HP 3400A Service Manual

Model
3400A
,
Theory
of
Operation
4-34.
The
output
of
the
filter
is
connected
to
the
output
amp
(U602).
The
purpose
of
the
amplifier
is
to
drive
the
meter
(M1)
and
to
provide
a
low
impedance
output
for
the
rear
D.C.
OUT
connector.
The
output
impedance
of
the
amplifier
is
approximately
1
ohm.
Since
there
are
two
499
ohm
resistors
(R624
and
R631)
between
the
amplifier
output
and
the
rear
ter-
minal,
the
output
impedance
at
the
terminal
is
approximately
1000
ohms.
4-35.
Other
circuits,
consisting
of
C611,
R629,
and
R630,
are
used
to
speed
up
the
step
response
of
the
3400A.
4-36. Power Supply Assembly A7
4-37.
The
power
supply
assembly
provides
dc
operating
voltages
for
the
tube
and
transistors
used
in
the
Model
3400A.
See
power
supply
assembly
schematic
diagram
illustrated
on
Figure
6-4.
4-38.
Either
115
or
230
volts
ac
is
connected
to
the
primary
of
power
transformer
Tl
through
fuse
F1
and
the
POWER
switch
S1.
Switch
S2
(slide
switch
on
rear
panel)
connects
Tl
primary
windings
in
series
for
230-volt
operation
or
in
parallel
for
115-volt
operation.
Neon
lamp
DSI
lights
to
indicate
LINE
power
ON
when
ac
power
is
applied
and
SI]
is
closed.
4-39. Regulator Operation
4-40.
The
series
regulator
acts
as
a
dynamic
variable
resistor
in
series
with
the
power
supply
output.
A
control
amplifier
senses
changes
in
the
output
voltage
by
comparing
the
output
with
a
fixed
reference
voltage.
The
control
amplifier
then
supplies
any
output
voltage
changes
to
the
driver
transistor,
which
in
turn
changes
the
resistance
of
the
series
regulator
to
oppose
the
change
in
output
voltage.
Diodes
CR704,
CR713
and
CR706
across
the
base
emitter
junction
of
the
series
regulator
provide
overload
current
protection.
4-41. +75 Volt Supply
4-42.
The
+75
volt
supply
consists
of
a
full-wave
rectifier
(CR701
and
CR702)
whose
out-
put
is
filtered
by
C1A
and
C1B
and
regulated
by
series
reguiator
QI.
The
+75
volt
supply
provides
regulated
+75
volts
which
is
used
as
the
plate
supply
voltage
for
V201.
Voltage
variation
from
the
output
is
felt
at
Q702
base
circuit
through
C704,
R715,
and
R716.
The
C703
and
R709
network
provides
phase
correction
for
power
supply
stability.
The
regulation
circuitry
is
in
the
negative
leg
of
the
+75
volt
supply,
and
uses
the
-17.5
volt
supply
as
a
reference.
4-43. —17.5 Volt Supply
4-44.
The
regulated
—
17.5
volt
supply
consists
of
a
full-wave
rectifier
(CR711,
and
CR712)
whose
output
is
filtered
by
C706
and
C707
and
regulated
by
Q2.
Breakdown
diode
CR715
provides
reference
voltage
at
the
base
of
Q704.
Regulation
operation
is
the
same
described
in
Paragraph
4-40.
4-5/4-6

HP 3400A Specifications

General

Brand	HP
Model	3400A
Category	Measuring Instruments
Language	English