HP Lab Series User Manual

•
•
•
ter
resistor
for
Q8,
is
connected
in
a
manner
which
minimizes
changes
in
the
reference
voltage
caused
by
variations
in
the
input
line.
Output
capacitor
C9
stabilizes
the
regulator
loop
•
4-46
METER
CIRCUiIT
4-4
7
The
meter
circuit
provides
continuous
indica-
tions
of
output
voltage
or
current
on
a
single
multi-
ple
range
meter.
The meter
can
be
used
either
as
a
voltmeter
or
anammeterdependinqupon
the
position
of
METER
switch
82 on
the
front
panel
of
the
supply.
This
switch
also
selects
one
of
two
meter
ranges
on
each
scale.
The metering
circuit
consists
basically
of
a
selection
circuit
(switch
82
and
associated
voltage
dividers), a
stable
differential
amplifier
stage
(Qll
through Ql4),
and
the
meter
movemen~.
4-48
The
selection'
cir,cuit
detennines
which
volt-.
age
divider
is
connected
to
the
differential
amplifier
input.
When
S2
is
1n
one
of
the
voltage
positions,
the
voltage
across
divider R59, R60,
and
R61
(eon-:>
nected
across
the
output of
the
supply)
is
the
input
to
the
differential
amplifier.
When
S2
is
in
one
of
the
current
positions,
the
voltage
across
divider
Rl4,
and
RSS
through
R58
(connected
across
the
sampling
resistor)
is
the
inp~
to
the
differential
amplifier.
The amplified
output
of
the
differential
amplifier
is
used
to
deflect
the
meter.
4-49
The
differential
amplifier
is
a
stable
device
having
a
fixed
gain
of
ten.
Stage
Ql3
of
the
differ-
ential
amplifier
receives
a
.negative
voltage
from
the
applicable
voltage
divider
when
82
is
in
one
of
the
voltage
positions
while
stage
Qll
ls
connected
to
the
+s
(common) terminal.
With
S2
in
a
current
position,
stage
Qll
receives
a
positive
voltage
from
the
applicable
voltage
divider
while
stage
Ql3
is
connected
to
the
+S
terminal.
The
differential
output
of
the
amplifier
is
taken
from
the
collectors
of
Ql2
and
Ql4.
Transistor
QlS
is
a
constant
cur-
rent
source
which
sets
up
the
proper
bias
current
for
the
amplifier.
Potentiometer
R63
permits
zero-
ing
of
the
meter.
The
meter
amplifier
stage
con-
tains
an
inherent·
current
limiting
feature
which
protects
the
meter
movement
against
overloads.
For
example,
if
METER
switch
S2
is
placed
in
posi-
tion
All,
0.ow
current
range)
when
the
power
supply
is
actually
delivering
a
higher
Ampere
output,
the
differential
amplifiers
are
quickly
driven
into
satu-
ration;
limiting
the
CUITent
through
the
meter
to
a
safe
value.
4-50
Figures
·4-5
and
4-6
show
the
meter
connec-
tions
when
S2
ls
·in
the
higher
voltage
and
current
positions,
respectively.
For
the
sa~e
of
simplicity,
some
of
the
actual
ciraiit
components
are
not
shown
on
these
drawings.
With
METER
switch
S2
in
the
higher
voltage
range,
position
(2),
the
voltage
drop
across
R59
is
the
input
to
the
meter
ampUfier
and
4-6
the
meter
indicates
the
output
voltage
across
the
+S
and
-s
terminals.
For
low
output
voltages,
S2
can
be
switched
to
position
(1)
resulting
in
the
applipa-
tion
of
a
larger
percentage
of
the
output
voltage
(drop
across
R59
and
R60)
to
the
meter
amplifier.
+S
A59
-S
RSI
R60
Figure
4-5.
Voltmeter
Connections,
Simplified
Schematic
4-51
With
S2
in
the
higher
current
range
position
(Figure
4-6)
the
voltage
drop
across
R58
is
applied
to
the
meter
amplifier
and
the
meter
indicates
the
output
current
which
flows
through
R54. For
low
values
of
output
current,
S2
can
be
switched
to
position
(4)
and
the
voltage
drop
across
RS7
and
R58
is
applied
to
the
meter
amplifier.
-3V
SERIES
t--4-...JVlfV---+--------'°"
ft£6.
CURRENT
SAMPLING
RESISTOR
Figure
4-6.
Ammeter
Conne~ions,
Simplified
Schematic
+o

HP Lab Series Specifications

General

Brand	HP
Model	Lab Series
Category	Power Supply
Language	English