Service
Model 214B
High
Voltage
Supply
(-155
V/-260
V)
A
functional
diagram
of
the high voltage supply
circuit
is
given
in
Figure 8-
2-2.
Basically, this
circuit
comprises
two
cascaded series regulators
(0601
and
0602)
and a
sense
amplifier
0607.
Series regulator
0601
in
conjunction
with
0603,0605
forms
a
Darlington
amplifier;
similarly
regulator
0602
together
with
0604
and
0606.
0601
0602
+
--,
0603
Q604
I
I
I
R612
I
I
CR606
I
I
I
C635
R622
rL.
.....
•
R618
/
;1"
LOAD
I
I
R6
11
---
I
I
,
--
-
I
I
I
I
I
I
I
R627
I
--
I
C632_
R617
I
FROM
U606
R621
I
I
K601
I
R620
I
__
J
Figure
8-2
- 2.
To
ensure
that
secondary
breakdown
of
the series regulators does
not
occur, the
collector
/
emitter
voltage
drop
across
0601
and
0602
is
equalized via voltage
divi
d
er
R610/ R614.
CR606, R611 and C632
form
a
current
source. (C632
is
charged
to
the positive
potential
; should
this
potential
then
drop
,
CR606
becomes reversed biased and C632
is
discharged via R611). Part
of
this
current
is
routed
to
the
base
of
0606
thus
switching
regulator
0602
on; the rest
of
the
current
is
routed via R616,
0607
and
VR601
to
the
negative
potential.
If
the
load at the
0602
emitter
increases, the voltage at the
junction
R618
/ R621 decreases,
which
in
turn
is
sensed
by
0607
.
The
current
flowing
to
the
negative
potential
is
thus reduced, and more
current
fed
to
the
0606
base.
This
causes
the series regulators
to
conduct
more, thus regulating the
output
voltage.
Due
to
the large load changes
which
occur,
for
example,
by
100
V
output
amplitude,
the
bias
current
for
VR601
is
supplied
by
U606,
thus making the zener voltage indpendent
of
load.
R622 ensures
correct
operation
of
the regulator
circuit
when no load exists,
while
L601 and C634 are used
to
damp
oscillations.
When
30
-
100
V amp
litude
range
is
seiected, the regulator
output
voltage is increased
from
-155
V
to
approximate
ly
-
260
V.
This
is
achieved via relay K601
which
switches
the
seco
ndary
voltage
of
T601,
and
changes the
potential
at the voltage
tap
-
off
from
divider
R618, R621,
R620
by
shorting R620.
8- 10
Scans by Artekmedia => 2009
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