HP 6296A - Page 58

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APPENDIX
A
Option
11, OVervoltaqe
Protection
"Crowbarn
D~CRIPTION:
This
option
is
installed
in
DC Power
Supplies,
6282A, 6285A, 6286A, 6290A, 6291A,
and
6296A,
and
tested
at
the
factory.
It
consists
of a printed
circuit
board,
screwdriver-type
front
panel
potentiometer,
and
six
wires
that
are
soldered
to
the
main
power
supply
board.
The
crowbar
monitors
the
output
voltaqe
of
the
power
supply
and
fires
an
SCR
that
effectively
shorts
the
output
when
it
exceeds
the
preset
trip
voltage.
The trip
voltage
is
determined by the
setting
of
the
CROWBAR
ADJUST
control
on
the
front
panel.
The
trip
voltage
range
is
as
follows:
Model
6282A
6285A 6286A
6290A
6291A
6296A
Trip
Voltage
Range
l-13V
2-22v
2-22V
5·42V
S-42V 6-66V
To
prevent
transients
from
falsely
tripping
the
crowbar,
the
trip
voltage
must
be
set
higher
than
the
power
supply
output
voltage
by
the
following margin:
7%
of
the
output
voltage
+lV. The
margin
represents
the
minimum
crowbar
trip
setting
for
a
given
output
voltage:
the
trip
voltage
can
always
be
set
higher
than
this
margin.
OPERATION:
1.
Tum
the
CROWBAR
ADJUST
fully
clockwise
to
set
the
trip
voltage
to
maximum.
2.
Set
the
power
supply
VOLTAGE
control
for
the
desired
crowbar
trip
voltage.
To prevent
false
crowbar
tripping,
the
trip
voltage
should
exceed
the
desired
output
voltage
by
the following
amount:
7%
of
the
output
voltage
+lV.
3.
Slowly
turn
the
CROWBAR
ADJUST
ccw
until
the
crowbar
trips,
output
goes
to
OV
or
a
small
positive
voltage.
4.
The
crowbar
will
remain
activated
and
the
output
shorted
until
the
supply
is
turned
off.
To
reset
the
crowbar,
tum
the
·supply
off,
then
on
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MPB-5
A-1