JPH07110269A - Temperature detecting device - Google Patents

Abstract

PURPOSE:To provide a temperature detecting device which can make accurate temperature measurement with only one thermistor. CONSTITUTION:When a plurality of temperatures is measured at the time of performing temperature measurement by comparing a voltage dividing signal S7 obtained by dividing a power supply voltage V0 by the resistance ratio between a thermistor 5 and a voltage dividing resistor 6 with a reference temperature voltage 11, the voltage value change of the signal S7 with the unit temperature change becomes smaller on the lower or higher temperature side. In order to perform highly accurate temperature measurement, therefore, a first reference voltage 23 which is lower than the reference temperature voltage 11 and second reference voltage 24 which is higher than the voltage 11 are set and circuit is so structured that, when the voltage of the signal S7 exceeds the second reference voltage 24, the voltage can be dropped to a voltage lower than the voltage 11 and, when the voltage of the signal S7 becomes lower than the first reference voltage 23, the voltage can be raised to a voltage higher than the voltage 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting device using a thermistor, and more particularly to a temperature detecting device for detecting a temperature of, for example, an electric stove or a gas stove in which it is difficult to arrange a plurality of thermistors in a heat source.

[0002]

2. Description of the Related Art Conventionally, a thermistor has been used as a temperature detecting element to detect the temperature of a heating element such as an electric stove or a gas stove. The temperature of the heating element is detected by electrically detecting the resistance value of the thermistor that changes in temperature.

A concrete explanation of this electrical detection is as follows.
In FIG. 6, the thermistor a1 and the resistor b1 are connected to form a voltage divider, the thermistor a1 of the voltage divider is connected to the power supply line d1, the resistor b1 is connected to the ground line d2, and the thermistor a1 and the resistor are connected. Using the connection point of b1 as an output terminal, the divided voltage signal e1 of the voltage obtained by dividing the power supply voltage E0 by the thermistor a1 and the resistor b1 is derived to the voltage dividing line d3, and the non-inversion of the comparators c2, c3, c4 is performed. While inputting to the input terminal, resistors b2, b3, b4 and resistors f2, f3, f4 are respectively connected, and reference voltages E2, E3, E4 are generated by dividing the power source voltage E0 from the respective connection points. The temperature is input to the inverting input terminal and the two are compared to detect the temperature of the heating element.

By the way, since the temperature coefficient of a general thermistor is negative, the resistance value of the thermistor a1 decreases as the temperature of the heating element rises, and the divided voltage signal e1 rises on the contrary. Here, the value of the divided voltage signal e1 at low temperature is E1, and the following equations, E1 <E2 <E3 <E4, are set so that the values of the reference voltages E2, E3, E4 are higher than E1. If the respective reference voltages E2, E3, E4 are set, the divided voltage signal e1 rises as the temperature of the thermistor a1 rises, and the comparator c2 rises every time the reference voltages E2, E3, E4 are exceeded. , C3, c4 outputs high, the thermistor a1 causes the reference voltages E2,
It is possible to detect when E3 and E4 are reached.

By the way, the temperature change of the resistance value of a general thermistor is, for example, 13 MΩ at −20 ° C.
It becomes about 1 MΩ at 80 ° C. and about 875Ω at 500 ° C. Therefore, when the resistance b1 of the voltage divider is set to, for example, 50 kΩ so that the temperature can be detected from −20 ° C. to 500 ° C., the value of the divided voltage signal e1 at −20 ° C., 80 ° C. and 500 ° C. Changes to e1 (−20 ° C.) = 0.0038 · E0 e1 (80 ° C.) = 0.0476 · E0 e1 (500 ° C.) = 0.9828 · E0. Then, the divided signal e1
The change per unit temperature becomes small especially at low temperature or high temperature. Therefore, when detecting a plurality of temperatures using one thermistor, it is necessary to set the reference voltage with high accuracy particularly on the low temperature side and the high temperature side.

