Temperature measurement circuit and temperature measurement device

Abstract

Provided is a temperature measuring circuit and a temperature measuring device that can cope with a wide range of temperature sensing element constants. The temperature measuring circuit uses a temperature sensing element to measure temperature, and includes: a voltage control circuit that applies a control voltage to the temperature sensing element; a first switching circuit that switches the value of the control voltage based on a current flowing through the temperature sensing element; a conversion circuit that converts the current flowing through the temperature sensing element to a voltage value corresponding to the measured temperature at a predetermined conversion gain; and a second switching circuit that switches the value of the conversion gain based on the voltage value.

Description

Technical Field

[0001] This disclosure relates to temperature measuring circuits and temperature measuring devices. Background Technology

[0002] A temperature sensing device is known that connects a thermistor and a voltage divider resistor in series, and detects the temperature based on the output voltage at the connection point of the thermistor and the voltage divider resistor. In such a temperature sensing device, when the thermistor is in a low resistance region, the increase in current flowing through the thermistor is sometimes suppressed by reducing the supply voltage to the thermistor (for example, see Patent Document 1).

[0003] However, in the technology of Patent Document 1, when the thermistor reaches a low resistance value, the resistance value of the voltage divider resistor connected in series with the thermistor also decreases, thus increasing the current flowing through the thermistor. This increase in current leads to, for example, increased power consumption. Furthermore, the temperature detection device in Patent Document 1 reads the change in voltage after voltage division by the thermistor and the voltage divider resistor; therefore, the constant of the voltage divider resistor needs to be changed according to the constant of the temperature-sensing element, such as the thermistor, used. Therefore, without changing the constant of the voltage divider resistor, it is difficult to handle a wide range of temperature-sensing element constants (nominal resistance values).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2015-145823 Summary of the Invention

[0005] This disclosure provides a temperature measuring circuit and a temperature measuring device capable of handling a wide range of temperature sensing element constants.

[0006] According to one aspect of this disclosure, a temperature measuring circuit that uses a temperature sensing element to measure temperature comprises:

[0007] A voltage control circuit applies a control voltage to the temperature sensing element;

[0008] The first switching circuit switches the value of the control voltage based on the current flowing through the temperature sensing element;

[0009] A conversion circuit that converts the current flowing through the temperature sensing element into a voltage value corresponding to the measured temperature with a predetermined conversion gain; and

[0010] The second switching circuit switches the value of the conversion gain based on the voltage value.

[0011] Furthermore, according to another aspect of this disclosure, a temperature measuring circuit that uses a temperature sensing element to measure temperature comprises:

[0012] A voltage control circuit that controls the gate of the transistor based on the output of a differential circuit that compares the output voltage of the transistor driving the temperature sensing element with a reference voltage, thereby applying a control voltage to the temperature sensing element; and

[0013] The conversion circuit converts the output current of the transistor into a voltage value corresponding to the measured temperature.

[0014] The output voltage of the transistor is obtained by converting the output current of the transistor based on the resistance value of the temperature sensing element. Attached Figure Description

[0015] Figure 1 This illustrates a structural example of a temperature measuring device equipped with a temperature measuring circuit according to one embodiment.

[0016] Figure 2 An example illustrating the correspondence between BIT1, BIT2, and n.

[0017] Figure 3 This is an example illustrating the change in voltage value VADC relative to the resistance value RNTC of the temperature sensing element.

[0018] Figure 4 This section illustrates the structure of a temperature measurement circuit using a comparison method.

[0019] Figure 5 This is an example of the change in voltage value VAD measured by a temperature measuring circuit of a temperature sensing element with a resistance value RNTC of 10kΩ at an ambient temperature of 25°C.

[0020] Figure 6 This is an example of the change in voltage value VAD measured by a temperature measuring circuit of a temperature sensing element with a resistance value RNTC of 100kΩ at an ambient temperature of 25°C.

[0021] Figure 7 This illustrates an example of the voltage VADC variation characteristics measured by a temperature measuring circuit of one embodiment using a temperature sensing element with a resistance value RNTC of 10kΩ at an ambient temperature of 25°C.

[0022] Figure 8 This illustrates an example of the change in voltage value VADC measured by a temperature measuring circuit of one embodiment using a temperature sensing element with a resistance value RNTC of 100kΩ at an ambient temperature of 25°C. Detailed Implementation

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0024] Figure 1This section illustrates a structural example of a temperature measuring device 301 equipped with a temperature measuring circuit 101 according to one embodiment. Figure 1 The temperature measuring device 301 shown uses a temperature sensing element 60 to measure the temperature of the object being measured. The object being measured can be a solid, liquid, or gas, and is not particularly limited. Specific examples of the object being measured include secondary batteries. The temperature measuring device 301 includes a temperature sensing element 60 and a temperature measuring circuit 101.

