TTI s Service manual

'S Series'

DC Power Supplies

Service Manual

Book Part Number 48511-0060 - Issue 3

GEilENAL Service Handling Precautions Service

that subjected to excessj-ve soldering iron attempting to remove a

Dismantling I{ARI{ITIG ! Openlng

be disconnected from alI voltage sources before any adjustment, maintenance and repalr during which adjustment,

inevitable, it

the

1. Remove the B

2. Liff

3.

work

the

hazards

screws

To

remove remove now be be rotafed clear of the case l-ower. the 4 MJ screws through the

should onLy

tracks on the

remove

and

the Instrrrnent

instrument

maintenance

shall

invol-ved.

side

on dual units) notOing

fhe

off

the J control knobs, pulled

case

a nain

(linear

clear of the front

be

printed

heat. Use

all solder with

component.

likely

is

repair

or

be carried out only

screws

upper.

carried out by skilled engineers. Please

circuit

to

(plus

the case upper.

supply)

which

rear

board

only a

expose live

it

shal-l be

Lhe

of

by a

2

Lop

pcb,

remove the 4 nyJ-on

are refalned

panel

To

panel-.

are

very

miniature Lemperature

sol-der wick

parts.

opened.

opened instrument under

skllled

screws on

by

the

and remove the logic supply

wiring harness

flne and

or

The instrumenl

If

person

triple

grub

units or 2 handle

fi-xing

screws. The

note

may lift if

controLled

suction

replacement

afterwards

who is aware

allows it to

before

shal-1

volLage is

screws and

pcb

pcb,

remove

or

any

of

can

4. Transistors on the logic supply

Reassembl-e

5.

Operating Voltage

the Power

See volfage units.

of

Supply section on

single

Q5, Q6

1n reverse order.

and

are

and dual unlts. See

on the linear supplies and

Q7

insul-ated from the heatsinks.

page

B

for det,ails of

page

20 for details

Q2

Q1,

changing

of

D10 and

Lhe operating

SCR1

triple

TECHIIICAL SPECIFICATION Ortput Voltage Setting: By

5mV across

Output

Ortput

Output

Output Output

Output

Load Line

Current Setting:

llode: The power

Sritch:

Ter"ninals:

Inpedance:

Constant

Regulation:

Voltage: Current: Typically

Protection:

By

constant display

Isolates

limits

4mm

Typically

Up to maximum diode reverse

<0.01$ of

<0.01[ of

coarse

single

voltage

annunciator

the

bo

terminals

clamped for reverse

cunrent.

maximum

naximum output

fine eontrols;

and

range.

the

logarithmic

supply operates

modes with automafic

output

be set

(5mOhm 5OkOhm

up

19nn

on

at with voltage

output

control.

indicates

penmits

and

before

lkHz

connecbing

(.75n)

voltage

for 50X

for

resolution

in

consfant

constant

voltage

spacing.

limif

voltages and up to

10[ ]ine voltage

at maximum

+20

Volts

Ioad change

better

current or

cross-over. A

current mode.

and

current

load.

the

forwardl

change

than

3A

Ripple Transient

Tenperature

l{eter

Heter

Power

hvironnental Range:

and

Type: Independent autoranging

Resolution: Voltage: Current:

Accuracy: Voltage:

Currenf:

Requirenents:

Input Input

Power

Voltage: VoJ.tage

Consumption:

Xoise:

Response:

Coefficient:

Rangez

OPerating

Typically (2Ousec

change.

Typica1ly

voltage and

10nV up

1mA

up Lo

0.2%

ot

0.5fi

ot

Internally +/' 10ft ot

150VA for

to

5oC

(1nV

to within

(10Oppm/oC

to

2A, 10mA

reading reading

single

40oc, 20ft

rms

current

20V,

set voltage

100mV

above

+

1

+

1

fon 110, 120,

setting

units,

to 80tr RH

5OmV

indication.

digit digit

of

above

2A

300VA

0.5''

20V

setting for

3.5-digit

220

for duai

240VAC

or

units

load

9Ol'

LCDs

50/60H2

for

Environnental

Penge: Size: Ueight:

Storage

-20oC

160mn wide

308nm

4.9kg

9.6tg

to

wide slngle duat

+60oC

160mm

x

160mn

x

unit

unit,

high x 238mn high x

238mn

deep deep

single dual

unlt

unib

FI]IICTIONAL

The

relati-onship

diagram The

They

opposite.

pass

transistors

are controlled by the emor anplifiens via the diode

DESCRIPTION

between

are mounted

the major

on

circuit

heatsinks

elements are showa in

at the rean of the instrunenL.

gate.

the

block

The

diode

current.

