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Valleylab CUSA EXcel-8 - Detailed Circuit Description

Valleylab CUSA EXcel-8
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Display
Board
Figure
7-1.
The
display
organization
on
the
control
panel
Due
to
the
quantity
of
LEDs,
space
restriction,
and
heating
considerations,
FET
switches
connected
to
a
multiplexing
display
driver
(Maxim
7218)
drive
the
displays.
A
resistor
in
series
with
the
LED
light
bar
limits
current
through
the
LEDs.
A
P-channel
FET
sources
the
voltage
to
the
resistor
and
LED
light
bar
series
combination.
An
N-channel
FET
sinks
the
current
to
ground
from
the
LED
light
bars.
The
outputs
of
the
7218
display
driver
control
the
gates
of
the
FETs.
To
reduce
the
number
of
display
drivers
and
the
quantity
of
logic
code,
a
coded
map
identifies
each
individual
LED
light
bar
location
so
that
a
single
display
driver
can
control
all
of
the
amplitude,
irrigation,
Tissue
Select,
and
aspiration
displays.
A
second
display
driver
controls
the
number
legends,
the
alerts,
the
status
indicators,
and
the
button
indicators.
Detailed
Circuit
Description
ÁJOSU
|
UND)
Each
“circuit”
works
the
same
way.
It
simply
repeats several
times
to
allow
individual
control
over
each
light
bar
package.
The
following
description
details
the
circuit
for
the
aspiration
column
at
a
setting
of
10%.
The
7218
display
driver
(U3)
receives
inputs
from
the
machine
control
board
via
the
50
pin
ribbon
cable
connector,
Ji.
The
segment
output
of
the
display
driver
connects
to
a
1k
pull-up
resistor
(RA2)
and
the
gate
of
an
N-channel
FET
(U66).
The
source
of
the
FET
ties
to
+5Vin
and
the
drain
connects
to
a
resistor
network
(RA32).
Several
of
the
resistors
are
tied
together
to
achieve
an
average
current
of
12
mA
through
each
LED
of
the
light
bar
for
a
total
of
96
mA
per
light
bar.
The
resistors,
in
parallel,
connect
in
series
with
the
light
bar
(U221).
All
diodes
in
the
light
bar
connect
in
parallel.
The
cathode
of
the
diode
connects
to
the
drain
of
the
N-channel
FET
(U65).
The
source
of
U65
connects
to
ground.
The
gate
connects
to
a
digit
output
of
U3
and
a
pull-down
resistor
(RA6).
E
+
CUSA
EXcel-8
System
Service
Manual
73

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