Download - Páginas DesdeRadio Electronics December 1992
-
8/18/2019 Páginas DesdeRadio Electronics December 1992
1/7
HA
ROU
T
R
lOO
PERIOD
Sawtooth
-wave
generators
The
555
with external com
nents
can
become
a
trigge
nonl in r (e xponent i
sawtooth
waveform genera
as shown in the schematic
I
2-a.
The circuit
is a modn
7
5
C3 C4
1 SEE
TABLE
1
a
555
+6VTO+15V
8
2
R4
K
/
RESET
TtIRES
rangement
of
functional
blocks
than the others given earlier, il
lustrating
yet
another
manufac
turer's preferred data book
presentation. Neither diagrams
nor data sheets
on
the 555 have
been standardized.
FIG. TRIGGERED SAWTOOTH GENERATORbased on the 555, a,and typical OL
waveform.
b,
FIG.
FUNCTIONAL
BLOCK DIAGRAM
and
pinouttor
the bipolar
555
timer
IC.
Use the
generate sawtooth
waves detect .V RS lIP
missingpulses /4. IL
convert
C
boost voltage
n
more.
THE
POPULAR 5 55 T IMER
rc HAS
been
the star
of three previous
Electronics
Now articles (Sep
tember
1992, page 58, October
1992,
page
69
and
November
1992, page 61.) Just
when
you
thought that all possible ap
plications for that versatile 555
had been
exhausted-surprise
This
article takes the
555
into
new territory-a
sawtooth
gen
erator, a
ramp
generator, a
time-base generator, a frequen
cy meter, and even a
tachometer
for your car.
But that's no t all-there is a
missing-pulse
detector,
and
DC
voltage
doubler,
tripler and
quadrupler. There
are also
negative and high-voltage gen
erators and a DC to ACinverter
you ve
been
following
the
previous articles
and
(we hope)
building
some or all of the cir
cuits
presented in them, you ll
be all set for the circuits pre
sented here. Who
said the
mi
croprocessor
was
the most
versatile IC, anyway?
The las t three articles on the
555 explained
its basic
operat
ing principles: You would have
learned
(or refreshedyour mem
ory) about how to place external
components
so
the timer
func
tions either
as a monostable
or
as tab le mul t iv ibra tor. You
might want to reread the intro
ductory
sections of those arti
cles to
brush
up on th e unusual
features of th e 555. A complete
schematic
of
th e
circuitry
con
tained in the 555 is given as Fig.
2 on page 64 of
the September
1992 issue.
Figure 1 is another functional
block diagram
and
pinout of the
bipolar
555 with
a different ar-
RAY M. MARSTON
62
-
8/18/2019 Páginas DesdeRadio Electronics December 1992
2/7
FIG. 3 LINEAR SAWTOOTHORRAMPwaveform generator based on the 555, a, and
ramp
waveform, b.
FIG. 4-OSCILLOSCOPE TIME-BASE GENERATOR circu it based on the 555, a, and
ramp and ramp brightness pulse waveforms for an oscil loscope s X and Z axes.
monos table multivibrator that
is
triggered by
a n external
square
wave TRIGG E R
pin
2 ob
t ai ne d t hr ou gh c ap ac it or
C2
from
th e
collector of
transistor
Q1. Note that oursur pm S of
th e
5
55 ,
used
in
most of
th e 555
based
circuits
presented earlier
is
unused here.
The
voltage
across
C4
the
timing
component)
is normally
zero,
but whenever th e circuit
is
triggered, C4 charges e
xponen
tially
through resistor R5 and
PERIOD potentiometerR6 to two
th
irds of
th e supply
voltage. At
t h a t time, t he m on osta ble
p
er
iod ends
and
the voltage
ac
r
oss C4 drops abruptly
to
ze r o . T he
o u t p u t
sa w to o th
waveform
Fi g
. 2-b)
is taken
a
cross
capacitor C4 through
buffer
transistors
Q2
and
Q3
an
d LEVEL potentiometer R7 .
