INSTRUCTION
MANUAL
MODEL
DLP 400-5-750A
25
as
the
voltage
is increased
by
adding
a
voltage
to
the
current
signal
so
that
the
current
limit
point
is reduced
as
the
input
voltage
rises.
To make
a
more
accurate constant
power
curve,
VR4
is introduced when
the
voltage
across
R6
and
R7
reaches approximately
30V.
This
draws some
of
the
introduced
signal
away
from
Q3
, preventing
excessive
reduction
in
the
current
limit
point
at
high
voltages.
This
results
in
an
almost
constant
power
limitation.
The
Dynaload
is
rated
at
5A
up
to
150V, and
the
bendback
is
normally
set
so
that
at
150V
input,
it
is
impossible
to draw
more
than
6A.
5.11
INSTRUMENTATION
CIRCUITS
Range
selector
switches and
calibrating
resistors
are
provided
for
the
front
panel
ammeter
and voltmeter.
5.12 OVERVOLTAGE
PROTECTION
If
the input
voltage
exceeds
approximately
460V,
zener
diodes
A2-VR1
through
A2-VR9 conduct,
allowing
current
to
flow
to
the
base
of
Q2
.
This
allows current
to flow
from
the
+16V reference
through
R5
to
the
gate
of
SCR101.
This
fires
the
SCR,
collapsing
the
input
voltage
and
blows
the
DC
input
fuse
F2
if sufficient
current
capability
is
available
from
the
DC
source under
test.
Resistors
R128 and
R129
are
added
to
limit
the peak
surge current
through SCR101,
which
could
damage
the
device.
Reverse
voltage
protection
is provided
by
CR101.
