JPH0511476Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a temperature detection circuit that detects temperature by measuring the resistance value of a temperature measuring resistor such as a thermistor.

<Prior Art> FIG. 3 is a circuit diagram showing a conventional temperature detection circuit. In the figure, A1 is an operational amplifier, a non-inverting input terminal is connected to a reference potential, and an inverting input terminal is provided with a reference voltage V _i via a resistor R1. SW1 is a resistance switching means connected between the output terminal and the inverting input terminal of the operational amplifier A1; It includes a temperature measuring resistor R _T such as a thermistor, and resistors R2 and R3 whose resistance values are known. One of these is selected and the other end of the selected resistor is connected to the output terminal of the operational amplifier A1. Connecting.

With this configuration, the temperature measuring resistor is connected as shown in the figure.
When R _T is selected, the output voltage V _p is expressed as:

V _p = -(R _T /R1) · _Vi + V _pf · {(R1 + R _T ) / R1} ...(1) (However, V _pf : Input offset voltage of operational amplifier A1.) Next, resistor R2 , R3, the respective output voltages V _p ′, V _p ″ are expressed as follows.

V _p ′=−(R2/R1)・V _i + V _pf・{(R1+R2)/R1} ……(2) V _p ″=−(R3/R1)・V _i + V _pf・{(R1+R3) /R1} ...(3) If the resistances R1, R2, and R3 are known, (1),
From equations (2) and (3), V _i , V _pf , and R _T can be determined and the temperature measuring resistance
Temperature can be measured from the resistance value of R _T.

By the way, in such a configuration, the resistance switching means
SW1's on-resistance must be zero, but commonly used analog switches have a resistance of 100Ω or more.
Since there is an on-resistance of about 500Ω, this resistance causes an output error. Of course, it is possible to realize a resistance switching means with zero on-resistance using a mechanical switch such as a relay or rotary switch, but this is not practical.

Furthermore, since the resistance value of the temperature measuring resistor R _T changes exponentially with respect to temperature, if the change due to this resistance is output as it is, there is a drawback that it becomes difficult to handle the signal in the subsequent circuit.

<Problems to be solved by the invention> The technical problems to be solved by the invention are such that the influence of the on-resistance in the resistance switching means does not appear on the output, and an output signal that is linear with respect to temperature changes can be obtained. The objective is to realize a temperature detection circuit.

<Means for solving the problem> The configuration of the present invention is such that a first operation is performed in which a reference input voltage V _i is applied to a non-inverting input terminal, and an inverting input terminal is connected to a reference potential via a reference resistor P _p . Amplifier A2
, the reference resistance P _p and the first operational amplifier A2
It includes a temperature measuring resistor R T whose one end is commonly connected to the connection point with the inverting input terminal of the resistor R _T and a plurality of resistors whose resistance values are known, one of which is selected and the first
One end is connected to a feedback circuit between the output terminal and the inverting input terminal, and the resistor switching means SW2 is connected to the output terminal of the operational amplifier A2 and the non-inverting input terminal of the second operational amplifier A3, which will be described later. a second operational amplifier A3 whose end includes a resistor R4 connected to a connection point between the reference resistor P _p and the inverting input terminal of the first operational amplifier A2; The configuration is connected in parallel to the temperature measuring resistor R _T.
Based on the input and output relationship between the input voltage V _i of the first operational amplifier A2 and the output voltage V _p of the second amplifier A3 when each resistor in the resistance switching means SW2 is switched and connected, The reason is that the resistance value of the temperature measuring resistor R _T is determined.

<Operation> The technical means described above operates as follows. That is,
The signal output from the resistance switching means SW2 is prevented from being directly output, and the signal output from the second operational amplifier A3 is
Since the output signal is output via the resistor switching means, the influence of the on-resistance of the resistance switching means does not appear on the output. Furthermore, since the circuit configuration is such that the resistor R4 is equivalently connected in parallel to the temperature measuring resistor _RT , an output in which the exponential characteristic of the temperature measuring resistor _RT is linearized can be obtained.

