JP2002340693A - Temperature detecting circuit, electronic equipment equipped therewith, and temperature detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a precise temperature detection over a long time by preventing the deterioration of an element even in a highly humid temperature detecting environment. SOLUTION: This circuit is made switchable to a mode for detecting temperature by use of the resistance change of an NTC thermistor 7 and a mode for self-heating the thermistor to remove the moisture adhered to the surface thereof. The NTC thermistor performs a temperature detection in the temperature detection mode, and removes the moisture adhered to the surface in the moisture removing mode. Accordingly, the migration in an electrode on the NTC thermistor surface can be suppressed, and the NTC thermistor can consequently perform the precise temperature detection over a long term.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a temperature detection circuit that uses a change in resistance of a thermistor for temperature detection, an electronic device including the same, and a temperature detection method.

[0002]

2. Description of the Related Art As shown in FIG. 5, such a temperature detecting circuit includes a voltage dividing circuit in which a fixed resistor 5 and an NTC thermistor 7 are connected in series. Here, the NTC thermistor 7 is an element having a characteristic (NTC characteristic) in which the resistance value decreases as the temperature rises.

In this temperature detection circuit, the divided voltage is used as temperature detection data because the divided voltage decreases as the temperature rises due to the NTC characteristics of the NTC thermistor 7.

[0004]

The NTC thermistor 7 used in such a temperature detection circuit is a state in which moisture is adhered to a surface of the NTC thermistor for a long time in a high humidity temperature detection environment. It may be.

In such a state, migration (electrode erosion) is likely to occur in the electrode portion of the NTC thermistor 7 due to generation of metal ions due to the presence of moisture and voltage.

[0006] The migration may cause deterioration of the NTC thermistor 7 and lower its temperature detection accuracy.

Therefore, it is a common solution of the present invention to prevent the element from deteriorating even under the above-mentioned high-humidity temperature detection environment and to enable highly accurate temperature detection for a long time. It is an issue.

[0008]

(1) A first temperature detecting circuit according to the present invention comprises a mode for detecting a temperature by using a resistance change of a thermistor, and a method for removing moisture adhering to the surface by causing the thermistor to self-heat. And a control mode for switching the mode.

According to the first temperature detecting circuit of the present invention, the temperature is detected in the temperature detecting mode. On the other hand, in the moisture removal mode, moisture adhering to the thermistor surface is removed.

Thus, in this temperature detection circuit, the occurrence of migration in the electrode portion on the thermistor surface is effectively suppressed even in a high-humidity temperature detection environment,
High-precision temperature detection can be performed for a long time.

Japanese Patent Application Laid-Open No. 5-264369 discloses a temperature detecting device for suppressing the occurrence of the migration. In the technology described in this publication,
An alternating current is applied to the thermistor to change the direction of the current flowing through the thermistor. As a result, generation of metal ions at the electrode portion of the thermistor is prevented, and generation of migration is prevented.

Therefore, in the case of the conventional temperature detection circuit, the occurrence of migration is prevented or suppressed by removing the water on the thermistor surface as in the present invention.

Japanese Patent Application Laid-Open No. 7-27630 discloses that
A temperature detection circuit for suppressing the occurrence of the migration is disclosed. In the technique described in this publication, a voltage is not continuously applied to the thermistor, and the application time is limited. As a result, the time for eliminating the potential difference required for the occurrence of migration is shortened.

Therefore, in the case of the conventional temperature detection circuit, the occurrence of migration is prevented or suppressed by removing the water on the thermistor surface as in the present invention.

As a first preferred embodiment of the present invention, first energizing means for applying a temperature detection voltage to the thermistor in the temperature detection mode, and a self-heating voltage to the thermistor in the moisture removal mode. And second mode switching means for switching between the two modes.

According to this embodiment, the operation mode is switched to the temperature detection mode by the mode switching means. In this mode, the thermistor is energized by the first energizing means to perform temperature detection. On the other hand, when the operation mode is switched to the moisture removal mode, the thermistor is caused to generate heat by the second energizing means. As a result, water that is to adhere to the thermistor surface in a high-humidity temperature detection environment is removed. As a result, generation of migration in the electrode portion on the thermistor surface is suppressed.

