REV.-A
2.2
Power Supply
This
computer
operates
with
a rechargeable Ni-Cd
battery
and is provided
with
features
for
mini-
mizing
power
consumption
and
controlling
battery
charge. The
power
supply
is summarized in
the
following:
• Batteries:
Two
batteries; main and auxiliary, are used.
Main
battery
....................... Supplies a
DC
voltage
of
4.SV and has a
capacity
of
1100
mAH.
It
can
power
all
the
computer
circuits; backing up
the
commercial
as
AC
power
when
not
used
or
unavailable.
It
also supplies
power
to
the
attached
option
units.
Auxiliary
battery
.................
Also
supplies
the
DC
4.SV power.
It
has a
capacity
of
90
mAH
and
backs up
the
main
battery
when
in
a
low
voltage
(discharged)
con-
dition.
• Charging
circuit:
Supplies
charging
current
to
the
main and auxiliary
battery
when
an AC adap-
tor
is connected.
This
circuit,
which
operates in either
of
two
modes;
normal and
tricle
(low
current) charges,
under
the
control
of
a sub-CPU
750S,
controls
the
charging current.
•
Voltage
detection
circuit:
Monitors
the
voltage
of
the
main
battery
using
an
internal
AD
con-
verter. The result is processed
by
the
sub-CPU
750S
to
cause
the
circuit
to
provide
two
func-
tions. One is
low
voltage
detection
which
allows
the
computer,
if it
is operating,
to
display
a
warning
message "CHARGE BATTERY" on
the
LCD screen,
when
the
battery
power
(i.e.,
vol-
tage) falls
below
a certain level. In addition,
this
function
causes
the
computer
to
stop
at
an
ap-
propriate
point
in
the
operation in progress. The
other
function
determines
the
normal charge
restart
timing;
causing a
switch
from
tricle
to
normal charge
when
AC adapter is connected.
• Backup circuit: Supplies
the
power
required
to
maintain data in
the
RAMs
when
the
power
switch
is
off
or
the
computer
is
not
connected
to
the
AC
power
line.
It
also serves
to
normally
operate
the
circuits
which
monitor
the
battery
voltage
and
detect
whether
power
is on.
• ± SV regulator:
This
voltage
regulator supplies
DC
voltages
of
± SV required
for
RS-232C
operations. The voltages are generated
from
the
battery
voltage
(VB)
only
when
the
RS-232C
or
serial interface is used.
•
-15V
regulator: Supplies a
-15V
DC
voltage
used
for
LCD display control.
This
voltage
is gen-
erated
from
the
battery
voltage
(VB) as
long
as
power
is on.
•
5V
regulator: Supplies a
+5V
DC
voltage
used
for
the
PROM capsule.
This
voltage
is generated
from
the
battery
voltage
(VB)
only
when
the
PROM is accessed. The regulator is provided in
order
to
prevent
a
transient
due
to
PROM access
from
directly
affecting
the
VB line.
2-4
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