HP 6236A, 6237A Operating And Service Manual

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HP

Part No. 5950-1737

TRIPLE

OUTPUT

POWER

SUPPLY

MODELS

6236A

AND

6237

A

OPERATING

AND

SERVICE

MANUAL

FOR;

MODEL 6236A, SERIALS 1507A-00141

AND

ABOVE

MODEL 6237A, SERIALS 1507A-00101

AND

ABOVE

*

For Serials above 1507A-00141or1507A-00101,

a change page may be included.

Hewlett-Packard

Printed: February 1975

tions

in additiolatothe

standard

104-127Vac

47-63Hz

unit

andisfurnished

withapermanently

attached

5-foot

3-wire

grounding-type

line

cord.

1-8 SPECIFICATIONS

1-9

Table

1-1

lists

detailed

specifications

for

the

power

supply.

SECTION I

GENERAL

INFORMATION

I

INTRODUCTION

1-1

1-2 This manual covers

two

triple

output

power

supply

models,

the

6236A

and

the

6237

A. Both models are

com-

pact

general

purpose

bench

supplies

that

are

particularly

useful for

powering

developmentalICcircuits,

both

linear

and

digital. Unless

one

modelorthe

otherisspecifically

identified,

all

informationinthis

manual appliestoboth

the

6236A

and

the

6237

A.

1-10 OPTIONS

---

CAUTION

---

Carefully read SectionsIIand

IIIofthis

manual before

attempting

to operate the

power

supply.

1-11

Options

are

factory

modificationsofa

standard

instrument

that

are

requestedbythe

customer.

The

follow-

ing

options

are available

for

the

instrument

coveredbythis

manual.

OPTION NO.

OESCR

IPTION

---CAUTION---

1-13 ACCESSORIES

The

user can

convertaninstrument

from

one

line voltage

optiontoanother

by following

the

instructionsinPara-

graph 3-4.

1-12 Before

the

supplyisshipped

from

the

factory,

an

internal line voltage

selector

switchisset

and

the

proper

fuse installed

for

the

line voltage specifiedonthe

order.

A

label

on

the

rear

heat

sink identifies this line voltage

option.

Input

Power:

87-106Vac,47-63Hz,
single-phase.
Input

Power:

191-233Vac,47-63Hz,
single-phase.
Input

Power:

208-250Vac,

47-63Hz,

single-phase.

220

240

100

Before

applying

powertothe supply, make cer-

tain

that

its line voltage selector switch (S3)

is

set

for

the line voltage to be

used.

(See

CA UTION

notice

in Paragraph 3-2

for

additional

information

on S3).

1-5

All

controls,

meters,

and

output

terminals

are loca-

tedonthe

front

panel.

Two

single-turn

potentiometers

con-

trol

the

+6V

(or

+18V)

and

±20V

outputs.Athree-position

meter

switch selects

oneofthe

supplies for displayofits

voltage

and

currentontwo

dual-range meters.

The

+6V

(or +18V)

and

±20V

outputs

share a

common

output

ter-

minal which

is

isolated

from

chassis

ground.

1-3 DESCRIPTION

1-4 Both models have a dual

outputof0to±20

volts

at0to

0.5amps.

The

voltagesofthe

two

20-volt

outputs

are

adjusted

by asingle

front-panel

control

and

track

one

another

within1%.

The

+20V

and

-20V

outputs

can

also be

used

in

series for a single 0to40V

0.5A

output.

The

third

output

differsinthe

two

models

andis0to+6 voltsatup

to

2.5ampsinthe

6236A

and0to

+18

voltsat0to1

amp

in

the

6237

A /

1-6

All

outputs

are

protected

against

overloadorshort-

circuit

damage.

The

+18V

outputinthe

6237Aand

the

±20V

outputsinboth

models are

protectedbycircuits

which limit

output

currentto110%ofits nominal

maximum.

The overload

protection

circuit

for

the

+6V

outputinthe

6236A

has a

current

foldback

characteristic

which

reduces

the

output

current

as an overload increases until only 1A

flows

throughashort

circuit.

For

this

output,

the

current

limit

dependsonthe

output

terminal

voltage

and

varies

linearly

between

2.75Aat6V

and1Aat

zero

volts.

1-7 The

instrumentisavailableinthree

line voltage op-

1-14

The

accessories listed

below

maybeordered

from

your

local

Hewlett-Packard

field sales

office

either

1-1

with

the

power

supplyorseparately.

(Refertothe

list

at

the

rearofthe

manual

for

addresses.)

HP

PART

NO.

14513A

14523A

DESCRIPTION

Rack

Mounting

Kit

for

mounting

one

3

1/2"

high

supply

in a

standard

19"

relay rack.

Rack

Mounting

Kit

for

mounting

two

3

1/2"

high

supplies

sidebysideina

standard

19"

relay rack.

ture.

The

first

two

digits

indicate

the

year

(10=1970,

11

=

1971,

etc.)

the

second

two

digits

indicate

the

week,

and

the

letter"

A"

designates

the

U.S.A. as

the

countryofmanufac-

ture.

