HP 6177B Operating And Service Manual
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r
(
(
se~ies
regulator
thus
controlling
the
conduction
of
the
regulating
stage.
4-35
If
the
voltage
programmin<;
terminals
we:e
to
open
when
the
output
was
open
circuited,
the
out-
put
voltage
could
go
up
as
high
as
200
Volts.
VR14
anc
VR1S
serve
as
a
protection
against
this
condi-
tiOD.
\!Vhen
the
voltage
reaches
approximately
140-
Volts,
the
Zener
diodes
reach
their
break
doVv"TI
po-
te;;.:ial
anc
clamp
the
output
to
140
Volts.
This
pre-
ven::s
break
down
of
other
elements
which
wruld
no::
be
able
to
withstand
this
very
high
voltage.
V::::'13
operates
in
the
same
capacity
should
the
volt-
a
ge
programming
of
the
guard
supply
fail.
4-36
SERIES REGUIATOR
4-37
The
series
regulator
regulates
the
output
of
ths
supply
by
altering
its
conduction
in
accordance
with
the
feedba
ck
error
signal.
The
circuit
cO::1sists
0:
se:-ies
regulating
transistors.
030
and
Q29.
and
a
base
biaSing
source,
025.
By
altering
its
con-
c.uction
in
accordance
with
the
error
signal
applied
to
it,
the
series
regulator
produces
a
well
regulated
out
puc.
at
the
level
established
by
the
currem
con-
troIs.
4-38
Notice
that
the
series
regulato';"
is
connected
in
a
common
base
configuration.
This
increases
the
output
impedance
of
the
supply
thus
givL"1g
it
the
desired
quality
of
a
constant
current
supply.
A
more
detailed
description
concerning
the
desired
features
of
a
constant
current
supply
is
contained
in
Application
Note
90
available
at
your
local
Hewlett-Packard
field
office.
4-39
TURN-OFF
CONTROL
4-40
The
turn-off
control
circuit
prevents
reverse
currents
from
flowing
through
the
series
regulator
at
turn-off.
It
accomplishes
this
by
sending
a.
turn-
down
signal
to
the
series
regulator
via
the
driver.
4-41
During
normal
operation
of
the
supply.
031
supplies
a
bias
potential
to
the
driver.
At
turn-off,
CR30
becomes
reversed
biased.
031
turns
off
quickly,
due
to
the
discharging
of
capacitor
C34.
This
creates
a
negative
potential
at
the
base
of
026.
turning
off
both
the
driver
and
the
series
reg-
ulator.
4-42
BLEED
CIRCUIT
4-43
The
bleed
cirCuit
provides
a
path
for
20mA
of
current
to
flow
through
the
series
regulator.
This
keeps
the
series
regulator
biased
in
its
active
re-
gion
at
all
times.
The
bleed
current
flows
from
the
+24, Volt
unregulated
reference
through
Q1,
back
up
to
the
collector
of
the
series
regulator,
through
the
.
driver
to
common
W
where
it
returns
to
the
-16.2
reference
voltage
tnrough
VR6.
Notice
that
this
4-4
current
aoes
not
go
through
the
loae
nor
through
the
sampling
resistors.
V,Then
the
supply
is
programmed
for
zero
current.
20mA
are
flowing
through
the
com-
mon
node,
however,
zero
current
is
actually
deli-
vered
to
the
load.
Keeping
the
series
regulator
biased
in
its
active
region
at
all
times
makes
it
possible
to
have
good
load
regulation
even
at
low
output
currents.
4-44
VOLTAGE LIMIT
CIRCUIT
4-45
The
voltage
limit
circuit
acts
to
limit
the
potential
across
the
output
terminals
to
some
preset
lL'11it
established
by
the
VOLTAGE
limit
control.
The
circuit
conSists
of
a
voltage
limit
control,
RBI,
feedback
amplifiers
04,
OS,
and
06,
shunt
regula-
tor
07,
voltage
limit
lamp
DS2,
and
lamp
driver
08.
Unaer
normal
operating
conditions,
07
is
turned
ofL
Vlhen
the
voltage
limit
tb...reshold
is
reached.
a
neg-
ative
feedback
signal
is
sent
to
the
feedback
ampli-
fiers.
The
signal
is
inverted,
amplified
and
fed
to
the
shunt
regulator
and
lamp
driver.
This
signal
causes
:)Oth
transistors
to
conduct.
The
output
voltage
is
limited
by
the
amount
of
conduction
of
07.
Also,
with
08
on,
a
current
path
is
completed
through
08
and
DS2.
thus
DS2
turns
on
warning
the
operator
of
the
voltage
limit
condition.
Notice
that
since
the
voltage
limit
section
of
the
supply
em-
ploys
a
separate
shunt
regulator.
the
main
series
regulator
continues
to
regulate
output
current
even
during
voltage
limit
operation.
4-46
Potentiometer
RBI
permits
adjustment
of
the
base
potential
of
04
with
respect-to
(-)
out,
thus
setting
the
point
at
which
the
voltage
limit
threshold
is
reached.
4-47
Constant
Current
Source.
The
constant
cur-
rent
source,
Q2
and
associated
components,
pro-
Vides
a
constant
programming
current
through
the
VOLTAGE
limit
control,
HB1,
thus
ensuring
linear
programming
of
the
voltage
limit
circuit.
VR2
keeps
the
ba
se
of
02
at
a
constant
voltage
ensuring
a
constant
current
output.
R6
is
selected
at
the
fac-
tory
to
bia
s
the
emitter
of
02
so
that
the
proper
pro-
gramming
current
is
obta
iDed.
4-48
Tum-On
Circuit.
C40
and
R41 form a
long
time
constant
Re
network.
When
the
supply
is
ini-
tially
turned
on.
a
turn-on
Signal
is
fed
to
07
via
Q6.
This
limits
the
output,
thus
preventing
turn-on
overshoot
from
damaging
delicate
loads.
After
the
supply
has
been
on
for
a
short
time,
C40
charges
up,
back
biasing
CR40
and
thus
the
turn-on
circuit
has
no
effect
on
nonnal
operation
of
the
supply.
4-49
VOLTAGE
LIMIT OVERSHOOT CONTROL
4-50
This
fast
acting
circuit
protects
the
load
from
initial
large,
fast
rises
in
output
voltage
that
the
voltage
limit
circuit
would
not
otherwise
be
eble
to