.

[0011]

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. In FIG. 1, 11 is a commercial power supply, 12 is a rectifier circuit, 13 is a switching means 13a and a heating coil 13b.
And an inverter circuit that performs induction heating by applying a high-frequency current to the heating coil 13b. The control circuit 14 includes a driving signal generating unit 15 for generating a signal for driving the switching unit 13a, and the driving signal is supplied to the switching unit 13a.
And a level shifter 17 for changing the amplitude of the output of the drive signal generator 15.

The operation of the above configuration will be described with reference to FIG. FIG. 2 shows the output of the drive signal generation means 15, the output of the level shift means 17, and the output of the drive means 16. By the signal (FIG. 2A) generated by the driving signal generating means 15, the driving means 16 causes the inverter circuit 13 as shown in FIG.
Of the commercial power supply 11 is converted by the rectifier circuit 12 into a high-frequency AC, and a high-frequency current is supplied to the heating coil 13b.
The load 13c such as a pot is induction-heated by the magnetic flux generated from b. The heating power of the load 13c is controlled by changing the drive timing of the switching means 13a with the output of the drive signal generating means 15 and changing the high frequency current supplied to the heating coil 13b. The timing at which the drive signal generation means 15 rises is X in FIG. 2, but the rise has a waveform having a time constant as shown in FIG. 2a due to the influence of the input impedance of the drive means 16 and the impedance of the signal line. The level shifter 17 changes the amplitude of the output of the drive signal generator 15 as shown in FIG. 2B. Driving means 16
Outputs high when the output of the level shift means 17 reaches a predetermined value Vx, and outputs low when the output of the level shift means 17 falls below the predetermined value Vx to drive the switching means 13a. If the level shifter 17 is not provided, the output of the drive signal generator 15 in FIG.
5, the drive signal generating means 1
The timing at which the driving unit 16 drives the switching unit 3a is shifted from the timing at which the driving unit 16 drives the switching unit 3a by the time t1 until the output of the switching unit 3 reaches the predetermined value Vx. When the level shift means 17 is provided, FIG.
b, the minimum value Vm of the output of the level shift means 17
Is set to be larger than 0, smaller than the predetermined value Vx, and close to Vx, a waveform having a time constant as shown in FIG. 2B is obtained due to the influence of the input impedance of the driving means 16 and the impedance of the signal line. However, the time lag of the timing from X can be set to t2 which is smaller than t1.

As described above, according to the present embodiment, it is possible to suppress the difference between the rising timing of the driving signal generating means 15 and the driving timing of the switching means 13a.

In this embodiment, the drive signal generating means 15
Is described, but the same effect can be obtained for the fall. In addition, although the inverter circuit 13 is configured to include one switching unit, it is needless to say that the same effect can be obtained even if the inverter circuit 13 includes two or more switching units.

(Embodiment 2) A second embodiment according to the present invention will be described with reference to FIG.
The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Reference numeral 19 denotes a power supply circuit for supplying an operation power supply Vdd for the control circuit 14. The driving means 16 is a drive IC integrated and molded with resin. The level shift unit 17 includes a noise prevention unit 18 that suppresses noise from being superimposed on a signal line from the drive signal generation unit 15 to the drive unit 16. Level shift means 1
7 is composed of resistors R1 and R2 and noise prevention means 1 as shown in FIG.
8 capacitors C. Further, the drive signal generating means 15
Is composed of a comparator Comp.

The operation of the above configuration will be described with reference to FIG. FIG. 4 shows the output of the drive signal generation means 15, the output of the level shift means 17, and the output of the drive means 16. As in the first embodiment, the driving means 16 drives the switching means 13a of the inverter circuit 13 as shown in FIG. 4c by the signal (FIG. 4a) generated by the driving signal generating means 15, thereby rectifying the commercial power supply 11. The DC rectified by the circuit 12 is converted into a high-frequency AC, a high-frequency current is supplied to the heating coil 13b, and a magnetic flux generated from the heating coil 13b heats a load 13c such as a pan. The heating power of the load 13c changes the drive timing of the switching means 13a by the output of the drive signal
The control is performed by changing the high-frequency current supplied to b.

Further, since the level shift means 17 is provided with the noise prevention means 18, it is possible to prevent external noise or noise due to its own switching from being superimposed on the signal lines from the drive signal generation means 15 to the drive means 16. If the driving means 16 drives the switching means 13a at a timing at which the switching means 13a is not originally driven, or does not drive at the driving timing, a malfunction occurs, the heating operation becomes unstable, and electric stress is applied to the switching means 13a and the like. Preventing them from joining. In this embodiment, the noise prevention means is a capacitor C. However, even without the capacitor C, since the resistor R1 is connected in series on a signal line connecting the drive signal generation means 15 and the drive means 16, Even if a noise current flows through this signal line, the resistance R1
Has the function of suppressing the noise current from flowing.

