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SECTION 6.
HIGH-VOLTAGE POWER SUPPLY-(A1)
6- 1.
GENERAL.
CRT
bias
and drive voltages are
provided by the high voltage
power supply.
The power supply
converts
a
nominal
15
VDC
input to
output
voltages of
+
4kV and
a - 2kV. In addition,
control
circuits
for
the CRT
focus
and
intensity grids
are
contained
in
this power
supply.
The
high voltage
power
supply
block and
schematic
diagrams are
shown
in
figures
6-1 and
6-2,
respectively.
6-2.
HIGH VOLTAGE
SUPPLY.
An
9
VDC at the
center
tap
of the high voltage
transformer
is
switched
,
through
the
transformer
primary
winding by the
chopper,
at
a
20
kHz
rate.
The
chopper
drive
signals
originate
in
the low voltage
power
supply.
One
transformer secondary winding
provides
a
6.3 VAC CRT heater
voltage.
The other
transformer
secondary winding
provides
a
1
kV to
a
X4
multiplier and a X2
multiplier.
The output
of
the X4
multiplier,
a nominal
+
4
kV is
the CRT
anode
voltage.
A
nominal
-
2 kV
output of
the
X2 multiplier is applied to the
intensity
and
focus
modulators.
The
-2 kV
is
regulated
by
comparing
a
sample
of
the
-
2 kV to a 6.3V
reference
signal.
The
resultant
signal
controls the
level of
the
DC
input
at
the
center
tap of the
high voltage
transformer.
A
bias
divider,
on
the
transformer
center
tap,
provides the
HV
CHOPPER BIAS
signal
to
the
low
voltage
power supply.
6-3.
INTENSITY
AND
FOCUS
CONTROL.
A
9
1
V
zener diode and
a resistive divider circuit provide the intensity
and
focus
voltages.
Each modulator
provides variable output
voltages,
within
their
bias
range,
under
the control
of
the
low voltage
INTENSITY
TV and FOCUS
TV
input
signals.
The
grid
and
focus
voltages are
stabilized
by using
DC
control
loops.
The
INTEN
SITY SAMPLE signal and the
HV
REF
signal are
compared,
on the
scope amplifier
module,
to an
input
control
signal.
The result of
this comparison
is
the INTENSITY TV
signal. In
a similar
manner,
the
FOCUS
SAMPLE
signal is compared
,
on
the
scope
amplifier
module,
to
the input control signal.
This
results
in
the
FOCUS
TV
signal.
6-1 (
6-2 blank)
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