REV.-A
2.2.2
Charging
Circuit
Two
4.BV, rechargeable, Ni-Cd batteries are connected
to
the MAPLE board. The main battery,
which
is housed the
bottom
case and can be replaced
by
loosening a single screw, has the larger
capacity
of
1100
mAH. Its charging circuit includes
an
overcharge protection circuit
which
pro-
tects the battery from overcharge
by
automatically discontinuing charge. The auxiliary battery,
which
is mounted on the MAPLE board, has a capacity
of
90
mAH. A
switch
is inserted in
both
the charging circuit and backup line
which
can disable the backup
by
the auxiliary battery.
2.2.2.1
Main
Battery
Charging
Circuit
2E
P41
7508
Main battery
VBof
Fig.
2-7
Main
Battery
Charging
Circuit
ACAdaptor
GND
The charging circuit includes jumper
A2
which
allows
two
modes
of
charging:
When
J2
is jumpered ..................... No Overcharge Protection Control
Jumpering
J2
causes the base
of
transistor
09
to
be always tied
to
ground, holding
it
in conduc-
tion. This effectively bypasses resistors
R3
and
R5,
inserted in the charging circuit in series, and
causes the charging current
to
be supplied
to
the battery through transistor
09,
current limiting
resistor
R1,
and reverse-current preventing diode
04.
This setting ecuses the battery
to
be con-
tinually charged
as
long
as
the AC adaptor is connected. Because
of
the
low
current limiting resis-
tance in the mode
of
operation, the battery is highly liable
to
overcharge.
When
J2
is open ............................ Shipment Setting
•
When
J2
is open, the charge current bypassing transistor
09
is controlled
by
the
port
41
out-
put
of
the
4-bit
sub-CPU 750B. This
CPU
has a clock feature built in and maintains
port
41
at
the
low
level only
for
the
first
eight hours after
it
detects
that
the AC adaptor is connected, pro-
viding the same charging mode
as
when the jumper
J2
is closed.
With
port
41
held low, tran-
sistor
033
is
cut
off, leaving its collector at the high level (The collector is pulled up
to
the
ac
adaptor
output
through the resistor R39.) This maintains transistor
030
in conduction; the col-
lector is held at the
low
level, providing the same effect
as
if
jumper
J2
were closed.
2-11
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