Th e
period
of
th e
sawtooth
or
wi
dth can
be
varied
from 9
mi
croseconds
to 1.2 seconds wi th
th e
capacitance
values for C4
listed in Table 1. The circuit s
maxim
um usable repetition
fre
qu
en
cy is
approximately
100
kHz.
Th e generator must be trig
ge
red
by re c t a n g u l a r i n p u t
waveforms
with
short
rise
and
fa ll times. Potentiometer R6
contr
ols
the
sawtooth
period
over a decade, and potentiome
te r R7 contro
ls th e amplitude of
th e
outp
u t waveform.
Figure 3-a. shows a
triggered
linea
r
sawtooth
or
r p
wave
form generator.
Capacitor
C4 is
cha
rged
by a
constant-current
generator that includes Q1. The
output waveform
Fig .
3-b)
is
taken
at the wiper of LEVEL
potentiometer
R6 ,
which
is
cou
pled
to
the
voltage
across
C4
t h
r o u g h
Q2. Note t h a t th e
curved
ramps of Fig . 2-b have
been flattened.
When
a
capacitor
is charged
f rom a constant
current source,
it s voltage
rises
at a predictable
linear rate that
c
an be
e
xpressed
as :
Volts/second
= amperes/farad
By introducing
m or e p ra ct ic al
values
,
altern
ative e
xpr
es
sions
for th e rate of voltage
rise
are:
V/Jl S
=
A/Jl F
or
V/ms =
mA/Jl F
Those
formulas s t
at
e th a t
voltage
rate-of-r ise
can be
in -
Q2
2 3704
OUTPUT
OUTPUT TO
XTIMEB SE
OUTPUT
TO
Z R MP BRIGHTNESS
R3
10K
R
10K
R4
33K
/)
7
6
5
C
.01
4
555
7
5
.01
8
REGUL TED
+9V
TO
+15V
555
8
3
2
Rl
4.7K
REGUL TED
+
9V
/ /
/ /
2
o
R
10K
v
/ l
/1
I
I
I I
... P I
I
I
I
I
I
I
V
I
C
.001
Q
U RE
W VE
INPUT
+
+
C
.001
SQU
RE W VE
INPUT fROM
TR
IGGER
SEL
ECTOR
-
8/18/2019 Páginas DesdeRadio Electronics December 1992
3/7
T h e s aw to ot h cycles of the
cuit
have periods variable
fl
666
microseconds
2/3 mill
cond) to
6 0
m ic r o s eco i
6/100 millisecond).
Periods c an be Increa
.
beyond
those
values
by
incre
in g th e value of C4, or redu
b y r ed uc in g t he value of C4
this
circuit, stable
timing
p
ods
depend
on
a
stable
volt
source.
Fig . 4 -a shows how th e eire
in Fig.
3- a can
be
modiflec
become an oscilloscope t i:
base generator. I t can be t
gered
by
external
square
We
through a suitable
trigger se
t or c ir cu it
.
The r p out
waveform top of Fig. 4- b is
to th e
X plates
of an oscillosc
with a suitable
amplifier
st:
The pulsed
OUTPUT
from
pin
the 555 showni n t he lower .
of Fi g. 4-b) is fed to the CR1
axis to
trace
the
ramps
higher
brightness.
The
s h o rt es t useful
ra
period
th a t
can
be o b t a i
from
the circuit in Fig. 4-a
v
a 0
.001
m i cr of a ra d c a pa c
C3) is
about
5 microsecor
That
value,
when expander
give full
deflection on a n
cilloscope
with
a
ten-dtvis
graticule,
yields a
maxim
timebase
rate
of
0.5
mien
cond per
division
.
The timebase circuit of Ft]
a can synchronize signal.
trigger frequencies up
to at
150 KHz. At
higher frequenc
the input signals
must
be d i
ed by a single- or multi-dec
frequency
divider.
With
that
proach, the timebase car
used
to
view
input signal
megahertz
frequencies.