The

second

partisthe

power

supply

serial

number;

a

different

sequential

numberisassignedtoeach

power

sup-

ply,

starting

with

001

01.

1-17

If

the

serial

numberonyour

instrument

does

not

agree

with

thoseonthe

title

pageofthe

manual,

Change

Sheets

supplied

with

the

manualorManual Backdating

Changes

define

the

difference

between

your

instrument

and

the

instrument

describedbythis

manual.

1-15

INSTRUMENT AND

MANUAL

IDENTIFICATION

1-18 ORDERING

ADDITIONAL

MANUALS

1-16

Hewlett-Packard

power

supplies

are

identifiedbya

two

part

serial

number.

The

first

partisthe

serial

number

prefic, a

number-letter

combination

that

denotes

the

date

ofasignificant

design

change

and

the

countryofmanufac-

1-19

One

manualisshipped

with

each

power

supply.

Additional

manuals

maybepurchased

from

your

local Hew--

lett-Packard field

office

(see

the

listatthe

rearofthis

manual

for

addresses).

Specify

the

model

number,

serial

number

prefix,

and

theHPPart

number

providedonthe

title

page.

NOTE

Table

1-1.

Specifications,

Models

6236A

and

6237

A

TRACKING:

The

+20V

and

-20V

outputs

track

within1%.

Specifications

applytoboth

models

unless otherwise indicated.

INPUT POWER:

Standard

Option:

104:127Vac

(120Vac

nominal),

47-

63Hz,

single-phase, 112W,

140VA

(Other

line voltage

options

are listed in Paragraph 1-11.)

DC

OUTPUT

AND

OVERLOAD

PROTECTION:

o

to

±20V

Outputs:

Maximum

rated

output

current

is

0.5A.

Short

circuit

output

currentis0.55A

±5%

and

a

fixed

current

limit

circuit

limits

the

outputofeach

sup-

ply

to

this

maximumatany

output

voltage

setting.

Unbal-

anced

loads

within

current

rating are

permitted.

Model

6236A

o

to

+6V

Output:

Maximum

rated

output

currentis2.5A

at

6V.

The

maximum

available

output

current

decreases

with

the

output

voltage

setting.Acurrent

foldback

current

limits

the

outputto2.75A

±5%at6 volts and,

with

decreasing

voltage,

reduces

the

current

limit

linearlyto1A ±15%atzero

volts

(short

circuited).

Model

6237A

o

to

+18V

Output:

Maximum

rated

output

current

is

1.0A.

Short

circuit

output

currentis1.1 A ±5%

andafixed

current

limit

circuit

limits

the

outputtothis

maximum

at

any

output

voltage

setting.

1-2

LOAD

EFFECT

(Load

Regulation):

All

Outputs:

Less

than

0.01 % plus

2mV

for

a full

load

tonoload

changeinoutput

current.

SOURCE

EFFECT

(Line

Regulation):

All

Outputs:

Less

than

0.01%

plus

2mV

for

any

line

voltage

change

within

rating.

PARD

(Ripple

and

Noise):

All

Outputs:

Less

than

0.35mV

rms

and

1.5mV

p-p

(20

Hito20

MHz).

DRIFT

(Stability):

All

Outputs:

Less

than

0.1 % plus

5mV(0to20Hz)

during8hoursatconstant

line,

load,

and

ambient

after

an

initial

warm-up

timeof30

minutes.

LOAD

TRANSIENT

RECOVERY

TIME:

All

Outputs:

Less

than

50psec

for

output

recovery

to

within

15mVofnominal

output

voltage

following

a load

change

from

full

loadtohalf load (or vice versa).

OUTPUT

VOLTAGE

OVERSHOOT:

All

Outputs:

During

turn-onorturn-offofac

power,

output

plus

overshoot

will

not

exceed

1V if

the

output

controlisset

for

less

than1V.Ifthe

controlisset

for

1V

or

higher,

thereisno

overshoot.

Table 1-1. Specifications, Models

6236A

and

6237A

(Continued)

TEMPERATURE

COEFFICIENT:

All

Outputs:

Less

than 0.02% plus 1mVvoltage change

per degree Celsius over the operating

range

from0to

40°C

after 30 minutes warm-up.

*OUTPUT

IMPEDANCE

(typical):

o

to

+20V

Output:

0.5mn

plus 1.5/lH

o

to

-20V

Output:

0.5mn

plus 1.5/lH

Model

6236A

o

to

+6V

Output:

0.3mn

plus 1/lH

Model

6237A

o

to

+18V

Output:

0.3n

plus 1.5/lH

* Operating characteristics listed

as

typical

are

provided

for

the user's

information

only

and

are

not

warranteed specifi-

cations.

RESOLUTION:

(Minimum

output

voltage change obtainable using

front

panel voltage

control)

o

to

±20V

Outputs: 70mV

Model

6236A

o

to

+6V

Output:

20mV

Model

6237A

o

to

+18V

Output:

70mV

1-3

TEMPERATURE

RANGES:

Operating: 0

to

+40°C ambient.Athigher temperatures,

output

currentisderated linearlyto50%

at 55°C.

Storage:

-40°Cto

+75°

C.

