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


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


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


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-


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


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-


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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.

páginas desderadio electronics december 1992

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