JP2009145195A - Temperature detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature detection circuit capable of preventing wrong detection caused by a noise. <P>SOLUTION: In this temperature detection circuit 20, a detection circuit 22 for detecting a detection voltage Vsen by a sensor element Sen uses a logic voltage Vcc for its driving power source, and the detection voltage Vsen and a reference potential Gnd' of a reference voltage Vref2 are connected not to the earth Gnd but to an output voltage Vref3 outputted from a voltage follower circuit 23, respectively. Hereby, since the detection voltage Vsen and the reference potential Gnd' of the reference voltage Vref2 inputted into a comparator Cp2 are separated from the earth Gnd, for example, even if an external noise NE enters via a battery voltage VB or the earth Gnd, direct affection therefrom can be avoided, and fluctuation of the detection voltage Vsen or the reference voltage Vref2 can be prevented in addition to constant voltage operation by a constant voltage circuit 21. Consequently, wrong detection caused by a noise can be prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a temperature detection circuit.

  As for the temperature detection circuit, for example, there is a technique disclosed in Patent Document 1 below. In this type of temperature detection circuit, as disclosed in FIG. 26 of Patent Document 1 below, the forward voltage drop value of the diode decreases as the ambient temperature increases and increases as the ambient temperature decreases. A diode is often used as a detection element because it has “negative temperature dependence” and has a linear increase / decrease if the forward current value is constant.

For example, the forward voltage (detection voltage) of the diode is compared with a predetermined comparison reference voltage by a comparison means such as a comparator, and the detected temperature is compared based on the voltage value output from the comparison means according to the magnitude relationship between the two. It is determined whether or not a predetermined temperature corresponding to the voltage has been reached.
JP-A-6-242176

  However, such a detection element such as a diode is generally connected between the drive power supply of the circuit and the ground via a constant current source in terms of the circuit configuration. When noise (hereinafter referred to as “external noise”) enters from the outside via the external diode, the forward voltage drop value of the diode fluctuates due to the external noise, which can lead to detection voltage errors and thus false detection. There's a problem.

  Such a problem is that, for example, by configuring the comparison means with a differential amplifier circuit such as a comparator, a detection voltage by a diode is input to one differential input, and a predetermined comparison reference voltage is input to the other differential input. Can be eliminated by canceling out noise from the characteristics of the differential amplifier circuit.

  However, for example, when there is a stray capacitance between the signal line wired to the input of the comparator or the like and the ground pattern, a temporal shift occurs in the external noise input to the differential input. Even a differential amplifier circuit cannot cancel out noise. Therefore, in such a case, there is a problem that even if the comparison means is constituted by a comparator or the like, the forward voltage drop value of the diode fluctuates due to noise, which may lead to erroneous detection.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a temperature detection circuit capable of preventing erroneous detection due to noise.

  In order to achieve the above object, the temperature detection circuit according to claim 1, which is provided so as to be capable of being thermally coupled to the object to be detected, detects when the current flows and increases or decreases depending on the temperature of the object to be detected. A detection element that generates a voltage; a voltage source that generates the detection voltage at a predetermined temperature as a comparison reference voltage; and a differential amplifier circuit configured to include the detection voltage input to one differential input and the other Comparing means for outputting a voltage indicating a magnitude relationship with the comparison reference voltage input to the differential input, and a voltage lower than the operating voltage of the comparing means and higher than the reference potential of the operating voltage, depending on the ambient temperature And a differential amplifying unit configured to output a constant voltage as a reference potential of the detection voltage and the comparison reference voltage.

  The temperature detection circuit according to claim 2, wherein the constant voltage input to the differential amplifying means is a bandgap voltage supplied by a bandgap voltage source. The detection element is technically characterized in that a high potential side is connected to one differential input of the comparison means and a low potential side is connected to an output of the differential amplification means.

  In the temperature detection circuit according to claim 3, the temperature detection circuit according to claim 1 is also configured on the semiconductor substrate on which the detection target is configured. In this case, the detection element is a diode formed on the semiconductor substrate whose forward direction is the direction in which the current flows, and the detection voltage is a forward voltage drop due to the diode. And

  In the temperature detection circuit according to claim 4, the diode is configured by connecting two or more diodes in series, and the detection voltage is determined by the diodes. The technical feature is that it is the sum of the forward voltage drop due to.

