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HP 811 OA Se r vice Guide
Overvoltage
P
rotect i o n
This section is on schematic 4Β
S
h o r t-Circuit Curr ent
P
rotectio n
This section is on schematic 4Β
±32 V is
p
rotected by primary
o
verload
p
rotection .
7- 1 0
F
u nctional Description
T
ranszorb diodes Χ 5403,
X
S404,
X
S405,
X
S406
p
rovide overvoltage
p
rotection for the
l
oads connected to the +5 .1 V, -5 .2 V
a
nd ±12 V
supplies .
Table 7-1 .
P
ower
S
u pply and Com ponents C ross-R eferences
DC Supply
+32 V
-32V
+12 V
-12 V
+5 .1V
-5.2V
Components:
Rectifier
C
R408 CR409 CR421 CR422
CR423
CR424
Blocking capacitor
C
E433 CE435 CE460 CE464
CE468
CE475
CE469
CE476
Filter l
C
E434 CE436 CE461 CE465
CE470
CE477
L
403
L
405
L
411
L
413
CE471
L
415
L
417
L
404
L
406
L
412
L
414
L
416
L
418
Series-pass element
Q406
Q407
Q411
Q412
Q413
η/ α
R
egulator VR401 VR402
V
R403 VR404
VR405
VR406
F
ilter 2
C
E438 CE440 CE463 CE467
CE473
CE479
C437
C439
C462
C468
C457
C458
C441
C442
C454
C455
L
419,L420
L
407
L
409
L
423
L
425
C
E474
L
421
L
408
L
410
L
424
L
426
C456
L
422
Overvoltage
p
rotect
η/ α
η/ α
ΧS403 Ι ΧS404 Ι
XS405
( XS406
S
hort-circuit current
p
rotection is
p
rovided
f
or the +5.1 V, -5 .2V
a
nd ±12 V DC power supplies . Q414, Q415, Q416 and Q417 are
connected as OR gates, one for each
o
f the regulators .
These transistors
m
onitor the current through their associated
inductors (L412 (+12 V)
L
413 (-12 V),
L
419/20 (+5 .1
V),
and
L
417/21 (-5 .2 V)) by sensing α
v
oltage drop across the inductor when
α short-circuit occurs, switching the transistor ON .
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