HP 6296A - Page 18

b. Open
output
terminals
and
adjust
VOLTAGE
controls
for maximum
output
voltage
al-
lowable
(voltage
limit),
as
determined
by
load
conditions.
If
a
load
change
causes
the
voltage
limit
to
be
exceeded,
the
power
supply
will
auto-
matically
crossover
to
constant
voltage
output
at
the
preset
voltage
limit
and
the
output
current
will
drop
proportionately.
In
setting
the
voltage
limit,
allowance
must
be
made
for
high
peak
voltages
which
can
cause
unwanted
crossover.
(Refer
to
Paragraph
3-46).
NOTE
When
Model
6291A
is
operated
continuously
in
the
crossover
region.
between
Constant
Voltage/Con-
stant
Current,
the
feedback
loop
may
break
into
os-
cillation;
particularly
in
the
0.
SA
to
l.
SA
output
current
range. Although
the
crossover
region
is
not
usually
an
area
of
continuous
operation,
this
prob-
lem
can
be
eliminated,
if
necessary,
by
connecting
the
emitter
of
Q300
to
+S
(instead
of
to
the
emitter
of
Q301)
and
readjusting
R307.
Note
that
when
this
is
done,
the
transient
recovery
time
of
Model
6291A
must
be
derated
to
"SOµsec
for
recovery
to
within
25mV"
(instead
of
lSmV).
3-11
CONNECTING
LOAD
3-12
Each
load
should
be
connected
to
the
power
supply
output
terminals
using
separate
pairs
of
connecting
wires.
This
will
minimize
mutual
cou-
pling
effects
between
loads
and
will
retain
full
advantage
of
the
low
output
impedance
of
the
power
supply.
Each
pair
of
connecting
wires
should
be
as
short
as
possible
and
twisted
or
shielded
to
reduce
noise
pickup.
(If
shield
is
used,
connect
one
end
to
power
supply
ground
terminal
and
leave
the
other
end
unconnected.
)
3-13
If
load
considerations
require
that
the
out-
put
power
distribution
terminals
be
remotely
located
from
the
power
supply,
then
the
power
supply
output
terminals
should
be
connected
to
the
remote
distribution
'terminals
via
a
pair
of
twisted
or
shielded
wlres
and
each
load
separate-
ly
connected
to
the
remote
distribution
terminals.
For
this
case.
remote
&ensing
should
be
used
{Paragraph
3-30).
3-14
OPERATION
OF
SUPPLY
BEYOND
RATED
OUTPUT
3-15
The
shaded
area
on
the
front
panel
meter
face
indicates
the
amount
of
output
voltage
or
current
that
is
available
in
excess
of
the
normal
output.
Althouoh
the
supply
can
be
operated
in
this
shaded
region
without
being
damaged,
it
can-
not
be
guaranteed
to
meet
all
of
its
performance
specifications.
Hawever,
if
the
line
voltage
is
maintained
above
115 Vac,
the
supply
wil~proba
bly
operate
within
its
specifications.
3-2
3-16
OPTIONAL
OPERATING
MODES
3-17
REMOTE
PROGRAMMING, CONSTANT
VOl~T
AGE
3-18
The
constant
voltage
output
of
the
power
supply
can
be
programmed (controlled) from a
remote
location
if
required. Either a
resistance
or
voltage
source
can
be
used
for
the
programming
device.
The
wires
connecting
the
programming
terminals
of
the
supply
to
the
remote
programmir1g
device
should
be
twisted
or
shielded
to
reduce
noise
pick-up.
The
VOLTAGE
controls
on
the
front
panel
are
disabled
according
to
the
followi.ng
procedures.
~
~
~
+·
+
G - -
~
~
M M M
~
M
1°1~1~1
PROGRAMMING
RESISTat
Figure
3-3.
Remote
Resistance
Programming
(Constant
Voltage)
3-19
Resistance
Programming (Figure
3-3).
In
this
mode.
the
output
voltage
will
vary
at
a
rate
•
determined
by
the
programming
coefficient,
200
•
ohms
per
volt
(300
ohms per
volt
for
Model
6296A).
The
output
voltage
will
increase
l
volt
for
each
200 ohms (or
300
ohms) added
in
series
with
the
programming
terminals.
The programming
coeffi--
cient
is
determined
by
the
pr09rammin9
current.
This
current
is
factory
adjusted
to
within
2%
of
S ma
(2%
of
3. 3 ma
for
Model
6296A).
If
greater
programming
accuracy
is
required,
it
may
be
achieved
by
changing
resistor
R806.
3-20
The
output
voltage
of
the
power
supply
should
be
zero
volts
z20
millivolts
when
zero
ohms
is
connected
across
the
programming
termi·-
nals.
3-21
To
maintain
the
stability
and
temperature
coefficient
of
the
power
supply,
use
programmin~;
resistors
that
have
stable,
low
noise,
and
low
temperature
(less
than
30 ppm
per
degree
Centi-
grade)
characteristics.
A
switch
can
be
used
in
conjunction
with
various
resistance
values
in
order
to
obtain
discrete
output
voltages.
The
switch
should
have
make-before-break
contacts
to
avoid
momentarily
opening
the
programming
terminals
during
the
switching
interval.
3-22
Voltage Programming (Figure
3-4).
Employ
the
strapping
pattern
shown
on
Figure
3-4
for
.
•
voltage
programming.
In
this
mode,
the
output
voltage
will
vary
in
a
1
to
1
ratio
with
the
pro-