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3.3 The Vottage'Divider
and Currcnt
Djvider
Circuiis
Eq.3.22,we
find that this mtio is satisfied wherever R,
:
;R1.
Other fac
tors that may enter into the selection of R1, and hence R2, include the
powei losses
that occur in dividing the source voltage and the effects of
connecting the voltagedivider circuit to other circuit components.
Consider connecting a resistor Rz fu parallel witl R2, as shown in
Fig. 3.13. The resistor R, acts as a load on the voltagedjvider
circuit. A
load on any circuit consists of one or more circuit elements
that draw
power from the circuit. With the load Rr connected,
the expression
for the
output voltage becomes
'
Rr + R.q
'"
RtRr
\3.23)
Figure
3.13 A A voLtage
djvjder
connected
to a toad
R..
Substituting
Eq.3.24
into Eq.3.23
yields
R2+ RL
R2
Rlt1 + (,R
/R')l + R"'
(3.21)
Note that Eq. 3.25 reduces
to F'q.3./2 as Rz+c!,
as it should.
Equation 3.25 shows
that, as
long as R, >> R2,
the voltage
ratio r,/?i" is
essentially undisturb€d by t})e addition of the load on the divider.
Atrother chaructedstic of the voltagedivider circuit of interest is the
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This note was uploaded on 07/05/2010 for the course EE 100 taught by Professor Boser during the Spring '07 term at University of California, Berkeley.
 Spring '07
 Boser

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