JPS634588A - Induction heating cooker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an induction heating cooker applying the principle of electromagnetic induction heating.

2. Description of the Related Art A conventional induction heating cooker will be described with reference to FIG. 1 is a DC power supply, and a switching element 16, such as a transistor, is inserted into the current supply circuit of the heating coil 15. A flywheel diode 17 is connected in antiparallel to the switching element 16, and a resonant capacitor 18 is connected in parallel to the heating coil 15.

and the heating coil 16, the switching element 16, the flywheel diode 1, and the resonant capacitor 1.
8 constitutes an inverter circuit. 19 is a blocking oscillation circuit with three windings n 1 + n 2 , n
3, and a transistor 21 is connected to one end of the winding n1.
1, the output of a time constant circuit consisting of a resistor 22 and a capacitor 23 is given to the base. 24 is a protection resistor for the transistor 21. The electromotive force e2 generated in the winding n2 of the transformer 2o is applied to the base of the switching element 16, turning it on and off. Also winding n3
The electromotive force e3 generated in is applied to the base of the transistor 21. The collector of switching element 16 is connected to the base of transistor 21 via diode 31. In addition, 25 in the figure is a smoothing capacitor for making the DC power supply voltage of the blocking oscillation circuit 19 constant, and 26 is a smoothing capacitor from the capacitor 25 to the inverter circuit section and the DC power supply 1.
2 is a resistor for limiting the base current of the switching element 16, and 28 is a diode for speeding up the operation of the switching element 16 when it is off. 29 is a capacitor that speeds up the on/off of the transistor 21, and 3o is a resistor for discharging the capacitor 29.

Next, the operation of the blocking oscillation circuit 19 will be explained. Assuming that the transistor 21 is currently off, when the potential reaches the level required to cause the base current of the transistor 21 to flow through the resistor 22 to charge the capacitor 23, the base current begins to flow, and along with this, the collector current also begins to flow. Both will increase.

When the collector current increases, an electromotive force e1 is induced in the winding n1 of the transformer 2o, as indicated by the arrow in the figure, and at the same time, the winding n1
2 r n 3 also have electromotive force in the direction of the arrow @ 2
+63 occurs. The electromotive force e3 is generated by the transistor 21
Since the direction is to increase the base current of , the pace current increases more and more, and the collector current also increases. At this time, the electromotive force e2 generated in the winding n2 is caused by the switching element 16
The direction is to turn off, so keep it off. After this operation, transistor 21 becomes saturated and the collector current becomes constant. As a result, each winding n 1r n 2 + n
3 electromotive force e 1. e 2 and e s are reversed in the opposite direction of the arrow in the figure, that is, −81, −92, and −83.

Due to the electromotive force .about.03, the transistor 21 is suddenly turned off, and the charge in the capacitor 23 is also discharged. Thereafter, charging of the capacitor 23 starts again, and at this time, after a certain period of time determined by the time constant of the time constant circuit, the transistor 21 is turned on again, and the above-described operation is repeated. In this way, e2 and -02 are alternately induced in the winding n2, and when -92 is induced, the switching element 16 is turned on.

Next, the operation of the inverter circuit at this time will be described with reference to FIG. 5. During the T1 period when the switching element 16 is in the on state, current flows through the heating coil 15 and into the switching element 16. When the switching element 16 is turned off, the energy stored in the heating coil 16 is charged into the capacitor 18. Thereafter, the charge stored in the capacitor 18 is discharged, and the collector-emitter voltage of the switching element 16 becomes as shown in FIG. 6B.

After the capacitor 18 is discharged, the cand side of the diode 17 has a lower potential than the anode side, and the diode 17 becomes conductive. During this conduction period, the charge in the capacitor 23 is discharged via the diode 31, acting in the direction of turning off the transistor 21.

When the diode current disappears, the potential of the capacitor 23 rises, and after a certain period of time determined by a time constant, the transistor 21 is turned on9, and the above-described operation is repeated, continuing oscillation.

Problems to be Solved by the Invention However, the conventional system described above has a complex circuit configuration and requires a relatively large transformer. It was hard to say that it was cheap.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a self-oscillation type rust induction heating cooker that has a simple configuration and is inexpensive.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides an inverter that includes a heating coil and a switching element provided in an energizing circuit of the heating coil, and supplies high-frequency power to the heating coil. , a coupling coil electromagnetically coupled to the heating coil, a resistor connected in series with the coupling coil, a capacitor connected in series with the coupling coil and the resistor, and a diode connected in parallel to the capacitor. and a voltage limiting element connected in series to the coupling coil, the resistor, and the capacitor, and the switching element is turned on and off by the voltage applied to the voltage limiting element to self-oscillate. It is something.