In

the

constant

load;

In the eurrent gate current

The incorporates the autorange circuitry and decinal

The drive cincultry

allows

The split low voltage

and mainlains constant

output

digibal

powen

gate provides

constant

output voltage, set by the

the voltage is

constant current

error arnplifier

is sensed across R27.

voltage is

current meter block

the set current limit

supply

voltage

for

provides supply for the control circuitry

automatic

node

sensed across

mode,

overrides

output cunrenf

displayed

constant current

the

high voltage and

cnoss over of consbant voltage

the

error voltage amplifier

coarse

the output terminals.

or when the

the voltage error amplifier via the diode

the

by

also

to be displayed.

presef

independent of

digital

incorporates the autonange circuitny,

annunicator and

and fine controls,

power

and consfant

mainbains the

independent of

current

voltmeter. This block also

point

for the output

(V1

linit is

load resistance; the

drive.

control

).

neached, the

logic which

(V2)

and

a

COARSE

VOLTAGE ERROR

IFIER

FINE

RENCE

CURRENT

VOLT

METER

LIMIT

CURRENT

ERROR AMPLIFIER AND REFERENCE

+V

SENSE

-V

SENSE

+I

SENSE SENSE

-I

-u2-€l

_V

SENSE

OUTPUT

SWITCH

SENSE

o+l

I

OUTPUT

TERMINALS

--€r

SENSE

-v1

+

V'l

CURRENT METER

Functional

+v2

-v2

+vl

OV

-v1

Block Diagrar

CIRCUIT

DESCRIPTIONS

-

Porer Supply

llains Operating

The operating voltage

of the instrument is

Yoltage

Should it be necessary to change diagran below.

240V

Operation 220V

987654321 109876s4321

shown on the rear

the operating voltage,

foll-ow bhe

@eration

panel

labeI.

appropriate

120V Operation

110V Operation

7654321

a change

If

is made, bhe

operating

voltage

label and

fuse

shoul-d

be changed.

a change

If

The

correct

made, the operati.ng

is fuse type is:

-

volEage

label

and

fuse

should

be changed.

1A 250V

2A 250V

HRC time-1ag,

HRC time-laq,

HRC

time-La9, 20rnm for

4A 250V HRC time-lag, 20mm for

WARNINC

I THIS

Any interruption of the or disconnection of the

instrument

Power Supply

Plns

of f load

reservoir

Pins off load

22 and 23

and

capacitor.

22 and

and

INSTRT'ITENT }TUST

protective

dangerous. Intentional interruption is

-

DC Requlrementg

on

the mains transformer of the 30V

this

is recEif

off

The

23 on the mains

this

is rectified by the bridge rect.ifier reservoir capacitors. The 26V.

20mm

for 220-240V)

for 110-L20V)

)

single

units

220-240V)

)

dual units

110-120V)

BE E.ARTHED

conductor inside

earEh terminal

outside

or

is likel,y to make

prohibited.

supplies

2A

i.ed

load

by the

voltage

bridge

across C1

rectif

j.er

Dl.

approximately

is

to

transformer of the 15V 4A supplies

C1

off load

voltage

BRI-;

across CL/C26

the instrument

the

provide

34Vrms

D4,' C1 is the

45V.

provide

l9Vrms

and C25 are the

is approximately

R14 discharges the

load connected; C5

reservoir capacitors supplies the

Diodes D5 to D8 wi.th

reservoir

capacitors C4

reservoir capacitors when the

R1

and

form a damping network.

pass

rectify

the

centre-tapped 20V

and C5

provide

Regulators ICl.0 and IC11 with diodes supplies for the error amplif

The above circuitry

Paee

Q5 They

TraneistorE

and

Q7

are

are mounted on separate

parallel

in

on a

is

and current sharing and R25. Driver transistor Q5

and

Q7

make

up

a darlington emitter heatsinks and R24, R25, R25 R25 are

on

the

power

supply

iers and di.gital met.eri.ng.

separate

pcb.

heatsinks and

shares one

Q5

on the

are

board. R25

no l-oad is connected.

Diode Gate

is

Q8 two error amplif

emitEer follower, the base of which is controlled by

an

via diodes D1,2 and

iers

unit is

transistors.

winding

approximately +/-13Y.

D22 and D23

provide

must

provided

is

the heat.sinks and

of

fol. l.ower

main

provides

stage.

board;

a discharge

D1,3.

turned

voltage

The

pins

on

18

regulated +/-5Y6

be H

by emi-tter

(hornetaxial)

resistors R24

altogether

R23 is on one of

On 15V

4A

units, R24 and

paEh

either

off with

across the

to

20 and

types.

C9

for

when

of

no

Q5, the

the

Voltage

It

Error

should

means that the

Arplifier

noted that 0V is referred to the

be

voltage

on the driver and

IC3a

j.s

summing amplifier; when

a

pass

from the

error

ampJ.ifier

positive

is

output termj-nal; this

sma11,

sufticient to

transistors and overcome resistive losses.

VR2

is fully

clockwise

2 is

at

turn

0V.

