Computer Power Supply Controlling Devices

l 115 vac, 400 Hz, 3 phase D l 220 vac, 60 Hz, 3 phase D l 115/200 vac, 400 Hz, 4 phase Y l 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, and 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: l System and calendar clock for the computer set l 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: 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 de-to-de converters provide the required dc 4-26