However, the resistance value of the fixed resistor is
Since there is a certain variation at the shipping stage, it is difficult to accurately set the reference voltage using only this fixed resistor. Therefore, for example, one of the resistors that determines the reference voltage is used as a variable resistor, and the resistance value needs to be finely adjusted and set precisely.

On the other hand, if a plurality of thermistors are used, the value of the fixed resistance connected to each thermistor is changed, and if the resistance value of the thermistor at the temperature to be detected is made equal to the resistance value of the fixed resistance connected to each thermistor, the temperature It is also possible to compare the divided voltage signal with a voltage near ½ of the power supply voltage E0, which has a large voltage change with respect to the change, as a reference voltage. In that case, temperature detection can be performed with a certain accuracy. .

However, it is difficult to dispose a plurality of thermistors in the heat source in the electric stove, the gas stove, etc. due to the internal restrictions of the equipment, and it is not desirable in terms of cost.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the disadvantages and inconveniences of the above-mentioned prior art, and its purpose is to detect a plurality of temperatures with high accuracy by using one thermistor. An object is to provide a space-saving temperature detecting device.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 connects a thermistor whose resistance value changes with a temperature change and a voltage dividing resistor switchable to the resistance value at an output point. A voltage divider in which the thermistor is arranged in a heat source, one end of the voltage divider is connected to a power supply and the other end is grounded, and a voltage division signal obtained by dividing the voltage of the power supply from the output point is output. A temperature detecting device including a voltage divider, a temperature detecting comparator that outputs a temperature detection signal by comparing the voltage dividing signal with the temperature reference voltage, and a voltage dividing resistor switcher that switches the resistance value of the voltage dividing resistor. The voltage dividing resistor switch includes a second reference voltage having a voltage higher than the temperature reference voltage and a first reference voltage having a voltage lower than the temperature reference voltage, and the voltage of the voltage dividing signal is When the voltage exceeds the second reference voltage, The resistance value of the divided voltage signal is switched to reduce the value of the divided voltage signal to a voltage value between the first reference voltage and the temperature reference voltage, and when the voltage of the divided signal falls below the first reference voltage, Switch the resistance value of the voltage dividing resistor,
The value of the voltage dividing signal is boosted to a voltage value between the second reference voltage and the temperature reference voltage. The divided voltage signal is input to one side, and a reference voltage comparator to which a reference voltage is input to the other end is provided. The reference voltage comparator includes the reference voltage comparator when the voltage value of the divided voltage signal increases. A reference voltage switching device that uses the reference voltage as the second reference voltage and uses the reference voltage input to the comparator as the first reference voltage after the voltage value of the divided signal exceeds the second reference voltage. It is characterized by being provided.

[0011]

[Operation] A thermistor whose resistance value changes with temperature changes and a voltage dividing resistor are connected at an output point to form a voltage divider, and the thermistor is arranged as a heat source and one end of the voltage divider is connected to a power source. Since the end is grounded, the resistance ratio between the thermistor and the voltage dividing resistor changes depending on the temperature. Then, since a voltage division signal obtained by dividing the voltage of the power supply according to the resistance ratio is output from the output point, the temperature detection comparator compares the magnitude of the voltage division signal with a predetermined temperature reference voltage to determine the temperature. By outputting the detection signal, the temperature of the thermistor corresponding to the reference voltage can be detected.

At this time, a first reference voltage and a second reference voltage higher than the first reference voltage are provided, and the temperature reference voltage is located between the first reference voltage and the second reference voltage. , The voltage dividing resistor value is switchable in advance,
When the voltage of the voltage dividing signal exceeds the second reference voltage, the resistance value of the voltage dividing resistor is switched to change the value of the voltage dividing signal to a voltage value between the first reference voltage and the temperature reference voltage. When the voltage of the voltage dividing signal is stepped down and the voltage of the voltage dividing signal becomes lower than the first reference voltage, the resistance value of the voltage dividing resistor is switched to change the value of the voltage dividing signal between the second reference voltage and the temperature reference voltage. If a voltage divider resistor switch that boosts the voltage value is provided,
Since a plurality of temperatures can be detected by locating the divided voltage signal in a range between the first reference voltage and the second reference voltage, a wide range of temperatures can be detected with a large voltage change per unit temperature change. The temperature reference voltage can be set to.

