Owner manual

For this section you will need some basi
c
understandin
g
about the operational amplifie
r
i
ntegrate
d
c
i
rcu
i
t.
Fi
rst, we can use separate powe
r
sources or we can use one power source for both th
e
circuit and the I
C
.
The o
p
erational am
p
lifier
(
often called “o
p
am
p
” fo
r
short
)
can be operated as a non-invertin
g
amplifier
,
an inverting ampli
f
ier, or a di
ff
erential ampli
f
ier. A
non-invertin
g
ampli
f
ier reproduces an input si
g
nal as
an output signal without any alteration in polarity. A
n
invertin
g
ampli
f
ier does the reverse: its output ha
s
the reverse polarity o
f
its input. The di
ff
erential
ampli
f
ier has an output that is the contrast between
the stren
g
ths o
f
the two input si
g
nals.
C
omparing two voltages and telling you which one i
s
stronger than the other is the job o
f
a comparator. We
call the controlled volta
g
e the reference volta
ge
because we use it as a re
f
erence
f
or measuring othe
r
voltages. The voltage that is compared is the inpu
t
volta
g
e
.
The re
f
erence volta
g
e in this experiment is about
3.7V. It is connected to terminal 68 o
f
one o
f
the op
amp integrated circuit. Input voltage is connected to
terminal 69 of the same IC. The LED will li
g
ht if thi
s
input voltage is higher than the re
f
erence voltage,
and the LED stays o
ff
i
f
it is lower. The operationa
l
amplifier acts as an inverting amplifier for th
e
re
f
erence voltage to keep the LED turned o
ff
, or as
a
non-invertin
g
amplifier to li
g
ht the LED
.
Build the ex
p
eriment and then set the switch t
o
position A. This supplies an input o
f
6V. The LED lights
because the input voltage is higher than the re
f
erence
volta
g
e. Now slide the switch to position B. Thi
s
supplies an input voltage of 1.5V. The comparator I
C
d
oes not turn on t
h
e
LED
,
b
ecause t
h
e
i
nput vo
l
tag
e
is now lower than the reference volta
g
e
.
No
t
es
:
EXPERIMENT #7
0
:
O
PERATI
O
NAL AMPLIFIER
CO
MPARAT
O
R
Schematic
-
89
-
Wiring Sequence
:
3
1-
67
84
-
82
-
33
-7
0
-
121
6
3-12
2
6
8-83-7
8
6
9-81-7
6
75-13
2
77-11
9
-12
4
120
-
133
123-13
1