JP2001091367A - Temperature detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a plurality of states of a temperature sensor by one A/D converting circuit. SOLUTION: This temperature detecting circuit comprises a plurality of comparing circuits 30 to receive the input of the states of a temperature sensor 1 for determining a plurality of its states, resistors 40 and 41 serially connected to the outputs of the comparing circuits 30, a resistor circuit 4 which connects the other ends of resistances 40 and 41 to each other and changes into a parallelly connected state by the output of each comparing circuit 30, and an A/D converter 6 to connect the resistor circuit 4 to a reference resistor 5 to connect the other end of the resistor 5 to a D.C. power source V to detect the voltage of the connecting point between the resistor circuit 4 and reference resistor 5. The temperature detecting circuit performs control on the basis of the result of the conversion of the A/D converter 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting circuit for use in a heating device or the like which uses a temperature sensor and changes a control operation according to the result of a comparing means.

[0002]

2. Description of the Related Art A heating device for cooking, for example, a rice cooker, a microwave oven, a cooking heater, and the like, inputs a temperature state of a load, a temperature of a control circuit itself, and the like, and controls a heating power so as to perform appropriate heating.

In general, in order to input such temperature information, a change in thermistor resistance value due to temperature is converted into a change in voltage using a thermistor having a negative characteristic, and this is input to an AD converter. is there.

Furthermore, it is necessary to simultaneously detect the voltage of the commercial power supply and the current supplied during heating. These inputs are also input to the AD converter. A plurality of A / D conversion results are comprehensively determined, and, for example, a control microcomputer performs increase / decrease of heating power and temperature control.

[0005]

However, if the number of heating elements of the heating device increases or the control of the heating device itself becomes complicated, the input information increases and the number of necessary AD converter circuits also increases. I do.

Generally, a multi-channel input AD converter built in a microcomputer is used,
Connect to an external AD converter.

[0007] In particular, in an A / D converter with a built-in microcomputer, which is frequently used in a heating device for cooking, it is common to use at most 8 channels. A plurality of A / D converters (6-A, 6-B) are connected as in the example, or a signal switching circuit such as an analog switch circuit 8 is required in the preceding stage of the A / D converter as in the example of FIG. (Sn indicates a sensor circuit) Therefore, the cost is increased, for example, by increasing the number of AD converters themselves or increasing the number of circuits around the AD converters.

For example, when a temperature sensor for protecting circuits and components is used, necessary control points are often many, and information on the entire temperature range detected by the temperature sensor is not always necessary. .

Further, depending on the mounting position of the temperature sensor, it may be necessary to take an insulating configuration from the control circuit.

Further, usually, the threshold value for determining the state of the temperature sensor from the AD conversion result is often fixed (masked) by control software of a control microcomputer.

The input of the temperature sensor relating to the product safety is performed in parallel with the determination of the structure of the product casing and the test, and the final setting of the threshold value may be shifted after the mask.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a plurality of comparison circuits for inputting a state of a temperature sensor and determining a plurality of states, and an output of the comparison circuit. A resistor connected in series to the other end of the resistor, the other end of the resistor is connected to each other, a resistance circuit portion that changes to a parallel connection state by the output of each comparison circuit, and the resistor circuit portion and a reference resistor are connected, The other end is connected to a DC power supply, and an AD for detecting a voltage at a connection point between the resistance circuit unit and a reference resistance is detected.
A converter is provided, and control is performed based on the conversion result.

In addition, the number of the temperature sensors is one, and there are a plurality of states to be detected.

In addition, there are a plurality of the temperature sensors and a plurality of states to be detected.

The output of the comparison section and the resistance circuit section are connected by an insulating circuit such as a photocoupler.

The resistance used in the resistance circuit section is as follows:
Each was appropriately weighted.

[0017]

According to the present invention, a plurality of states of a temperature sensor or states of a plurality of temperature sensors can be detected by one AD converter.

Further, by forming an insulating circuit between a portion for detecting and comparing the state of the temperature sensor and a portion for synthesizing a resistance from the comparison result, a failure such as a power supply failure of the comparison portion or a cable disconnection can be prevented. The detection can be performed on the control unit side having the converter.

Further, by appropriately weighting the resistance value of the combined resistance circuit section, the state of a plurality of temperature sensors can be detected by one AD converter.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is an electric circuit diagram showing one embodiment of the present invention. A temperature sensor 1 is connected in series with a resistor 2 and connected to positive and negative power supply terminals, respectively.

The voltage at the connection point between the temperature sensor 1 and the resistor 2 is defined as Vin.

The comparator 3 comprises a comparator and a reference voltage circuit. The comparator 30 comprises a comparator 300 and resistors 301 and 302.
Are connected in series, and the outputs of the reference voltage circuits respectively connected to the positive and negative power supplies are connected to the non-inverting input terminal.

Further, Vin is input to the inverting input terminal.

