JPH02114486A - Induction heating cooker - Google Patents

Abstract

PURPOSE:To prevent every inadequate load from being heated so as to attempt improving the operational safety of the cooker in the title, by allowing an oscillation control unit to vary the period of stopping an inverter circuit from oscillating according to the value of an input current being detected when a load detector judges the load inadequate. CONSTITUTION:The cooker in the title has a load detector 5 which judges the adequacy or inadequacy of every load being inductively heated by a heating coil 2, an input current detector 6 which detects an input current from a current spreading power source 1, and an oscillation control unit 7 which turns off a switching element 3 only for a given time so as to stop an inverter circuit 8 from oscillating when the load detector 5 judges the load inadequate. Moreover, the oscillation control unit 7 can vary the period of stopping the inverter circuit 8 from oscillating according to the value of an input current being detected when the load detector 5 judges the load inadequate. Thus, when it happens to supply comparatively high power during the period of judgment, the subsequent period of stoppage is set to a long span of time for lowering mean power to inhibit the load from being heated, so that the operational safety of the cooker may be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an induction heating cooker that determines suitability of a load to be induction heated and controls oscillation of an inverter circuit.

Conventional Technology In an induction heating cooker, a high-frequency current is applied to a heating coil to generate high-frequency magnetic flux to induce an eddy current in a load magnetically coupled to the heating coil, and the load is heated by the resulting J/L' heat. Initial load detection system that is equipped with a load detection device that determines whether the load is appropriate or inappropriate so that even if the user accidentally places a load of small items such as knives and forks on the induction heating cooker, the small items will not be heated. Generally, the load is determined based on the balance between the input current to the induction heating cooker and the voltage/current generated within the induction heating cooker. Furthermore, when it is determined that the load is inappropriate, the application of current to the heating coil is stopped for a certain period of time and then restarted. In other words, the heating operation--detection of unsuitable load--stopping is repeated. Hereinafter, this series of operations will be referred to as intermittent oscillation, and one period thereof will be referred to as intermittent oscillation period.

Conventionally, the period during which this intermittent oscillation stopped was fixed.

Problems to be Solved by the Invention However, the time it takes for the load detection device to determine that the load is inappropriate is not constant and varies depending on the material and shape of the load.
For some kinds of loads that are difficult to judge, it takes time to detect load unsuitability. Therefore, in the conventional control method where the stop period of intermittent oscillation is fixed, for loads that require time to detect load unsuitability, the heating time is stopped. It takes a long time, and the load is sufficiently heated, so that if the user accidentally comes into contact with the load, there is a problem that an accident such as burns may occur.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a highly safe induction heating cooker that does not overheat an inappropriate load.

Means for Solving the Problems In order to achieve the above objects, the present invention provides an inverter circuit consisting of a DC power source, a heating coil for converting the DC power to AC, a resonant capacitor, and a switching element, and a converter circuit configured by the heating coil. a load detection device that determines whether the load to be inductively heated is appropriate or not; an input current detection device that detects the input current from the DC power source; an oscillation control section that turns off the switching element to stop the oscillation of the inverter circuit; The structure is such that the period during which the oscillation is stopped is varied.

Effect According to the above configuration, the load detection device detects the input current at the time when the load is judged to be unsuitable, and when the time required for that input current is long, that is, when a relatively large amount of power is supplied during the judgment period. sets the subsequent outage period to be longer,
It is possible to reduce the average power to the load and suppress the heating of the load.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of the induction heating cooker in this embodiment. 1 is a DC power supply, heating coil 2. Resonant capacitor 4
．． An inverter circuit 8 consisting of a switching element 3 having a bipolar transistor and an anti-parallel diode is connected. 5 is a load detection bag d that determines whether the load magnetically coupled with the heating coil/L'2 is appropriate or inappropriate; 6 is a DC power supply 1
This is an input current detection device that detects the input current from the inverter circuit 8 to the inverter circuit 8. Further, 7 is an oscillation control unit that controls on/off of the switching element 3, and the input current detecting device 6 detects the input current at the time when the load detecting device 6 determines that the heavy load is inappropriate, and detects that the input current is large. It has a function of making the oscillation stop period of the next switching element 3 longer.

FIG. 2 shows the relationship between the input current and the oscillation stop period of the oscillation control section 7.

In this graph, the horizontal axis is the input current at the time when load inadequacy is detected, and the vertical axis is the oscillation stop period.

In the conventional characteristic, the oscillation stop period is constant regardless of the input current at the time when the load is detected to be unsuitable, but in this embodiment, the larger the input current is, the longer the oscillation stop period is, and the oscillation stop period is fixed until the load is detected to be unsuitable. Even in a load that requires a long time, since the oscillation stop period, that is, the heating non-operation time is long, it is possible to suppress the supply of power to the load determined to be unsuitable and prevent the load from heating up further.

Effects of the Invention As is clear from the above-described embodiments, according to the present invention, the oscillation stop period is determined by the input current at the time when the load to be heated is determined to be unsuitable (correlation with the time required until the unsuitability determination). Since it is variable, the power supply can be suppressed even to any unsuitable loads, and even if the user accidentally comes into contact with such heated loads, it is possible to prevent accidents such as burns.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an induction cooking device according to an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the oscillation stop period and the input current of the induction cooking device. 1...DC power supply, 2...Heating carp μ,
3...Switching element, 4...Resonance capacitor, 6...Load detection device, 6...
...Input current detection device, 7...Oscillation control section, 8.
...Inverter circuit.

Claims (1)

[Claims] an inverter circuit consisting of a DC power source, a heating coil for converting the DC power to AC, a resonant capacitor, and a switching element; a load detection device for determining whether the load to be inductively heated by the heating coil is appropriate or unsuitable; and the DC power source. an oscillation control section that turns off the switching element for a predetermined period to stop oscillation of the inverter circuit when the load detection device determines that the load is inappropriate; The induction heating cooker is characterized in that the oscillation control section changes the period during which the oscillation of the inverter circuit is stopped depending on the value of the input current when the load is determined to be inappropriate by the load detection device.