[0025] The resistance of the temperature sensing element 60 changes according to the temperature change of the object being measured. The temperature sensing element 60 is, for example, an NTC (Negative Temperature Coefficient) thermistor. An NTC thermistor is a temperature-sensing resistor whose resistance changes with a negative temperature characteristic.

[0026] The temperature measuring circuit 101 is a semiconductor integrated circuit that uses a temperature sensing element 60 to measure the temperature of the object being measured. In this example, the temperature measuring circuit 101 has terminals 11-16 for external connection to the temperature measuring circuit 101. The temperature measuring circuit 101 can be a single semiconductor integrated circuit with temperature measuring function, or it can be a part of a circuit within a semiconductor integrated circuit with a function different from temperature measuring function (e.g., secondary battery protection function).

[0027] Terminal 11 is a power supply terminal, and terminal 12 is a ground terminal. Terminal 11 is electrically connected to the positive terminal of the power supply 201, such as a secondary battery, and terminal 12 is electrically connected to the negative terminal of the power supply 201. The temperature measuring circuit 101 operates by the power supply voltage applied by the power supply 201 between terminals 11 and 12, for example, by the voltage VB generated by a constant voltage source 29, such as a voltage regulator. The constant voltage source 29 can be located inside or outside the temperature measuring circuit 101.

[0028] Terminal 13 is a temperature measuring terminal for connecting one end of the temperature sensing element 60. One end of the temperature sensing element 60 is connected to terminal 13, and the other end is connected to terminal 12. Terminal 14 is a first output terminal that outputs a first information BIT1 to the outside of the temperature measuring circuit 101, which varies according to the value of the control voltage VTH applied to the temperature sensing element 60. Terminal 15 is a second output terminal that outputs a second information BIT2 to the outside of the temperature measuring circuit 101, which varies according to the value of the conversion gain β (described later). Terminal 16 is an output terminal that outputs the measured value obtained by the temperature measuring circuit 101 using the temperature sensing element 60 to the outside of the temperature measuring circuit 101.

[0029] The temperature measuring circuit 101 includes a voltage control circuit 20, a first switching circuit 30, a conversion circuit 40, and a second switching circuit 50.

[0030] The voltage control circuit 20 applies a control voltage VTH to the temperature sensing element 60. In this example, the control voltage VTH is applied to the temperature sensing element 60 by driving the transistor 21. The voltage control circuit 20 controls the gate of the transistor 21, for example, based on the output of the differential circuit 23 that compares the control voltage VTH with a reference voltage Vr, thereby applying the control voltage VTH across the temperature sensing element 60. The voltage control circuit 20 applies the control voltage VTH to the temperature sensing element 60, which is connected between terminals 13 and 12, by applying the control voltage VTH between terminals 13 and 12. In this example, the output voltage of the transistor 21 is the voltage obtained by converting the output current of the transistor 21 through the resistance value RNTC of the temperature sensing element 60, and it is consistent with the control voltage VTH.

[0031] exist Figure 1 In the example shown, the voltage control circuit 20 has a reference voltage circuit 22, a differential circuit 23, and a transistor 21.

[0032] The reference voltage circuit 22 generates multiple reference voltages Vr with different values. In this example, the reference voltage circuit 22 divides the power supply voltage VB using a voltage divider circuit composed of multiple resistors, thereby generating two reference voltages Vr: Vref and Vref×a. Vref is an example of the first voltage value, and Vref×a is an example of the second voltage value, which is higher than the first voltage value.

[0033] 'a' is a positive coefficient greater than 1. In this example, 'a' is determined by the ratio of the resistance values ​​of the multiple resistors included in the voltage divider circuit of the reference voltage circuit 22. To allow adjustment of the value of coefficient 'a', the voltage divider circuit of the reference voltage circuit 22 may include adjustable resistors.

[0034] The differential circuit 23 controls the gate voltage of transistor 21 so that the deviation between the control voltage VTH and the reference voltage Vr becomes zero. The differential circuit 23 is, for example, an operational amplifier, which has an inverting input section for inputting the reference voltage Vr, a non-inverting input section for applying the control voltage VTH, and an output section connected to the gate of transistor 21.

