A power supply is a standalone device or a component within a device that provides power. It is required when a different voltage and current is required than that provided by the utility grid.

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What is a power supply?

A power supply is a standalone device or a component within a device that provides power. It is required when a different voltage and current is required than that provided by the utility grid.

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A power supply unit commonly used in Europe for a notebook can, for example, have an input voltage from 100 volts (V) to 240 V. This is then converted into an output voltage of around 19 V with an output current of 2 to 3 amps. With so-called universal power supplies, the output voltage can be set to different values ​​using a switch.

The power supply of a PC is able to convert the input voltage into different output voltages, since the individual components within the computer work with different values. It also converts the AC power from the grid into the DC power required by the computer components.

Types of power supplies

There are different variants of power supplies, depending on the intended use. Regardless of their type, they are divided according to their design into plug-in power supplies (mobile phone, notebook, external hard drives) and built-in power supplies (PC, refrigerator, TV set). The way they work is classified as

  • Transformer power supply unit
  • Switching power supply
  • Capacitor power supply
  • Power supply for constant current (constant current source)
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Transformer power supply

Transformer power supplies were the most common version before switching power supplies were invented. Today they can only be found occasionally in special devices. The transformer inside uses an iron core to convert the AC voltage to the desired output value while ensuring galvanic isolation from the mains. A major disadvantage of transformer power supplies is the relatively high power consumption of several watts from the mains, even when no consumer is connected.

Switching power supply

Most electronic devices today are operated with switching power supplies. Since their frequency (a few 10 kHz to a few 100 kHz) for energy transmission is usually significantly higher than, for example, the European mains frequency (50 Hz), smaller transformers can be installed to achieve the same performance.

Switching power supplies generate a regulated direct current or a regulated direct current voltage. Thanks to their wide-range input, they can be operated worldwide on all standard power grids with a voltage between 85 V and 250 V. They are short-circuit proof, but have to be suppressed due to their high switching frequencies. Their no-load power is significantly lower than that of transformer power supplies.

Capacitor power supply

Capacitor power supplies can be produced particularly cheaply. They use the so-called reactance of capacitors to reduce the mains voltage and are only suitable for low currents. They are used, for example, in LED lights or motion detectors.

constant current source

This is a rarer variant used in semiconductor lasers, energy-saving lamps and battery chargers. Universal power packs in laboratories can also be used in this operating mode.

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