Figure
5
illustrates
a
si n
but versatile trigger
selector
cuit for the timebase gener
.
.in Fig. 4- a.
Operational an
fier IC1 a f lA741
has
a n
e nc e v ol ta ge
fe d
to
its
n
i n v ert i n g
i n p u t p in 3
TRIGGER LEVEL
potenttorn .
R4. The
signal
voltage is t
fe d to
IC1 s
i nv er ti ng p i
through switch 51 , resistoi
an d
S E N S I T IVY
poten
ttorm
R3 .
Switch 51 selects either
p ha s e o r
out-of
-phase input
nals
from th e
Y-driving an
fier of th e oscilloscope ,
per
6
- 9V
.......- · 9V
R2
lMEG
in g the capacitance value.
T he c ha rg in g
current
in the
Fi g
. 3 -a
circuit can
be
varied
over the range of about 90 mi
cr oamper es to 1
milliampere
with PERIOD potentiometer R5,
thus giving th e
0.01
microfarad
timing capacitor rates-of-rise of
9 volts
per millisecond
to 100
volts per
millisecond.
Each on e-shot or
monos
table
cycle of the 555 e nd s w he n the
voltage
across
C4
reaches
two
thirds of
the supply
voltage.
As
s ho wn i n
Fig. 3-a, the
supply
is
9 vo lt s, so two -thirds of9 volts is
6
volts, the amplitude
of
the
ramp waveforms in Fig. 3-b.
R4
lOOK
TRIGGER
lEVEL
III
lMEG
S
-
TRIGGER
RS ,.........- 1
SELECT lOOK
.
SENSITIVITY
TOY2
PLATE
REGULATED
6V
R7
R4
lOOK
10K
SET 1kHz
FUll
8
4
SCAlE
R6
2
6
10K
Rl
10K
555
3
7
SQUARE
5
WAVE
R2
C2
C3
INPUT
10K
.01
1
12VFROM
Rl
R3
R4
IGNITION
680
SWITCH
Dl
4
.7K 47K
1H756A
8
.2V}.
1
8
4
2
D3
6
3
1N4148
R2
C3
555
lK
1
7
TO
BREAKER
5
POINTS
02
C4
05
02
1N752A
1
1
.01
5.6V\
5VTO 15V
R2
R3
4.7K
8
4
CALIBRATE
2
6
555
SQUARE
7
WAVE
INPUT
1
5
02
C3
creased either by increas in g the
charging c u rr e nt o r by
decreas-
FIG. B ALTERNATIVE ANALOG TA
CHOMETERCIRCUIT to Fig. 6.
FIG. A1-kHz LINEAR·SCALE ANALOG FREQUENCY meter circuit based on the
555.
FIG.
VEHICULAR
TACHOMETER CIRCUIT based on the 555.
FIG.
5
TRIGGER SELECTIONCIRCUIT
for
the Fig. 4 circuit
64
-
8/18/2019 Páginas DesdeRadio Electronics December 1992
4/7
TPUT
UPPL
Y
T
AG
E
TPUT
PPlY
AGE
UT
PPLY
AGE
I
I
I
I
I
I
I
I
...-j---
OUTPUT
3
C2
.01
4
5
I
I
sV
I
I
I
I
+5VTO+15V
,,' +
, +
C
02 ,
C6
R1
10 1F
1
4148
10I-lF
3.3K
8 4
2
01
03
R2
1 4148'
18K
555
au
6
3
\1+
'l.3XSU
7
C5
VOLT
;F-
C
.01
0.1
1 5
;FC2
...
C3
.01
.01
+5VTO+15V
\1 +
+
C5
C7
R1
10 1F
02
10 1F 04
3
.3K
8
4
1 4148
1N4148
2
C4 '
.. 01
..