[0035] Transistor 21 is a semiconductor device that allows current ITH to flow through the temperature sensing element 60. In this example, transistor 21 is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with an output terminal connected to one end of the temperature sensing element 60. Transistor 21 is, for example, a P-channel MOSFET with a gate connected to the output of the differential circuit 23, a source connected to terminal 11, and a drain connected to one end of the temperature sensing element 60 and the non-inverting input of the differential circuit 23. In this case, the drain of the P-channel MOSFET corresponds to the output terminal of transistor 21.

[0036] The first switching circuit 30 switches the value of the control voltage VTH based on the current ITH flowing through the temperature sensing element 60. Therefore, the voltage control circuit 20 can selectively switch the value of the control voltage VTH applied to the temperature sensing element 60 according to the magnitude of the current ITH. Figure 1 In the example shown, the first switching circuit 30 switches the value of the reference voltage Vr according to the current ITH flowing through the transistor 21, thereby switching the value of the control voltage VTH.

[0037] When the current ITH flowing through transistor 21 exceeds the first current threshold I1, the first switching circuit 30 switches the reference voltage Vr to reduce the control voltage VTH from Vref×a to Vref. Therefore, even if the current ITH increases due to the decrease in the resistance RNTC of the temperature sensing element 60, the excessive increase in the current ITH can be suppressed because the control voltage VTH applied to the temperature sensing element 60 is reduced. Figure 1 In the example shown, the first switching circuit 30 uses switch 31 to switch the value of the reference voltage Vr from Vref×a to Vref, thereby reducing the value of the control voltage VTH from Vref×a to Vref.

[0038] On the other hand, when the current ITH flowing through transistor 21 is lower than the second current threshold I2, which is lower than the first current threshold I1, the first switching circuit 30 switches the reference voltage Vr to raise the control voltage VTH from Vref to Vref×a. Therefore, even if the current ITH decreases due to the increase in the resistance RNTC of the temperature sensing element 60, the excessive decrease in the current ITH can be suppressed because the control voltage VTH applied to the temperature sensing element 60 increases. Figure 1 In the example shown, the first switching circuit 30 uses switch 31 to switch the value of the reference voltage Vr from Vref to Vref×a, thereby causing the value of the control voltage VTH to rise from Vref to Vref×a.

[0039] exist Figure 1 In the example shown, the first switching circuit 30 has a switch 31, a transistor 32, and a current detection circuit 33.

[0040] In this example, the first switching circuit 30 switches the value of the reference voltage Vr based on the first mirror current Im output from the first current mirror circuit 71 corresponding to the current ITH flowing through transistor 21, thereby switching the value of the control voltage VTH output from the voltage control circuit 20. The first current mirror circuit 71 is a circuit formed by transistors 21 and 32. The first mirror current Im is output from transistor 32 based on the magnitude of the current ITH flowing through transistor 21. In this example, the ratio of the current ITH to the first mirror current Im (the mirror ratio of the first current mirror circuit 71) is 1:1, but it is not limited to this.

[0041] Thus, the first switching circuit 30 switches the value of the control voltage VTH based on the first mirror current Im output from the first current mirror circuit 71 corresponding to the current ITH flowing through the transistor 21. By using the second current mirror circuit 72, the first switching circuit 30 can switch the value of the control voltage VTH without directly operating the current ITH flowing through the temperature sensing element 60, thereby ensuring the accuracy of the current ITH flowing through the temperature sensing element 60 to which the control voltage VTH is applied. Therefore, the accuracy of temperature measurement using the temperature sensing element 60 is improved.

[0042] exist Figure 1 In the example shown, the first switching circuit 30 and the voltage control circuit 20 share transistor 21. That is, transistor 21 is used as a driving transistor to allow current ITH to flow through the temperature sensing element 60, and also as a detection transistor to detect the magnitude of current ITH. Because the shared transistor 21 is used in both the driving and detection functions, miniaturization of the temperature measuring circuit 101 is possible.

[0043] In this example, transistor 32 is a P-channel MOSFET having a gate connected to the gate of transistor 21, a source connected to terminal 11, and a drain connected to current detection circuit 33.

[0044] The current detection circuit 33 detects the magnitude of the current ITH by monitoring the first mirror current Im. When the value of the current ITH flowing through the transistor 21 is detected to be higher than the first current threshold I1 based on the first mirror current Im, the current detection circuit 33 switches the value of the reference voltage Vr from Vref×a to Vref via switch 31. On the other hand, when the value of the current ITH flowing through the transistor 21 is detected to be lower than the second current threshold I2 based on the first mirror current Im, the current detection circuit 33 switches the value of the reference voltage Vr from Vref to Vref×a via switch 31.

