How does a computer get its electricity

PC power supplies / computer power supplies

A normal PC has an output of 10 to 300 watts, depending on the equipment. Sometimes even more. Processors, chipsets and, above all, graphics cards are some of the biggest power guzzlers. However, this cannot be said exactly because, thanks to various energy-saving measures, many components consume very little power when not in use. The actual power requirement of a PC depends on the workload of the system and on the main use. In addition to stability, efficiency and operating noise are also important performance parameters of computer power supplies.

The task of computer power supplies is to generate small voltages and supply large currents. The working voltages in a computer are -12V, -5V, + 12V, + 5V and +3.3 V. Some PC power supplies are made without -5V and -12V. Processors, memories and chipsets work internally with an even lower voltage. Voltage regulators on the motherboard and processor take care of regulating this low voltage.

Switching power supply

Stepping down a voltage at the high power a computer consumes is not possible with a linear power supply with a transformer. The transformer would be very large and very heavy. That is why switching power supplies are used.
The components in a computer are also very sensitive. The applied voltage may deviate from the defined operating voltage by a maximum of 5%. Unstable voltages can damage the components. Processors in particular are sensitive to voltage fluctuations. However, damage does not necessarily occur. Most of the time, the system responds with inexplicable system crashes. Therefore the supply voltages have to be kept absolutely constant with a complex regulation. This is not possible with the usual transformer stabilization power supplies. That is why there are switched-mode power supplies that are specially designed for these tasks.

Structure of a switching power supply


A switching power supply consists of several units. First the Mains voltage filtered. Overvoltages, harmonics and other network disturbances should not even get into the further circuit. After that, through Rectification and screening Turning the alternating voltage of 230 V into a direct voltage of 350 V. With a transistor switching stage an alternating voltage from the direct voltage generated between 35 and 500 kHz. With this high frequency you can small transformers transmit high performance. These transformers have multiple secondary windings. Different voltages can be generated in this way. A special circuit ensures that the voltages always remain constant. This closed control loop also ensures that the power supply unit can always deliver the required currents. They can be of different sizes. Because a computer doesn't always draw the same amount of electricity. The control circuit is set up for this.
In order for the control to work, it must work with a base load. This is also the reason why switching power supplies have to be loaded with a consumer so that it works when switched on. If the load is not present, voltage flashovers occur. This will destroy the power supply unit. Therefore, a switching power supply must never be switched on without a consumer.

Using the voltages of a PC power supply

+ 3.3V
  • Drive electronics of S-ATA drives
  • processor
  • random access memory
  • Chipset
  • Graphics cards
+ 5V
  • Drive electronics
  • Processor (AT compatible)
  • RAM (AT-compatible)
  • Chipset
  • Expansion cards
+ 12V
  • Drive motors
  • Fan
  • Expansion cards
- 5 V
- 12 V
  • Expansion cards (ISA, PCI)

How many watts should a PC power supply have?

A simple PC power supply unit with 150 to 200 watts would be sufficient for a PC with a dual-core processor, onboard graphics and a few drives. PC power supplies usually start at around 300 watts.
If you think about overclocking or use a high-end graphics card, you should expect a 600 watt power supply.
An even higher nominal power on the part of the PC power supply is actually only useful or necessary in exceptional cases.

PFC - Power Factor Correction

The power factor correction (PFC) is a Europe-wide standard DIN EN 61000-3-2 (EMC standard for harmonic currents, supplement A14) and is a means of counteracting the negative effects on the power supply network due to the asymmetrical and non-sinusoidal current consumption by switched-mode power supplies.

Efficiency

The degree of efficiency indicates the ratio of supplied and output power in percent. There is practically no efficiency of 100%. Because each circuit also consumes some energy. The higher the efficiency, the more economically the switched-mode power supply works.
Today's switched-mode power supplies have an efficiency of 50 to 90 percent. The higher the efficiency, the more expensive the switched-mode power supply. Good components have their price.

Energy Star 4.0 and 80-plus specification


According to the 80-plus specification, efficient power supply units have an efficiency of at least 80 percent from 20 percent of their secondary network load. There are hardly any PC power supplies with an efficiency below 80 percent anymore. Below 20 percent network load, the efficiency often falls below 80 percent. Power packs in high performance classes rarely achieve more than 60 percent of the rated output below 20 percent.
The 80-plus specification provides an efficiency of at least 80 percent for three exemplary load cases. At the beginning of 2008, the classifications were made in the form of bronze, silver and gold. The data in percent relate to the degree of efficiency.

Overview: form factors

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Everything you need to know about computer technology.

Computer technology primer

The computer technology primer is a book about the basics of computer technology, processor technology, semiconductor memories, interfaces, data storage devices, drives and important hardware components.

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Everything you need to know about computer technology.

Computer technology primer

The computer technology primer is a book about the basics of computer technology, processor technology, semiconductor memories, interfaces, data storage devices, drives and important hardware components.

I want that!