JPS6215795A - Inverter for 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 inverter for an induction cooking device used in general households.

2. Description of the Related Art As shown in FIG. 6, a conventional inverter for an induction heating cooker includes a series circuit of a DC power supply 1, a heating coil 2, and a transistor 3, and a resonant capacitor 4 connected in parallel to the heating coil 2, or Generally, a resonant capacitor was connected in parallel to the transistor 3. (Tokuko Showa 60
14585 Publication) Problems to be Solved by the Invention However, inverters for induction heating cookers need to vary the power within a predetermined range for various pots or loads. A mode like the one shown occurs. In FIG. 6, vc8 is the collector-emitter voltage of the transistor 3, Ic is the collector current, and Q is a waveform diagram showing conduction/cutoff of the transistor 3.

V shown in FIG. 8 shows that when a small power is set for a pan such that the reduction coefficient of the heating coil 2 becomes large, the power does not reach zero during the cutoff period of the transistor 3 as shown by the broken line, and resonance occurs when the transistor 3 is turned off. 1. Through capacitor 4. Short-circuit current flows through the circuit, resulting in large switching losses.

The present invention has been made in view of the above, and an object of the present invention is to provide a low-loss induction heating cooker.

Means for Solving the Problems In order to solve the above problems, the inverter for induction heating cookers of the present invention connects a series circuit of a heating coil, an inductor, and a switching element to a DC power source, and the heating coil has a first resonance. The configuration is such that capacitors are connected in parallel, and a second resonant capacitor is connected in parallel to the inductor or the switching element.

Function: With the above configuration, the present invention obtains a current limiting effect of the inductor and suppresses short circuit current, thereby reducing switching loss. Further, the spike voltage due to the energy stored in the inductor when the switching element is turned on/off is suppressed by the second resonant capacitor, and since no resistance is used to suppress current and voltage, loss is extremely small.

Embodiment FIG. 1 shows an embodiment of the inverter for an induction heating cooker according to the present invention. In FIG. 1, a heating coil 12, an inductor 13, and a transistor 14, which is a switching element, are connected in series to a DC power source 11. A first resonant capacitor is connected in parallel to the heating coil 12. Further, a second resonant capacitor 16 is connected in parallel to the transistor 14. An inverter control circuit 17 for controlling conduction/cutoff of the transistor 14 is provided.

A waveform diagram showing the operation of the induction heating cooker configured as described above is shown in FIG. In the same figure, V. 8 is a voltage between collector and emitter of the transistor 14, IC is a collector current thereof, and Q is a waveform diagram showing conduction/cutoff of the transistor 14. These waveform diagrams are for inductor 13. The value of the second resonant capacitor 16 is set to the value of the heating coil 13. 1st
This is the case when the resonant capacitor 15 is made sufficiently smaller than the resonant capacitor 15. As can be seen from FIG. 2, the rush current when the transistor 14 is turned on can be reduced. That is, the short-circuit current of the capacitor 15 is suppressed by the inductor 13, and the short-circuit current of the second resonant capacitor 16 is also small due to its small capacity.
As shown in C, the inrush current becomes smaller. The dashed line of the IC in FIG. 2 indicates the rush current in the case of the conventional example in FIG.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the figure, the inductor 13 also serves as a part of the heating coil 12, and the current of the inductor 13 can be used for heating, which is efficient. If the center tap method is used as shown in Figure 3, the number of parts can be reduced. , it is possible to achieve smaller size and lower cost.

Further, a third embodiment of the present invention will be explained with reference to FIG.

In the figure, an inductor 13 also serves as the primary side of a current transformer 18 for driving the base of a transistor 14, and when current transformer driving is used, the number of parts can be reduced and the device can be made smaller and cheaper. Also, the current transformer 18
may be used for collector current detection for transistor protection.

Although the embodiment in which the second resonant capacitor is connected in parallel to the transistor has been described above, it goes without saying that the same effect can be obtained even if the second resonant capacitor is connected in parallel to the inductor.

Effects of the Invention As described above, according to the present invention, by providing an inductor and a second resonant capacitor, switching loss is reduced and spike voltage caused by the inductor is kept low, thereby achieving low switching loss and protection of switching elements. It can satisfy both.

A circuit diagram of the inverter, FIG. 2 is a waveform diagram of the same operation, FIGS. 3 and 4 are circuit diagrams of an inverter for an induction cooking device according to another embodiment of the present invention, and FIG. 5 is a diagram of a conventional inverter for an induction cooking device. FIG. 6 is an operating waveform diagram of FIG. 5.

11...DC power supply, 12...Heating Koinope 13...Inductor, 14...Transistor, 15...First resonance capacitor,
16... Second resonant capacitor, 18...
...Current transformer.

Name of agent: Patent attorney Toshio Nakao and 1 other person1/
-1 DC power supply f2-@processing coil No. 1m 13-
Inductor +4=transistor 15-m-resonant capacitor 16--second resonant capacitor (Fig. 2, Fig. 3). Figure I8-
Current transformer Fig. 5 Fig. 6 (a-FF

Claims (3)

[Claims] (1) A heating coil connected to a DC power supply, an inductor, and a switching element series circuit are connected, a first resonant capacitor is connected in parallel to the heating coil, and a second resonance capacitor is connected to the inductor or the switching element. Inverter for induction heating cookers with capacitors connected in parallel. (2) The inverter for an induction heating cooker according to claim 1, wherein the inductor also serves as a part of the heating coil. (3) The inductor also serves as the primary side of a transformer for driving a switching element or for detecting current.
Inverter for induction heating cooker as described in section.