JP3743129B2 - Temperature detection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a temperature detection circuit for rubber products and liquid crystals whose characteristics deteriorate at low temperatures.
[0002]
[Prior art]
As shown in FIG. 7, a conventional temperature detection circuit used in a rubber product or a liquid crystal whose characteristics deteriorate at a low temperature is connected to a non-inverting input terminal 1a of a comparator 1 in series. 2 and a constant voltage source 3 such as a diode 3 are connected to a series connection point 4, and the inverting input terminal 1 b of the comparator 1 is connected to a connection point 7 of a constant current source 5 and a Zener diode 6 in series. Is connected. In this case, the diode 3 is connected in the forward direction, the cathode is grounded, and operates as a temperature detecting element having linear temperature characteristics. The constant voltage source 6 operates as a reference voltage source having a temperature characteristic 0 in which the voltage does not change with respect to the temperature.
[0003]
The voltage at the node 4 on the anode side of the diode 3 connected to the input terminal 1a of the comparator 1 changes with temperature change. When the temperature is lower than Ta, the output Vout of the comparator 1 is shown in FIG. As shown, maintained at a high level. That is, when the temperature becomes lower than Ta, the voltage at the connection point 4 becomes lower than the voltage at the connection point 7, and the output Vout of the comparator 1 is maintained at a low level. It operates so as to detect a change in temperature from a change in the output of the comparator 1.
[0004]
[Problems to be solved by the invention]
However, recent devices are generally devised in various ways to reduce the size. Considering the circuit of FIG. 7 from such a viewpoint, in addition to the temperature detection element absolutely necessary for detecting the temperature and the comparator necessary for detecting the change with respect to the reference voltage, the temperature characteristic “0” If the Zener diode, which is a constant voltage source, can be used as the reference voltage source for other parts, the number of parts can be reduced and the cost can be reduced.
An object of the present invention is to obtain a temperature detection circuit that does not require the use of a reference voltage source having a temperature characteristic “0”.
[0005]
[Means for Solving the Problems]
In order to achieve this object, the present invention is based on the fact that it is not necessary to use a reference voltage source having a temperature characteristic of “0” as in the prior art, if a comparator having a constant input offset between input terminals is used. A temperature detection circuit is provided, wherein a series body of at least three resistance elements is connected in parallel with the temperature detection element, and both ends of one intermediate resistance element are connected to an input end of a comparator.
[0006]
With this configuration, the resistance element connected to the input terminal of the comparator acts as an offset reference voltage source with a temperature characteristic of 0 for the comparator, and the number of parts can be reduced as compared with the conventional case. Therefore, the mounting area when this temperature detection circuit is mounted on the apparatus can be reduced as compared with the conventional case.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a temperature detection circuit according to the present invention. In FIG. 1, a temperature detection circuit 10 includes a current source 11 and a diode 12 connected in series between a positive voltage source and ground. The cathode of the diode 12 is grounded. A series body of three resistors 14, 15 and 16 is connected between the connection point 13 of the current source 11 and the temperature detection diode 12 and the ground. This state means that the series body of the resistors 14, 15, 16 is connected in parallel with the temperature detection diode 12. Although the comparator and amplifier are originally designed so that the input offset voltage is zero, the present invention makes it possible to eliminate the reference voltage source by positively providing the comparator 18 with the input offset voltage. Yes.
[0008]
Of the three series-connected resistors described above, both ends of the intermediate resistor 15 are connected to the input ends 18a and 18b of the comparator 18, respectively. That is, the non-inverting input terminal 18 a is connected to the connection point 20 between the resistors 14 and 15, and the inverting input terminal 18 b is connected to the connection point 21 between the resistors 15 and 16.
[0009]
With such a configuration, the voltage drop due to the resistor 15 gives an offset to the input of the comparator 18. The characteristics shown in FIG. 2 indicate the voltage-temperature change characteristics of the connection points 13, 20, and 21 as characteristics a, b, and c, respectively. In the figure, as the temperature rises, the potential at the connection point 13 on the anode side of the diode 12 serving as the temperature detection element decreases, and the potential at the connection points 20 and 21 of the resistor series body also decreases, and the comparator 18 changes its state. The voltage across resistor 15 at temperature Ta, in other words, the potential difference between characteristics b and c is provided to comparator 18 as a potential difference that varies with temperature.
[0010]
