KR900005331Y1 - Load detection circuit for electromagnetic cooker - Google Patents

Abstract

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Description

Small Detection Circuit of Induction Heating Cooker

1 is a circuit diagram of the present invention.

2 is a waveform diagram of FIG.

* Explanation of symbols for main parts of the drawings

1: rectifier 2: resonator

3: Object detection unit 4: Inverter control unit

7: container PT: pulse trans

L ₁ , L ₂ : Coil BD: Bridge Diode

The present invention relates to the small load detection circuit of the induction heating cooker to detect the small load by electrically insulating the resonator and the microcomputer control unit using a pulse transformer.

As a safety device for induction cookers, there is a small load detection circuit that prevents heat generation during small loads such as spoons or forks. Conventionally, a current detector is installed at the inlet of the induction cooker to operate the power supply when the induction cooker is operated. According to the current flowing through the line, the current detector compares the induced voltage proportional to the detection current on the secondary side and the collector side voltage of the switching transistor of the inverter part passing through the low pass filter.

In the case of controlling a cooker composed of two or more burners with a microcomputer, the high voltage part of the resonator part and the low pressure part of the control part are electrically connected to each other, which directly affects the control circuit in case of unstable operation of the resonator part due to external conditions or damage of parts. There is a problem that is damaged, and because the high voltage and low voltage is electrically connected to the microcomputer to transmit the signal to the microcomputer to protect the microcomputer by using a separate photocoupler, etc. to electrically insulated, and to configure the circuit in the manner described above In this case, there is a problem that the circuit is complicated and the number of parts is increased, thereby reducing the reliability.

The present invention is a circuit designed to solve the above problems, it is to provide a small load detection circuit of the induction heating cooker to detect the small load by electrically insulating the high voltage portion of the resonator portion and the low pressure portion of the control unit using a pulse transformer. Purpose.

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

Referring to FIG. 1, the small load detection circuit of the induction cooker includes a rectifier 1 comprising a bridge diode BD, a choke coil L ₁ , and a smoothing capacitor C ₁ , which rectifies AC power into a DC power source. And driven according to the output signal of the heating coil L ₂ , the resonant capacitor C ₂ , the transistor Q ₁ , the protective diode D ₁ , and the inverter controller 4 for heating the container 7 to cook. In addition to the resonator unit 2 composed of the transistor Q ₁ , the transistor Q ₂ and the pulse transformer PT which are subjected to the rising voltage during the resonant operation of the resonator unit 2 and are sheared to the microcomputer control unit 5 by detecting the small object. ), The inverter receives the control signal of the object detection unit 3, the object detection unit 3, and the output selector 6 composed of a resistor (R ₁ -R ₆ ), a diode (D ₂ ) and a variable resistor (VR). The microcomputer control unit 5 which transmits the selected output to the control unit 4 and the resonator unit 2 by receiving a signal from the microcomputer control unit 5 By inverter control unit 4 for driving the switching transistor (Q ₁₎ it was conducted.

Referring to the operation of the small load detection circuit of the induction heating cooker having the above structure as follows.

The sinusoidal AC power is smoothed to DC voltage through the bridge diode BD, the choke coil L ₁ , and the smoothing capacitor C ₁ , and is applied to the resonator 2, and the microcomputer control unit 5 is connected to the output selector ( Receiving the signal selected in 6) and transmitting the signal to the inverter control unit 4 to operate at the selected output, the inverter control unit 4 drives the transistor Q ₁ in accordance with the output signal, thereby driving the resonator unit 2 The heating operation.

At resonance, the collector side voltage Vc ₁ of the transistor Q ₁ rises, but the rising voltage waveform is the same as that of FIG.

At this time, the waveform (a) is a waveform of the collector voltage (Vc ₁ ) at resonance when the load is large, the waveform (b) is an intermediate load, and the waveform (c) is a small load.

