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Unformatted text preview: 98 Chapter 5 Diodes and Selected Applications 511 QUESTIONS AND PROBLEMS 1. Design a power supply using a 24 V, centertapped
transformer to supply 12 V at 500 mA, — 12 V at 100 mA
and 5 V at 250 mA. What is the minimum current rating of
the transformer? 2. Design a variable voltage power supply which ranges
from 5 to 15 V and is capable of supplying 250 mA. 3. In the circuit in Figure A, what would happen if the
load resistor were shorted? What would happen if the load resistor were removed? Hint: think in terms of power ratings. kw
1009
12v 4
5.1 V FIGURE A Circuit for problem 3. 4. You have two 120 V AC224 V AC transformers, 16
highvoltage capacitors and 10 highvoltage diodes. Design,
on paper, a circuit that maximizes output voltage. What is
the maximum voltage of your circuit? 5. What conditions might favor selection of a full—wave
rectiﬁer over the bridge rectiﬁer? 6. Design, on paper, a transformerless 300 V power sup—
ply with a ripple of 1% or less, capable of supplying up to
100 mA. 7. Determine the necessary values of the components for
the circuit of Figure B, with the requirements that the output
be 15 V at 100 mV with 0.01 percent or less ripple. 15 V at 100 mA
RL (0.01% ripple) FIGURE B Circuit for problems 7 and 8. 8. Repeat the previous problem to achieve an output of
500 V at 10 mA with 0.1 percent or less ripple. 9. The output and ripple expressions for the simple choke
ﬁlter of Figure C are V _2V, R
Dc_w R+Rc and /
r = 3.1 X 10'3R/L where RC is the choke resistance. What is the effect upon the
ripple of increasing the current? L Full
wave rectiﬁed
signal FIGURE C Circuit for problem 9. 10. A typical power choke, at 10 H, has a resistance of ap
proximately 200 0. Using the equations supplied in the pre—
vious problem, and R = 1000 Q, compute the output voltage
and the ripple factor of this ﬁlter for a power supply with the
transformer secondary at 200 V rms. 11. Design a 12V, lOOmA power supply using a Zener
diode as a regulator. 12. Sketch the output waveforms expected when a 100 Hz
sine wave (5 VP) is applied to each of the circuits in
Figure D. 13. Sketch the output waveforms expected when a 100 Hz
square wave (10 Vpp) is applied to each of the circuits in Figure D. put of IE choke ‘l‘unthe of ap
PreT
oltage ut I the MHZ MHz . u 6.3 V 3.0 V I :50 V D
FIGURE D Circuit for problems 12 and 13. Chapter 5 Diodes and Selected Applications ‘99 ...
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 Spring '09
 GAMEROCASTANO

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