HP 3000 III Series Manual page 335

HP 32421A SERIES III POWER SUPPLIES
~
This section contains principles of operation and servicing in-
formation for the HP 3242lA Series III Computer System power sup-
plies. The HP 32435A Series III power supplies are discussed in
Section X of this manual.
9-1. INTRODUCTION
The HP 32421A Ser ies II I Compute r
Sy
stern has four power suppl ies:
two HP 303l0A Power Supplies, one HP 303llA Power Supply, and one
HP 303l2A Power Supply.
9-2.
HP 30310A OPERATION
The HP 303l0A Power Supply provides +20V, +15V, +5V, -20V, -15V,
and -5V regulated dc supply voltages by converting a 208/240volt,
single-phase, 50- or 60-Hz power source. The ac input to the
power supply is controlled by the front panel POWER switch shown
in figure 9-1. The dc output voltges are controlled by the
Dc
Control Panel SYSTEM switch also shown in figure 9-1. The output
voltages provide status signals for protection of the software
stored in CPU memory. The computer system hardware i"s protected
by circuits that sense overvoltage, overcurrent, or overtempera-
'ture conditions. Circuits within the power supply are protected
by various overvoltage and overtemperature circuits, current lim-
it circuits, and fuses. The power supply is designed to immedi-
ately turn the power off when an oyervoltage condition occurs.
For undervoltage or overtemperature conditions, a short delay is
generated before the power is turned off. This delay permits the
CPU to store data which, in turn, makes power on and restart much
easier.
A block diagram of the power supply is shown in figure 9-2 and
discussed in paragraphs 9-3 through 9-11. (Complete specifica-
tions and detailed theory of operation for the power supply are
contained in the HP 3000 Series II/III Computer Systems service
Manual, part no. 30000-90018.)
9-3.
Primary Power Circuit
The ac line voltage enters the power supply through a connector
and passes through a 5-ampere fuse and radio frequency interfer-
ence (RFI) filter to the POWER switch. The POWER switch is lo-
cated on the front panel of the power supply. with the POWER
switch in the ON position, line voltage is applied to the pre-
regulator, cooling fan, and a step-down transformer. The fan and
transformer circui t are protected by a 1- ampere fuse.
9-1