HP 6296A - Page 21

•
•
•
3-38
In order
to
maintain
the
temperature
coeffi-
cient
and
stability
specifications
of
the
pc)wer
supply,
the
external
resistor
(Rx)
shown in Figure
3-9
should
be
stable,
low
noise,
low
temperature
coefficient
(less
than
30
ppm
per
degree
Centi-
grade)
resistors.
The
value
of
this
resistor
is
dependant
on
the
maximum
voltage
rating
of
the
"master"
supply. The
value
of
Rx
is
this
voltage
divided
by
the
voltage
programming
current
of
the
slave
supply
(l/Kp
where
Kp
is
the
voltage
pro-
gramming
coefficient).
The
voltage
contribution
of
the
slave
is
determined by
its
voltage
control
set-
ting.
3-39
PARALLEL
OPERATION
3-40
Normal
Parallel
Connections
(Figure 3-10).
Two
or
more power
supplies
can
be
connected
in
parallel
to
obtain
a
total
output
current
greater
than
that
available
from one power
supply,
The
total
output
current
is
the
sum of
the
output
cur-
rents
of
the
individual
power
supplies.
The
output
CURRENT
controls
of
each
power
supply
can
be
separately
set.
The
output
voltage
controls
of one
power
supply
should
be
set
to
the
desired
output
voltage:
the
other power
supply
should
be
set
for
a
slightly
larger
output
voltage.
The
supply
set
to
the
lower
output
voltage
will
act
as
a
constant
voltage
source:
the
supply
set
to
the
higher
output
will
act
as
a
constant
current
source,
dropping
its
output
voltage
until
it
equals
that
of
the
other
supply.
The
constant
voltage
source
will
deliver
only
that
fraction
of
its
total
rated
output
current
which
is
necessary
to
fulfill
the
total
current
demand.
Figure
3-10.
Normal
Parallel
Connections
3-41
Auto-Parallel.
The
strapping
patterns
for
Auto-parallel
operation
of
two
power
supplies
are
shown in Figure
3-11.
Auto-Parallel
operation
permits
equal
current
sharing
under
all
load
con-
ditions,
and
allows
complete
control
of
output
current
fron:i
one
master
power
supply.
The output
current
of
each
slave
will
be
approximately
equal
3-S
Figure
3-11.
Auto-Parallel.
Two Units
to
the
master's
regardless
of
the
load
conditions.
Because
the
output
current
controls
ot
each
slave
are
operative,
they
should
be
set
to
maximum
to
avoid
having
the
slave
revert to
constant
current
operation:
this
would
occur
if
the
master
output
current
setting
exceeded
the
slave's.
3-42
AUTO-TRACKING
OPERATION
(See
Figure
3-12)
St.Avt
•MASTER
MUST
Bl:
MOST
FOS111VE
SUPPLY
Figure
3-12.
Auto-Tracki~g,
Two
Units
3-43
The Auto-Tracking configuration
is
used
when
it
is
necessary
that
several
different
volt-
ages
referred
to
a common
bus,
vary
in proportion
to
the
setting
of
a
particular
instrument (the
con-
trol
or
master).
A fraction
of
the
master's
output
voltage
is
fed
to
the
comparison
amplifier
of
the
slave
supply,
thus
controlling
the
slave's
output.
The
master
must
have
the
largest
output
voltage
of
any
power
supply
in
the group (must be
the
most
positive
supply
in
the·example
shown on Figure
3-12).