Epson L90P - TM Two-color Thermal Line Printer Manual de usuario descargar pdf (Pagina 33)

LI

SOmH

CI

.022yF

DI

C2 NI91

1000

pF

SI

R4

4.7K

02

R2

IOK

VI

R3

RS

20K

4.7K

BI

9V

C3

1000

p1<

S2

/'

OUTPUT

82

0

SD

E

81

01

Q2

Fig.

3. With

the

addition of a

MOSFET,

only

positive

-going

pulses

from

Q1

are

used. Phase

splitting

then

provides

a

repetition

rate

of

400

pps of either polarity.

PARTS

LIST

B1 -9

-volt

transistor battery

C1-

0.022 -µF, 109

-voll illylar capacitor

C2, C3-1000-pi;

silver -mica or polystyrene ca-

pacitor

1.1- 1.A'191 diode

1,1

50ml1,

high

-Q

inductor,

powdered

-iron

Core

01-

UniJunetio,

transistor !Texas Instruments

type 7 1S43

Q2- MOSFET

transistor

(Motorola

type

:11PF157 *)

R 1-

56,000 -ohm

R2- 10,000 -ohm,

All

resistors

1/3- 20.000

-ohm ,A-watt

R4,

R5-

4700

-olio,

SI- s.p.s.t. switch

52- -s.p.d.t.

switch

*Available

from

Robert .1. Glassman.

29

Hamp-

ton Rd.. Massapequa, X.I'. 11758.

$1.30

each,

postpaid.

ly

at

B2. Other

than this,

ringing

is

negligible.

For

the component

values

giv-

en,

pulse

amplitudes are approximately

equal.

Because the

inductor is

effectively

in

parallel

with

the output,

differentia-

tion

occurs,

with the result that

both of

the

output

pulses are quite narrow. The

simple

arrangement of two diodes and a

s.p.d.t.

switch

makes it possible

to have

either

positive

or negative

pulses at the

output.

Performance

with this

circuit is quite

good

provided

it is not

too heavily load-

ed. (That

is, it should

preferably

be used

with a

fairly

high- impedance

load.)

If

resistors R2 and

R3

are sufficiently

high

in value, and

loading is very

light,

the

amplitude

of

the output

pulse can

ap-

proach the level of the power-

supply po-

tential.

In the

circuit shown in Fig.

3,

only

the

positive -going

pulses

from B2

of

Q1

are used since MOSFET Q2 is

an n -chan-

nel

type.

Negative pulses

are suppressed

by diode D1. The

type MPF157

MOSFET

was chosen

for the phase

splitter

be-

cause

of its

ability to

handle

the signal

level

and its excellent

high-

frequency

re-

sponse, rather than

because

of

its high

input impedance. The latter

does permit

loading

of the UJT almost entirely

with

resistors, however.

With this circuit,

differentiation

oc-

curs

in the C2

-R2 circuit as well as in

Li. Repetition rate is

about

400

pulses

per second, while pulse duration is

about

12 /sec and output

amplitude

is

3 volts.

Amplitudes

of the positive and negative

pulses

are

equal.

When

working with

any

MOSFET,

take

care that you

do

not

touch the

isolated

gate

lead

since any static charge can

de-

stroy the fine gate insulation

within the

semiconductor.

Keep

the three

leads in

direct electrical contact

until the

MOS-

FET

is

soldered into

the circuit.

If a slower pulse rate is

desired, in-

crease the value of

either

RI

or

Cl,

in small steps,

until the desired rate is

obtained.

April, 1969

35

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