JPH05109466A - Induction-heated cooking appliance - Google Patents

Abstract

PURPOSE:To perform high-precision, stable a piece of food load detection minimizing a comparison error by comparing the input current detection A/D- conversion value with the gadget current value data in response to the input power level. CONSTITUTION:An input current detecting circuit 9 converts the input current into a proper voltage value and outputs it to an A/D converter 13. An input power level setting circuit 11 feeds the excitation rate setting signal to an inverter oscillation control circuit 15 based on the output of an operation section 10 and outputs the set level to a piece of food current value data table 12. A comparator 14 compares the output of the converter 13 and the output of a table 2, if the output of the converter 13 is smaller, it judges the load as a piece of food load, and it outputs the stop signal to the circuit 15. The input current detection value is ADD-converted and compared with the piece of food current data, thus a comparison error can be minimized, and high-precision, stable piece of food load detection can be performed.

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 for detecting small load.

[0002]

2. Description of the Related Art A high-frequency current is applied to a heating coil to generate a high-frequency magnetic flux to induce an eddy current in a load magnetically coupled to the heating coil, and the Joule heat heats the load. If a small load such as a spoon or a spoon is heated, there is a risk of burns, so a small load detection method that distinguishes by comparing the input current with the input voltage or the resonance voltage of the heating coil is disclosed in Japanese Patent Publication No.
It was proposed in Japanese Patent Publication No. 9-32878 and Japanese Patent Publication No. 61-29117.

[0003]

However, in the above method, the resistance voltage dividing circuit is required to detect the input voltage, and the control circuit is not insulated. There is also a problem that the detection level changes when the input power changes due to the change of the input voltage.

[0004]

The present invention has been made to solve the above problems, and a rectifier circuit for converting an AC power supply into a DC power supply and a high-frequency current supplied from the DC power supply to a heating coil. In an induction heating cooker comprising an inverter circuit for controlling the inverter circuit and a control circuit for controlling the inverter circuit, an input current detection circuit for detecting an input current of an AC power supply or an input current of the inverter circuit in the control circuit, and the detection value. Is provided with an A / D converter for converting the input power into a digital value, an input power level setting circuit for setting the input power, and an accessory current value data table selected according to each level of the input power level setting circuit is provided. The current detection A / D conversion value and the small object current value data corresponding to the input power setting level are compared, and when the A / D conversion value of the input current detection value is small, Determines that the object load, but to stop the drive of the inverter circuit.

[0005]

With the above configuration, the input current detection circuit detects the input current of the AC power supply or the input current of the inverter circuit, and the detected input current value is converted by the A / D converter. The / D conversion value is compared with the accessory current value data in the accessory current value data table corresponding to the input power setting level set by the input power level setting circuit,
When the A / D converted value of the detected input current is small, it is determined that the load is a small object, and the driving of the inverter circuit is stopped.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block circuit diagram of an induction heating cooker to which an embodiment of the present invention is applied, and FIG. 2 is an example of data for detecting the load of the small article.

In the figure, 1 is an AC power source, 2 is a rectifying circuit for rectifying the AC power source 1, and 18 is a choke coil 3 for smoothing the output of the rectifying circuit 2 to DC, a smoothing capacitor 4, and a heating coil 5. , A resonance capacitor 6, a damper diode 7, and a switching element 8.

Reference numeral 19 denotes an input current detection circuit 9, an operating section 10,
Input level setting circuit 11, small item current data table 1
2, a control circuit including an A / D converter 13, a comparator 14, an inverter oscillation control circuit 15, a drive circuit 16 and a timing generation circuit 17. The current transformer CT detects the primary side input current and inputs it to the input current detection circuit 9,
After converting to an appropriate voltage value, it is output to the A / D converter 13. The operation unit 10 is an input unit for the user to set the thermal power level and the like, and the output of the operation unit causes the input power level setting circuit 11 to output the duty ratio setting signal to the inverter oscillation control circuit 15 and to also set the small object current value. Data table 1
The set level is output to 2. The digital output of the A / D converter 13 and the output of the small object current value data table 12 are compared by the comparator 14, and when the output of the A / D converter 13 is small, it is judged as a small object load, and the inverter oscillation control circuit 15
The stop signal is output to.

The inverter oscillation control circuit 15 inputs a duty factor setting signal and a stop signal, and outputs a pulse to the drive circuit 16 of the switching element 8 if the stop state is not reached. The drive circuit 16 amplifies and outputs a signal sufficient to drive the switching element 8. The operation timings of the A / D converter 13 and the comparator 14 are the same as those of the timing generation circuit 1
Set according to 7. This timing generation circuit 17
The output of is synchronized with the power cycle.

Next, a small object load detection method will be described.
In FIG. 2, the horizontal axis represents the input power setting level, and the vertical axis represents the input current detection A / D conversion value and the input current data. In this example, it is assumed that the input power setting level on the horizontal axis is from 1 to 10, and the current increases according to the setting level during that period. A is a proper load (pots etc. that can be used for induction heating cookers)
In the case of, the input power data example is shown, and B is the input current detection data example in the case of a small load. As is apparent from this example, in order to detect the small article load, the comparison data selected from the small article current value data table 12 may be set as C. Furthermore, by setting the timing generation circuit 17,
Since the A / D conversion is performed by the / D converter 13, it is possible to avoid an unstable portion of the current-voltage waveform near the zero cross of the input voltage, minimize the comparison error, and improve the accuracy. Highly stable small object load detection can be performed.

Unlike the conventional small load detection method, since it is not necessary to detect the input voltage and the like, the control circuit 19 can be left as an insulating circuit, and the detachable temperature sensor can be used even when it is incorporated in the metal housing. Can be used.

In the present embodiment, the input current is the current on the AC power supply side 1, but the same small load detection can be performed by detecting the input current of the inverter circuit 18 after rectification. It is also possible to configure a part of these circuit configurations with an additional circuit built in the microcomputer, and in that case, the number of parts can be reduced.

[0013]

According to the present invention, since it is not necessary to detect the input voltage and the like as in the conventional case, the control circuit may remain an insulating circuit, and the input current detection value may be A / D converted to be a small item. Since the comparison is made with the current data, the comparison error can be minimized, and highly accurate and stable small object load detection can be performed.

[Brief description of drawings]

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

FIG. 2 is a diagram similarly showing an example of small object load detection data.

[Explanation of symbols]

 1 AC power supply 2 Rectifier circuit 5 Heating coil 9 Input current detection circuit 11 Input power level setting circuit 12 Small current value data table 13 A / D converter 18 Inverter circuit 19 Control circuit

Claims (3)

[Claims] 1. A rectifier circuit (2) for converting an AC power supply (1) into a DC power supply, an inverter circuit (18) for converting the DC power supply into a high frequency current and supplying the heating coil (5), and the inverter circuit. In an induction heating cooker comprising a control circuit (19) for controlling (18), an input current detection circuit (9) for detecting an input current in the control circuit (19) and the input current detection circuit (9) A / which converts the detected value detected by
D converter (13), input power level setting circuit (11) for setting input power, and accessory current value data table (12) selected according to each level of the input power level setting circuit (11)
Is provided, and the input current detection A / D conversion value is compared with the small object current value data corresponding to the input power setting level. If the A / D conversion value of the input current detection value is small, it is judged as a small object load, and the inverter circuit An induction heating cooker characterized in that the drive of (18) is stopped. 2. The induction cooking device according to claim 1, wherein the input current detection circuit (9) detects an input current of the AC power supply (1). 3. The induction heating cooker according to claim 1, wherein the input current detection circuit (9) detects an input current of the inverter circuit (18).