Temperature detection circuit

Abstract

This invention provides a temperature detection circuit that, despite its simple configuration, can expand the detectable temperature range. [Solution] The temperature detection circuit 10 comprises two thermistors, a first thermistor 14 and a second thermistor 15. The temperature ranges in which the change in resistance of the first thermistor 14 and the second thermistor 15 is within a predetermined range are different. The temperature range in which the change in resistance of the first thermistor 14 is within a predetermined range and the temperature range in which the change in resistance of the second thermistor 15 is within a predetermined range overlap in part. The first thermistor 14 and the second thermistor 15 are connected in series with each other. The detection unit 16 of the temperature detection circuit 10 detects the divided voltage in the second thermistor 15.

Description

Technical Field

[0001] The present invention relates to a temperature detection circuit.

Background Art

[0002] Conventionally, a temperature detection circuit including a thermistor and a resistor has been known. In the temperature detection circuit, the thermistor is connected in series with a resistor having a constant resistance value. A voltage is applied to the thermistor and the resistor. The temperature detection circuit detects the temperature from the voltage division related to the voltage in the thermistor. The temperature detection circuit detects the temperature by using the temperature characteristic of the thermistor whose resistance value decreases as the temperature increases.

[0003] The greater the change in the resistance value of the thermistor with respect to the change in temperature, the narrower the temperature range in which the resistance value changes. Therefore, a thermistor that can detect temperature with high accuracy has a narrow temperature detection range. The fixing device described in Patent Document 1 corrects the temperature sensitivity of the thermistor according to the temperature of the object by controlling a circuit including the thermistor and the resistor. Thereby, the fixing device expands the range in which the temperature can be detected with high accuracy while suppressing the decrease in the temperature sensitivity.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When expanding the temperature detection range by controlling a circuit including a thermistor as in Patent Document 1, the temperature detection circuit may become complicated.

Means for Solving the Problems

[0006] A temperature detection circuit that solves the above problem comprises two thermistors, each having a different temperature range over which the change in resistance value falls within a predetermined range, wherein the temperature ranges of one thermistor and the other thermistor partially overlap, and the two thermistors are connected in series with each other, and the voltage division in one of the thermistors is detected.

[0007] The temperature detection circuit with the above configuration connects two thermistors in series. Therefore, the combined resistance of the temperature detection circuit is large. While the change in the divided voltage across one thermistor in response to temperature changes is small, the temperature range over which the combined resistance changes is broadened by the contribution of the other thermistor. The change in combined resistance is reflected in the divided voltage across each thermistor. As a result, the temperature detection circuit can achieve a wide detectable temperature range. [Effects of the Invention]

[0008] According to the present invention, the detectable temperature range can be expanded despite the simple configuration. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing the temperature detection circuit. [Figure 2] Figure 2 is a graph showing the relationship between the first temperature sensitivity, the second temperature sensitivity, and the detected temperature sensitivity, and the temperature of the object. [Modes for carrying out the invention]

[0010] Below, one embodiment of the temperature detection circuit will be described with reference to Figures 1 and 2. As shown in Figure 1, the temperature detection circuit 10 comprises a constant voltage power supply 11, a pull-up resistor 12, a ground 13, two thermistors, a first thermistor 14 and a second thermistor 15, and a detection unit 16. The temperature detection circuit 10 is electrically connected to the constant voltage power supply 11, the pull-up resistor 12, the ground 13, the first thermistor 14, the second thermistor 15, and the detection unit 16. The ECU 100 detects the temperature of the object 101 using the temperature detection circuit 10.

[0011] The constant voltage power supply 11 applies a constant voltage to the temperature detection circuit 10. Hereafter, the voltage applied by the constant voltage power supply 11 to the temperature detection circuit 10 will be referred to as the total voltage. The constant voltage power supply 11 is connected to ground 13. The pull-up resistor 12 is connected in series between the constant voltage power supply 11 and ground 13. The pull-up resistor 12 is connected to the high-voltage side of the constant voltage power supply 11. The resistance value of the pull-up resistor 12 is negligibly small compared to the resistance values ​​of the first thermistor 14 and the second thermistor 15. For this reason, the resistance value of the pull-up resistor 12 will be ignored in the following explanation.

[0012] The first thermistor 14 is installed on the object 101. The temperature of the first thermistor 14 changes with the temperature of the object 101. The resistance of the first thermistor 14 changes with the temperature of the object 101. The first thermistor 14 is connected to a pull-up resistor 12. The first thermistor 14 is connected to the high-voltage side of the constant voltage power supply 11 via the pull-up resistor 12.

[0013] The second thermistor 15 is installed on the object 101. The temperature of the second thermistor 15 changes with the temperature of the object 101. The resistance of the second thermistor 15 also changes with the temperature of the object 101. The second thermistor 15 is connected to the first thermistor 14. The first thermistor 14 and the second thermistor 15 are connected in series with each other. The combined resistance of the temperature detection circuit 10 is the sum of the resistance of the first thermistor 14 and the resistance of the second thermistor 15.