METER RANGES:

o

to

+20V

Output:

0-25V,O-0.6A

o

to

-20V

Output:

0-25V,O-0.6A

Model

6236A

o

to

+6V

Output:

0-7V,

0-3A

Model

6237A

o

to

+18V

Output:

0-21

V, 0-1.2A

METER

ACCURACY:

±4%offull

scale

DIMENSIONS:

3

15/32

H x

87/32

W x

129/16

D

(88mm H

x 208mm W x 319mm D)

WEIGHT:

9.5 Ib (4.3kg)

SECTION II

INSTALLATION

2-1

INITIAL

INSPECTION

2-2 Before

shipment,

this

instrument

was

inspected

and

foundtobe freeofmechanical

and

electrical

defects.

As

soonasthe

instrumentisunpacked,

inspect

for

any

damage

that

may

have

occurredintransit.

Save all

packing

materials

until

the

inspectioniscompleted.Ifdamageisfound,

file

claim

with

carrier

immediately.

The

Hewlett-Packard

Sales

and

Service

office

shouldbenotifiedassoon

as possible.

2-3 Mechanical Check

2-4 This

check

should

confirm

that

there

arenobroken

knobsorconnectors,

that

the

cabinet

and

panel surfaces are

free

of

dents

and

scratches,

and

that

the

meterisnot

scratch-

edorcracked.

NOTE:

ACCESSORY

KITS

FOR19INCH

RACK

IIOUNTIIG

AIlE:

HI'

IIOOEL

1451~

FOR

CIlE

SUI'l\.Y

HP

lOlELl4523A RJlTlI09..PPL£S

$10£

VIEW

2-5 Electrical Check

Figure 2-1. Outline Diagram

2-6

The

instrument

shouldbechecked

against

its elec-

trical

specifications.

Section

V includes an

"in-cabinet"

per-

formance

checktoverify

proper

instrument

operation.

2-7

INSTALLATION

DATA

2-8

The

instrumentisshipped

ready

for

bench

opera-

tion.

Before

applying

powertothe

instrument,

see

the

CAUTION

notice

in Paragraph 3-2.

2-9 Location

2-11

Outline Diagram

2-12

Figure

2-1

illustrates

the

outline

shape

and

dimen-

sionsofthis

supply.

Figure 2-2. Rack

Mounting,

One

Unit

Figure 2-3. Rack

Mounting,

Two

Units

Rack Mounting

2-10

This

instrumentisair

cooled.

Sufficient

space

shouldbeallottedsothat

a free

flowofcooling

air

can

reach

the

rearofthe

instrument

whenitisinoperation.

It

shouldbeusedinan

area

where

the

ambient

temperature

does

not

exceed

40°C

(upto55°C

with

derating).

2-13

2-14

This

instrument

mayberack

mountedina

standard

19-inch

rack

panel

either

by itselforalongside a similar

unit.

Figures 2-2

and

2-3

show

the

componentsofthe

rack

mount-

ing kits available

for

this

power

supply.

Ordering

informa-

tion

for

rack

mounting

accessoriesisgiven in Paragraph 1-13.

2-1

2-15

Input

Power Requirements

2-16 Dependingonthe

line voltage

option

ordered,

the

supplyisreadytobe

operated

from

oneofthe

power

sources

listed in

Table

2-1.

The

input

voltage range,

and

the

input

current

and

powerathigh line voltage

and

full loadislisted

for

each

option.

A labelonthe

rear

heat

sink

identifies

the

line voltage

optionofyour

supply.

All

optionsofthis

model

operate

froma47-63Hzsingle-phase line.

2-17

If

desired,

the

user

can

easily

convert

the

unit

from

anyofthese

optionstoanother

by following

the

instructions

in Paragraph 3-4. A

unitisconvertedbyresetting

an internal

line voltage

selector

switch,

replacing

the

fuse,

and

changing

the

line voltage tag.

2-20

To

preserve

the

protection

feature

when

operating

the

instrument

fromatwo-contact

outlet,

use a

three-prong

to

two-prong

adapter

(if

permitted

by local regulations) and

connect

the

green leadonthe

adaptertoground.

2-21 Model

6236A

and

6237

A supplies are

equipped

at

the

factory

withapower

cord

plug

appropriate

for

the

user's

location.

Figure 2-4 illustrates

the

standard

configu-

rations

of

power

cord

plugs used by HP. Above each draw-

ing

is

theHPoption

number

for

that

configurationofpower

connector

pins. Below each drawingistheHPpart

number

for a

replacement

power

cord

equipped

with

a plugofthat

configuration.

Notify

the

nearest

HP Sales

and

Service

Office if

the

appropriate

power

cordisnot

included

with

the

instru

ment.

2-22 Repackaging

for

Shipment

--

CAUTION

--

If

the

supply

might

possibly have been

converted

to a line voltage

option

other

than the one

marked

on its

identifying

label

without

being relabeledinsome way,

check the setting

of

the line voltage selector

switch

and

the fuse rating before

applying

power.

(See

CAUTIONinParagraph 3-2)

2-23

To

insure safe

shipmentofthe

instrument,itis

recommended

that

the

package designed

for

the

instrument

be used.