As a first more preferred embodiment of the present invention, the first energizing means includes a resistive element connected to a power supply, the second energizing means includes a short-circuiting element connected to a power supply, and the mode switching means. Switches the connection of the thermistor to a resistance element or a short-circuit element in accordance with both modes.

In such a case, a voltage required for self-heating is applied to the thermistor from the power supply via a short-circuiting element, and a voltage required for temperature detection is applied from the power supply via a resistance element. This enables highly accurate temperature detection while preventing the occurrence of migration.

(2) The second temperature detecting circuit according to the present invention relates to a circuit including a series connection circuit of a resistance element and a first switch element, and a second switch element connected in parallel to the series connection circuit. In a temperature detection mode in which a thermistor is configured to be connected in series and a temperature is detected by using a resistance change of the thermistor, the first switch element is controlled to be closed, and the thermistor is caused to generate heat by itself. In the moisture removal mode for removing moisture adhering to the surface, the second switch element is controlled to be closed.

According to the second temperature detection circuit of the present invention, the temperature is detected in the temperature detection mode. On the other hand, in the moisture removal mode, the thermistor is caused to generate heat by itself, and moisture adhering to its surface is removed. Therefore, even in a high-humidity temperature detection environment, the occurrence of migration in the electrode portion of the thermistor is suppressed, so that high-accuracy temperature detection can be performed for a long time.

In the second case of the present invention, the thermistor can be kept in a self-heating state by closing the second switch element. Therefore, in a high-humidity temperature detection environment, the water that is going to adhere to the surface is evaporated, and the water that is indispensable for the occurrence of migration does not exist. After that, the switch element is opened, and the temperature detection circuit is configured by the voltage dividing circuit of the resistance element and the thermistor. Thereby, required temperature detection can be performed.

(3) The third temperature detecting circuit according to the present invention includes a series connection circuit of a resistance element and a thermistor, and a switch element connected in parallel to the resistance element, wherein the switch element has a resistance change of the thermistor. The control is performed in a temperature detection mode for detecting the temperature by using the control, and the control is performed to close the thermistor in a moisture removal mode in which the thermistor self-heats to remove moisture attached to the surface.

According to the third temperature detecting circuit of the present invention, the temperature is detected in the temperature detecting mode by opening the switch element. On the other hand, when the switch element is closed, moisture adhering to the surface is removed in a moisture removal mode. Therefore, even in a high-humidity temperature detection environment, the occurrence of migration in the electrode portion on the thermistor surface is suppressed, and high-accuracy temperature detection can be performed for a long time.

In the third case of the present invention, the switch element is further closed and the thermistor can be kept in a self-heating state. Therefore, in a high-humidity temperature detection environment, the water that is going to adhere to the surface is evaporated, and the water that is indispensable for the occurrence of migration does not exist. After that, the switch element is opened, and the temperature detection circuit is configured by the voltage dividing circuit of the resistance element and the thermistor, and the required temperature can be detected.

In the first to third temperature detecting circuits according to the present invention, preferably, the thermistor may be constituted by an NTC thermistor.

(4) The electronic apparatus of the present invention includes a temperature detection circuit and a control unit, and the temperature detection circuit detects a temperature of the thermistor in a temperature detection mode in which a temperature is detected using a resistance change of the thermistor. First energizing means for energizing a voltage for self-heating, second energizing means for energizing a voltage for self-heating to the thermistor in a moisture removal mode for self-heating the thermistor and removing moisture attached to the surface thereof,
A mode switching unit for switching between the two modes, wherein the control unit controls the operation of the mode switching unit and processes a temperature detection signal from a temperature detection circuit.

According to the electronic apparatus of the present invention, the connection of the thermistor to the second energizing means is switched to the self-heating state by the mode switching means. Therefore, in a high-humidity temperature detection environment, water that is going to adhere to the surface of the thermistor is evaporated, and water that is indispensable for occurrence of migration does not exist. As a result, even if the connection of the thermistor is switched to the first energizing means for temperature detection by the mode switching means and the energized state is maintained for a long time, migration does not occur. As a result, the temperature detection circuit of the electronic device can perform highly accurate temperature detection.

The control section may control the mode switching means so as to connect the thermistor to the second energizing means for a predetermined time and then to the first energizing means when the temperature detecting circuit is started.

