JPH04296486A - Inductive heating cooker - Google Patents

Abstract

PURPOSE:To improve the durability of a relay by providing such a constitution as never operating the relay for connecting a resonance capacitor to an inverter circuit even when a small material detecting operation is repeated. CONSTITUTION:A microcomputer 20 inputs the output of a small material detecting circuit 16 and the output of a pan detecting circuit 17, controls the operation of an inverter circuit 11 through a drive circuit 18, and also switches a relay 12 through a driving circuit 19 to operate the inverter circuit 11 in the state of an interter I and in the state of an inverter II. When the small material detecting circuit 16 judges that a load is not a small material after starting in the state of the inverter I, the inverter circuit is switched to the state of the inverter II, and then to the state of the inverter II in which the small material is judged in this state. The inverter I detects the small material more easily than the inverter II. Thus, even if the small material detecting operation is repeated, the relay 12 is never operated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker having a resonant capacitor switching means for switching a resonant capacitor of an inverter circuit.

0002

2. Description of the Related Art In recent years, it has been proposed to heat cooking pots with inverters suitable for each cooking pot by switching resonant capacitors.

Conventionally, this type of induction heating cooker has been constructed as shown in FIG. The configuration will be explained below.

As shown in the figure, a DC power source is constructed by rectifying an AC power source 1 with a diode bridge 2 and smoothing it with a smoothing capacitor 3, which includes a heating coil 4, transistors 5 and 6, diodes 7 and 8, and a resonant capacitor 9. , 10 constitute an inverter circuit 11. Resonant capacitor 1
0 is a relay 12 constituting a resonant capacitor switching means.
The capacitor 9 is connected or disconnected in parallel with the capacitor 9. This causes the inverter circuit 11 to have two states. That is, the state in which the resonant capacitor 10 is disconnected from the inverter circuit 11 (hereinafter referred to as inverter I
) and a state in which the resonant capacitor 10 is connected to the inverter circuit 11 (hereinafter referred to as inverter II). Inverter I is suitable for heating magnetic pots, and inverter II is suitable for heating non-magnetic pots. Further, the output of the input current detection circuit 13 and the output of the resonant capacitor voltage detection circuit 14 are respectively input A to the microcomputer (hereinafter referred to as microcomputer) 15.
It is connected to N0 and AN1, and these constitute a small object detection circuit 16 that determines whether the load is a small object below a predetermined level. That is, FIG. 4 shows the output VAN0 of the input current detection circuit 13 of each load and the output VA of the resonant capacitor voltage detection circuit 14.
It shows the relationship of N1 (VAN0-VAN1 characteristics),
In the inverter I as shown in FIG. 4(A),
Inverter II as shown in (B) also has a load (e
) Separated by the VAN0-VAN1 characteristics of SUS304t1.6, there is an area where the load is determined to be a small object (hereinafter referred to as small object detection) (hereinafter referred to as the small object area) and an area where the load is determined to be not a small object (hereinafter referred to as the operating area). It is divided into two areas. (SUS304t1.6 means a non-magnetic stainless steel pot with a pot bottom thickness of 1.6 mm, and enamel φ20 cm means an enamel pot with a pot bottom diameter of 20 cm.) A pot detection circuit 17 is connected to the microcomputer 15 for determining whether the load is a magnetic pot or a non-magnetic pot based on the operating state. Note that the drive circuit 18 is connected to the inverter circuit 11 by the output of the microcomputer 15.
The drive circuit 19 drives the relay 12 based on the output of the microcomputer 15.

