JPH0435776Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a temperature detection device using a temperature sensing element.

[Conventional technology]

A commonly used temperature detection device is a bridge circuit as shown in FIG. That is, in Fig. 2, R ₁ to _{R 4} are resistors forming a bridge circuit, and a thermistor Th for temperature detection (its resistance value is Rt) is connected in parallel to resistor R ₄ . There is. Further, _R7 is a variable resistor for adjusting the zero point of the bridge circuit, and E is a DC power supply connected between the opposite vertices 10 and 12 of the bridge circuit. The unbalanced voltage between the voltage detection terminals (ground point and 14) of the bridge circuit is sent to the output terminal 15 via the operational amplifier 11. Furthermore, R ₅ and R ₆
is a resistor that determines the gain of the amplifier 11.

Next, its operation will be explained. First, operational amplifier 1
It is assumed that the magnitude of the offset voltage 1 is so small that it can be ignored. So, for example, the reference temperature is
When the temperature is 25° C., the movable element of the variable resistor _R7 is adjusted so that the voltage at the voltage detection terminal 14 and the output terminal 15 are both zero volts. At this time,
Let the resistance value of the resistor _R1 side of the variable resistor _R7 be _R10 ,
Let that of the resistor _R2 side be _R20 . Next the thermistor
When the temperature at Th rises above the reference temperature of 25°C, the resistance value (Rt) of the thermistor Th increases, so the voltage at the terminal 14 also increases, and the output terminal 15
The voltage V ₀ becomes a positive voltage. On the other hand, if the temperature of the thermistor Th becomes 25℃ or less, the output voltage increases.
V ₀ becomes a negative voltage.

Note that the voltage at terminal 12 of the bridge circuit
V ₁₂ and the voltage V ₁₄ at terminal 14 are each expressed by the following equations.

V ₁₂ = -E・(R ₂₀ + R ₂ )/(R ₁ + R ₂ + R ₁₀ +
R ₂₀ ) ...[1] V ₁₄ = (E・R ₄・R ₈ )/(R ₄ +R ₈ )/R ₃ +(R ₄・R ₈ )
/(R ₄ +R ₈ ) -E・(R ₂ +R ₂₀ )/R ₁ +R ₂ +R ₁₀ +R ₂₀ ... [2] [Problem to be solved by the invention] Here, the resistance value of the thermistor with respect to temperature is The change is small, and when calculated using formula [2], it is 1
This results in a voltage change of approximately 3mV per °C. Therefore,
As is clear from equation [2], when the power supply voltage (E) fluctuates, it is divided into 1/n and output, so the amount of fluctuation in voltage (E) is smaller than the voltage difference due to the resistance value fluctuation of the thermistor. There were cases where the size became large and there was a problem of poor stability.

This invention was made to solve the above problems, and provides a circuit that does not affect the output even if the power supply voltage fluctuates.

[Means for solving problems]

The temperature detection device according to this invention includes a series circuit in which a resistor and a first diode are inserted in series between a DC power supply terminal and a ground point, and a voltage across the first diode is between base and emitter. A first constant current circuit having a transistor applied therebetween and supplying a constant current, and a second diode based on the constant current of the first constant current circuit are inserted in series, and the constant current is A constant voltage circuit that supplies the constant voltage obtained across the diode, and a third diode are inserted in series, and the voltage across the first diode of the series circuit is applied between the base and emitter of the transistor. a second constant current circuit that supplies a constant current to the third diode, and a temperature sensing element inserted in series, and a voltage across the third diode is applied between the emitter and the base of the transistor. a third constant current circuit that supplies a constant current to the temperature sensing element; and a differential amplifier circuit that determines the difference between the constant voltage of the constant voltage circuit and the voltage obtained across the temperature sensing element. It is equipped with the following.

[Function] As mentioned above, since the power supplied to the temperature sensing element is a constant current, even if the power supply voltage fluctuates, it has little effect on the output. can be easily detected.