[0045] The current detection circuit 33 includes a Schmitt trigger inverter 34, a first constant current source 35, a second constant current source 36, and a switch 37. The first current threshold I1 is set based on the sum of the constant current values ​​flowing through the first constant current source 35 and the second constant current source 36.

[0046] The mirror ratio of the first current mirror circuit 71 is set to 1:1. When the current value of the current ITH (first mirror current Im) increases, the voltage value of the input of the Schmitt trigger inverter 34 increases. When the current value of the current ITH (first mirror current Im) exceeds the first current threshold I1, the logic level of the output of the Schmitt trigger inverter 34 switches from high level to low level. As a result, the switch 37 switches from the on state to the off state, and the value of the reference voltage Vr switches from Vref×a to Vref through the switch 31. As a result, the current threshold of the current detection circuit 33 switches from the first current threshold I1 to the second current threshold I2, and the value of the control voltage VTH switches from Vref×a to Vref. The current detection circuit 33 outputs the first information BIT1, indicating that the value of the control voltage VTH is low (Vref), from terminal 14 to the outside of the temperature measuring circuit 101.

[0047] On the other hand, when the current value of ITH (first mirror current Im) decreases, the voltage value at the input of the Schmitt trigger inverter 34 decreases. When the current value of ITH (first mirror current Im) is less than the second current threshold I2, the logic level of the output of the Schmitt trigger inverter 34 switches from low to high. As a result, switch 37 switches from the off state to the on state, and the value of the reference voltage Vr switches from Vref to Vref×a via switch 31. Consequently, the current threshold of the current detection circuit 33 switches from the second current threshold I2 to the first current threshold I1, and the value of the control voltage VTH switches from Vref to Vref×a. The current detection circuit 33 outputs a first information BIT1, indicating that the value of the control voltage VTH is Vref×a (high level), from terminal 14 to the outside of the temperature measuring circuit 101.

[0048] The conversion circuit 40 converts the current ITH flowing through the temperature sensing element 60 into a voltage value VADC corresponding to the measured temperature with a predetermined conversion gain β. In this example, the current ITH flowing through the transistor 21 is converted using the second current mirror circuit 72, thereby generating the voltage value VADC. The second current mirror circuit 72 is a circuit formed by transistors 21, 41, and 42.

[0049] The conversion circuit 40 converts the current ITH flowing through the transistor 21 into a second mirror current Iref via the second current mirror circuit 72, and outputs the analog voltage generated by allowing the second mirror current Iref to flow through the resistor 43 as a voltage value VADC. The conversion circuit 40 outputs the measured value (voltage value VADC or a value corresponding to voltage value VADC) from terminal 16 to the outside of the temperature measuring circuit 101. Thus, the temperature measuring circuit 101 can provide an external device with a measured value corresponding to the temperature obtained using the temperature sensing element 60. The second mirror current Iref is a reference current flowing through the resistor 43.

[0050] The conversion circuit 40 has an AD converter 44 that performs an AD (Analog to Digital) conversion on the analog voltage value VADC generated by allowing a second mirror current Iref to flow through the resistor 43, thereby converting it into a digital measurement value. In this case, the conversion circuit 40 outputs the digital measurement value from terminal 16 to the outside of the temperature measuring circuit 101. The digital measurement value is an example of a value corresponding to the voltage value VADC.

[0051] The conversion circuit 40 may also replace the AD converter 44 with a comparator that compares the analog voltage value VADC with a predetermined judgment value. The conversion circuit 40 outputs the output of this comparator, along with first information BIT1 and second information BIT2 output from terminals 14 and 15, from terminal 16 to the outside of the temperature measuring circuit 101, thereby providing an external device with information on whether the predetermined judgment value (temperature) has been exceeded. The comparator output is an example of a value corresponding to the voltage value VADC.

[0052] The external device uses the measured value provided by the temperature measuring circuit 101 for predetermined control. The content of the predetermined control is not particularly limited. For example, the external device can use the measured value to correct the detected value of the remaining capacity of the secondary battery, or it can use the measured value for the temperature protection of the secondary battery.

[0053] exist Figure 1 In the example shown, the conversion circuit 40 has transistor 41, transistor 42, resistor 43, and AD converter 44.

[0054] The conversion circuit 40 and the voltage control circuit 20 share the transistor 21. That is, the transistor 21 is used as a driving transistor to allow current ITH to flow through the temperature sensing element 60, and as a conversion transistor to convert current ITH into voltage value VADC. Since the driving function and the conversion function share the same transistor 21, the temperature measuring circuit 101 can be miniaturized.

