Tektronix 576 - Section 3 Circuit Description; Block Diagram Description; Detailed Circuit Operation; Collector Supply Circuit Details

General
SE
CTIO N 3
CIRCUIT DESCRIPTION
C hange
information, if any, affecting this section will b e foun d at
the rear of this manual .
This
discussion
of the Ty p e
576 internal operation is
divi ded into two p arts
:
B
loc
k
diagram d escri p tion an d
circuit descri p tion . T h e bloc k d iagram descri
p tio n
d
iscusses
t he f u nctions of t he ma j or circuits wit h in t
h
e
instrument,
using t he overall bloc k d iagram . T he circ u it descri
p tio n p ro-
vi d es α d etailed descri p tion of all t he
ma j
or
circuits an d t he
sig n al switc h ing wit h in t h e instrument .
It is suggested t
h
at t
h
e bloc
k
d
iagrams and sc h ematics
w h
ic
h h
ave been
inclu
d e d
in t h is manual be referred to
w h ile reading t
h
is
circuit
d
escri p tion . Individual bloc k d ia-
grams
an d simp lified sc h ematics of most of t h e ma j or cir-
cuits and
signal switc h ing accom p a ny t he text of t h is
section . An overall bloc k d iagram of t
h
e
instrument,
s h owing all t h e ma j or circuits an d α sim
p lifie
d
version
of
t h e signal switc
h ing,
is p rovided in t
h
e d
iagrams section at
t h
e
bac k of t he
manual .
Also in t h
e
diagrams section are
com p lete sc h ematics of
all
t he circuitry wit h in t he Ty pe
576 w h ic h i n clu d e com ponent p art numbers and values .
BL OC K DIAG R A M D E SC R I P TIO N
T he Ty pe 576 is α d ynamic semiconductor tester w h ic h
d is p lays and allows measurement of semiconductor charac-
teristics obtaine d und er simulate d o p erating conditions .
T he collector su pp ly circuit and t h e ste p ge n erator produce
op erating voltages an d currents w h
ic h
are
a pp lie d
to
t h e
d evice und
er
test . T h
e
d is p lay am p lifiers measu re t h e
effects of t h ese applied co
n
d
itions
.
T he tests
result in
curves of
transistor,
d
ί
od e, an
d
ot
h
er
semiconductor d evice
c h aracteristics trace d on t h e face of α C R T .
T h
e
collector su pp ly circuit p rod u ces full-wave rectifie d
sine- waves w h ic h may be eit h er p ositive-going or negative-
going or ιι nrectifie d sine waves, d e pend i n g on t he p osi-
tion of t h e P OLA R ITY switc h . T h e am p litude of t he signal
can be
varie
d from
0
to
1500 volts as determined by t he
MAX PEAK VO L TS
switc h and t h e V A R IA BLE CO LLE C-
TO R S UPPL Y
control . The Collector Supply output is
a pp lied to t h e collector (or equivalent) ter m inal of t he
d evice under test .
T
h
e ste p ge n erator
p
roduces ascen
d ing ste
p
s
of current
or voltage at α n ormal rate of on e
ste
p
for eac
h h
alf-sine
wave of t h e collector su pp ly . T h e amount of c u rrent or
voltage p er step is controlled by t h e A MPL IT UD E switc h
an
d
th e total number of ste p
s
is
controlle d by t h
e
NUM-
BER O F STEP S switc h . T h e Ste p Generator output may be
applie d to eit h er t he base or
t h e emitter (or equivalent)
terminals of t h e d evice under
test .
Α
Collector Supp
ly
CI R
C
U
IT D E SC R I P TIO N
Ty p
e 576
T he d is p lay am p lifiers are connecte d to the d evice un der
test . These am
p lifiers measure the effects of the collector
su pp
ly
an
d t h e step generato r on t he d evice und er test,
am p lify t he
measure m ents, and apply t he resulting voltages
to t h e deflection
p lates of t he CRT, T h e sensitivities of
t h ese am p lifiers
are controlle d by t he VER TICA L
C UR β EN T/DI V switc
h
an d
t h
e
H O R IZO N TA L V OL TS/
DI V switc h .
T h e following discussion provi
d es α d etaile d circuit
descri p tion of all t
h
e ma j or
circuits wit h in t h e Ty pe 576
and t h e Standar d
Test
Fixture .
T h is d escription ex p lains
t he operation of t h e various circuits
wit h in t he instrument,
an d t h e voltages an d waveforms w h
ic h can be ex p ected
from t h em . Discussion of basic electronics
and sim p le
electronic circuits will be k e p t at α
minimum .
T h
e
collector
supply
circuit p
ro
d uces
an
unrectifie d sine
wave or
α full-wave rectifie d sine wave wit h α p ea k am p li-
tude w h ic h may be varied from 0 to 1500 volts p ea k in four
ranges . T he initial voltage for t he collector su pp ly comes
from variable autotransformer Τ 300 Isee F ig . 3-1) w h ic h
h as α source voltage of 115 volts AC . T he out p ut of Τ 300 is
connecte d to t he p rimary of swee p transformer Τ 301 an d is
controlle d by t h e
V A
R IA BLE CO LLE CTO
R
S
UPPL Y
V O L TS
control and varies from 0 to 115 volts . T h e MAX
PEAK VO L TS switc
h allows
t h
e ch oice of fo u r collector
sweep voltage ranges by c
h
oosing p airs of
transformer ta p s
from t h e secondary of
Τ 301 . Th
e voltage from
t h ese ta p s is
rectified by one of two d io d e bri d ge rectifier assemblies
:
t he 500 volt assembly for t h e 15, 75 and 350 volt ranges
and t h e 2 k ilovolt assembly for t he 1500 volt range .
T h e 500 volt rectifier assembly is use d eit h er as α center
ta pp ed full-wave
rectifier or α bri d ge rectifier de p ending on
t he
connection of the current return i np ut to t h e collector
supply . T he c ιι rrent return comes from t he non-grounded
side of t h e current sensing resistor . Since t he voltage level
of t h e curre n t ret u rn in p ut is dependent on t he current
flowing through t h e current sensi n g resistor, t h e collector
supply can
be consi d ere d to be floating . F or t he 15 volt or
75
volt ranges, t h e current retur n is connected to t h e center
tap of t he sweep transformer secon d ary . In t h is case only
two d iodes of t
h
e
500 volt r ectifier assembly are used as α
full-wave rectifier . F or t h e 350 volt range, t h e curre
n t
r eturn goes to t h e bri d ge r at h er t h an t he center tap of
t h e
transformer . In t h is erase, t he w h ole 500 volt rectifier