Operation The present invention controls oscillation based on a signal obtained from a coupling coil that is electromagnetically coupled to a heating coil, and uses a time constant circuit consisting of a capacitor and a resistor to control the on-→off timing. , and the off->on timing is obtained by inverting the signal of the coupling coil.

Embodiment FIG. 1 shows a circuit diagram of an induction heating cooker which is an embodiment of the present invention. 1 is a DC power supply, 2 is a heating coil, 3 is a switching element inserted in the energizing circuit of the heating coil 2,
For example, MOSFET. The switching element 3
A flywheel diode 4 is connected in antiparallel to the heating coil, and a resonant condenser 5 is connected in parallel to the heating coil. The heating coil 2, switching element 3, flywheel diode 4, and resonance capacitor 5 constitute an inverter circuit. 14 is a cooking pot placed near the heating coil 2. A coupling coil 6 that is electromagnetically coupled to the heating coil 2 is provided near the heating coil 2, and a current limiting resistor 7 and a time constant circuit capacitor 8 are connected in series to the coupling coil 6. Zener diodes 10, 12, and diodes 11.13
are connected in antiparallel to each other in order to limit the positive and negative voltages, and are connected in series to the coupling coils, the resistor 7, and the capacitor 8, and are also connected to the gate of the switching element 3.

Next, the operation of this circuit will be explained with reference to FIG.

First, when the switching element 3 is in the on state, the drain current of the switching element 3 and the current of the heating coil 2 increase. At this time, an electromotive force ea is generated in the coupling coil 6 in the direction of the arrow in the figure, and is applied in a direction to maintain the on state, that is, to maintain the gate-source voltage ed in the positive direction. However, since the capacitor 8 is then charged, ed attenuates accordingly.

When ed becomes less than the gate-source threshold voltage of the switching element 3, the switching element 3 is turned off. When the switching element 3 is turned off, the drain current drops rapidly, and the voltage ea of the coupling coil 6 is reversed in the direction opposite to the arrow in the figure, that is, -ea. At this time, the energy stored in the heating coil 2 is temporarily absorbed by the resonant capacitor 5, and then discharged to the heating coil 2 again, performing a resonant operation. As a result, the voltage ea of the coupling coil 6 increases after the resonant operation. , it is reversed again and becomes in the direction of the arrow in the figure. As a result, the switching element 3 is turned on, the above-described operation is repeated, and oscillation continues.

FIG. 3 shows a second embodiment of the induction heating cooker according to the present invention.
A variable resistor 32 is connected in parallel to 1.13 as a constant current means. By increasing or decreasing this variable resistor 32, the coupling coil 6
As a result, the on-time of the switching element 3 can be increased or decreased, and as a result, the input power of the induction heating cooker can be adjusted variable.

In this embodiment, a Zener diode is used as the voltage limiting element, but other voltage limiting elements may be used as well.Also, although a variable resistor is used as the constant current means in the second embodiment, other constant current means may be used. It is clear that similar effects can be obtained using current means.

Effects of the Invention As described above, according to the present invention, a self-oscillation type induction heating cooker can be realized with a simple structure and low cost, and its practical effects are outstanding.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of FIG. 1, and FIG. 3 is an induction heating cooking apparatus according to a second embodiment of the present invention. FIG. 4 is a circuit diagram of a conventional induction heating cooker, and FIG. 6 is a waveform diagram showing the operation of FIG. 4. 1... DC power supply, 2... Heating Koinope 3,
1e...Switching element, 4, 17...
...Flywheel diode, 5,18...
Resonance capacitor, e...Coupling Koinope 14...
...Pot, 2o...Trance, 32...
...Variable resistance. Name of agent: Patent attorney Toshio Nakao and 1 other person
2 Figure 1

Claims (2)

[Claims] (1) A heating coil, an inverter having a switching element provided in a current-carrying circuit of the heating coil and supplying high-frequency power to the heating coil, a coupling coil electromagnetically coupled to the heating coil, and the coupling coil. a resistor connected in series with the coupling coil, a capacitor connected in series with the coupling coil and the resistor, a diode connected in parallel with the capacitor, and a resistor connected in series with the coupling coil, the resistor, and the capacitor. What is claimed is: 1. An induction heating cooker comprising: a voltage limiting element; the switching element is turned on and off by a voltage applied to the voltage limiting element to self-oscillate; (2) The induction heating cooker according to claim 1, wherein the on-time of the switching element is increased or decreased by increasing or decreasing the current value of a constant current means parallel to the voltage limiting element.