[0055] In this example, transistor 41 is a P-channel MOSFET having a gate connected to the gate of transistor 21, a source connected to terminal 11, and a drain connected to the end of resistor 43. In this example, transistor 42 is a P-channel MOSFET having a gate connected to the gate of transistor 21, a source connected to terminal 11, and a drain connected to the end of resistor 43 via switch 54.

[0056] The second switching circuit 50 switches the conversion gain β of the conversion circuit 40 based on the voltage value VADC. Therefore, the conversion circuit 40 can selectively switch the conversion gain β according to the magnitude of the voltage value VADC. The second switching circuit 50 switches the conversion gain β based on the voltage value VADC, thereby switching the voltage value VADC within a predetermined range. This allows the voltage value VADC to vary within a predetermined range.

[0057] When the voltage value VADC exceeds the first threshold Vd1, the second switching circuit 50 switches the value of the conversion gain β to the first conversion gain value β1 (1 in this example). On the other hand, when the voltage value VADC is lower than the second threshold Vd2, which is lower than the first threshold Vd1, the second switching circuit 50 switches the value of the conversion gain β to the second conversion gain value β2 (b in this example). b is a positive coefficient greater than 1. In this example, the conversion gain β and the coefficient b are determined by the mirror ratio of the second current mirror circuit 72.

[0058] In this example, the second switching circuit 50 switches the value of the conversion gain β based on the voltage value VADC generated by converting the current ITH flowing in the transistor 21 through the second current mirror circuit 72. By using the second current mirror circuit 72, the second switching circuit 50 can switch the value of the conversion gain β without directly operating the current ITH flowing in the temperature sensing element 60, thus ensuring the accuracy of the current ITH flowing in the temperature sensing element 60 under the applied control voltage VTH. Therefore, the accuracy of temperature measurement using the temperature sensing element 60 is improved.

[0059] exist Figure 1 In the example shown, the second switching circuit 50 has a threshold generation circuit 51, a switch 52, a comparator 53, and a switch 54.

[0060] The threshold generation circuit 51 generates multiple thresholds Vd with different voltage values. In this example, the threshold generation circuit 51 divides the power supply voltage VB using a voltage divider circuit composed of multiple resistors, thereby generating two thresholds Vd: a first threshold Vd1 and a second threshold Vd2. The voltage value of the second threshold Vd2 is lower than that of the first threshold Vd1.

[0061] Comparator 53 compares the threshold Vd with the voltage value VADC, and based on the comparison result, turns switch 54 on or off, and switches switch 52.

[0062] When comparator 53 detects a voltage value VADC exceeding the first threshold Vd1, it switches the value of the conversion gain β from β2 (b in this example) to β1 (1 in this example) by opening switch 54, and switches the threshold Vd from Vd1 to Vd2 by switching switch 52. Comparator 53 outputs a second information BIT2, representing a low level indicating that the conversion gain β is β1, from terminal 15 to the outside of the temperature measuring circuit 101.

[0063] On the other hand, when comparator 53 detects a voltage value VADC less than the second threshold Vd2, it switches the value of the conversion gain β from β1 (1 in this example) to β2 (b in this example) by turning on switch 54, and switches the threshold Vd from Vd2 to Vd1 by switching on switch 52. Comparator 53 outputs a second information BIT2, indicating that the value of the conversion gain β is β2 (high level), from terminal 15 to the outside of the temperature measuring circuit 101.

[0064] Here, the resistance value of the temperature sensing element 60 is set to RNTC, the control voltage VTH applied across the temperature sensing element 60 is set to Vref×α, the current flowing through the temperature sensing element 60 is set to ITH, the second mirror current Iref flowing through the resistor 43 is set to β×ITH, and the resistance value of the resistor 43 is set to Rref.

[0065] RNTC = VTH / ITH

[0066] = (Vref×α) / ITH

[0067] = (Vref×α)×(β / Iref)

[0068] =(Vref×α)×(β×Rref / VADC)

[0069] =Rref×Vref×n / VADC

[0070] This expression holds true. The coefficient n is α × β. Furthermore, in this example, α is 1 or a, and β is 1 or b.

[0071] Figure 2 This is an example illustrating the correspondence between the first information BIT1, the second information BIT2, and the coefficient n. L represents a low level, and H represents a high level. The external device obtains the logic levels of the first information BIT1 and the second information BIT2 from the temperature measuring circuit 101 and... Figure 2By comparing the corresponding relationships shown, the coefficient n of the above formula is determined. The temperature measuring circuit 101 can provide information representing the coefficient n to an external device.

