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Voltage step-down and isolation is provided by power
transformer Tt.
A dual primary winding is provided
to allow operation
at either 120 VAC
or 240 VAC.
The power supply is protected against faults by a
fuse or fuses wired into the primary circuit, depending
on the scale's particular configuration.
Depending on the particular scale and configuration,
a special safety rated capacitor
may
be used to
remove noise from the AC line which might interfere
with the scale's operation.
An additional capacitor,
and a fertite toroid, may
be added fo the primary
wiring to form a complete line filter.
Full-wave rectification of the transformers secondary
voltage
is provided
by
diodes
CR-1
and
CR-2.
Capacitor C-1 provides filtering. A power-on indicator
is provided by light-emitting diode LED-1 and resistor
R-1.
Diode
CR-3
prevents
the
battery
from
discharging into the power-on indicator and connects
the rectified, filtered DC voltage to output connector
4-1 for use by the scale's instrument board.
The
6.0 voit nickel-cadmium
battery,
composed
of
five (5) size "AA" cells, is charged
by the current
through resistor R-2. Schottky diode CR-4 is used as
a "switch" to couple the battery voltage to output
connector J-1 when AC power is removed and the
battery is need to operate the scale.
A charge indicator circuit is provided by transistor Q-1
and light emitting diode LED-2.
The voltage across
charging resistor R-2 is monitored by Q-1, a pnp
darlington transistor.
Resistor R-3 provides current
-
limiting for Q-1's base.
When the battery is properly
connected
and charging,
Q-1 will be switched
"on"
and provide a current path through limiting resistor R-
4 and the "CHARGE" indicator located on the front
panel of the readout.
Note that if the battery is
disconnected from the power supply board; or the
power
cable,
instrument
board,
display
cable,
or
display
board
are disconnected,
the LED-2
charge
indicator will not light.
4.40.2
MODEL 23PWR-7 POWER SUPPLY
This
is a
larger
power
supply
that
is
used
in
conjunction
with
a
7.2
volt,
1500
Milli-amp
hour
nickel-cadmium battery pack. The larger battery pack
is needed to operate the internal printer option on the
mode! 6102 and other scales,
Voltage step-down and isolation is provided by power
transformer T301. A dual primary winding is provided
to allow operation at either 120 VAC or 240 VAC. The
power supply is protected against faults by two fuses
wired into the primary circuit, which are mounted in
holders on the pawer supply board.
Capacitor "CF", a special safety rated capacitor, is
used to remove noise from the AC line which might
interfere with the scale's operation.
An additional
capacitor,
and a ferrite toroid, may
be added to the
primary wiring to form a line filter.
Diode
rectifiers
D301,
D302,
D303,
and
D304
are
connected
on T301's secondary to form a ful-wave
rectifier network with center-tap.
Use of the center-
tapped
configuration
provides
two
output
voltage
levels:
А
lower
level
for
operating
the
scale's
electronics, and a higher voltage to charge the battery
pack.
Diode D305 connects the lower rectified voltage to
capacitor C301 for filtering. This prevents the filtered
DC voltage from appearing in the battery charging
circuit. A power indicator is formed from the network
of LED301
and current limiting resistor R301.
Diode
D306
connects
the rectified,
filtered
DC
voltage to
connector
J301
for use
by the scale's instrument
board.
The 7.2V battery pack consists of six (6) size "C*
cells. Charging current for the battery pack is supplied
through
R303.
No provision is made to fitter this
charging voltage.
Since
the
battery
charging
voltage
is doubied
in
respect to the scale's operating voltage, operating the
scale without the battery could apply potentially large
voltages to the readout's instrument board.
Zener
diodes D309 and D310 clamp this voltage to a safe
level if the
battery
is removed.
Diode
D308
is
provided to prevent damage to D309 and D310 if the
battery is somehow incorrectly connected.
The battery pack is directly connected to connector
J302 to provide voltage to operate the internal printer.
Diode D307, a schottky rectifier, is used to couple the
battery voltage to the instrument
board when
AC
power is not present.
Palymer fuse F303 is used to protect the battery pack
from
damage
should
a short
occur
in the
scale's
$002, 5102, 5602, 6002, 6102, 6202, 6502, 6702
23
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