[0005] To explain the operation in the above configuration, first, the load (f) SUS3 is located in the small object area shown in FIG.
04t1.8 or a load (g) knife, when started with inverter I, the small object detection circuit 16 determines that the load is a small object, stops the operation of the inverter circuit 11, and after a while starts again with inverter I, and the above Repeat the action. Next, when the load is in the operating region shown in Fig. 4 (a) to (d)
), when the inverter I starts the pot, the small object detection circuit 16 determines that the load is not a small object, and detects the magnetic pots (a) enamel φ20cm and load (c) enamel φ8c.
m is heated by the inverter I, and the load (b) SU is detected as a non-magnetic pot by the pot detection circuit 17.
S304t1.0 and load (c) SUS304t1.4 will be heated by inverter II.

[0006]

[Problems to be Solved by the Invention] In such a conventional induction heating cooker, the load (e) shown in FIG.
1.6, V near the boundary line between the small object area and the motion area
In the case of a load with AN0-VAN1 characteristics, the small object detection circuit 16 does not detect a small object at inverter I, but switches to inverter II.
In this case, small objects may be detected. To explain the operation at this time, when the inverter I starts, the small object detection circuit 16 determines that the load is not a small object, and the pot detection circuit 17 detects that the load is a non-magnetic pot.
The inverter circuit 11 includes inverter I to inverter II
Switch to . When it comes to inverter II, small object detection circuit 1
6 determines that the load is a small object and stops the operation of the inverter circuit 11. As a result, the inverter circuit 11 returns to the initial state of the inverter I, starts up with the inverter I again, and repeats the above operation. When such an operation is performed, the inverter circuit 11 switches from inverter I to inverter II, returns to inverter I again,
Since the operation of switching to inverter II is repeated, the relay 12 that connects the resonant capacitor 10 to the inverter circuit 11 is repeatedly turned on and off, causing a problem in that the relay 12 deteriorates more quickly.

The present invention has been made to solve the above-mentioned problems, and aims to improve the durability of the relay by preventing the relay that connects the resonant capacitor to the inverter circuit from operating even if small object detection operations are repeated.

[0008]

Means for Solving the Problems In order to achieve the above objects, the present invention provides a heating coil for heating a cooking pot, an inverter circuit for supplying a high frequency current to the heating coil, and a control circuit for controlling the inverter circuit. The inverter circuit includes a plurality of resonant capacitors, and resonant capacitor switching means for connecting at least one of the resonant capacitors to or disconnecting from the inverter circuit, and the control circuit includes a plurality of resonant capacitors. The resonant capacitor switching means includes a first operating state detecting means for detecting the operating state of the circuit and a second operating state detecting means, and the resonant capacitor switching means specifies whether the inverter circuit is connected or disconnected when the inverter circuit is started. After startup, the connection state of the resonant capacitor is switched according to the output of the first operating state detecting means, and the second operating state detecting means determines the operating state of the inverter circuit and detects the load. The operation of the inverter circuit is stopped when the small object is determined to be below a predetermined level. The solution to this problem is to make it easier to distinguish them from small items.

[0009]

[Operation] The present invention uses the above-mentioned problem-solving means to make it easier to detect small objects in the state of the inverter before the resonant capacitor is switched than in the state of the inverter after the resonant capacitor is switched. A load for which a small object was not detected in Even if the operation is repeated, the relay will not turn on and off repeatedly, and the relay will not deteriorate prematurely.

0010

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Note that components having the same configuration as those of the conventional example are given the same reference numerals, and description thereof will be omitted.

As shown in the figure, the microcomputer 20 inputs the output of the small object detection circuit (first operating state detecting means) 16 and the output of the pot detecting circuit (second operating state detecting means) 17, and outputs the output from the drive circuit 18. The operation of the inverter circuit 11 is controlled via the drive circuit 19, and the relay 12 is switched via the drive circuit 19, so that the inverter circuit 11 is operated in the state of the inverter I and the state of the inverter II. Here, in the inverter I as shown in FIG. 2(A), (a) SUS304t1.
The load is divided into the accessory area and the operating area by the VAN0-VAN1 characteristics of 4. In the inverter II shown in Fig. 2(B), the load (f) VA of SUS304t1.8
The N0-VAN1 characteristics are used to divide the load into an accessory area and an operating area. Load (e) V of SUS304t1.6
The AN0-VAN1 characteristic is in the small object region for inverter I and in the operating region for inverter II, and the level at which the small object detection circuit 16 determines that the load is a small object is easier for inverter I than for inverter II. are doing.

