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Unformatted text preview: A, what is the minimum value for Solution
The regulator maintains a constant 5 V across
so that the current flowing through
⁄ . The current flowing through
is then
. The output voltage is
( ) (
Choose
( ( is ) so that variations in
⁄(
. Then, are minimized. For example, choose
. Choose
the nearest standard value. Then
(
Solving for
yields
If
then ) . These calculations assume ( ) ( 7 ) , the maximum value. 55:041 Electronic Circuits. The University of Iowa. Fall 2011. Problem 4 The datasheet for a 5 V, threeterminal regulator indicate that the output voltage
typically changes by 3 mV when the input voltage is varied from 7 V to 25 V, and by 5 mV
when the load current is varied from 0.25 A to 0.75 A. Further, the ripple rejection ratio is 78 dB
at 120 Hz.
(a) Estimate the typical line and load regulation for the regulator.
(b) What is the output resistance of the regulator?
(c) Estimate the output ripple amplitude for every volt of input ripple at 120 Hz.
Solution
Part(a)
(
( (
( Part (b)
( Part (c)
( ( ) (
Thus, a 1V, 120Hz ripple at the input will result in an output ripple of 0.126 mV 8 55:041 Electronic Circuits. The University of Iowa. Fall 2011. Problem 5 Briefly explain why semiconductor companies often specify the ripple rejection ratio
of their threeterminal regulators at frequencies in the range 100—120 Hz. In other words, why
is it important to know the ripp...
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 Fall '11
 Kruger

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