In such a case, even if moisture adheres to the thermistor surface in a high-humidity atmosphere, the thermistor is self-heated at the time of startup to remove moisture present on the surface, so that the thermistor is in a good state and temperature is detected. Is preferred.

(5) The temperature detecting method according to the present invention is a temperature detecting method utilizing a resistance change of the thermistor for temperature detection, wherein a first step of detecting a temperature by lowering an energizing value to the thermistor, It is characterized by switching to the second step of increasing the energization value and causing self-heating.

According to the temperature detecting method of the present invention, while the temperature is detected in the first step, the water adhering to the surface can be removed in the second step. As a result, the occurrence of migration is suppressed even in a high-humidity temperature detection environment, and the thermistor can perform temperature detection with high accuracy for a long period of time.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on embodiments shown in the drawings.

FIGS. 1 and 2 relate to an embodiment of the present invention. FIG. 1 is a diagram showing a schematic configuration of an electronic device having a temperature detecting circuit of the present invention. FIG. 2 is a diagram showing the NTC thermistor of FIG. FIG. 4 is a diagram illustrating resistance-temperature characteristics.

1 is a temperature detection circuit, 2 is an A / D converter, 3 is a control unit, and 4 is a temperature display unit.

The temperature detecting circuit 1 includes a fixed resistor 5, a short circuiter 6, an NTC thermistor 7, and a relay 8.

The fixed resistor 5 has a DC power source + at one end.
Vcc, and the other end is connected to one contact of the relay 8.

The fixed resistor 5 constitutes a voltage dividing circuit together with the NTC thermistor 7 as a first energizing means while being connected to the NTC thermistor 7 via the relay 8.

This voltage dividing circuit comprises an NTC thermistor 7 corresponding to the resistance value specific to the fixed resistor 5 and the environmental temperature at that time.
, The voltage of the DC power supply + Vcc is divided, and a voltage Vout corresponding to the environmental temperature can be output to the A / D converter 2 from the voltage dividing point A.

As shown in FIG. 2, the NTC thermistor 7 has an NTC characteristic that decreases with an increase in temperature. However, the embodiment is not limited to the NTC thermistor having such an NTC characteristic. In FIG. 2, the horizontal axis represents temperature (° C.), and the vertical axis represents resistance (kΩ).

The short-circuit device 6 has one end connected to a DC power supply and the other end connected to the other contact of the relay 8.

Then, the short-circuit device 6 can supply a voltage of DC power supply + Vcc to the NTC thermistor 7 and a voltage for self-heating as the second current supply means.

The relay 8 serves as mode switching means.
The two contacts can be switched to connect the NTC thermistor 7 to the fixed resistor 5 or the short-circuit device 6.

The A / D converter 2 converts the divided voltage Vout from the temperature detection circuit 1 into a digital signal and inputs the digital signal to the control unit 3 as temperature data.

The control unit 3 is preferably composed of a microcomputer, and displays the detected temperature on the temperature display unit 4 based on the temperature data from the temperature detection circuit 1 via the A / D converter 2. , And outputs a control signal to various parts (not shown).

The control unit 3 also applies control signals S11 and S12 to the relay 8 to switch and drive both contacts.
As a result, control is performed to connect the NTC thermistor 7 to either the fixed resistor 5 or the short-circuit device 6.

In the component configuration of such an electronic device, among the electronic components constituting the temperature detection circuit 1, N
The TC thermistor 7 is mounted on the sub board 10. On the other hand, the fixed resistor 5 and the relay 8 as other electronic components constituting the temperature detection circuit 1, the A / D converter 2, the control unit 3, and the temperature display unit 4 are mounted on the main board 11.

The two substrates 10 and 11 are routed by the wiring 12 so that the sub-substrate 10 can be arranged near the target whose temperature is to be detected. As a result, the NTC thermistor 7 can be made as close as possible to the object, and more accurate temperature detection is possible.

The features of the present embodiment will be described below.

The control section 3 inputs the control signals S11 and S12 to the relay 8 for switching between the temperature detection mode and the moisture removal mode.

In this case, the control unit 3 controls the relay 8 to set the moisture removal mode to the control signal S when starting the temperature detection.
Enter 11.

