ECEN 2250
Introduction to Circuits & Electronics
10-16-11
Fall 2011
P. Mathys
Problem Set 7
(Solutions are due Fri. 10-21-11)
Note: For all problems you have to explain how you arrived at the solution legibly and in
a logical order. This includes (i) Statement of problem, (ii) strategie(s) for solution, (iii)
execution of the strategy, identifying each step and including a check of the solution(s), and
(iv) logical and legible presentation and clear identification of the solution.
1) The voltage and current produced by a 9V battery for different loads were measured as
follows:
Voltage [V]
8.91
8.72
8.30
7.91
7.49
Current [mA]
89.4
171
377
549
750
(a) Determine the Thévenin equivalent circuit of the battery.
(b) What is maximum power that the battery can deliver? Which load draws this power?
2) Problem 8-56 in the book.
3) Problem 8-58 in the book. Use LTspice instead of OrCAD.
4) The schematic below shows the simplified version of an ac power distribution system.
The voltage source on the left is a generator that produces a voltage of the form vS (t) =
AS cos(ωt + θS ) V. The two 1 Ω resistors represent the losses of the power distribution line.
The resistance RL and the reactance XL represent the load connected to the distribution
line.
1Ω
vS (t)
→ Irms
+
−
•
RL
+
XL
−
•
1Ω
Vrms
The following values were measured (at the load RL , XL ) for a computer power supply:
Voltage [Vrms ]
Current [Arms ]
Real Power [W ]
Frequency [Hz]
120
3.08
166.3
60
(a) Determine the efficiency
η=
Avg power absorbed by load
Avg power generated
1
of this power distribution system (without power factor compensation at the load).
(b) Assume that the load is capacitive. What is the best efficiency η that you can achieve
by using power factor compensation at the load? How can this power factor compensation
be achieved (show element(s) and the element value(s) to be used).
c
2001–2011,
P. Mathys.
Last revised: 10-16-11, PM.
2