Further, when the voltage division signal is switched only once each time the temperature is raised or the temperature is high, the first reference voltage is not necessary when the voltage division signal becomes large. Since the second reference voltage is not necessary when becomes smaller, the reference voltage comparator in which the voltage dividing signal is input to one of the input terminals and the reference voltage is input to the other end of the voltage dividing resistor switch. And the reference voltage is set to the second reference voltage when the voltage value of the divided signal increases, and the comparator is used after the voltage value of the divided signal exceeds the second reference voltage. If a reference voltage switch that uses the reference voltage input to the first reference voltage as the first reference voltage is provided in the reference voltage comparator, the voltage dividing resistor can be switched by one comparator, so that the circuit configuration is simple. Become.

[0014]

FIG. 1 is a block diagram showing an embodiment of the present invention. Referring to FIG. 1, reference numeral 2 denotes a voltage divider, one end of a thermistor 5 whose resistance value changes with a temperature change and a voltage dividing resistor 6
Of the thermistor 5 is connected to a power supply line 8 to which a power supply voltage V0 is applied, and the other end of the voltage dividing resistor 6 is connected to a ground line 9. Then configured.

From the output point 7, a voltage division signal obtained by dividing the power supply voltage V0 by the resistance value of the thermistor 5 and the resistance value of the voltage dividing resistor 6 is output from the output point 7 and is output from the temperature detection comparator 10. It is input to the non-inverting input terminal. The temperature reference voltage 11 is input to the inverting input terminal of the temperature detection comparator 10, and the temperature detection comparator 10 compares the divided voltage signal with the temperature reference voltage 11 and outputs the comparison result. A certain temperature detection signal is output from the output terminal 15 to an external device (not shown).

Reference numeral 3 is a voltage dividing resistance switch, which is a comparator 21,
22, a logic circuit 26, a resistance switching circuit 31, a delay circuit 32, and a counter 33. The divided signal is supplied to the inverting input terminal of the comparator 21 and the comparator 2.
2 non-inverting input terminal. The comparator 21,
Reference numeral 22 includes a first reference voltage 23 and a second reference voltage 24 at the non-inverting input terminals, respectively, and performs comparison with the divided voltage signal and outputs the result to the logic circuit 26 as a low or high state. Output.

Here, the relationship between the values of the first reference voltage 23 and the second reference voltage 24 and the value of the temperature reference voltage 11 is as shown in FIG. The voltage is higher than the voltage 23, and the temperature reference voltage 11 is set to be located between them. Now, assuming that the value of the divided voltage signal S7 is at the position of the point P1 as an initial state, the thermistor 5 is heated by a heat source (not shown) and then cooled, for example. The circuit operation of the present invention shown will be described.

If the temperature reference voltage 11 is set to a voltage value (V0 / 2) which divides the power supply voltage V0 into 1: 1, the change in the divided voltage signal with respect to the unit temperature change becomes the largest. Therefore, it is possible to accurately detect the temperature. Therefore, in order to specifically explain the operation of the circuit of this embodiment, the temperature reference voltage 11 is 1/2 of the power supply voltage V0.
And the value of the first reference voltage 23 is set to a value obtained by dividing the power supply voltage V0 into 18: 2 (2/20), and the second reference voltage is the power supply voltage V0. 2:18
It is assumed that the divided value is set to (18/20). Also, at the point P1 in the initial state, the resistance value of the thermistor 5 is 72 MΩ, and the value of the voltage dividing resistor 6 is 18
If it is set to MΩ, the value of the divided signal S7 at this time is the value of 4/20 of the power supply voltage V0, the output of the temperature detection comparator 10 is low, and the comparator 2
The outputs of 1 and 22 are both low.

