HP Lab Series User Manual

•
••
•
comes
£orward
biased.
Summing capacitoi' C22
is
tl\en
allowed
to
completely
discharge
through
CRlS.
Diodes-CR16
and
CR17
become
reverse
biased
at
reset
and
transistor
Ql8
reverts':to
its
"on"
state
•
Consequently,
Ql9
ls
turned
off
and
capacitor
Cl7
charges
up through
R96
at
a comparatively
slow
rate
until
the
collector
voltage
of
Q19
reaches
approx1-
mately
+16
Volts.
The
above
action
causes
the
small
negative
spike
that
appears
across
the
wind-
ing
of
pulse
transformer
T2
at
reset
time.
4-20
TURN-ON
CONTROL
CIRCUIT
4-21
This
circuit
is
a
long
time-constant-network
which
protects
the
SCR
and
series
regulator
from
possible
damage
during
turn-on.
When
the
power
supply
is
first
turned
on,
C26
provides
a
poSitive
voltage
to
the
anode
of
CR19
which
is
connected
to
the
base
of Q3.
Q3
inverts
this
voltage
and
passes
it
on.to
the
series
regulator
via
Q4. The
series
regulator
is
thus
turned
off,
until
C26
becomes
sufficiently
charged
to
reverse
bias
CR19.
4-22
C26
initially
passes
a
positive
voltage
to
the
cathode
of
CR16,
in
the
SCR
control
circuit,
via
R98
and
R99. This
ensures
that
this
diode
1s
reverse
biased
and
that
no firing
pulses
are
gener-
ated
until
C26
is
sufficiently
charged
to
provide
the
proper
bias
to
CR16.
CR18
provides a
discharge
path
for
C26 during
turn-off.
4-2a
Capacitor
C26,
diode
CR18,
and
resistor
R98
form a long
time
constant
network
which
achieves
a
slow
turn-on
characteristic.
When
the
unit
is
first
turned
on,
C26
provides a
positive
voltage
to
the
cathode
of
CR16
to
ensure
that
it
is
intially
reverse
biased.
After
C26
becomes
fully
charged,
the
con-
trol
circuit
is
permitted
to
fire
the
SCR.
Diode CR18
provides
a di,scharge
path
for
C26
when
the
unit
is
turned-off.
4-24
SERIES
REGUIATOR
4-25
The
sefies
regulator,
{transistor Q6)
serves
as
the
series
element,
or
pass
transistor,
which
provides
precise
and
fast
control of
the
output.
The
conduction
of
Q6
is
varied
in
accordance
with
feed-
back
control
signals
obtained
from
driver
Q4.
Zener
diode
VR3,
connected
across
Q6
arid
R54,
protects
the
series
transistor
if
the
output
terminals
of
the
supply
are
shorted.
Resistor
RSI
limits
the
current
through
VR3.
4-26
CONSTANT
VOLTAGE
COMPARATOR
CIRCUIT
4-27
The
circuit
consists
of
the
programming
re-
sistor
(RIO}
and
a
differential
amplifier
stage
{QI
and
associated
components).
Transistor
Ql
con-
sists
of
two
silicon
transistors
housed
in
a
single
package.
The
transistors
have
matched
character-
4-4
istics
minimizing
differential
voltages
due
to
mis-
matched
stages.
Moreover,
drift
due
to
thermal
differentials
is
minimized.
since
both
transistors
operate
at
essentially
the
same
temperature.
4-28
The
constant
voltage
comparator
circuit
con-
tinuously
compares
a
fixed
reference
voltage
with
a portion
of
the
output
voltage
and.
if
a
difference
exists,
produces
an
error
voltage
whose
amplitude
and
phase
is
proportional
to
the
difference.
The
error output
is
fed
back
to
the
series
regulator,
through
OR
gate
diode
CR3
and
the
mixer
and
driver
amplifiers.
The error
voltage
changes
the
conduc-
tion
of
the
series
regulator
which,
in
turn,
alters
the
output
voltage
so
that
the
difference
between
the
two
inpat
voltages
applied
to
the
differential
amplifier
is
reduced
to
zero.
This
action
maintains
the
output
voltage
constant.
4-29
Stage Q lB
of
the
differential
amplifier
is
con-
.
nected
to
a common
(+S)
potential
through
impedance
equalizing
resistor
RS.
Resistor
R6
and
RS
are
used
to
zero
bias
the
input
stage,
~ffsetUng
minor
base
to
emitter
voltage
differences
in
Q
1.
The
base
of
QlA
is
connected
to
a summing point
(A6)
at
the
junction
of
the
programming
resistors
and
the
cur-
rent
pullout
resistor
Rl2.
Instantaneous
changes
in
the
output (due
to
load
variations)
or
changes
due
to
the
manipulation
of
RlO,
result
in
an
increase
or
decrease
in
the
summing
point
potential.
QlA
is
then
made
to
conduct
more
or
less,
in
accordance
with
summing
point
voltage
change.·
The
resultant
output
"error"
voltage
is
fed
back
to
the
series
reg-
ulator
via
the
remaining components
of
the
feedbaCk
loop.
Resistor
Rl,
in
series
with
the
base
of
QlA,
limits
the
current
through
the
programming
resistor
during rapid
voltage
tum-down.
Diodes
CRl
and
CR2
fonn a
limiting
network
which
prevents
exces-
sive
voltage
excursions
from
over
driving
stage
QlA
Capacitors
Cl
and
C2,
shunting
the
programming
resistor,
increase
the
high frequency
gain
of
the
in-
put
amplifier.
4-30
During
constant
voltage
operation,
the
pro-
gramming
current
that
flows through
the
programming
resistors
(VOLTAGE
controls)
is
constant
because
the
value
of
shunt
resistor
Rl2
is
factory
selected
so
that
all
of
the
+6.2 Volt
reference
is
dropped
across
Rl2
and
Rl3.
Linear
constant
voltage
pro-
gramming
is
assured
with
a
constant
current
flowing
through
RIO.
4-31
Main
output
capacitor
C20,
connected
across
the
output
terminals
of
the
supply,
stabilizes
the
series
regulator
feedback
loop
when
the
normal
strapping
pattern
shown
on
the
schematic
is
employ-
ed.
Note
that
this
capacitor
can
be
removed
to
avoid
output
current
surges
or
to
increase
the
pro-
gramming
speed
of
the
supply.
If
C20
is
removed,
capacitor
Cl9
serves
to
insure
loop
stability.

HP Lab Series Specifications

General

Brand	HP
Model	Lab Series
Category	Power Supply
Language	English