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Philips PM3208 - 4.5 Power Supply

Philips PM3208
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4
CIRCUIT
DESCRIPTION
4-7
4.5
POWER
SUPPLY
Input
to
the
power
supply
is
the
mains-voltage;
outputs
are
6,3
V
(AC)
to
the
CRT
and
4
DC
voltages:
-12
V,
+5
V,
+12
V
and
+160
V.
The
power
supply
consists
of
a
line-transformer,
rectifiers
and
stabilising
circuits.
The
function
of
the
line-transformer
is:
-
Providing
a
galvanic
isolation
between
the
mains-voltage
and
the
electronic
circuitry
in
the
oscilloscope.
-
Adaptation
to
the
right
mains-voltage
by
means
of
different
primary
windings.
—
Transforming
the
mains-voltage
into
the
low
voltages
needed
by
the
instrument.
The
rectifiers
convert
the
AC
voltages
from
the
line-transformer
into
DC
voltages.
The
output
from
D1002
at
C1012
is
about
190
V.
The
output
from
D1001
is
about
+18
V
at
C1001
and
—18
V
at
C1010.
Stabilisation
is
obtained
by
series-pass
transistors
Q1001-1002-1003-1004
which
are
controlled
by
the
operational
amplifiers
1C1001
and
1002.
The
reference
voltage
to
the
+12
V
is
about
+6,2
V
from
diodes
D1004
and
D1005.
Adjustment
of
the
+12
V
is
done
by
means
of
potmeter
VR1006.
As
reference
voltage
to
the
-12
V,
+5
V
and
+160
V
stabilisers,
the
+12
V
is
used.
So,
VR1006
will
control
all
voltages
and
only
one
adjusting
element
is
needed.
4.5
POWER
SUPPLY

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