JPS5826362Y2 - Temperature measurement circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a temperature measuring circuit using a semiconductor element having a PN junction.

2. Description of the Related Art A temperature measuring circuit shown in FIG. 1 has been known as a temperature measuring circuit that takes into consideration the temperature dependence of a semiconductor element such as a transistor having a PN junction.

In FIG. 1, 1 is a variable resistor with a resistance value R1, 2 is a resistor with a resistance value R2, and 3 is a reference voltage source that generates a voltage Eref.

A reference voltage source 3 connects a variable resistor 1 with a resistance value R1 to one input terminal of an operational amplifier 4 whose ten input terminals are connected to the common line.
and is connected via a resistor 2 having a resistance value R2.

5 is a transistor whose collector and base are connected,
It is inserted into the feedback path of the operational amplifier 4, with its collector connected to one input terminal of the operational amplifier 4, and its emitter connected to the output terminal of the operational amplifier 4, respectively.

In such a configuration, the output voltage VBE generated at the output terminal of the operational amplifier 4 at around room temperature is expressed by the following equation, assuming that Ic is the current flowing through the transistor 5.

Here, Vg□: Silicon energy gap extrapolated to 0°K k: Boltzmann constant q: Electron charge, r:) Constant determined by transistor T: Absolute temperature As is clear from equation (1), output voltage Since VBE is a function of temperature T, by measuring VBE, temperature T
- can be found.

However, for transistors of the same type, there are variations in go and r in equation (1), so the output voltage VBE
This causes variation in the

This variation is corrected by changing the resistance value R1 of the variable resistor 1 to increase or decrease the current Ic as appropriate.

The range of increase/decrease in current Ic is generally about 172Ic to 2Ic
It is.

However, as seen in equation (1), the output voltage VBE is 7
It is a linear function of nIc, and the change in current Ic is the output voltage V
It is not linearly proportional to the change in BE.

Therefore, it is extremely difficult to increase or decrease the current Ic to correct variations in the output voltage VBE.

Furthermore, since the current Ic is Eref/(R1+R2), equation (1) can be expressed as the following equation.

This is the change in the output voltage VBE with respect to the change in the resistance value Rx.

In order to change the current Ic by <172 Ic to 2Ic as described above, it is necessary to change the resistance value R1 to three times the resistance value R2.

When (R1+R2) becomes smaller, it becomes larger as is clear from equation (3), and in order to obtain minute changes in the output voltage VBE, it is necessary to use variable resistor 1 with extremely high resolution. There were drawbacks.

The present invention was developed in view of these points, and by changing the resistance value of a variable resistor without using a variable resistor with high resolution, the output voltage can be adjusted almost linearly with high resolution. This is an attempt to create a temperature measurement circuit that can be changed.

The present invention will be explained in detail below using the drawings.

FIG. 2 is an electrical circuit diagram showing an embodiment of the temperature measuring circuit according to the present invention.

In FIG. 2, the same reference numerals as in FIG. 1 represent the same elements, and their explanations will be omitted here.

21 is a resistor with a resistance value R3, and 22 is a variable resistor with a resistance value R4, one end of which is connected to one input end of the operational amplifier 4, and the other end connected to the common line.

Further, the sliding end of the variable resistor 22 is connected to the high voltage side of the reference voltage source 3 via the resistor 21.

In such a configuration, when the resistance value R4 is divided by the division ratio X (however, O≦X≦1) and the resistance value between the sliding end and the common line is R4·X, the current flowing through the transistor 5 Ic is expressed as follows.

According to equation (4), the output voltage VBE of the operational amplifier 4 is as follows.

Output voltage VB with respect to change in division ratio X in equation (5)
The change in E is as follows.

FIG. 4 is a diagram showing the relationship between aVBB;/ax and X in equation (6) for each of the ratios R3/R4 of R3 and R4.

As is clear from the figure, if R3/R4≧fold and X varies within the range of approximately 0.3 to 1, then
θVBE/ax can be considered virtually constant,
Changes in the division ratio X are approximately linearly proportional to changes in the output voltage VBE.

Furthermore, when the displacement of the sliding end of the variable resistor 21 is linearly proportional to the division ratio X, the output voltage VBE is changed almost linearly with high resolution in proportion to the displacement of the sliding end. You can do it.

FIG. 3 shows a case where a combination of a variable resistor 221 and a fixed resistor 222 is used as the resistor 22.

In this case, the resistance value R41 of the variable resistor 221 and the resistance fUt 42 of the fixed resistor 222 are set as R41+R42=R4
, R42/(R41 + R42) = 0.3, the output voltage VBE changes almost linearly in proportion to the displacement of the sliding end in the range of 0≦X≦1. Be able to do that.

As explained above, according to the temperature measurement circuit of the present invention, the output voltage can be adjusted with high resolution in proportion to the change in the resistance value of the variable resistor without using a high resolution resistor due to the simple circuit configuration. Moreover, it can be changed almost linearly, and the effect is good in practical use.

[Brief explanation of the drawing]

Fig. 1 is an electrical circuit diagram of a conventional temperature measuring circuit, and Fig. 2 is an electrical circuit diagram showing one embodiment of the temperature measuring circuit according to the present invention. Fig. 3 is an electrical circuit diagram showing another embodiment of the circuit of Fig. 2. The circuit diagram, FIG. 4, is a characteristic curve diagram of the rate of change of the output voltage with respect to the division ratio of the variable resistor of the circuit of FIG. 3... Reference voltage source, 4... Operational amplifier, 5... Transistor, 21, 41...
・Resistor, 22...Variable resistor.

Claims (1)

[Scope of utility model registration request] By inserting and connecting a semiconductor element having a PN junction in the feedback path of an operational amplifier and flowing a predetermined current given to the input terminal of this operational amplifier through the semiconductor element, the temperature of the semiconductor element part can be lowered from the output terminal of the operational amplifier. In the temperature measurement circuit that obtains the corresponding voltage signal, a resistor 22 including at least a variable resistor is connected between the input terminal of the operational amplifier and the common line, and the sliding end of the variable resistor is connected through the resistor 21. The resistance value of the resistor 21 is selected to be more than twice the resistance value of the resistor 22, and the sliding end of the variable resistor is connected to a reference voltage source with respect to the resistor 22. The voltage ratio can be slid within a range of about 0.3 to 1, and when the voltage division ratio is changed, the output of the operational amplifier changes substantially linearly in proportion to the voltage division ratio. Characteristic temperature measurement circuit.