03
R2
l0I-lF
1N4148
1H4148
au
18K
6
555
3
IV4XS
7
T
+
Val
\1 +
I
6
1
5
; i C
;
F;C2
C3
l0I-lF
0.1
.01
.01
+12V
CLOCK
INPUT
(PU
LSE
OR
S
WITCH
}
+5VTO+ 15V
\1+
R
65
3.3K
10 1F
8 4
2 01 02
R2
1 4148
1 4148
18K
555
OUTP
6 3
/\ 2XSU
C1
7
C
YOU
0.1
10 1F
1
5
* C2
C3
.01
.01
FIG.
~ D C
VOLTAGE QUADRUPLER based on the 555.
FIG. l1
D C
VOLTAGE TRIPLER based on the 555.
FIG. 1O DC VOLTAGE·DOUBLER based on the 555.
FIG. 9 MISSING PULSE DETECTORwith LED or relay output.
ting the
selection
of either the
plus
or
minus
trigger modes .
The
ou
tpu
t of the circu it in Fig.
5 is
coupled di r
ectly to
the
CI
input
of Fig. 4 .
Analog frequency meters
Figure 6 shows
the 555
IC or
ganized as a linear-scale
analo
g
frequen cy
meter with
a full
scale
sensiti
vity of I kHz .
Th
e
circuit's power is obtained from
a regulated 6-volt suppl
y and
its
input signals can be pulses
or
square-wave signals with
peak
to-peak
amplitudes
of
2 vol ts or
greater. Tranststor QI amplifies
this
input
signal
enough
to
tri
g
ger
the 555
. The
output
from
pin
3 is fed to the l
-mtlliamper
e
full -scale deflection moving-coil
meter
MI
through
offse
t-canc
el
ing diode DI and multiplier re
sistor R5 .
Each time the monos
table
multivibrator
is triggered,
it
generates a pulse with a fixed
dura
t
ion
and amplitude. If each
generated pulse has a peak am
plitude
of 6 volts
and
a
period
of
I
millisecond, and the multi
vibrator is triggered a t an inpu t
frequency of 500 Hz, the pulse
will be
high
(at 6 volts ) for
500
milliseconds
in
each 1000 milli
seconds
. Moreover, th e
m n
value
of
output vol tage mea
sured over this period is 500
milliseconds/IOOO
milliseconds
x 6 volts
=
3 volts or half of 6
volts.
Similarly
,
if the
input fre
quency is 250 Hz, the pulse is
high
for
250 milliseconds in
each 1000-millisecond period.
Therefore, the mean
outpu t
voltage
e
qu
a ls 25 0
millise
conds/
1000
milliseconds x 6
volts = 1.5 volts
or
one quarter
of 6 volts .
Thus,
the circuit s
m ean value of
outpu
t voltage,
me
asured
o
ve r
a re
asonabl
e
total number
of
pulse
s , is di
rectly proportional to the repeti
tion
frequency
of the monosta
ble multivibra
to r.
Moving-coil
me
t er s give
m n
readings.
In the circu it of Fig. 6
a
l-rn
tllta
mper
e
meter is
con
nec ted in series w
it
h multiplier
resistor R5, which sets meter 's
sensitivity
at
about
3.4 volts
full-scale deflec
tion. The
meter
is connected to give the mean
ou tput value of th e multi-
-
8/18/2019 Páginas DesdeRadio Electronics December 1992
5/7
4
ATlV
E
LTS
TPUT
55 5 can become
th e
key comp
nent in a missing puls t
t t h a t
closes
a
rela
y I
illuminates a LED if a
norma
expected event fails to OCCl
The 555
is
c onn ec te d as
monostable multivibrator
e
cept that QI is p la ce d a er o
timing
capacitor CI and i
base
is connected to TR IGG)
pin
2 of th e IC through
Rl.
