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Type 5STIA
|
Page 3-13
Q254
off.
After
the
trigger
pulse
passes,
Q254
remains
cut
off,
held by D255 which remains
in the low state.
0261 col-
lector
current
now
flows
through
ramp-slope
capacitor
c260,
whose value is selected by SWEEP TIME/CM switch SW260.
Be-
fore
the beginning
of the
fast-ramp
rundown,
comparator
diode
D270
is back
biased,
and
all
current
from
Q261
is
fed
to
C260.
The
ramp
voltage
runs
down
until
D270
becomes
for-
ward biased.
Collector
current
from Q261
is now fed through
D270 and Q276,
and the
collector voltage
of 9276 drops.
D275
switches
to the
high
state.
Before
D275
switches, the voltage
on either
side
of D276
is about
zero volts.
When the current
from Q261 passes
through 9276,
it causes.a step at D275,
quickly switching
D275 to the high
state.
Because
D276 was not
conducting,
it
appears
as
an
open
circuit
as
D275
switches.
When
D275 switches,
D276 becomes back biased.
Because
it is a tunnel diode,
D276 conducts
current easily,
coupling
the
step caused by the
switching
of D275 to D285.
This
causes
D285 to switch.
When D285
switches,
a step is fed to
T284,
which
is a doubling transformer.
The output
of T28h
forward biases
Q284,
causing
the
collector
voltage
of QP84
to rise.
This gate,
which appears
at the
collector
of Q28h,
is
connected
directly
through
interconnecting
cables
to
the
'h'
Series
sampling unit.
The gate
is also
sent,
through
isolation
resistance
network
R285,
R286,
and R287,
to the
stairstep
generator,
where
it
is used
to advance
the
stair-
step one step.
When the current through T28h (fed from R288
and R289) rises,
D285 is switched back to the low state.
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