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Unformatted text preview: EE 2001 Fall 2008
Problem Set 4 Source Transformation  Thevenin  Norton Source transformation: Solve for io in the circuit diagrammed below using source transformations and resistor simpliﬁcations.75 Q 25:2
25:2
25:2
5  a 25:2
/2 : loo; 75'///.2“o I =
R :(5‘0 25:2
., Vaoa __
I ' 7&7 ~35
2é.é'7
g  R l“ r 1333
s a . 0 ~ ——
' a 25“ 10 WfZS‘fzr
r2 ;/5a/{/'75' = 5'0 + .
' (a: UK? ?4
25:2 EV Thevenin, Norton Equivalents: Just as two points deﬁne a line, two measurements
deﬁne a Thevenin or Norton circuit. For each problem below, plot the vi characteristic
and determine the Norton and Thevenin equivalents from measurements A and B. i
L + 50 U
I VT“ V 0 I / IL—
Thevenin I — _
or
Norton '
Rs + 1 5004
——> v
_ 0 I / .12..
I
v + 6‘ V
——> VTH v
 Thevenin I — _ (0 J}—
A1R5=10§2 . 01'
B: 150:0.5A Norton 0’94
i >
I 0 .17..
i
V + ( o (I
———> VTH v
1) Thevenjn ! — _ 2 17.
Q; I. > 01'
Q1, 5 Norton Rs + i
i > v Finding source resistance directly: Find the source resistance Rs for each of the following
circuits by turning off the independent sources. (Voltage sources become shorts; Current sources become opens). 119 Q 109 1509 390m H
N 10A” 2:: (.RS The roblem with de endent sources: Find the Thevenin equivalent for the circuits
diagrammed below. In the circuit diagrammed below both Voc and Isc are zero. Find the source resistance by assuming v = vm and ﬁnding the resultant current i.
The v—i plot will pass through the point (vm, i) and the origin (because Voc and
Isa are both zero). ('7: lot/,0
Z : '62” yfly : ”(4’9 [2’ g 5 ~— / 0 Al" g
The vi plot in the second circuit passes through the origin so ﬁnding Voc and Isc
gives us only one data point. In either circuit the equivalent source resistance Rs carmot be found by simply
turning off all the sources. In particular, dependent sources can never be turned off to ﬁnd Rs. (They may in fact be modeling a resistor.) Find the Thevenin equivalent for the following transistor modeling circuit by ﬁnding Voc
and 130. 100 Q i Circuit to ﬁnd V CC. P 100:2 60 }" (1" i Find the load current if R; is 25 K ohms. 525'
50(4 Item: : ” / t 733 “/1
Ito“; 73K / Thevenin Theorem:
An engineer connects a 14 Q resistor to a two terminal network and measures 14 watts absorbed by the resistor. He then connects a 1/14 (2 resistor to the network and measures
14 watts absorbed by the resistor. Common sense tells the engineer that it should be safe to connect a 25 watt 1 Q resistor to the network.
Is he right? Find the Thevenin equivalent for the network and calculate the actual power absorbed by the 1 Q resistor. \... La—Ia , (D
/ 'I‘KA \/ + (A (/7 :[//4)/ZTA+I$/ All \le’l v few (7J1, ' “by ' (c/w ,3/14 ‘//4
4 W0 1 V,” :(IVA) ’zm 4 I @ ...
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 Fall '08
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