CONCEPTS

# What is power supply?

We explain what a power supply is, the functions that this device fulfills and the types of power supplies there are.

1. ### What is power supply?

The  source of power or power ( PSU in English) is the device that is responsible for transforming the alternating current of the commercial power line that is received in the homes (220 volts in Argentina) into direct or direct current ; which is the one used by electronic devices such as televisions and computers , providing the different voltages required by the components, usually including protection against possible inconveniences in the electrical supply, such as overvoltage.

The power supplies can be linear or commutative:

• Linear sources.  They follow the scheme of transformer (voltage reducer), rectifier (conversion ofalternating voltage to full wave), filter (conversion of full wave to continuous) and regulation (maintenance of the output voltage before variations in the load).
• Commutative sources.  These, on the other hand, convert electrical energy by means of high-frequency switching overpower transistors . Linear sources are typically inefficiently regulated, compared to commutative sources of similar power. The latter are the most used when a compact and low-cost design is required.
1. ### Power supply functions

The essential functions of the source are four:

• Transformation. There it is possible to reduce the input voltage to the source (220 V or 125 V), which are those supplied by the power grid. There participates a transformer in coil. The output of this process will generate 5 to 12 volts.
• Rectification. It aims to ensure that voltage oscillations do not occur over time . This phase is attempted to pass from alternating current to direct current through a component called a rectifier or Graetz bridge. This allows the voltage not to drop below 0 volts, and always remain above this figure.
• Filtered out. In this phase the signal is flattened to the maximum, that is achieved with one or several capacitors, which retain the current and let it pass slowly, which achieves the desired effect.
• Stabilization. When the continuous and almost completely flat signal is already available, it only remains to stabilize it completely.
1. ### Types of power supplies

The power sources that feed the PCs are inside the cabinet and are usually of the AT or ATX type. The AT power supplies were used approximately until the Pentium MMX appeared, at which time the ATXs began to be used.

The AT sources have motherboard connectors (this differentiates them from the ATX) and in addition, the source is activated through a switch in which there is a voltage of 220 v, which poses a risk when handling the PC. Technologically they are quite rudimentary and are almost no longer used. There was also the problem that having two connectors that had to be connected to the motherboard, confusions and short circuits were frequent.

In the ATX sources the source circuit is more modern and always active , that is, the source is always fed with a small voltage to keep it on hold. An additional advantage of ATX power sources is that they do not have an on / off switch, but work with a push button connected to the motherboard, this facilitates connections / disconnections. According to their power and the type of box, they are classified into sources on AT table (150-200 W), semitorre (200-300), tower (230-250 W), slim (75-100 W), on ATX table ( 200-250 W).