Tektronix 576 - Page 57

Circuit Desc r i p tio n -Ty pe 576
R 422
To Horizontal
Dis p lay
Switc h i ng
Dis p lay Se n sitivity
Switc h i ng Sc h
ematic
F ig . 3-10 . Sim p
li f ied sc h e m atic o f D isplay Sensit i vity sw
i
tc
h ing and
Standard
T est F ixture sc h ematics for m eas ur
ement o f emitter cur r ent (Ι g)
collector-base curre n t
( ΙςΒΟ )
collector-emitter vo
l tage
( V ςΕ
)
or collector-base vo l tage
(V ςβ
)
.
t he value of t h is current se n sing resisto r (R s ), t h e d eflection
factor of t h e d is p lay on t he C R T may be varie d .
L ea k age Current
Sensing . If t he M OD E switc h is set to
LE A K AG E,
emitter current ( ΙΕ ) or collector-base
current
(IC B O)
is measured on t he vertical axis of t he C R T .
E mitter
current
is measure d by p lacing α current sensing
resistance
between t h
e emitter terminal of t he d evice und er test an d
ground,
an
d
measuri ng t h
e
voltage d evelope d across it (see
F ig . 3-10) . If
emitter curre n t is to be measure d , t he Term-
inal Selector switc
h must be set to GR OUND E D EM ITT ER
B AS E T ERM OPEN or B
AS E T ERM S H O R T . Wh en t he
Terminal Selector switc
h is set to B AS E G R OUN D E D
EM ITT ER T ERM OPEN,
collector-base cu r rent is measured
on t he vertical axis . In t h is case t he cu r rent se
n si ng resisto r
is connected between t h e base terminal an
d groun d . As
w hen measuring collector curre
n
t, t h
e d eflection factor of
t h e d is p lay, w h en measuring emitter
current and collector-
3- 1 6
base current, can be varied by
varying t h e current sensing
resistance . It s h oul d be
n ote d t h at t h e deflection factor of
t he vertical d is p
lay is always d ecreased 1000 times w h en
t h e M OD E switc
h is set to LE A K AG E a nd t he collector
su pp ly o p erates in its DC
mo d
e .
V oltage Sensing N ormal
M
o
d
e .
Either collecto r or base
voltage may be
measure
d on
t he h orizontal axis of t he
CR T, d epending on t
h e p osition of t he H O R IZO N TA L
switc h . Wh en
t he H O R IZO N TA L switc h is in its COLLEC-
TOR ra n ge,
voltage is measure d between t h e
collector an d
emitter terminals
of t h e d evice und er test,
V ςΕ (Terminal
Selector
switc h set to EM ITT ER GR OUND ED), or
between
t he collector and
base terminals, V ςΒ , (Terminal
Selector
switc h set at B AS E G
R OUN D ED) . Wh en t h e H O R IZO
N -
TA L switc
h
is
in its B AS E range, voltage is measure
d be-
tween t he base
an d emitter terminals,
VB E (EM ITT ER
GR OUND ED),
or between t he emitter an d base
terminals,
*S h ort not availa b le
N ote
R
L
R
401 t hr o u gh R 409
i n B AS E G R O UN D E D
P i n n um b ers
r efe r
R
434 t hr ou g h R438
p ositio n .
to co nn ecto r J360
Ν ote
R
A
overla p RB
R
437 t hr ou g h R440 (or open)
R 442 t hr ou g
h
R
444
N ote
RA'
ove r lap
Ι
RB'
R 442 t h ro u g h R445