The

original packaging materialisreusable. If it

is

not

available,

contact

your

local Hewlett-Packard field

office

to

obtain

the

materials. This office will also furnish

the

addressofthe

nearest

service officetowhich

the

instru-

ment

canbeshipped

and

provide

the

Authorized

Return

label necessarytoexpedite

the

handlingofyour

instrument

return.Besuretoattach

a tagtothe

instrument

which

specifies

the

owner,

model

number,

full serial

number,

and

service

required,ora brief

descriptionofthe

trouble.

2-18 Power Cable

8120-0050

OPTION

903

8120-1691

OPTION

902

8120-1369

OPTION

901

Figure 2-4.

Power

Cord

Configurations

8120-1351

OPTION

900

2-19

To

protect

operating

personnel,

the

National

Electrical

Manufacturers

Association (NEMA)

recommends

that

the

instrument

panel

and

cabinetbegrounded.

"This

instrumentisequipped

withathree

conductor

power

cable.

The

third

conductoristhe

ground

conductor

and

when

the

cableisplugged

intoanappropriate

receptacle,

the

instru-

mentisgrounded.

The

offset

pinonthe

power

cable

three-

prong

connectoristhe

ground

connection.

Innoevent

shall

this

instrumentbeoperated

withoutanadequate

cabi

net

ground

connection.

Table

2-1.

Input

Power

Requirements

Option

Line Voltage Range

Input

Current

Input

Power

100

(100

Vac)

87-106

Vac

1.3A

140

VA

Standard

(120

Vac)

104-127

Vac

1.1A

140

VA

220

(220

Vac)

191-233

Vac

0.6A

140

VA

240

(240

Vac)

208-250

Vac

0.55A

140

VA

2-2

SECTION

III

OPERATING INSTRUCTIONS

3-1

m

=~=::

OU~https://manualmachine.com/~~2~:

"If"

_---

........

1

Figure 3-1. Controls and Indicators

TURN-ON CHECKOUT PROCEDURE

a.

Connect

line

cordtopower

source

and

turn

LINE

switch

G)

on.

LINE ON

indicator

® will light.

b.

Set

METER

switch

®

to

the

+6V

position

and,

with

no

load

connected,

vary

+6V

VOLTAGE-control

@ over

its range

and

check

that

the

voltmeter

respondstothe

con-

trol

setting

and

the

ammeter

indicates

zero.

c.

Set

the

+6V

VOLTAG E

control

fora6-volt

meter

indication

and

short

the

+6V

output

terminaltoCOM

(common)

terminal

®

withaninsulated

test

lead.

The

ammeter

should

indicateashort-circuit

output

current

of

approximately

1.0A

(1.1Ainthe

6237A).

Remove

the

short

from

the

output

terminals.

d.

Set

the

METER

switchtothe

+20V

position

and,

withnoload

connected,

vary

±20V

VOLTAGE

control

®

over its range

and

check

that

the

voltmeter

respondstothe

control

setting

and

the

ammeter

indicates

zero.

3-2

The

following

steps

describe

the

useofthe

Model

6236Aor6237Afront

panel

controls

and

indicators

illus-

trated

in Figure 3-1

and

serve as a

brief

check

that

the

sup-

plyisoperational.

This

checkout

procedureorthe

more

detailed

performance

testofParagraph 5-6

should

be follow-

ed

when

the

instrumentisreceived

and

beforeitis

connect-

edtoany

load

equipment.

Proceedtothe

more

detailed

procedures

beginning in Paragraph 5-6 if

any

difficulties

are

encountered.

--

CAUTION--

e.

Set

the

±20V

VOLTAGE

control

fora20-volt

meter

indication

and

short

the

+20V

output

terminaltothe

com-

mon

terminal

withaninsulated

test

lead.

The

ammeter

should

indicateashort-circuit

output

currentofO.55A

±5%.

Remove

the

short

from

the

output

terminals.

f.

Repeat

steps

(d)

and

(e),

but

substitute

the

-20V

positionofthe

METER

switch

and

the

-20V

output

ter-

minal.

Figure 3-2. Line Voltage Selector (Set for

120

Vac)

Before applying power to the supply, make certain
that its line voltage selector switch

(53)

is

set

for

the line voltage to be used. This switch

is

mounted

on the circuit board behind the voltmeter and

is
visible through the perforations in the top cover.
The positions

of

the two white marks on the switch

indicate the switch setting

(see

Figure 3-2).Ifthe

switch setting does

not

correspond to the intended

power source, proceed to

Paragraph

3-4 before

applying power.

.r--

240----,

(

r-

220

----,

0_

0

L-,OO--.J

'---120

---J

t

FRONT

OF

SUPPLY

NOTE

For the Model 6237A, substitute. +18V

for +6V in the following steps.

3-1

3-3

If

this

brief

checkout

procedureorlater

useofthe

supply

reveals a possible

malfunction,

see

SectionVof

this

manual

for

detailed

test,

troubleshooting,

and

adjustment

procedures.

