HP 721A Manual del propietario

721A

SERIALS

PREFIXED:

024

OPERATING

AND

SERVICING

MANUAL

PRINTED

1/61

00010-2

MODEL

721

POWER

SUPPLY

SERIALS

PREFIXED:

024

HEWLETT-PACKARD

COMPANY

1959

1501

PAGE

MILL

ROAD,

PALO

ALTO,

CALIFORNIA,

U.S.A

printed

1/61

00010-2

Model

721A

SPECIFICATIONS

REGULATED

OUTPUT

VOLTAGE:

volts

dc,

continuously

variable

FULL

LOAD

OUTPUT

CURRENT:

150

over

entire

voltage

range.

LOAD

REGULATION:

With

the

meter

monitoring

voltage,

the

change

output

voltage

from

load

full

load

less

than

30mv

whichever

the

greater.

LINE

REGULATION:

The

change

output

voltage

for

change

from

nominal

line

voltage

±10%

less

than

±0.

±15

whichever

greater.

RIPPLE

AND

NOISE:

Less

than

150

^j.v

rms.

OUTPUT

IMPEDANCE:

Less

than

ohm

series

with

less

than

;ih

with

meter

monitoring

voltage.

METER

RANGES:

Full

scale

indications

of:

ma,

100

ma,

300

ma,

and

OVERLOAD

PROTECTION:

Maximum

current

selected

switch

four

steps,

ma,

ma.

100

ma,

225

ma.

OUTPUT

TERMINALS:

Three

banana

jacks

spaced

3/4"

apart.

Positive

and

negative

terminals

are

isolated

from

chassis.

maximum

400

volts

may

connected

between

ground

and

either

output

terminal.

POWER:

115/230

volts

±10%,

cps,

watts.

WEIGHT:

Net

lbs.,

shipping

lbs.

DIMENSIONS:

7”

wide,

4-3/8”

high,

5-1/4”

deep.

Model

721A

SECTION

III

SECTION

CONTENTS

GENERAL

INFORMATION

Page

Manual

Content.

1-2

General

Description.

1.-3

Inspection.

1-4

Power

Cable.

230

Volt

Operation.

OPERATING

INSTRUCTIONS

2-1

Operating

Controls

2-2

Meter

Range

Switch.

2-3

Short

Circuit

Current

Switch

2-4

Series

Operation

Supplies

2-5

Parallel

Operation

Supplies

THEORY

OPERATION

.Ill

3-1

...

Ill

........

Ill

.Ill

3-4

.Ill

•“

.Ill

3-0

Frequency

Response

Control.

.Ill

MAINTENANCE

4-1

Contents.

4-2

General

Maintenance

Information.

4-3

Trouble

Localization.

4-4

Checking

Voltage

Regulation

and

Ripple

4-5

Measuring

Internal

Impedance.

4-6

Meter

Calibration.

4-7

Setting

Maximum

Output

Voltage.

4-8

Calibrating

the

Short

Circuit

Current

Circuit

4-9

Replacing

the

Power

Transistor.

4-10

Replacing

Diodes

CR5,

CR6

and

CR7.

TABLE

REPLACEABLE

PARTS

5-1

Table

Replaceable

Parts

-5

Model

721A

Sect.

Page

SECTION

GENERAL

INFORMATION

1-1

MANUAL

CONTENT

The

material

for

this

instruction

manual

written

five

sections:

Section

contains

material

general

nature.

Section

explains

how

operate

the

power

supply.

Section

III

explains

how

the

circuit

operates.

Section

covers

maintenance

and

trouble

shooting

procedures.

Section

table

replaceable

parts.

1-2

GENERAL

DESCRIPTION

The

Model

721A

Power

Supply

produces

regulated

voltage

adjustable

from

volts.

The

supply

makes

load

circuit

performance

inde¬

pendent

external

power

supply

influences.

The

supply

has

very

low

source

impedance

and

ex¬

cellent

regulation

against

change

line

and/or

load.

This

supply

especially

useful

source

power

for

transistor

circuits.

circuit

provided

which

electronically

limits

the

maximum

output

cur¬

rent

that

can

supplied

four

nominal

values

selected

front

panel

switch.

This

feature

helps

prevent

the

accidental

destruction

expensive

transistor

should

accident

occur

that

would

nor¬

mally

allow

excessive

current

flow

through

it.