A series of short pulse
switch-derived clock input si
nals from the
monitored
eve
is
sent
to pin 2. The values of I
and
CI were selected so
that
t
natural monos t ab le p er io d
01
TlP A
D
3
H4 4
R3 R4
470
22 K
DC
5
VOL
TS
OUTPUT
C2
C3
.01
SEE
lF
TOO)
a
R3
R4
555
3
loon
47K
6
FR
Eal
7
5
Cl
C3
0.1
.01
r
~ +5VTO +15V
+5VTO+ 5V
R
8
4
3.3K
2 02
R2
3
+
1 H ~ 4 8
-
8K
6
555
;
NJ
10IlF
1 5
VO
..:::C
;::::: C2
; ...C3
01
..... C5
°
.1
.01
.01
H 8
+ lOIlF
-
r - -
~ - - - ~
.
+5VTO+ 5V
Th e
diagram
of Fig. 8 shows
th e
outline
schematic
for an al
ternative
analog
frequency
meter
that
requires neither a
multiplier
resistor
nor
a regu
lated
power
supply. In this
ci r
cuit
OUTPUT pin
3 of t he 555 is
connected to
th e
meter
through
JFET transistor Ql . Configued
as a constant-current generator
through
potentiometer
R3 ,
it
sends a fixed-amplitude pulse
to
the
meter regardless of varia
tions in
th e
supply voltage.
Missing-pulse detector
Figure 9 illustrates how the
FIG. l4 NEON-LAMP DRIVER based on the 555, a, and DC-to-DC converter
v
rectifier and filter replacing lamp, b.
FIG. l5 DC to AC INVERTER based on the 555.
FIG.
l3 DC
NEGATIVE·VOLTAGE GENERATOR based on the 555.
vibrator, and
its
reading is di
rectly proportional to th e
input
frequency.
With
t h e component values
shown the circuit is organized
to read full-scale deflection at I
kHz . To set
up
t he c ir cu it ini
tially, a I-kl-Iz square-wave sig
na l
is fed to
i ts i np ut
an d
full
scale-adjust potentiometer R7
(it controls pulse length) is set
to give a full-scale reading on
the meter.
Th e
full-scale frequency of the
circuit in Fig. 6 can be varied
f
ro m
about 100 Hz to 100 kHz by
selecti
ng th e value of C3. Th e
circuit can read frequencies up
to tens of megahertz by intro
ducing
th e
input
signals
to
the
m o n o s t a b l e m u l t i v i b r a t o r
through either
a single or multi
decade digital divider. The di
viders can
reduce th e
input fre
quencies to values th
at
can be
r
ead on
the meter.
Figure
7 shows ho w
the
cir
cu i
t in Fig. 6 can be modified to
become an
analog .tachometer
or revolutions
per minute
(rpm)
meter for
motor
vehicles. The
circuit is powered by a regulated
8. 2 volt s derived from th e vehi
cle s 12-volt
batterywith
resistor
RI, Ze ner diode DI, capacitor
CI, and the ignition switch. Th e
55 5 is
triggered
by a
signal
from
the veh icle s breaker points con
ditioned by the network of re
sistor R2 , capacitor C2, and
Zener diode D2.
The
50-microampere
moving
coil
me t
er MI, th e rpm indica
tor, is ac tivated from
OUTPUT
pin
3 of the 55 5 through diode D3.
Curren
t is
applied
to
th e meter
throu
gh
s eries- conn ected re
s is t o r R5 nd C A L I B R AT E
po ten t iom eter R6 from the
power supply wh en the
555 s
ou tput is high . But
curren
t is
dropped nearly to zero by diode
DI when the 555 s output is low;
B ot h t he
circuits of
Figures
6
an d
7
ar e
powered from regu
lated sources to ensure a con
s t a n t
p u l
se a m pl itu de a nd
provide
accu r ate , r
ep
eatable
re a
d
ings
fr om
th
e met
er
.
The
me ter is
act
uallya current-indi
cating device , b u t it is con
nec ted
as
a vo
lt
age-read ing
meter with su itable
multiplying
res istors. They ar e R6 and R7 in
Fig. 6 an d R5 and R6 in Fig. 7.