[Example of idea]

The temperature detection circuit according to this invention will be explained below with reference to FIG. In Figure 1, R ₁₂ to R ₂₇ are resistors, R ₂₈ is a thermistor, Q ₁ to _{Q 4} are PNP transistors, Q ₅ and Q ₆ are NPN transistors, and D ₁ to
D ₅ is an NPN diode, D ₆ and D ₇ are PNP diodes, among which resistor R ₂₄ and diodes D ₁ and D ₂
A series circuit is constructed and voltage Vcc is supplied. Further, a first constant current circuit is configured by resistors R ₂₁ , R ₂₂ , R ₂₃ and transistors Q ₁ , Q ₂ , Q ₃ , Q ₅ , and a constant voltage circuit is configured by diodes D ₃ and D ₄ .
Diodes D ₆ , D ₇ , transistor Q ₆ and resistor
A second constant current circuit is constituted by _R26 , and a third constant current circuit is constituted by resistor _R25 and transistor _Q4 . Therefore, the potential difference generated in the diode _D2 by the reference current _I24 flowing in this series circuit (between the connection point 31 and the grounding point G in the figure) is supplied between the base and emitter of the NPN transistor _Q5 and to the resistor _R23 . As a result, the current I ₂₃ flowing through the resistor R ₂₃ is determined. This current I ₂₃ determines the potential at the common connection point 32 between the collector of the PNP transistor Q ₂ , the base of Q ₅ , and the collector of Q ₅ , and this is stabilized by the resistors R ₂₁ and R _{22 and} the potential of the transistor
The collector current I ₂₁ of Q ₁ is determined.

The current I ₂₁ flows through the diodes D ₃ and D ₄ connected in series with the ground point G, which connects the connection point 3.
3 is fixed, so that the voltage at the inverting input terminal of amplifier 41 is held at a constant value. On the other hand, the voltage across series diodes D ₁ , D ₂ (between node 30 and ground G) biases the base of transistor Q ₆ , thereby
The emitter potential of Q ₆ is determined. A current I ₂₆ obtained by dividing this emitter potential by the resistance value of the resistor R ₂₆ flows through the series circuit of diodes D ₆ and D ₇ , thereby fixing the potential at the connection point 34. Next, connection point 34
When the potential at is determined, the emitter potential of transistor _Q4 is determined, and this voltage is applied to the resistor.
A current I ₂₅ divided by the resistance value of R ₂₅ flows through the series circuit of thermistor R ₂₈ and diode D ₅ . Note that the voltage at the connection point 35 is applied to the non-inverting input terminal of the amplifier 41, and the difference voltage between both input voltages introduced into the amplifier 41 is sent out to the output terminal 42.

Here, the voltage VBE generally applied between the base and emitter of a transistor and its collector
The relationship with the current Ic flowing between the emitters is shown by the following equation. However, it is assumed that the current amplification factor of the transistor is sufficiently larger than 1.

Ic=IE=Isε ^q

Claims (1)

[Claims for Utility Model Registration] A series circuit in which a resistor and a first diode are inserted in series between a DC power supply terminal and a ground point, and a voltage across the first diode is between the base and the emitter. a first constant current circuit having a transistor applied to the constant current and supplying a constant current; and a second constant current circuit having a constant current of the first constant current circuit as a reference.
a constant voltage circuit in which a third diode is inserted in series and supplies a constant voltage obtained across the diode by the constant current, and a third diode is inserted in series, and a second constant current circuit having a transistor to which a voltage is applied between the base and emitter and supplying a constant current to the third diode; and a temperature sensing element inserted in series, the temperature sensing element being connected to both ends of the third diode. a third constant current circuit having a transistor to which a voltage is applied between the emitter and the base and supplying a constant current to the temperature sensing element; A temperature detection device characterized by comprising a differential amplifier circuit for determining the difference between the voltage and the voltage.