[0072] The external device obtains a measured value (voltage value VADC or a value corresponding to voltage value VADC) from the temperature measuring circuit 101, substitutes this measured value and coefficient n into the above calculation formula, and thereby calculates the resistance value RNTC of the temperature sensing element 60. The external device calculates the temperature of the object being measured based on the calculated resistance value RNTC. For example, the external device calculates the temperature of the object being measured (ambient temperature T) by substituting the calculated resistance value RNTC into the following relationship.

[0073] R = R0 × exp(B × (1 / T - 1 / T0)) ... Equation 1a

[0074] 1 / T = 1 / B × ln(R / R0) + 1 / T0……Equation 1b

[0075] T: Ambient temperature (K)

[0076] T0: Reference temperature (K)

[0077] R: Resistance value of the temperature sensing element 60 at ambient temperature T (=RNTC)

[0078] R0: Resistance value of the temperature sensing element 60 at the reference temperature T0.

[0079] B: Constant

[0080] Equation 1b is a modified version of Equation 1a, where T0, R0, and B are the parameters of the temperature sensing element 60.

[0081] Figure 3 This is an example illustrating the characteristic of the change in voltage value VADC relative to the resistance value RNTC of the temperature sensing element 60. According to the temperature measuring circuit 101 described above, the change in voltage value VADC relative to the resistance value RNTC for each logic level of the first information BIT1 and the second information BIT2 has… Figure 3The temperature measuring circuit 101 reads the change in current flowing through the temperature sensing element 60, thus allowing the circuit constants of the voltage control circuit 20 and the like in the temperature measuring circuit 101 to be set independently of the constant of the temperature sensing element 60. Therefore, a wide range of temperature sensing element constants can be handled without changing the circuit constants of the voltage control circuit 20 and the like. That is, the temperature measuring circuit 101 can accurately measure a wide range of resistance values ​​RNTC. As a result, for example, the temperature measuring circuit 101 can handle multiple types of temperature sensing elements 60 with different resistance values ​​and temperature characteristics. Furthermore, an external device can accurately calculate the temperature based on the measured value (voltage value VADC or a value corresponding to the voltage value VADC), the first information BIT1, and the second information BIT. In addition, the temperature measuring circuit 101 does not have the circuit structure of Patent Document 1 (a structure that reduces the resistance value of the resistor connected in series with the temperature sensing element 60 when the temperature sensing element 60 is in a low resistance region), thus suppressing the increase in current flowing through the temperature sensing element 60.

[0082] Figure 4 This section illustrates the structure of a temperature measurement circuit using a comparison method. Figure 4 The temperature measuring circuit 100 shown uses a temperature sensing element 60 to measure the temperature of the object being measured. The temperature measuring circuit 100 differs from the first embodiment of this disclosure in that it has a resistor 124 connected in series with the temperature sensing element 60, and outputs a voltage value VAD from the connection point between the resistor 124 and the temperature sensing element 60.

[0083] Terminal 111 is a power supply terminal, and terminal 112 is a grounding terminal. Terminal 111 is electrically connected to the positive terminal of the power supply 201, such as a secondary battery, and terminal 112 is electrically connected to the negative terminal of the power supply 201. The temperature measuring circuit 101 operates by the power supply voltage applied by the power supply 201 between terminals 111 and 112, for example, by the voltage VB generated by a constant voltage source 129 such as a voltage regulator. Terminal 113 is a temperature measuring terminal connected to one end of the temperature sensing element 60. One end of the temperature sensing element 60 is connected to terminal 113, and the other end is connected to terminal 112.

[0084] The temperature measuring circuit 100 includes a reference voltage circuit 122, a differential circuit 123, a transistor 121, a resistor 124, and an AD converter 144.

[0085] The reference voltage circuit 122 generates a reference voltage Vr (3.0 volts in this example). The differential circuit 123 controls the gate voltage of the transistor 121 so that the deviation between the constant voltage applied across the series circuit of the temperature sensing element 60 and the resistor 124 and the reference voltage Vr generated by the reference voltage circuit 122 is zero.

[0086] Figure 5 This example illustrates the change in voltage value VAD measured by a temperature measuring circuit 100 using a temperature sensing element with a resistance value RNTC of 10kΩ at an ambient temperature of 25°C. Figure 6 This is an example of the change in voltage value VAD measured by a temperature measuring circuit 100 using a temperature sensing element with a resistance value RNTC of 100kΩ at an ambient temperature of 25°C.

