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A.
Flip-Flop
Rr8
-V
R20
fr
tz
i.l_r
=*rt
|NPUT 'ci
RESET
R23
(TURNS ON OI)
B.Trigger Circuit
G.
One-Shot Multivibrator
NOTE:
l=
INITIALLY
CONDUCTING TRANSISTOR
tNPUr
/'
tr
tz
{v{"
Model 5245L
Figure
2-3.
Basic Transistor Circuits
02349-1
ooooo-
c-35
Section
II
Paragraphs
2-19 to
Z-24
trigger circuit
is
similar
to the
flip-flop
except
that
the
RC network
in
one
half
is
replaced by the input
signal.
Capacitor
Cl
bypasses
R3
to
couple fast
changes
in
voltage
at
the
Q1
collector to
the base
of
Q2.
Either
Q1
or
Q2 can conduct
depending
on
the
voltage
at the
input.
Note
that there
is
a
slight dif-
ference
in
input
voltage
(called
hysteresis)
between
switching
with a
negative-going
input
(time
t1)
and
switching with
a
positive-going input (time
t):
2-19.
ONE-SHOT
MULTIVIBRATOR. The
one-shot
multivibrator
is
a
circuit
which generates
a
pulse
of
some specified duration following
the
application
of
a
suitable triggering
pulse.
The
circuit is similar
to
the flip-flop
except one DC coupling path has
been
removed
so
the
circuit is
stable
only
in the
state
with
Ql
conducting.
2-20.
In the typical one-shot
multivibrator
shown
in
Figure 2-3C the following conditions
exist during
the
initial
stable
period: the
R5-R6
divider delivers
a
sufficientlynegative potential tothe base
of
Q1
to
hold
Ql in
saturation; the
Q1
collector
and Q1
emitter
are
therefore slightly
negative;
the R3-R4 divider delivers
the
Q2 base an even smaller negative
voltage
to
hold
Q2
cut off.
2-2L.
Thepositivetriggering pulse
at
timetl
reduces
conduction
of Q1;
the
resulting
negative-going voltage
at the
Q1 collector
is
applied
to the
Q2 base
through
the R3-R4
divider
(C2 bypasses R3
to provide coupling
for
the rapidly
changing
voltage at the
Q1
collector);
Q2 begins
to
conduct;
the resulting
positive-going
change
in
Q2
collector
voltage
is
coupled
through
C3
to
the
Q1
base
to further decrease
Q1
conduction.
The
process
is regenerative
and
quickly
results
in
Q1
being
cut off
and
Q2
being saturated.
2-22.
Capacitor C3 now charges
at a rate
mainly
determined
by
the values
of R6
and
C3
(main
charge
path: R1-Q2-C3-R5).
When
the
Q1
base voltage be-
comes
sufficiently negative, Q1
begins conduction;
the resulting positive-going
Q1
collector
voltage is
coupled
to the
Q2
base; the
Q2
collector
voltage
goes
negative and
is
coupled
through
C3
to the
Q1 base
to
further
increase
Q1
conduction.
The
process
is re-
generative and ends
with the circuit
in its
original
quiescent
state,
Ql
saturated
and Q2
cut off.
2-23.
FIELD EFFECT
TRANSISTOR
(FET).
Field
effect transistors
have
three
terminals:
source,
drain,
and
gate
which correspond in function to emit-
ter,
collector,
and base of junction
transistors.
Source
and
drain
leads
are attached
to
the
same
block
(channel)
of N
or P
semiconductor
material.
A
band
of oppositely
doped
material
around
the
channel (be-
tween
the source
and
drain leads) is
connected
to the
gate
lead.
2-24. In
normal FET operation, the
gate-source
voltage reverse-biases
the PN junction,
causing
an
electric freld that creates a
depletion region in
the
source-drain
channel.
In
the
depletion region
the
number
of
available current
carriers
is
reduced
as
the
reverse-biasing voltage increases,
making
source-
2-3
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