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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
. The output voltage is
( ) (
( ( is ) so that variations in
. Then, are minimized. For example, choose
the nearest standard value. Then
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, three-terminal 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.
( Part (b)
( Part (c)
( ( ) (
Thus, a 1-V, 120-Hz 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 three-terminal 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