SECTION
VI
TYPICAL
PERFORMANCE
AND
APPLICATIONS
1.
VOLTAGE
PROGRAMMING
All
units
can be
programmed by
means of
external
resistors
to
any
voltage
below the
specified
maximum
voltage,
the program-
ming
terminal
being
the
"1
const"
or
"—
F/B"
terminal.
The
link
on the
bottom of the
unit is set to "CI"
and the
"VOLTAGE
ADJUST"
controls
turned fully
anticlockwise.
The
programming
resistor
should
now be
connected
between the
"I
const" and
"O/P
—
"
terminals.
The value
of
programming
resistor is
given
by
:
—
25-25
R prog
—
X
V required,
Kilohms
(L30A)
R
prog
50
25,25
30
5.1
-X
V
required,
Kilohms
(L30B,
D
&
E}
R prog
=
—X
V required,
Kilohms
(L30C)
10
The
tolerance
on
V required for
an accurate
R prog is
±
10%.
In order to
obtain greater
accuracy, the
voltage of
the reference
zener-diode
Z3,
(V ref)
and the
resistance of R7
-•
Tl must
be
determined.
R
prog is now
given by
:
—
R7
-1-
Tl
R
prog
—
X
V required,
ohms
Vref
The
tolerance on
V
required for an
accurate
R prog is now
the
tolerance
on
the
V ref
measurement
plus
the tolerance
on
the R7
H-
Tl measurement.
2.
SERIES
OPERATION
Units may be
connected
in
series ONLY
IN THE
"CV"
MODE
OF OPERATION.
3.
PARALLEL
OPERATION
[A)
"CV"
OPERATION
Units
which are set to
approximately
the
same
output voltage
may
be
connected
directly in
parellel. On
increasing
load, the
unit
having the highest
output voltage
will cany
the load until
it
current limits,
thereafter the
unit having
the next
highest
10
voltage
will
supply
the extra
current until it limits, and
so on.
A typical output
characteristic
for a
parallel combination
of three
units
is
shown
in Fig.
(3).
The characteristic
shows
a series of
descending
steps in output
voltage
at the current limit
points
of individual units, the ampli-
tude of
the
steps
depends
on how closely
the output voltages
have
been
set and it may not be
possible to adjust this to better than
50mV.
It is
recommended that not
more
than three units are paralleled
in this way.
(B) "CI" OPERATION
Units can be
connected
directly in
parallel
in
either "APPROX-
IMATE
CI"
or "ACCURATE CI"
operation, the load current
being the sum of the two
output
currents, Fig. (I)
shows
the connec
tions for
"ACCURATE
CI"
operation.
4. TYPICAL
PERFORMANCE
Stability
Output variations
are due in the
main
to
the
following
causes
:
—
Load
Change.
Mains supply change.
Component
temperature
change.
(a) Load Change
(I) Steady load—For a
change in steady load from zero to full
load, the typical
change is
:
—
ImV at
full
voltage output.
(II) Transient
Response
—The
typical response
to a pulsed load
is
shown
in Fig.
(4),
(III)
Output
Impedance.
For alternating load
superimposed on a steady load, the output
impedance of the
supply
increases
with
frequency
due to the fall
off in
gain of the
amplifier
until it is determined only
by
the
capacitor across the
output terminals.
A
typical
output
impedance/frequency curve
is shown in Fig.
(2)
11
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