Tektronix PG 508 User Manual

to
t he m
ai
n frame tra n
sistor used as t he series pass
eleme n t, un til t he i n verti n g an d n o n -i n verti ng i np uts are
a pp roxi m ately eq ual . At t h is co nd itio n , t he series pass
tra n sistor d rops t he voltage from t he raw su pp ly un til t he
out
p
ut is -+-5 .2 V . C u rre n t limiti n g is provided by R 1215 .
Wh en t h e current fro m
th e su pp
ly
excee d s app r oximately
1 .1 Α , t he regulator p rovi
des no
furt h er base d rive current
to t he series pass element and current limiting occ u rs .
T h e -1-33
.5
V
dc
fro m
t he
mai
n frame is t he raw su pp ly for
t h e regulate d -1-15 Vd
c .
T he 3-termi n al
voltage
reg
u lator,
U 1205, p erforms t he entire reg u lating function . Current
li m iti n g occurs wit h in U 1205 .
T h e --33 .5 V dc from t he mainframe is t he r αω supply for
t h e regulate d --15 Vd c . As in the -1-15 Vd c supply α 3-
ter m i n al voltage r egulator, U 1335, p rovi d es t he regu lating
fu n ctio n . H owever, due to a d ditional loa d consi d erations,
t he raw su p ply is pre-regulated to d ecrease power dis-
sipate
d by t
h
e integrate d circ u it . Α shunt c u rrent path to
t he loa d is fur n
is
hed b y V
R1330
and R
1330 .
T h
e
zener
voltage is also use d
to
mai n tain
base
drive
to
t h
e series
pass mai n frame tra n sistor . T h is transistor is u sed as α pre-
regu lator to d rop t h e voltage across U 1335 to ap-
proximately 3 .6 V . Current limiti n g
is also
provide d
by
t he
reg u lator, U1335 .
'The d ual trac k ing supplies p rovide t he positive and
negative voltages re q uire d by t he
outp
u t am p lifier . T h
e
voltage at t he base of Q1255 varies from 0V to -1-5 .2 V
de p end ing on t he setti n g
of
t he HIG H LEV E L control .
Wh e n the voltage at t he base of Q1255 varies fro m 0 V
to
-12
.6 V, t he voltage at t he collector of t h e series p ass
transistor
is -i-6
V .
As t he voltage at t h e base of Q1255
varies fro m
42 .6 V to +5 .2 V, t he voltage at t he collector of
t he
series pass tra n sistor va
r
ies f r om -1-6 V to
-+-26
V
.
Tra n sistor 01255 a nd 01270 form
α
differential
com-
parator . T he voltage at t h e b ase of Q1270 is r eferenced
b etween t h e - Ι -5 .2 V supply, grou nd and th e o u t p ut
REV . Α , ΜΑΥ , 1976
T h eory of O p eratio n -- P E G 508
voltage .
As
t
h
e H
IG
H L
EV EL co n trol is move d in t he
p ositive directio n , t he collector of Q1255 goes n egative .
T h is i ncreases cu rre n t flow t h ro u g h 01280 and t h erefore
t he series pass transistor i n t he mai n f r ame w h ic h raises
t he +- trac k ing
s
u pply voltage
to
t h
e output am p lifier .
F ee dbac k to t he d ifferential comparator
is p
rovided
by
R 1275 . Tra n sistor Q1265 p revents t he IN tracking su pp ly
from goi n g lower t han about -+-6 V . T h e b ase of Q1265 is
set at abo u t 2 .6 V . Wh en t h e base of 01255 goes more
n egative t han about 2 .6 V, Q1265 comes i n to co nd uctio n
h
oldi ng t he commo n emitter circuit ato n ed io d e d rop fro m
t he base of Q1265 . If t he b
ase of
Q1255
is lowered
furt
h er,
Q1255 looses co n trol of t he circuit and th e s u pply voltage
remains at t he level d etermi n ed by Q1265, +6 V .
Curre n t limiters for t h is circuit are Q1285, Q1290 and
01300 . Α d ifferential com p arator is formed by Q1285 and
Q1290 . If t h e loa d on t he +V supply excee ds t he maximum
current allowe d for t he voltagesu pp lie d , t h e voltage drop
across R 1282 becomes great e n oug h t h at Q1285 comes
into co nduction . T h
is
action increases
conduction
in
Q1270 re du cing t he cu rrent flow in 01255
.
F inally, t he
con d uction t h ro ugh th e series
p
ass tra n sistor is limite d
to
α safe val ue . T he cu rrent t hr oug h Q1300 is d etermi n ed by
t h e
act u al s u p p
ly
output voltage . T he r efore, t h e cu r re n t
limit varies proportionally wit h t h e
sup p
ly voltage .
In most
overload con d itions, t he s upp ly fol d
s bac
k
to
minim u m
curren t . Diode C R 1310 cond ucts s hou ld t he -1 -V su pply go
more n egative t h an ground .
T he ---V sup p ly operates i n t he same ma nn e r as t he +V
supp
ly .
Only
t he p
olarities are reverse d . Transistors
01355 an d 01370 are t h e b asic com p arator t r a n sistors .
the base of Q1355 varies betwee n 0 V an d 1-5 .2 V . T he --V
outp ut is p reve n te d from goin g m ore p ositive t han ab out
--6 V by 01365 . T h e series pass tra n sistor is d rive n b y
01380 .
T h e comparator
tra
n
sistors fort he current
limiting
circuitry are Q1385 an d Q1395 . T he cu rre n t so u rce for t h e
cu rre n t co m parator is Q1400 . Dio d e C R 1410 preven ts t h e
V outp u t from goi ng more p ositive t h a n g r ound .
2- 7

Tektronix PG 508 Specifications

General

Brand	Tektronix
Model	PG 508
Category	Pulse Generator
Language	English