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Unit catu daya ATX dengan penutup atas dilepas

Sebuah Unit Suplai Daya (PSU) mengubah AC utama menjadi daya DC yang diatur tegangan rendah untuk komponen internal komputer. Komputer pribadi modern secara universal menggunakan catu daya mode-sakelar. Beberapa catu daya memiliki sakelar manual untuk memilih tegangan input, sementara yang lain secara otomatis menyesuaikan dengan tegangan listrik.

Sebagian besar catu daya komputer pribadi desktop modern sesuai dengan spesifikasi ATX, yang mencakup toleransi faktor bentuk dan tegangan. Saat catu daya ATX disambungkan ke catu daya, ia selalu menyediakan daya siaga 5 volt (5VSB) sehingga fungsi siaga di komputer dan periferal tertentu diberi daya. Catu daya ATX dihidupkan dan dimatikan dengan sinyal dari motherboard. Mereka juga memberikan sinyal ke motherboard untuk menunjukkan kapan tegangan DC dalam spesifikasi, sehingga komputer dapat menyala dan boot dengan aman. Standar ATX PSU terbaru adalah versi 2.31 pada pertengahan 2008.

Fungsi

Diagram sirkuit sederhana dari PSU tipikal

Diagram rangkaian pengatur tegangan XT dan AT yang khas

Internals of a PSU with passive PFC (left) and active PFC (right)

Catu daya komputer desktop mengubah arus bolak-balik dari stopkontak listrik ke arus searah bertegangan rendah untuk mengoperasikan prosesor dan perangkat periferal. Diperlukan beberapa tegangan arus searah, dan tegangan tersebut harus diatur dengan cukup akurat untuk memberikan operasi komputer yang stabil. Rel catu daya atau rel voltase mengacu pada voltase tunggal yang disediakan oleh unit catu daya (PSU).

Power rating

The overall power draw on a PSU is limited by the fact that all of the supply rails come through one transformer and any of its primary side circuitry, like switching components. Total power requirements for a personal computer may range from 250 W to more than 1000 W for a high-performance computer with multiple graphics cards. Personal computers without especially high performing CPUs or graphics cards usually require 300 to 500 W. Power supplies are designed around 40% greater than the calculated system power consumption. This protects against system performance degradation, and against power supply overloading. Power supplies label their total power output, and label how this is determined by the electric current limits for each of the voltages supplied. Some power supplies have no-overload protection.

The system power consumption is a sum of the power ratings for all of the components of the computer system that draw on the power supply. Some graphics cards (especially multiple cards) and large groups of hard drives can place very heavy demands on the 12v lines of the PSU, and for these loads, the PSU's 12 V rating is crucial. The total 12 V rating on the power supply must be higher than the current required by such devices so that the PSU can fully serve the system when its other 12 V system components are taken into account. The manufacturers of these computer system components, especially graphics cards, tend to over-rate their power requirements, to minimize support issues due to too low of a power supply.

Efficiency

Lihat pula: Green computing dan 80 Plus

Various initiatives exist to improve the efficiency of computer power supplies. Climate Savers Computing Initiative promotes energy saving and reduction of greenhouse gas emissions by encouraging development and use of more efficient power supplies. 80 Plus certifies a variety of efficiency levels for power supplies and encourages their use via financial incentives. Efficient power supplies also save money by wasting less power; as a result, they use less electricity to power the same computer, and they emit less waste heat which results significant energy savings on central air conditioning in the summer. The gains of using an efficient power supply are more substantial in computers that use a lot of power.

Although a power supply with a larger than needed power rating will have an extra margin of safety against overloading, such a unit is often less efficient and wastes more electricity at lower loads than a more appropriately sized unit. For example, a 900-watt power supply with the 80 Plus Silver efficiency rating (which means that such a power supply is designed to be at least 85% efficient for loads above 180 W) may only be 73% efficient when the load is lower than 100 W, which is a typical idle power for a desktop computer. Thus, for a 100 W load, losses for this supply would be 27 W; if the same power supply was put under a 450 W load, for which the supply's efficiency peaks at 89%, the loss would be only 56 W despite supplying 4.5 times the useful power. For a comparison, a 500-watt power supply carrying the 80 Plus Bronze efficiency rating (which means that such a power supply is designed to be at least 82% efficient for loads above 100 W) may provide an 84% efficiency for a 100 W load, wasting only 19 W. Other ratings such as 80 plus gold, 80 plus platinum and 80 plus titanium also provide the same ratings respectively. 80 plus gold providing an 87% efficiency under 100% load, 80 plus platinum providing a 90% efficiency and 80 plus titanium providing the best efficiency at 94%.[1]