3-4

LINE

VOLTAGE

OPTION CONVERSION

3-5

To

convert

the

supply

from

one

line voltage

option

to

another,

the

following

three

steps

are necessary:

1.

After

making

certain

that

the

line

cordisdiscon-

nected

fromasourceofpower,

remove

the

top

cover

from

the

supply

and.

set

the

two

sectionsofthe

li:1e

voltage selec-

tor

switch

for

the

desired

line voltage (see Figure 3-2),

2.

Check

the

ratingofthe

installed fuse

and

replace

it

with

the

correct

value, if necessary.

For

Options

100

or

120,

use a

normal

time-constant

2-amp

fuse (HP

Part

No.

2110-0002);

for

Options

220or240,

use a

normal

time-

constant

1-amp

fuse (HP

Part

No.

2110-0001).

3. Mark

the

instrument

clearly

withatagorlabel

indicating

the

correct

line voltagetobe used.

3-6

OPERATION

3-7 This

power

supply

canbeoperated

individually

or

in parallel

with

another

supply

(see Paragraph

3-17).

All

output

terminals

are

isolated

from

ground.

The

±20V

and

+6Vor+18V

outputs

use a single

common

output

terminal.

This

common

(COM)

terminaloranyoneofthe

other

output

terminals

maybegroundedtothe

chassisatthe

front

panel

ground

terminal

(

G)

in Figure

3-1),orall

outputs

may

be

left

floating. Loads can be

connected

separately

between

eachofthe0to

20V

output

terminals

and

the

COM ter-

minal,

or

between

the

-20V

and

the

+20V

terminals

for

a

o

to

40V

output.

3-8 Overload Protection Circuits

3-9

±20-Volt

Current

Limit.

The

+20V

and

-20V

outputs

are individually

protected

against

overloadorshort-

circuit

damagebyseparate

current

limit

circuits

which

are

adjustedatthe

factorytolimit

the

output

currentto0.55A

±5%. (Thisis110%ofthe

rated

maximum

outputof0.5A.)

The

current

limits can be

setbyadjusting

resistor R6

for

the

+20V

output

and

R26

for

the

-20V

output.

(See Paragraph

5-47

for

current

limit

calibration

instructions.)

No

deteri-

orationofsupply

performance

occursifthe

output

current

remains

below

the

current

limit

setting.

If a single load

is

connected

between

the

+20V

and

-20V

outputs,

the

circuit

set

for

the

lesser

current

limit

will

limit

the

output.

3-10

+6V

Current

Foldback

(Model

6236A).

The

over-

load

and

short-circuit

protection

circuit

for

the

+6V

output

of

the

Model

6236A

reduces

the

output

current

limitasthe

output

terminal

voltage decreases.

(The

operating

region

of

the

+6V

outputisenclosedbyheavy lines in Figure 3-3).

The

maximum

rated

output

currentis2.5A

and

the

current

limitisfactory-adjustedtooperateat2.75A

±5%

when

the

3-2

outputis6 volts.

At

lower

output

voltages,

the

circuit

reduces

the

maximum

obtainable

output

current

linearly

until 1A

±15%

flows vvhen

the

outputisshorted.

The

short-

circuit

current

cannotbeadjusted,

but

R46

canbeset

to

limit

the

maximum

currentat6Vto2.75A

±5%. (See Para-

graph

5-47

for

current

limit

calibration

instructions.)

3-11

+18-Volt

Current

Limit

(Model

6237

A).

The

+18-

volt

outputofthe

Model

6237Ais

protectedbya

fixed

cur-

rent

limit

circuit

which

operatesat1.1 A

(110%ofits max-

imum

rated

outputof1.0A).

The

circuitissimilartothe

onesinthe

±20-volt

supplies. (See Paragraph 5-47

for

cal ibrationi

nstructi

ons.)

3-12 Operation Beyond Rated

Output

3-13

The

supply

maybeabletoprovide

voltages

and

currents

greater

than

its

rated

maximum

outputsifthe

line

voltage

isator

above

its

nominal

value.

Operation

can

ex-

tend

into

the

shaded

areasonthe

meter

faces

without

dam-

agetothe

supply,

but

performance

cannotbeguaranteed

to

meet

specifications.Ifthe

line voltageismaintainedinthe

upper

endofthe

input

voltage range,

however,

the

supply

probably

will

operate

within

its

specifications.

3-14 Connecting Loads

3-15

Each

load

shouldbeconnectedtothe

power

supply

output

terminals

using

separate

pairsofconnecting

wires.

This

minimizes

mutual

coupling

between

loads

and

takes

full

advantageofthe

low

output

impedanceofthe

power

supply.

Connecting

wirestothe

load

mustbeof

adequately

heavy gagetomaintain

satisfactory

regulationatthe

load.

Each pair

of

connecting

wires

should

be as

short

as possible

and

twistedorshieldedtoreduce

noise

pickup.Ifshielded

wireisused,

connect

one

endofthe

shieldtothe

power

supply

ground

terminal

and

leave

the

other

end

unconnect-

ed.