Q)
..Q
Q»
a
z
f l
u
c
e
t3
Cll
W
66
-
8/18/2019 Páginas DesdeRadio Electronics December 1992
6/7
+
vI 1FlIPFlOP
, , , RES
8
4
I , I
I I
I I
I I
I I
THRESHOL
I
, , I
ONTROL
T
3
QYTPUT
V O L T G ~ _ t
, I
T
I
I ( t:: , GE
I I
T R I G G ~ ~
:
:
I I
I I
I I
I , , _ I
L i 1
t ---- ----------
----
--------- ----
J
,
fGROUNO
FIG.
16 F
UNCTIONAL BLOCK DIAGRAM and pinout of the CMOS7555.
the
ICis
slight
lylonger
than
the
repetition
period
of
the
clock in
put
signals.
Thus , each time a short clock
pulse arrives,
Cl
is rapidly dis
charged
thr
ough Ql and
sim
ul
ta
neously
a
one-shot t iming
per iod is
ini tiated through
TR
IGGER
pin 2 of the IC. forcing
OUTPUT pin 3
high.
Before
each
m onostable period can termi
na
te naturally. however. a
new
clock pulse
arrives
and starts a
n ew
timing
period. Therefore
OUTPUT pin 3 remains high as
lo
ng as
clock
-input
pulses
c
on
tinue to arrivewithin
the
preset
time
limits.
If a cl
ock pulse
is
missing
or
its peri
od exceeds the pre-set
lim its. th e monos
tab le
period
will end on
it s
own . If that hap
pens. pin
3 of
the
IC will go low
an
d drive
either
the relay or LED
on.
As
a
result
,
the
circuit
be
comes a missing-pulse detector.
I t will produce a
pulse
output
w
hen an
input
pulse
fails to oc
c
ur
within the
timer
delay.
Missing-pulse detectors like
this
can
automatical
ly warn of
ga
ps
or one or more
missing
pu
lses
in
a
stream
of
pulses at
the input. They are used in com
municat ions systems.
c
on
tinuity
testers
.
and security
systems.
With
the
component
val
ues
shown. the
timer
has a
n
atural per
iod of about
30
sec
onds.
This period
can
be
changed by changing R3
or
Cl
to satisfy specific
needs
.
Voltage
con
ve rte
rs
.
Th
e
555
IC
can
be
instrumen
tal in converting a DCvoltage to
a h
igh
er DC voltage, reversing
the pola
rity
of a DC voltage or
converting it to
an
ACvoltage.
Figures 10 to 15
show
variations
of those c
irc
uits.
Figure 10. for example.
show
s
how the 555 functions in a DC
voltage doubler.
The 555
is orga
n ized as a free-
ru
nning
astable
mu
ltivibrator or square-wave
generator
that
oscillates at
about 3 kHz. (The oscillation
fre
quency
is se t by th e values of
a i.
R2
an
d C2 .)
The
circuit s
output
is se
nt
to the c
apacitor
/
diode voltage-doubler
net
work
made up of C4, Dt C5. and D2.
T
hat netw
ork
produces
a volt
age that is about twice the
sup
plyvoltage. Capacitor
Cl
,
across
the
su
ppl
y, prev
en
ts the 3-kHz
output
of
the
555
from be
ing
fed
back to
th
e IC,
an
dC3 stabilizes
the
circuit
.
The
voltage-doubler circuit of
Fig. 10 will operate from any DC
supply
off
er
in g from 5 to 15
volts .As a voltage
doubler
it can
provide ou t
pu
ts f
rom about
10
to
30
volts. Highe r output volt
ages
can
be
obt
aine
d by
addin
g
more mult
iplier
sta
ges to the
circuit circuit
. Figure 11 is the
schematic
for a DC-voltage trt
pler
that
c
an
supply from 15 to
45 volts.
an
d Fig. 12 is the
sche
matic for a DC voltage
quad
rupler
that
supplies from 20 to
60 volts.
The DC negative-voltage gen
erator
is a
particularl
y
use
ful
555-based converter circuit. I t
supp
lies
an
ou
tpu
t vo
ltag
e t
hat
is
almost equal
in ampli tude
but opposite in polarity to that
of
th
e IC
suppl
y.