Feedback summed wifh

achieved oufput

used by

is from

with

swing

fhe

fhe negafive output terminal via R19

the current

VR2

which

of 1C3a

voltmeter

below

from

moves the

0V. D10 is

circuitry.

to

VR'1. Fine confrol of the output voltage

psuedo ground

2.45Y

a

VR5

sets

the

maximum output

of IC3a.

voltage

reference which

where if

3

D11

limits

voltage.

is also

is

the

Gunenb If

anplifier via Lhe diode drop across R27

IC4b. D17 current and

the

(100nDA).

meter. Output SW2a

terminal ibself. oubput feedback loop from

SW2b switches switch

cument Xote: SW2 contacts

must sane way round. on and

Bror

preset

the

output cunrent linit are equal.

Sritch

switches

on

is in the

meter

be

used.

SW2b conbacts

will have

lnPlifier

curnent

and bhis is compared

linits the

VR12

D25

and

trims the offseb of IC4b

is

the

to

to display the

normal

2.45V

a

+V

Thls is fo overcone

malntaln feedback when the oufput

going

the supply output

ofl

are

Note

This

will

limit is reached,

gate.

output

volfage

sense

complebely

posifion,

gold

also that if SW2 is disconnecfed

is because

have been

silver contacts

IC4b

Output current

to

swing of

connection between the

set

curent

plated

vapourised

IC4b below

This

reference which is also used by the current

SW2bts contacb

open

fo the outpuf tenminal. When

rAr

on

SW2a must

between

is

limi-t.

silven

as a result.

is sensed

the volLage on bhe

so

thaf

done at

is

connected

and

have due to

overrides

0V. VR8 sets

fhe set current limit and

low

supply

is

switch

fo

the correct

gold

contacLs while

the high switching current

fhe voltage

measuring

by

wipen

maximum output

output cunrent

output

neslstance with

off.

positions.

0V which signals

it nust be rewired

and

D15

replacemenf

the

of VR3 by

the sense

prevents

the oufput

the

error

volt

levels

bhe

fhe

the

type

fhe

gold

Voltneter ICl

is

a standard

complete

approximately oscilloscope

C11

the auto zero

are

C15 R16

ranges switching fhe meten reference. the output switching

approxinately ICl5ts

analogue ranges. They when in-phase with trins

Curent lleter IC2 is the

fron the output signals R27

to

with

input

and

R17 attenuate

on

output,

switches

the voltmeter on the

to

measure

display drivers,

40kHz

probe

capacitor.

filter

the

30V

is

below

point

ICTa and b. With

is adjusted by VR4; R5

+/-0.5Y

providing

in IC8 selecting the two

also select the decimal

same type as fhat

switch

output current.

digib

3.5 which, if necessary, can

on

componenLs.

2A

'l

bhe back-plane signal,

J8.

the output voJ-tage to suit

supplies

and low when the

9V

hysteresis

of

complementary conLrol

low

drives

panel

R56 and C12

C13

range

used Q10

the

meter

R57 and C14

is

between the

The outpuf of the

in

and IC5b which

output switch

reference

the

provides

the output

at

point

VR6

and

the volLmeter.

IC.

output voltage

This

define

the integrator

are

high and Iow

positive

refenences for the

via IC9. The

and on

trims

on,

is a dual

the clock

be

checked

capacitor and

IC1. The volfmeter

comparafon IC3b

is above

feedback whlch

terminals.

signals. These drive

decimal

when in

the high range.

The control

provides

ICTa

complemenLary

eonnects

slope A to D

frequency

using a

components

R58, R59 and

nanges by

is

high when

1

9V.

Q1

high

point

anfi-phase.

slgnal

the

neter

x10

auto-

IC3b

gives

inverts

and

is off

drive

of

and

The

the low

VR7

rAl

to

With currenb

The currenf poinb conparator IC4a

the current

hysberesis.

the output

tinib setfing.

meter

and IC4a

reading

switch

autonanges

selects

is high when

off, ICTb

the appropriate

above 1.9A.

is

the 15V

on

the

conneets

4A

current

R41

the meter

supplies; VR9

neter

reading is

provides

referenee. The output

positive

VR3

to

sets the change over

below

to display the

1.9A

and

feedback and sone

1ow

of

when

l{hen

turned on which triangle

-V1 generabed

Level Protectlon D16

provide protection

current

supply whilst fhe

shifting

provi.des

limit

enables

in the display.

IC2

by

is

protection

is reached, IC4b

low

frequency

Note that the

ground

for the

provided

against

LCD

and is

R54

by

against

forward voltages.

takes controL via the diode

lead

between

and

r"everse

osci-llaton IC5c and d

ground

IC6

of R63.

lead of IC5

is connected

4

and 6 volts wibh nespecb bo

voltages.

D9, D14,

gate;

which flashes

ig

connected to the

DGI, whlch

bo

Q2, 03

a9

+V1.

and

is

the

is

a4