TL051ACD datasheet(45/67 Pages) STMICROELECTRONICS

45 / 67 page

TL05x, TL05xA

ENHANCED-JFET LOW-OFFSET

OPERATIONAL AMPLIFIERS

SLOS178A – FEBRUARY 1997 - REVISED FEBRUARY 2003

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

analog thermometer

By combining a current source that does not vary over temperature with an instrumentation amplifier, a precise

analog thermometer can be built (see Figure 89). Amplifier U1A and IC1 establish a constant current through

the temperature-sensing diode D1. For this section of the circuit to operate correctly, the TL05x must use split

supplies, and R3 must be a metal-film resistor with a low temperature coefficient.

The temperature-sensitive voltage from the diode is compared to a temperature-stable voltage reference set

by IC2. R4 should be adjusted to provide the correct output voltage when the diode is at a known temperature.

Although this potentiometer resistance varies with temperature, the divider ratio of the potentiometer remains

constant.

Amplifiers U1B, U2A, and U2B form the instrumentation amplifier that converts the difference between the diode

and reference voltage to a voltage proportional to the temperature. With switch S1 closed, the amplifier gain

equals 5 and the output voltage is proportional to temperature in degrees Celsius. With S1 open, the amplifier

gain is 9 and the output is proportional to temperature in degrees Fahrenheit. Every time S1 is changed, R4 must

be recalibrated. By setting S1 correctly, the output voltage equals 10 mV per degree (C or F).

–

IC1

150 pF

100 k

Ω

U1A

10 k

Ω

(see Note B)

(see Note A)

+15 V

100 k

Ω

IC2

50 k

Ω

U1B

10 k

Ω

5 k

Ω

5 k

Ω

(see Note C)

10 k

Ω

U2A

R10

10 k

Ω

R11

R12

10 k

Ω

10 k

Ω

+15 V

–15 V

10 k

Ω

(see Note D)

U2B

NOTES: A. Temperature-sensing diode

≈ (–2 mV/°C)

B. Metal-film resistor (low temperature coefficient)

C. Switch open for

°F and closed for °C

D. VO α temperature; 10 mV/°C or 10 mV/°F

E. U1, U2 = TL05x. IC1, IC2 = LM385, LT1004, or LT1009 voltage reference

Figure 89. Analog Thermometer

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