KR900005324Y1 - Electromagnetic cooker - Google Patents

Abstract

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Description

Induction heating cooker

1 is a block diagram of an induction heating cooker applied to the present invention.

FIG. 2 shows an embodiment of the feedback unit 2 in FIG.

FIG. 3 is a diagram showing an embodiment of the appropriate load detection section 5 in FIG.

4 is a view showing waveforms of the inverter unit 1 and respective portions of the inverter control unit.

5 is a waveform diagram of output of each part by the appropriate load detection unit 5.

* Explanation of symbols for main parts of the drawings

1: Inverter part of the cooker 2: Return part

3: Differentiator 4: Sawtooth wave generating part

5: Proper load detection unit 6: Output setting unit

7 display unit 8 pulse width modulator

9: inverter drive unit

The present invention detects the output voltage of the inverter unit 1 and returns it to the control circuit to determine the time when the switching element of the inverter unit 1 is "on" and at the same time whether the vessel placed on top of the cooker is appropriately loaded. It relates to an induction heating cooker that can be detected.

In general, the safety device of the induction heating loop used in kitchens is a means of detecting heat from small loads such as spoons and forks, and using a container detection circuit using a permanent magnet and a current transformer. The small load was detected by using the magnetic switch, and a magnet switch was used to prevent the heating of the nonmagnetic material.

Therefore, the small load detection circuit of the designed induction heating cooker has become a huge obstacle to the development of a small electronic cooker due to its complex structure and the large number of parts.

Therefore, the object of the present invention is to prevent the heating of the metal container, even if the metal container suitable for use in the induction heating cooker when the user inadvertently put a knife or fork on the cooker during cooking, the risk of being burned It also provides induction heating cookers that prevent electricity from being consumed by detecting heat when a container made of a metal that is not suitable for induction heating such as aluminum or copper is placed or when there is no load. There is.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an induction heating cooker applied to the present invention, the inverter unit 1 of the cooker is filtering the high frequency of the commercial power radio wave rectified by the choke coil (L ₁ ) and condenser (C ₁ ) It consists of a series resonant circuit composed of a work coil (L ₂ ) and a resonant capacitor (C ₂ ) at a DC voltage, a switching transistor (Q ₁ ) and a damper diode (D ₁ ) connected in parallel with the resonant capacitor (C ₂ ). Will. In normal operation, the transistor Q ₁ is switched at high speed to match the resonant frequency (about 25 KHz) of the series resonant circuit composed of the work coil L ₂ and the resonant capacitor C ₂ so that the work coil L ₂ has a high frequency. The sympathetic current flows to induce heating in the metal container on top of the cooker.

The feedback unit 2 is configured to apply the voltage output from the inverter unit 1 of the cooker according to the load to the differentiator 3 and the proper load detection unit 5 which will be described later. An example is composed of a resistor (R _1- R ₆ ), a diode (D ₂ ), a capacitor (C ₁ ) (C ₄ ), a transistor (Q ₁ ) as shown in FIG.

The proper load detection unit 5 is configured to receive the voltage output from the feedback unit 2 to determine the load suitability of the metal container placed on the upper portion of the cooker, and FIG. 3 shows an embodiment of the proper load detection unit 5. It consists of a resistor (R ₆ -R ₉ ), a capacitor (C ₅ ), a comparator (COM ₂ ).

The pulse width modulator 8 compares the voltage output from the feedback unit 2 with the voltage generated through the differentiator 3 and the sawtooth generator 4 and the reference voltage output from the output setting unit 6 to drive the inverter. The furnace 9 is configured to drive the transistor Q ₁ of the inverter section 1.

The display unit 7 compares the voltage output from the proper load detection unit 5 and the output setting unit 6 to indicate whether the metal container placed on the upper portion of the cooker is a proper load.

It describes the circuit operation and the effect according to the present invention having the configuration as described above.

First, when the operation of the inverter unit 1 of the cooker is observed by dividing step by step using the waveform of FIG. 4, the waveforms A and B of FIG. 4 are the power transistor Q ₁ and the diode in the inverter unit 1 of the cooker. The current L _L flowing through the work coil L ₂ and the collector voltage Vc of the power transistor Q ₁ according to the operations of “on” and “off” of (D ₁ ) are shown step by step. When the power transistor Q ₁ is switched on, current flows through the work coil L ₂ to the collector terminal of the power transistor Q ₁ , and at this time, the work coil _L of the current L L. _When transient current flows due to the inductance and the equivalent resistance component of ₂ ), the waveform is the same as the shape of Ta period in FIG.

On the contrary, when the power transistor Q ₁ is "off", the current flowing through the work coil L ₂ is charged and discharged to the resonant capacitor C ₂ , and the series resonant current flows, and the waveform is a period of Tb of FIG. Is the same as

In addition, at this time, the voltage Vc of the resonant capacitor shows the charge and discharge voltage as shown in FIG.

On the other hand, the current flowing through the work coil (L ₂ ) is a period during which the diode (D ₁ ) is "on" does not stop quickly even when the voltage of the resonant capacitor (C ₂ ) is "zero" and the current through the diode (D ₁ ) In this case, the voltage vc of the resonant capacitor becomes a "low" voltage as in the shape of the Tc period of B in FIG.

As described above, the inverter unit 1 of the cooker is repeatedly generated with the current and voltage having the waveforms as shown in FIGS. 4A and 4B according to the switching operation, and the waveform is the switching time of the transistor Q ₁ . And the inductance of the work coil (L ₂ ), the equivalent resistance, and the resonant capacitor (C).