When the temperature of the heat source in which the thermistor 5 is arranged rises and the temperature of the thermistor 5 also rises accordingly, the resistance value thereof decreases. On the other hand, even if the resistance value of the thermistor 5 decreases, the value of the voltage dividing resistor 6 is maintained as it is, and the value of the voltage dividing signal S7 increases.

Thus, when the value of the divided voltage signal S7 rises and the resistance value of the thermistor 5 becomes smaller than 18 MΩ which is the resistance value of the voltage dividing resistor 6, the divided voltage signal S
7 reaches a point P2 at which the temperature reference voltage 11 which is half the power supply voltage V0 is exceeded, and the output S15 of the temperature detection comparator 10 is inverted from low to high.

When the temperature further rises and the resistance value of the thermistor 5 becomes smaller than 2 MΩ, the value of the divided voltage signal S7 becomes larger than 18/20 of the power source voltage V0 and reaches the point P3 which exceeds the second reference voltage 24. . At this time, the comparator 2
2 output S22 is inverted from low to high, and the logic circuit 2
6 is input. The logic circuit 26 includes a signal S21 input from the comparator 21 and a signal S22 input from the comparator 22.
If either one of the two is high, a pulse signal is output, so the output S22 of the comparator 22 is
Is detected, the pulse signal is divided into voltage dividing resistor switching circuits 31
Output to. The voltage dividing resistor switch 31 outputs a resistance value switching signal to the voltage dividing resistor 6 included in the voltage divider 2 via the delay circuit 32.

The delay circuit 32 integrates the resistance value switching signal, for example, so that the voltage dividing resistor 6 does not malfunction due to the influence of noise or the like, and when the value exceeds a certain threshold value, the resistance value switching signal is output. The resistance value switching signal is transmitted to the voltage dividing resistor 6, and the resistance value switching signal is output to the voltage dividing resistor 6 of the voltage divider 2 with a delay of a predetermined delay time determined by the delay circuit 32. When the value switching signal is output to the voltage dividing resistor 6, the resistance value of the voltage dividing resistor 6 is 18 MΩ.
To 500 kΩ.

Along with this switching of the resistance value, the divided voltage signal S7 at the position of the point P3 having the value of 18/20 of the power supply voltage V0 is at the point P4 having the value of 4/20 of the power supply voltage V0. It is stepped down to the position. However, at this time, the delay circuit 3
Since the temperature of the thermistor 5 continues to rise for the delay time determined by 2, the voltage value of the divided voltage signal S7 is also higher than the position of point P3 and is at the position of point P5. The value of is reduced from the position of this point P5 to the position of a point P6 which is slightly larger than the above P4.

Since the voltage value at the point P6 is smaller than the second reference voltage and the temperature reference voltage 11, the output signal S22 of the comparator 22 and the output S15 of the temperature detection comparator 10 are obtained. Both invert from high to low.

When the temperature of the thermistor 5 further rises and its resistance value falls below the resistance value of the voltage dividing resistor of 500 kΩ, the voltage dividing signal S7 reaches the point P8 where the temperature reference voltage 11 is exceeded, and the temperature detecting signal is detected. The output of S15 is inverted from low to high.

Then, when the temperature of the thermistor 5 further rises and its resistance value becomes lower than about 55.6 kΩ, the divided voltage signal S7 becomes 18 of the power supply voltage V0 which is the voltage of the second reference voltage 24. A point P9 that exceeds the voltage value of / 20 is reached, the output S22 of the comparator 22 is inverted from low to high, and the output of the comparator 22 is reduced by the operation of the logic circuit 26, the voltage dividing resistor switch 31, and the delay circuit 32. The value of piezoresistor 6 is 50
It is switched from 0 kΩ to 13.9 kΩ. Due to the switching of the resistance value, the divided voltage signal S7 at the position of the point P9 at the voltage of 18/20 of the power supply voltage V0 becomes 4/20 of the power supply voltage from the position of the point P11 due to the lapse of the predetermined delay time. The voltage is lowered to a point P12 where the voltage is slightly higher than the point P10, and the temperature detection signal S15 and the output of the comparator 22 are inverted from high to low.

