JPH0541276A - Temperature control device for induction heating cooker - Google Patents

Abstract

PURPOSE:To provide a temperature control device which stably functions even against the noise of an induction heating cooker, and is accurate equally in measurement and resolution even in the wide temperature range of measurement by switching the value of base resistance. CONSTITUTION:When a pan 9 is heated, input voltage to the input terminal of the A/D converter of a temperature measuring means 5 starts increasing. And if an increase in temperature is continued as it is, input voltage comes up to Vdd as close as possible, so that input voltage is hardly changed even when temperature is changed to a great extent. When combined resistance Rx which is the sum of base resistance R0 and R1 through R8, is therefore made to be new base resistance by closing the SW8 of a base resistance changing means 6, input voltage can thereby be lowered. When closing SW1 is then kept on in order while being started from the SW8, the A/D conversion is carried out in the specified temperature range and in the specified input voltage range for the change of the measured temperature of a thermister 4. By this constitution, temperature can be measured with almost equal accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device for an induction heating cooker used in general households.

[0002]

2. Description of the Related Art FIGS. 3 and 4 show a temperature measuring method in a general cooking appliance having a temperature control function using a conventional microcomputer.

First, in FIG. 3, Rth is a thermistor of the temperature detecting means, and the resistance value of this thermistor decreases as the temperature rises.

COMP is a comparator that compares the voltages at points a and b, outputs High when point a is a higher voltage than point b, and outputs Low in the opposite case, and outputs the result. Is input to the input 1 terminal of the microcomputer.

R24 to R31 are resistors that change the voltage at point b by dividing the DC power supply by the thermistors Rth and R23 by opening or closing a switch composed of a transistor or the like in the microcomputer.

The operation at that time is shown in FIG. First, in the F section, SW21 to SW28 are in the open state and b
The voltage at the point is a voltage determined by the resistance values of the thermistors Rth and R23. Here, when SW21 is closed, the voltage at the point b is the combined resistance value of R23 and R24 = 1 / like the G part.
(1 / R23 + 1 / R24) becomes the partial pressure of Rth,
When this voltage is compared with the voltage at the point a by the comparator COMP, the output of the comparator COMP is High. As described above, when the SW21 is sequentially opened and closed from the SW21, the voltage at the point b becomes higher than the voltage at the point a at the point H, that is, when the switch SW23 is closed, and the output of the comparator COMP is different from the previous one. Invert. At this time, when the SW23 is closed, the input to the input 1 terminal of the microcomputer is inverted, so that the temperature measured by the thermistor Rth at that time is R
If the temperature is set by the total resistance value of 24 to R26,
It is judged by a microcomputer. When the measured temperature of the thermistor Rth further rises and its resistance value decreases, the output of the comparator COMP does not invert even if SW23 is closed, and the output of the comparator COMP inverts only after SW24 is closed. The total resistance value of R27 is used to judge that the set temperature is reached.

Further, in the circuit configuration of the conventional example shown in FIG.
The control temperature can be easily changed by changing the resistance values of 24 to R31.

Another conventional temperature measuring method has a circuit configuration shown in FIG. Rth is a thermistor of the temperature detection means as in FIG. 3, and the resistance value of the thermistor decreases as the temperature rises. R41
Is a resistance, and this resistance value is generally set substantially at the center of the change of Rth in the temperature measurement range by the thermistor.

In the temperature measuring operation according to this configuration, when Rth changes due to a temperature change, the voltage at the point c obtained by dividing the DC power supply Vdd by Rth and R41 is read by the A / D input terminal of the microcomputer according to the change. The resistance value of Rth, that is, the temperature detected by the thermistor is determined by comparing the voltage read in in advance with the data programmed in the microcomputer. In this configuration, the high speed is achieved as in the first conventional example of FIG. Since such a switching operation is not performed, the operation is stable even against noise entering from the thermistor or the like.
Further, in the circuit configuration of FIG. 5, C41 and C42 are for absorbing noise entering from the thermistor or the like.

In both FIGS. 3 and 5, the control means controls the high frequency power source based on the measured temperature result to maintain the temperature of the load as set.

[0011]

However, in the structure of the conventional temperature controller for the heating cooker shown in FIG. 3, which is shown above,
The number of measurement temperature points is only the number of output terminals of the microcomputer, and it is impossible to make delicate measurements such as the difference in the slope of the temperature change, and it malfunctions even with large noise generated from the high frequency power source of the induction heating cooker. There was a problem that there was a fear of.

