JPS628492A - 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 that performs proper pot detection.

BACKGROUND OF THE INVENTION FIG. 7 shows a conventional example of an induction heating cooker. In FIG. 7, an inverter is comprised of an induction heating coil L, a commutating capacitor C, a transistor Q, and a diode D. ``This inverter and bridge rectifier Re are connected via a smoothing capacitor d, and the inverter obtains DC power. A control circuit 1 that controls switching of the transistor Q of the inverter stops the inverter when one or both of the magnetic load detection circuit 2 and the oscillation stop signals e and t of the comparator 6 are at L level. The magnetic load detection circuit 2 has a pot switch SW that is activated when a magnetic pot is placed, and this switch SW is composed of, for example, a magnet and a microswitch. The oscillation stop signal e goes to the L level when the switch SW is cut off, that is, even when the magnetic pot is not placed, and stops the inverter. Further, a potential difference vL between both ends of the heating coil L is detected by a detection circuit 3, and a voltage proportional to this vL is generated. A comparator 6 is connected to the current transformer CT that detects the input current 11 of the inverter and compares the output of the inverter input current detection circuit 4 that generates a voltage proportional to the input current with the output of the detection circuit 3. ing. The input current detection circuit 4° detection circuit 3 and the comparator 5 constitute a small object detection circuit 6. The operation of the small object detection circuit 6 will be explained using FIG. In FIG. 8, the horizontal axis is the input current It, and the vertical axis is the voltage VL across the heating coil L. The solid line a is a characteristic curve of a normal load such as an enamel pot, and the solid line A is a characteristic curve of a small load such as a knife. In addition, the dashed line C is the small object detection level, and in the two areas S and 100 divided by this small object detection level C, the area S
Then, the If detection circuit 4 is set so that the output f of the small object detection circuit is at the L level, and the f is at the H level in the area 100.
VL detection circuit 3. The characteristics of the comparator 6 are determined.

Therefore, the inverter stops in the region S and oscillates in the region 100. FIG. 9 is a conceptual diagram showing the operation of the conventional example. In the same figure, 100 represents a set of loads belonging to area 100 in FIG.
represents the set of magnetic loads. Therefore, the heating load of the conventional induction heating cooker in FIG. 1 is the set Mn of diagonal lines in FIG.
“It was s.

Problems to be Solved by the Invention However, with the conventional configuration, non-magnetic items such as 5 US-304 pots could not be heated under loads in the 100 range. In order to heat this 5O3-304 pot, there are four things required except for the magnetic load detection circuit, but without this, small items such as aluminum foil could not be detected and the temperature would rise abnormally, which was dangerous.

As described above, the conventional structure has a problem in that the load that can be heated is limited, and there is no way to alleviate this limitation unless the risk of combustion when aluminum foil is placed on the device is accepted.

The present invention solves these conventional problems and provides an induction heating cooker that expands the heatable load range and ensures safety.

Means for Solving the Problems In order to achieve the above object, the induction heating cooker of the present invention has the following features:
an inverter that has an induction heating coil and causes resonance oscillation;
A control circuit that controls the output of the inverter, a magnetic load detection means that detects whether or not the material is magnetic, an output of a detection circuit that detects the voltage of the induction heating coil, and an output of the input current detection circuit of the inverter. The control circuit includes small object detection means for determining whether the object is a small object, and resonance period detection means for detecting the resonance period of the inverter. It is configured to determine whether or not the value is equal to or greater than a predetermined value, and if the value is equal to or greater than the predetermined value, the inverter is driven regardless of the output from the small object detection means.

With this configuration, even if a 5US304 pot or the like is detected and judged as a small object, the magnetic load detection means detects it as a non-magnetic material, and the resonance period detection means works accordingly, and the 5US304 pot with a long resonance period is detected as a predetermined value. It is determined that the above is true. The control circuit can then drive the inverter while ignoring the output from the small object detection means. Further, since the resonance period of aluminum foil or the like is short, the resonance period detection means determines that the resonance period is less than a predetermined value, so the control circuit stops the inverter based on the output from the small object detection means.

Embodiment Hereinafter, an embodiment of the present invention will be described based on the accompanying drawings. In Fig. 1, L is an induction heating coil, C is a commutating capacitor, Q is a transistor, and D is a diode.The small object detection circuit 6 is a bridge. The rectifier Re, smoothing capacitor control circuit, magnetic load detection circuit 2, and pot switch SW are the same as those of the conventional example.

In the present invention, a resonance period detection circuit 7 is newly provided which inputs the voltage across the heating coil L and the output of the magnetic load detection circuit 2 and outputs the input to the invert control circuit. The output of the magnetic pot detection circuit 2 is at the L level when the magnetic pot is placed, and when the output is at the L level, the output q of the resonance period detection circuit 7 is fixed at the H level. When the output q is at H level, the output q is at H level when the resonance period T of the inverter is above a predetermined level Tth, and at L level when it is below Tth. Then, the control circuit 1 stops the inverter when both the output of the resonance period detection circuit 7 and the output of the small object detection circuit are L.

The operation of this embodiment will be explained below with reference to FIGS. 2 and 3. In FIG. 2, the horizontal axis represents the magnetic permeability μ of the load, and the vertical axis represents the resonant period T of the inverter.

The resonance period T varies depending on the load, and the aluminum foil.

