03_diodes_app_zener_led_aai.pdf
TRANSCRIPT
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Applications with diodes
Half-wave rectifier
Pulses selector
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2 / 9
Full wave rectifier,
diode bridge
vI>0V vI0
D1, D3 (on) D2, D4 (off)
negative half, vI
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Power-supply filtering
Half-wave rectifier with capacitive filter
If the current is (can be approximated as) constant: I
tIvC C
dttitCdv CC )()( For the capacitor:
)0()(1
)(0
C
t
CC vdttiC
tv
)0(1
)( CC vItC
tv
CiC
vC
tDuring a finite time interval ,the capacitor discharges at a constant current, giving a voltage variation Cv
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Power-supply filtering Half-wave rectifier with capacitive filter cont.
Lets assume that during the capacitor discharges at a constant current (when D is off )
dt
R
VI IO
because
IVv
RC
VTI
C
TI
C
tv IOO
do
dOo tIvC
Od
o IC
tv
lets approximate Ttd
o
rippleoutput ov
RC
V
fRC
VTv IIo
1
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Example
V10 IV f=50Hz, 100LR 5.1v V C=?
We chose an electrolytic capacitor C =1500F/25V
What is the value of the output ripple?
How should be a new value of C if the output ripple
have to be reduce to the half?
Solve again in the case of full-wave rectification.
V5.1
fRC
Vv I
F1333100505.1
10
5.1
VfR
VC I
F1333C
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Backup Supply
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Zener Diode
relative regulation factor of ZD
Z
Z
Z
Z
Z
I
i
V
v
F
Z
zZ
r
rF
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Regulation region of ZD
Z
dZ
V
PI maxmax
ZZ IV @
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Excerpt from datasheet
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Parametric voltage regulator
The parametric regulator uses as operating principle
the nonlinear current-voltage characteristic of the ZD.
];[ maxmin III VVv
];[ maxmin OOO III
];[ maxmin ZZZ IIi
OZZOO VViIV ,,,,
ORZ Iii ZO VV
ZD
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OZnom
ZI
II
VVR
Parametric voltage regulator cont.
Exercise
?
mA70,V5.7V,12
R
IVv OOI
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Light-Emitting Diode: LED
Behaves similar with semiconductor diodes, but:
1.5V to 2.5V forward voltage drop
in forward bias the LED lights up: red,
yellow, green, blue, white (infrared remote
control)
typical forward current: 5mA to 20mA
Current through LED?
A
K
vD
iD
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13/10
Excerpt from datasheet
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Problem
To the output of a circuit the voltage can be +9V, 0V, or -9V.
How can one signalize the output voltage value using two
LEDs (green for +9V and red for -9V)?
The current through the conducting LED should be 10mA.