When the temperature of the thermistor 5 further rises and its resistance value becomes a value lower than 13.9 kΩ of the voltage dividing resistor 6, the voltage dividing signal S7 reaches a point P13 which exceeds the temperature reference voltage 11, and The detection signal S15 is inverted from low to high.

Since the circuit operation at the time of temperature rise has been described above, the case where the temperature drops will now be described. As the temperature of the thermistor 5 decreases, its resistance value increases and the voltage value of the divided voltage signal S7 decreases. The divided voltage signal S7 starts to drop from a voltage value higher than the temperature reference voltage 11, and the resistance value of the thermistor 5 is 13.9.
When the value exceeds kΩ, the divided voltage signal S7 reaches the point U1 below the temperature reference voltage 11, and the temperature detection comparator 10
S15's output S15 is inverted from high to low.

Then, when the temperature of the thermistor 5 further decreases and its resistance value rises to a value exceeding 125 kΩ, the divided voltage signal S7 indicates that the voltage is 2/20 of the power source voltage V0 which is the first reference voltage. When it reaches a point U2 below the value, the output S21 of the comparator 21 is inverted from low to high, and the resistance value of the voltage dividing resistor 6 becomes 13 due to the operation of the logic circuit 26, the resistance switching circuit 31, and the delay circuit 32. 0.99kΩ to 50
It is returned to 0 kΩ. At this time, 2/20 of the power supply voltage V0
The voltage-divided signal S7, which was at the position of the point U2 of the voltage value of, is changed from the position of the point U4 to 1 of the power supply voltage V0 by the passage of the delay time.
The voltage is boosted to the position of a point U5 having a voltage value slightly smaller than the point U3 having a voltage value of 6/20.

Since the voltage value at the point U5 is higher than the first reference voltage 23 and the temperature reference voltage 11, the output S15 of the temperature detection comparator 10 is inverted from low to high. The output S21 of the comparator 21 is inverted from high to low.

When the temperature of the thermistor 5 further decreases and its resistance value exceeds 500 kΩ, a point U6 below the temperature reference voltage 11 is reached, and the output S15 of the temperature detection comparator 10 is inverted from high to low. To do.

When the temperature further decreases and the resistance value of the thermistor 5 exceeds 4 MΩ, the divided voltage signal S7 reaches the point U8 below the first reference voltage 23, and the output S21 of the comparator 21 changes from low to low. It is inverted to high, and by the operation of the logic circuit 26, the resistance switching circuit 31, and the delay circuit 32,
The resistance value of the voltage dividing resistor 6 is returned from 500 kΩ to 18 MΩ. At this time, the divided voltage signal S7 at the position of the point U8 having the voltage value of 2/20 of the power supply voltage V0 is changed from the position of the point U10 to 16/20 of the power supply voltage V0 due to the lapse of the delay time.
The voltage is boosted to the position of a point U11 having a voltage value slightly smaller than the point U9 of the voltage value.

If the divided voltage signal S7 is below the first reference voltage and above the second reference voltage, the signal output from the resistance switching circuit 31 is the same pulse signal. The voltage dividing resistance switch 6 cannot determine whether to perform the switching for increasing the resistance value or the switching for decreasing the resistance value. Therefore, UP / DO is added to the voltage dividing resistor switch 3.
If the WN counter 33 is provided and the output S22 of the comparator 22 is input to the UP terminal of the UP / DOWN counter 33 and the output S21 of the comparator 21 is input to the DOWN terminal, When S7 exceeds the second reference voltage and the logic circuit 26 outputs a pulse signal,
The count value of the UP / DOWN counter 33 increases,
When the divided voltage signal S7 is lower than the first reference voltage and the logic circuit 26 outputs a pulse signal, the count value decreases. Therefore, a logic circuit is provided in the voltage dividing resistor 6,
If this increase or decrease in the count value is detected, it is possible to determine whether the resistance value should be increased or decreased when the pulse signal is received.