  In the first aspect of the present invention, the differential amplifying means constitutes a voltage follower circuit that inputs a constant voltage that is lower than the operating voltage of the comparing means and higher than the reference potential of the operating voltage and does not depend on the ambient temperature, This constant voltage is output as the reference potential of the detection voltage and the comparison reference voltage. As a result, the reference potential of the detection voltage and the comparison reference voltage becomes a constant voltage output from the voltage follower circuit configured by the differential amplifying means, so even if noise enters the temperature detection circuit, Noise can be offset from the characteristics of the differential amplifying means, and fluctuations in the detection voltage or comparison reference voltage due to the noise can be eliminated. Therefore, erroneous detection due to noise can be prevented.

  In the invention of claim 2, the constant voltage input to the differential amplifying means is a band gap voltage supplied from a band gap voltage source. Thereby, since the reference potential of the detection voltage and the reference potential of the comparison reference voltage are not easily affected by temperature, detection errors can be suppressed as compared with the case where they are affected by temperature. The detection element has a high potential side connected to one differential input of the comparison means and a low potential side connected to the output of the differential amplification means. As a result, the detection voltage generated by the detection element is generated with reference to the reference potential output from the differential amplifying means, that is, the band gap voltage. It will be stable. Therefore, erroneous detection due to noise and temperature can be prevented.

  According to a third aspect of the present invention, the detection element is a diode formed on a semiconductor substrate whose forward direction is the direction in which current flows, and the detection voltage is a forward drop voltage due to the diode. Thus, in addition to being able to configure a diode as a detection element in the vicinity of the detection target, by making the forward current of the diode constant, the diode decreases as the ambient temperature of the diode increases and the ambient temperature Temperature detection using “negative temperature dependence” that increases with a decrease in the temperature becomes possible.

  In the invention of claim 4, the diode is configured by connecting two or more diodes in series, and the detection voltage is the sum of the forward drop voltages due to these diodes. The voltage fluctuation range can be increased. Thereby, detection accuracy can be improved.

  Hereinafter, embodiments of a temperature detection circuit of the present invention will be described with reference to the drawings. First, the configuration of the temperature detection circuit 20 according to the present embodiment will be described with reference to FIGS. FIG. 1 is a circuit diagram showing a configuration example of the temperature detection circuit 20 according to the present embodiment. 2 is a circuit diagram showing a basic configuration of the temperature detection circuit 20 shown in FIG. 1, and FIG. 3 is a circuit diagram showing another basic configuration of the temperature detection circuit. Yes.

  As shown in FIG. 1, the temperature detection circuit 20 includes a constant voltage circuit 21, a detection circuit 22, and a voltage follower circuit 23. For example, a power transistor Tr (target to be detected) that drives a vehicle-mounted actuator. It is possible to detect whether or not the exothermic temperature exceeds a predetermined temperature. For this reason, the temperature detection circuit 20 is built in the drive IC together with such a power transistor Tr and mounted in the vehicle, and is configured to be able to be driven by receiving the battery voltage VB supplied from the battery Batt. Yes. The driving IC is electrically connected to a microcomputer (hereinafter referred to as “microcomputer”) constituting an ECU (Electronic Control Unit), and the microcomputer receives detection information (output voltage Vout) output from the temperature detection circuit 20. It is configured so that it can be acquired.

  The constant voltage circuit 21 is a stabilized power supply circuit that stably supplies the logic voltage Vcc (DC5V) by stepping down the battery voltage VB (DC12V) supplied from the battery Batt to, for example, DC5V, and includes an operational amplifier OP1, a transistor Q11, a resistor It consists of R11, R12 and a band gap voltage source.

  The operational amplifier OP1 is a differential amplifier that compares the voltages input to the inverting input (−) and the non-inverting input (+) and outputs the voltage difference multiplied by a gain G. In this embodiment, the output voltage is the output voltage. A voltage 1 / G obtained by dividing the voltage by resistors R11 and R12 is input to the inverting input (−), and a reference voltage Vref1 to be compared with this voltage can be input to the non-inverting input (+). . The output of the operational amplifier OP1 is connected to the base of the transistor Q11 so that the base voltage of the transistor Q11 can be controlled.

  The reference voltage Vref1 is supplied by a band gap voltage source that can output 1.2V, for example. The operational amplifier OP1 is operated by the battery voltage VB supplied from the battery Batt.

  The transistor Q11 is a current control element that can control the emitter current according to the voltage (base voltage) output from the operational amplifier OP1, and has a collector connected to the battery Batt and an emitter connected to the resistor R11.

  The resistors R11 and R12 are resistors that determine the gain G of the operational amplifier OP1, and in this embodiment, for example, the reference voltage Vref1 is set to 1.2 V so that the logic voltage Vcc of 5 V can be output as the output voltage. In this case, the resistance values of the resistors R11 and R12 are set so that 1.2V is input to the inverting input (−) of the operational amplifier OP1 and the gain G is 4.17 (= 5 / 1.2). Has been.

