HP 6296A - Page 26

SERIE.;
H:IO
-0
REG.
"'~
-0
-0
+v
•V
R708
•V
-6.Zv
1710~
R707
CRSQQ
~E
CJ
R9QJ
CR902
;iti=t~
4 SCll"S
10
11
12
Cll708
C700
SUMMING
CAPACJroR
R701
C701
0702
~I
~
:;~p
C70Z
AJ>J.
R709
•15.
4V
•6.2V
CR900
R900
R705
CR711
CR710
R706
Figure
4-4.
SCR
Control
Circuit,
Simplified Schematic
Resistor
R713,
connected
between
the
negative
output
line
and
the
emitter
of
Q702,
furnishes
a
signal
which
is
proportional
to
the
output
voltage.
Resistors
R708
and
R707
sample
the
voltage
across,
and
the
current
through,
the
series
regu-
lator.
Capacitor
C702
and
resistor
R709
stabi-
lize
the
control
circuit
feedback
loop.
Resistors
R7ll
and
R712
are
the
source
of
a
constant
offset
current
which
sustains
a
net
negative
charging
current
to
the
summing
point,
ensuring
that
the
SCR's
will
fire
at
low
output
voltages.
4-16
The summation of
the
input
signals
results
in
the
generation
of
a
voltage
waveform
at
TP
59
similar
to
that
~hewn
on
Figure
4-S.
When
the
linear
ramp
portion
of
the
waveform
reaches
a
certain
negative
threshold
voltage,
diodes
CR711
and
CR710
become
forward
biased.
The
negative
voltage
then
is
coupled
to
the
base
of
transistor
Q701.
Transistors
Q701
and
Q700
form a
squaring
circuit
resembling
a Schmitt
trigger
configuration.
Q701
is
conducting,
prior
to
firing
time,
due
to
·the
positive
bias
connected
to
its
base
through
R705.
Transistor
Q700
is
cut
off
at
this
time
be-
cause
its
base
is
connected
directly
to
the
collec-
tor
of
conducting
transistor
Q701.
When
the
neg-
ative
threshold
voltage
is
reached,
transistor
Q701
is
turned
off
which
turns
Q700
on.
The
conduction
of
Q700
allows
capacitor
C703
to
dis-
charge
rapidly
through
pulse
transformer
T700
resulting
in
the
SCR
firing
pulse
shown
on
the
4-4
FIRING
. -
-r
l:V
TP59
THR£5HOU>
SUMMING
POINT
I I
l
-
-~-.....:
"'-8.
lMS
I
I
I
I
TP47
OUTPUT
0700
~NOTE
3)
nn
l
11
'-1:-
l!iV
_J_
; : I
TP46
l'llUNG
PULSE
(EXPANDED)
I
I
I
l
c··-J
, ' •
J_
NOTES;
'
I
I
I
TPSZ
RESET
----r
l.
ALL
WAVEFORMS REFERENCED
TO
INBOARD
SIDE
or
CURRENT
SAM-
PLING
RESISTOR
R800
EXCEPT
l'IRJNG
PULSE
WHICH
IS
REFEll·
ENCED TO T.
P.
45.
2.
FOR
CLAllJTY
WAVEFORMS
ARE
NOT
DRAWN
TO
SCALE.
3.
AMPLITUDE OF THIS WAVEFORM IS
APPROXIMATE
ANO
VAIUES
SUGHTLY
l'ROM
MODEL
'TO
MODEL
IN
AC·
COROANCE
WITH
THE
POSmvE
COLLECTOR
BIAS
OBTAINED
FROM
caoo.
1911
--1.
Figure
4-5.
SCR
Control
Circuit
Waveforms
•
•
•