
Principles of Analog Electronics
216
ANSWER
According to Thévenin’s theorem, the
previous bridge topology is equiva-
lent to a voltage source V
TH
in series
with a resistor R
TH
. We have to calculate
them (Figure 6.36).
V
TH
is the voltage “seen” at the output
“1-2” port, so we can determine it as the dif-
ference between the voltage at the node “1”
V
1
, and the one at the node “2” V
2
.
Considering the node connecting V
B
, R
2
,
and R
4
as a reference, we have
V
R
RR
V
B1
2
=
+
and
V
RR
V
B2
4
=
+
therefore
V
R
RR
R
RR
V
TH B
=
+
−
+
2
142
4
34
To determine the value of the resistor R
TH
, we need to nullify the effect of
the voltage source (a short-circuit across it) (Figure 6.37 ...