The relay 8 responds to this input by turning on the short-circuit device 6.
Is connected to the NTC thermistor 7. With this, NT
The C thermistor 7 is directly applied with a voltage from a DC power supply, generates heat, and removes water on its surface.

Further, after the start, the control unit 3 controls the relay 8
, A control signal S12 for setting the temperature detection mode is input. The relay 8 connects the fixed resistor 5 to the NTC thermistor 7 in response to the input of the control signal S12. As a result, in the voltage dividing circuit composed of the fixed resistor 5 and the NTC thermistor 7, the divided voltage Vout is A / D converted by the A / D converter 2 and input to the control unit 3.

The control section 3 performs various controls such as calculating temperature data from the divided voltage Vout and displaying the temperature data on the temperature display section 4.

The control unit 3 controls both control signals S11 and S11.
A first step of controlling the output timing of the DCT 12 to lower the energizing value to the NTC thermistor 7 in the temperature detection mode to perform temperature detection; and increasing the energizing value to the NTC thermistor 7 in the moisture removal mode to increase the self-heating. In addition to switching to the second step, both steps may be time-controlled and switched.

By such switching, while the temperature is detected in the first step, the water adhering to the surface can be removed in the second step. As a result, even in a humid temperature detecting environment, the occurrence of migration at the electrode portion on the surface of the NTC thermistor 7 is suppressed,
Deterioration of the C thermistor 7 is prevented, and highly accurate temperature detection can be performed for a long time.

As a result, in the water removal mode, N
Since moisture on the surface of the TC thermistor 7 has been removed, no migration occurs in the element electrode of the NTC thermistor 7 in the subsequent temperature detection mode, and deterioration of the NTC thermistor 7 is suppressed.

The present invention is not limited to the above embodiment, and various applications and modifications are possible.

(1) FIG. 3 is a diagram showing a temperature detecting circuit according to another embodiment of the present invention.

In this temperature detecting circuit 1a, the fixed resistor 5
A second switch element 21 is connected in parallel to a series connection circuit of the first switch element 20 and the first switch element 20. An NTC thermistor 7 is connected in series to these circuit configurations.

Each of the switch elements 20 and 21 is
It is composed of transistors.

The type of the transistor is bipolar in this embodiment, but may be another type.

In addition, any switching element can be used as long as it is a switching element that can be turned on and off by a control signal instead of a transistor.

In the temperature detecting circuit 1a, in the moisture removal mode, the control signal S11 from the controller 3
Applied to the switch element 21 and the second switch element 2
1 closes. As a result, a voltage for self-heating is applied to the NTC thermistor 7 and water on the surface of the NTC thermistor 7 can be removed.

In the temperature detection mode, the control signal S12 from the control unit 3 is applied to the first switch element 20 to close the first switch element 20 in the temperature detection mode. As a result, a voltage for temperature detection is applied to the NTC thermistor 7.

(2) FIG. 4 is a diagram showing a temperature detecting circuit according to still another embodiment of the present invention.

In the case of this temperature detecting circuit 1b, a series connection circuit of a fixed resistor 5 as a resistance element and an NTC thermistor 7 and a switch element 6 'as a short-circuiting device connected in parallel to the fixed resistor 5 are provided. Including. The switch element 6 '
It is possible to control to open in the temperature detection mode and close in the moisture removal mode.

In the temperature detection circuit 1b, a control signal S12 for setting the mode to the temperature detection mode is input from the control unit 3 to the base of the switch element 6 '. As a result, the switch element 6 'is cut off and the fixed resistor 5 and NT
The temperature is detected by a series connection circuit including the C thermistor 7.

On the other hand, when the control signal S11 for setting the mode to the moisture removal mode is input from the control unit 3 to the base of the switch element 6 ', the switch element 6' conducts and the NT
The C thermistor 7 generates heat by itself.

By the self-heating, the water adhering to the surface of the NTC thermistor 7 is removed. As a result, the occurrence of migration is suppressed even in a high-humidity temperature detection environment, and the NTC thermistor 7 can perform temperature detection with high accuracy for a long period of time.

Also in the case of this embodiment, the switch element 6 'is constituted by a transistor.

The type of the transistor is bipolar in this embodiment, but may be another type.

The switch element is not only an electronically operated element such as a transistor, but also an element having a mechanically operated part such as a relay contact as long as it can be turned on and off by a control signal. However, the form of the element is not limited.

