Electric Circuits 8th Edition 87

Electric Circuits 8th Edition 87 - 3 .3 T he...

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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 voltage-divider 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 voltage-djvider 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 voltage-divider 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.

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