3-16

If

load

considerations

require

that

the

output

power

distribution

terminalsberemotely

located

from

the

power

supply,

then

the

power

supply

output

terminals

should

be

connectedtothe

remote

distribution

terminalsbya

pair

of

twistedorshielded

wires

and

each

load

separately

connect-

edtothe

remote

distribution

terminals.

3-17 Parallel Operation

3-18

Twoormore

power

suppl

ies

canbeconnected

in

parallel

to

obtainatotal

output

current

greater

than

that

available

from

one

power

supply.

The

total

output

current

is

the

sumofthe

output

currentsofthe

individual

power

supplies.

The

output

voltage

controlsofone

power

supply

should

be

settothe

desired

output

voltage,

and

the

other

power

supply shouldbeset

for

a slightly larger

output

volt-

NOTE:

THE LOWER END - POINT

OF

THE

CURRENT

LIMIT

LINEISNOT

AD-

JUSTABLE;

THE UPPER END-POINT

IS SET AT THE FACTORY

FOR

2.75A

±

5%.

BETWEEN ITS

END-

POINTS,

THE ACTUAL CURRENT

LIMITISA

STRAIGHT-LINE FUNCTION.

OPERATING

REGION

+6V

SUPPLY,

MODEL

6236A

2V

IV

5V

~-----+------+------+------+---~~-,4

__

--------4

4V

~-----+------+-----+------+-~~-+-"---+-------4

3V

OUTPUT

TERMINAL

VOLTAGE

6V

OUTPUT

CURRENT (AMPERES)

o

0.5

t

1.0

\

0.85A

115A

SHORT

CIRCUIT CURRENT

MAY

VARY

±15%

FRav1

UNITTOUNIT.

1.5

2.0

2.5

3.0

Figure

3-3:

Current

Limit

Characteristicsofthe6VSupply

(Model

6236A)

3-21

Output

Capacitance.

An internal

capacitor

across

the

output

terminalsofthe

power

supply

helpstosupply

high-current

pulsesofshort

duration

during

constant

volt-

age

operation.

Any

capacitance

added

externally

will im-

prove

the

pulse

current

capability,

but

will decrease

the

load

protection

provided by

the

current

limiting circuit. A

3-20

Pulse Loading.

The

power

supply

will

automati-

cally cross over

from

constant

voltagetocurrent

limit

operationinresponsetoan increaseinthe

output

current

over

the

preset

limit.

Although

the

preset

limit

maybeset

higher

than

the

average

output

current,

high

peak

currents

as

occurinpulse loading

may

exceed

the

preset

current

limit

and cause crossover

to

occur

and

degrade

performance.

age.

The

supply

settothe

lower

output

voltage will

act

as

a

constant

voltage

source,

while

the

supply

settothe

higher

output

will

act

as a

current-limited

source,

dropping

its

out-

put

voltage untilitequals

thatofthe

other

supply.

The

constant

voltage

source

will deliver

only

that

fraction

of

its

total

rated

output

current

whichisnecessarytofulfill

the

total

current

demand.

3-19 Special Operating Considerations

high-current

output

pulse

may

damage load

components

before

the

average

output

currentislarge

enoughtocause

the

current

limiting

circuittooperate.

3-22

Reverse

Current

Loading. An active load

connect-

edtothe

power

supply

may

actually

deliver a reverse cur-

renttothe

power

supply

duringaportionofits

operating

cycle. An

external

source

cannot

be allowedtopump

cur-

rent

into

the

supply

without

lossofregulation

and

possible

damage

to

the

output

capacitor.Toavoid

these

effects,

it

is

necessarytopreload

the

supply

withadummy

load

resistor so

that

the

power

supply

delivers

current

through

the

entire

operating

cycleofthe

load device.

3-23

Reverse Voltage

Protection.

Internal

diodes

con-

nected

with

reverse

polarity

across

the

output

terminals

protect

the

output

electrolytic

capacitors

and

the

driver

transistors

from

the

effectsofa reverse voltage applied

across a

supply

output.

Since series

regulator

transistors

cannot

withstand

reverse voltage

either,

diodes

are also

connected

across

them.

When

operating

supplies in parallel,

these

diodes

protectanunenergized

supply

thatisin para-

llel

with

an energized

supply.

3-3

SECTION

IV

PRINCIPLES OF OPERATION

4-1

OVERALL

DESCRIPTION

4-2 This section presents

the

principlesofoperation

of

the

Models

6236A

and

6237

A Triple

Output

Power

Supply.

Throughout

this

section

refertothe

combined

schematic

diagram

of

Figure 7-1.

NOTE

All information in this section applies to

both

models unless otherwise indicated.

4-3 The

two

primary

windingsofthe

power

transformer

are

connectedinoneoffour

different

ways by setting

the

two

slide switches

mountedonthe

circuit

board. These

switches select

oneofthe

nominal ac

input

voltages

for

which

the

supplyisdesigned:

100V,

120V,

220V,or240V.

4-4 The

transformer

secondaries,

together

with

recti-

fiers

and

capacitor

filters, provide rawdcfor

the

three

out-

put

regulator circuits and for

another

regulator which pro-

vides reference and bias voltagestothe

output

regulators.

