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IEC 30 Series - Circuit Description

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Section
3
CIRCUIT
DESCRIPTION
3-1.
INTRODUCTION
Figure
3-1,
the
simplified
block
diagram,
shows
the
major
functional
blocks
of
the
system.
For
more
detailed
reference,
see
the
circuit
schematic
at
the
back
of
manual.
3-2.
POWER
SUPPLY
a.
UNREGULATED
D-C
AND
RECTIFIERS.-
Two
unregulated
d-c
voltages,
+
22
volts
and
-22
volts,
are
generated
to
supply
the
output
amplifier
directly
and
to
supply
power
to
the
regulator
circuits
which
serve
the
balance
of
the
instrument.
One
tapped
secondary
trans-
former
winding
serves
two full wave
rectifiers.
b.
REGULATED
SUPPLIES.
-
There
are
two
regulated
d-c
supplies,
±15
volts,
with
medium
current
capabilities.
The
+
15-volt
supply
is
used
as
a
reference
for
the
other
regulated
supplies.
NOTE
If
the
+
15-volt
supply
is
inoper-
ative
all
other
supplies
are
also
inoperative.
The
+
15-volt
supply
uses
VR4
as
a
refer-
ence
voltage
for
its
error
signal.
The
+
15-
volt
level
is
adjusted
by
R145.
Alow-impedance
output
is
provided
by
the
Darlington
pair
Q23
and
Q24. A
current-limit
circuit
is
formed
by
Q25
and
R140.
This
circuit
provides
protec-
tion
for
Q23
and
Q24 in
the
event
the
~15
volt
supply
is
shorted
or
overloaded.
The
+
5-volt
supply
derives
its
output
cur-
rent
and
reference
voltage
from
the
+
15-volt
supply.
Q26
provides
a
low-output
impedance
for
the
+
5-volt
supply,
and
Q27
provides
the
output
current
for
the
+
5-volt
supply.
The
-15-volt
and
-5-volt
supplies
operate
in
the
same
man-
ner
as
the
+
15-volt
and
+5-volt
supplies.
The
-15-volt
supply
derives
its
reference
voltage
from
the
+
15-volt
supply
and
the
resistor
divider
circuit
R158
and
R159.
3-3.
TRIANGLE
GENERATION
The
basic
loop
concept
consists
of
gener-
ating
a
voltage
proportional
to
desired
frequency
and
converting
this
level
to
a
constant
current
used
to
charge
a
capacitor.
At
some
defined
positive
voltage
level
across
the
capacitor,
a
voltage-level
sensor
operates
to
cause
an
equal
and
opposite
current
to
be
applied
to
the
integrating
capacitor.
When
an
equal
negative
voltage
level
is
detected,
the
process
repeats.
a. FREQUENCY CONTROL. - A
single
oper-
ational
amplifier,
IC
12,
is
used
to
generate
a
voltage
representing
the
summation
of
all
fre-
quency
commands.
In
addition
to
the
voltage
derived
fron1
the
Frequency
Dial
control,
R5,
voltages
present
on
the
VCG
input
connector
and
any
sweep
voltage
appearing
on Sweep
3-1

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