![]() ![]() That is not to say, however, that a high- quality power supply is a waste. An extremely high-wattage power supply in a lightly loaded system is a waste, because the system draws only what it needs in terms of amps. The wattage of the power supply refers to the maximum wattage of which it is capable. When a drive is spinning up, it requires about twice the normal amount of +12V power, so when calculating the needed +12V amps, double the measurement. 5 Œ” floppy drives-1 amp of +5V and 2 amps of +12V.3 œ” floppy drives-0.5 amps of +5V and 1 amp of +12V.CD-ROM drives-1 amp of +5V and 1 amp of +12V.PCI circuit boards-5 amps of +5V, 0.5 amps of +12V, and 7.6 amps of +3.3V.Motherboard-5 amps of +5V or +3.3V and.These numbers represent the maximum for each component the actual amount of draw will likely be less. It isn’t always easy to get power consumption data for the various components in your system, but you can use the following rough numbers for conservative calculation. ![]() That allows for maximum power flexibility while still maintaining the 235-watt limit. Notice that for the above specs, the combination of +5V and +3.3V cannot exceed 125 watts. +5V and +3.3V combined-Maximum of 125 watts.Power supply manufacturers will provide you with specs on request for their power supplies, but a typical 250-watt LPX power supply might break down like this:įor a 235-watt ATX, you might see something like this: For example, all the red wires are +5V and all the black wires are ground. Notice that on an ATX-style connector, all the wires with the same colors have the same voltages or functions. See Table A and Table B for a breakdown on what each pin does. ![]() ![]() LPX-style power supplies have two six-pin connectors to the motherboard, while ATX-style power supplies have a single 20 pin. When selecting a power supply, you must make sure that it not only matches up with the motherboard type (so the connectors will fit) but also that it fits inside the case you are using. The ATX style is used with ATX, Micro-ATX, and NLX-style motherboards. LPX style is a descendant of the Baby-AT, AT/Tower, and AT/Desk type of power supply and is used primarily with Baby-AT style motherboards. For example, you might see an ATX-style 250-watt power supply or an LPX-style 200-watt power supply. Power supplies are sold using two main specifications: the form factor and the wattage. All the other plugs coming out of the power supply-called Molex connectors-are for drives, and they provide +12V (yellow) and +5V (red) power, as well as two ground wires (black). Integrated serial ports on older systems use +12V while on newer systems, they use +3.3V or +5V. Other voltages are routed to the ISA bus: -5V on pin B5, -12V on B7, and +12V on B9. Have you ever wondered why the plug from the power supply to the motherboard has so many different colored pins and wires? It’s to provide different voltages of power signals to the motherboard, which then parses them out to connected devices. Support for -5V is part of the ISA standard, but new systems being produced today are typically PCI-only, so they do not require this support. Many power supplies also generate -5V and -12V, but those negative voltages are rarely used in modern systems and some of the newer power supplies do not even provide -5V support. Generally speaking, the motherboard and any circuit cards use +3.3V or +5V, (newer motherboards and processors tend toward +3.3V, while older ones are usually +5V) and fans and disk drives use +12V. Depending on the component, this can be +3.3V, +5V, or +12V. The power supply takes wall current (120-volt, 60-Hz AC) and converts it to an appropriate level of DC voltage for the various components in a PC. In this Daily Drill Down, I’ll explain some of the basics of power supplies, including how they work, what types are available, and how to test one for proper operation. That’s unfortunate because power supplies are not all that complicated, and they are often the cause of puzzling, tough-to-troubleshoot problems. Of all the components in a PC, most technicians understand the power supply the least. For more info, visit our Terms of Use page. This may influence how and where their products appear on our site, but vendors cannot pay to influence the content of our reviews. We may be compensated by vendors who appear on this page through methods such as affiliate links or sponsored partnerships. Still having problems? Have you tried testing the power supply? This Daily Drill Down by Faithe Wempen gives you the scoop on what to look for. So you have tested everything from the motherboard to the floppy drive. Untangling the wires: Getting to know your power supply ![]()
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