By the way, the output of the cooker is thus there is the variation which the work coil (L ₂₎ due to the inductance and the equivalent resistance component of the work coil (L ₂₎ varies depending on the size and material of the placed in the top load on the size and material of the load do.

Therefore, when the load changes, the waveforms and periods of Figs. 4A and 4B change, which is detected to determine the " on " time of the power transistor Q ₁ and to stop the heating in the case of no load or an unsuitable load. .

As described above, as shown in FIG. 1, the voltage Vc of the resonant capacitor C ₂ is input to the feedback unit 2, and the pulse width modulator (4) is applied through the differentiator 3 and the sawtooth wave generator 4. 8) is compared with the reference voltage Vr inputted from the output setting section 6 to determine the width and "on" time of the pulse for driving the power transistor Q ₁ , which is a switching element.

The waveform C of FIG. 4 is an output waveform diagram of the feedback unit 2. Referring to FIG. 2, which is an embodiment of the feedback unit 2, the feedback unit 2 has a waveform such as B in FIG. In this case, when the "high" waveform is applied, the transistor Q ₂ is "on" by the diode D ₂ , but when the "low" waveform is applied, the transistor Q ₂ is "off" and the output terminal C of FIG. A square wave pulse like this is output.

By the way, the differentiator 3 consists of a simple C-R circuit, and the sawtooth wave generation part 4 is an oscillation circuit which generate | occur | produces a sawtooth oscillation wave like the dotted line of E of FIG.

Therefore, the square wave output from the feedback unit 2 becomes the differential wave like the D of FIG. 4 through the differentiator 3, and the differential wave on the (+) side is the sawtooth wave (ship line part) oscillated by the sawtooth wave generating unit 4 By determining the discharge time T _{1 at} , a sawtooth wave waveform such as the solid line of FIG. 4E is generated and input to the comparator COM inverting terminal (-) of the pulse width modulator 8.

Meanwhile, the reference voltage Vr set by the output setting unit 6 is input to the inverting terminal (+) of the comparator COM and the width of the pulse is modulated so that the power transistor Q ₁ of the inverter unit 1 of the cooker. Will determine the "on" time and width of the pulse.

And the output of the cooker is fixed to the reference voltage (Vr) applied to one input terminal of the pulse width modulator 8 in the output setting unit 6 and the reference voltage (Vr) in the output setting unit 6 The output pulse is adjusted by changing the output pulse generation time ratio of the pulse width modulator 8 by intermittently controlling the output voltage to a ground with a time ratio appropriate to the output stage.

Next, a circuit operation similar to that of FIG. 3, which is an embodiment of the appropriate load detection unit 5, will be described with reference to the output waveform diagram of FIG.

The first half (solid line) of the circuit is the feedback section 2 of FIG. 2, and the voltage output from the feedback section 2 is the same as the waveform of FIG.

Therefore, the waveform of FIG. 4C is integrated through an integrated circuit consisting of a resistor (R ₆ ) and a capacitor (C ₅ ) and then compared through a comparator (COM ₂ ) to determine the suitability of the load. The waveform of is shown in FIG.

First, when a container of an appropriate size, that is, a suitable load, is placed on top of the cooker, the period Tc during which the dam diode D ₁ of the inverter unit 1 of the cooker is "on", that is, Tc of FIG. Is shortened, and the voltage obtained by integrating the square wave is lowered as indicated by the dotted line in FIG. 5B so that the output of the comparator COM ₂ is maintained at the "high" level as in FIG.

On the other hand, in the case of a container smaller than the reference load or no load, the period Tc during which the dam diode D ₁ is "on" becomes long, so that the pulse width of the square wave becomes long, and the integrated voltage is the reference of the comparator COM ₂ . It is higher than the voltage Vr so that the output of the comparator COM ₂ becomes a "low" level as shown in FIG.

In this way, when the output of the appropriate load detection unit 5 is at the "low" level, the reference voltage Vr drops to "zero" and pulses cannot be emitted from the pulse width tank 8, so that the inverter unit 1 of the cooker 1 ) Will also stop oscillation.

At this time, the cooker displays on the display unit 7 to recognize that the heating is stopped.

In addition, the proper load detection unit 5 also causes the "on" time of the damper diode D ₁ to be longer even in a bamagnetic metal such as aluminum, copper, or the like to stop the oscillation of the inverter unit 1 of the cooker. .

According to the present invention operating as described above, even if a small metal object such as a knife or fork on the cooker inadvertently by the user there is an advantage that can be ensured by not heating.

Claims (4)

In order to detect whether the load placed in the cooking is the proper load, the time of the conduction period of the damper diode D ₁ of the inverter unit 1 of the cooker or the time of the negative voltage applied to the collector terminal of the switching wave transistor Q ₁ is detected. Induction heating cooker characterized in that configured to detect the small load. 2. The circuit according to claim 1, wherein the feedback unit 2, the appropriate load detection unit 5, and the output setting unit (1) determine the " on " time of the switching transistor Ql by the pulse wave generated in the inverter unit 1 of the cooker. 6), an induction heating cooker comprising a pulse width modulator (8) or the like. 3. The feedback unit (2) according to claim 2, wherein the feedback unit (2) for returning the pulse output from the inverter unit (1) of the cooker to each unit is a resistor (R _1- R ₅ ) capacitor (C ₄ ) (C ₃ ) transistor (Q). Induction heating cooker, characterized in that consisting of ₂ ). The induction heating cooker according to claim 2, wherein the proper load detection unit (5) comprises a resistor (R ₆ -R ₉ ), a condenser (C ₅ ), and a comparator (COM ₂ ).