HP 6296A - Page 30

4-42
REFERENCE
CIRCUIT (See
Schematic
at
Rear)
4-43
The reference
circuit
is
a
feedback
power
supply
similar
to
the
main
supply.
It
provides
stable
reference
voltages
which
are
used
through-
out
the
unit. The
reference
voltages
are
all
derived
from
smoothed de
obtained
from
the
full
wave
rectifier
(CR600
and
CR601)
and
filter
capac-
itor
C600. The +9.4
and
-6.2
voltages
are
devel-
oped
across
temperature
compensated
Zener
diodes
VR600
and
VR60l.
Resistor
R611
limits
the
current
through
the
Zener
diodes
to
establish
an
optimum
bias
level.
4-44
The
regulating
circuit
consists
of
series
regulating
transistor
Q600,
error
ammplifier
Q601,
and
differential
amplifier
Q602
and
Q603.
The
voltage
across
the
Zener
reference
diode
VR600
and
the
voltage
at
the
junction
of
divider
R605
and
R606
are
compared,
and
any
differences
are
de-
R872
R857
QH2
HOtt:
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I
RB62
RB61
R8'1
S2
FOSmoNS
FOR
I>IFFERENT
MOI>EU
ARE
SHOW?-!
BELOW:
MODEL
S2
TERl\.!TN&
NOS.
I
2
3
4
628ZA
l.2V
12V
HA
l.ZA
628;.\
2.
4V
24V
6A
.6A
6286A
2.4V
Z4V
IZA
l.ZA
629~A
;v
;ov
4A
.4A
6291.\
sv.
sov
6A
.6A
6Z96A
7V
70V
4A
.u.
RB&O
tected
by
Q602
and
Q603.
The error
voltage
is
amplified
and
inverted
by
Q601
and
appli.ed
to
series
requlator
Q600
in
the
correct
phase
and
amplitude
to
maintain
the
+15.4
volt
output
con.
stant.
4-45
Zener
diode
VR601
provides
an
add:ltional
bias
voltage
of
-6.2
volts.
Resistor
R60l,
con-
nected
across
Q600, minimiZes
power
di:;sipation
in
the
series
element.
Output
capacitor
C602
stabilizes
the
reference
regulator
loop.
4-46
METER
CIRCUIT
4-47
The
meter
circuit
(see
Figure
4-8)
provides
continuous
indications
of
output
voltage
•lr
cur-
rent
on
a
single
multiple
range
meter. The meter
can
be
used
either
as
a
voltmeter
or
an
ammeter
depending
upon the
position
of
METER
switch
S2
on
the
front
panel
of
the
supply.
This
SVl'itch
1800
CtJRllENT
SAM
PUNG
Rl:SJSTOR
CSI
R853
18SZ
11851
RISO
•
Figure
4-8.
Meter
Circuit.
Simplified
Schematic
•
4-8