The

SHORT

CIRCUIT

CURRENT

switch

can

set

the

value

which

closest

above

the

normal

operating

current.

The

supply

will

automatically

limit

the

peak

current

flow

this

nominal

value

regardless

the

load

resistance.

Built-In

Metering

built-in

meter

allows

either

output

voltage

current

monitored

selected

the

METER

RANGE

switch.

Isolated

Output

The

power

supply

has

both

output

terminals

in¬

sulated

from

chassis

ground.

Either

terminal

may

grounded

number

supplies

may

con¬

nected

series

obtain

higher

voltages.

Insula¬

tion

such

that

the

supply

may

operated

high

400

volts

off

ground.

Parallel

Operation

Parallel

operation

two

supplies

pos¬

sible

due

the

unique

electronic

current

limiting

switch.

The

supplies

will

each

contribute

only

the

number

milliamperes

selected

the

SHORT

CIRCUIT

CURRENT

switch.

The

individual

supplies

may

loaded

approximately

225

with

some

reduction

ripple

and

regulation

characteristics.

Reliability

The

Model

72XA

Power

Supply

very

compact,

and

has

low

internal

losses,

which

are

made

possible

fully

transistorized

circuitry.

The

trouble

free

characteristics

transistors

together

with

the

use

high

quality

components

throughout,

will

result

minimum

maintenance.

1-3

INSPECTION

When

the

Model

721A

received,

inspect

for

damage

received

transit.

Operate

the

instrument

make

certain

that

functioning

satisfactorily.

damage

evident,

the

procedures

outlined

the

“CLAIM

FOR

DAMAGE

SHIPMENT”

page

this

manual.

1-4

POWER

CABLE

The

power

cable

consists

three

conductors

and

terminated

three-prong

male

connector

rec¬

ommended

the

National

Electrical

Manufac-

Sect,

Page

00010-2

Model

72iA

turers’

Association.

The

third

contact

offset

round

added

standard

two-blade

connector

which

grounds

the

instrument

chassis

when

used

with

appropriate

receptacle.

use

this

NEMA

connector

two-contact

receptacle,

three-

prong

two-prong

adapter

should

used.

When

the

adapter

used,

the

third

contact

terminated

short

lead

from

the

adapter

which

can

con¬

nected

the

outlet

mounting

box

order

ground

the

instrument

cabinet.

1-5

230

VOLT

OPERATION

This

instrument

may

easily

converted

from

115

230

volt

operation

removing

two

jumpers

and

installing

one

jumper.

This

changes

the

dual

115

volt

primary

windings

from

parallel

series

connection.

Refer

the

schematic

diagram

and

Figure

4-6

for

details.

The

main

fuse

(FI)

should

changed

(see

Table

Replaceable

Parts

for

the

correct

type

fuse).

Model

721A

Sect.

Page

SECTION

OPERATING

INSTRUCTIONS

2-1

OPERATING

CONTROLS

Figure

2-1

shows

the

function

o'Peach

the

controls

and

normally

self

explanatory.

There

are

few

additional

facts

considered

which

may

im¬

portant

some

applications.

2-2

METER

RANGE

SWITCH

This

switch

connects

precision

internal

resistors

into

the

meter

circuit

obtain

the

various

voltage

and

current

ranges.

When

measuring

current,

the

meter

shunt

resistor

series

with

the

output

terminals.

The

meter

shunt

resistance

adds

the

source

impedance

the

supply

which

normally

less

than

0.2

ohm

series

with

less

than

30p,h.

The

Table

2-1

lists

the

additional

resistance

for

each

current

range.

Where

minimum

source

im¬

pedance

important,

the

METER

RANGE

switch

should

left

one

the

voltage

ranges

except

when

actually

measuring

load

current.

accidental

short

circuit

can

damage

the

meter

one

the

lower

ranges

and

the

SHORT

CIRCUIT

CUR¬

RENT

switch

set

high

value.

Short

time

overloads

two

times

full

scale

will

not

damage

the

meter

movement.

2-3

SHORT

CIRCUIT

CURRENT

SWITCH

This

switch

controls

circuit

which

adjusts

the

peak

current

output

capability

the

supply.

The

cali¬

bration

nominal.

The

actual

value

may

read

shorting

the

supply

and

reading

the

value

the

monitor

meter.

