12

FN3086.6

July 21, 2005

FIGURE 10. ICL7136 USED AS A DIGITAL CENTIGRADE

THERMOMETER

FIGURE 11. CIRCUIT FOR DEVELOPING UNDERRANGE AND

OVERRANGE SIGNAL FROM ICL7136 OUTPUTS

FIGURE 12. AC TO DC CONVERTER WITH ICL7136

28

40

39

38

37

36

35

34

33

32

31

30

29

27

26

25

24

23

22

21

OSC 1

OSC 2

OSC 3

TEST

REF HI

REF LO

COMMON

IN HI

IN LO

A-Z

BUFF

INT

V

-

G2

C3

A3

G3

BP

50pF

TO PIN 1

0.1

µF

0.01

µF

†

100k

Ω 1MΩ

9V

390k

Ω

†

0.47

µF

TO BACKPLANE

TO DISPLAY

A silicon diode-connected transistor has a temperature coefficient

transistor in ice water and adjusting the zeroing potentiometer for a

000.0 reading. The sensor should then be placed in boiling water

and the scale-factor potentiometer adjusted for a 100.0 reading.

SCALE

FACTOR

ADJUST

200k

Ω 470kΩ

22k

Ω

SILICON NPN

MPS 3704 OR

SIMILAR

ZERO

ADJUST

+

-

13

1

2

3

4

5

6

7

8

9

10

11

12

14

15

16

17

18

19

20

V+

D1

C1

B1

A1

F1

G1

E1

D2

C2

B2

A2

F2

E2

D3

B3

F3

E3

AB4

POL

28

40

39

38

37

36

35

34

33

32

31

30

29

27

26

25

24

23

22

21

OSC 1

OSC 2

OSC 3

TEST

REF HI

REF LO

COMMON

IN HI

IN LO

A-Z

BUFF

INT

V

-

G2

C3

A3

G3

BP

O /RANGE

U /RANGE

CD4023 OR

74C10

CD4077

TO LOGIC

V+

TO

LOGIC

V-

GND

28

40

39

38

37

36

35

34

33

32

31

30

29

27

26

25

24

23

22

21

OSC 1

OSC 2

OSC 3

TEST

REF HI

REF LO

COMMON

IN HI

IN LO

A-Z

BUFF

INT

V

-

G2

C3

A3

G3

BP

50pF

TO PIN 1

0.1

µF

180k

Ω

20k

Ω

220k

Ω

180k

Ω

0.047

µF

0.47

µF

TO BACKPLANE

TO DISPLAY

Test is used as a common-mode reference level to ensure compatibility with most op amps.

10

µF

9V

10

µF

470k

Ω

1

µF

4.3k

Ω

100pF

(FOR OPTIMUM

BANDWIDTH)

1

µF

10k

Ω

10k

Ω

1N914

1

µF

0.22

µF

5

µF

CA3140

2.2M

Ω

+

-

100k

Ω

AC IN

SCALE FACTOR ADJUST

+

-

ICL7136