The above-mentioned set values of the resistance value of the thermistor and the value of the voltage dividing resistance have been described by showing particularly specific values in order to facilitate understanding of the present invention, and the resistance value itself is practically used. It doesn't make sense. Therefore, it is possible to use a desired value for the resistance value of the thermistor or the resistance value of the voltage dividing resistor, and the voltage dividing resistor may be switched twice or more. Further, in the present embodiment, when the value of the voltage dividing resistor 6 is switched, the value of the divided voltage signal S7 after switching is set to 4/20 of the power supply voltage V0 when the temperature is raised,
The reason why the voltage is set to 16/20 of the power supply voltage V0 during the temperature decrease is to facilitate understanding of the circuit operation, and the first and second switching values are different. You may set it to such a value.

Further, the temperature reference voltage 11 is the power supply voltage V
Although the value is fixed to 1/2 of 0, a variable power source 11a is used as shown in FIG. 3A, and when the resistance value of the voltage dividing resistor 6 is switched, the value of the variable power source 11a is switched to a temperature detection comparator. 1
The temperature reference voltage input to 0 is, for example, 2 / of the power supply voltage.
It may be set to a voltage equal to the voltage of the divided voltage signal S7 output when the resistance value of the thermistor reaches a desired value such as 3 or 1/4.

Further, as shown in FIG. 3 (b), a plurality of comparators 10a, 10b, 10c having a desired temperature reference voltage are provided, and one of them is used when the resistance value of the voltage dividing resistor 6 is switched. The optimum temperature reference voltage may be selected while the comparator is operating.

FIG. 4 is a block diagram showing another embodiment of the present invention.

Referring to FIG. 4, 102 is a voltage divider,
The thermistor 105 connected to the power supply line 108 and the voltage dividing resistor 106 connected to the ground line 109 are configured to be connected at an output point 107 so that a voltage division signal is output from the output point 107. It is configured. The voltage dividing resistor 106 connects the other end of the first resistor R151 whose one end is connected to the output point 107 and the other end of the second resistor R152 whose one end is connected to the ground line 109 at the connection point 141. , A resistor R15 between the emitter and the base at the connection point 141.
It is constituted by connecting the collector terminal of a grounded NPN transistor Q201 having 3 and connecting the output terminal 143 of the voltage dividing resistor switch 103 to the base terminal of the NPN transistor Q201. The value,
When the output of the voltage dividing resistor switch 103 is low, the NP
Since the N transistor Q201 is turned off, the resistance R151
And the resistor R152 are connected in series, and when the output of the voltage dividing resistor switch 103 is high, the NPN transistor Q201 is turned on and its collector terminal becomes almost the same potential as the ground line 109. The resistance value can be switched so that it becomes the resistance value of the resistor R151.

The output point 107 is connected to the voltage dividing resistance switch 103, and the voltage dividing resistance switch 103 is
The other end of the resistor R155 whose one end is connected to the power supply line 108 and the other end of the resistor R158 whose one end is connected to the ground line 109 are connected at a connection point 142, and the resistor R155 and the resistor R158 connect the power supply line. The voltage is divided and the connection point 14
2 is provided with a reference voltage comparator 120 which receives the reference voltage from its output terminal 107 and inputs the divided voltage from the output point 107 to its non-inverting input terminal. There is.

The collector terminal of a grounded-emitter NPN transistor Q202 having a resistor R159 between the emitter and the base is connected to the connection point 142 via a resistor R159, and the output terminal of the reference voltage comparator 120 is a delay circuit 132. Is connected to the output terminal 143 via the resistor R160 and is also connected to the base terminal of the NPN transistor Q202 via the resistor R160, and the output of the reference voltage comparator goes high, turning on the NPN transistor Q202.
The resistor R159 and the resistor R158 are connected in parallel so that the value of the reference voltage can be switched.

