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CHAP. 15]

15.9

CIRCUIT ANALYSIS USING SPICE AND PSPICE

375

MUTUAL INDUCTANCE AND TRANSFORMERS

The mutual inductance between inductors is modeled by a device whose name begins with K. The data statement syntax is hnamei

hinductor 1i

hinductor 2i

hcoupling coefficienti

The dot rule, which determines the sign of the mutual inductance term, is observed by making the dotted end of each inductor the first node entered in its data statement. EXAMPLE 15.15

Write the three data statements which describe the coupled coils of Fig. 15-15.

Fig. 15-15 pffiffiffiffiffiffiffiffi The coupling coefficient is k12 ¼ 1:5= 2ð3Þ ¼ 0:61. The netlist contains the following: L1 L2 K12

1 3 L1

2 4 L2

2 3 0.61

EXAMPLE 15.16 Plot the input impedance Zin ¼ V1 =I1 in the circuit of Fig. 15-16(a) for f varying from 0.01 to 1 Hz. To find Zin , we connect a 1-A ac current source running from node 0 to node 1 and plot the magnitude and phase of the voltage V(1) across it. The source file is AC analysis of coupled coils, Fig. 15-16 IADD 0 1 AC 1 C 0 1 1 000 000 uF R 0 2 3 L1 1 2 2H L2 3 2 5H K12 L1 L2 0.6325 H L3 0 3 1H .AC LIN 20 .01 1 .PRINT AC Vm(1) Vp(1) .PROBE .END

0

Vm(1) and Vp(1), which are the magnitude and phase of Zin , are plotted by using Probe and the graph is shown in Fig. 15-16(b). Note that the maximum occurs at about 100 mHz.

15.10

MODELING DEVICES WITH VARYING PARAMETERS

.MODEL Statement The parameters of a passive element can be varied by using .MODEL statement. The syntax is :MODEL

hnamei

htypei

where hnamei is the name assigned to the element.

½ðhparameteri ¼ hvalueiÞ For passive linear elements, htypei is

RES for resistor IND for inductor CAP for capacitor

Mahmood_Nahvi_eBook_Schaum_s_Outlines_Theory_An