Due to the magnetic field generated by the heating coil L ₂ during resonance, an eddy current is generated at the bottom of the container 7, causing the container 7 to generate heat by the resistive component of the container 7, which is similar to the trans principle. Since the heating coil L ₂ becomes the primary side and the load corresponds to the secondary side, the voltage rise of the collector side changes according to the magnitude of the impedance of the load corresponding to the secondary side.

In other words, the smaller the load, the smaller the impedance, and the smaller the secondary impedance, the larger the voltage rise.The voltage rise (Vc ₁ ) on the collector side is shown in FIG. It becomes the same as the waveform (a), and when the load is small, it becomes the same as the waveform (c), and when the intermediate load is the same as the waveform (b).

In order to perform the object detection operation, the rising voltage Vc ₁ of the transistor Q ₁ is distributed to the resistor R ₁ and the variable resistor VR, and the divided voltage is transferred to the primary side of the pulse transformer PT.

The collector voltage Vc ₁ transferred to the primary side is transferred to the secondary side and distributed by the resistors R ₂ and R ₃ and then rectified by the diode D ₂ , and the rectified voltage is resistors R ₄ , R ₅ is redistributed and applied to the base of the switching transistor Q ₂ .

When the resonator 2 is operated by the inverter controller 4, the voltage is applied to the primary side of the pulse transformer PT by dividing the voltage by the variable resistor VR and the resistor R ₁ . By adjusting the voltage, the voltage delivered to the secondary side of the transformer PT can be adjusted, and the voltage delivered to the secondary side of the transformer PT is divided and rectified as described above and applied to the base of the transistor Q ₂ . Q ₂ ) will be driven.

The collector voltage Vc ₁ is below the operating voltage of the transistor Q _{2 in the} case of the normal load as shown in the waveforms a and b of FIG. 2A and the transistor Q ₂ in the case of the small load as shown in the waveform C. The variable resistor VR is adjusted to be equal to or higher than the driving voltage of.

That is, the object detection point (e point) is adjusted. Therefore, under normal load, the transistor Q ₂ is turned off so that the collector voltage Vc ₂ of the transistor Q ₂ becomes a high state H as shown in FIG. It is applied to the control unit 5 to recognize that it is in a normal state. In the case of the small load, the transistor Q _{2 of} FIG. 2B is driven so that the collector voltage Vc ₂ is equal to "d" of FIG. Since the low state L is applied, the voltage of the low state L is applied to the microcomputer control unit 5 so as to recognize the small load.

At this time, the microcomputer control unit 5 transmits the object detection signal to the inverter control unit 4 to stop the normal output and to only output the object detection output.

Therefore, the present invention can detect the object by the operation as described above, so that the reliability of the circuit is improved by reducing components compared to the conventional circuit, and the resonator and the controller which are induced with high voltage are electrically insulated. Even if the operation of the resonator is unstable or the component is damaged, the high voltage is not transmitted to the controller, so the safety of the circuit can be maintained. Also, since the resonator and the controller are electrically insulated, the microcomputer control circuit can be used without using a thermal insulation product. You can connect directly to

Claims (1)

In the small load detection circuit that prevents heat generation during small loads such as spoons or forks to maintain the stability of the induction cooker, the voltage rectified by the rectifying unit 1 is applied and is output through the microcomputer control unit 5. In response to the output signal of the inverter control unit 4 to which the selected signal of the selecting unit 6 is applied, the resonator unit 2 for heating the container 7 by driving the transistor Q ₁ and the variable resistor VR Adjust the collector voltage Vc ₁ of the resonator transistor Q ₁ , rectify and distribute the collector voltage Vc _l to the diode D ₂ and the resistors R _2- R ₅ , and then transistor Q _2. ) Is applied to drive the switching transistor Q ₂ to detect the small object and transmit the small object detection signal to the microcomputer control unit 5, and the small object detection signal of the small load detection unit 3. Receives and delivers to the inverter control unit (4) The controller 4 is guided which comprises a microcomputer control section 5 to stop the normal output, and detection output to only somul heating somul load sensing circuit of the cooker.