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3330B
3-69.
High Voltage
Power Supply (A4A6)
3-70.
The
High
Voltage
Power
Supply produces
the
required voltage necessary
to
obtain
the pre-selected out-
put.
Additional
circuitry
consisting
of
a
sink
supply and
a
portion of
the
automatic
"crowbar"
circuitry
is
also
included
and
allows rapid
downranging of
the
instrument.
The
automatic
''crowbar"
circuit also
prevents
damaging
of
the
series
pass
elements
if
the
output
terminals
are
shorted
or
an
overload occurs.
The
high voltage
power
supply
consists
of
the bridge
rectifier
CRl
through
CR4.
The
sink
supply
is
composed
of
the voltage
doubler
CR5
through
CR8,
and
the
automatic
''crowbar"
circuit
con-
sists
of
K1
and
R7
with
the
rate limiter
of
Q1
thru
Q4
acting to
limit the
number
of times
the
crowbar
may
be
activated
at a
given time.
3-71.
HIGH
VOLTAGE POWER
SUPPLY.
AC
input
voltage
from
the pre-regulator
at
terminals
15 and
16
is
rectified
by
CRl
through
CR4
to
provide high
level
opera-
ting voltage for the
instrument.
Resistors
A4R6
through
A4R8
and
capacitors
A4C5
through
C7
filter
the
resulting
output
appearing
on
terminal
5.
3-72.
SINK SUPPLY.
AC
input voltage
af
terminals
1
and 2
is
rectified
and
filtered
by
CR5
through
CR8,
Cl,
C2, R4,
and R5.
The
resulting
-700
volts
output
at
terminal 12
is
applied
to the
A4A5
Series
Pass
assembly
and
ensures
a
minimum
current
through
the
series-pass
element
when
the
instrument
is
downranged.
3-73.
AUTOMATIC CROWBAR.
Relay
K1
and
the
resistor
R7
are part
of
the
automatic ''crowbar"
circuit
used
to
provide
a
quick
discharge
path of
the
filter
capa-
citors
contained within
the instrument.
When
an
over-
voltage condition
across the
series
pass
elements
is
detected,
A4A5Q10
will
conduct and
energize
Kl.
The
contacts
of
Kl
place
R7
in parallel
with
the
high voltage
power
supply
which
provides
a
discharge
path
for the
filter
capacitors.
11/72
3-74.
RATE
LIMITER.
The
rate limiter, in
conjunction
with
the
automatic crowbar,
protects the
series
pass tran-
sistors,
If
the
automatic crowbar
activates
more
often
than
the
times given
in
Figure
1-1
of Section
I,
the
rate limiter
relay
K2
will
supply
—35
v to the voltage
trip
circuitry,
placing
the
instrument
in
the voltage
trip
mode.
Q1
thru
Q4,
CR12
thru
CR19,
R3,
R9
thru
R14,
C4
thru
C6, and
K2
comprise
the
rate limiter circuitry.
When
the
crowbar
acti-
vates
due
to excessive voltage across the
series
pass, a
voltage
develops
across
R3
charging
C5
directly
and
charging
C4
througli
R9.
If
there
is
excessive
crowbar
action,
C4
will
charge
sufficiently
to turn
on Q1 and Q2,
energizing
K2.
If
the
crowbar
rate
is
not
excessive,
the charge
on
C4
will
not
become
great
enough
to
turn
on Q1
and Q2. Mean-
while,
as
a
result
of
the
crowbar
action,
C5 becomes
charged;
when
the charge
is
high
enough,
Q4
conducts,
turning off
Q3.
Some
time
later,
it
will
discharge,
turning
off
Q4
and
allowing
Q3
to
conduct.
When Q3
turns on,
it
discharges
C4,
and
the
rate limiter
is
reset.
However,
the
3330B
must
be manually
reset.
3-75.
Current Limiter
(A4A7)
3-76.
The
Current
Limiter contains
two
separate plus
and minus 35
volt
dc
power
supplies
and
part
of
the current
limit circuitry.
The
±35
volt
power
supply
is
a
bridge
supply
with
rectifiers
CRl
through
CR4
and
the
regulators
Q1
and Q2.
The
current
limit
circuitry consists
of
a
three-stage amplifier,
Q3 throu^
Q5, and
the
1
LIMIT/
V
TRIP
drivers
Q6
and Q7.
3-77.
±35
VOLT DC POWER
SUPPLIES. The
ac
input
voltage applied
to terminals 7
and
9
is
rectified
and
filtered
by
CRl
through,
CR4,
Rl,
Cl,
R4, and
C4.
Positive
un-
regulated voltage
is
applied to
Ql, and
negative
unregulated
voltage
is
applied to
Q2.
Zener
diodes
CR5
and
CR7
establish
a reference voltage
at
the base of
Ql
and
Q2.
The
conduction of
Ql
and
Q2
produces
±35
volt
dc out-
put
voltages
available at
terminals
1
and
3.
A
-3.9
volt
dc output
at
terminal
15
is
developed
by
CR6
and
R6
for
use
as
a bias voltage in the
A4A3
Differential Amplifier.
3-9
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