[0012] To explain the operation in the above configuration, first, the load is in the small object area shown in Fig. 2 (e) SUS3
04t1.6, (f) SUS304t1.8 or (g
) In the case of a knife, when the inverter I starts the operation, the small object detection circuit 16 determines that the load is a small object, stops the operation of the inverter circuit 11, and after a while starts the inverter I again.
Start it up, detect small objects again, and repeat the above operation. In this case, the small object detection operation is repeated, but since the inverter circuit 11 remains unchanged as the inverter I, the relay 12 is not repeatedly turned on and off. Next, in the case of pots with loads (a) to (c) in the operating region shown in FIG. (c) The 8 cm enamel will be heated by the inverter I, and the load (b) SUS304t1.0, which is detected as a non-magnetic pot by the pot detection circuit 17, will be heated by the inverter II. In addition, in the inverter I, the load (d) SUS near the boundary line between the accessory area and the operating area
Regarding 304t1.4, if inverter I detects a small object after startup, the operation will be the same as loads (e) to (g), and relay 12 will not repeat turning on and off. Also, if inverter I does not detect a small object after startup , inverter circuit 11
is switched to Inverter II, but in Inverter II, the load (f) SUS304t is changed as shown in Fig. 2(B).
Since the small object area and the operating area are separated by the VAN0-VAN1 characteristic of 1.8, the load (d) SUS304t1.
4 is the operating area, load (b) SUS304t1.0
The operation is the same as that, and small objects will not be detected after the device started with inverter I switches to inverter II.

As described above, according to the induction heating cooker according to the embodiment of the present invention, since the small object area is set so that inverter I can more easily detect small objects than inverter II, the small object area is always set before the resonance capacitor 10 is switched. The small object is detected by the inverter I, and even if the small object detection operation is repeated, the relay 12 does not turn on or off, and the durability of the relay 12 does not deteriorate.

[0014]

[Effects of the Invention] As is clear from the above embodiments, according to the present invention, it is easier to detect small objects before the resonant capacitor is switched than after it is switched, so even if the small object detection operation is repeated. Since the resonant capacitor switching means does not operate, deterioration of the portion used as the resonant capacitor switching means can be prevented, and a highly reliable inverter circuit can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention.

[
Figure 2: Diagram explaining the accessory area and operating area of the induction heating cooker

[Figure 3] Circuit diagram of a conventional induction heating cooker

[Figure 4] Diagram explaining the accessory area and operation area of the induction heating cooker

[Explanation of symbols]

4 Heating coil 9 Resonance capacitor 10 Resonance capacitor 11 Inverter circuit

Claims (1)

[Claims] 1. A heating coil that heats a cooking pot, an inverter circuit that supplies high-frequency current to the heating coil, and a control circuit that controls the inverter circuit, the inverter circuit including a plurality of resonant capacitors, resonant capacitor switching means for connecting at least one of the resonant capacitors to or disconnecting from the inverter circuit, the control circuit comprising: first operating state detecting means for detecting an operating state of the inverter circuit; ,
the resonant capacitor switching means is specifically set to either connection or disconnection when the inverter circuit is started, and after the inverter circuit is started, the resonant capacitor switching means outputs an output from the first operation state detection means. The connection state of the resonant capacitor is switched depending on the state of the resonant capacitor, and the second operating state detecting means detects the operating state of the inverter circuit when the load is a small item below a predetermined level. The operation of the induction heating cooker is stopped, and the discrimination level is such that it is easier to determine that the object is a small object before the resonant capacitor switching means switches the connection state of the resonant capacitor after activation than after switching the connection state of the resonant capacitor.