Epson L90P - TM Two-color Thermal Line Printer Manual de usuario descargar pdf (Pagina 89)

Cost Control Circuits,"

a section of Seminar

Applications

booklet No. 671.9, published by

General Electric's

Semiconductor

Products

Department

(Electronics

Park, Syracuse,

New York 13200).

Referring to Fig. 3, we find that the de-

sign

features an npn photo- Darlington

de-

vice (Q2)

controlled by a conventional npn

bipolar

transistor, Ql.

Resistors 121 and R2

form a

voltage divider which establishes

a net positive

charge across CI when the

circuit is in its off (nonconducting)

state.

Both R3 and R4 serve as base

current -

limiting resistors.

The

load is

a conventional

incandescent lamp while a 12

-volt

d.c.

source

furnishes

circuit power.

operation, a momentary high- resistance

contact (such

that

caused

a person's

touch) across the

control terminals applies

base bias current

through resistor

R3, permitting QI

to conduct and apply

Cl's charge to Q2's base

through R4.

Thus,

Q2 is switched to

a conducting state, light-

ing lamp

Il.

Q2 is held "on" by

light cou-

pled from It to its photo-

sensitive surface.

Under

these conditions, most

of the supply

voltage

is dropped

across 11

that

very

little

voltage

is applied

to voltage-

divider

-R2. As

result,

CI's

charge is

near

zero and

its

d.c. potential is less

than

that

between Q2's base

and El's negative

termi-

nal due to

internal

current

flow. If,

at this

time, another momentary contact

made

across

the

control terminals, Ql again

con-

ducts, and Cl, discharged,

acts as an

effec-

tive short across

Q2's

base

and emitter

termi-

nals. This switches Q2 back

to a

noncon-

ducting (or high- resistance)

state and

turns

off

II.

The circuit cycles between its

and

off

states

each time the

control terminals

are

touched. If

steady contact is

made,

the

circuit

recycles

automatically,

flashing

the

lamp at a

rate

determined primarily

the bias circuit's R -C time constant

con-

junction with II's thermal lag.

With neither layout nor lead

dress

criti-

cal,

the circuit may be assembled

bread-

board

fashion

for

experimental

study

or on

small

chassis or board.

Regardless

con-

struction

technique,

however,

care

must

taken

to provide adequate light

coupling

between 11 and Q2's photo- sensitive

elec-

trode (the

curved surface).

The

completed

unit may

be mounted in a

wooden,

plastic,

or metal

cabinet,

depending

application

needs.

Industry

Items. A new

series of

low

-cost

complementary

silicon power

transistors

has

been

introduced by Motorola

Semi-

conductor

Products, Inc.

(P.O. Box

955,

Phoenix, Arizona

85001). Identified

types

2N5190

through 2N5195,

the

six new

units

April, 1969

The

remarkable

difference

about

Pearce -Simpson's

Guardian

23 and

Guardian

23 -B:

they work.

What's the

most important

thing

about

a CB

base -station

and mobile -unit

combination?

When some guy

says something,

the guy at

the other

end should

be able to hear

it.

other words,

"10

-4"

should sound

"10

-4"

- not "snap,

crackle and

pop."

So the great

thing about the

Pearce

Guardian

23 and

Guardian 23 -B

(in fact all

Pearce

-Simpson's

radios)

is that the transmitters

transmit and

the receivers

receive.

Don't

laugh.

Not every

CB manufacturer

can

make

that statement.

you want to

get

technical,

here's the

explanation.

Pearce -Simpson's

exclusive

HetroSync circuitry

sharpens

transmitted signals.

High

level saturation

limiting

provides

automatic

speech clipping.

And the Superhet

receiver

hears

signals

that ordinary

sets distort or

fade.

Guardian

23 comes

with palm microphone,

mounting cradle,

and

DC power cords.

Guardian

23 -B comes

complete

with

built

-in, all

transistor,

solid state pre -amplifier

that

lets you

stay a comfortable

distance from your mike

and

still broadcast

loud and clear.

And

Pearce -Simpson's

new

SuperMod

desk mike

available

as an option.

Guardian 23 and Guardian

23 -B-

Pearce- Simpson's

super

twins.

They

work.

For more details on all

our New

CB Radios

write

Pearce

-Simpson,

Inc., Dept. PE -469,

P.O. Box 800,

Biscayne Annex,

Miami, Fla. 33152

Pearce-

Simpson

Division of

GLAmINNG

Corp.

CIRCLE NO. 38

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