Similarly, the comparison circuit 31 comprises a comparator 310 and resistors 311 and 312.

At this time, the outputs of the reference voltage circuits of the comparison circuit 30 and the comparison circuit 31 are different voltages (Vth30, Vth3
1) shall be set.

The output terminals of the comparison circuits 30 and 31 are connected to the resistors 40 and 41 of the resistance circuit section 4, respectively.
To one end.

The other end of the resistor 5 is connected to the positive power supply.

The voltage at the connection point between the resistors 40, 41 and 5 is Vo
ut.

The AD converter 6 has a voltage reference AVr
ef is connected to the positive power supply, the reference voltage terminal AVss is connected to the negative power supply, and Vout is input to the AD conversion input terminal.

With such a configuration, the connection state of the resistance circuit section 4 and the resistance 5 to the positive and negative power supplies changes depending on the state of the comparison section 3.

Therefore, V which is changed by the temperature sensor 1
in is converted to Vout and output.

FIG. 2 shows Vin and Vou with respect to the sensor temperature.
It is an example showing the change of t.

Here, a negative temperature coefficient thermistor is used as the temperature sensor 1.

When the sensor temperature rises, the resistance value of the thermistor decreases, and Vin rises.

Assuming that the reference voltages of the comparison circuits 30 and 31 are Vth30 and Vth31, respectively, the output of the comparison circuit is inverted when Vin becomes the voltage.

Regions where Vin is less than Vth30 are A, Vt
The region from h30 to Vth31 is B, and the region above Vth31 is C.

If the output terminal configuration of the comparators 300 and 310 is an oven collector, in the area A, the comparison section 3 side of the resistors 40 and 41 is not connected, in the area B only the resistor 40 is connected to the negative power supply side, and in the area C Then, both the resistors 40 and 41 are connected to the negative power supply side.

FIG. 3 shows a simplified circuit state in each of the regions A, B and C.

Each of the comparison circuits 30 and 31 can be replaced with a switch.

FIG. 4 shows an example in which a threshold value for determining the state of the temperature sensor 1 is set from the conversion result of the AD converter 6 in the circuit example of FIG.

In the area A, Vout = V In the area B, In region C, Becomes

Since two thresholds are required for discriminating each area, if the discrimination between the area A and the area B is VthAB and the discrimination between the area B and the area C is VthBC, Where a + b = 1 However, c + d = 1 may be set.

FIG. 5 shows a second embodiment in which a plurality of temperature sensors 11 and 12 are input.

Here, two temperature sensors 11 and 12 are used as inputs, but the same circuit configuration is used even when three or more temperature sensors are used.

In FIG. 5, temperature sensors 11 and 12 are connected in series with resistors 21 and 22, respectively, and connected to positive and negative power supplies, respectively.

The respective connection point voltages are Vin1,
Vin2.

The configuration from the comparison unit 3 to the AD converter 6 is the same as the configuration in FIG. 1, but the reference voltage circuit output Vth3
0 and 31 are set according to the temperature detected by each temperature sensor.

FIG. 6 shows an example of a change in the detected temperature with respect to the sensor temperature, and an output voltage Vout in the circuit of this configuration.

FIG. 7 shows a simplified circuit state in each of the regions D, E, F and G.

As in the case of FIG. 3, each of the comparison circuits 30 and 31 can be replaced with a switch.

Since there are two states (D, E) of the sensor 11 and two states (F, G) of the sensor 12, Vout is a four-level output.

The voltage when each of them is combined is Vo
outDF, VoutDG, VoutEF, VoutEG
Then Becomes

Since three thresholds are required to determine each state, the determination of the combination (D & F) and (D & G) is made by Vt
hDFDG, determination of combination (D & G) and (E & F)
thDGEF, and the discrimination between the combination (E & F) and (E & G) is VthEFEG, Where e + f = 1 Where g + h = 1 However, it is sufficient to set i + j = 1.

FIG. 8 shows a third embodiment in which the output of the comparison section 3 is constituted by an insulating circuit, compared to the embodiment of FIG.

In FIG. 5, current limiting resistors 303 and 313 for photocoupler light emitting elements are connected to the output sides of comparators 300 and 310, and photocouplers 304 and 314 are connected.
To the light-emitting side terminal. Here, the light emitting side power supply terminals of the sensor circuit section, the comparison section and the photocoupler are connected to the common power supply V1.
And G1.

The power supply for connecting the resistor 5 is connected to the power supply V2-G2 which is insulated from the common power supplies V1 and G1.

One of the output terminals of the photocouplers 304 and 314 is connected to the resistance circuit unit 4 and the other is connected to G2.

In the AD converter 6, the voltage reference AVref is connected to the positive power supply V2, and the reference voltage terminal AVss is connected to the negative power supply G2.

With such a configuration, the power supply constituting the sensor comparison unit and the power supply constituting the control unit including the AD converter can be separated.

