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2
1.
CIRCUIT DESCRIPTION
1.1.
GENERAL
The
PM2521/22
version
is
a
standard
PM2521
that includes
a built-in
battery
power
supply.
The
battery
power
supply
part consists of
one Pb
cell
and
a circuit that
converts the battery voltage
into
-I-5V,
-M3Vand-13V.
The
circuit
of the battery
power
supply can be subdivided
into three
main
parts:
—
Charging
circuit
—
Two
level
convertors
—
Schmitt
trigger
+
13V
COMMON
-13V
LOGIC
1
=
-5V
LOGIC 0= -10V
Lo.bRk
INDICATION
5T3487
82
0318
Fig.
1.
Block
diagram-battery
power
supply
1.2.
CHARGING
CIRCUIT
(refer
to the
overall circuit
Fig.
6.).
If
the battery
is
charged,
by
the
power
supply (power switch
in
position
"OFF", PM2521
connected
to the
mains) the voltage
on
point
2
of
X101
is
stabilized
by A101.
The
output
voltage of
A101
is
the charging
voltage for
the
battery.
When
the
temperature
changes, the
output
voltage
is
compensated by V101,
so
the required charging voltage
is
always
available.
In
the position
"OFF"
the convertors
are disabled
by means
of
two
diodes
V202
and
V203.
By
this
means,
the battery
is
prevented
from
discharging
via
the
convertors.
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