[0014] The second thermistor 15 is connected in series with the pull-up resistor 12 via the first thermistor 14. The second thermistor 15 is connected to the high-voltage side of the constant voltage power supply 11 via the first thermistor 14 and the pull-up resistor 12. The second thermistor 15 is connected to the ground 13. The second thermistor 15 is connected in series between the first thermistor 14 and the ground 13. As described above, the constant voltage power supply 11, the pull-up resistor 12, the first thermistor 14, the second thermistor 15, and the ground 13 are connected in this order.

[0015] The detection unit 16 is connected in parallel to the second thermistor 15. The detection unit 16 detects the voltage applied to the second thermistor 15 from the constant voltage power supply 11. In other words, the temperature detection circuit 10 detects the divided voltage at the second thermistor 15. The ECU 100 receives the divided voltage detected by the detection unit 16 as input. The ECU 100 detects the temperature of the object 101 from the divided voltage input from the detection unit 16, for example, based on a pre-set table.

[0016] In a second thermistor 15 connected in series with the first thermistor 14, the accuracy with which the detection unit 16 detects the partial pressure of the second thermistor 15 depends on the magnitude of the change in the partial pressure of the second thermistor 15. The greater the magnitude of the change in the partial pressure of the second thermistor 15 in response to the temperature change of the object 101, the more accurately the detection unit 16 can detect the partial pressure of the second thermistor 15. Hereafter, the value required for the magnitude of the change in the partial pressure described above in order for the detection unit 16 to achieve the desired accuracy will be referred to as threshold X. Threshold X can also be said to be the magnitude of the change in the partial pressure of the second thermistor 15 required in a second thermistor 15 connected in series with the first thermistor 14.

[0017] The threshold X is pre-set for the ECU 100. The threshold X can be set arbitrarily. The threshold X is set, for example, according to the environment in which the temperature detection circuit 10 is applied. The threshold X may also be set, for example, according to the temperature of the object 101 and the performance of the second thermistor 15. The accuracy with which the ECU 100 detects the temperature of the object 101 depends on the accuracy of the detection unit 16. The threshold X is set according to the temperature detection accuracy required by the ECU 100.

[0018] Figure 2 shows a graph with the temperature of the object 101 on the horizontal axis and the temperature sensitivity on the vertical axis. In this specification, "thermistor temperature sensitivity" refers to the change in the partial pressure in the thermistor in response to a change in the thermistor's temperature. The partial pressure related to the thermistor temperature sensitivity is the partial pressure of the thermistor due to the combined resistance of the thermistor and a resistor having a constant resistance value. The dashed line shown in the graph of Figure 2 shows the relationship between the temperature of the object 101 and the temperature sensitivity of the first thermistor 14. The double dashed line shown in the graph of Figure 2 shows the relationship between the temperature of the object 101 and the temperature sensitivity of the second thermistor 15.

[0019] The temperature sensitivity of the first thermistor 14 is the change in the divided voltage of the first thermistor 14 in response to a temperature change in the first thermistor 14, when the sum of the resistance values ​​of the pull-up resistor 12 and the first thermistor 14 is used as the combined resistance. Hereafter, the temperature sensitivity of the first thermistor 14 will be referred to as the first temperature sensitivity. The first temperature sensitivity does not depend on the resistance value of the second thermistor 15.

[0020] The temperature sensitivity of the second thermistor 15 is the change in the voltage division of the second thermistor 15 in response to a temperature change in the second thermistor 15, when the sum of the resistance values ​​of the pull-up resistor 12 and the second thermistor 15 is used as the combined resistance. Hereafter, the temperature sensitivity of the second thermistor 15 will be referred to as the second temperature sensitivity. The second temperature sensitivity does not depend on the resistance value of the first thermistor 14.

[0021] The temperature range of the object 101 in which the change amount of the resistance value of the first thermistor 14 becomes a value within a predetermined range is described as the first temperature range T1. The predetermined range in the change amount of the resistance value of the first thermistor 14 is a range of values in which the first temperature sensitivity calculated based on the change amount of the resistance value within the range is greater than the threshold value X. That is, when the change amount of the resistance value of the first thermistor 14 is a value within a predetermined range, the first temperature sensitivity is a value greater than the threshold value X.

[0022] The temperature range of the object 101 in which the change amount of the resistance value of the second thermistor 15 becomes a value within a predetermined range is described as the second temperature range T2. The predetermined range in the change amount of the resistance value of the second thermistor 15 is a range of values in which the second temperature sensitivity calculated based on the change amount of the resistance value within the range is greater than the threshold value X. That is, when the change amount of the resistance value of the second thermistor 15 is a value within a predetermined range, the second temperature sensitivity is a value greater than the threshold value X. Note that the predetermined range related to the change amount of the resistance value of the first thermistor 14 and the predetermined range related to the change amount of the resistance value of the second thermistor 15 may be different from each other.

