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Section
fI
Paragraphs
2-11 to 2-18
2-II.
THE TRANSISTOR.
2-t2.
GENERAL. Transistors are
used
throughout
the counter in
circuit
configurations
such as
the ampli-
fier,
the flip-flop or binary,
the
trigger circuit,
and
the
one-shot
multivibrator, Irl
the folqu/ing para-
graphs, basic transistor
operation and
a few
basic
transistor circuits
are discussed. These paragraphs
discuss
the easily
observed
changes
in currents
and
voltages in
transistor circuits
which help technicians
Iocate
circuit
faults butdo not attempt todescribe
horv
transistors work internally.
2-13.
BIASING AI.{D
CONDUCTION.
VACUUM
tUbCS
and
transistors
are functionally
similar.
Irr
the
tube
a
small
grid-to-cathode voltage controls
a
larger
plate-to-cathode
current flow. In
a
transistor
a
small
base-to-emitter current controls
a
large collector-to-
emitter current. A
comparison of
basic vacuum
tube,
NPN transistor,
and PNP transistor
operation is
shown
in
Figure 2-2A; indicated current
represents
conventional
florv of positive
charges
external to the
transistor
and
is
not
intended
to indicate
florp
of car-
riers
inside the
transistor structure.
Notice
that ilre
effect
of
emitter-base-collector voltages
is
totally
reversed
between
NPN
and
PNp
transistorsl circuits
which
are
arranged
for
an
NpN
transistor
usually
func-
tion normally for
a PNP
transistor
if
supply voltages
are reversed.
2-t4.
AMPLIFIERS. As
witl
vacuum
tubes, three
basic amplifier
types are available
(figure-Z-2l)
,
These
amplifiers
maybe used alone
orin
combination
to form complex circuits.
2-15.
FLIP-FLOP.
The
flip-flop is
a
bi-stabte two-
transistor circuit in which
one
transistor
conducts,
holding
the other cut
off.
Each
input pulse causes
a
reversal of states; that
is,
the cut
off
transistor is
turned
on and
the conducting transistor
is
cut
off.
In
the
flip-flop
shorrn
in
Figure 2-gA, e1
is initially
con-
ducting heavily;
its
collector
voltage
is
only slightly
negativel
a near-zero
voltage
is
supplied
to the
base
of Q2 (junction of R2?-28
divider). -ine
voltage drop
across
R24
produces
a sufficienily
negative voltage
at the emitter of
Q2
to hold e2 cut
off.
With e2
cut
off the R18-R19-R20 divider delivers
a
negative
volt-
age
to the base
of
Q1
to keep
it
conducting.
2-16.
At time
t1
the
positive input pulsecutsoff
el;
the Q1 collector voltage
goes
negative
and
drives
ez
into conduction
(R2?-R2B
divider to e2 base); the
e2
collector
voltage and
the
Ql
base
voltage
(R1g-R20
divider)
then become considerably
less negative, per-
mitting Q1
to
remain
cut
off.
The
R26-R2?-R2B
divider delivers
a
sufficiently
negative voltage
to
the
base
of
Q2
to drive
it
into conduction. In
a
similar
manner the
positive input pulse at time t2 cuts off e2
and
starts a
sequence
of
events which
6nds
with
el
conducting
and
Q2
cut
off.
Note
that
a
positive input
pulse has no effect on
Ql
if it
is
already cut
off.
A
negative
reset pulse applied to the base of
et
returns
the
flip-flop to its initial
condition
(e1 conducting, e2
cutoff).
The diode
CRg
removes the negative pulse
from the
differentiated square wave
input.
Wilhout
this
diode, the negative pulse
would
drive
el
which
is
cut off
and
the
stage
would switch from one
state
2-2
Model 5245L
Figure
2-2.
Transistor
Operation
to the
other but would not divide by
two.
The
AC
coupling through C2 and C3 insures
fast
switching.
The
DC
coupling through R1g and R2? insures
bi-
stable characteristics.
2-L7.
BINARY
CIRCUIT.
In this manual
a
flip,flop
which completes
its
operating cycle
and
produces
an
output pulse after receipt of two
similar
input pulses
is called
a
binary circuit, since
it
is
a counting device
in
a
binary system. The binary
circuit is
driven from
a
single inputwhich is connectedeither through
a
pair
of resistors or through
a
pairof
gating diodes toeach
transistor
base.
2-18.
TRIGGER
CIRCUIT.
The
trigger circuit is
a
limiter or
squaring
circuit
which produces an
output
waveform
with very fast
rise
and
fall
times.
The
02349-1
ooooo-c-36
A.
Amplifier Characteristics
SHARACTERISTIC
COMMON
BASE
COMMON
EMITTER
COMMON
COLLECTOR
lnpul
lmpedonce
Oulpul
lmpedonce
Volloge
Goin
Currenl
Goin
Power
Goin
300-50J)
300Ko-500Ko
500-
1500
<t
20dB-30d8
5000-1500J}
30KO-50KO
300-tooo
25-50
25dB-40d8
20K0-500Ko
500-loooo
<l
2s-50
todB-20d8
(Emitler
Follower)
B.
Transistor Biasing
TYPE
CUTOFF
CONDUCTION
NPN
COLLECTOR
,orr.d
\5/
EMITTER
+v
.,df.Ht^,,
comnoNtl\
,/
CURRENT
\-Y
L
PNP
COLLECTOR
,O"Q
EMITTER
-V
I
,-^6
lggg$'\y'uarr,r
I
CURRENT
r/7
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