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668 ⏐⏐⏐ SERIES AND PARALLEL ac CIRCUITS<br />

220 �<br />

Z T<br />

R<br />

0 f<br />

R 220 � L<br />

Z R-LI T<br />

(1 ��j 8 �)(5 A �30°)<br />

IC ��� ����<br />

ZR-L � ZC 6.08 � �80.54°<br />

(8.06 �82.87°)(5 A�30°) 40.30 A�112.87°<br />

���� ���<br />

6.08 �80.54° 6.083 �80.54°<br />

� 6.625 A �32.33°<br />

15.10 FREQUENCY RESPONSE OF THE<br />

PARALLEL R-L NETWORK<br />

In Section 15.5 the frequency response of a series R-C circuit was analyzed.<br />

Let us now note the impact of frequency on the total impedance<br />

and inductive current for the parallel R-L network of Fig. 15.79 for a<br />

frequency range of zero through 40 kHz.<br />

I = 100 mA ∠0°<br />

f : 0 to 20 kHz<br />

Z T<br />

+<br />

V s<br />

–<br />

R 220 � L 4 mH<br />

FIG. 15.79<br />

Determining the frequency response of a parallel R-L network.<br />

ZT Before getting into specifics, let us first develop a “sense” for the<br />

impact of frequency on the network of Fig. 15.79 by noting the impedance-versus-frequency<br />

curves of the individual elements, as shown in<br />

Fig. 15.80. The fact that the elements are now in parallel requires that<br />

we consider their characteristics in a different manner than occurred for<br />

the series R-C circuit of Section 15.5. Recall that for parallel elements,<br />

the element with the smallest impedance will have the greatest impact<br />

L = 4 mH<br />

XL = 2 �fL<br />

220 Ω<br />

X L<br />

0 f2 f<br />

XL < R XL > R<br />

FIG. 15.80<br />

The frequency response of the individual elements of a parallel R-L network.<br />

I L<br />

a c

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