TC 9-62
Since:
EIN = Efdbk
Then:
E
Gain = OUT
Efdbk
7-71. The feedback signal (Efdbk) can be shown in terms of the output signal (EOUT) and
the voltage divider (R1and R2). The voltage divider has the output signal on one end and
ground (0 volts) on the other end. The feedback signal is that part of the output signal
developed by R1 (at point A). Another way to look at it is that the feedback signal is the
amount of output signal left (at point A) after part of the output signal has been dropped by
R2. In either case, the feedback signal (Efdbk) is the ratio of R1 to the entire voltage divider
(R1 + R2) multiplied by the output signal (EOUT).
7-72. Mathematically, the relationship of the output signal, feedback signal, and voltage
divider is computed as follows:
R1
Efdbk =
(E )
R1 + R2 OUT
If you divide both sides of the equation by EOUT:
Efdbk =
R1
EOUT R1 + R2
By inverting both sides of the equation:
+
EOUT
= R1 R2
Efdbk
R1
Separating the right-hand side:
E OUT
= R1 + R2
Efdbk
R1 R1
Remember:
E
Gain = OUT
Efdbk
Therefore, by substitution:
R2
Gain =
+1
R1
7-73. You can now see that the resisters determine the gain of the noninverting
configuration. The formula is different from the one used for the inverting configuration;
however, the gain is still determined by the values of R1 and R2.
7-22
TC 9-62
23 June 2005
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