HP Lab Series User Manual

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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.
3-50
OUTPUT CAPACITANCE
3-51
An
internal
capacitor
(C20}.
connected
across
the
output
terminals
of
the
power
supply.
helps
to
supply
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
current
is
large
enough
to
cause
the
constant
cur-
rent
circuit
to
operate.
3i-S2
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
...
3-7
er
dissipation
in
the
load
occurs
when
the
load
re-
sistance
is
reduced
rapidly.
3-53
REVERSE
VOLTAGE LOADING
3-54
A
diode
(CR34)
is
connected
across
the
output
terminals.
Under
normal
operating
conditions,
the
diode
is
reverse
biased
(anode
connected
to
nega-
tive
terminal).
If
a
reverse
voltage
is
applied
to
the
output
terminals
(positive
voltage
applied
to
nega-
tive
terminal),
the
diode
will
conduct,
shunting
cur-
rent
across
the
output
terminals
and
limiting
the
voltage
to
the
forward
voltage
drop
of
the
diode.
This
diode
protects
the
series
transistors
and
the
output
electrolytic
capacitors.
3'-55
REVERSE
CURRENT LOADING
3,-56
Active
loads
connected
to
the
power
supply
may
actually
deliver
a
reverse
current
to
the
power
supply
during
a
portion
of
its
operating
cycle.
An
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
supply
with
a dummy
load
resistor
so
that
the
power
supply
delivers
CUITent
through
the
entire
operating
cycle
of
the
load
device.

HP Lab Series Specifications

General

Brand	HP
Model	Lab Series
Category	Power Supply
Language	English