The

clipping

action

gradual.

Consideration

should

given

this

characteristic

pulse

type

circuits

are

being

supplied.

The

average

current

may

within

the

supply

rating

(150

ma)

but

peak

currents

may

high

enough

cause

the

supply

clip.

the

switch

set

low

peak

value

this

situation

can

occur

low

average

current

levels.

When

pulse

circuits

are

being

supplied,

this

switch

must

set

value

which

greater

than

the

peak

cur¬

rent

requirements

the

circuit.

The

output

circuit

has

jif

capacity

shunting

it,

which

helps

supply

high

current

peaks,.providing

they

are

extremely

short

duration.

The

value

any

external

capacity

added

will

improve

the

peak

current

capability

but

will

decrease

the

safety

provided

the

SHORT

CIRCUIT

CURRENT

switch,

since

the

external

capacity

will

provide

high

surge

currents.

The

surge

currents

may

destroy

external

components

before

the

average

current

increases

sufficiently

inside

the

supply

cause

the

limiting

circuits

operate.

TABLE

2-1.

ADDITIONAL

INTERNAL

RESISTANCE

Monitor

Meter

Current

Added

Internal

Range

(f.s.)

Resistance

ohms

3.33

ohms

100

ohm

300

0.33

ohm

2-4

SERIES

OPERATION

SUPPLIES

When

operating

the

Model

721A

voltage

than

few

volts

off

ground

careful

not

accidentally

short

circuit

the

external

circuits

the

Model

721A

subjected

voltages

reverse

polarity

high

voltages

the

same

polarity.

will

instantly

destroy

the

electrolytic

capa¬

citors

the

power

supply

and

possibly

the

transis¬

tors.

When

number

supplies

are

operated

series,

sure

the

SHORT

CIRCUIT

CURRENT

switch

each

supply

set

the

same

(or

higher)

value

than

maximum

peak

current

desired.

Sect.

Page

Model

721A

METER

range

SHORT

CIRCUIT

CURRENT

VOLTAGE.

ADJUST.

METER

READS

OUTPUT

VOLTS

CURRENT

SELECTED

METER

RANGE

SWITCH

SELECT

MAXIMUM

CURRENT

OUTPUT

SELECT

METER

FUNC¬

TION

AND

RANGE

Note:

Meter

shunt

resistance

series

with

load

ma.

Leave

volts

for

lowest

(rated)

internal

impedance.

POWER

Output

increases

with

clockwise

rotation

CONNECT

LOAD

(+)

AND

(-)

TERMINALS

Either

terminal

may

connected

grounded

cabinet

terminal.

(+)

and

(-)

terminals

may

operated

±400

volts

from

cabinet

ground

ON/OFF

ADJUST

OUTPUT

VOLT¬

AGE

CURRENT

CABINET

GROUND

CAUTION

NOT

SUBJECT

POWER

SUPPLY

OUTPUT

TERMINALS

VOLTAGE

SOURCE

REVERSE

POLARITY.

WILL

DE¬

STROY

TANTALUM

CAPACITOR

CONNEC¬

TED

ACROSS

THESE

TERMINALS

-S-445

Figure

2-1

model

721A

Power

Supply

Operating

Controls

Model

21A

Sect.n

Page

2-5

PARALLEL

OPERATION

SUPPLIES

Two

supplies

may

operated

parallel

supply

loads

excess

150

ma.

Set

the

SHORT

CIR¬

CUIT

CURRENT

switch

the

first

unit

maximum

(225

ma).

The

first

supply

becomes

225

con¬

stant

current

source.

The

supply

will

furnish

this

amount

current

without

harm,

however

the

regulation

and

ripple

specifications

can

longer

guaranteed.

Adjust

the

voltage

of"

the

second

supply

the

same

the

first

unit

before

con¬

necting

them

together.

The

second

supply

can

made

load

advancing

the

VOLTAGE

ADJUST

control

slightly

clockwise.

The

second

supply

will

furnish

the

regulation

action

the

limit

its

capacity

(150

ma).

The

second

supply

may

loaded

beyond

the

150

point

maximum

225

ma,

making

total

450

available.

The

usefulness

this

extra

out¬

put

capacity

depends

the

performance

required

from

the

supplies.