[0023] The first thermistor 14 and the second thermistor 15 have different temperature ranges in which the change amount of the resistance value becomes a value within a predetermined range. That is, the first temperature range T1 and the second temperature range T2 correspond to different temperature ranges. Also, the temperature range in which the change amount of the resistance value of the first thermistor 14 becomes a value within a predetermined range and the temperature range in which the change amount of the resistance value of the second thermistor 15 becomes a value within a predetermined range partially overlap. That is, the first temperature range T1 and the second temperature range T2 partially coincide.

[0024] The solid line in the graph shown in FIG. 2 indicates the temperature sensitivity related to the change amount of the divided voltage detected by the detection unit 16 in the second thermistor 15. Hereinafter, the temperature sensitivity will be described as the "detection temperature sensitivity". The detection temperature sensitivity is the change amount of the divided voltage with respect to the temperature change of the object 101 in the second thermistor 15 connected in series with the first thermistor 14.

[0025] The divided pressure related to the detected temperature sensitivity is the divided pressure of the second thermistor 15 in the temperature detection circuit 10. The combined resistance related to this divided pressure includes the contribution of the resistance values ​​of the first thermistor 14 and the second thermistor 15. In Figure 2, the temperature range of the object 101 in which the detected temperature sensitivity exceeds the threshold X is indicated as the detected temperature range T0.

[0026] The temperature detection sensitivity is less sensitive compared to the temperature sensitivities of the first thermistor 14 and the second thermistor 15, respectively. The temperature detection sensitivity changes more gradually in response to temperature changes of the object 101 compared to the temperature sensitivities of the first and second thermistors, respectively. The maximum value of the temperature detection sensitivity is smaller than the maximum value of the temperature sensitivities of the first thermistor 14 and the second thermistor 15, respectively. In addition, the temperature detection range T0 is expanded compared to the temperature ranges T1 and T2.

[0027] The blunting of the temperature detection sensitivity is due to the change in the resistance value of the first thermistor 14 contributing to the change in the combined resistance of the temperature detection circuit 10 in response to the temperature change of the object 101. More specifically, the blunting of the temperature detection sensitivity is due to the fact that the combined resistance changes by the amount of the change in the resistance values ​​of the first thermistor 14 and the second thermistor 15 in response to the temperature change of the object 101.

[0028] The detection temperature range T0 is wider than the first temperature range T1 and the second temperature range T2, respectively. In other words, the temperature detection circuit 10 expands the temperature range over which the temperature of the object 101 can be detected with the required accuracy, compared to the case where either the first thermistor 14 or the second thermistor 15 and the pull-up resistor 12 are included.

[0029] The detection temperature range T0 depends on the range in which the resistance value of the second thermistor 15 and the combined resistance of the temperature detection circuit 10 change. This combined resistance includes the contribution of the resistance value of the first temperature range T1. The temperature detection circuit 10 expands the detection temperature range T0 by including the contribution of the change in the resistance value of the first thermistor 14, in addition to the change in the resistance value of the second thermistor 15.

[0030] The effects of this embodiment will now be explained. (1) The temperature detection circuit 10 includes the resistance values ​​of both the first thermistor 14 and the second thermistor 15 in its combined resistance by connecting the first thermistor 14 and the second thermistor 15 in series. The accuracy of temperature detection by the temperature detection circuit 10 depends on the magnitude of the change in the divided voltage in the second thermistor 15 connected in series with the first thermistor 14. This change in divided voltage depends on the combined resistance of the temperature detection circuit 10. By including the respective resistance values ​​of the first thermistor 14 and the second thermistor 15 in its combined resistance, the temperature detection circuit 10 can expand the temperature range over which it can detect temperature with the required accuracy.

[0031] (2) The temperature detection circuit 10 includes a first thermistor 14 and a second thermistor 15 connected in series with each other, thereby expanding the temperature range of the object 101 in which the temperature can be detected with the required accuracy by the second thermistor 15. Compared to, for example, a case in which the circuit is configured to be switchable and a control device is provided to perform the switching, the temperature detection circuit 10 has a simpler configuration while expanding the temperature range in which the temperature can be detected with the required accuracy. [Explanation of Symbols]

[0032] 10...Temperature detection circuit, 11...Constant voltage power supply, 12...Pull-up resistor, 13...Ground, 14...First thermistor, 15...Second thermistor, 16...Detection unit, 101...Target object, 100...ECU, T1...First temperature range, T2...Second temperature range.

Claims

[Claim 1] The present invention comprises two thermistors having different temperature ranges over which the change in resistance value falls within a predetermined range, wherein the temperature range of one thermistor and the temperature range of the other thermistor partially overlap. The two thermistors mentioned above are connected in series with each other. One of the thermistors detects the partial pressure. Temperature detection circuit.

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