This
circuit can
pro
vide bo
th
positive
and
nega
tive
voltages
for po
wering
op
amps
and
other
IC s
with
dual
.power
requirement
s
from
a
posit
ive supply.
The
DC nega
tive-voltage generator in Fig. 13,
like that shown inFig . 10, is a 3
kHz oscillator that drives a volt
age-doubler o
utput
stage made
up
of C4, C5.
rn.
and D2.
Figures 14-a and 15
show
DC
to AC inverters
that change
in
put DC voltage to output AC
voltage by
means
of
transformer
coupling
.
The
AC voltage from
these
inverters
needs
no
further
conditioning.
and it can be con
verted
back
into
higher
DCvolt
ages w
ith the addition
of only a
half- wave rectifier
and
a capaci
tor filter.
The inverter
shown in Fig. 14
a
can
drive a
neon lamp
with
its
AC output. If the lamp and re
sistor
R4
are
replaced by
the
di
ode and capacitor
filter
as
shown in
Fig. 14-b,
the
AC out
put
can be
converted
back
to a
low-current high-voltage DC
output. For e
xample
,
with
a 5
to 15-volt DC input. the inverter
can
produce an output
of sev
eral hundred volts DC.
The 555 in
Fig. 14-a is config
ured as
a 4-kHz oscillator and
it s square-waveoutput from
pin
3 is fed back to the
input
of
au
dio
transformer Tl
through re
sistor
R3.
Transformer Tl has
the
necessary ratio
of
primary
to
secondary
turns
to
produce
the
desir
ed output voltage. For ex
ample. with a lO-volt
supply
and
a 1:20
turns ratio
on
TI the un
loaded output of Tl will be
200
volts , peak.
The
DC-to-AC
inverter sche
ma
tic of Fig. 15
produ
ces
an
AC
outpu
t at
line
frequency
and
voltage.
The 555
is configured
as a
low
-frequ
ency oscillator
.
tunable over the
frequenc
y
ra n g e
of
50
to 60
Hz by
FR
EQUENC
Y
potentiometer
R4 .
The 555
feeds
its
output
(ampli
fied by Ql
and
Q2) to the input
tu
rn
s of transformer T I, a re
verse-connected filam
ent
trans-
-
8/18/2019 Páginas DesdeRadio Electronics December 1992
7/7
E N Engineering
dmart
Rates:
Ads are
Y x
Ja
One insertion
995 each. x insertions 950
each
insertions
925 each. Closing date same
as
regular rate card . Send order with remi
Computer
Admart,
Electron ics Now Magazine, 500-B Bi-County Blvd ., Farmingc
11735 . Direct telephone inquir
ies
to Arline Fshman ,
area
code·1·516·293·30
·5 6·293·3 5 Only
1 Computer
ads are
accepted
for
this
dman
68
Chip experts agree with Dr. Munk.
TECl s PC based microcontroller devel
opment tools are the most cost effective
for veterans or beginners .
6805PRIMER FOR BEGINNERS. • • • • • • • • • SI9S00
68OSI68HC05I68HClI CROSS
ASSEMBLERS
. $99.00
68OSI68HCOS SIMULATOR DEBUGGERS 99.00
687OSP3,PS,U3,US,R3,RS PROGRAMMERS FROM
349.00
68HC705/68HC805 PROGRAMMERS FROM $395.00
COMPLETE PC BASED
DEY.
SYSTEMSFROM -149.00
681ICOS 68HCll REALTIME
EMUlATORS
FRQ. \1 895.00
T E ~
CALL TOLL
FREE
1·800·336·8321
The Engineers Collaborative, Inc.
Rt 3 Box 8C, Barton, VT 05822 USA
TEL:(802)525:3458 FAX:(802)525·3451
CIRCLE184ONFREE
INFORMATION
CARD
f
ormer
with the
necessary
step
up
,turn s ratio. Capacitor C4
and
coil Ll filter
the
input to T'I,
assuring
that
it
is effectively a
sinewave.
