JPH0430158B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an induction cooker having a static power converter.

Conventional configuration and its problems The general configuration of a conventional induction heating cooker is a resonant circuit consisting of a resonant capacitor connected in series or parallel to a heating coil, a switching element that excites the resonant circuit, and an operation of the switching element. It consists of a control circuit that controls the Here, the control circuit includes circuits that require low voltage and relatively high power, such as a drive circuit that drives the switching elements and a display circuit that displays the operating status, so the power supply circuit is also required to have a large capacity. There is. Therefore, in the past, a dedicated large-capacity power transformer was used to obtain power for the control circuit from its secondary winding. However, in this case, since the switching element stopped operating during non-heating, its drive circuit also stopped operating, and the excess power was consumed in the power supply circuit, etc., reducing overall efficiency. . In order to improve this problem, a method has also been proposed in which a detection coil is provided that is magnetically coupled to the heating coil, and its output is used as a power source for the control circuit. However, in this case, the placement location of the detection coil is a factor that determines the quality of magnetic coupling, and securing the placement space not only becomes a constraint on product design, but also has the disadvantage of increased costs due to an increase in the number of parts. It is a thing,
Furthermore, if an attempt was made to supply sufficient power to the control circuit, the detection coil would also become larger, making it impossible to save space.

Purpose of the Invention The present invention solves the above problems and is small and lightweight.
The aim is to provide an efficient induction heating cooker at a low cost.

Structure of the Invention The induction heating cooker of the present invention has a resonant circuit including a heating coil and a resonant capacitor, a switching element that excites this resonant circuit, and a control circuit that controls the operation of this switching element, The coil is configured by twisting a plurality of insulated conductive wires and winding them in a spiral shape, and a part of the plurality of wires is used as a detection coil magnetically coupled to the heating coil,
The output thereof is used as a power source for the control circuit.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. In Fig. 1, a filter circuit consisting of a choke coil 3 and a filter capacitor 4 is connected to the output terminal of a full-wave rectifier 2 connected to a commercial power supply 1, which prevents high-frequency current from flowing back toward the power supply. ing. A parallel resonant circuit of a heating coil 5 and a resonant capacitor 6, and a series circuit of a power transistor 7 as a switching element are connected to both ends of the filter capacitor 4, and an antiparallel circuit is connected between the collector and emitter of the power transistor 7. A flywheel diode 8 is connected.
The control circuit 9 controls the on/off operation of the power transistor 7 by its output, and the on/off operation of the power transistor 7 excites the resonant circuit composed of the heating coil 5 and the resonant capacitor 6, and the heated pot is heated. 10 is heated by induction.

Here, a smoothing capacitor 11 acts on the power supply of the control circuit 9, and the output of the secondary winding of a transformer 12 connected between the AC input terminals of the full-wave rectifier 2 is half-wave rectified by a diode 13 and charged. At the same time, the output voltage of the detection coil 14 magnetically coupled to the heating coil 5 is also half-wave rectified by the diode 15 for charging. Therefore, when the power transistor 7 stops its switching operation and stops its heating operation, the output voltage of the detection coil 14 is zero, and the transformer 1
The smoothing capacitor 1 is connected only by the output of the secondary winding 2.
1 is charged. On the other hand, when the control circuit 9 excites the resonant circuit, most of the power consumption of the control circuit 9 is spent on the switching operation of the power transistor 7, so the power consumption of the control circuit 9 increases and the terminal of the smoothing capacitor 11 Although an attempt is made to lower the voltage, the terminal voltage of the smoothing capacitor 11 does not drop due to the backup from the detection coil 14. If the output voltage of the detection coil 14 is set higher than the output of the secondary winding of the transformer 12, the smoothing capacitor 11 will be dominantly charged by the detection coil 14 during the heating operation, and the two
It is also possible to set the proportion of the charging current from the output of the next winding to a small value, and the transformer 12 can be designed with the minimum power capacity necessary to start the excitation of the resonant circuit.

FIG. 2 shows an external view of the heating coil 5 and detection coil 14 of the present invention. The heating coil 5 consists of a plurality of insulated conductors twisted together and wound in a spiral shape.
It is fixed by means of adhesive or heat fusion. By using a portion of the plurality of twisted insulated conductive wires as the detection coil 14, the detection coil 14 with good magnetic coupling can be obtained. In addition, since the detection coil 14 is constructed by being twisted together with the heating coil 5, not only does it not require space for arranging the detection coil, but it also eliminates the need for an increase in the number of parts, making it possible to construct the detection coil at a low cost. Needless to say, it can be provided. Furthermore, in order to treat the terminals of the heating coil 5 and the detection coil 14, if the surface of the insulation coating of the conductor corresponding to the detection coil 14 is colored differently from the color of the surface of the insulation coating of the conductor corresponding to the heating coil 5, it is possible to identify them. is easy.

Here, in one embodiment of the present invention, the operation was explained using a transistor inverter, but a thyristor, etc.
There are no restrictions as long as it is a switching element.

Effects of the Invention The induction heating cooker of the present invention has the following excellent effects.

Only the minimum necessary power is supplied to the control circuit during non-heating, and when the power consumption of the control circuit increases during heating, it automatically tracks and only the necessary power is always supplied, resulting in high efficiency.

By arranging the detection coil and the heating coil in a twisted configuration, good magnetic coupling is achieved, sufficient power is supplied to the control circuit, and there is no need to secure space for the detection coil. It is possible to provide a detection coil that does not impose restrictions on product design and is also inexpensive in terms of cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an induction heating cooker showing an embodiment of the present invention, and FIG. 2 is a perspective view showing the configuration of the heating coil and detection coil. 5...Heating coil, 6...Resonance capacitor, 7
...switching element (power transistor),
9...Control circuit, 14...Detection coil.

Claims (1)

[Scope of Claims] 1. A resonant circuit consisting of a heating coil and a resonant capacitor, a switching element that excites this resonant circuit, and a control circuit that controls the operation of this switching element. An induction heating cooker having a configuration in which insulated conductive wires are twisted together and wound in a spiral shape, a portion of the plurality of wires is used as a detection coil magnetically coupled to the heating coil, and the output thereof is used as a power source for the control circuit. 2. The induction heating cooker according to claim 1, wherein the detection coil has an insulating coating on its surface colored differently from the insulating coating on the surface of the heating coil.