The output point 107 is also connected to the non-inverting terminal of the temperature detecting comparator 110. The temperature detecting comparator 110 outputs the temperature reference voltage 111 input to the inverting input terminal and the output point 107. Is compared with the divided voltage signal input to the non-inversion terminal, and the comparison result is output from the output terminal 115 to an external device (not shown).

The operation of this circuit will be described with reference to FIG. With reference to FIG. 5, S107 is a voltage division signal which is the potential of the output point 107, S142 is the potential of the connection point 142, which is a reference voltage input to the inverting input terminal of the comparator 120. Further, 111 is a temperature reference voltage, and S11
5 is the voltage of the output terminal 115 of the temperature detection comparator 110.

It is assumed that the divided voltage signal S107 is at the position of the point W1 of a voltage lower than the temperature reference voltage 111 as an initial state, and the reference input to the inverting input terminal of the reference voltage comparator 120 at this time. The voltage S142 is the divided voltage signal S1.
It is assumed that it is set higher than 07 and the temperature reference voltage 111. Therefore, at this time, the reference voltage S
Since 142 functions to detect the maximum value of the divided voltage signal S107, the second circuit in the circuit shown in FIG.
It is the same as the reference voltage.

When the divided voltage signal S107 is located at the point W1 in this initial state, the voltage at the inverting input terminal of the reference voltage comparator 120 is higher than the voltage at the non-inverting input terminal. The output of the reference voltage comparator 120 is low and the NPN transistor Q202 is off.

From this state, as the temperature of the heat source (not shown) rises, the temperature of the thermistor 105 rises, and the value of the divided voltage signal S107 also rises accordingly, and when the value exceeds the temperature reference voltage 111. The temperature detection comparator 1
The output S115 of 10 is inverted from low to high. And
When the value of the divided voltage signal S107 further rises and reaches a point W2 that exceeds the reference voltage S142, which is the second reference voltage,
The output of the reference voltage comparator 120 is inverted from low to high to immediately turn on the NPN transistor Q202 to connect the resistor R159 to the ground line and lower the value of the reference voltage S142. Then, after the delay time determined by the delay circuit 132 has elapsed, the NPN transistor Q201 is also turned on to reduce the resistance value of the voltage dividing resistor 106. At this time, the divided voltage signal S107
Shifts from the point W2 to the point W3, and the value of the voltage dividing signal S107 at the position of the point W3 is lowered to the point W4 by decreasing the resistance value of the voltage dividing resistor 106. Since this point W4 is set to be between the reference voltage S142 and the temperature reference voltage 111, the output S115 of the temperature detection comparator 110 is inverted from high to low. After the divided voltage signal S107 is lowered to the point W4, the reference voltage S142 is located at a lower value than the divided voltage signal S107 and the lower limit when the divided voltage signal S107 drops is detected.
The reference voltage S142 has the same function as the first reference voltage of the circuit shown in FIG.

The divided voltage signal S142 once further rises to exceed the temperature reference voltage 111, and the temperature detection comparator 1
Invert the output S115 of 10 from low to high. Then, when the temperature of the thermistor 105 decreases, for example, when the heat generation of the heat source is stopped and the resistance value thereof starts to increase, the value of the divided voltage signal S107 starts to decrease from the position of the point Y1. The divided voltage signal S107 is generated more than the temperature reference voltage 111.
Is less than the value of, the output S11 of the temperature detection comparator 110 is output.
5 reverses from high to low. Then, when the temperature of the thermistor 105 further decreases and the divided voltage signal S107 drops to reach a point Y2 below the reference voltage S142, the output of the reference voltage comparator 120 included in the voltage dividing resistor switch 103 is changed. Invert from high to low, NPN transistor Q20
2 is turned off immediately to return the reference voltage to its original value,
After the elapse of a predetermined delay time determined by the delay circuit 132, the NPN transistor Q201 provided in the first voltage divider 106 is turned off, and the divided voltage signal S107 that has moved from the point Y2 to the point Y3 is changed to the point Y4. Move to position.

