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