The

supplies

become

constant

current

sources

when

the

SHORT

CIRCUIT

CUR¬

RENT

limiting

circuit

operating.

this

point

the

ripple,

source

impedance

and

voltage

regulation

specifications

cannot

apply.

Operation

than

two

instruments

parallel

not

recommended

the

total

current

capacity

becomes

greater

and

accidental

gross

misadjusted

controls

may

result

instability.

THEORY

OPERATION

3-1

GENERAL

CIRCUIT

DESCRIPTION

The

regulation

accomplished

manner

which

similar

vacuum

tube

type

circuits

power

type

transistor

series

with

the

rectified

output

and

the

load,

acts

variable

resistor

which

maintains

constant

output

voltage

current

selected

the

controls.

The

power

transistor

controlled

two

stage

amplifier

which

amplifies

any

changes

the

relative

amplitudes

the

output

voltage

and

the

reference

voltage.

The

electronic

short

circuit

current

limiting

switch

unique

feature

which

not

normally

found

the

vacuum

tube

counterpart

the

supply.

This

circuit

senses

any

increase

current

above

pre-selected

value

and

turn

controls

the

conduction

the

power

transistor

limit

the

peak

current

the

pre-selected

value.

detailed

description

the

Power

Supply

and

its

operation

follows.

Refer

the

schematic

diagram

identify

the

various

com¬

ponents.

3-2

MAIN

AND

AUXILIARY

SUPPLY

DESCRIPTION

Transformer

supplies

voltages

the

main

and

auxiliary

supplies.

The

main

supply

consists

silicon

rectifiers

CR1

and

CR2

and

capacitor

C2.

This

supply

furnishes

about

volts

the

regulator

circuit.

Silicon

rectifier

CR3,

CR4

and

capacitors

C3,

and

supply

-20

volts,

which

required

for

operation

the

control

circuits.

Regulator

transistor

acts

variable

series

resistance

lower

the

voltage

the

desired

value,

set

the

front

panel

VOLTAGE

ADJUST

control

R19.

conducts

current

when

the

base

volt¬

age

goes

negative

with

respect

the

emitter.

3-3

REFERENCE

VOLTAGE

CR7

reversed

biased

diode

operating

the

break-down

condition.

The

diode

maintains

con¬

stant

nominal

volts

across

itself,

establishing

constant

reference

voltage

between

the

negative

out¬

put

lead

and

the

base

Q4.

emitter

follower

which

repeats

the

reference

voltage

its

emitter

terminal,

less

constant

internal

base-

emitter

drop

about

0.2

volt.

The

voltage

the

emitter

has

low

source

impedance,

making

insensitive

normal

variations

current

flow.

The

output

voltage

from

the

(+)

output

bus

sampled

VOLTAGE

ADJUST

control

R19

which

causes

current

flow

through

R20

and

R21.

The

regulator

action

maintains

constant

current

through

R19

and

R20.

3-4

REGULATION

CYCLE

DESCRIPTION

Assume

the

output

level

has

been

set

with

R19

and

some

change

has

occurred

which

causes

the

output

voltage

rise.

The

voltage

the

base

that

which

would

appear

across

forward

biased

diode

and

essentially

constant.

The

electron

current

flow

through

R20

constant.

When

the

output

voltage

rises,

part

the

normal

electron

flow

into

the

base

diverted

through

R19.

The

reduced

base-emitter

electron

current

reduces

the

collector-emitter

electron

current

flow

from

R17

factor

approximately

100.

Since

fewer

electrons

flow

into

the

collector

from

R17

and

thte

volt

bus,

the

voltage

R16

goes

negative

direction.

This

causes

electrons

flow

through

R16

into

the

base

Q2.

Increased

base

emitter

current

causes

much

higher

collector-emitter

current.

Increased

collector

current

raises

the

voltage

which

reduces

the

base

emitter

current

Ql.

The

reduced

base-emitter

current

increases

its

collector-emitter

resistance

electron

current

flow,

hence

increases

its

collector

emitter

volt¬

age

drop.

That

voltage

drop

increases

just

enough

compensate

for

the

initial

output

voltage

rise,

maintaining

the

output

voltage

constant

level.

3-5

SHORT

CIRCUIT

CURRENT

LIMITING

CIRCUIT

The

current

flow

the

load

sensed

voltage

drop

across

Rll

ABCD.

Silicon

diode

CR5

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