TC 9-62
the output should be:
EOUT = [(2 x E1) + (4 X E2) + (3 x E3)]
EOUT = [(2 x + 12 V) + (4 x + 3 V) + (3 x + 8 V)]
EOUT = [(+24 V) + (+12 V) + (+24 V)]
EOUT = -60 V
Calculate the current for each input:
E1
IR1 =
R1
+12 V
IR1 =
6 kΩ
IR1 = + 2 mA
--------
E2
IR2 =
R2
+3 V
IR2 =
3 kΩ
IR2 = +1mA
--------
E3
IR3 =
R3
+8V
IR3 =
4 kΩ
IR3 = + 2 mA
--------
IR4 = - (IR1 + IR2 + IR3)
IR4 = - (2 mA +1mA + 2 mA)
IR4 = - 5 mA
Calculate the output voltage:
EOUT = BR4
EOUT = (IR4 x R4)
EOUT = (-5 mA) x 12 kΩ
EOUT = -60 V
You have now seen how an operational amplifier can be used in a circuit as an adder, a
summing amplifier, and a scaling amplifier.
Difference Amplifier (Subtractor)
7-91. A difference amplifier will produce an output based on the difference between the
input signals. The subtractor circuit (see Figure 7-24) will produce the following output:
EOUT = E2 - E1
7-30
TC 9-62
23 June 2005
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