[0087] exist Figure 5 , 6 In this case, the change in voltage value VAD relative to the change in temperature (resistance value RNTC) is small, indicating poor sensitivity (accuracy) in temperature measurement. Figure 5 In this case, although the measurement accuracy is relatively good near 25℃, the measurement accuracy decreases in the high-temperature and low-temperature regions. Figure 6 In low-temperature regions, there is almost no change in the voltage value VAD, resulting in reduced measurement accuracy. The temperature measurement circuit 100 in a comparison method reads the voltage change after voltage division by the temperature sensing element 60 and the resistor 124. Therefore, the constants of the temperature sensing element 60 and the resistor 124 must correspond one-to-one; the constant of the temperature sensing element 60 cannot be arbitrarily changed. Thus, in the temperature measurement circuit 100 in a comparison method, the resistance value of the comparison resistor 124 needs to be changed according to the characteristics of the temperature sensing element 60 and the temperature range.

[0088] In contrast, Figure 7 This illustrates an example of the change in voltage value VADC measured by a temperature measuring circuit 101 in one embodiment using a temperature sensing element with a resistance value RNTC of 10kΩ at an ambient temperature of 25°C. Figure 8 This illustrates an example of the change in voltage value VADC measured by a temperature measuring circuit 101 in one embodiment using a temperature sensing element with a resistance value RNTC of 100kΩ at an ambient temperature of 25°C.

[0089] like Figure 7 , Figure 8As shown, according to the temperature measuring circuit 101, the voltage value VADC changes significantly relative to the change in temperature (resistance value RNTC), thus improving the temperature measurement sensitivity (measurement accuracy). One embodiment of the temperature measuring circuit 101 reads the change in current flowing through the temperature sensing element 60, therefore the circuit constants of the voltage control circuit 20 and the like in the temperature measuring circuit 101 can be set without relying on the constant of the temperature sensing element 60. Therefore, a wide range of temperature sensing element constants can be accommodated without changing the circuit constants of the voltage control circuit 20 and the like. Furthermore, in one embodiment of the temperature measuring circuit 101, the change in resistance value RNTC can be measured over a wide range, thus enabling the accommodating of various types of temperature sensing elements with different resistance values ​​and temperature characteristics.

[0090] The embodiments have been described above, but the present invention is not limited to the above embodiments. It can be combined with or substituted with some or all of the other embodiments for various modifications and improvements.

[0091] For example, temperature measuring circuits are not limited to integrated circuits; they can also be discrete circuits composed of multiple discrete components. Furthermore, the object of temperature measurement can be a solid, liquid, or gas. The temperature sensing element can also be a component other than an NTC thermistor.

[0092] Explanation of reference numerals in the attached figures

[0093] 11, 12, 13, 14, 15, 16 terminals

[0094] 20 Voltage control circuit

[0095] 21 transistors

[0096] 22 Reference Voltage Circuit

[0097] 23 Differential Circuit

[0098] 29 Constant power supply

[0099] 30 First switching circuit

[0100] 31 Switch

[0101] 32 transistors

[0102] 33 Current Detection Circuit

[0103] 34 Schmitt-triggered inverter

[0104] 35 First Constant Current Source

[0105] 36 Second constant current source

[0106] 37 Switch

[0107] 40 Conversion Circuit

[0108] 41, 42 transistors

[0109] 43 Resistor

[0110] 44 AD converter

[0111] 50 Second switching circuit

[0112] 51 Threshold Generation Circuit

[0113] 52 switches

[0114] 53 Comparator

[0115] 54 switches

[0116] 60 Temperature sensing element

[0117] 71 First Current Mirror Circuit

[0118] 72 Second Current Mirror Circuit

[0119] 101 Temperature Measurement Circuit

[0120] 201 Power Supply

[0121] 301 Temperature measuring device.

Claims

1. A temperature measuring circuit that uses a temperature sensing element to measure temperature, characterized in that, The temperature measuring circuit includes: A voltage control circuit applies a control voltage to the temperature sensing element; and The first switching circuit switches the value of the control voltage based on the current flowing through the temperature sensing element. The voltage control circuit has a transistor that drives the temperature sensing element. The control voltage is compared with a reference voltage to control the gate of the transistor, thereby applying the control voltage to the temperature sensing element. The first switching circuit switches the value of the reference voltage based on the current flowing through the transistor, thereby switching the value of the control voltage.

2. The temperature measuring circuit according to claim 1, characterized in that, The voltage control circuit controls the gate based on the output of a differential circuit that compares the control voltage with the reference voltage, thereby applying the control voltage to the temperature sensing element.