  By configuring the constant voltage circuit 21 in this way, when the emitter voltage of the transistor Q11 exceeds the logic voltage Vcc, the divided voltage of the logic voltage Vcc input to the non-inverting input (+) of the operational amplifier OP1 is also inverted (- ) Exceeds the reference voltage Vref1, the output voltage from the operational amplifier OP1 decreases, the base voltage of the transistor Q11 decreases, and the emitter voltage of the transistor Q11 decreases toward the logic voltage Vcc.

  On the other hand, when the emitter voltage is lower than the logic voltage Vcc, the divided voltage of the logic voltage Vcc inputted to the non-inverting input (+) of the operational amplifier OP1 is also lower than the reference voltage Vref1 of the inverting input (−). Output voltage increases, the base voltage of the transistor Q11 rises, and the emitter voltage rises toward the logic voltage Vcc. As a result, a stable logic voltage Vcc is supplied from the emitter of the transistor Q11, that is, the output of the constant voltage circuit 21. Further, the constant voltage circuit 21 can remove the external noise NE as described later by such constant voltage operation.

  Next, the detection circuit 22 will be described. As shown in FIG. 1 and FIG. 2, the detection circuit 22 detects the temperature of the power transistor Tr, and outputs 5V of H level if the temperature exceeds a predetermined temperature, and outputs L if the temperature is lower than the predetermined temperature. This circuit outputs a level of 0 V, and is composed of a comparator Cp2, a constant current source Cur, a sensor element Sen, and resistors R21 and R22.

  The comparator Cp2 is a comparator composed of a differential amplifier circuit that compares the voltage input to the inverting input (−) and the non-inverting input (+) and outputs the result as an H level or L level logic signal. In the present embodiment, the detection voltage Vsen output from the sensor element Sen is input to the non-inverting input (+), and the reference voltage Vref2 to be compared with the detection voltage Vsen can be input to the inverting input (−). Yes.

  Thereby, when the detection voltage Vsen exceeds the reference voltage Vref2, the output voltage Vout of the H level is output from the comparator Cp2, and when the detection voltage Vsen is equal to or lower than the reference voltage Vref2, the output of the L level from the comparator Cp2 is output. The voltage Vout is output. The comparator Cp2 is operated by the battery voltage VB supplied from the battery Batt.

  The constant current source Cur is capable of supplying a constant current, and is constituted by, for example, a current mirror circuit. In the present embodiment, a constant current of, for example, 100 μA can be supplied to the sensor element Sen from the logic voltage Vcc toward the output voltage Vref3 of the follower circuit 23. The constant current source Cur receives the supply of the logic voltage Vcc from the constant voltage circuit 21 and outputs such a constant current.

  The sensor element Sen is formed by connecting a plurality of diodes in series in the forward direction between the constant current source Cur and the output side of the follower circuit 23. In the present embodiment, the four diodes D21, D22, D23, D24 (hereinafter “diodes D21 to D24”) are connected in series. As described in the “Background Art” section, a diode has a “negative temperature dependency” in which its forward voltage drop value decreases with an increase in ambient temperature and increases with a decrease in ambient temperature. If the forward current value is constant, the increase / decrease has linearity. Therefore, the sensor element Sen is arranged at a position where it can be thermally coupled to the power transistor Tr to be detected. It is used as a “detection element that generates a detection voltage that increases or decreases depending on the temperature of the object”.

  In this embodiment, four times the forward drop voltage VF (VF × 4) per line is input to the comparator Cp2 as the detection voltage Vsen of the sensor element Sen, so that the sensor element Sen is a single diode. Compared to the configuration, the detection voltage Vsen is increased, and the voltage fluctuation range with respect to the temperature fluctuation can be increased. Thereby, the detection accuracy can be improved. The sensor element Sen is disposed at a position where it can be thermally coupled to the power transistor Tr. For example, the sensor element Sen is laid out on the semiconductor substrate of the driving IC so as to be close to the power transistor Tr, and the diodes D21 to D24 are formed on the semiconductor substrate. There are cases.

  The resistors R21 and R22 are resistors that are connected in series between the logic voltage Vcc and the output side of the follower circuit 23 and determine the reference voltage Vref2 that is input to the inverting input (−) of the comparator Cp2. In the present embodiment, since it is detected whether or not the heat generation temperature of the power transistor Tr exceeds a predetermined temperature, the detection voltage Vsen of the sensor element Sen at the predetermined temperature is set as the reference voltage Vref2. For example, four times the forward drop voltage VF of the diodes D21 to D24 at 150 ° C. (predetermined temperature) is set as the reference voltage Vref2.