Since the equivalent inductance of the heating coil L is low in Altite pots etc., ordinary enamel pots, cast iron pots, 5O8
-30.It will be shorter than 4 pots etc. And area E1 in the figure
Enamel pots, cast iron pots, 5O8-430 pots, knives, etc.
Area E2 is an Altite pot, etc., area E3 is no-load, aluminum foil, etc., and area E4 is a 5US-304 pot, etc. Area Ea
, threshold Tth so that E4 can be separated.
defines areas H and H. M and M are magnetic, respectively.
Indicates a non-magnetic region. In FIG. 3, M represents a set of magnetic loads, H represents a set of loads such as Altite pots and 5US-304 pans, and 100 represents a set that is not subject to small object detection. Then, the loads indicated by diagonal lines and mesh lines, which are the intersections of these sets, are heated. That is, for a magnetic load M, a load of MnS is heated, and for a non-magnetic load material, a load of HnS is heated. Mng.

Inverters are stopped for loads other than HnS. The above operations can be summarized as follows.

A normal non-magnetic load with a short resonance period T, a load with a long resonance period T, and the relationship between the signal state of each part of this example and the load are first explained.
Shown in the table.

Table 1 As shown in Table 1, the induction heating cooker of the present invention can heat 5US-304 pots, etc. in addition to magnetic non-small object loads, and stops when it detects aluminum foil, etc. in addition to small object loads. can do.

FIG. 4 is a specific circuit diagram of this embodiment. In this figure, the same components as in FIG. 1 are given the same symbols. 8
1 is a resistor, -9 is a diode, and 10 is a capacitor, which together with CT constitute an input current detection circuit. 11.12,1
3.14 divides the voltage ■L across the induction heating coil L using a resistor.

15 and 16 are resistors, which together with the operational amplifier 17 constitute a differential amplifier. 33 is a diode, 34 is a resistor, 35
holds the peak of the positive signal output from the differential amplifier using a capacitor. 18, 19, 20, and 21 are resistors that divide the voltage VL, and 22 is a comparator that determines the polarity of the voltage L. 23 is a constant current source, 24 is a capacitor, and transistor 26. Resistance 26. Together with the peak hold circuit constituted by the capacitor 27, the voltage proportional to the open time of the comparator output is expressed as e=
29 is a comparator. 28 is a DC voltage source that determines the threshold 7th.

31 is an OR circuit and resistor 32. This is a gate that allows the output of the comparator 29 to pass only when the output of the magnetic load detection circuit 2 composed of the pot switch SW is H. Figure 5 is the 4th
FIG. 3 is a waveform chart showing the operation of the resonance period detection circuit 7 shown in the figure. In the figure, k, 1°m, and n indicate the waveforms of the signals at each part in FIG.

When the transistor Q inputs a pulse with a waveform as shown in the figure, the waveform between the heating coils L becomes 1. m. Then, a voltage vT proportional to the time during which the waveform m becomes higher than the waveform l, that is, the resonance period T, is outputted to the output section n of the comparator 22 as the waveform n. And the voltage vT at the top of this waveform n and the DC voltage V
By comparing r with the comparator 29, it is possible to determine whether T is greater than or equal to the threshold Tth.

FIG. 6 is a specific circuit diagram of another embodiment of the present invention. In this figure, the same components as in FIG. 4 are given the same symbols. 36 is a transistor, 37 is a diode, 38 is a capacitor, and 39.40 is a resistor. In this embodiment, the electric potential at one end of the induction heating coil L is detected to detect small objects and the resonance period. That is, it is possible to easily detect the voltage from one end of the induction heating coil, and there is an advantage that the circuit and wiring are particularly simple.

Effects of the Invention As is clear from the examples, the induction heating cooker of the present invention performs appropriate load detection particularly for magnetic pots by detecting small objects, and for non-magnetic pots by detecting small objects and resonance period detection. As a result, it is possible to heat a non-magnetic pot such as a 5US-304 pot without heating aluminum foil, etc., thereby expanding the heatable load range and ensuring set meals.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the induction heating cooker of the present invention, Fig. 2 is an explanatory diagram of the operation of the induction heating cooker of Fig. 1, and Fig. 3 shows the operating range of the induction heating cooker of Fig. 1. 4 is a specific circuit diagram of an induction heating cooker according to an embodiment of the present invention, FIG. 6 is a waveform diagram showing the operation of the induction heating cooker, and FIG. 6 is a diagram showing another embodiment of the present invention. FIG. 7 is a block diagram showing the configuration of a conventional induction heating cooker, FIG. 8 is an explanatory diagram of the same operation, and FIG. 9 is a conceptual diagram showing the same operation range. . L...Induction heating coil, Q...Transistor, 1...Control circuit, 2...Magnetic pot detection circuit, 3...Heating coil voltage detection circuit,
4... Input current detection circuit, 6... Small object detection circuit, 7... Resonance period detection circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
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Claims (3)

[Claims] (1) An inverter that has an induction heating coil and causes resonance oscillation, a control circuit that controls the output of this inverter, a magnetic load detection means that detects whether or not it is a magnetic material, and a detection circuit that detects the voltage of the induction heating coil. and a resonant period detecting means for detecting a resonant period of the inverter. If a body is detected, it is determined whether the detection period from the resonance period detection means is equal to or greater than a predetermined value, and if it is equal to or greater than the predetermined value, the induction is configured to drive the inverter regardless of the output from the small object detection means. Heating cooker. (2) The induction heating cooker according to claim 1, wherein the detection circuit for detecting voltage is connected to one end of the induction heating coil. (3) The induction heating cooker according to claim 1, wherein the resonance period detection means is constituted by a non-conduction time detection circuit of a switching element of an inverter.