4-5

By

comparing

its

outputtoa high-stability refer-

ence,

the0to

+6-volt regulator (6236A)or0to+18-volt

regulator

(6237

A) holds its

output

voltageatthe

value

determined

by a

front

panel

control.

Any

errorinthe

actual

outputascomparedtothe

desired

output

is

am-

plified by an operational amplifier

and

applied as

fe~dback

to

control

the

conductionofa series

regulator

transistor.

As

a result,

the

voltage across

the

series

transistor

varies so

astohold

the

output

voltage

constantatthe

desired level.

The high gain

of

the

voltage

comparison

amplifier

and

the

stabilityofthe

reference voltage ensure

that

input

voltage

or load

current

variations have Iittle

effectonthe

output

voltage.

4-6

The0to

+6-volt

outputinthe

Model

6236A

is

protected

by a

current

foldback

limiter which minimizes

dissipation in

the

series regulator

transistor

during

overloads.

Inacurrent

foldback

circuit,

the

current

limit

depends

on

the

output

terminal voltage

and

in this

regulator

ranges

from 2.

75A

±5%at6 voltsto1A ±15%

with

the

output

short-

ed. (An

outputof2.

75Ais110%ofthe

rated

maximum

of

2.5Aat6 volts.)

The

operating regionofthe

+6-volt regu-

lator

outputisenclosed by a heavy lineinFigure 3-3.

If

the

operating

point

reaches

the

diagonal

current

limit line,

a decrease in load resistance moves

the

operating

point

4-1

down

the

line, reducing

the

output

voltage

and

current.

Current

foldbackiscontrolledbya

second

operational

amplifier in

the

regulator which

monitors

thedcoutput

current.

This

current

comparison

amplifier

takes

control

of

the

'output

away

from

the

voltage

comparison

amplifier

when

the

current

reaches

the

design limit. Removing

the

overload restores

constant

voltage

operation

automatically.

4-7

The

+20-volt regulator has a fixed

current

limit

at

110%ofits

0.5

amp

maximum

rated

output

butisotherwise

similartothe

+6-volt regulator.

4-8

The0to

-20-volt

regulator is,inturn,

similartothe

+20-volt regulator

except

that

it resembles a

complementary

mirror

imageofthe

latter.

The

output

voltagesofthe

+20-

volt

and

-20-volt

supplies are

both

setbythe

same

front

panel

control

and

track

each

other

within

1%. Precise track-

ing

of

the

two

outputsisachievedbycontrolling

the

positive

output

conventionally

and

using

that

outputasthe

reference

voltage

for

the

negative

output.

4-9

The0to

+18-volt regulator in

the

Model

6237

A

is

similartothe

+20-volt regulator. It has a fixed

current

limitat110%ofits

1.0

amp

output.

4-10

The

reference

and

bias

supply

provides reference

and

bias voltages

for

the

output

regulators.

4-11

The

turn-onlturn-off

control

circuit

prevents

out-

put

transients

when

the

supplyisturnedonor

off. It does

this by delaying

the

applicationofcertain

bias

and

reference

voltages

at

turn-on

and

removing

them

shortly

after

turn-off.

4-12

A

three-position

meter

switch selects whichofthe

supplies has its

output

voltage

and

current

indicatedonthe

front

panel meters.

The

proper

rangeofthe

dual-range

metersisselected

automatically.

4-13

DETAILED

CIRCUIT

DESCRIPTION

4-14 0 To

+20-Volt

Regulator

4-15

Voltage

Comparison

Amplifier.

The

voltage

com-

parison amplifier in

the

+20-volt

supply

controls

the

conduc-

tionofseries regulator

transistorQ1so

that

the

voltages

at

the

two

inputsofthe

amplifier remain equal. A fixed volt-

age divider holds its inverting

input

(U1-2)at-16mV.

Its

non-inverting

input

(U1-3)

monitors

the

output

voltage in

series

with

the

voltage across R1. Since R2isconnected

between

the

-6.2V

reference

supply

andapoint

which feed-

back

action

holds near

-16mV,

its

current

remains

constant.

This

current

flows

throughR1to

produce

a voltage

drop

acrossR1proportionaltoits resistance setting,

thus

the

output

voltageofthe

supplyisproportionaltothe

resistance

settingofR1.Atthe

outputofthe

voltage

comparison

amplifier (U1-1), a positive voltage change

correspondstoa

decrease in

the

conductionofQ1.

4-16

CR2

and

CR3

protect

the

inputofthe

amplifier

against

transient

overloads, C2

andR4speeduploop

re,.

sponse

time,

andC4and

R12 stabilize

the

supply's

high

frequency

characteristics.

4-17

OR-Gate.

To

permit

either

the

voltage

comparison

amplifierorthe

current

comparison

amplifiertocontrol

the

series regulator

transistor,

the

outputsofboth

amplifiers

are

connectedtothe

baseofdriverQ2through

an OR-gate

composedofCR5

and

CR6.

CR5isnormally reverse

biased by a negative

output

from

the

current

comparison

amplifier,

permitting

the

voltage

comparison

amplifier

to

driveQ2through

CR6. An overload drives

the

output

of

the

current

comparison

amplifier positive,

forward

biasing

CR5

and

reducing

the

supply

output.

