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413

SERIES

BENCH

VARIABLE

POWER

SUPPLIES

-

Types

413/423

10

INTRODUCTION

The

bench

power

supplies

types

413

and

423

are

four

range

units

providing

the

following

outputs:-

413

0-30V

at

1.04;

0-15V

at

2.04;

0-7.5V

at

4.04;

5V

at

4.0A

423

0-60V

at

0-9A;

0-30V

at

1-0A;

0-15V

at

2-04;

oV

at

2-0A

In

addition,

a

'D'

option

on

each

unit

provides

a

centre

tap,

the

accuracy

of

which

is

specified

down

to

a

total

supply

voltage

of

4V

(i.e.,+2V

supply).

A

further

'T'

option

gives

a

10-turn

voltage

control

with

dial

for

increased

resolution

and

resettability.

All

units

use

the

same

basic

case

and

internal

construction

with

identical

heatsinks

and

main

printed

circuit

board,

changes

to

component

values

and

types

determining

the

difference

between

the

units.

The

'D'

option

variants

have

an

additional

circuit

board

which

controls

the

centre

tap,

together

with

a

pair

of

extra

power

transistors

on

the

heatsink.

2.0

OPERATING

INS

TRUC

TIONS

The

unit

requires

a

50

to

60Hz

AC

ONLY

input

power

supply.

The

captive

power

lead

to

the

instrument

should

be

connected

to

a

3-pin

power

plug.

The

lead

is

colour

coded:-

brown

=

live,

blue

=

neutral

and

green/yellow

=

earth

(see

Safety

Regulations

64.2

(a)

3

and

64.3

(c)

5).

INCORRECT

CONNECTION

OF

THE

POWER

LEAD,

OR

CONNECTION

TO

A

SUPPLY

WITH

NO

EARTH,

IS

DANGEROUS.

Set

the

voltage

selector

on

the

rear

of

the

unit

to

the

correct

input

supply

voltage

and

check

the

fuse

rating

(see

Parts

List

and

Safety

Regulations

64.5

(c)),

connect

the

a.c.

supply

and

switch

on

by

depressing

the

red

push-button

which

latches

in.

The

unit

is

switched

off

by

a

second

depression

of

the

button

which

releases

the

latch.

With

none

of

the

grey

‘range

select'

push-buttons

depressed,

the

supply

gives

no

output.

Depress

the

push-

button

for

the

supply

range

desired,

noting

that

the

lowest

grey

button

gives

a

5V

output

regardless

of

the

position

of

the

voltage

potentiometer.

In

order

to

avoid

possible

damage

to

loads

caused

by

inadvertent

range

changing,

the

push-buttons

are

independently

operated.

To

change

ranges,

release

the

already

selected

range

by

pushing

the

button

a

second

time,

then

depress

the

button

for

the

new

range

required.

If

more

than

one

grey

button

is

depressed

at

a

time,

the

output

supply

will

correspond

to

the

lowest

selected

voltage

and

the

output

current

limit

to

the

lowest

selected

current.

This

facility

can

be

of

use

if

a

current

limit

lower

than

the

maximum

is

required

on

any

of

the

lower

voltage

ranges.

The

output

voltage

control

potentiometer

is

not

calibrated;

however,

the

front

panel

markings

(or

the

dial

settings

on

'T'

versions)

can

be

used

for

resetting

to

a

previously

set

voltage.

Note

that,

in

order

to

ensure

full

voltage

availability

on

all

ranges,

a

small

amount

of

voltage

overrange

is

provided.

Similarly,

in

order

to

ensure

full

current

availability,

the

nominal

current

limit

values

are

10%

higher

than

the

values

marked.

On

'D'

versions,

the

centre

tap

voltage

is

guaranteed

to

be 49

to

51%

of

the

output

voltage

+100mV

down

to

4V

total

output.

The

current

limit

will

operate

if

the

current

in

either

half

of

the

supply

exceeds

the

limit

value.

Both

halves

of

the

supply,

however,

will

be

reduced

in

voltage

together

as

the

current

limit

operates.

with

both

black

push-buttons

released,

the

meter

reads

output

voltage

with

a

full

scale

equal

to

the

highest

range.

Depressing

the

top

meter

push-button

changes

the

meter

to

current

reading.

Depressing

the

lower

button

increases

the

meter

sensitivity

by

a

factor

of

3

on

both

voltage

and

current.

There

are,

thus,

a

total

of

four

meter

ranges.

On

centre

tapped

units

('D'

option),

the

meter

reads

the

total

supply

voltage

on

voltage

ranges

and

whichever

is

the

highest

of

the

load

currents

on

current

ranges.

To

obtain

extra

power,

higher

voltage

or

multi-rail

configurations,

units

may

be

connected

in

series.

Parallel

operation

is

not

recommended;

unless

the

output

voltages

are

set

precisely

egual,

a

step

in

output

voltage

will

occur

at

half

the

total

output

current

as

one

unit

enters

'current

limit'.

The

multi-range

capability

of

these

units

largely

obviates

the

need

for

parallel

operation.

For

example,

if

30V

at

2A

is

reguired

from

two

413

or

423

units,

set

both

to

15V

at

2A

and

connect

them

in

series,

rather

than

setting

them

to

30V

at

1A

and

connecting

them

in

parallel.