As a result, a reference voltage having a temperature characteristic of 0 is unnecessary as in the prior art, and the mounting area of the temperature detection circuit when incorporated in the apparatus can be reduced by reducing the number of components. According to experiments, it has been confirmed that the temperature detection circuit having the configuration shown in FIG. 1 can reduce the mounting area to about two-thirds compared to the conventional circuit.
[0011]
FIG. 3 shows another embodiment of the present invention, in which the connection of the temperature detection diode and the current source to the power source is reversed from that in FIG. 1, and the same components are denoted by the same reference numerals. . Of course, the connection of the three resistors connected in parallel with the diode to the power supply is also reversed, and is connected to the positive voltage source along with the anode of the diode. Even if configured in this way, it operates in the same manner as in FIG. 1 and produces the same effect.
[0012]
FIG. 4 shows still another embodiment of the present invention. In the circuit shown in FIG. 1, in addition to the comparator 18 at both ends of the resistor 15, that is, connection points 20 and 21 of the resistor series body, the comparator 23 , 24 input terminals are connected in parallel. In this case, the offset voltages of the comparators 18, 23 and 24 are set to different voltages V1, V2 and V3. With this configuration, the temperature Ta at which each of the comparators 18, 23, and 24 changes state is changed as indicated by T1, T2, and T3 in FIG. 6 corresponding to the different offset voltages. The operation timings of the comparators 18, 23, and 24 according to the change are different, and a plurality of temperatures can be detected. Vout1, Vout2, and Vout3 are outputs of the comparators 18, 23, and 24, respectively. Note that the number of comparators is not limited to three, and the same operation can be performed with an arbitrary number.
[0013]
FIG. 5 shows still another embodiment of the present invention. In the circuit shown in FIG. 1, an intermediate resistor 15 is connected in series among resistors 14, 15, and 16 in series. The input terminals of the comparators 18, 23, and 24 are connected to both ends of the resistors 15-1, 15-2, and 15-3. . The only difference from FIG. 4 is that the resistors connected to the input ends of the comparators 18, 23, and 24 are different, and the offset voltages of the comparators 26, 27, and 28 are V1, V2, and V3. The temperature detection operation
The same as FIG.
[0014]
Further, in the above-described embodiments shown in FIGS. 4 and 5, by providing hysteresis characteristics to the respective comparators, a fluctuation (oscillation) in the vicinity of temperature detection can be prevented.
[0015]
【The invention's effect】
As described above, when the temperature detection circuit according to the present invention is used, the reference voltage of the temperature characteristic 0 is unnecessary as in the prior art, and the actual phase area of the temperature detection circuit when the number of components is reduced and incorporated in the apparatus is reduced. can do. The temperature detection circuit having such a configuration is applied to, for example, a device that forcibly warms an element such as a rubber product or a liquid crystal whose characteristics deteriorate at a low temperature of 0 degrees or less at a low temperature.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a temperature detection circuit according to the present invention.
FIG. 2 is a voltage-temperature characteristic diagram for explaining the operation of FIG. 1;
FIG. 3 is a diagram showing another embodiment of the present invention.
FIG. 4 is a diagram showing still another embodiment of the present invention.
FIG. 5 is a diagram showing still another embodiment of the present invention.
6 is a characteristic diagram for explaining the operation of FIGS. 5 and 6. FIG.
FIG. 7 is a diagram illustrating an example of a conventional temperature detection circuit.
FIG. 8 is a characteristic diagram for explaining the operation of a conventional temperature detection circuit.
[Explanation of symbols]
1,18,23,24 comparator,
1a, 18a Non-inverting input terminal,
1b, 18b inverting input terminal,
2, 5, 11 current source,
3,12 diode,
4, 7, 13, 20, 21 connection point,
6 constant voltage source,
10 Temperature detection circuit,
14, 15, 16, 15-1 to 15-3 resistance.

Claims (5)

A temperature detection circuit, wherein a series body of at least three resistance elements is connected in parallel with a temperature detection element, and both ends of at least one intermediate resistance element are connected to an input terminal of a comparator. 2. The temperature detection circuit according to claim 1, wherein there is one intermediate resistance element, and input terminals of a plurality of comparators having different offset voltages are connected to both ends of the intermediate resistance element. 2. The intermediate resistance element is constituted by a series body of a plurality of resistance elements, and input terminals of comparators having different offset voltages are respectively connected to both ends of each of the intermediate resistance elements. The temperature detection circuit described. The temperature detection circuit according to claim 1, wherein the temperature detection element is connected in series with a current source. The temperature detection circuit according to claim 1, wherein the temperature detection element is a diode.

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