When

the

overload

is

removed,

CR5isreverse biased again

and

the

voltage

com-

parison amplifier resumes

controlofthe

output.

4-18

Driver

and

Series Regulator.

The

-12.4Voutput

of

the

bias

supply

provides

the

turn-on

bias

for

series regu-

lator

transistor

Q1. Its

complete

current

path

includes

Q15,

CR59,

R14,

and

Q1,

and

returnstocommon

through

current

monitoring

resistor R8. (Itisbecause this bias

current

flows

throughR8that

the

output

ammeter

requires

the

zero

off-

set

bias

circuit

describedinparagraph 4-43.)

Through

the

OR-gate,

either

the

voltageorthe

current

comparison

ampli-

fier

controls

the

conductionofdriver Q2, which regulates

the

flowofturn-off

bias

through

Q1's

base-emitter

circuit.

The

algebraic sumofthe

nearly

constant

turn-on

bias

through

R14

and

the

variable

turn-off

bias

throughQ2controls

the

conductionofseries

regulator

transistor

Q1.

4-19

Current

limit

Circuit.Inthe

+20-volt regulator,

the

current

comparison

amplifier

compares

the

voltage

across

current

monitoring

resistor R8tothe

fixed voltage

across

partofcurrent

limit

adjust

potentiometer

R6.

The

current

limit

adjustmentissetsothat

the

input

voltage

to

the

current

comparison

amplifierisnegative in

the

normal

operating

region,

but

becomes zero

when

the

output

current

increasesto0.55

amps. When

the

amplifier's

input

voltage

reaches zero, it

takes

controlofthe

regulator

output

voltage

and

reduces it as necessarytokeep

the

output

current

from

exceeding

0.55

amps. When

the

overloadisremoved,

the

outputofthe

current

comparison

amplifier goes negative,

reverse biasing

CR5

and

returning

controltothe

voltage

4-2

comparison

amplifier.

4-20

Turn-On/Turn-Off

Control.

When

the

power

supply

is

turnedonor

off,

Q15inthe

turn-on

control

circuit

with-

holds

turn-on

bias

fromQ1while

the

regulator

bias voltages

are

too

low. This prevents an

output

voltage

transient

from

occurring before

the

amplifiers are

properly

biased.

The

outputofthe

-6.2V

reference

supplyisalso

temporarily

heldata low voltage by

Q14,

which

conductstoshort

that

output.

4-21 Circuit

Protection

Components.

Diodes CR1,

CR7,

and

CR9

each

protect

the

+20-volt

supply

from

spe-

cific hazards.

Output

diode

CR1

protects

the

supply

com-

ponents

if a reverse voltageisappliedtothe

output

terminals.

A

common

way

for

thistooccurisfor

an unenergized

supply

tobeconnectedinseries

with

another

thatisenergized.

If

the

output

voltageisturned

down

quickly

while a large

capacitorisconnected

across

the

output,

CR7

protects

driverQ2from

excessive dissipationbyshunting

someofits

base

currenttocommon.

The

series

regulator

diode,

CR9

protects

the

series regulator

transistor

from

reverse voltage.

Series regulator voltage

could

occur

if a deenergized sup-

ply were

connectedinparallel

with

an energized one.

4-22 0 To

-20-Volt

Regulator

4-23 Insteadofusing an

NPN

driver

and

a

PNP

series

regulator in

the

negative

output

line asinthe

+20-volt regu-

lator,

the

-20-volt

regulator uses a

PNP

driver

and

an

NPN

series regulator in

the

positive

output

line.

The

-20-volt

regulator

circuitisthe

complementary

equivalentofthe

+20-volt

circuitinother

respects, as well.

Their

current

limit

circuits

operate

similarly.Atthe

outputsofthe

current

and

voltage

comparison

amplifiers in

the

-20-volt

circuit, a neg-

ative voltage change

correspondstoa decreaseinseries regu-

lator

conduction.

The

turn-on

bias

for

its series regulator

transistor,

Q3,issupplied

from

a positive voltage source,

the

+7.5V bias

supply,

andisswitchedonand

offbyQ13

in

the

turn-on

control

circuit.

4-24

The

-20-volt

supply

uses

the

outputofthe

+20-volt

supply

as

its reference voltage. As a result,

both

outputs

are

set

by a single

front

panel

control

and

track

each

other

with-

in

1%.Two

resistorsinresistor

networkZ1are

connected

in

series

between

the

+20-volt

and

-20-volt

outputs.

These

resistors are closely

matchedinresistance

and

temperature

coefficientsothat

the

voltage across eachisexactly

half

of

the

total.

The

midpointofthis dividerisconnectedtothe

non-inverting

inputofthe

-20-volt

supply's

voltage com-

parison amplifier.

The

amplifier's inverting

inputisconnect-

edtocommon

through

R32tohold itatzero volts.

The

amplifier keeps its differential

input

voltageatzerobymatch-

ing

the

output

voltageofthe

-20-volt

supplytothatofthe

+20-volt

supply.