3. The temperature measuring circuit according to claim 1 or 2, characterized in that, When the current flowing through the transistor exceeds a first current threshold, the first switching circuit switches the reference voltage to a value that reduces the control voltage to a first voltage value. When the current flowing through the transistor is lower than a second current threshold that is lower than the first current threshold, the first switching circuit switches the reference voltage to a value that raises the control voltage to a second voltage value that is higher than the first voltage value.

4. The temperature measuring circuit according to claim 1 or 2, characterized in that, The first switching circuit switches the value of the reference voltage according to a first mirror current output from the first current mirror circuit corresponding to the current flowing through the transistor.

5. The temperature measuring circuit according to claim 1 or 2, characterized in that, When the current flowing through the transistor exceeds a first current threshold, the first switching circuit switches the control voltage to a first voltage value. When the current flowing through the transistor is lower than a second current threshold that is lower than the first current threshold, the first switching circuit switches the control voltage to a second voltage value that is higher than the first voltage value.

6. The temperature measuring circuit according to claim 5, characterized in that, The first switching circuit switches the value of the control voltage according to a first mirror current output from the first current mirror circuit corresponding to the current flowing through the transistor.

7. The temperature measuring circuit according to any one of claims 1, 2, and 6, characterized in that, The temperature measuring circuit has a first output terminal, which outputs first information that changes according to the value of the control voltage to the outside of the temperature measuring circuit.

8. The temperature measuring circuit according to any one of claims 1, 2, and 6, characterized in that, The temperature measuring circuit includes a conversion circuit that converts the current flowing through the temperature sensing element into a voltage value corresponding to the measured temperature through a predetermined conversion gain.

9. The temperature measuring circuit according to claim 8, characterized in that, The conversion circuit converts the current flowing through the transistor using a second current mirror circuit, thereby generating the voltage value.

10. The temperature measuring circuit according to claim 9, characterized in that, The conversion circuit converts the current flowing through the transistor into a second mirror current through the second current mirror circuit, and generates the voltage value by allowing the second mirror current to flow through a resistor.

11. The temperature measuring circuit according to claim 10, characterized in that, The conversion circuit has an AD converter that converts the analog voltage value generated by causing the second mirror current to flow through the resistor into a digital value.

12. The temperature measuring circuit according to claim 8, characterized in that, The temperature measuring circuit includes a second switching circuit that switches the value of the conversion gain according to the voltage value.

13. The temperature measuring circuit according to claim 12, characterized in that, The second switching circuit switches the value of the conversion gain based on the voltage value, so that the voltage value is converted within a predetermined range.

14. The temperature measuring circuit according to claim 12 or 13, characterized in that, When the voltage value exceeds the first threshold, the second switching circuit switches the conversion gain value to the first conversion gain value. When the voltage value is lower than the second threshold, which is lower than the first threshold, the second switching circuit switches the conversion gain value to the second conversion gain value, which is higher than the first conversion gain value.

15. The temperature measuring circuit according to claim 8, characterized in that, The temperature measuring circuit has a second output terminal, which outputs second information, which varies according to the value of the conversion gain, to the outside of the temperature measuring circuit.

16. A temperature measuring circuit that uses a temperature sensing element to measure temperature, characterized in that, The temperature measuring circuit includes a voltage control circuit that controls the gate of the transistor based on the output of a differential circuit that compares the output voltage of the transistor driving the temperature sensing element with a reference voltage, thereby applying a control voltage to the temperature sensing element. The value of the reference voltage is switched according to the output current of the transistor.

17. The temperature measuring circuit according to claim 16, characterized in that, The temperature measuring circuit includes a conversion circuit that converts the output current of the transistor into a voltage value corresponding to the measured temperature.

18. The temperature measuring circuit according to claim 16 or 17, characterized in that, The output voltage of the transistor is obtained by converting the output current of the transistor based on the resistance value of the temperature sensing element.

19. The temperature measuring circuit according to any one of claims 1, 2, 6, 9-13, 15-17, characterized in that, The output terminal of the transistor is connected to one end of the temperature sensing element.

20. The temperature measuring circuit according to claim 19, characterized in that, The transistor is a P-channel MOSFET.

21. The temperature measuring circuit according to any one of claims 1, 2, 6, 9-13, 15-17, 20, characterized in that, The temperature sensing element is an NTC thermistor.

22. A temperature measuring device, characterized in that, The temperature measuring device comprises the temperature measuring circuit and the temperature sensing element as described in any one of claims 1 to 21.

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