The drive signal generating means 15 rises at the moment when the comparator Comp no longer outputs Low (Y in FIG. 4).
8 and the driving means 16
The rise due to the influence of the input impedance and the impedance of the signal line has a waveform having a time constant as shown in FIG. 3A. As shown in FIG. 4B, the level shift means 17 changes the output voltage Vdd of the power supply circuit 19 during the period in which the comparator Comp of the drive signal generation means 15 outputs Low as shown in FIG.
The amplitude of the output of the drive signal generating means 15 is changed to the value Vm obtained by dividing the voltage Vm by the voltage Vm. The driving means 16 outputs High when the output of the level shift means 17 reaches a predetermined value Vx, and outputs Low when the output of the level shift means 17 falls below the predetermined value Vx to drive the switching means 13a. ing.

If the resistor R1 does not exist, the output of the drive signal generating means 15 shown in FIG. Is shifted from the timing at which the driving means 16 drives the switching means 13a by the time t3 until the output of the switching means 13a reaches the predetermined value Vx. If the resistor R1 is present, as shown in FIG. 4B, the minimum value Vm of the output of the level shift means 17 is set to a value greater than 0 and a predetermined value Vx
If it is set smaller and close to Vx, a waveform having a time constant as shown in FIG. 4B due to the influence of the impedance of the resistor R2 and the capacitor C of the noise prevention means 18, the input impedance of the driving means 16 and the impedance of the signal line. , The time lag from Y can be t4, which is smaller than t3. In addition, even when the values of the resistor R2 and the capacitor C vary and the rising waveform in FIG. 4B varies as indicated by the broken line, the variation width t5 of the drive timing of the switching means 13a is larger than the variation width t6 when the resistor R1 is not provided. Can also be set small. Here, the reason that Vm is changed by changing the values of the resistors R1 and R2 without changing Vx is that the drive IC of the driving means 16 is integrated, so that Vx cannot be easily changed. That's why.

As described above, according to this embodiment, malfunction of the switching means 13a due to noise is prevented, and
It is possible to suppress a difference between the rising timing of the drive signal generation unit 15 and the drive timing of the switching unit 13a.

In this embodiment, the drive signal generating means 15
Is described, but the same effect can be obtained for the fall. In addition, although the inverter circuit 13 is configured to include one switching unit, it is needless to say that the same effect can be obtained even if the inverter circuit 13 includes two or more switching units.

[0022]

As described above, according to the first aspect of the present invention, since the level shift means is provided, the shift in the drive timing of the switching means is suppressed, and the variation in the desired heating power is suppressed, and the cooking performance is improved. Can be improved.

According to the second aspect of the present invention, since the level shift means includes the noise prevention means, a shift in the drive timing of the switching means is suppressed, and a desired variation in heating power is suppressed, and cooking performance is reduced. In addition, it is possible to prevent the switching means from malfunctioning due to noise, thereby preventing the heating operation from becoming unstable, further improving the cooking performance, and preventing the electrical stress from being applied to the switching means and the like.

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram of the induction heating cooker.

FIG. 3 is a block diagram showing a configuration of an induction heating cooker according to a second embodiment of the present invention.

FIG. 4 is an operation waveform diagram of the induction heating cooker.

FIG. 5 is a block diagram showing a configuration of a conventional induction heating cooker.

FIG. 6 is an operation waveform diagram of the induction heating cooker.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 Inverter circuit 13a Switching means 13b Heating coil 14 Control circuit 15 Drive signal generation means 16 Drive means 17 Level shift means 18 Noise prevention means

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hirofumi Noma 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Masashi Kanbara 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Tetsuro Nagahisa 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-5-22956 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H05B 6/12

Claims (2)

(57) [Claims] An inverter circuit having switching means for supplying a high-frequency current to a heating coil, and a control circuit for controlling the operation of the inverter circuit, the control circuit comprising: a drive signal generating means; Is greater than 0,
Less than a constant value, and a level shift means for changing the amplitude of the output of said predetermined value to close as before <br/> SL drive signal generating means, an output signal of said level shift means said predetermined
Drive means for driving the switching means when the value of
An induction heating cooker having a step . 2. The induction heating cooker according to claim 1, wherein the level shift means includes noise prevention means for suppressing output of noise components of the drive signal generation means.