Further, in the structure of the conventional temperature controller for the heating cooker shown in FIG. 5, the exponential function is usually several hundred kΩ to several hundred Ω.
The voltage obtained by dividing the DC power supply Vdd by the thermistor of the temperature detecting element whose resistance value changes up to R41, which is the resistance value around the center of the change in the resistance value Rth of the thermistor, is A /
Although it is being input to the D input terminal, the input voltage at high temperature is close to Vdd, and at low temperature it is V
The value is close to ss. In other words, even for the same temperature change,
In the high temperature region and the low temperature region, the change in the input voltage to the A / D input terminal becomes relatively small, and the measurement accuracy decreases.

Therefore, in such a high temperature region and a low temperature region, the resolution of the A / D conversion is relatively lowered with respect to the change of the temperature in the central region of the measurement, and the noise of the same magnitude is received. However, the measurement error of temperature becomes large,
There was a problem that.

The present invention solves the above-mentioned problems, and operates stably against a large noise of an induction heating cooker,
Moreover, it is an object of the present invention to provide a temperature control device for an induction heating cooker that has the same measurement accuracy and resolution even in a wide temperature range.

[0015]

In order to achieve the above object, the present invention is directed to an induction heating device including a high frequency power source and a heating coil, a direct current power source for outputting a predetermined direct current voltage, and an operation using the direct current power source. A microcomputer having an A / D conversion input terminal and a plurality of output terminals, a thermistor of a temperature detecting element for measuring the temperature of a load such as a pan heated by the induction heating device, a reference resistance and the temperature detecting element. A DC power source is applied to both ends of a circuit in which the thermistors are connected in series, and a voltage obtained by dividing the voltage of the DC power source by the reference resistance and the resistance value of the thermistor is input to the A / D conversion input terminal of the microcomputer. As a result, temperature measuring means for measuring the temperature detected by the thermistor by comparing the divided voltage with the voltage value stored in advance in the microcomputer. A plurality of resistors are connected to a plurality of output terminals of the microcomputer, the output terminals are connected to the positive voltage side or the negative voltage side of the DC power source, or the resistance value of the reference resistor is switched to a state in which the output terminals are not connected to any of them. By changing the reference resistance changing means for changing the voltage input to the A / D input terminal of the microcomputer in a predetermined temperature measurement range by the thermistor of the temperature detecting element to a predetermined voltage V1 or less and V2 or more. A control means for controlling the output of the induction heating cooker so as to reach a predetermined temperature stored in the microcomputer based on the output of the temperature measuring means.

[0016]

According to the above construction, even if the resistance value of the thermistor, which is an exponential temperature detecting element, changes exponentially, the reference resistance changing means switches the value of the reference resistance in a necessary temperature measuring range. , The input voltage to the A / D conversion input terminal is always set in a range from the predetermined voltage V2 to V1. Therefore, even if the temperature changes in a wide range from low temperature to high temperature, the temperature can be measured with almost constant resolution.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of a temperature control device for a heating cooker according to the present invention. In FIG. 1, reference numeral 1 denotes an induction heating device, which is composed of a high frequency power source 1a for generating a high frequency voltage from a commercial AC power source and a heating coil 1b. 2 is a direct current power source for generating a direct current voltage Vdd = 5V (DC) from a commercial alternating current power source as a power source for a microcomputer or a control circuit. 3 is a microcomputer having an A / D conversion input terminal and a plurality of output terminals. ing.
4 is a thermistor which is a temperature detecting element and is a pan 9 which is a load.
Is measuring the temperature. Reference numeral 5 denotes a temperature measuring means, which stores a voltage obtained by dividing the Vdd of the DC power supply 2 by the reference resistance R0 and the resistance value Rth of the thermistor 4 into the A / D input terminal of the microcomputer to store it in the memory of the microcomputer. The resistance value of the thermistor 4, that is, the temperature detected by the thermistor 4 at that time is measured in comparison with the data shown in FIG. 6 is a reference resistance changing means,
Switches SW1 to S inside the microcomputer 3
The resistance value of the reference resistance R0 of the temperature measuring means 5 is changed by opening or closing W8.

Reference numeral 7 is a noise prevention means for preventing high frequency noise generated from the induction heating device 1 from entering the A / D input terminal and causing the temperature measuring means 5 to malfunction. It is composed of C2.

Reference numeral 8 is a control means for controlling the temperature of the pan 9 as a load to be kept at a predetermined temperature based on the measurement result of the memory inside the microcomputer and the temperature measuring means 5.

Next, the operation of this embodiment will be described with reference to the drawings. FIG. 2 is a diagram showing the operation of the embodiment of the present invention. Here, FIG. 2- (a) shows the microcomputer 3 with respect to the temperature change of the pot 9 measured by the thermistor 4.
Fig.2- (b) shows the voltage change of the A / D conversion input terminal of
The change of the resistance value of the thermistor 4 with respect to the temperature change of the pan 11 measured by the thermistor 4 is shown.