A CMOS version of the .
The standard bipolar 555
timer IC is sti ll
one
of the most
popular and versatile IC's today,
bu t it has some drawbacks that
were overcome by a CMOS ver
sion. For example,
the
555
will
n
ot
operate from voltages less
than
about 5 volts. Moreover, it
typically draws 10 milliamperes
of quiescent current when run
from a I5-volt supply. This
rather large current drain
makes
it
unsatisfactory
for
most battery-powered
circuits
.
In addition to those short
comings, the
555 produces
a
massive 400
-milliampere cur
rent
spike
from
the
supply
as
it s
output is switched from one
state
to
the
other. A
spike,
last
ing only a fraction of a microse
cond, can cause lost bits
in
digital circuits near the 555 or .
powered from
the
same supply.
MIDI
PROJE TS
BP182-MIDI
interfacing
enables
an
y so
equipped ins
trum
en ts, regardless of theman
ufacturer, to be easily connected together and
us
ed
as
asyst
em
with
easy
c
om
puter
co
ntro
l
ofth
ese
musicsyst
em
s.
Co
mbine acom
pu
ter
and
s
om
eM
ID
I ins
trume
nts
and
y
ou
can
ha
ve
whatisvirtually aprogrammableorch
estr
a.To
order y
ou
r
cop
y send 6.9 5 plus 2.50 for
shipping
intheU.S. toEectronic
Technology
Today
Inc., P.O.
Box 240,
Massapeq
ua Park,
NY 11762-0240.
The
CMOS ver
sion
of
th
e
555
timer,
also
able
to operate in
both monostable and
astable
modes
, is
known
generically
as
the 7555. Figure 16
shows
the
functional
block diagram
and
pinout
of the 7555. This
can
be
compared with the functional
block diagram ofFig
1.
Note
that
the
pinout is identical.
Harris
Semiconductor s
ver
sion ofthe 7555, for example, is
des igna ted the
ICM7
555.
In
commonwith all other 7555 's, it
will run from a
2- to
I8-volt
DC supply. Notice that
the
re
sistors in
it s
internal voltage di
vider are 50 K rather
than
the
5K of the 555 . Other sources of
the
7555 are Maxim (ICM7555)
and Sanyo (LC7555).
Supply current to the 7555 is
typically only 60 microamperes
when
run from an I8-volt
sup
ply.In
addition,
typ ical
TRIGGER,
THRESHOLD,
and
RESET
currents
are 20 picoamps, orders of mag
nitude
lower
than those
of the
bipolar 555 .Those low currents
permit the use of higher imped
ance timing elements for longer
HIGH
POWER
UDIO
MPLIFIER
CONSTRUCTION
BP277-He re s
background
and practica
l
sign information
on
high power audio arr
fiers
capa
bleof
300
± 400
watts
r.m.s.
V
fi
nd MOSFET
and b
ipo
laroutput transistor
inverting
and
non-inverting
circuits
.
To 01
your
copy
send 6.25 plus
2.50for
shiPI
in
the
U.S. to Electronic Technology To
Inc.,
P.O
.
Box
240, Massapequa Park,
11762-0240 .
RC
time
constants. The
7
can
be organized to time ou
periods from microsecond:
hours.
Table 2 compares
the ch
i
teristics
of the 7555 to
thos
the
555.
The 7555 permits:
• Lower supply
current
• Wider
supply
voltage rang
• Lower
power dissipation
• Lower
current
spikes in (
put transitions
•
Higher
switching
freque
performance
These improvements mus
balanced against
the
htg
cost of
the
7555. The
7
should be specified only if:
•
is to be used in a batt
powered circuit where po
economy is critical
• Available power is 5 volt:
less (too low for the 555)
•
is to be in digital circu
whose
signal
output
coule
degraded
by noise .
The 7556 is the dual CIv
counterpart of the
bipolar
E
The 7555 can directly rep]
any 555 in all the circuits ]
sented
in
this
series.