HP 3478A Technical Manual page 117

3478A 3478A
connected to ground (by the switch). connected to ground (by the switch). This state shows
that the Front/Rear Switch is in the rear position. that the Front/Rear Switch is in the rear position.
7-F-83. 3. Power 7-F-8 Power Supplie Supplies s
7-F-84 7-F -84. . Gen Genera eral l . . The 3478A has The 3478A has one set of
supplies for the Floating Common Circuitry and another supplies for the Floating Common Circuitry and another
set of supplies for the Chassis Common set of supplies for the Chassis Common Circuitry.
Floating Common Circuitry has three supplies: + 15SV, - Floating Common Circuitry has three supplies: + 15SV, -
I5V, and + SV. The Chassis Common I5V, and + SV. The Chassis Common Circuitry has two
+ SV supplies. + SV supplies. One of the supplies is us One of the supplies is used by the CMOS
RAM (US 12) and the other supply is used RAM (US 12) and the other supply is used by the rest of
the chassis common the chassis common logic circuitry. logic circuitry. Refer to Schemat
4 for the following explanation on the 3478A's power 4 for the following explanation on the 3478A's power
supplies. supplies.
7-F-85. 5. 15V and -15V Powe 7-F-8 15V and -15V Power Supplies (F
Common) Common). . A full-wave br A full-wave bridge rectifier,
CR701 through CR706, develops the raw (unregulated) CR701 through CR706, develops the
voltages for the supplies. voltages for the supplies. The regulated
developed by voltage regulator U703 and the -15V by developed by voltage regulator U703 and the -15V by
U702. Breakdown diodes U702. Breakdown diodes CR711 and CR712
for overvoltage for overvoltage protection. protection. Overvoltage prot
regulators U702 and U703 is by diodes CR715 and regulators U702 and U703 is by diodes CR715 and
CR714, respectively. The diodes conduct CR714, respectively. The diodes conduct if the raw
(unregulated) volta (unregulated) voltage is too ge is too large.
C703, and C706 are filter ca C703, and C706 are filter capacitors.
sensitive resistor RT706 and RT707 are used to protect sensitive resistor RT706 and RT707 are used to protect
supplies from excessive output currents supplies from excessive
circuitry operates as follows: circuitry operates as follows:
a. a. If t If the ou he outpu tput cu t curre rrent o
excessive, RT707 heats up. excessive, RT707 heats
current, RT706 heats up. current, RT706 heats up.
b. b. Sin Since R ce RT70 T706 an 6 and RT
temperature coefficients, their resistance increases to a temperature coefficients, their resistance increases to a
large value due to high temperature. large value due to high temperature.
This state shows
one set of power power
Circuitry. The
Circuitry has two
ed by the CMOS
by the rest of
Refer to Schematic ic
r Supplies (Floatin loating g
idge rectifier, consisting of consisting of
raw (unregulated)
The regulated + 15V is + 15V is
CR711 and CR712 are used are used
Overvoltage protection of ection of
if the raw
large. Capacitors C702, Capacitors C702,
pacitors. Temperature Temperature
output currents. . The protection The protection
nt of th f the + 15V e + 15V sup supply i ply is s
up. If the -15V has If the -15V has excessive excessive
d RT707 707 hav have po e posit sitive ive
c. c. The h The high r
voltage to drop across RT706 and RT707, shutting down voltage to drop across RT706 and RT707, shutting down
the respective supply. the respective supply.
d. d. The la The large r
or RT707 cool down (the supply draws normal current). or RT707 cool down (the supply draws normal current).
7-F-86. 7-F- 86. +5V Power Supp +5V Power Supply (Floati
The
power supply receives its raw (unregulated) voltage from power supply receives its raw
full-wave rectifier full-wave rectifiers CR703 and
developed by voltage regulator developed by vo
CR715 is used CR715 is
C711 is a filter capacitor. C711 is a filter capacitor.
7-F-87. 7-F- 87. +5V Power Supp +5V Power Supply (Chassi
power supply receives its raw power supply receives its raw (unregulated) voltage from
full-wave rectifier CR760 and CR761. full-wave rectifier
developed by voltage regulator developed by vo
CR766 is used for overvoltage protection and capacitor CR766 is used
C766 and C761 are filter ca C766 and C761
U850C and U8SOD are used to reset the Chassis U850C and U8SOD are used to reset the Chassis
Common CPU (USO1). Refer to paragrap Common CPU (USO1).
information on the comparators operation. information on the
7-F-88. 7-F- 88. +5V Powe +5V Power Supply (
3478A is turned on, the CMOS RAM receives its supply 3478A is turned on, the CMOS RAM receives its supply
voltage (+ SV) fr voltage (+ SV) from regulator tr
(unregulated) voltage for Q701 also comes from CR760 (unregulated) voltage for Q701 also comes from
and CR761 (see previous para and CR761 (se
level for Q701 comes from the Chassis Common + SV level for Q701 comes from the Chassis Common + SV
power supply. power supply. When the 3478A is t
Chassis Common + SV goes low and transistor Q701 Chassis Common + SV goes low and transistor Q701
turns off (st turns off (stops conducting).
conduct and the voltage from battery BT701 is used to conduct and the voltage from battery BT701 is used to
supply the CMOS RAM. supply the CMOS RAM.
7-F-22 7-F-22
igh resi esista stance c nce caus auses mo es most of t
rge resi esista stance v nce valu alue rem
ly (Floating Commo
(unregulated) voltage from
s CR703 and CR704. CR704. The + 5V
ltage regulator U701. U701. Breakdown diode
used for for overvoltage overvoltage protection. protection. Capacitor
ly (Chassis Common
(unregulated) voltage from
CR760 and CR761. The + 5V
ltage regulator U760. U760. Breakdown diode
for overvoltage protection and capacitor
are filter capacitors. pacitors. Comparators
Refer to paragraph 7-F-59 for
comparators operation.
r Supply (CMOS RAM) CMOS RAM). . When
om regulator transistor Q701. ansistor Q701. The raw
e previous paragraph). graph). The reference
When the 3478A is turned off, the
ops conducting). Diode CR764 then start Diode CR764 then starts to
TM 11-6625-3071-14 TM 11-6625-3071-14
st of the su he suppl pply y
e remain ains unt s until RT7 il RT706 06
ng Common) n). This . This
The + 5V is is
Breakdown diode
Capacitor
s Common) ) . This . This
The + 5V is is
Breakdown diode
Comparators
h 7-F-59 for
When the the
The raw
CR760
The reference
urned off, the
s to