<Example> An example device of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, the same elements as those in FIG. 3 are given the same reference numerals, and explanations thereof will be omitted. A2 is a first operational amplifier whose non-inverting input terminal is supplied with a reference input voltage V _i and whose inverting input terminal is connected to a reference potential via a reference resistor P _p . SW2 is a resistance switching means, such as a C-MOS ( It includes a switching section using a complementary metal oxide film semiconductor (complementary metal oxide film semiconductor) switch, a temperature measuring resistor R _T such as a thermistor, resistors R2 and R3 with known resistance values, and a short path SP. One end of each of these resistors is commonly connected to the connection point between the reference resistor P _p and the inverting input terminal of the first operational amplifier A2, and one of these is selected and connected to the output terminal of the first operational amplifier A2 as well as the inverting input terminal of the first operational amplifier A2. Second operational amplifier A
It is connected to the non-inverting input terminal of No. 3. A feedback circuit is provided between the output terminal and the inverting input terminal of the second operational amplifier A3, and this feedback circuit and the reference resistor P _p
A resistor R4 is connected between the node and the inverting input terminal of the first operational amplifier A2. still,
R _o1 and R _o2 represent the on-resistance of the resistance switching means SW2.

With this configuration, the temperature measuring resistor is connected as shown in the figure.
When R _T is selected, if the current flowing through this temperature measuring resistor is i ₁ and the current flowing through resistor R4 is i ₂ , then the current i _p flowing through the reference resistor P _p is as follows: i _p = (V _i −V _pf2 )/R _p = i ₁ + i ₂ ...(4). However, V _pf2 : Input offset voltage of operational amplifier A2.

On the other hand, between the reference input voltage V _i to the operational amplifier A2 and the output voltage V _p of the operational amplifier A3, V _i −V _pf2 +R4・i ₂ =V _p ...(5) V _i −V _pf2 +R The following relationship holds: _T・i ₁ −V _pf3 =V _p ……(6). However, V _pf3 : Operational amplifier A
3 input offset voltage. From equations (4), (5), and (6), V _p = [1+(1/R _p )・{(R4・R _T )/(R4+R _T )}]・V _z +V _pf3・[1+(1 /R _p )・{(R4・R _T )/(R4+R _T )}] However, V _z = V _i −V _pf2 −V _pf3 .

Here, if V _pf3 ≒O, then V _p = (V _i −V _pf2 )・[1+(1/R _p )・{(R4・R _T )/(R4+R _T )}] …(7) , an output that is independent of on-resistances R _o1 and R _o2 can be obtained.

Moreover, the relationship of this equation is the same as the equivalent circuit shown in FIG. 2, and has a configuration in which a resistor R4 is connected in parallel to the temperature measuring resistor _RT .

<Effects of the invention> According to the invention, as is clear from equation (7), the influence of the on-resistances R _o1 and R _o2 of the resistance switching means SW2 does not appear on the output, and furthermore, the resistance R4 is equivalently Since the circuit configuration is connected in parallel to the temperature measuring resistor _RT , an output that linearizes the exponential characteristic of the temperature measuring resistor _RT can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention; FIG. 2 is an equivalent circuit diagram of the embodiment of the present invention shown in FIG. 1;
FIG. 3 is a circuit diagram showing a conventional device. A2...first operational amplifier, _Rp ...reference resistor,
R _T ...Resistance for temperature measurement, A3...Second operational amplifier,
R4...Resistor, SW2...Resistance switching means, R _o1 ,
R _o2 ...On resistance of resistance switching means SW2.

Claims (1)

[Scope of utility model registration request] A reference input voltage V _i is applied to the non-inverting input terminal,
a first operational amplifier A2 whose inverting input terminal is connected to a reference potential via a reference resistor R _p ;
A temperature measuring resistor whose one end is commonly connected to the connection point between R _p and the inverting input terminal of the first operational amplifier A2
_R
Resistance switching means SW connected to the non-inverting input terminal of 3
2, and a resistor having one end connected to the feedback circuit between the output terminal and the inverting input terminal, and the other end connected to the connection point between the reference resistor R _p and the inverting input terminal of the first operational amplifier A2. a second operational amplifier A3 including R4, the resistor R4 is equivalently connected in parallel to the temperature measuring resistor R _T , and when each resistor in the resistor switching means SW2 is switched and connected; The resistance value of the temperature measuring resistor R _T is determined based on the input and output relationship between the input voltage V _i of the first operational amplifier A2 and the output voltage V _p of the second amplifier A3. Temperature detection circuit.