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Electric Circuits 8th Edition 87

# Electric Circuits 8th Edition 87 - 3.3 T he ottage'DividerC...

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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 lossesthat 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 asR, >> 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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• Spring '07
• Boser
• Trigraph, parallel witl R2, resistor Rz fu, voltage-divider circuit, noload orltput voltage, possible values.The resistancesof

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