FIG. 9 shows an example in which the mounting portion is divided in the configuration of FIG. 8 and the sensor comparison section A and the control section B are connected by a signal cable C.

In this embodiment, for example, (1) when the power supply 1 breaks down, (2) when the cable C is not connected, the photocoupler in the output stage of the comparison unit is in a non-driving state or is in a non-driving state. Since the output signal level becomes the same as that of the above, there is an advantage that a failure can be determined.

As the resistance value of the resistance circuit unit 4 connected in parallel by the comparison unit 3, the minimum resistance value is R
(Ω), weights R, 2R, 4R,...

FIG. 10 shows an equivalent circuit diagram in the case where the number of resistors constituting the resistance circuit section 4 is three. FIG. 11 shows the combined resistance value when the resistance value is weighted and the power supply voltage as 1. It shows the output voltage ratio in the case of performing. (In the case where the resistance value is set to 2R / 3 as the resistor 5) In FIG. 11, １１ indicates that the resistor is connected to the reference potential by a switch (comparing unit), and x indicates that the resistor is not connected.

By setting the resistance value in this manner, a plurality of states of the temperature sensor or the states of the plurality of temperature sensors are detected and converted into voltage information. The state can be determined.

By adopting the configuration as in the first to third embodiments, the threshold value for determining the state of the temperature sensor is kept as it is, and the resistance constant constituting the reference voltage circuit in the comparison section is changed. The software of the control microcomputer can be used without changing the threshold value.

[0067]

According to the present invention, a plurality of states of the temperature sensor or the states of the plurality of temperature sensors can be detected by one AD converter.

Therefore, when a large number of A / D converters are required, such as a heating device that requires a large number of sensor inputs at the same time, the number of A / D converters can be satisfied with a small number.

Further, by forming an insulating circuit between a portion for detecting and comparing the state of the temperature sensor and a portion for synthesizing a resistance based on the comparison result, malfunctions such as a power failure of the comparing portion and a broken cable can be prevented. The detection can be performed on the control unit side having the converter.

Further, by appropriately weighting the resistance value of the combined resistance circuit section, the state of a plurality of temperature sensors can be detected by one AD converter.

By adopting such a configuration, the threshold value for determining the state of the temperature sensor is kept as it is, and the control is performed without changing the threshold value by changing the resistance constant constituting the reference voltage circuit in the comparison section. Microcomputer software can be used.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a temperature detection circuit showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a sensor temperature and an input / output voltage in FIG. 1;

FIG. 3 is a simplified diagram of a circuit example output part in FIG. 1;

FIG. 4 is a schematic diagram of setting an output voltage and a threshold in FIG. 1;

FIG. 5 is a circuit diagram of a temperature detection circuit showing a second embodiment of the present invention.

FIG. 6 is a relationship diagram between a sensor temperature, an input / output voltage, and a threshold value in FIG. 5;

FIG. 7 is a simplified diagram of a circuit example output part in FIG. 5;

FIG. 8 is a circuit diagram of a temperature detection circuit showing a third embodiment of the present invention.

FIG. 9 is a circuit diagram showing a mounting example in FIG. 8;

FIG. 10 is a simplified diagram of an output portion when there are three comparison units.

FIG. 11 is a diagram illustrating a relationship between a combined resistance and an output voltage in the example of FIG. 10;

FIG. 12 is a block diagram of a temperature detection circuit showing a conventional example. (When using multiple AD converters)

FIG. 13 is a block diagram of a temperature detection circuit showing a conventional example. (When a signal switching circuit is connected before the AD converter)

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Temperature sensor 2 Resistance 3 Comparison part 4 Resistance circuit part 5 Resistance 6 AD converter

Claims (5)

[Claims] A plurality of comparison circuits for inputting a state of a temperature sensor and discriminating a plurality of states, and a resistor connected in series to an output of the comparison circuit.
41), the other ends of the resistors (40, 41) are connected to each other, and a resistance circuit section (4) that changes to a parallel connection state by an output of each comparison circuit (30); A reference resistor (5) is connected, the other end of the resistor (5) is connected to a DC power supply (V), and a voltage at a connection point between the resistor circuit section (4) and the reference resistor (5) is connected. A temperature detection circuit having an AD converter (6) for detecting the temperature and performing control based on the conversion result. 2. The temperature detection circuit according to claim 1, wherein the number of the temperature sensors is one and a plurality of states are detected. 3. The temperature detection circuit according to claim 1, wherein there are a plurality of said temperature sensors and a plurality of states to be detected. 4. An insulation circuit (304, 31) such as a photocoupler between the output of the comparison section (3) and the resistance circuit section (4).
2. The temperature detection circuit according to claim 1, wherein the connection is established in 4). 5. The temperature detecting circuit according to claim 1, wherein each of the resistors used in the resistor circuit section is appropriately weighted.