First, when the pot 9 is heated by the induction heating device 1, the input voltage to the A / D conversion input terminal of the temperature measuring means 5 is from the point a'as shown in FIG. 2 (a). Start climbing. In other words, the resistance value Rth of the thermistor 4 becomes smaller as the temperature of the pot 9 rises, and thus the voltage Vdd of the DC power supply 2 is divided by this Rth and the reference resistance R0 to the A / D conversion input terminal. The input voltage of is increasing. If the temperature continues to rise as it is, the input voltage to the A / D conversion input terminal becomes as close to Vdd as shown by the chain line after the point a, and is almost A / D even with a large temperature change. D
The input voltage to the conversion input terminal does not change. At this time, even if the noise is small, if the input voltage to the A / D conversion input terminal changes due to the influence, the voltage change becomes very large when converted into temperature.

Therefore, by closing SW8 of the reference resistance changing means 6 at the point a, the reference resistances R0 and R1 to R1.
If the combined resistance Rx with the total resistance value of 8 is newly used as the reference resistance, the input voltage to the A / D conversion input terminal will decrease. By sequentially closing SW8 to SW1 in this way, the input voltage to the A / D conversion input terminal is within a predetermined voltage V1 or less and V2 or more in the temperature range T0 to T1 even if the temperature measured by the thermistor 4 changes. A / D in the range
The conversion is performed and the temperature is measured.

[0023]

As described above, the effect of the present invention is to provide a direct current power source which outputs a predetermined direct current voltage, a microcomputer having an A / D conversion input terminal and a plurality of output terminals which are operated by the direct current power source, A thermistor of a temperature detecting element that measures the temperature of a load such as a pot heated by the induction heating device, and a DC power source is applied to both ends of a circuit in which a reference resistance and the thermistor of the temperature detecting element are connected in series, and this reference is used. By inputting the voltage obtained by dividing the voltage of the DC power supply by the resistance value of the resistor and the thermistor to the A / D conversion input terminal of the microcomputer, the divided voltage is stored in advance as a voltage value stored in the microcomputer. Temperature measuring means for measuring the temperature detected by the thermistor by comparing,
A plurality of resistors are connected to a plurality of output terminals of the microcomputer, the output terminals are connected to the positive voltage side or the negative voltage side of the DC power source, or the resistance value of the reference resistor is switched to a state in which the output terminals are not connected to any of them. By changing the reference resistance changing means for changing the voltage input to the A / D input terminal of the microcomputer in a predetermined temperature measurement range by the thermistor of the temperature detecting element to a predetermined voltage V1 or less and V2 or more. Since the input voltage to the A / D conversion input terminal is limited to the predetermined voltage range in the predetermined temperature range, the temperature can be measured with almost the same accuracy even when the temperature changes. Since it is possible to prevent the influence of noise from the high frequency power source from increasing,
It is possible to obtain a temperature control device for an induction heating cooker that stably performs temperature adjustment operation.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an input voltage characteristic to a measurement temperature-A / D conversion input terminal and a measurement temperature-resistance value Rth characteristic of a thermistor.

FIG. 3 is a configuration diagram of a heating cooker of a first conventional example.

FIG. 4 is a timing chart showing the operation of the heating cooker of the first conventional example.

FIG. 5 is a configuration diagram of a heating cooker of a second conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Induction heating device 2 DC power supply 3 Microcomputer 4 Thermistor of temperature detecting element 5 Temperature measuring means 6 Reference resistance changing means 7 Noise prevention means 8 Control means 9 Pan

Claims (1)

[Claims] Claim: What is claimed is: 1. An induction heating device comprising a high frequency power supply and a heating coil, a direct current power supply for outputting a predetermined direct current voltage, an A / D conversion input terminal operated by the direct current power supply, and a plurality of output terminals. A DC power supply is applied to both ends of a circuit in which a computer, a thermistor of a temperature detecting element that measures the temperature of a load such as a pot heated by the induction heating device, and a reference resistance and the thermistor of the temperature detecting element are connected in series. By dividing the voltage of the DC power supply by the resistance value of the reference resistance and the thermistor into the A / D conversion input terminal of the microcomputer, the divided voltage is stored in advance in the microcomputer. A temperature measuring means for measuring the temperature detected by the thermistor by comparing it with a voltage value, and a plurality of output terminals of the microcomputer. By connecting a resistor, the output terminal is connected to the positive voltage side or the negative voltage side of the DC power supply, or by switching to a state in which it is not connected to any, by changing the resistance value of the reference resistor, the temperature sensing element Based on the output of the temperature measuring means, reference resistance changing means for changing the voltage input to the A / D input terminal of the microcomputer in the predetermined temperature measuring range by the thermistor to a predetermined voltage V1 or less and V2 or more, A temperature control device for a heating cooker, comprising: a control means for controlling the output of the induction heating cooker so that a predetermined temperature stored in a computer is reached.