(3) In the above embodiment, the NTC thermistor was used as the temperature detecting element. However, the present invention is not limited to this, and a PTC thermistor may be used.

(4) In the above embodiment, the self-heating voltage is applied to the NTC thermistor 7 via the relay 8, but the present invention is not limited to this. For example, a current may be forcibly supplied from the current source directly to the NTC thermistor 7, thereby causing the NTC thermistor 7 to generate heat.

[0075]

As described above, according to the present invention,
While temperature detection is performed in the temperature detection mode, moisture adhering to the surface can be removed in the moisture removal mode. Therefore, in the present invention, the occurrence of migration to the thermistor is suppressed even in a high-humidity temperature detection environment, so that high-accuracy temperature detection using the thermistor is maintained for a long time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature detection circuit according to an embodiment of the present invention inside an electronic device.

FIG. 2 is a voltage-temperature characteristic diagram of the NTC thermistor of FIG. 1;

FIG. 3 is a diagram showing a temperature detection circuit according to another embodiment of the present invention inside an electronic device.

FIG. 4 is a diagram showing a temperature detection circuit according to still another embodiment of the present invention inside an electronic device.

FIG. 5 is a diagram showing a conventional temperature detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Temperature detection circuit 2 A / D converter 3 Control part 4 Temperature display part 4 Fixed resistor 6 Short circuiter 7 NTC thermistor 8 Relay

Claims (10)

[Claims] 1. A mode in which a temperature is detected by using a resistance change of a thermistor, and a mode in which the thermistor self-generates heat and removes moisture adhering to the surface thereof is switchable and controllable. Temperature detection circuit. 2. The temperature detection circuit according to claim 1, wherein a first power supply means for supplying a temperature detection voltage to the thermistor in the temperature detection mode; A temperature detecting circuit comprising: a second energizing unit that energizes a voltage; and a mode switching unit that switches between the two modes. 3. The temperature detection circuit according to claim 2, wherein the first power supply means includes a resistance element connected to a power supply, the second power supply means includes a short-circuit element connected to a power supply, and the mode switching means. Switches the connection of the thermistor to a resistance element or a short-circuit element according to the two modes,
A temperature detection circuit characterized by the above-mentioned. 4. A thermistor is connected in series to a circuit including a series connection circuit of a resistance element and a first switch element and a second switch element connected in parallel to the series connection circuit. In the temperature detection mode in which the temperature is detected by using the resistance change of the thermistor, control for closing the first switch element is performed, and moisture removal for removing moisture adhering to the surface by causing the thermistor to self-heat. In the mode, a closing control is performed on the second switch element.
A temperature detection circuit characterized by the above-mentioned. 5. A circuit, comprising: a series connection circuit of a resistance element and a thermistor; and a switch element connected in parallel to the resistance element, wherein the temperature of the switch element is detected by using a resistance change of the thermistor. A temperature detection circuit that performs control to open in a temperature detection mode and performs control to close in a moisture removal mode in which the thermistor self-heats to remove moisture attached to the surface. 6. The temperature detection circuit according to claim 1, wherein the thermistor is an NTC thermistor. 7. A temperature detection circuit comprising: a temperature detection circuit; and a control unit, wherein the temperature detection circuit supplies a temperature detection voltage to the thermistor in a temperature detection mode in which temperature is detected using a resistance change of the thermistor. Energizing means, second energizing means for energizing a self-heating voltage to the thermistor in a moisture removal mode for self-heating the thermistor to remove moisture adhering to its surface, and mode switching means for switching between the two modes. The control unit controls the operation of the mode switching means and processes a temperature detection signal from a temperature detection circuit.
Electronic equipment characterized by the above-mentioned. 8. The electronic device according to claim 7, wherein the control unit connects the thermistor to the second energizing unit for a predetermined time when the temperature detecting circuit is started, and then connects the thermistor to the first energizing unit. Controlling electronic devices. 9. A temperature detection method using a change in resistance of a thermistor for temperature detection, comprising: a first step of detecting a temperature by lowering an energization value of the thermistor; 2. A temperature detecting method, comprising: switching to a second step. 10. The temperature detection method according to claim 9, wherein said two steps are time-controlled and switched.