FIGURE 22. DISPLAY BUFFERING FOR INCREASED DRIVE CURRENT

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

100pF

TO PIN 1

0.1

µF

100k

Ω

1k

Ω

22k

Ω

47k

Ω

0.22

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

+

-

ICL7107

130

Ω

130

Ω

130

Ω

LED

SEGMENTS

+5V

DM7407

WS7106 / WS7107

FIGURE 21. AC TO DC CONVERTER WITH WS7106

13