  By configuring the detection circuit 22 in this manner, when the heat generation temperature of the power transistor Tr exceeds a predetermined temperature, the detection voltage Vsen detected by the sensor element Sen exceeds the reference voltage Vref2, so that the L level when the temperature is lower than the predetermined temperature. The output voltage Vout of the comparator Cp2 changed to H level and output from the comparator Cp2. Thereby, the microcomputer of the ECU or the like that has received this can detect that the heat generation temperature of the power transistor Tr to be detected exceeds a predetermined temperature.

  Further, as described above, the detection circuit 22 has the sensor element Sen interposed between the constant current source Cur and the output side of the follower circuit 23, and a resistor between the logic voltage Vcc and the output side of the follower circuit 23. R21 and R22 are interposed. That is, the reference potential Gnd 'of the detection voltage Vsen and the reference potential Gnd' of the reference voltage Vref2 are set to the output voltage Vref3 output from the voltage follower circuit 23 to be described next without setting the ground Gnd.

  As shown in FIGS. 1 and 2, the voltage follower circuit 23 includes an operational amplifier OP3 (differential amplifier). That is, by inputting a predetermined reference voltage Vref3 to the non-inverting input (+) of the operational amplifier OP3 and inputting the output of the operational amplifier OP3 to the inverting input (−), the reference voltage input to the non-inverting input (+). A differential amplifying means for outputting Vref3 with a gain of 1 as it is is constituted. The reference voltage Vref3 is supplied by, for example, a band gap voltage source that can output 1.2V. The operational amplifier OP3 is operated by the battery voltage VB supplied from the battery Batt.

  As described above, in the temperature detection circuit 20 according to the present embodiment, the detection circuit 22 for detecting the detection voltage Vsen by the sensor element Sen uses the drive power supply as the logic voltage Vcc, and the reference potential Gnd of the detection voltage Vsen and the reference voltage Vref2. 'Is not the ground Gnd, and the output voltage Vref3 output from the voltage follower circuit 23 is used. As a result, the detection voltage Vsen and the reference potential Gnd ′ of the reference voltage Vref2 input to the comparator Cp2 are separated from the ground Gnd. For example, as shown in FIG. 1, via the battery voltage VB or the ground Gnd. Even if the external noise NE enters, it is possible to prevent fluctuations in the detected voltage Vsen and the reference voltage Vref2 in addition to the constant voltage operation by the constant voltage circuit 21 described above without being directly affected by the influence. Note that, in the circuit diagram of FIG. 1, a portion where the external noise NE can enter is represented by a thick line.

  The operational amplifier OP1 constituting the constant voltage circuit 21, the comparator Cp2 constituting the detection circuit 22, and the operational amplifier OP3 constituting the voltage follower circuit 23 are all constituted by a differential amplifier circuit. As a result, even if the battery voltage VB having the ground Gnd as a reference potential is supplied to these, such external noise NE can be offset from the characteristics of the differential amplifier circuit, and the detected voltage Vsen and the reference voltage due to the external noise NE can be offset. It becomes possible to remove the fluctuation of Vref2. Therefore, erroneous detection due to the external noise NE can be prevented.

  Furthermore, in the detection circuit 22 of the temperature detection circuit 20 according to the present embodiment, the voltage follower circuit 23 is provided to prevent the intrusion of the external noise NE. Therefore, the non-inverting input (+) and the inverting input (−) of the comparator Cp2 are provided. In routing the wiring pattern, it is not necessary to consider the non-formation of stray capacitance, the difference in wiring length, and the like. Therefore, the layout design and wiring pattern design of the semiconductor element on the semiconductor substrate can be facilitated.

  As a comparative example for the temperature detection circuit 20 according to the present embodiment, a configuration example in which the reference potential of the detection voltage Vsen and the reference voltage Vref2 input to the comparator Cp2 is the ground Gnd without the voltage follower circuit 23 is shown. 4 shows. 4, components that are substantially the same as those shown in FIG.

  In the temperature detection circuit 120 shown in FIG. 4, the reference voltage of the detection voltage Vsen and the reference voltage Vref2 is not directly received by the output voltage Vref3 of the voltage follower circuit 23, and is directly connected to the ground Gnd into which the external noise NE can enter. The detection voltage Vsen and the reference voltage Vref2 fluctuate due to the intrusion of the external noise NE (within the two-dot chain line circle shown in FIG. 4). For this reason, as described in the section “Problems to be Solved by the Invention”, there is a problem that an error of the detection voltage Vsen, and thus erroneous detection, may be caused. However, the temperature detection circuit 20 according to the present embodiment has the problem described above. Such a problem is solved by adopting the configuration described above.

