DurstEST500
synchionsation
(OK
1)
RepaiaInstruclions EST
500- 2
ThisvoliagereachesthebaseoJlC1candconirols
transisiorlC1dvlaemilterresistorR28.Thebiasvoltage
torlC1cldisJurthermorestabilisedviaD14.Theiran-
sistorslC1c/diunclionasdifferenialamplifiers
and
make
uptheR.M.S,valueofthe
phase
angleconlrolled
voltage.ThisvoltageappearsatPin11oflC1d
(see
oscillogram1b)
and s screened
via
condensatorC 10
andifansferredio Pin2 of lCla. AlsolClalb isa
dfterentlalamplifier.Al Pin4 oi lC 1/bthereis the
referencevoltage,
stabilisedby D 10,D 1T,evened
ouibyC12and
picked
oii
al
thebrushofP1.Thisvolt-
age
amolnts10approximately14
V.
AtP
n 1ol lC
1a
thereappearsthedlfferenialvoltagebelweenaclual
and reierencevohagewhlch is then lransfefiedvia
transistorT 3lo ihe
pu
se
generation.
CondensalorC 4 functionswiihPUT
(Th
3)forihe
generat
onofthetrigger
pulses.
Thecurrentsopplied
byiransisiorT 3 chargescondensatorC4.Assoon
asihecondensatorvoltagereachesthevalue
oJ
the
gate
voltage
of PUT
(Th
3) approximaiely6 V - ihe laiier
cutslhrough
(see
osc
llogram2b).The
pulsegeneraied
byPUT
(Th
3) is amplilledviatranslsiorT 4 and
transferred
tothe
gales
ofthyristorsTh1andTh2(see
oscillogram3a/b).
TheopticalcouplerOK1,whlchisdirecilyconnected
io themalnsvoliagev
a diodes
D
3- D
6,hasthelask
ofcompleielydischargingcondensatorC
4 during
eachzero
phasepassage
oftheslnewave.The
pholo-
lransstorntheoptca couplerocks
brieflyduring
the zero passage
phase,
transistorT1 becomesthere-
lorecondLrct
ve
and
dischargescondensaiorC4(see
oscillograms2 a/b).
Thecircultboardfeaturesa proleciive
circuii,
loo.
11makes
sureihalfuseSi
1doesn'iburnlhrough
if
eiiheroneolihetwolhyrislors
(Th
1and
Th2)should
m
slire
ithis
wouldbeihecaseonaccountofa D.C-
voltageshareappearingsuddenly
in theprimary
windingof
Tr1).
The
phase
anglecontrolledvoliageispicked
oflvia
resistorsR 34and Fl35andlransferredto the baseol
iransjsiorT5 (see
oscillogram
4a).At thesameiime
theoutpLrt
pulse
of
PUT
(Th
3)isatthecollecloror
transistorT5.Theseiwo
pulses
bringabout
thecharging
ofcondensatorC
5 (see
oscillogram4 b).
mainsvollage
(R34/R35)
prolection circull (C5/F 10)
Condensator
C5dischargescontinuosly
vialransislor
T 2,butil isalwayschargedagain
allereachignjlion.
lf either
oneof thetwolhyrisiorsshouldn
t ignte,
condensatorC5 iscompletely
discharged,lransislor
T2locksand
transistoflC1ebecomesthus
conductive,
slmulatingtoohighanactual
voliageaiihebase
oflC
1a.Theoutpulvoliagefallsthereloreoff
unlilitreaches
anrnnocuos
value.
5. ADJUSTMENTOF
THEOUTPUTVOLTAGE
The23,5V output
voltageof the EST500maybe
adjustedbyturnlng
potentiometer
P1.
Noie:
- Themeasur€menimusibetakenoffthelampsockel,
- Thestabllisefsoutpul
mustbeloaded.
Sirce I isa phase
anqecontrollFd
alerraL'19-cLr-
rent
voltage,
a trueR.M.S.metermustbe!sed.
Welurthermore
suggesito usea 2,3Ohm(250
W)
wireresislancein
place
of
lhelampwhenmakingthe
a)tr
sser
pulse
(Rl
rB2)
b)lrigger
pulse(R6/Th
3)