As described above, in the present embodiment, the reference voltage comparator 120 included in the voltage dividing resistor switch 103 has the same function as the reference voltage comparator 120 when the value of the voltage dividing signal S107 increases. The input reference voltage S142 is used to detect the upper limit of the rise of the divided voltage signal S107, and after the voltage value of the divided voltage signal S107 exceeds the reference voltage,
The value of the divided voltage signal S107 is lowered, and the value of the reference voltage S142 input to the reference voltage comparator 120 is set to a value lower than the lowered divided voltage signal S107. The lower limit of S107 is set.

In the present invention, it is needless to say that the heat source includes a cold heat source and can be widely applied to a circuit in which a plurality of temperature detection points are set for one thermistor.

[0049]

According to the present invention, in the case of detecting the temperature in a wide temperature range by using one thermistor, the voltage division signal is switched so that the voltage change of the voltage division signal is large with respect to the unit temperature change. Since the comparison with the temperature reference voltage can be performed with, it is possible to detect the temperature with high accuracy by the circuit that saves space. Therefore, it is convenient when it is difficult to arrange a plurality of thermistors, especially when detecting the temperature of a small-sized heat generator or cooler.

Further, when the voltage dividing resistor switcher compares the voltage dividing signal with the reference voltage by the reference voltage comparator and switches the voltage dividing resistor, if the reference voltage itself is switched, the reference voltage comparator can be operated. Since it is sufficient to provide only one, it is advantageous in terms of cost and space.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation.

3A and 3B are block diagrams of another embodiment of the present invention.

FIG. 4 is a circuit diagram of an embodiment of the present invention that switches between a first reference voltage and a second reference voltage.

FIG. 5 is a timing chart for explaining the operation.

FIG. 6 is a block diagram of a circuit of a conventional temperature detecting device.

[Explanation of symbols]

2, 102 ...... Voltage divider 3, 103 ...... Voltage division resistance switcher 5, 105 ...... Thermistor 6, 106 ...... Voltage division resistance 10, 110 ...... Temperature detection comparator 120 ...... Reference voltage comparator 133 ...... Reference voltage switcher 23 ... First reference voltage 24 ... Second reference voltage S7, S107 ... Divided voltage signal 11, 111 ... Temperature reference voltage

Claims (2)

[Claims] 1. A voltage divider in which a thermistor whose resistance value changes with a temperature change and a voltage-dividing resistor capable of switching to a resistance value are connected at an output point, wherein the thermistor is arranged at a heat source and the voltage-divider of the voltage divider is connected. A voltage divider that connects one end to a power supply and grounds the other end, and outputs a voltage division signal obtained by dividing the voltage of the power supply from the output point, and detects the temperature by comparing the voltage division signal with the temperature reference voltage. A temperature detection device comprising a temperature detection comparator that outputs a signal, and a voltage dividing resistance switching device that switches the resistance value of the voltage dividing resistor, wherein the voltage dividing resistance switching device is higher than the temperature reference voltage. A second reference voltage of a voltage and a first reference voltage of a voltage lower than the temperature reference voltage, and switching the resistance value of the voltage dividing resistor when the voltage of the voltage dividing signal exceeds the second reference voltage, The value of the divided voltage signal is set to the first reference voltage. When the voltage of the voltage dividing signal falls below the first reference voltage, the resistance value of the voltage dividing resistor is switched to change the value of the voltage dividing signal to the second value. A temperature detecting device, which boosts a voltage value between a reference voltage and the temperature reference voltage. 2. The voltage dividing resistor changer includes a reference voltage comparator to which the voltage dividing signal is input to one of the input terminals and a reference voltage is input to the other end. Is the second reference voltage when the voltage value of the divided signal increases, and is input to the comparator after the voltage value of the divided signal exceeds the second reference voltage. 2. The temperature detecting device according to claim 1, further comprising a reference voltage switching device that uses a reference voltage as the first reference voltage.