HP 5245L Service Manual

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

HP 5245L Specifications

General

Brand	HP
Model	5245L
Category	Cash Counter
Language	English