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Model 5245L
Section
fI
Paragraphs 2-1 to 2-10
sEcTtoN
il
PRINCIPTES
OF
OPERATION
2.I.
INTRODUCTION.
2-2.
This section describes
horv
the Model
5245L
operates.
Basic circuitsused in
the
counter are des-
cribed
first
(Paragraphs
%3
through
2
-24).
Operation
of decimal counters
and decade
dividers is thoroughly
discussed
in
Paragraphs 2-25 through
2-35.
A
dis-
cussionof basic counter functions isgiven next(Para-
graphs 2-36
through 2-43).
Pulse
timing circuits
and
overall operation of the entire
counter
are discussed
in
Paragraphs 2-44 through
2-50. At
the
end
of
the
section each assembly
is
described
in
order of its
assembly designation
(A
)
(Paragraphs 2-51 through
2-L22.
)
-
2-3.
THE
DIODE.
2-4.
GENERAL.
Semiconductor
diodes are
used
in
signal-handling
circuits
and
in pover
supply
rectifier
and
regulator circuits.
2-5.
THE "OR"
GATE.
TVo
or
more diodes
are
sometimes used
as an
OR
gate.
The OR gate is
a
multiple-input
circuit
which requires only
one
input
to
produce an
output. Figure
2-1A
shorvs
some
OR
gate
configurations.
2-6.
THE
"AI.ID"
GATE.
The AI.ID
gate
or coincidence
circuit
is
a
multiple-input circuit which requires
the
presence
of all
input signals
to
produce an
output.
Figure 2-18
shows
anANDgate configuration in which
an
input signal is
passed
only when
a
properly polar-
ized control voltage
is
applied.
2-7.
THE
"INHIBII" GATE. The
signal normally
passes through
an
INHIBIT
gate;
adding
a
second
signal
closes the gate
and
prevents
the signal from
going
through.
One
of the most
common
forms of
the
IN-
IIIBIT
gate
is
the series
gate
shown
in Figure
z-LC.
If
thediode is biased offrthe gate is
closed, and
pulses
do not reach the decade divider or decimal counterl
when
the diode is biased
on,
the pulses
go
through
the
gate and
reach
the
decade
divider
or decimal counter.
2-8.
LIMITER
OR
CLIPPER.
The
limiter or
clipper
is
a
circuit
which removes positive or negative
peaks
of waveforms.
It
can be used either as
a
waveform
shaping
circuit or as a
protective
device
to prevent
excessive voltages from reaching a sensitive
circuit.
Figure 2-1D
shonrs
a
limiterwhich
prevents
the nega-
tive
peak
of a
pulse
from
going more negative than
about -0.
6
volt.
Note
that
for
a
conducting
silicon
diode
the
cathode
voltage
is
about
0.6
to
0.8
volt
more
negative than
the
anode.
2-9.
CLAIVIPER OR
DC RESTORER.
The clamper or
DC restorer
is
a
circuit
which establishes either
the
positive ornegative peakof awaveformat
a
particular
DC reference voltagel
in
other words,
it
provides
a
definite baseline
voltage
f
or
the wavef
orm.
Figure
2-1E
shols a
clamper which provides
a
baseline of
about
+20
volts
for
a negative pulse.
02349-1
2-10,
REGULATOR.
A
diode regulator uses either
the
constant
reverse-bias
breakdonrn
voltage
charac-
teristic
of
a
breakdown
diodeorthe
constant
fonpard-
bias
voltage
drop characteristic of
a
silicon
diode.
Power supply reference voltages are generally pro-
vided by
breakdorpn
diodes
which maintain a
constant
voltage when supplied
with a
reverse-bias
voltage
greater than
their
specified
breakdorpn
voltage. Regu-
Iated
voltages
can
also be provided
by
a
fonvard-
biased
silicon
diode
which maintains a constant
0.6
to
0.8volt drop. Figure 2-1F
shorps
connections
forboth
types of
diodes.
A.
"Or"
Gate
D-
B.
"And" Gatg
+
C.
"lnhibit"
Gate
s_
D.
Limiter
E.
Clampel
+2oV
-v
(>
-0.8v)
-v
(>-s6v)
REGULATED
}
REGULATED
ry-s6v
-o.8v
F.
Regulator
Figure
2-1.
Basic Diode Circuits
2-L
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