Author: Jorge Pichard
Date: 16:11:57 06/22/04
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On June 22, 2004 at 16:49:08, James T. Walker wrote: >Seems to me the best way to go would be to just change the power supply for one >that works on your line frequency. >Jim But a switchable power supply that can be switch from 50Hz to 60Hz could be more expensive than a frequency converter, Since most computer nowadays come with a dual switch in which the electrical power available from the wall socket which is 50Hz (in Europe or 60Hz in the USA) can be converted to what most computer circuitry use +5- and 12v DC current and 3.3v as well on some system. Power Supply Function and Operation The basic function of the power supply is to convert the type of electrical power available at the wall socket to that which is usable by the computer circuitry. The power supply in a conventional desktop system is designed to convert the 120-volt, 60Hz, AC current into something the computer can use--specifically, +5- and +12v DC current, and +3.3v as well on some systems. Usually, the digital electronic components and circuits in the system (motherboard, adapter cards, and disk drive logic boards) use the 3.3v or +5v power, and the motors (disk drive motors and any fans) use the +12v power. The power supply must ensure a good, steady supply of DC current so that the system can operate properly. If you look at a specification sheet for a typical PC power supply, you see that the supply generates not only +5v and +12v, but also -5v and -12v. Because it would seem that the +5v and +12v signals power everything in the system (logic and motors), what are the negative voltages used for? The answer is, not much! In fact, these additional negative voltages are not used at all in many modern systems, although they are still required for backwards compatibility. Although -5v and -12v are supplied to the motherboard via the power supply connectors, the motherboard itself uses only the +5v. The -5v signal is simply routed to the ISA bus on pin B5 and is not used in any way by the mother-board. It was originally used by the analog data separator circuits found in older floppy controllers, which is why it was supplied to the bus. Because modern controllers do not need the -5v, it is no longer used but is still required because it is part of the ISA Bus standard.
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