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Texas Instruments 99/4A - Page 94

Texas Instruments 99/4A
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S
WIT
C
HIN
G
R
E
G
U
L
A
T
0
F
Switching
regulator
U3
(UA
723
C)
uses
the
following
circuitry
R
E
F
E
R
E
N
C
E
V
0
L
T
A
G
E
The
reference
voltage
on
pin
2
of
U4
is
connected
to
the
non
—
inverting
input
of
U3
(pin
5).
F
E
h
D
E
A
C
K
V
0
L
T
A
G
E
The
+5
volt
is
directly
connected
to
the
inverting
mout
of
U3
(
p
J
p
4)
ROWER
CONNECTION
Power
is
connected
to
pin
12
of
U3
via
R3.
C13
is
voltage
swings
on
the
power
line.
Since
the
power
+12
volt
supply,
the
switching
regulator
only
works
tage
is
present.
Ground
connection
is
to
pin
7.
used
to
reduce
comes
from
the
Hen
t
h
i
s
v
o
1
—
FREQUENCY
COMPENSATION
Frequency
compensation
is
per-For
med
by
Cll
on
pin
13.
REGULATING
CIRCUIT
The
output
o-F
U3
on
pin
11
is
used
to
switch
the
current
through
L4
after
amplification
by
01
and
02.
R5
reduces
the
input
current
current
of
01.
R4
and
R6
are
used
to
ensure
that
both
01
and
02
are
in
the
non-conducting
state
when
not
enabled
by
U3.
The
fly
back
circuitry
consists
of
L4
and
DF.
The
output
voltage
ripple
is
reduced
by
Cl
4
and
Cl
5.
CURRENT
LIMITING
Current
limiting
is
done
by
using
the
voltage
drop
over
RF-R1O
and
comparing
this
with
the
voltage
on
the
cathode
of
the
diode,
the
divider
circuit
consisting
of
R7,
RS
and
D10.
D10
is
used
for
tem
perature
compensation
.

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