Induction heating cooking apparatus

#1. Field of the Invention

#The present invention relates to an induction heating cooking apparatus. More specifically, the present invention relates to an apparatus for controlling an inverter depending on a load state or a load kind in an induction heating cooking apparatus.

#2. Description of the Prior Art

#FIG. 1 is a perspective view showing an outline of one embodiment of the present invention;

#FIG. 2 is a schematic diagram of one embodiment of the present invention;

#FIG. 3 is a schematic diagram showing in more detail a control voltage source circuit;

#FIG. 1 is a perspective view showing one embodiment of the present invention. The induction heating cooking apparatus 1 comprises a housing or casing 2. An electrically insulating top plate 3 of such as a ceramic plate is provided on the top surface of the casing 2. Although not shown, an induction heating coil of a spiral shape is provided beneath the top plate 3. A control panel 4 is provided on the front surface of the casing 2. A power source switch 5 and a light emitting diode 51 for displaying an on state or an off state of the power supply switch are provided on the control panel 4. A selecting switch knob 6 is also provided on the control panel 4. The selecting switch knob 6 is commonly used to adjust the temperature or to adjust the output power by means of variable resistors, not shown, provided in a ganged fashion with a control knob 7. More specifically, the apparatus 1 is adapted to set the temperature of a load being heated, not shown, or to set the output power as a function of the position of the control knob 7. The settable temperature range is divided into two ranges, one being a relatively lower temperature range of 60.degree. C. to 100.degree. C. and the other being a relatively high temperature range of 160.degree. C. to 200.degree. C. Accordingly, the selecting switch knob 6 is structured to be switchable to three positions. The three positions are the first position for use in setting the temperature within a relatively low temperature range using a variable resistor, not shown, the second position for use in setting the temperature within a relatively high temperature range using a variable resistor, and a third position for use in adjusting the output power using a variable resistor. The control panel 4 is further provided with five light emitting diodes 81 to 85. These light emitting diodes 81 to 85 are aimed to display the level of the output power. More specifically, since the inventive apparatus 1 does not use a flame for the purpose of heating, it is not impossible to discern with what heating intensity a load being heating is being heated. Therefore, the light emitting diodes 81 to 85 are used to display the heating intensity by a light emitting state. A thermistor 9 is further provided beneath the top plate 3 for the purpose of detecting the temperature of a load being heated placed on the top plate 3. The control panel 4 is further provided with a switch 10, to be described subsequently in more detail. The switch 10 is aimed to forcibly render disabled a detecting circuit and so on to be described subsequently.

#FIG. 2 is a schematic diagram of one embodiment of the present invention. A commercial alternating current voltage source 101 is used as a power supply of the induction heating cooking apparatus shown. The commercial alternating current voltage source 101 is connected through a power supply switch 5 to a full wave rectifying circuit 103 and is also connected to a control voltage source 151. A choke coil 105 is connected to one output terminal of the full wave rectifying circuit 103 and a capacitor 107 is connected in parallel with the rectifying circuit 103. The choke coil 105 is aimed to remove a high frequency component and the capacitor 107 is connected as a high frequency bypassing capacitor. Accordingly, the capacitor 107 is selected to be of a small capacitance value as small as 10 microfarad, so as to exhibit a sufficiently high impedance with respect to the frequency of the commercial alternating current voltage source 101, say 50 Hz or 60 Hz, and also to exhibit a low impedance with respect to a high frequency signal. Thus, a ripple source voltage VCC1 varying between 0 to 140 V is obtained from the junction between the choke coil 105 and the capacitor 107. The ripple source voltage VCC1 is applied to a driver circuit 200. The capacitor 107 is shunted by a series connection of an induction heating coil 109 and a self-excited inverter 115. As described previously, the induction heating coil 109 is wound in a spiral shape beneath the top plate 3. A pan 113 made of metal including iron as a constituent serving as a load being heated is illustratively placed on the top plate 3. The self-excited inverter 115 comprises a parallel circuit of a transistor 117, a capacitor 119 and a diode 121. A drive voltage is applied from the driver circuit 200 to the base electrode of the transistor 117. A high frequency current obtained from the inverter 115 including the transistor 117, the resonance capacitor 119 and the diode 121 is applied to the induction heating coil 109 and accordingly the induction heating coil 109 generates a high frequency alternating magnetic field. The high frequency alternating magnetic field is applied through the top plate 3 to the load 113 being heated such as a pan or tray.

#The control voltage source circuit 151 provides three kinds of voltage sources or signals. Referring to FIG. 3, the control voltage source circuit 151 will be described in detail.