HP 6296A - Page 22

3-44
The
output
voltage
of
the
slave
is
a
percent-
age
of
the
master's
output
voltage,
and
is
deter-
mined
by
the
voltage
divider
consisting
of
Rx
and
the
voltage
control
of
the
slave
supply,
Rp.
where:
Es=
Rp/Rx
+
Rp.
Tum-on
and
tum-off
the
power
supplies
is
controlled
by
the
master.
Remote
sensing
and
programming
can
be
used;
although
the
strapping
patterns
for
these
modes
show
only
local
sensing
and
programming.
In
order
to
maintain
the
temperature
coefficient
and
stability
specifications
of
the
power
supply,
the
external
resistors
should
be
stable,
low
noise,
low
temperature
(less
than
30
ppm
per
0
c)
resistors.
3-45
SPECIAL
OPERATING
CONSIDERATIONS
3-46
PULSE
LOADING
3-47
The
power
supply
will
automatically
cross
over
from
constant
voltage
to
constant
current
op-
eration,
or
the
reverse,
in
response
to
an
increase
(over
the
preset
limit)
in
the
output
current
or
volt-
age,
respectively.
Although
the
preset
limit
may
be
set
higher
than
the
average
output
current
or
voltage.
high
peak
currents
or
voltages
(as
occur
in
pulse
loading)
may
exceed
the
preset
limit
and
cause
crossover
to
occur.
If
this
crossover
limit-
ing
is
not
desired,
set
the
preset
limit
for
the
peak
requirement
and
not
the
average.
3-48
OUTPUT CAPACITANCE
3-49
An
internal
capacitor,
connected
across
the
output
terminals
of
the
power
supply,
helps
to
sup-
ply
high-current
pulses
of
short
duration
during
constant
voltage
operation.
Any
capacitance
added
externally
will
improve
the
pulse
current
capability,
but
will
decrease
the
safety
provided
by
the
con-
stant
current
circuit.
A
high-current
pulse
may
damage
load
components
before
the·
average
output
3-6
current
is
large
enough
to
cause
the
constant
cur-
-rent
circuit
to
operate.
3-50
The
effects
of
the
output
capacitor
during
•
constant
current
operation
are
as
follows:
a.
The
output
impedance
of
the
power
supply
decreases
with
increasing
frequency.
b.
The
recovery
time
of
the
output
voltage
is
longer
for
load
resistance
changes.
c.
A
large
surge
current
causing
a
high
pow-
er
dissipation
in
the
load
occurs
when
the
load
re-
sistance
is
reduced
rapidly.
3-51
REVERSE
VOLTAGE
LOADING
3-52
A
diode
is
connected
across
the
output
ter-
minals.
Under normal
operating
conditions,
the
diode
is
reverse
'biased
(anode
connected
to
neg-
ative
terminal).
If
a
reverse
voltage
is
applied
to
the
output
terminals
(positive
voltage
applied
to
negative
terminal),
the
diode
will
conduct,
shunt-
ing
current
across
the
output
terminals
an1d
limit-
ing
the
voltage
to
the
forward
voltage
drop
of
the
diode.
This
diode
protects
the
series
transistors
and
the
output
electrolytic
capacitor.
3-5
3
REVERSE
CURRENT
LOADING
3-54
Active
loads
connected
to
the
poweir
supply
may
actually
deliver
a
reverse
current
to
the
P°"'tA
supply
during a
portion
of
its
oper~ting
C}'Cle.
A19
external
source
cannot
be
allowed
to
pump
current
into
the
supply
without
loss
of
regulation
and
pos-
sible
damage
to
the
output
capacitor.
To
avoid
these
effects,
it
is
necessary
to
preload
the
sup-
ply
with
a dummy
load
resistor
so
that
thei
power
supply
delivers
current
through
the
entire
operat-
ing
cycle
of
the
load
device.
•