L Ow-Voltage R Ectifiers And U Nregulate D Out P Ut; Low-Voltage R Egulators; L Ine Trigger; Calibrator - Tektronix 5440 Instruction Manual

L
ow-
V
oltage
R
ectifiers and
U
nregulate
d
Out
p
ut
T
h e full-wave bri
d
ge rectifiers and associate
d
filter
components in t he secon
d
aries of Τ800 provi
d
e filtere d
d
o
voltages . The unregulate
d
out
p
uts are +200 volts, Ι-18
volts, +38 volts, -18 volts an
d
-38 volts. The +200-volt
outputs to the dis play unit are protecte
d
by F
800.
L
ow-Voltage Regulators
-30
V
olt Supp ly . Th e -30-volt su
p
ply, besides
provi
d
i n g p ower to circuitry throug h out t h e instrument,
provid es α reference-voltage source to establis h
o
p
eratin g
levels for t h e fee
d
back regulators in
t
h e -15-volt, +15-
volt, -30-volt an
d
+5-volt su
pp
lies . Th e regulator for the
30-volt su pp ly is α feedbac k am
p
lifier system w
h
ic h
op erates between groun
d
and the unregulated -38 volts.
Current to the loa
d
is delivered by th e series-pass
transistor, 0940 . Th e sup ply voltage is establis hed by t h e
drop across
R
948,
R
950, and
R
952, wh ic h is com p
are
d
to
the voltage drop across VR 950 and t he emitter-base
j
unctio n of 0950 . T h e fee
d
back pat h is th roug h R949,
0955, an d 0958 to t h e base of Q940 . Any variataion in
output voltage d ue to ri pp le, c h an ge of current th roug h
th e load, etc., is imme
d
iately transmitted to the base of
0940 an
d
nullifie
d
by α ch ange in 0940 conduction, t h us
maintaining α stea
d
y out
p
ut . T h e output of the su
p
ply is
set to exactly -30 volts by ad j ustment of
R
950, -30 V a
d
j .
Th is control sets th e co n
d
uction of 0950, w h ic h controls
the bias levels of 0958 and Q940 . CR 955 an
d
0958 p rovi
d
e
s hort-circuit protection by limiting th e current t h roug h
0940 wh e n
t
h e voltage drop across
R
940 exceeds 1 .1
V .
L
ine Trigger
tablis h ed by com
p
aring t h e su
pp
ly voltage sample at the
base of error sensing transistor 0894 with the reference at
t he base of error se nsing transistor Q896 . Any d ifferences
Calibrator
Circuit Description-5440
+30-
V
olt Supply .
T
h e regulator for
the +30-volt
supply
consists of series-
p
ass transistor Q910 and error amplifier
0925 . T
h
is is α feedbac
k
am
p lifier system similar to t
h
at
j
ust
d escribed for the --30-volt su
pp
ly .
R
920, +30 V ad j,
provi
d
es an ad j ustment to set th e out
p
ut of the su
p
ply at
exactly +30 volts. 0915 protects t h e su
pp
ly, if the out
p
ut is
sh orte
d
, by limiti ng the curre nt dema nded from t h e series-
p
ass transistor un
d
er excessive load . During
n ormal
o
p
eration, 0915 is biase
d
off.
+5-Volt Su
pp
ly . Th e regulator for the +5-volt su p
p
ly
consists of series-
p
ass transistor Q820, error am plifier
0824-Q832, and error-se nsi n g transistor Q838 . T his is α
feedback amplifier system w h ic h o
p
erates between +5
volts a n
d
--30 volts . Current to th e loa
d
is delivere
d
by th e
series-
p
ass transistor, 0820 . The su
pp
ly voltage is es-
tablis he
d
by th e dro p across
R
845 an d R
846 . Th e error
fee
d
back pat h is th roug h R 845 to the base of Q838 . Any
variatio n
i
n out
p
ut voltage is immediately transmitted to
th e base of 0820 and nullifie
d
by α ch ange in the
co nductio n of Q820, wh ic h sh ifts t he w hole su
pp
ly . 0830
protects the su
pp
ly, if the outp ut is s horte
d
, by limiti n g the
curre nt
d
eman
d
e
d
by the error amplifier transistor, Q824 .
During
n
ormal o
p
eration, 0830 is biased off.
Α li n e-fre
q
uency signal is obtaine
d
from th esecon dary
of Τ800 and attenuated by
R
935, R
936, an d R937 to
provide α li ne-trigger source for the time-base plug-in
un it .
-15-Volt Sup
p
ly . Th e regulator for the -15-volt su pp
ly C
RT
H
eater W inding
consists of series-pass transistor 0880, error am
p
lifier
Α
0900 an
d
error-se nsing transistors Q894 an
d
0896 . T h is is
separate seco ndary win d ing is
p
rovided for the crt
α fee
d
bac k amplifier system w h ic h
o
p
erates between +30
w
riting-gun heaters . T h e writing-gu n h eaters are elevate
d
volts an d -20 volts. Current to the load is delivered by the
to -3000 volts in t h e crt circuit ( d isplay unit) to maintain α
series-pass transistor, 0880 . T he su
pp
ly voltage is es-
p oten tial near that of th e crt cath ode.
between t h e bases of the error-sensing transistors causes
The Calibrator circuit, composed of 0982, Q984, an
d
α ch a n ge in the 0894 collector . Ther error-sensing circuit
th eir associated passive com
p
onents, pro
d
uces α sq uare-
c h ange is a
p
plied to the base of the error am
p
lifier, 0900 .
wave output with accurate am
p
litude an
d
at α rate of twice
The output of the error amplifier ch anges the con
d
uction
the power-line fre
q
uency. Th is out
p
ut is available at the
of th e series-pass transistor 0880 to correct for any output
probe test loop on the dis
p
lay unit front pa nel as α 4-
error. 0885 protects the su
pp
ly, i n
t
he event t h e output is
milliam
p
ere (pea k to pea k ) sq uare-wave current, or as α
sh orte
d
, by limiting th e current demande
d
from t h e series-
400-millivolt (ground to
p
ea k ) s
q
uare-wave voltage .
pass trnsistor tinder excessive loa
d
. During normal o
p
era-
tion, 0885 is biased off .
The resistive-ca pacitive networ k at t h e base of Q982
receives α pulsating do voltage from full-wave rectifier
C R 980-CR 981 an
d p
ro
d
uces α nearly symmetrical
+ 15-Volt Su pp ly . Th e regulator for the +15-volt supply
switc h ing signal forQ982 an
d
0984 . As Q984 is alternately
consists of series-pass transistor Q850, error am
p
lifier switc h ed on an d off at twice th e li n e frequency, current
Q870 an
d
error-sensi ng transistors 0864 a n d Q866 .
t h roug h R986 is alternately switc hed throug h
t
h e tran-
Operation of th is fee
d
back am p lifier system is similar to sistor or th roug h CR 986, th e p
robe test loop, an
d R
987,
that describe
d
for the -15-volt su pply.
pro
d
uci n g the re q uire
d
test signal .
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