115 vac, 400 Hz, 3 phase D
220 vac, 60 Hz, 3 phase D
115/200 vac, 400 Hz, 4 phase Y
230 vac, 50 Hz, 3 phase D
Mainframe and minicomputers aboard ship and
ashore are preset to receive a specific line voltage.
Microcomputers aboard ship use 115 vac, 60 Hz, 3
phase D. Microcomputers ashore generally use 115 vac,
60 Hz, 1 phase D. However, they have a line select
switch located on the back of the micro’s chassis to
select an alternate line voltage, if needed ashore. In
some cases a microcomputer is equipped with a feature
that automatically switches over to alternate 220 vac,
50 Hz power. Your ship’s electronics doctrine or
equivalent document ashore provides the specific
voltage and frequency values, as well as the location of
power. For reference when dealing with input power,
refer to MIL-STD-1399, Section 300A, Interface
Standard for Shipboard Systems, Electrical Power,
Alternating Current for Shipboard, a n d
MIL-HDBK-411, Power and the Environment for
Sensitive DOD Electronic Equipment, Volume I
(General), and Volume II (Power), for ashore.
COMPUTER POWER SUPPLY
CONTROLLING DEVICES
Before the input line voltage goes to the transformer
section of the primary power supply, it must first go to
the computer’s man/machine interface, a controlling
device. This controls the power supply of the computer,
and will vary with the type of computer. Some have an
ON/OFF switch at the rear of a computer where
blower/fan power and logic power are controlled by one
switch. Others have an operator’s panel where you can
control blower power and logic power separately. Still
others have a separate unit where the power is
controlled to every major unit in the computer including
blower power and the modules in each of the functional
areas. You should be thoroughly familiar with the
power up and down procedures for your computer.
Consult your computer’s owner/technical manual
and/or electronics doctrine or equivalent.
COMPUTER POWER SUPPLY
COMPONENTS
Computer power components include a
transformer, a rectifier, a filter, and a regulator.
Transformer
The transformer receives the line voltage from the com-
puter’s power controls. This input line voltage is stepped
up or stepped down. The transformer isolates the power
supply from the input line voltage. Most computers use
some means of sampling the input power and/or provide
protection before the line voltage is received by the
transformer section. Examples are as follows:
AC line filters —AC line filters eliminate high
frequency noise from the input power. They also
filter returns from the regulator section.
Circuit breakers —Circuit breakers protect the
transformer when an overcurrent or power fault
condition occurs.
Rectifier
The rectifier section converts the ac input signal to
a pulsating dc voltage or ripple. This pulsating voltage
is not desirable and must be filtered. In some
computers, this section provides the power necessary
for the following:
System and calendar clock for the computer set
Display control unit (DCU) interface and power
panel control
Termination resistors for the bus system
Filter
The filter section removes the ripple” sent from the
rectifier section and produces it into a use able dc
voltage. There will still be a small amount of ac ripple
on the filtered dc voltage.
Regulator
The final section, the regulator, maintains the
output of the power supply at a constant level in spite
of large changes in load current or input line voltages.
For microcomputers, this is the final section before the
power is distributed throughout the computer. For
larger computers, the regulator section can provide
regulated power to additional circuits where it is further
filtered and/or converted. Converters include the
following types:
4-26
Regulating converters —Regulating converters
provide dc power to the backplane wire harness,
and to remote, operator, and maintenance
consoles
Module DC-to-DC converters —Module
dc-to-dc converters provide the required dc