  The temperature detection circuit 20 described above uses the diodes D21 to D24 as the sensor element Sen, but may also be configured using a thermistor whose resistance value varies with the ambient temperature. However, in the case of the thermistor, the resistance value of the thermistor increases as the ambient temperature increases and decreases as the ambient temperature decreases. However, the setting conditions are basically the same as the circuit shown in FIG.

  The temperature detection circuit 20 described above is configured by connecting four diodes D21 to D24 in series as the sensor element Sen, but the number of diodes may be five or more, or three or less. Also good. As the number of diodes increases, the forward drop voltage VF increases, so that there is an advantage that the detection accuracy is improved. On the other hand, as the number of diodes decreases, the area occupied by the semiconductor substrate as the sensor element Sen can be reduced and it can contribute to downsizing. is there.

  Further, in the above-described temperature detection circuit 20, as shown in FIG. 2, a circuit configuration in which the cathode side of the diodes D21 to D24 as the sensor element Sen is fixed at the reference potential Gnd ′ by the band gap voltage of the voltage follower circuit 23 (cathode side). Therefore, for example, as shown in FIG. 3, the temperature is higher than the circuit configuration (anode side reference) in which the anode side of the diodes D21 to D24 is fixed by the logic voltage Vcc by the constant voltage circuit 21. In addition, the reference potential of the detection voltage Vsen can be stabilized in terms of voltage. Therefore, erroneous detection due to noise and temperature can be prevented. 3, components that are substantially the same as those shown in FIG. 2 are given the same reference numerals.

It is a circuit diagram which shows the structural example of the temperature detection circuit which concerns on embodiment of this invention. It is a circuit diagram which shows the basic composition of the temperature detection circuit shown in FIG. It is a circuit diagram which shows the other basic composition of the temperature detection circuit which concerns on this embodiment. It is a circuit diagram which shows the structure of the comparative example of a temperature detection circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Temperature detection circuit 21 ... Constant voltage circuit 22 ... Detection circuit 23 ... Voltage follower circuit Batt ... Battery Cp2 ... Comparator (comparison means)
Cur ... Constant current source D21, D22, D23, D24 ... Diode (detection element)
Gnd: Earth (operating voltage reference potential)
Gnd '... reference potential (reference potential of detection voltage and comparison reference voltage)
NE ... External noise OP1 ... Operational amplifier OP3 ... Operational amplifier (differential amplification means)
R11, R12, R21, R22 ... Resistance (voltage source)
Sen ... Sensor element (detection element)
Tr ... Power transistor (to be detected)
VB ... Battery voltage (operating voltage)
Vcc ... logic voltage Vsen ... detection voltage Vout ... output voltage Vref2 ... reference voltage (predetermined comparison reference voltage)
Vref3: Reference voltage (constant voltage, band gap voltage)

Claims (4)

A detection element that is provided so as to be thermally coupled to the detection target and generates a detection voltage that increases or decreases depending on the temperature of the detection target when current flows;
A voltage source that generates the detection voltage at a predetermined temperature as a comparison reference voltage;
A comparison unit configured to include a differential amplifier circuit and output a voltage indicating a magnitude relationship between the detection voltage input to one differential input and the comparison reference voltage input to the other differential input;
A voltage follower circuit for inputting a constant voltage that is lower than the operating voltage of the comparing means and higher than the reference potential of the operating voltage and that does not depend on the ambient temperature is configured to use the constant voltage as the detection voltage and the comparison reference voltage. Differential amplification means for outputting as a reference potential;
A temperature detection circuit comprising: The constant voltage input to the differential amplifier is a band gap voltage supplied by a band gap voltage source,
2. The temperature detection circuit according to claim 1, wherein the detection element has a high potential side connected to one differential input of the comparison means and a low potential side connected to an output of the differential amplification means. In the case where the temperature detection circuit according to claim 1 is also configured on the semiconductor substrate on which the detection target is configured,
The detection element is a diode formed on the semiconductor substrate whose forward direction is the direction in which the current flows, and the detection voltage is a forward voltage drop due to the diode. The temperature detection circuit described.   4. The temperature detection circuit according to claim 3, wherein the diode is configured by connecting two or more diodes in series, and the detection voltage is a sum of forward drop voltages of the diodes.

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